ptuomov

You should ask John Speake to look at your logs (MAF voltage in particular) and compare it to his data.

I don't know on the camshaft. One just would have to try.

Cheburator had some luck with an exhaust duration almost as long as the intake duration (I think exhaust duration two degrees less than intake duration), but only with 39mm intake valves, ITB's, and those great flowing M5 intake runners. That's a very good intake side, not replicated by many here. Anything less well flowing than that is going to want less exhaust duration given the 928 4-valve heads.

Marti

As I am back working on this engine I will be advancing the timing as per your suggestion. Your explanation is good and I think this might help pull maximum power into a usable rev range. I was going to start with +2 and see how it reacts to that.

The original power run shows no flattening out of the power band even at 6500 revs unlike most graphs I have seen where power starts to flatten at 5500 revs. So to me it looks like at the current cam timing that maximum power is somewhere around 7500 - 8000 revs given 1000 - 1500 revs past what I have seen.

Having looked at various RR graphs for 32v 928s I find the torque curve interesting in so much as it's staying power. It is fair to say that many S4 or GT power runs show torque declining heavily after 5000 revs and as much as 50lbf/ft drops off by 6500. In my case I am loosing only 20lbf/ft, it would be good to get people's thoughts on what might be causing this.

SwayBar

Here's what I'd suggest to do:

Make your timing change on one head only, and then do a compression test to see where you are. Since your cams are bigger than GT's, adjust your timing to shoot for around 175 psi. (..GT's run 180-185 psi)

For the second head, apply what you learned from the first one timing-wise, and again do your compression tests to dial the timing in to register around 175 psi.

The beauty of this approach is there is no guessing/wondering/hoping where the engine is at. However, it will take extra work to get right, and is the price to pay for running unknown/unfamiliar hardware - but, it does appear to be a practical solution.

Once done, this should clear up and fix your power curve.

Marti

So I advanced one bank (1-4) by 3 degrees and took a before and after compression measurement on two different cylinders to check the effect. Both increased as below

Cylinder 2 before 175 and after 182
Cylinder 3 before 168 and after 186

So these this small adjustment shows quite a change and it also evened up the static compression between the two cylinders. I know you said shoot for 175 but the 182/186 is in line with a GT range and the 3 degrees is quite a small adjustment.

Hopefully this will pull the breathing capabilities down into the operating rev range

Just to remind - cam specs are
IN: .437" lift, 230 duration @.050"
EX: .437" lift, 228 duration @.050"
LSA 114 deg.

Lizard928

Advancing the cams will pull the compression numbers up some yes.
It is best to do the compression test hot and adjust the cams to balance the numbers bank to bank.

Glad to see that you are back at it. Did you correct the injector issues?

Marti

Hi Colin

Yes, new set of genuine Bosch injectors installed so engine is in now in top running condition. I was also able to inspect the bores while doing the head gaskets which look perfect.

When pulling the plugs this time they look great, as plugs should look for a healthy engine so I am very happy with it health wise. Previously I knew there was an issue with how it was running which was the poor quality injectors.

I will advance the other bank today and re-test on the road and see where we are.

FredR

Marti,

Interesting as your problem is advancing the cams can be expected to increase the pressure you get in a compression test so nothing unusual there. However, as I recall the trigger for all this was the less than expected dyno curves. Appreciate you changed out the injectors but have you dyno'd the car since that change?

Advancing the cam timing will give you more low end grunt at the expense of some top end ponies so basically I am struggling to comprehend the current goal as it were.

Apologies if I have missed something somewhere along the journey

SwayBar

Here's what he posted earlier:

So as you correctly stated, advancing the cam timing will move his power curve lower, hopefully peaking at 6500 vs ~8000 RPM.

FredR

Excellent- I did read the post but failed to spot the inference from that perspective.

Even so, Marti was not happy with his top end power on the dyno run so logic suggests he is going to be even less happy with top end after the adjustment. Knowing how fastidious Colin is with whatever he does I am still left wondering why this adjustment is needed if it is not in Colin's instructions/guidance in the first place.

Thus I still feel as though I am missing something here but then I am under viral attack at the moment [hopefully the common cold type]..

Marti

Bang on, I am attempting to pull the power band down the rev range, if the curve is consistent with a typical 928 the peak looks to be around 8000. The power curve translates (no surprises) to what you feel on the road - which is the engine pulling harder and harder until it changes up to the next gear.

