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Thread: Removing Choke Butterflies from 32/36

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    Re: Removing Choke Butterflies from 32/36

    just out of curiosity -
    instead of fitting a pair of twin 40s, how about two modded inlets and using twin 32/36s.
    it may not be as good, but i could do it for less than half the cost.

    Does anybody think itl work, or would i just be wasting my time?

    I love to experiment!

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    Re: Removing Choke Butterflies from 32/36

    i've been playing with a ported big valve pinto head on the flow bench, not to find more flow from the head but to flow test the induction, i tested a bare head and a head with just a manifold, and with first a 32/36dgav then a 38dgas



    in all tests i flowed cylinders 3 and 4, this is because the inlet manifold branches are considerably different in shape, i came up with some interesting results, firstly the std inlet manifold flows better on cyls 1+4,

    secondly, thers not a lot of flow difference between the 32/36 and 38 dgas in std form, which is something i remember dave walker finding out on his bench years ago, from seeing how closing the throttles off on my bmw head effected flow and having seen how a similar amount of closure effects power on the dyno i would have to say that simply swapping a 32/36 for a 38dags would be worth only about 5bhp at best!

    3rdly its not the carb thats really holding back the engine its the inlet manifold! although the inlet manifold isnt a great match for the head (the manifolds smaller) opening it up to match the head did nothing,

    the manifold needs serious work at the carb end the roof of the ports where they meet up under the carb need a serious amount of work to widen and lift them up and give them a long gentle radius porting the manifold in this way gave 4 times the flow increase that swapping the 32/36 for teh 38dgas gave


    in the pic below i've only ported the branch to no3



    to give a comparison this is the other side of the manifold going to no2 which is a mirror image of no3

    Last edited by Graham; 07-07-2009 at 09:08.

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    Re: Removing Choke Butterflies from 32/36

    Interesting findings there Graham, Is there much material left in the top of the ports when you are finished or do you risk breaking through? I will be watching the progress of this with interest.

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    Re: Removing Choke Butterflies from 32/36

    because of the thickness of the vertical part of the casting that carries the carb you can take a huge amount of material out at the top of the port without any fear of breaking through because by the time you get anywhere near the actual manifold branch you will of tapered down to the height of the origonal port

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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by DEATHYARD TIM View Post
    just out of curiosity -
    instead of fitting a pair of twin 40s, how about two modded inlets and using twin 32/36s.
    it may not be as good, but i could do it for less than half the cost.

    Does anybody think itl work, or would i just be wasting my time?

    I love to experiment!
    i guess its possible and would work, i think it would be a huge amount of work, i personally dont think it would be worth it, either fit a pair of 45's OR mod the manifold as shown above and tweek the carb.

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    Re: Removing Choke Butterflies from 32/36

    Great work there graham

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    Re: Removing Choke Butterflies from 32/36

    yesterday i made a pretty bold statement and that was its the manifold which holds a pinto back not the carb, today im sticking to it!

    and going one step further and say ing the 32/36 is a really well designed carb which is hard to improve on flowwise.

    i might of found bigger better improvements if i had been testing the carb bolted directly to the flowbench rather than the head and manifold it will be used with but seeing as cars are not powered by flowbenches that seemed pointless, the object was to find what i needed to do to to the carb to minimise flow loss,

    the head was set with a valve 0.500" open so as to stretch the carb, as i was looking for very small changes and the vacuum and therefore as reading on the manometer can vary slightly as time goes on, before doing each test i took a flow reading with just the manifold on the head, and if the reading on the manimter wasnt exactly at my previous starting point i would open or close the valve a fraction until it was, then after removing the carb checked the reading was the same as it was at the start of the test.

    what i wanted to do was maximise flow for minimum choke size, so i modified the chokes last


    shortening the screws where they stuck through the throttle spindle produced an immediate gain putting the 32/36 very close to a 38 dgas flowise




    thinning and knfie edging the aux vents did NOTHING to improve flow only one is done in the pic but i did both, i also tried the thinned aux vents on a DGAS they showed no gain in that either, removing the choke flaps again made no flow difference, i then took the screws out the throttle spindles all together to simulale countersunk screws, that had a big impact on low, lots worse as a butterfly fell out , so i tested with no butterflies at all just the spindles and flow went up a very small amount, suggesting (especially when considering shortened screws were a gain) that countersunk screws are a good thing



    finally i started opening out the chokes, first to 27/28 that have very little effect then to 28/29 not much effect there eithe with teh chokes opened out there was a slight and i mean slight gain from the knife edge aux vents, which was a bit suprising until you do some maths

    an engine on a pair of 45's will breath normally through an inlet manifold with practically no flow loss and a 36mm choke which has an area of 1017mm,

    an engine on a 32/36 breaths through an inlet manifold which does restrict flow (even my much improved ported manifold cant flow like a sidedraft manifold) through a 26 and 27mm chokes added together these have an area of 1102mm, thats bigger than the sidedraft choke!

