Weber DCOE/SP emulsion tube selection/effects on power curve

[RWD fords rule]

I will be tuning a 2 litre pinto tarmac rally engine soon with twin 50 webers which have a unique set of high velocity chokes, I have a number of different emulsion tubes, F7, F11, F16 and one or two more, can someone tell me what the differences will be on the fuel map vs rpm?

As I understand it F16 will be rich in the low rpm range, F7 also rich at low rpm but a little less than F16 and the F11's have a more even spread, is this correct?

The random numbering of weber emulsion tubes is a little confusing to say the least
When comparing emulsion tube hole placement and diameter of the tubes how does this effect the fuel delivery?

I know the fuel is sucked in the main jet at the bottom and up through the holes at the bottom of the tube then fuel flows along the outside of the tube upwards, the holes in the middle and top of the E tubes are where air mixes with the fuel at low-mid to high revs, low rpm being the top of the emulsion tube and the holes in the middle would be for higher rpm, is that correct?
The larger the emulsion tube diameter the less fuel can flow to the auxiliary venturi so that would mean the larger the E tube diameter the leaner the mixture at high rpm, is that how it works?
Any information would be great

I will be tuning with a wideband AFR but just want to know what effect the different emulsion tubes will have, where hey will add or remove fuel in the rpm range as compared to another tube, initially I am using F7's as they were recommended to me, I usually use F11's but the chokes with this setup may require different E tubes than usual

New crappy image uploader is actiing up again..... will upload some pics later

Cheers
Jason

[RWD fords rule]

Pics

[Miniliteman]

Jason,

my 2 cents: forget comments like that "the F7 is also rich at the low end but not as much as the F16".
Just use the facts about tube diametre and holes-placement that you wrote.

Normally the 50DCO/SP carb is fitted with 46mm chokes; unless you have a race cam and want a peaky engine you'd better use 44mm chokes.
Start with the F11 tube or even better the F15 (a bit richer on topend) and see how it goes.
With a high-power engine 2 degrees more/less advance on ignition or camtiming makes a big difference plus the floatlevel of the carbs needs to be spot-on and the same.

Good luck, Leon.

[RWD fords rule]

Hello Leon
Thank you for that information

We are running a totally different set of chokes so I expect they may need a different E tube than I normally use, time will tell, I can't really say any more about the choke setup

Have t oget the fueling sorted out as good as I can while running in the engine, and a little bit of cam timing adjustment when I have the afr very close, then fine tune everything on a rolling road

When setting the float levels with the newer plastic floats what is the measurement fully up and fully down?

I have read 12mm float heights but that doesn't mean much to me without having a description of where it is measured from and at what position the floats are at when measuring

Regards
Jason

[Miniliteman]

Float level setting: with the carb top cover upside down and the tab just touching the needle the distance between the top of the floats and the level of the top cover with the gasket in-place must be 12mm. If it isn't bend the tab slightly to adjust.

[Group4_Mark2]

I am no expert on Weber carbs but my understanding of the emulsion tubes is as follows:

When idling the fuel level around the emulsion tubes is the same as that in the float chamber which is why it is so important to set the float level. The holes at the top of the emulsion tubes are exposed to air so these effect the low rpm enritchment. If there are more holes at the top then the air fuel ratio will be weak at low rpms.

As the rpms rise the fuel level around the emulsion tubes drops exposing holes gradually farther down the emulsion tube so the lower the holes are around the emulsion tube the weaker the mixture will be at high rpms.

There is also an effect caused by the diameter of the emulsion tubes but I am not certain how this effects the engine running

Some pictures from a google search so not sure of accuracy. Both pictures also seem to disagree.





If anyone has better or more accurate information on this it would be appreciated

[Group4_Mark2]

A short talk by David Vizard on selecting emulsion tubes.

http://youtu.be/1pkFSA_rRFI

[RWD fords rule]

Thanks to both of you for the explanations, I re set the float levels today and found a partially blocked pump jet that was causing some trouble, also brazed up the small bleed hole on the side of a spare pair of accelerator inlet valves yesterday and fitted them today, I noticed the older valves have steel balls and newer have what looks like ptfe, both brazed up fine and the ball valves are working perfectly

Acceleration from idle straight to WOT is much better now still not perfect but is that even possible with large 50mm carbs?

Tom, the emulsion tube descriptions are making a lot mroe sense now thanks to your imput, I was searching for some useful information like this, most books are very vauge about emulsion selection and don't bother to explain how the actualy work, jsut listening to the Vizard audio now, a great find there Tom, thanks again

[Miniliteman]

Thanks Tom for that Vizard-youtube vid.
Only thing I would never do is drilling emulsion tubes and also blocking some of the holes in them.

