Roller Barrel Idle Issues

[flak monkey]

I am having problems with my roller barrels on my duratec. I cant seem to adjust the idle speed down under 1300rpm.

There arent any vac leaks anywhere that I can find.

Its to the point that the barrels can be completely shut (i.e. no visible opening at all) and the engine still ticks over at 1300rpm or so. And you can also feel a decent amount of air being drawn into the engine if you put your hand over each port, or put a synchro there.

The throttle bodies bolt direct to the head, the sealing faces are good and all fitted as per the titan/cosworth instructions. There arent any other joints in the intake system beyond the rollers.

It seems as if there is too much air leaking past the rollers.

[Graham]

fast idle is usually an air leak, but could also be a lot of ignition adavance

[flak monkey]

I cant find any leaks, and the idle advance is set at around 9-10 deg and I have checked it with a stobe.

The only joints on the engine side of the rollers is the mating face between the head and throttle bodies which have o-rings fitted as per instructions. There are then 4 map take offs which are connected, pipes are clipped and double checked for leaks. Unused MAP take offs are blanked too. Other than that there are only the injectors which are fitted with std o-rings and seem to be sealing.

My concern is that so much air seems to be getting drawn past the rollers even when totally shut (i.e no visible opening)

[team_zi]

Can you listen with a pipe to your ear, to each intake runner, and determine if one is drawing more air than the others?

Could the o-rings be supplemented with some gasket compound to remove any chance of a leak?

[boXXer]

get a load of aerosol brake cleaner or wd40 and spray it everywhere around the inlet side. If the revs pick up you should find the leak. I had a similiar problem with my pinto and it did my head in.

[flak monkey]

Thanks guys.

Had the throttle bodies off yesterday afternoon. Fanatically cleaned everything and put it all back together, checked all hose connections etc etc and now I have a hunting idle. Which screams air leak to me, though it could equally be one of the 2 different problems I found in the ECU map too.

Pulled them off again, refitted with the same result.

Up shot is that tomorrow evening the o-rings will be suplemented with some hylomar, I have removed and refitted the MAP take offs with another liberal dose of hydraulic thread sealant. All the MAP pipes are a good tight push fit, so I doubt any of those are leaking but I will go around with some brake cleaner and see if I can find any in the multiude of joints.

[team_zi]

If you cant fix this, try Northampton Motorsport as Titan said that they have a lot of experienc with the roller barrels.
I've yet to bolt mine on, and am hoping I dont have the same issues.

[flak monkey]

I have spoken to Troy at Northampton Motorsport (on Titans recommendation) and he was very helpful. I have yet to get everything back together again and see if I have found the air leak and if I can then get my idle down to a reasonable speed. If I can then I will be happy, if not I'll be on the phone again to a few people.

It wouldnt suprise me if the leak was on the injector o-rings or something equally as silly. My only thought is that *IF* my original fast idle was cuased by a bigger air leak I think it would have to be across all the cylinders as the engine was running relatively smoothly just too fast.

I now also have a much better idea of what sort of idle advance etc I should be aiming for.

[team_zi]

Fitted the Titans on permanently tonight. I've put silicone compound on the face of the TB's where they mate to the cylinder head, to hopefully avoid any air-leaks, and to hold the o-rings in place whilst being fitted.

[dobuy]

Probably worth doing, the only slight problems I have had with my engine was caused by a small air leak on the Jenvey's. This was because one of the manifold nuts thread was a bit dodgy and I could not get decent torque on it. Once I re-cut a lengthened thread and put in a longer bolt, it was all good.

[team_zi]

The Cosworth manual says to use a blank 6mm drill as a means of holding the barrels open, and setting the idle stops.
Surely a 6mm throttle opening is way too large for idle?

[flak monkey]

The Cosworth manual says to use a blank 6mm drill as a means of holding the barrels open, and setting the idle stops.
Surely a 6mm throttle opening is way too large for idle?

6mm sounds large until you look around the back of the throttle bodies where they mate to the head. There is essentially no opening at the back with a 6mm gap at the front.

I still havent got around to sorting mine. Been tied up doing other things the last couple of days.

[flak monkey]

Well I still have idle problems.

Refitted everything again with no sealant or anything. Idle was a little rough to start with difficult to tell if it was hunting, if it was it was small.

However I still have a 1300rpm or more idle

So I now either have one massive air leak across all cylinders or no air leak and a still high idle.

Spraying brake cleaner in the each barrel results in the idle speed slowing down. Spraying it around all joint has zero effect.

Thats with 4 deg ignition advance too.

I need of a little motivation now

[flak monkey]

Apologies for the multi posting.

After finding out that I am not the only one who has problems setting up roller barrels with high idles (a few respected RR guys appear to have the same problems) I am probably going to change them to std Jenvey type throttle bodies and be done with it.

I dont really want the hassle. But I am 99.99999% certain I dont have any leaks anywhere causing such a high idle (I am looking at a LEAK in the region of at least 200CFM! Which is hardly minor!) and I am not prepared to live with a crap 1300rpm idle just for a few % more flow at WOT which is probably irrelevant with force induction anyway!

David

[flak monkey]

Again just an update to this.

Done some calcs which indicate that my 1300rpm idle on my 2.0 engine would equate to a 1100rpm idle on a 2.3.