    ultimately modding the carb didnt improve matters much, the manifold even when modified is still the biggest hurdle powerwise, the flow loss through the carb is less than half the flow loss the manifold produces.

    my conclusions,

    you must concentrate on the inlet manifold not the carb
    and unless you have an ultimate spec head and megga high lift cam, as opposed to my good big valve head and fast road cam, then, the 32/36 is nearly as good as a std dgas and if you mod the throttle spindle screws its as good as the dgas, fully modded my dgav was better than a std dgas.
    removing the choke flaps is a waste of time as is opening the chokes out more than maybe a mm or 2, thinning the aux vents is also pointless unless you have done everything else.

    the 32/36 is just a really well designed carb with no real weakness,
    Last edited by Graham; 08-07-2009 at 10:07.

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    Re: Removing Choke Butterflies from 32/36

    Good work there Graham and as usual some interesting findings. I wonder if you have tested the effect of different spacers under the carb and also the effect of putting some sort of trumpet on the inlet side. (maybe using clay or plastacine) Also would be interesting to see what effect different air filters had on the flow.



    Tom

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    Re: Removing Choke Butterflies from 32/36

    Graham this is all good work, however I had a 2.1 and had a 32/36 on it it was RR @ 142 and we swapped it for a 38/38 and got 148BHP same rollers back to back, standard manifolds both carbs jetted and the power valve modified in the 38.

    Both carbs were standard the manifold was only port matched to the head.

    I wonder if you could complete your mods on both carbs and spend a little more time at the rolling road and do the same back to back test to find the real difference with all the mods done.... this to me would be really interesting.

    I also have some data that gives the 32/36 a CFM rating of 260 and the 38/38 at 290 thats 11% which is a lot more than the 2.5% gain I found.

    Having said all this I have absolutly no data on average torque or BHP OR fuel economy.

    Good work and good luck
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    Re: Removing Choke Butterflies from 32/36

    i remember vizard did some flow testing with ram stacks and filters he didnt find any flow gain but a small power inrease on the dyno but that is going to be down to ram tuning not airflow, i.e my bmw head flows the same whatever you attach to it, t/b, t/b plus ram pipe t/b plus stuidly long ram pipe but it makes different power with each setup,

    although i never tried a ram pipe i did play with the carb mouth on the bench, by holding my hand close to its opening and partically bloocking off the intakes, unless you blocked off a sizeable air flow change was negligable, but then again if you lok at teh intake area and compair it to the chaoke area its massive

    interstingly with the carb on the bench you can remove the whole lid and it wont effect flow! this says toi me flow is as much restricted by the thrttles and yet more corners for teh air to go round as anything

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    Re: Removing Choke Butterflies from 32/36

    however I had a 2.1 and had a 32/36 on it it was RR @ 142 and we swapped it for a 38/38 and got 148BHP same rollers back to back, standard manifolds both carbs jetted and the power valve modified in the 38.
    thats interesting clint a 6bhp difference on a 2.1, but then again the 38 does actually flow more air from my testing i predicated a 5bhp difference as a max, so were in the same ball park, whats clear though is that for years everyone has said a 38 would give a lot more power, it simply doesnt! i'm not saying the 32/36 is a better carb, just a modified 32/36 is better than a std 38, no doubt a modded 38 would be better still

    I also have some data that gives the 32/36 a CFM rating of 260 and the 38/38 at 290 thats 11% which is a lot more than the 2.5% gain I found.
    which backs up what im saying the manifold is restrictive
    Last edited by Graham; 08-07-2009 at 11:16.

