Split: Why doesnt drunkenalan's car make more power!!! little bump

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it was good to meet some new faces and the guys a GS again and get the car on the rollers again, it feels much better to drive and seems to pull stronger than before but just doesnt make anymore power than it did last time!![:^(]

i was comparing the graphs from last time


it almost identical!! so at least i know not much has changed!!

 

I'm amazed that this car hasn't made more top end power, given it's got the same spec of head, a similar cam, and the same management as mine, and 60cc more. After the initial dyno sessions a year or two ago, I assumed it would deliver more power when it loosened up a bit, as it was a fresh build. Has it done many miles since?

Maybe it is a question of the longer stroke and resultant characteristics, but I can't help wondering if there's another, simpler problem causing the restriction in the airflow, resulting in partial cylinder fill at higher rpms - like a badly mismatched manifold gasket, blocked exhaust, or maybe the exhaust manifold isn't giving enough extraction help?

I'm running a Supersprint manifold and Jetex 2" system on mine, and as the head was originally ported for carbs and matched to a mangoletsi manifold, I ported the inlet and ground out the gasket a bit to suit. I also did a little bit of porting on the Supersprint manifold to match it to the gasket.

I can't help thinking that there 'must' be a simpler cause, or at least that there needs to be some further investigation, before getting into a major engineering exercise.

 

Are you runnning the same intake manifold?

 

I strongly believe all the adjustments, both mechanically and from calibration have been optimised as best as they could be. I do have a very repeatable torque profile just after 4500- 4700rpm as you saw in both graphs, that would suggest a restriction, which I am of the strong opinion is coming from intake manifold pressure waves and their mismatch with STD PB inlet plenum. The plenum you use on yours is a ABK 2.0 unit and is larger than the PB unit plus you use a "tamer" cam on less CC. Alan's engine is far from the original PB spec and requires focused thinking to get it to run right. If this engine was on throttles I do believe that drop in torque after 4700rpm would not have happened. I also think these pressure waves are strong enough to upset the flow in neighbouring cylinders. This seems to be evident by the WOT oscillations in manifold vacuum that were present between 100-85kPa and got worse as the revs increased.
My money is on a manifold update.

 

Very interesting stuff, I hope alan gets to the bottom of the missing high end power and look forward to reading how, are there any quick OEM manifolds he could pop on and try?

 

Short answer is NO. Plus if there was you would still need to address the plenum, if the best performance was to be extracted.

Alan understands what is required and has the skills to carry out any modifications.

 

Im working on it Eddie, ill put some photos up with my progress

 

Super

 

Mine's actually a DX inlet manifold, with an Audi 80 TB (same butterflies as the PB), and the manifold ported to suit, which leaves a less than ideal shape behind the small butterfly. It's only my fuel rail that came from an ABK.

The Slick 50 Engines used a DX inlet with a much wilder cam, albeit on a smaller engine with 9mm less stroke than Alan's.

I wondered if part of problem might be the bore:stroke ratio, although I think FThaiMike's car was up around 165bhp at TSR - 2.1 8v on Kjet. Again, I'm assuming that's a DX manifold.

It would be interesting to see a back to back comparison of DX Vs PB inlet on this one, although I always assumed that the PB Inlet would work just as well as the DX, and others have had near/over 150bhp using them (ChrisMc, VR6Will on his 8v before the X-Flow).

So that leads me to think that either:

- There's a simple mechanical restriction in Al's Setup - manifold gasket / TB Gasket / Other
- The engine stroke is a big factor in the resonance
- Or maybe the MS MAP Sensor is struggling due to the cam, whereas a KJet Fuel flap and Dizzy might not react as quickly - in which case, Alpha N mapping might help, as you suggested.
- Or a restriction on the exhaust side might be preventing the right sort of scavenging effect at high RPM, which combined with the overlap on the cam, gives a pulsing effect back up the inlet side.

I'd be inclined to pursue the cheaper solutions first... I may have a DX inlet I could contribute to the cause as well, although it would take a bit of work to get the inlet tract over to the other side of the bay.

