Chris Prack

Richard, I would be inclined to take Gary's suggestion and do a compression test and see what you get. It's a good idea. If you find that it is indeed too high and you get "permission" you should find that the cumbustion chamber volume to be about 36cc's or something very close.

As far as tightening torque, I would follow Raceware's spec.

As far as air/fuel ratios go, you will need to get a precise measurement of each individual cylinder to get the results that you want. As Danno said, just a wideband O2 downstream is an average of all four cylinders. I have dyno'd quite a few cars/engines and have seen one cyl. be lean and the one next to it pig rich and me O2 is telling me that it's cash money. Do you have a chassis dyno near you? Find out if they can chart EGT's and set up your car with the proper fittings and do some pulls. If you get any cylinders running too hot then you know your A/F ratio is not good. This can be corrected a couple of differant ways depending on the results.

If you need anything click on the web link on my signature and give me a call and I will see what I can do.

In the meantime do a compression test and see what you get.

Bill

Richard,

My guess is that you are running lean. I just installed a SFR stage II turbo and my stock injectors are at their limit. My boost is set at 14psi and on the dyno my afr runs from 12.4 to 11.9 at the top. I can crank my ArcII to full rich with no affect, thus injectors are maxed. Car put down 275 hp. In a couple of weeks I will be installing Guru Racings 65lb injectors and their version 7 chips with switch. A little more dyno time with Danno tweeking and hopefully I will have 350 rwhp at 18 psi, a perfect idle and fuel curve.

K27w

I would have the head checked for true, not all machine shops are created equal.
My neighbor blew a head gasket and then had the head machined and has blown two more since, and he is not running any boost.

IanM

Bill - just because your ARCII is set full rich doesn't necessarily mean your stock injectors are maxed out. What fuel pressure are you running? The stock injectors will respond to fuel pressures of over 3bar (mine maxed out on the dyno at a fp of about 50psi). Yours should be able to squeek out a few ponies more than 275.

Chris Prack

I would very much err on the side of caution when you get close to 50psi with stock injectors. They can't handle too much pressure and 50psi is about their limit. The pintle in the injector will lock up and flow little to no fuel. VERY BAD!

Just a word of caution.

IanM

I agree. I found 50psi to be the limit for my stock injectors, and they couldn't deliver enough fuel above 14psi and 305rwhp with my setup. I've since moved to Bosch 52# injectors, and I've now got my a/f ratios dialled in perfectly at a low 2.5 bar of fuel pressure.

Bill

Ian/Chris,

I have the FPR set at 55psi. Maybe that is the issue, too high.

Turbo Tim and Danno both had the same thought that my car should get more than 275.

With the new GURU 65lb injectors, we shall see.

Richard Bennett

Latest up date as follows:

I have done some testing and found that right now the car will only hold 11psi boost. Anything higher and it starts to pressurize the coolant reservoir and you can smell the combustion fumes in the tank. If I drop the boost everything is fine again so I don't think it can't be a burnt head gasket.

I have noticed that the crappy LED A/F gage actually stabilizes at WOT. The gage reads a steady 1 bar into the rich zone.

I checked compression with the engine warm and throttle closed, and got 140-145psi on all cylinders so it doesn't seem to be a too high static compression ratio problem.

I checked the plugs, they were not very tight in the head for some reason, they were a nice burnt brown.

I re-torqued the top row of cylinder head nuts, I maybe got 1/4 turn extra (raceware studs remember).

I am going to start increasing boost again to see if the re-tightening has helped at all. I then have to think long and hard about where to go next. I am considering going back to a stock head gasket as the smaller fire ring should result in a higher clamping pressure around the cylinder.

Anyone else got any ideas.

GaryK

Richard - the motor in my '89 is setup similar to yours, except I don't have Raceware studs, only the Widefire gasket. I have a Garrett T04E 46, test pipe/upgraded exhaust, Autothority hot wire MAF and K27 chips, MBC, but otherwise stock. I have the static fuel pressure set at 42psi with the stock injectors, which were serviced by Marren. The car dyno'd at 295rwhp, 328rwtq @ 1 bar boost. The A/F ratio went from 13:1 @ 3500rpm, where the boost really starts, to <11:1 @6500rpm, definitely rich up top.
With your 50 trim compressor and lower altitude, you may need more fuel.
Gary

Richard Bennett

Ok,

I tend to agree with the concensus that I am running weak at WOT hence blowing gaskets etc,etc. (and I forgot to mention previously that I have burned up 3 exhaust valves in the past also)
As I can't go much higher with fuel pressure I guess I have to go for bigger injectors. Anyone got a set of the 52/55lb injectors that I could try/buy for a reasonable price (plus I would have at least one set of stock injectors to trade). Normally I would have no hesitation getting a brand new set of injectors, but as I am not yet convinced its going to fix things, I am hesitating throwing another bunch of money at it and getting nowhere.