Google for pics of all the emulsion tubes from Weber, I have them somewhere but also have the Weber book with all the data for the emulsion tubes.
If you acnnot find them I will scan these and post them here.

Emulsion tubes (Weber) come in families: for example F1, F2, F3, F5, F9, F11, F15 is a family.
Say if you start of with a F11 and you need a richer mixture on high rpm, try the F15 it has less holes at the high rpm side.
If you start with a F11 and need a bit more fuel overall (especially on acceleration), try the F3 as it's a thinner tube.
Unless the mixture accross the rev range is completely wrong do not change to a tube from another family, at least not at first.
An F7 for example is a completely different tube compared to the F11.

I found that with a relatively mild engine the choice of emulsion tube is not that critical; when we dyno'd my first BD (1700, BD3 cams, 40's) the differences in torquecurve with the F9, F11 and F16 tubes was minimal. When we dyno'd the rallycar BDG (2000, big cams, 55's) last year the differences between emulsion tubes used was very big. After several runs with all the usual suspects (F2, F9, F11) we looked at the results in the same way Vizard describes and I changed to another 'family' and things improved.

I now have most of the Weber emulsion tubes (except a set of F10's, anyone has 4 of these?) so when tuning an engine now in most cases I have the correct tube for that engine but it is a big investment.

[RWD fords rule]

Thanks Leon

A problem I am having at the moment is throttle accelertion from idle straight to WOT in neutral, the engine baulks, revs do not pick up straight away but when they do it sounds fine, no misfiring or anything like that

If I press the throttle easier there doesn't seem to be any problem, it sounds clean and snap off throttle also sounds fine

I have tried fitting 45 and 40 pump jets with size 0 acceleration valves, initially one of the pump jets were blocked and was causing a misfire then that went away when I blew out the jets an tested them on a spare carb, the acceleration with both F11 and F7 tubes and 40 vs 45 pump jets is about the same

Sounds like it is eather getting starved of fuel or too much, don't know which yet but also have 50 and 55 pump jets if needed

The car hasn't been driven yet so I don't know what the AFR is like and what is happening under sudden acceration but any advise about this would be great

Will be running in the engine on monday and fine tuning the jetting, cam timing etc, the distributor has a fast advance rate and was working perfectly on my engine so I can't see there being a big problem in that area

It is a strange problem as I was expecting pretty fast throttle response with the combination of parts, bit of a pain in the ass tbh but with a bit of luck we will get it sorted

Leon, what was the immediate throttle response like with the 55mm carbs on the BDG or did you ever test from idle straight to WOT in one go?

What size pump jets did you end up using for best throttle response?

Regards
Jason

[Group4_Mark2]

I am thinking that you are expecting too much from the engine to rev all the way from idle with wide open throttle without bogging down a little until the revs pick up. How does it rev from say 2000rpms. Is the cam much longer duration than before as this would effect it a little bit also. I would not worry too much about it as it should never occur when out on the stages. The revs should rarely get below 3000rpms.

Tom

[RWD fords rule]

I think you are probably right Tom, we may be being far too fusy with snap on throttle, its not a bike engine with nearly no weight to accelerate, the throttle response from about 3000rpm or a bit lower upwards sounds pretty much spot on, very fast

You are right the BF63 cam has a little more seat timing and also more overlap than the last one, its still a mild enough cam in terms of duration and lift on overlap but it is a step up from the RL31 we were using, also the 50mm carbs don't compare to 45's at all really since the throttle plates are so much larger, half throttle with the 50's most likely flow most of what 45's can with 38 chokes

That's it until monday, I am doing the best I can with it anyway and that's all that really matters, tbh a certain persons unrealistic expectations of ilde to WOT throttle response here at home and criticism of the performance isn't helping things at all, while he doesn't have any helpful suggestions or have any clue about tuning the engine himself, some things are never good enough for some people

[Group4_Mark2]

I suppose it is not a bad thing to expect perfection. However reality often falls somewhat short of this. All you can do it try to get as close as possible within the boundaries of the parts, equipment and time you have available to you.

Have you tried advancing the timing a little or advancing the cam a degree or two. both should help the low down response of the engine. Maybe it is not the carbs that are your problem at the moment.