Then, just thinking out loud, I remember a forum member called VRSteve (I think) who had a lairy cam in a Mk3 (friendly MOT tester) on a modded AGG Inlet, with the TB coming out the front of the manifold. Claimed over 160 bhp IIRC. Sadly that was never validated on the 'Tough Love' Rollers at GS

 

Cheers for putting clear on the manifold used on your engine.
Those other engines you mentioned and their claimed outputs, have no effect on my suggestions, as from the evidence from above as there is a clearly and issue which is being dealt with.

Not confimred but unlikey.

It does have a part to play in intake pressure waves yes.

MAP sensor was affected by the strong pressure pluses, but was ruled out as a cause of the torque oscillation/step, due the calibration tables set with the same LBT and MBT values from 90-100kPa - the average delta for MAP after 4500rpm in WOT. The torque still oscillated in spite of this. Alpha_ N would not fix this.

Unlikely.

My suggestions come after considering and trying all "cheap" solutions to solve the root cause of the torque profiles as seen above. Plus there were hours of in car development where the vehicle felt very strong from low engine speeds/high loads speeds but not as urgent at high rpm/loads. This did concern me and my concerns where confirmed during the clinic. Hence the focus on the plenum.

I am aware of some of these engines settings, build history, development or claims. However I am not sure how much optimisation was done to them, what they would be like if tested at Garage Streamline and if they experienced any of the issues as demonstrated.
The peak outputs of these engines may give slight confidence to what this engine should do as a "peak" achievement at GS, but in light of the data we shared here on CGTi, from the clinic and the past year, the focus is on solving what is obviously not right.
What I do know is after a half day of on the road tuning and then 2 hours at the dyno clinic, sweeping spark, fuel mixture and cam settings, in a controlled manner, Alan's engine stops making torque at 4500rpm and something happens to reduce this torque in oscillating steps. The intake noise is very rasp when this happens.
I would have expected the torque profile to continue raising near 4800-4900rpm and then drop off slowly with around 115lbft @7000rpm. This is still what I have in mind.
I am not interested in fitted another manifold from a VW engine when we can modify the existing or a doner to suit the larger engine size and cam and dampen the pressure pluses.
In the end I am sure this engine has the potential to make "numbers" like the you quoted, but the focus is fix the torque oscillations and you will have "numbers".

 

eddie in order to tidy the 8v validation thread up, ill ask chris split it into a specific thread, 'Why doesnt drunkenalan' car make more power!!!'

 

I appreciate that you've put a massive amount of time and expertise into trying to prise the potential ponies from this powerplant. As you've said, I'd have expected a peak torque somewhere around the rev range you mentioned (and similar to mine).

I've been in touch with Al about a manifold, and will dig out my spare PB one tomorrow night, assuming I finish work at a reasonable hour, for the first time this week.

 

ok to clear a few things up,

the head is pack c, a autosprint copy of the schrick 288, a ported PB inlet done at the same time as the head by the same man, the TB is a vagobonds one, the ex manifold is a wrapped raceland one, not the best design but not that bad either... a scorpion 8v exhaust with a powerflow back box.

the bottom end is a big 2.0 with 95.5mm crank using 82.5mm pistons CR is 10.9 ~ 11 to 1

the manifolds were assembled to the head prior to putting the engine in, so i'm confident the gaskets are good.

the only slight unknown in my mind is the cam, but i have no real reason to doubt it

 

Never seen a raceland manifold close up.

Some of the cheap manifolds I've seen looked very rough where the primaries are welded to the flange (big steps in the port), and the fit to the head ports wasn't great.

A 'bitsa' exhaust system doesn't sound ideal though. I've not heard much good about Scorpion, and one that passed through my hands was nice and shiny, but a poser product not a power product.

Others may have a different view though.

 

Thread split as requested.

 

Thanks Chris,

 

Mike, the finish on the raceland was very good for the money! The flanges and joints to the flanges was also good, the ports were as big as the gasket after a little fettling! The only question could be the design and primary lengths.




The exhaust is something I'm going to change, the back box isn't great powerflow have had a few attempts now! and I think a baffle is starting rattle, although I'm have been impressed by the scorpion the quality of workmanship is good, how it flows who knows

 

What bore is the scorpion exhaust? Seem to remember them being smaller than the usual aftermarket stuff.

 

It's the standard 8v size 2 inch, ill be keeping an eye out for a 2.25 or 2.5

 

Not close up but heres mine