I adjusted the 5-8 bank timing today and checked static compression. A 3 degree change resulted in the same improvement in static CR

Cylinder 5 went from 174 to 183
Cylinder 6 went from 176 to 185

I will give it a run tonight to see how it feels and carry out some data logging. The next steps will be to change to the standard manifold and carry out some data logging and see how it feels.

Then I have the option to use a spare set of GT cams that I have, these can be used in any way - i.e using just the exhaust cam and continuing to use stage 2 inlet cam as a combination.

My original engine felt pretty strong with the GT cams, with very good higher up grunt of at least equal to what I am currently experiencing. And at that point I had the standard headers and exhaust and had not performed any level of shark tuning - absolutely no ignition advance at all. So with my current set up I should really be well above that.

ptuomov

Can you log the MAF voltage/signal and have that translated to kg/h? Unless you are severely knock limited with ignition timing, that should give you a good idea of the power you’re making (since the cams don’t have that much overlap).

Marti

Not sure about the log files, I am looking at them just now and comparing MAF readings from different configurations. I will give it a try.

The run tonight was a step forward, a noticeable increase in power both down the rev range and top end, this was with the cams timed around 3 degrees advanced. Much better.

Next I will try a couple more runs as it is now before changing to a completely standard manifold and going back out for more logging.

Marti

Hi, I have some data and feedback which will hopefully help

I changed the manifold today for a standard-ish manifold and went out data logging. I have a nice open piece of road that allows me to do a full throttle third gear run which really helps both from a feel perspective and also data as I can log max load for a little time

I it feels up on power again from the test manifold - I have some ideas on what might be affecting the test manifold

So, comparing MAF data between different runs I have noticed that the max load numbers are different between the different changes I have made on the engine which I hope corresponds to overall breathing ability

Engine with the standard manifold, stg 2 cams running stock timing (0 degrees)
Max MAF signal is around 350. Power was tested and found to be 330HP

Engine as tested tonight running standard manifold, stg 2 cams running around 2.5-3 degrees advance
Max MAF signal is around 380
It took me a bit of time to think about the feel of the power delivery and the effect of the flappy. I have it programmed to open at around 3800 and shut again around 5500 which is close to stock. What I could feel (during a straight power run) at the closing point was a distinct drop in power before power came back in. To me this is suggesting that the flappy is closing too early and is killing the torque curve. Would it be fair to assume that the torque curve is still peaking higher up the rev range (than a GT) despite the cams being advanced a couple of degrees?
Does it translate that the flappy operating cycle should simply be moved up the rev range, also moving the opening point?

Engine running experimental manifold, cams running stock timing
Max MAF signal is around 285

Engine running experimental manifold, cams running 2.5-3 degrees advance
Max MAF signal is around 310

From a feel perspective the advanced cams and stock manifold feels the most powerful and there was a noticeable change with the experimental manifold when I changed the timing. Obviously the cam timing is affecting power output and the stock timing set up is affecting it's breathing ability. Question is should I go further advanced, any thoughts on why?

SwayBar

I've been thinking about this for several days, and here's my thoughts - you have too many unknown variables operating at the same time.

Firstly, since you have a set of GT cams, I would install those and do a baseline with the stock intake and you should dyno 320-325 rwhp.

Next, once satisfied with the GT cams, install the new prototype manifold. This will be a good test since it is the only unknown variable on the engine, and this test will tell you exactly what the intake is worth, for better or worse.

Finally, once satisfied with the prototype intake, then install the new cams and take it from there.

The new cams are still pretty much an unknown with MAF equipped cars, and MAY cause a problem with reversion, upsetting your results. However, we know that they are exceptional cams with ITB's as Alex did 435 rwhp and John Gill did 450 rwhp with them.

So, simplify your testing by narrowing down the number of unknown variables at a given time.

Marti

I have really moved in the direction of eliminating too many moving parts by switching back to the standard manifold. The only non standard parts are the manifold and exhaust which are proven hardware. The engine is in 100% health now with the injectors changed.

So I am expecting someone else running these cams to post exactly the same low static CR numbers that I did with the stock timing. And if they have a similar exhaust I would expect around the same HP number I posted, maybe little more making allowance for the poor injectors.

However that is a country mile away from the numbers John and Alex have posted. Can you recall their engine spec other than the ITB which I don’t think accounts for this difference?

My current train of thought is to play a bit more with timing before starting to swap cams about. The change of timing might just be masking an issue of overall timing rather than properly addressing it.

Several posts ago there was some theory about the exhaust timing which would be good to explore further