This thread will be built up to provide information & experiences from my intake manifold project. With a lot of NASP fans on CGTI, I thought this might be of interest & of course discussion is encouraged Aim: Improve engine output without compromising packaging. Increased torque output at higher RPM is desirable. Range: Strictly limited to the 52mm (runner diameter) ABF Intake manifolds. KR & 9A 42mm & 50mm are out of the scope of this project. Standard ABF intake, 52mm dia runners, plenum Shortened ABF intake, runner length reduced by 30mm, standard plenum volume Larger plenum ABF intake, as per shortened intake, but with plenum volume increased Standard The standard intake is obviously the cheapest option out of the three tested. It either comes with your ABF engine or can be purchased from breakers / online for a few notes. If fitting to a KR or 9A, you will need the lower section aswell, which the fuel rail & intake manifold attach to. Shortened ABF manifold that has been shortened as much as possible without interference with the ignition plug leads & vacuum line for the fuel pressure regulator. 30mm of runner length has been cut out. Requires either silicone joiners or welding. In order to connect to the support brackets at the rear, longer bolts & spacers are required. I simply used washers taped together. Larger Plenum The shortened manifold has had the plenum volume increased by the same distance as the runners were shortened by, 30mm. This allows the manifold to be packaged exactly the same as the factory item, yet has different geometry. Is the most expensive of the three as some fabrication is required Basics: Intake manifold geometry affects the engine output. Runner length affects the point at which peak torque occurs. Plenum volume can affect the amplitude of the torque peaks & width of powerband. Adjusting the runner length affects pressure waves within the runners. Typically short runners provide torque peaks at higher engine rpm & are found on race engines, bike engines etc. Long runners have peak engine torque at lower rpm & are found on passenger vehicles. Will be adding findings so far in an upcoming post...
Very good idea with a thread. Any idea what a short runner mani from audi s2 ( modified to fit 4cyl) would do to torque curve?
Just shows, if ever we believe we're all out of n/a 16v ideas, someone is looking to the next level. Looking forward to more
Have just fit the standard ABF plenum back to the vehicle & completed a reasonable map for it. The vehicle in question is running on Megasquirt & hasn't run a standard plenum for quite sometime. Initial development last year saw the short manifold produce more torque than the stock item. Both manifolds had well developed engine maps & testing was done on the same dyno, same evening. The engine at that time was restricted somewhat by a standard 8V GTI exhaust system. Vehicle has since been fitted with a 2.5" exhaust, so is now up to the task. Engine details: '96 ABF 16V 1984cc Block, head, camshafts all standard Exhaust = Mk2 8V downpipe into Jetex 2.5" 2-box exhaust "non-resonated" Megasquirt ECU Ford 4-pole coilpack Thanks, hopefully it will be interesting / useful when tested & conclusions made. I think the S2 manifold chopped down would be too short for a NASP engine, without the positive manifold pressure from a boosted setup, it would be tuned for peak torque at an rpm that is out of the operating range. This is similar to when bike throttles / ITBs are fitted direct to the head of a standard engine & have either no trumpets or very short ones. If the S2 item was to have the runners lengthened & packaged close to the slam panel, then this might be usable. Failing that the S2 item is great for turbo vehicles as it leaves space at the rear of the engine for turbo placement.
Great work so far, reading in with much interest. As for this, SteveR runs one and on the 16v dyno day his plot was comparable to the other 16v ABF's using the plenums and also the ITB's. I remember his torque curve being quite flat, missing the mid range peaks of normal plenom and the ITB's. This resulted in less breathing over all but slower decay at the top end. When i was making my ITB manifold and trumpets the inlet track length was one of the most important aspects. The distance was worked out by knowing peak torque rpm and engine size etc 330mm+ distance would make a good starting point for a plenom car so 'short runner' is not really a given it needs to be a 'matched/optimised' inlet track. As said, runners that are to short will not help the peak torque, you want to give it a ram air effect/boost that a matched manifold can acheive. Out of interest Ben, do you know the length of the runners in your optimised manifold? are they close to 330mm?
Steve's plot: Engine: Base ABF head and block. 1.8T AGU Manifold integrated on 16v runners. ECU MS V3 extra w/road/dyno optimisation. It is believed the power and torque profiles as seen in the plots, were greatly influenced when the plenum is placed on runners that are too short. This reduced the low and mid speed torque, but allowed the torque at higher engine speeds to decay at a reduced rate compared to a full plenum vehicle.