Having spoken to Raceline this morning, and they gave similar opinions on the roller barrels as several other knowledgable people have, I decided to order a set of DTH Jenvey throttle bodies and associated gubbins from them and they should arrive tomorrow morning. I then have some stuff to get made to blank off the injector ports for MAP signal and make some throttle cable brackets then I should be up and running. Though I am not counting my chickens just yet!

The major downside to this is that I am not going to be able to keep the plenum inside the bonnet, which is disappointing as this was the main reason for going with roller barrels in the first place because they are so short.

Anyway, onwards and upwards. Lets see if things improve from here.

[team_zi]

Bad news. I'm sticking with my Titans. I'll let you know how I get on.

[dobuy]

My mate Mick Attree has used the Titans on many of his Caterhams without any problems, might be worth giving him a bell. He also has built many engines for the Caterham factory as well

[flak monkey]

I reckon they would be ok on a 2.3 or a highly tuned 2.0 running lairy cams but the amount of air that leaks past when closed is just too much for a 2 litre on std cams.

I'll let you know if the same problem persists with the Jenveys....

[Roadsport]

So there is not exactly anything wrong with the roller barrels they just are that way?
Is it impossible for you to return them and try antoher pair or roller bodies? Just to make sure the pair you now have is not faulty ?

[team_zi]

So if you ignored the 6mm drill cosworth setup guide, and just unwind the throttle stop, completely closing the throttles, do you still get the high tickover?

[flak monkey]

Nothing happens until the rollers start to open up in the opposite direction (you start to get an opening at the top of the barrel). There is absolutely no effect on the idle speed. Which doesnt suprise me as when you look around the engine side of the throttle bodies there is no visible opening at all even with a 6mm opening.

Solved the problem with the DTH Jenveys from Raceline. Idles perfectly at 950rpm now.

[team_zi]

So the air must be flowing around the circumference of the barrels. Hmm... pics of the Jenvey setup please.

[flak monkey]

Yes that is the conclusion I came to in the end. I couldnt find leaks anywhere else.

Heres a pic of the jenvey set up



I'll nip outside and grab a couple of pics of the rollers now they are off and show you what I mean with the idle gap on them.

[flak monkey]

Just to clarify.

This is a pic from the front with the recommended 6mm idle gap



And this is from the back. As you can see there is no opening on this side. (Its a shadow from the flash at the top BTW) You need to open the roller about another 1mm before you start to get an opening on the back and it will start to open at the top of the port.

[Graham]

very interesting,

having seen all sorts of throttle dodies, slides, rollers, fancy double rollers, spindless, i've come to the conclusion, that a simple conventional butterfly is best!

even if you have to use a slightly bigger one to over come the drag from the butterfly

[flak monkey]

Thanks for all the input anyway guys - always appreciated.

You live and learn and from now on I will just fit standard butterfly throttle bodies unless I build a balls out racer! I wasnt even really interested in the performance bit of them it was because they were so compact I went for them.

Anyway - the rollers are now on ebay if anyone is building a 2.3 or racer

[Roadsport]

very interesting,

having seen all sorts of throttle dodies, slides, rollers, fancy double rollers, spindless, i've come to the conclusion, that a simple conventional butterfly is best!

even if you have to use a slightly bigger one to over come the drag from the butterfly

I've been thinking the exact same thing. only I have no experience on slide/ giljotin bodies. Whats the down side with them?

[Graham]

slides are difficult to seal properly and tend to stick due to teh incoming air forcing them sideways against there own body, also the way they work they will favour one side of a port or just one valve on a multivalve except at full throttle

[Roadsport]

When I was choosing my throtle bodies this MBE race engines diagram made my choise a bit easier.
That and the fact that there were only DCOE flange rollers available for the sigma. So the runners would not be exactly alingned with the inlet ports.
The rollers flow more only after 75 degrees opended throttle. And the butterflys curve is a bit more predictable and that could make for a more reliable consistant throttle response.
And when compiting on short Finnish circuits the time is made in the corners where the throttle angle most propably is below the 75 degrees.

AT Powershop started to produce DTH slides to sighma just after I had ordered TB's from Jenvey and I was a bit bummed about that. But maybe its all good after all.

Heres the link to the MBE site

http://www.mberaceengines.co.uk/throttle/index.htm
Page 3/4 on the flash player screen.

[team_zi]

Were the titans brand new? I know they stress how important it is to run with filters, to protect against wear.

[flak monkey]

They were indeed brand new.

[Vxlgsi]

problem with roller barels is sealing them up where the shaft runs through.. if everything else is sealed up thats probably where the air is coming from

[team_zi]

Could it be that the barrels are aluminium in an aluminium casting, and until the casting and barrels have warmed up and expanded, there is a tolerance issue, allowing air to flow around the barrels?

Did you actually get the engine warmed up with the Titans on, to see if the RPM then dropped down? I wouldn't be worried about this side effect, as a cold engine usually needs a bit more throttle to keep it ticking over until its fully warmed up anyway.

[flak monkey]

Yep it got up to temp (90deg) for a good 15mins at a time over 2 or 3 runs trying to get to the bottom of the problem.

Its all aluminium so would all expand at the same rate anyway, so the cold clearance should be the same as the hot clearance.

To be honest it doesnt suprise me that I had such a high idle having had a look at how much gap is between the throttle plate and bore on the Jenveys, I reckon you can just get a fag paper in there. They are virtually closed with no air bleed.

[Vxlgsi]

I wouldn't be worried about this side effect, as a cold engine usually needs a bit more throttle to keep it ticking over until its fully warmed up anyway.

It shouldnt if its set up properly.