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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by graham bahr View Post
    which backs up what im saying the manifold is restrictive
    Almost certianly, be very interesting to see a back to back with your manifold mods.
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    Re: Removing Choke Butterflies from 32/36

    Very interesting stuff there!
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    Re: Removing Choke Butterflies from 32/36

    i thought i'd finished flow testing but then thought of another angle, adding the carb to the manifold drops the flow but i seem to of reached a point where by making the carb "bigger" isnt gaining me anything, which suggests that its a case of teh air is struggling to get around so many corners, so perhaps a spacer under the carb may help as it gives the air a bit more "distance" to travel and sort itself out before going up a port,



    as you can see its not one spacer but a stack of carb insulators, the flow did go up, its only a small amount but up is up, i back to back tested it half a dozen times with both the modded 32/36 and the 38dgas to be sure i was seeing a gain, the results being the same with both carbs.

    a one piece spacer may pick up a fraction more flow due to having a smoother inside.

    a spacer should be good for power in that engines with restricted intakes usually benifit from having more "area" under the carb
    Last edited by Graham; 08-07-2009 at 18:42.

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    Re: Removing Choke Butterflies from 32/36

    with a nice alloy spacer you could start a nice turn much earlier into the manifold by robbing abit of the gasket face.
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    Re: Removing Choke Butterflies from 32/36

    Interesting results, it seems that the first step should be to modify the manifold as near as you can to not restricting the head flow itself and then modify the carb so that it just reaches the same flow figure of the manifold with the smallest size chokes and stop boring the chokes out right there so that you have the highest airspeed velocity throught the carb.............

    Although you say adding a trumpet did little or nothing for the airflow, you did not test the difference in airspeed.
    It makes sense that having a more streamlined shape funneling down into the chokes would give a higher airspeed.

    The main thing to consider is that an ideal intake system should gradually taper down from the trumpet to a high velocity choke point in the intake port before the throat area and then get larger again after that.
    The choke point in the port has the highest airspeed velocity but not the highest flow rate, if we fitted a carb that had a choke diameter the same size as this it might seem adequate but in reality it would not be anwhere near the optimum size for best cylinder filling,
    that's why 200bhp+ pinto's need at least 48's with 42mm chokes to make that sort of power, and the choke point of the inlet port will never be that big.

    All of these points have to be taken into account.

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    Re: Removing Choke Butterflies from 32/36

    I am still interested in the effect of different air filters. I would expect that many of the aftermarket foam type filters might cause a lot of obstruction to airflow. If the engine is going to be used in a road car then this has to be taken into account.

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    Re: Removing Choke Butterflies from 32/36

    The main thing to consider is that an ideal intake system should gradually taper down from the trumpet to a high velocity choke point in the intake port before the throat area and then get larger again after that.
    yes but thats an impossibility without going to sidedrafts

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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by graham bahr View Post
    yes but thats an impossibility without going to sidedrafts
    Hold on, translating the above information to the engine you are building you will need more flow through the carb than you have going through your inlet manifold.

    It might not seem like opening up the chokes did anything much for the airflow and bhp potential but what I am saying is that if the carb flows more air than the manifold (which it should) then you should be flowing the carb on its own, not throught the inlet manifold.

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    Re: Removing Choke Butterflies from 32/36

    Just to throw a bit of a spanner in the works.....
    What do you knowledgable people think of these?



    Or is that just a silly question?

    I was thinking of reducing induction noise, but if it is a silly idea just say so.

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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by Group4_Mark2 View Post
    I am still interested in the effect of different air filters. I would expect that many of the aftermarket foam type filters might cause a lot of obstruction to airflow. If the engine is going to be used in a road car then this has to be taken into account.
    I think you won't beat a tall K&N for unrestricted airflow and its long lasting filter design.

    Foam filters go hard over time are are much lower quality however they are the most common type available.

    The taller the filter the better, K&N style is best, as tested in vizards book, no flowbench testing necessary.

    Regards
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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by Dave View Post
    Just to throw a bit of a spanner in the works.....
    What do you knowledgable people think of these?



    Or is that just a silly question?

    I was thinking of reducing induction noise, but if it is a silly idea just say so.
    Looks ok to me, shouldn't restrict bhp at all, although personally I would only fit a tall K&N

    Regards
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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by Dave View Post
    Just to throw a bit of a spanner in the works.....
    What do you knowledgable people think of these?



    Or is that just a silly question?