Tom

[Graham]

sounds like what you really want are t/b's

[Group4_Mark2]

This is a new engine also which has not even been run in. Once the rings are properly bedded then compression especially at low rpms should increase. This should free up the engine and make it rev better at low rpms. I expect that after a good run on the track on Monday that things will be much better.

Tom

[RWD fords rule]

Agree with everything that has been said and I have also been thinking of the many things I can try to improve the throttle response

Graham, I agree there is no question if this was running on Tb's there would not be any issues at all after being fully mapped, it would be a right beast then but the budget isn't there at the moment tbh I can't see it happening on this engine

It is always a compromise when tuning on a budget, I think when I do go the TB route I won't ever go back because of the huge increase in performance, carbs can perform very well but its an awful lot of work plus you can never get the same level of performance TB's give over such a wide rpm range that is needed in rallying


Fingers crossed everything will go well on monday, it will be nice to see the car out on track with the engine under load, then start tuning from there

5 days after that we have the first event next saturday, talk about cutting it fine lol

[Graham]

your right when you do go the route your never look back, ive had mental race cams give fast road cam flexability

[Group4_Mark2]

A nice intermediate step is to use mappable ignition such as megajolt. It is relatively inexpensive and allows for ignition maps to be changed easily. It would be possible to fit megajolt and keep the normal distributor ignition in case of problems when it could be swapped over in a matter of minutes.

It would be a first step in going throttle bodies and full engine managment as you would need to fit the trigger wheel and pickup for the megajolt which could later be used for the ECU.

[Miniliteman]

Leon, what was the immediate throttle response like with the 55mm carbs on the BDG or did you ever test from idle straight to WOT in one go?

What size pump jets did you end up using for best throttle response?

In the end we used a 45 pump jet and a 40 spill back valve. Not 100% perfect and it still has a spit when you start a powerrun on the dyno but there isn't a hesitation whilst driving.
The BDG 'idles' at about 1800-1900 rpm and it will accept WOT from 2500 rpm onwards.
With big venturis, cams with a lot of overlap there is no smooth idle and it won't take WOT from 800 rpm.
There has to be a 'momentum' of the airflow to overcome the pushback from the cam-overlap and that takes a higher rpm than normal idle.
F1 engines idle at something like 6000 rpm.

Years ago I drove a Mk2 Escort from a friend in the UK; 2.1 Pinto, twin 48's and a BVH with a BF63 cam. Nothing there under 3000 rpm and by the time you shift in a normal car (5500 rpm) all hell broke loose.

If you use new carbs, take the cover off and put it all in petrol for a day. This clears out all the gum thats inside.
Lots of people use a flowmeter to sync the carbs. Have one also but found it not very accurate and not easy to work with.
Find that a set of vacuum-gauges is more easy to work with and more accurate but most times I synchronise the carbs by looking at the throttle plate through the progression holes (remove plug) and checking it all by measuring the temp of each the exhaust-manifold-runners with a IR-temp-meter. Properly synced the temperatures of all runners should be very similar.

[Roger Miller]

A line up

[RWD fords rule]

Had a rolling road tuning session yesterday, initially started off with F7's and they were too rich at low to mid rpm's, then I selected F11's to lean out the low to mid rpm range a little and they worked very well as expected, we also tried F15 and F16 as I hd them with me but the engine did not like them at all so went back to F11's

Thanks for the help with this, I think the majority of pinto's run very well with F11's throughout the rev range

Regards
Jason

[Miniliteman]

Interesting as the F15 is an F11 with no holes in the lower part; was it really that different than an F11?

Tip: check the emulsion tubes that your are gonna use and make sure the markings (F2 for example) are the same, have the same orientation, have the same size and place on the tube. Tubes with different markings are of a different batch or manufacturer and especially the newer ones (re-made by Eurocarb etc) have slightly different positions and angles of the holes so best not mix different tubes in an engine.

[RWD fords rule]

Interesting as the F15 is an F11 with no holes in the lower part; was it really that different than an F11?

Yes F11's and F15's have no holes in the upper rpm range with leaning from low to mid range compared to n F7 or F8, I can't remember the exact effects on hte power curve with the F15's but as I said we are running a unique set of chokes with this engine so the emulsion tube selection was a bit of an unknown until we got a few power runs done, we did a run with all of the E tube sets I had, the F7's, F15's and F16's did not perform as well as the F11's and the F15's and F16's did not work very well, I might be able to get a copy of all of the power runs with AFR if the rolling road operator still has them, but I am thinking he probably doesn't

[JRatto]

thanks to everybody that contributed. You guys got me to finally understand the how's and why's of Weber IDF/IDA/DCOE e-tubes. I've been trying to understand this and have been testing them in my 48IDA Webers for over 15 years, without a clear understanding. Your discussion here got me to understand it!