1.8T manifold adapted to a NA engine, I will say for a standard engine the runners are too short. With the standard 16V manifolds you can make 160bhp @ 6000rpm instead of 7000rpm + enjoy having at least 10lbft more everywhere except after ~6500rpm. Adapted 1.8T setup either requires longer runners, or hardware changes that support the higher rpm delivery. Introducing this to the initial aim listed in post1, yes it can be packaged in ok, and yes output is increased at high rpms. However, comparing this to the output of the shortened ABF item (first graph I had to hand), the adapted 1.8T manifold makes less torque everywhere below 6800rpm. Perhaps there is an advantage 6800rpm onwards when gearing comes into play, allowing you to stay in a lower gear for longer.
Cheers Tom, Steve's and your own setup highlight the effect of runner length. Diameter also has an effect, but if your hardware already comes in a certain diameter, it is best to stick with it when making simple changes. The length reduction was limited to the packaging constraints, I recall the base manifold being pretty much 400mm, making the shortened version 370mm. Any shorter would require the intake to be repositioned, like the S2 / 1.8T in that it does not go over the cam cover but heads towards the slam panel.
370mm should be pretty good, I think mine, overall ended at just under 360mm (measured from back of valve to radious of trumpet) (again packaging and fabrication restraints came into play) running a 42mm intake diameter.
I know im jumping the gun here but do you know the volume of the new plenom vs the OEM one? It will be interesting to see the differences. Reading in I have always thought that the bigger the plenom the better and a miniumim guide of 1.5 x engine capacity works for NA but looking at the info Alan posted here yesturday it says a smaller plenum is more benifical? For NA As said earlier, looking forward to the results to see what holds true with plenum volume.
This topic brings into full focus the airboxes seen on the n/a Touring Cars and S2000 IRC rally cars. I'll skip adding pics, as it'll become a motorsport conversation, but they have pretty big carbon airboxes and a single throttle flap.
Initially, plenum volume measurements weren't planned for the thread but I did think about it & they can be done fairly easily, especially as I have both normal & increased volume items minus the runners. As for what is best, I am not too sure about the magic numbers that are on various websites. 1.5x may have worked for a particular setup, then again 0.8x may have worked for someone working with different engines. I think there is more to it, e.g. the size of the throttle body & restrictor if present in a race car. Lets measure the volume(s), conduct some tests and go from there.
that quote confused me too, looking at the skunk2 and other aftermarket Honda inlets, it seems the try to shorten but enlarge the runners and the plenum is usually increased in volume, have look at the link i put up today, from rising sun performance, there must be lesson we can learn from the honda engines, as they are streets ahead in power terms.
I'm a firm believer of big plenums, and matching the runner length, my inspiration has always been touring cars, rally cars and some of the super cars aka some Ferraris.(same as Chris) I take a pinch of salt when I see an after Market manifold! How much testing have they had? And are there any proven gains with them? The skunk works look nice but no 1 runner air flow has a tight bend to make. What makes aftermarket better than OEM, is it the new inlet track lengths (if they are different), the plenum size or the aesthetics that mark them better? Or is it the smoother runners and bigger TB size? If any gains are actually made. (the hondas are much higher revving engines so will have shorter inlet tracks by nature anyway). There is so much theory but it always comes down to application and hardware Specifics, trial and error. Hence why this thread is hopefully going to be so good once all the data is up, nothing beats trial and development. I will do some plenum testing myself in the future once I have cutup my slam panel and have some time! I have started to make some but have had to put it on hold.
Test1 completed this eve. Testing is being done using a Gtech pro. This test featured the original ABF manifold. Initial thoughts = output is reduced & fairly flat e.g. you can't feel it pull massively harder at a given rpm. The three tests from this vehicle will be posted up when the whole set is completed. Meanwhile I can dig out some dyno plots & run simulations that show effect of geometry changes.
any plans to trial a tapered plenum? the theory being it helps speed the air up, however the JDM scene mostly uses tapered plenums on boosted engines!! i was going to use a tapered design on my engine but the JDM manifolds are changing my mind.