    I was thinking of reducing induction noise, but if it is a silly idea just say so.
    you could buy it send it to me and ill give it a proper look over

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    Re: Removing Choke Butterflies from 32/36

    Hold on, translating the above information to the engine you are building you will need more flow through the carb than you have going through your inlet manifold.
    maybe, but over carbing the engine to wring every last drop of topend out of it at the expenise of reasonably ecomonmy and good flexability isnt what this engines about,

    its proven that a 32/36 will make a little over 140bhp, so my modded one should be just the ticket

    as im trying to build an engine with more grunt but same or better economy than the "dave" pinto without the noise and cost of sidedrafts hense the 32/36

    if REAL power was the name of the game it would be an RL32 and 48's, the owner wouldnt like the fuel bill though......

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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by graham bahr View Post
    maybe, but over carbing the engine to wring every last drop of topend out of it at the expenise of reasonably ecomonmy and good flexability isnt what this engines about,

    its proven that a 32/36 will make a little over 140bhp, so my modded one should be just the ticket

    as im trying to build an engine with more grunt but same or better economy than the "dave" pinto without the noise and cost of sidedrafts hense the 32/36

    if REAL power was the name of the game it would be an RL32 and 48's, the owner wouldnt like the fuel bill though......
    Of course, if you bored the chokes out too far it would be a pig to drive at low speeds and have very bad fuel econemy.

    However, as with everything there is a ballance, I believe the best compromise would be to have the carb capable of flowing slightly more air than the inlet manifold.

    You said boring the chokes out to 27/28 had very little effect, and 28/29 not much effect either, you should be flow testing the carb on its own as your intake is restricting the flow rate probably even with the std carb let alone one with bigger chokes, that is why you are seeing very little gains for such a big difference in choke size, 26/27 compared to 28/29, this would show a BIG difference on the flowbench if you flowed the carb on its own.

    The carb should flow at the very least 10% more than the most restrictive point in the intake system, in this case the intake manifold.

    Your 28/29 choke sizes should be about optimum for that engine if a little on the large side.

    It would be very interesting to test the difference in flow comparing the pressure drop you had flowing the carb through the entire intake system and then flowing the carb on its own, the difference would be very noticeable.

    Nice work

    Jason

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    Re: Removing Choke Butterflies from 32/36

    I believe the best compromise would be to have the carb capable of flowing slightly more air than the inlet manifold.
    i understand what your saying just dont see any point to it, bearing in mind this is going on a road car which will probably speend all of 0.001% of its life at full throttle,

    the opposite is my race car which has 50mm throttle bodies which i thought would be way oversized but interestingly still reduce flow a little when attached to a manifold which has zero flow restriction

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    Racer Decade Plus User RWD fords rule's Avatar

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    Re: Removing Choke Butterflies from 32/36

    On the subject of narrower throttle spinles and countersunk screws, here is the ultimate butterfly throttle body setup which has no spindles to interfere with the airflow.

    AT POWER throttle bodies


    I wonder how he holds the butterflies in place?
    Maybe he assemles the throttle bodies with dummy solid bearings and spot welds the stub shafts to the butterfly plates? and then fit the proper bearings afterwards.

    7% increase in airflow for a given throttle size is quite a big advantage.

    Regards
    Jason

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    Re: Removing Choke Butterflies from 32/36

    thers a lot to be said for modifying throttle spindles,

    starting again with another 32/36 i removed the spindles, put a bigger radius on teh edge of them countersunk them lightly inserted countersunk screws and ground flush






    std 38 dgas

    modded 32/36



    i put both carbs on the bench without lids or aux vents, i did a nicer job on the spindles on this carb than the previous 32/36, that one matched the 38, this one out flows it, not by a lot but repeated back to back tests showed the 32/36 to be flowing more air, and thats still on std unmodded 26/27 chokes,

    of course modding the 38dgas would probably make even more air flow but thats one for another day

    update, i've opened the chokes out a bit, to 27/28 well more like 27 and 28.5, as before testing with the carb on the head and manifold, shows the carb now to be restricting things very little, again very little difference between std and modded aux vents i think these would come into there own on a 38dags with modded spindles and big chokes, in my opinion, modded spindles and 27/28 chokes is as far as you should go with the 32/36, after that mod the 38 dgas, but the deficencies of the twin choke manifolding means you should really go to 45's if you want more than a few bhp more than the 32/36 can provide
    Last edited by Graham; 11-07-2009 at 14:59.