Thanks again!

Jim

[Dyno]

If you want more torque and more top-end power, fit 45 mm Webers. Forget about 48 or 50 DCO/SP.

[RWD fords rule]

With respect Onyd, you could not be more wrong about 48's and 50's, 45's are fine for fast road and up to 180 to 185bhp or so without restricting top end power from a 2.0 pinto engine, with a proper 200bhp+ pinto engine you would loose a load of top end power with 45's

If you know how to tune big 48 and 50mm webers very well you can get them to pull almost like throttle bodies

Don't believe me? here is a 2.0 pinto engine we ran in last wednesday at our local race track, Tom Grp4mk2 on here built the engine, ported the head to a high degree etc, I tuned the carbs with an lm2 wideband afr meter (already knowing what emulsion tubes, main and air jets sizes pinto's like to run on best when I tune them at a rolling road), and mapped the distributor advance rate to suit tarmac rallying with a rapid advance rate

Here is the engine in action at its first tarmac rally 3 days after the running in session with only a minor alteration to the idle jets to improve low end throttle response, the engine has not been to a rolling road yet but I believe it will be difficult to find more power from the engine in its current tune





There were 101 entries in this rally, Enda was the joint fastest 2 wheel drive car over this stage, with a joint 4th fastest time on the stage, beating a load of mk2 escorts with much more power, having 2.1 16v engines with 250bhp+ and even 1 or 2 2.5 millington engined mk2 with over 300bhp, I can send you a link to the stage times if you don't believe me

An extremely fast driver, best in the rally I would say, the engine has a roller cam, very nice flowing head, 136mm rods, 2024cc, twin 50's, custom mapped distributor, dry sump, 12 to 1 etc

Power figures are unknown as of yet but it is certainly making over 200bhp, not mental power but a lot for a barely over 2.0 engine

If this engine was fitted with 45's it would loose a ton of top end power, the throttle response with the tuned 50's is very good, 45's would be a big mistake on this engine

You live and learn, be open to trying new thing and you will find what works best, we know there is more to come from the pinto engine, I am planning a one off roller pinto with lets just say well over 200bhp and massive torque, and all for little extra than what people charge for 200bhp 2.1 pinto's with off the shelf parts, it can be done with the right know how and enough time to develop the necessary parts working 100% in combination with each other to get maximum performance

Sometimes you learn more from the mistakes you make than anything else, have to be willing to try new things otherwise you would be stuck under 100bhp per litre like a lot of pinto tuners are
When you get enough experience of what really works best then you start to see big results

[RWD fords rule]

The problem we were having at the start of this thread was due to the idle jets being too small, not saying what size we ended up using but it was larger, idle jets have more of an effect that one would think, thanks to Tom (Group4_Mark2) for suggesting this, after a lot of research + some testing I found a solution to the problem, big webers can be made pull well from low rpm's, takes some tuning but it can be done, distributor map is also critical for this

[Dyno]

I'm not saying you can't make a Pinto run perfect with 48 DCO/SP. At least, I can but I found out more than once (not only on Pinto's) that upto 240 BHP you can better still use 45 mm. Problems is they have 36 mm choke as standard. And people stick with them. Use 38, 40 or even bore out everything untill you have 45 mm on big power engine. If you can get carbs work this way you have a smaller trumpet and inlet track. Always the best.

There will never be a 2 Ltr Pinto who can outflow a 45 mm carb. Pinto's just don't turn high enough RPM's. Talking about 9000+ . Most Pinto's will work better with a fully reworked 40 mm carb. Depending on the engine they go easy upto 180 Bhp and even more. I'm talking about fully reworked carburetors, not just fitting a bigger choke and a different jetting.

[RWD fords rule]

We will have to agree to disagree on this one, my experience and countless others is that 45mm webers are too small for anything over 185bhp from a 2.0 pinto for rally and race, if you can personally ever achieve a genuine 200bhp+ from a 2.0 pinto on 45mm weber carbs AND compare this to the exact same engine on 48's back to back and not see a very substantial gain in high rpm power I will eat my hat..

