944 Turbo S Engine Rebuild Thread

[Eldavo]

AFAIK Autotune just works on the fuelling VE table - even then it was nowhere near and was very very rich in places. And that was after running the Live VE analyser AND the one that analyses log files looking at 1 hour plus runs!!!

Standard VEMS map is very conservative - we got lots of additional ignition timing in as well as profiling the boost curve and duty cycle so it goes from 18 up to 21psi and holds it as long as you dare keep your foot in.


What will be interesting will be logging a long run now and seeing what the VE autotune can do with the log file now it’s there or thereabouts already.

 

[James0]

If VEMS Autotune is anything like Tunerstudio/megasquirt, then yes it simply adjusts the VE table to try to match fuelling to whatever is in the AFR target table.
This obviously relies on the accuracy of the wideband sensor and the time delay between combustion and the gas hitting the sensor. What can also happen, if too rich the sensor gives a lean output due to poor combustion so the ECU adds more fuel and makes it worse.

 

[Waylander]

Goes pretty well

Brilliant photo

 

[Eldavo]

Guy’s a decent amateur tog

 

[Eldavo]

When I rebuilt the engine I fitted a Steam Vent kit as per Lindsey Racing - but I should’ve listened to others as it’s crap and leaks.

 

[Eldavo]

So I replaced it all with AN fittings and hose, AN4 would’ve been fine but I had some spare AN6 bits already so there you go!

 

[Eldavo]

Also fitted a new Forge recirc valve as the old Bailey DV30 was sticking despite servicing it and they’re not around any more to get parts for.

 

[Eldavo]

And then fitted one of these little doofers as well - it’s effectively an external dual port valve for the recirc valve. Uses a t-eed boost line to hold the BOV shut under boost and then uses vacuum to open it when you come off the throttle.

Means I can use the lightest spring going to get instantaneous BOV opening with no turbo-flutter when coming off mid-throttle BUT it also stays firmly shut as boost pressure rises rather than opening slightly due to increased vacuum.


Not done any definitive testing but the bum dyno is happy and the ears are happy that they can’t hear flutter.

 

[nick_968]

Great thread just read the whole thing from start to end!
Some nice research and interesting finds along the way. Sounds like a great machine shop too.
These 8v engines really drop off after 5500 rpm. Definitely try the cam timing.
Hope it is still running well and well done for the persistence []

 

[blade7]

These 8v engines really drop off after 5500 rpm.

Sounds like something is wrong with yours then.

 

[PSH]

These 8v engines really drop off after 5500 rpm.

Sounds like something is wrong with yours then.

Very wrong Paul....??????

 

[blade7]

These 8v engines really drop off after 5500 rpm.

Sounds like something is wrong with yours then.

Very wrong Paul....??????

I know a lot more about the background than you think Pete....

 

[TTM]

If there is one thing that most folks still running on the Bosch Motronic don't know, it's that it makes the rev counter over reads by between 10 and 15%, so whilst they believe their engine runs out of breathe slightly above 6000 rpm, the engine is actually turning no more than about 5500 rpm...

 

[924Srr27l]

If there is one thing that most folks still running on the Bosch Motronic don't know, it's that it makes the rev counter over reads by between 10 and 15%, so whilst they believe their engine runs out of breathe slightly above 6000 rpm, the engine is actually turning no more than about 5500 rpm...

Really?? does this mean the rev limiter is also not correct, Only when the needle hits the 6350 limit the engine cuts which would suggest the needle and ECU set limit is the same..?

R

 

[PSH]

These 8v engines really drop off after 5500 rpm.

Sounds like something is wrong with yours then.

Very wrong Paul....??????

I know a lot more about the background than you think Pete....

Just in case there's a misunderstanding, I was agreeing with you Paul, plus I have never doubted your knowledge.

Pete

 

[blade7]

Very wrong Paul....??????

I know a lot more about the background than you think Pete....

[/quote]
Just in case there's a misunderstanding, I was agreeing with you Paul, plus I have never doubted your knowledge.

Pete

[/quote]


Thanks for that Pete, likewise mate.

 

[nick_968]

I have seen a fair few dyno charts for 2.5 and 3.0 turbos and most show the torque dropping off fairly consistently after 5500 rpm. I have seen the odd one staying flatter over the years but usually a lot of effort will have gone into that with some well matched components and the factory intake has normally gone in the bin.
Nothing wrong with my engine as far as I know apart from it gathering too much dust.....must clean that off!
Getting a flatter torque curve at the top end has been a mission for many people tuning their engines over the years and what leads many of the big block engines to switch to 16v as so much more easily available power at the top end where the 8v just runs out of breath.

 

[PSH]

To be fair a standard 951 doesn't rev much higher than that anywsy so I don't see how you can say it drops off at 5500 as if that's some type of flaw? The engine was designed to lose power, it looses boost even before it hits max boost, Porsche said this was to make the car more driveable for the average driver, those close to the company said it was to keep the 951 slower than the 930, something Porsche failed to do.
At the end of the day the 951 package is (even today) in a league of its own among cars as has been proved on the race track over the years when it still beat the then new 996 GT3 before Porsche finally banned it after a few seasons of employing failed handicaps.

Pete

 

[blade7]

I remember not long after I'd bought my turbo, overtaking 3 or 4 cars on the local bypass. I was in 4th and kept my foot in it, suddenly there was a cut in power and I wondered WTF had happened. Looked down and the tach needle was way past 6000 revs, and I'd hit the limiter. No running out of breath or slowing up just before. TTM and nick_968 do seem to have a long standing mutual appreciation situation going on....

 

[TTM]

The flow limitations of the 8V heads used on the factory 2.5/2.7/3.0 engines have been well documented over the years. I am not sure where there is any point discussing this. The ports are small and air stalls at higher rpm, and that's fine as long as we recognise that the factory's intention was to design easy-going engines for road use with a bias towards low and mid range torque.
I will gladly admit though that this flow limitation is less obvious on 2.5 engines, as they obviously pump far less air than their larger siblings. The 2.5 engine remains I think pretty well-balanced as long as we don't get too greedy with turbo size. Small head ports have always been about low rpm torque as they allow for better air velocity, thus filling, at lower engine speeds.

Whilst all of the above is facts, they do not necessarily go along with what we experience from the driver's seat. For instance my 3L 16V engine is faster everywhere than my 3.0 8V although it feels clearly lazier below 3k rpm, and this is simply because it has to work nowhere near as hard as either of my previous 8V engines under comparable circumstances. It is deceptively fast in a nonchalant manner, to the point where all these recurring talks about how to make boost as early as possible in the rev range become redundant, as thanks to superior air flow at any RPM the engine makes enough power without needing much boost at all.

PS : Nick and I have been comparing notes for quite a while and got to observe ourselves what others had already observed before - the 8V head really isn't that great for top end horsepower.