Engine build progress

[marcoturbo]

A quick update: after a 1000 miles road trip, everything is fine on my 2.5L [] A/C is cold, AFR is almost perfect, EGT is fine, Audi S Series stay behind ! []

 

[TTM]

Upon further examination it appears the headgasket on Sly's engine failed on cylinder 4th, letting coolant get into the combustion chamber, which, under continued and intensive use, ended up bending the rod. The happy side to the story is that the rod bent in a direction so the pistons didn't do any damage to the bores. A set of aftermarket rods and a metal headgasket will be installed.

 

[DivineE]

I would advise you stay clear of the metal head gaskets on the 944. I had a cometic one but after reading all the horror stories about people struggling to get them to seal and eventually going back to a standard gasket I decided it would probably be more trouble than its worth and sold it on. People have run 18-21psi on a standard gasket for years and not had a failure so I think so long as the fuelling is right there's probably not a whole lot of point.

 

[DivineE]

I cant find the story I was looking for by Duke which went on over many months of untraced leaks, troubles before he changed back to a regular gasket but found this post: "Just another data point, I put a MLS headgasket on my freshly rebuilt engine which has Darton liners. It lasted maybe 20 miles and started pressuring the coolant tank and upon taking the spark plugs out number one showed significant signs of water/glycol in the combustion chambers. Lots of discussions and having machinists check the head and flatness of the blockand conclusion was that nothing was wrong. So instead of going back together with MLS gasket I put a WFHG and 2300 miles later no blown headgasket. I used ARP studs which I got from Engine builders Supply [link=http://ebsracing.com/]http://ebsracing.com/[/link] and in both cases did the torque of the head myself so I am comfortable that in my case the MLS didn't want to work with my block and head and I don't really know why."

 

[sawood12]

The issue with the metal Cometic head gaskets is not that there is an issue withe metal head gaskets - these are not new and are tried and tested in a number of applications. The problem is that Cometic never produced a gasket specifically for the 944T. They lifted the gasket for the 928 which contrary to many misconceptions though looks the same thing it is not. The difference is either in the diameter of some of the holes for the cooling passages or the location. The result is that sometimes they work and sometimes they don't depending upon which side of the manufacturing tolerance band the holes are made. According to a thread on Rennlist about a year ago, Lindsey Racing have recently been working with Cometic to develop one specifically for the 944T and though I didn't read if they managed to successfully develop one that is now available there is no reason why one shouldn't work. These gaskets are multi-laytered and designed to conform to the mating surfaces of the head and block so any slight deviations to flatness should be accommodated as with a standard gasket. Though I agree there is no reason to go for one even in high boost applications. If your car is running well and combustion temps are kept in check then the stock gasket has been proved to be good for 500bhp+.

 

[marcoturbo]

I agree with others comments. Switching to a metallic HG isn't a good idea... With correct EGTs (thanks to the MAF pipe), a standard HG should be fine.

 

[333pg333]

I will wave the metal h/g flag to a point. I also had 2 motors that had h/g failures with Cometics but both times I was able to drive home from the track. No 5 min journey either. Closer to 2.5 hours. Now clearly that is out of the question with stock h/gaskets so there is something to be said for the Cometics. We finally came to the conclusion that under higher loads (1.5 bar) it was either / both from head lift or that the cylinders were shifting and tearing the edge of the gasket through the movement itself or through the leaking combustion chamber. So we have now replaced the stock headstuds with some ARPs. From all reports getting the old studs out is not an easy job. This is in a '83 n/a block so perhaps those extra few years didn't help. [] Anyway, so far so good. We did run most of the last 2 trackdays on a lower boost level but did run it up to 1.4bar late in the day. My general temps on the gauge are just below the first line. On the track it's still below the 2nd line which is excellent. I shall report if we have any negative findings at the next day in a few weeks time. Oh, we also use Silastic sealant quite liberally when installing the gasket.

 

[TTM]

Here is a picture showing late vs early rod design. Later rod comes from a new block (M44/52 ATR), earlier rod comes from a M44/52 J (original turbo S engine).

 

[barks944]

Which is which?

 

[TTM]

Top = late design Bottom = early design

 

[barks944]

Interesting, did you install constantines TT bearings? Any feedback? Ive got my TT out and I'm thinking of getting a set.

 

[TTM]

My spare S2 torque tube is apart and cleaned but I don't think I will put it back together before a good pair of months. The new bearings look very good though, they are 6008 against 6006 for the original ones, which apprently means both a larger outer and inner diameter. Most vibrations are supposed to be absorbed by the inner sleeve which is much beefier than on the originals, meaning probably a much longer life expectancy. That's all theory though, will take several years and miles to find out.

 

[TTM]

Today I realigned and reindexed the MAF housing with the SFR MAF pipe, and ta-da - the lean spike is still here but has much reduced, and, above all, the KnockView doesn't blink one bit anymore - HURRAY!! [] I test drove with the base fuel map included in the chipboard (=no corrections with the Piggyback) and though the car runs leaner than advised at wide open throttle (AFR between 12.5 and 13), I was stunned not being able to spot any single blink of Knock! Fantastic! The MAF sensor inside the MAF housing seems to need being aligned exactly with the radius of curvature of the MAF pipe, which, physically, makes sense, and the SFR MAF pipe doesn't seem to be curved the same way as the Vitesse MAF pipe - searching for an excuse here as to why I didn't figure it out/tried it earlier [&:] Though the terrific weather must have some positive effect I must say I've never been more pleased with the car than today! []

 

[marcoturbo]

Send me a pic of the reindexed MAF ASAP []

 

[JarmoL]

Great news Thom Please post a picture to show how the MAF is located now.

 

[TTM]

Here is a couple of pictures. Picture 1.

 

[TTM]

... and here is picture 2.

 

[TTM]

I put the hose clips as close as possible within each other in order to align the MAF housing with the J-pipe as well as possible - Though it cannot be seen they actually are in contact, meaning there shouldn't be any odd change of direction in the air flow as the end section of the J-pipe and the section of the MAF housing are now parallel. Then, I rotated the MAF housing so that the MAF sensor would align as well as possible with the radius of curvature of the J-pipe - said differently, the visible, squarish outer part of the MAF sensor is now perpendicular to the plane of curvature of the J-pipe.

 

[Diver944]

That's good news Thom. So when you say re-indexed, do you just mean rotated the pipe so the MAF itself was in a number of different positions? How is the SFR MAF pipe different to the Vitess version and what made you think to try it (I would never have thought the pipe made much difference)

 

[TTM]

I must make more tests before commenting further, as plugging back the piggyback yesterday in order to add some fuel has given unwanted results again.