48's are a good compromise between 45's and 50's, but even 50's can be made pull from low revs

Getting back to the 45's the issue is that they will never flow enough air with the std chokes available, get it on a flowbench and you will see, there is a massive difference in flow between 45's and 48's, 48's or 50's are needed to make proper power from a 2.0 pinto, you should be well aware of this if you have done any proper dyno tuning or flowbench work, either will prove what I am saying, the thing you are missing is that carbs have to flow considerably MORE air than the ports do in order to not restrict high rpm power, an ideal intake system is shaped like a long trumpet tapering down into a high velocity point in the inlet ports and then expanding into the valve throat area, past the seats and into the chamber, simulating a long venturi shape, the further out your carbs are placed the larger the throttle plates need to be

Choke wise 45's perform best with 38mm chokes for low budget competition engines, 40mm chokes are too large, there is not enough of a ventrui shape left pull any decent vacuum signal to the main jets, they will give more top end power but 38's will be faster in competition over all on most engines with better throttle response, been there done that..

Perhaps you should try what I am saying and see what results you get on a 2.0 pinto race engine, the dyno will tell all

[Miniliteman]

First: WOT response from idle can be made good from Webers with big cams and big carbs as Jason said. Just do not expect a smooth idle @ 800 rpm from such a combination.
Second: after some more experience plus talking to Pinto/BDA tuners I must agree to some degree with onyd here. The point is throttle plate diametre does not determine power, choke size does. I've seen some top BD's with 45's with 42mm chokes that have a very good torque curve and make good power also.
The airflow is highest at the choke, if after the choke (say 42mm) the volume expands again (say to a 48mm plate of a 48DCO) the airflowspeed goes down again whereas with a 45DCOE carb the airflowspeed would be higher because the volume does not expand that much.
So the plan with the rally BDG was to dyno it with the new cams and the 55's first then fit 50's with the same size chokes but sadly this opportunity never arose as the engine went bang 4 miles from the finish of the last stage of the rally (a year ago, idler pulley stud broke ...).

Regards, Leon.

[Dyno]

There is indeed theory and practice. I will close this case until I can prove it on the dyno. Unfortunately, we don't do so many race engines anymore. So will have to wait for a good 200 Bhp+ engine. But I did this kind of testing in the past. I can only relay on the result's I've seen.

PS. Boring out chokes or using big chokes has nothing to do not pulling fuel anymore. You don't pull fuel anymore if the choke is to big for the engine. (or should I say, you can get the engine tuned anymore over the full Rpm range). I've got more than enough engines running with virtual no choke. Most 40 mm of course to outperform 45 where 45 is not directly needed.

[RWD fords rule]

Interesting Onyd, I would be interested to see one of these engines with 45mm carbs and very large chokes in competition driven from very low rpm right up through the rev range, creating a decent vacuum signal to the 40mm chokes at light throttle openings would certainly be a problem to be overcome

All in all whatever the combination the ONLY things I am interested in is maximum acceleration, throttle response and an unrestricted power curve, in Reality you will need 48's to get over 200bhp out of a 2.0 pinto engine, I am sure I could achieve this power level out of a 2.0 or 2.1 engine on 45's just about making 200, BUT and this is the KILLER if I fitted 48's to that exact same engine it would make at least 15 to 20bhp more peak power and the power would not drop like a stone after peak hp as it would with restrictive 45mm carbs

If you think 45mm carbs with 40mm chokes flow the same air as 48mm with 40mm chokes you better think agan, massive diffence in airflow, WHY? because there is almost NO venturi shape with the 45 x 40mm chokes (almost a square edge leading into the choke) and a vastly better venturi shape with the 48 x 40mm choke with a gradual flared entry

If you can Prove your theories about 45mm webers being able to flow enough air for an unrestricted 200bhp vs 48's on a 2.0 pinto and have the same or better throttle response than 48's then please do, but theories are one thing and what really works can be quite different, I will stick to what I know works very well in competition, which is ultimately what is most important

Now If I were using throttle bodies I would choose a 45mm bore or possibly slightly smaller but not much, I tune for best mid range torque and best acceleration from near idle to max rpm, but if I loose 10 or 15bhp from using a small throttle bore or small choke with carbs I had better see a very substantial gain in mid range to justify such a big power loss, it all has to be at least dyno tested first and then tested in the car to make a final decision, a dyno does not test at light throttle openings with carbs or snap on off throttle use, it only simulates WOT which is not all that an engine sees in competiton

As always I am open to new ideas, once I see good results I can change my mind in an instant and often have in the past, it is good to be open to new ideas, especially when they have already been proven to work

[Dyno]

Why should a 45 mm DCOE with 40 mm chokes not pull from low down? And why should it have less accelerations than his bigger brother?

Please do the test.