Thanks Richard

PerformanceDevelopments

Reading your problems with holding down your head,
I have a few questions I would like you to answer, so that I may be of help here. I do not usually reply to these sorts of things as this information is why I'm in business building race engines.

Did you perform Compression test or leak down. If you did compression test, then this should be done
with throttle open. Your numbers are very low showing closed throttle or serious leakage. I suspect its from closed throttle, then test results are not to be considered. I am not that familiar with 944T engine lean condition but I do not suspect that A/F problem or more important a detenation problem is causing your problem.

You mention surfacing the head pior to this rebuild. How much was taken off. If you do not know, always ask how much. Measure your Combustion chamber volume and calc your comp ratio. A higher than allowable comp ratio will cause more detenation problems than lean mixture typically.

What was your water temps?

My advice is to measure your comp ratio, make sure that the block deck is flat without surface flaws, block is not cracked, (you can pressure each cylinder with piston in place ), check cylinder head for flat and no surface flaws, pressure check for cracks. I would also recommend using wide fire ring gasket and 'O' block. I have never had a problem with this type of application in the past.

I would strongly recommend you seek professional help now. I do understand how most of the people here wish to do their own work, but your continuing problems show that there is still a big difference between the professional builder and the DIY guy. In this case you probably need tooling and the ability to check certain things, which the DIY person does not have at the ready.

I have been in the business of building race engines for a long time and live by the saying that nothing can humble a man more that an engine or an angry wife. Sometimes its worth getting this sort of repair done professionally. You pay a liitle more up front, but eliminate the continuing hassle.

Neil Harvey
Performance Developments
Link Electro Systems USA
949 646 7461

Richard Bennett

Neil,

I appreciate any input that I can get. Your are correct the compression numbers were throttle closed. Throttle wide open results are very similar at 147/145/145/143 which are in the correct range for a 944T. I did think that maybe the head had originally been overmachined but the compression numbers show that this wasn't the case. The car has never been seriously overheated, it has never steamed the coolant and even the loss of coolant doesn't push the temps up.

Head and block were checked for flatness before the rebuild and confirmed as OK. I have considered a hairline crack in block or head but this would not make sense because when I first replace the head gasket everything is ok for a while.

I was also not convinced of a lean condition initially as the previous head gaskets never appeared to be burnt just faint signs of blowby from #2 towards the inlet manifold. The two previous headgasket failures were also accompanied by burned exhaust valves which supports the lean theory. So far there have been no burnt valves just the failure to hold boost.

At 11psi the car runs great and doesn't pump coolant, but if this is all I am able to run I may as well go back to stock.
Injectors are my last attempt, before giving up, and going back to stock.

Any insight greatly appreciated.

Richard

PerformanceDevelopments

Richard,

I suppose we have to now consider that there could be several factors contributing to your problems. We should not rule out anything at this stage. I also would not rule out at any point the lean theory, as many other owners seem to have had first hand experience with this problem. The more information you can gather the better. Also my best and most important advice to you is don't give up. Before attempting further work, lets explore all possibilities. If you like, call me @ 949 646 7461 PST, and let me see if I can add further light on your fix. I think you have to go back over what work has already been done and make sure it is correct.

Typically, there are many other tell tale signs of a lean mixture. Plug color, detenation noise etc. Inside you can usually see erosion on the Piston normally always on the Intake side, as the combustion gases become conductive rather than combustive, causing the flame to travel around instead of through the mixture. Without becoming really boring here, the results are always the same. I do not have a lot of experience with this type of engine with repect to failure, but the Piston is the softest component here. Burnt Valves are normally from a sealing isssue, but in some engines I have seem extreme damage due to fuelling and Ignition timing faults. How did the Plugs look? Did they show signs of detenation?

A simle test for flatness is to get a very good straight edge and feeler gauge. Check across the block deck surface and Head surface particulary around the area that has shown the blow by. You should be able to insert the smablade which is usually 0.002" Make sure no covers brackets etc are touching the block holding off the head. Start with looking at the basics and simple things working up to the more technical things. REMEMBER HERE, this is a problem and that others have run successfully without problems where you want to be. With this in your mind have confidence you will find it and fix it.

Your compression test numbers don't seem right to me. I am not questioning the totals, but typically you always see alot higher numbers with WOT than closed. I could go on for ever here, I won't as I am sure I'm not adding anything of value now. Call me at Performance Developments and I will try to go thro' this with you over the phone. If necessary, if you can afford you could send me your parts for evaluation. You are either missing something really obvious or you have sparked my curiousity.

Neil Harvey
Performance Developments
Link Electro Systems USA

PerformanceDevelopments

Richard, Just re read my dibble and saw I left out the word "not" when checking the deck surfaces. Again, you should NOT be able to insert a 0.002" feeler gauge.

Sorry for that.

Neil