968 Turbo conversion
02-20-2003, 12:36 AM
#32
Rennlist Member
Nick, I did not turbo charge but bought it turbo charged. It does not use the 16 valve head, instead it uses a 1989 NA 8 valve head which is a direct bolt-on but very hard to come by.
The reason behind this was 3 folds.
First, they wanted to replicate the 968 turbo S which was a 8 valve head as well.
Second, 8 valve heads make more torque at lower rpm range, as much as 100 rpm sooner and are much more fun to drive around town. This car was going to be a street car, so it suited it better to have an 8 valve head.
Third, turbo charging a 16 valve head requires a lot of custom plumbing and for the sake of simplicity, it is a lot easier to do a 8 valve as most parts from 944 turbo can be used and are readily available. You would need custom intake, exhaust and bunch of other things to turbo charge a 16 valve.
Also, the 968 DME was not built with turbo charging in mind, so it does not handle the parameters as well. A 944 turbo had a DME for engine control and KLR computer for boost management and ignition retardation. A 968 DME cannot compensate for any of these variables.
One can say, hey why not change the harness to DME/KLR, well that is a problem as 944 turbo harness reads its TDC from the flywheel while a 968 reads it from the cam pulley so you cannot swap the two unless you figure out a way to get TDC working on a 968 flywheel.
My car is in infancy state and I plan to turn the wick up soon. I will be going to a 16 valve head and then get rid of my complete 8 valve setup. I wanted a high hp motor and prefer the 16 valves just for originality purposes.
It will cost me a lot of money but it will not be so bad as all I would need to swap is the head, the intake and exhaust manifold. The rest of it can stay. I will not be able to use 968s variable cam but if I go to a stand alone I can get that as well.
I hope my mumbo jumbo made some sense.
The reason behind this was 3 folds.
First, they wanted to replicate the 968 turbo S which was a 8 valve head as well.
Second, 8 valve heads make more torque at lower rpm range, as much as 100 rpm sooner and are much more fun to drive around town. This car was going to be a street car, so it suited it better to have an 8 valve head.
Third, turbo charging a 16 valve head requires a lot of custom plumbing and for the sake of simplicity, it is a lot easier to do a 8 valve as most parts from 944 turbo can be used and are readily available. You would need custom intake, exhaust and bunch of other things to turbo charge a 16 valve.
Also, the 968 DME was not built with turbo charging in mind, so it does not handle the parameters as well. A 944 turbo had a DME for engine control and KLR computer for boost management and ignition retardation. A 968 DME cannot compensate for any of these variables.
One can say, hey why not change the harness to DME/KLR, well that is a problem as 944 turbo harness reads its TDC from the flywheel while a 968 reads it from the cam pulley so you cannot swap the two unless you figure out a way to get TDC working on a 968 flywheel.
My car is in infancy state and I plan to turn the wick up soon. I will be going to a 16 valve head and then get rid of my complete 8 valve setup. I wanted a high hp motor and prefer the 16 valves just for originality purposes.
It will cost me a lot of money but it will not be so bad as all I would need to swap is the head, the intake and exhaust manifold. The rest of it can stay. I will not be able to use 968s variable cam but if I go to a stand alone I can get that as well.
I hope my mumbo jumbo made some sense.
02-20-2003, 03:07 AM
#33
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If you replace the 2.7L 8v head with a 16v head your compression will change big time. I doubt you'll see that much gain...
02-20-2003, 04:45 AM
#34
Drifting
raj,
why swap out the turbo? can you make more hp without it?
does your car perform similarly to the factory model ie 5sec 0-60 and 175mph top?
i would have thought the turbo in a 968 would be the best way to go short of v8 power!
why swap out the turbo? can you make more hp without it?
does your car perform similarly to the factory model ie 5sec 0-60 and 175mph top?
i would have thought the turbo in a 968 would be the best way to go short of v8 power!
02-20-2003, 12:04 PM
#35
Rennlist Member
Nick, I want to swap the turbo out because I have had a garrett before and I like the way it feels. Its a personal preference. I would say if anything, I have more power because I have a MAF system while the factory car has a flapper style intake system which is pretty restrictive.
As far as top speed, I have a stock transaxle, so top speed will be the same as any 968, ie around 160 mph or so. The factory turbo cars had different gearing so they could go faster.
It is an excellent way of making tons of torque. These things are torque monsters. The factory car had 369 lbs/ft of torque at around 3k. That is monstrous.
Going to a 16 valve head will only add maybe half a point to my compression the most. As stated, I have 2mm shorter rods and shaved pistons, so the compression has been lowered quite a bit already.
Raj
As far as top speed, I have a stock transaxle, so top speed will be the same as any 968, ie around 160 mph or so. The factory turbo cars had different gearing so they could go faster.
It is an excellent way of making tons of torque. These things are torque monsters. The factory car had 369 lbs/ft of torque at around 3k. That is monstrous.
Going to a 16 valve head will only add maybe half a point to my compression the most. As stated, I have 2mm shorter rods and shaved pistons, so the compression has been lowered quite a bit already.
Raj
02-20-2003, 12:06 PM
#36
Rennlist Member
Nick, can we open another discussion thread for this as I am not sure the originators are happy about us having this discussion. Maybe we need to start a new thread on this.
Raj
Raj
02-20-2003, 03:38 PM
#38
Rennlist Member
A racing 928 could become a very expensive endeavor and as its not forced induction, you will eventually be limited to how much power you can make. The engine bay on a 928 is very very tight and forced induction is pretty much out of the question.
I would think a 968 would be a good platform as it did race and is much lighter and better handling without the excessive weight of a GT as the 928.
Raj
I would think a 968 would be a good platform as it did race and is much lighter and better handling without the excessive weight of a GT as the 928.
Raj
03-01-2003, 07:05 AM
#39
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I am hearing more and more about 16 valve 968 motors w/turbos. I'll wait for someone else to sudsidise the R/D. There is some expensive maching to do it right and the barrell valve manifold does not fit. 500+ H/P should be as easy as falling off a log with those heads. Milledge was sizing a turbo for a 3L 16V motor. Calculations put it at 750H/P with less than 20lbs. boost. 8 inj. Huge, huge intercooler, dry sump, sloid lifters (quieter than stock ones). Sounds like a good street motor to me.