[RWD fords rule]

Unfortunately I don't have time nor a reason to test such things, all I can say is I personally used 40mm chokes in a rally pinto engine and it would not pull well from low rpm's, I fitted 38mm chokes and suitable jetting which markedly improved the throttle response to the point that it was very responsive, have never used 40mm chokes since and most likely never will

With pinto engines I never use a choke diameter larger than 38mm for 45's, 42mm for 48's and 50's, this is part of the reason why 48's can be made pull from low rpm, using a sensible choke size to increase velocity through the chokes and get a good vacuum level to the main jets at part throttle

Choke airflow is less about internal diameter and more about the shape, to get good velocity and airflow through a 40mm choke it needs to be a 48mm weber choke, rather than a 45mm weber with almost no flared entry and exit in its 40mm choke, this shows up on the flowbench, I may have some flowbench data here comparing 45mm webers with 38mm chokes vs 48mm with 38mm chokes if you are interested

Here we go found it, taken from DV's A series tuning book, flow depression = 1.5" mercury or 21.3" of water

45mm weber with 38mm choke = 242CFM per barrel or 968CFM per 4 chokes

48mm delloroto with 38mm choke = 283CFM per barrel or 1132CFM per 4 chokes

Same diameter chokes, 17% increase in aiflow with the 48's and small 38mm chokes, the difference in airflow with a 40mm choke in a 45weber vs 40mm choke in 48mm weber would be greater again, added to that 42mm chokes are usually needed in 48's to not restrict top end power with high spec pinto's

[Dyno]

I'm glad you reference to David Vizard and his my book. Hope I'm not going to get into troubles with Mini engine builders as well but years ago I had to do testing work for a few "frog" drivers. They where using the same 1275 A+ engine as in the Mini with a different crankshaft. The guy was retired, sold his company, went into racing an had lots of money to spend. Asked me to test all kind of things on his engine, including every possible carburetor setup. He bought and borrowed everything available.

Vizard says 48 IDA would be best, at least 45mm DCOE, preferable "split setup". We tested everything, split against normal setup, just name it. Most carburetor setups made about the same power and torque, despite some cabs where much bigger. What we found out was that the 40 DCOE with 36 chokes on a long inlet manifold made the same power and torque than any other combination. Some give less. We where most surprised about the trumpets on this engine. Very long and straight tubes, no flares. Nothing seemed to work, we had a serious dip in the torque rev until I used 2 straight tubes and started cutting them until we found a nice compromise.

I'm not saying Dave Vizard his test work is fake. Not at all but results depend on other things to. Those days everybody was cutting Webers for split setup. I feel a waste of money. We where finally driving a 40 mm DCOE using 36 mm chokes. Engine was 1300 cc (within regulations) made over 115 Bhp and revved easy to 8000 RPM +

I'm never talking about air flow and air speed here. I feel if you use a 48 DCO/SP your trumpet is to big an give less pulse tuning (wherever pulse tuning is coming from, have no theory about that, I just fit different setups and try to leave the best one on the engine). The problem I always have with Pinto's is that the trumpets I need for full power are always much to long to fit an Escort shell. `

But I do believe you can have a complete different setup needed than most of us. First you refer to engine 200 Bhp+ , does this guy make 200 Bhp+ ?and you are also using other cams. Comparing is difficult. Sometimes you need a crazy part that never work on other engines to make this one work.

Hope we can do some dyno testing together in the future. Why not further test all these setups together?

PS, Mikuni HS carbs don't use chokes, go like hell and make very good throttle response, even in low revs flat out.

[RWD fords rule]

Comparing what works on a 1300cc 8v pushrod rally engine vs a 2.0 ohc rally engine is not anywhere near a close comparison but I can see the point you are trying to make

It is very clear to me now for 2.0 race engines you use a mild rally cam that is not capable of producing enough high rpm power to need to use 48mm carbs, what profiles do you use for example? I have mapped lot of the kent cams for list vs degrees on an excel spreadsheet I made, taking the very precise measurements in a test engine I have on the stand, doing this you will learn what profiles are really like in an engine with lash vs what is printed on paper

In the old engine with same carbs, same exhaust, same bottom end with wet sump, similar head flow, same valve sizes, we had a cam with 244* @.050", and a true 12mm inlet lift, this was a mild profile and was restricting top end power aswel as peak torque, the .010" lift timing was pretty decent being short duration so we could get a high DCR figure but the valve lift and .050" duration was insufficient, this was an off the shelf profile selected to give best response from 2500rpm up to 7500 to 8000rpm, nowhere near an ideal profile bit the best I could find at the time, which has massively changed since we started working on custom cams

The engine above with roller cam has a tad over 14.5mm inlet lift and more .050" duration, the improvement in top end power is massive vs the old cam, it will certainly make over 200bhp I can say that with conviction

Head flow is also very important, this engine has a very well flowing flowbench developed head with raised and filled ports based on an injection casting (ported and built by Group4_Mark2 on here) you are wasting your time if you are using carb heads without port filler, in a high output engine 200bhp+ injection heads are the ones to use

Have you done any flowbench work with your engines or are you assembling them without checking what parts will be best to use in combination with each other?