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    Re: Removing Choke Butterflies from 32/36

    Graham,
    do you think that the crossflow twinchoke manifold would flow better than the pinto one?
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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by exboyracer View Post
    Graham,
    do you think that the crossflow twinchoke manifold would flow better than the pinto one?
    I think it would flow much worse than the pinto manifold as it has much tighter bends, but wether it would flow well enough for the smaller x/flow or not I can't say, it would definately benefit from a porting job guided by a flowbench.

    Regards
    Jason

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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by graham bahr View Post
    thers a lot to be said for modifying throttle spindles,



    modded 32/36

    Those spindles look very nice, bike carbs have narrow spindles like that and countersunk screws, the worste throttle spindles I have ever seen are on a fiesta XR2 carb, they are much larger in diameter than the dgas with smaller butterfly sizes than the 32/36!

    What thread size are the countersunk screws you used?

    Regards
    Jason

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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by RWD fords rule View Post
    I think it would flow much worse than the pinto manifold as it has much tighter bends, but wether it would flow well enough for the smaller x/flow or not I can't say, it would definately benefit from a porting job guided by a flowbench.

    Regards
    Jason
    my thoughts absolutely

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    Re: Removing Choke Butterflies from 32/36

    What thread size are the countersunk screws you used?
    no idea, one of the screws was a weber dcd the others dcoe

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    Re: Removing Choke Butterflies from 32/36

    Finally have my pinto running and driving! Its running on a modded 32 36 as in these pages. Bored chokes, knifed aux, knifed throtlle plates and spindles no choke. Thing is, i never drove it before i put this engine in so i dont know if it's better or worse! Idles very rough but the cam is unknown as well. Planning on buying a weber ADM 34 as used on aussie 4l sixes to see how it goes in comparrison. Also considering a DCD as ive seen another one for sale.

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    Re: Removing Choke Butterflies from 32/36

    what you need to do isnt try another carb but get to a rolling road and get the one you have fitted properly jetted!

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    Re: Removing Choke Butterflies from 32/36

    Yeah i'd like to do that but funds wont allow it at this stage. The adm can be had for $20-$50 here so i figure its a worth while experiment. Can always resel and try something else.

    Would also like to try a stock DGV in case my rough idle is due to the knifed butterflys etc.

    Anyone know of good DCD info online?

    Aaron

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    Re: Removing Choke Butterflies from 32/36

    the dcd was a great little carb, but with a tiny 28mm primary and 36mm secondary i cant for one moment imagine it outflowing a modded 32/36.

    if you have bored the chokes in your carb you WILL need bigger main jets so it might be worth just trying a couple of sizes bigger, wont help the idle though.........

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    Re: Removing Choke Butterflies from 32/36

    Yeah i did put in a few sizes bigger, will check tomorrow what they are.

    Im thinking the knifed butterflys have got alot to do with it. Might even find a buggered one for parts and switch to standard butterflys to check if that makes any difference.

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    Re: Removing Choke Butterflies from 32/36

    Interesting results that in many respects go against the findings of Dave Vizard in his SOHC book. Dave states that the standard manifold is very good for flow and that all runners flow within 1.5% of each other - he confirms that large radii on the entry to the runner improves the flow of the manifold as well.

    However he is very clear that the restriction is the carb and not the manifold and that without changing the manifold every modification to improve the flow of the carb resulted in additional power.

    Having fully modified both a 32/36DGAV and 38DGAS I can confirm that there is very little if nothing to choose from the carbs apart on a mild tune engine from the 32/36 being more drivable. However both were a significant improvement on the stock carb on a standard manifold. Indicating to me that changes to the carb net the biggest gains.

    I made the radii changes to the manifold as per Vizard but nothing more as he stated that the stock manifold will out flow the carb right up to a 500CFM holley - stock carb rated at 288CFM @ 3"HG and fully modified at 337CFM@3"HG

    Measuring airflow accurately is a tricky business and why flowbenches cost £K's - measuring pressure drops without a fixed reference point with a fixed depression will lead to all sorts of erroneous data.

    Andrew

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    Re: Removing Choke Butterflies from 32/36

    Quote Originally Posted by Darkspeed View Post

    Measuring airflow accurately is a tricky business and why flowbenches cost £K's - measuring pressure drops without a fixed reference point with a fixed depression will lead to all sorts of erroneous data.

    Andrew
    I think this is a bit harsh, a vacuum cleaner type flow bench can be a useful tool. Although it will never be accurate to give cfm readings, it will however show improvement increases in flow. In the past many a good cylinder head has been developed on a flowbench like this.

    ncoll

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