Our testing have revealed that a minimum of 13mm inlet lift is needed to make any decent torque and hp from a 2.0 engine, let alone 2.3, will roller profiles I believe the optimum lift with a well developed head is at least 14mm lift, otherwise you are loosing power by not unlocking the head's flow potential, this is the very reason why we have different opinions about what carb size is ideal for a 190 to 200bhp+ pinto engine, with the through flow we get we need those 48's to make the power we need to be in competition with the best cars/drivers in the class, honestly using 45's you would be blown away over here with them in a stage rally, most of the top cars are running throttle bodies with over 200bhp, one of the cars we beat has 208bhp in fact, there are some 2.1 pinto engines over here with around the 220bhp mark but not many, try competing against them with 45's..

We have very stiff competition over here in our tarmac rallies, if someone else has well over 200bhp and throttle bodies that pull from very low rpm's upwards how are you going to compete against them with 45's?

Maybe now you have a better understanding of where I am coming from


Have you ever thought about fuel atomisation? this is one of the biggest reasons why I prefer not to use larger than 38mm chokes in 45mm webers, he stronger the vacuum you can send to the main jets from the choke and aux vent the better the fuel atomisation, which with webers and the pinto engine is certainly needed

With overly large chokes you will not be able to pull a decent vacuum sent to the main jets, then you need to use a much larger main jet to correct the afr, BUT now what you have is reduced fuel atomisation

Everything has to be though of and tested as one thing effects another and another, every bit of extra power adds up

[Dyno]

No, we did not flow test any of the heads and we will never do. My job is carburetors, not cylinder heads. Told you before, as a hobby I started buying cylinders heads advertised 200 Bhp+ incl. the camshafts and there specifications. Tested all of them and until now, best power is 190 Bhp. I tested with carbs, fuel injection, all kind of setups, including straight inlet ports. 200 Bhp+ engines are very rare, let alone 220 but OK I will never say it's not possible unless nobody can ever show me. I'm not chasing 200 Bhp but it would be nice. I want to find a good working combination, normal priced so I can advise my customers what and where to buy if they want to build a good rally engine (hoping we can sell the carbs and dyno testing).

The carb tests 45 versus 50 mm where done on all kind of 16V 200 Bhp+ engines, most 240 Bhp (mainly Honda and Nissan). I'm not sure the engine of this Topic is making 200 Bhp+. If not I keep advising 45 mm. If he does have more, from what I've been testing...... 45 mm.

About fuel atomization, we saw no different in power, carbs against Webers. No idea it is working. But I did had a word with a race engine builder who was using double injectors on a 2 Ltr Ford Duratec rally engine. He told me there was a power difference (injectors where side by side). I do know we had the same power on 1 big injector as with 2 smaller in the Honda turbo. Only, the "one injector" setup was using a lot more fuel and making a lot more flames. Power was the same but I switched to double setup.

Last time I changed my turbo test engine from Ford Pinto fuel injection plenum to DMTL carb setup and received 200 Bhp instead of the 183 Bhp (fuel injection power). Call this a miracle but it is a fact. Why, no idea.

[RWD fords rule]

If you are non prepared to do flowbench work with your pinto engines and use a suitable cam profile you will never see over 200bhp, every part has to work in combination with each other, if there is one part that does not work as well as the rest you will fall short of what the engine could make

What cam profiles are or were you using?

It is important to be very specific to the 2.0 pinto engine as this is what the thread is about, talking about other engines, 16v, A series pushrod etc is of little use here, each engine is different and will perform best with a different combination of parts than another engine, you can easily get over 200bhp with a 2.0 16v engine on 45's even 200bhp from a 1600 16v engine is certainly possible but that is a different engine and not the one we are specifically talking about

Off the shelf parts will never give best performance, that is why most people hit a wall at 190bhp from a 2.0 pinto engine even with high duration cams
45's and low lift short timing cams will never make a winning 2.0 tarmac rally engine over here, it will make a very nice fast road/moderate rally engine that would be good for very tight sprints but give it an open road and an engine with more lift reasonably short timing cam, a decent flowing head and 48's (to mention just a few important parts in the whole combination of an engine) will blow it away in terms of stage times and I am not talking a dead straight roads either, corners as tight as you like with some straights and it will still win by a big margin

Not going to say any more, I have made my point, if you don't believe what I am saying then please continue do your own thing, there are many ways to do things and none of them are right or wrong but some are faster than others in competition especially where the other competitors have big budgets and try all sorts of combinations to see what works best, a lot different than bolting together an engine with off the shelf parts and expecting it to be a winner

[Dyno]

try all sorts of combinations to see what works best, a lot different than bolting together an engine with off the shelf parts and expecting it to be a winner[/QUOTE]

I thought this was what we where doing for the last 12 years ?!?

short duration cams and small carbs where always my secret weapon. OK, not anymore.

I've compared one of my engine (I feel very fast and easy to drive) with the power graph of your engine in the other topic. Both are making approx the same power and torque but your maximum torque is about 160 RPM lower but maximum power is 400 RPM higher. I feel you can compare this engines as having the same potentials in rally. I did tried other combinations, even made over 193 Bhp but when I asking my computer to calculate average power and torque over a given RPM, this was the best setup.

I do find your torque curve very unusual. From 2000 to 2500 RPM torque comes in like a bang and than stay fully flat until it reached maximum power. We always have bumps and pikes all over and never see torque raising so fast in the low RPM. Most engines are struggling to stay running so low in the RPM's.

[RWD fords rule]

Hello Onyd, of course we are both trying new things, most people do not do this kind of work as it is quite time consuming but worth it in the long run

Yes the torque curve was very nice with the older engine, even with a lean spick which you can see just before 3000rpm, I later found this was due to the idle jets being too small, the idles have more of an effect than I once thought as they feed the progression holes, if too small or too large an idle jet is used the initial throttle response will be reduced, pump jets have much less of an effect here that the progression holes and idle jet size does

Anyway yes the torque curve is nice and flat, I always get torque curves like this, it is something to do with the tuning I am doing aiming for the best spread of torque and unrestricted high rpm power if we can manage both, the 12mm lift was really choking high rpm breathing

I have seen many power curves with the bumps and dips you describe but have not yet got this sort of a power curve, hard to say what exactly what is making this happen but intake and exhaust length may be the answer, I tune intake length for peak power, and exhaust for peak torque rpm's, to tune out some of those peaks and valleys to make a smoother power curve, I could make more peak torque or peak hp if tuning both intake and exhaust for the same rpm but then I would have a more "peak and valley" power curve as you described, I prefer a more even spread of power as it is easier to drive creating a little more confidence for the driver when he/she is on the limit of tyre grip and can progressively add more power as it is needed, makes a more flexible engine over all and faster stage times

The engine would accept full throttle from 2500 to 3000rpm on the dyno, this would have been a little better with large idle jets lowering those figures by a few hundred rpm, I have noticed when using very large chokes they will not want to pull well from low rpm which I suspect is due to a weak vacuum signal to the main jets, I would sooner use a slightly larger carb and small chokes rather than using a small carb and massive chokes in terms of over all performance, the internal diameter of the trumpet is important as you said, making it as small as possible without restricting high rpm airflow will produce a stronger intake pulse, we were using 50mm ID trumpets on this engine, same as on the roller cam engine, can't remember what ID the std 50 trumpets are but they are larger than this, 45mm ID trumpets would flow enough air for big peak hp numbers but making a 45mm carb would be a big task, maybe not impossible but would need some custom parts developed to flow more air through them while still having a good vacuum signal to the main jets, the aux vents can loose the opposite booster "leg" like the dell carbs to gain a little more airflow but that is not a large gain, still worth doing all the same

I would be happy to work with you if you are doing any dyno testing on this engine in the future, two heads are better than one, you seem to have a lot more experience than I do with downdraft carbs and cam setups to get best performance, I am mostly interested in maximum effort rally engines with wide torque curves but getting good power out of a road engine can be a challenge in itself, we are on the same page about cams and I agree with you about smaller carbs being better over all up to a point where the 45's are restricting top end power I would never place 48's on a 2.0 pinto engine making less than 180bhp but over that point I choose 48's if the application needs good peak power aswel as mid range punch and low end power, for tight gravel rallies 45's are often better over all but it does depend on the power levels needed on the straights