16v head and turbo myths
03-31-2015, 02:51 PM
#121
Am I reading this right....900hp
I ran a turbo'd S2 head for about 4 years with the car tuned for 400rwhp and had no issues with cracking. I over built it for my application and ended up swapping it out for a 968 head that I kept a lot closer to stock.
Another data point for the S2 head is that at least one of the two 968 based Doom engines used one. Initially it was used as a test bed engine then ultimately made it into a hill climb car. The engine ended up cracking two cylinders during a race at Pikes Peak. I'm a little foggy on the numbers now, but the engine was set up for higher rpm, and was making something like 900hp. I would say that's a high stressed application, and the S2 head managed to survived when the block did not.
A friend of mine bought that particular engine, and when the head was refreshed, all it needed was a cleaning and a couple of valves needed to be lapped.
You can break just about any part if its assembled or applied incorrectly. Even if you get those two correct, you can still break parts with improper tune, misuse, or neglect.
Another data point for the S2 head is that at least one of the two 968 based Doom engines used one. Initially it was used as a test bed engine then ultimately made it into a hill climb car. The engine ended up cracking two cylinders during a race at Pikes Peak. I'm a little foggy on the numbers now, but the engine was set up for higher rpm, and was making something like 900hp. I would say that's a high stressed application, and the S2 head managed to survived when the block did not.
A friend of mine bought that particular engine, and when the head was refreshed, all it needed was a cleaning and a couple of valves needed to be lapped.
You can break just about any part if its assembled or applied incorrectly. Even if you get those two correct, you can still break parts with improper tune, misuse, or neglect.
03-31-2015, 04:18 PM
#123
Drifting
I've got a question that maybe you guys can answer now that this thread has so much attention.
Can the S2 cams and tensioner assembly be swapped into a 968 head? I have a 968 head with no cams and an S2 head with cams. It's sounding like the best option is to run the 968 head with S2 cams and variocam delete with the S2 cover.
Can the S2 cams and tensioner assembly be swapped into a 968 head? I have a 968 head with no cams and an S2 head with cams. It's sounding like the best option is to run the 968 head with S2 cams and variocam delete with the S2 cover.
04-01-2015, 09:01 AM
#124
Rennlist Member
So I'm about one reply away from blocking Voith to return this thread to something useful. I know there are quite a few myths about turbocharging the 16V motors and I'd like to point out some of them below to invite a *TECHNICAL* discussion regarding their merits.
- You must use heavier valve springs in a 16V turbocharged application
- You cannot turbocharge a 16V motor with the stock pistons
- Stock S/S2/968 rods will not support turbocharging
- 16V heads flow so much they kill the low end torque
I'm sure there are quite a few more "myths" out there and I'd like to hear from others.
I've done quite a bit of research on the above points and I believe they are all truly myths. Ultimately, the desired application and end result will directly impact parts and materials selection. For a track oriented car, the stock valve springs, valves, pistons and rods are unsuitable. Long periods of on-boost time will overly tax the valve train and boost levels above about 10psi will over tax the bottom end. There are quite a few 968 owners running low boost superchargers without issue and a handful of turbocharged 16V cars using the stock top and bottom ends without blowing up. But the key point is they are all low boost applications. In order to run 1-1.5 bar the bottom end must be reinforced with forged connecting rods and lower compression pistons must be used. But the 16V heads support a higher static compression ratio than the 8V heads. For the naysayers, this has been documented ad nauseam and if you disagree, please run 8:1 for your mental health and leave the rest of us to run what very clearly works well.
Unlike the 8V cars, there isn't a quick "roadmap" of components to grab from the parts bin to create a safely running motor. After talking with a number of fellow RL'ers about building 16V turbo motors, it seems the technical challenges and cost are what scare away most people. As others have pointed out in this thread, there is a degree of fabrication necessary and for those without the ability or means, then you'll have to pay someone else for their efforts. This dramatically increases the overall cost of the build and most people find this unacceptable.
Looking forward to getting this discussion back on track and reviewing the old wives tales associated with building a modern 16V turbo engine.
- You must use heavier valve springs in a 16V turbocharged application
- You cannot turbocharge a 16V motor with the stock pistons
- Stock S/S2/968 rods will not support turbocharging
- 16V heads flow so much they kill the low end torque
I'm sure there are quite a few more "myths" out there and I'd like to hear from others.
I've done quite a bit of research on the above points and I believe they are all truly myths. Ultimately, the desired application and end result will directly impact parts and materials selection. For a track oriented car, the stock valve springs, valves, pistons and rods are unsuitable. Long periods of on-boost time will overly tax the valve train and boost levels above about 10psi will over tax the bottom end. There are quite a few 968 owners running low boost superchargers without issue and a handful of turbocharged 16V cars using the stock top and bottom ends without blowing up. But the key point is they are all low boost applications. In order to run 1-1.5 bar the bottom end must be reinforced with forged connecting rods and lower compression pistons must be used. But the 16V heads support a higher static compression ratio than the 8V heads. For the naysayers, this has been documented ad nauseam and if you disagree, please run 8:1 for your mental health and leave the rest of us to run what very clearly works well.
Unlike the 8V cars, there isn't a quick "roadmap" of components to grab from the parts bin to create a safely running motor. After talking with a number of fellow RL'ers about building 16V turbo motors, it seems the technical challenges and cost are what scare away most people. As others have pointed out in this thread, there is a degree of fabrication necessary and for those without the ability or means, then you'll have to pay someone else for their efforts. This dramatically increases the overall cost of the build and most people find this unacceptable.
Looking forward to getting this discussion back on track and reviewing the old wives tales associated with building a modern 16V turbo engine.
04-01-2015, 11:13 AM
#125
Addict
Rennlist Member
Rennlist Member
Not really sure what you're trying to 'Win' here Voith? Yes, it's possible that some of the 16v heads are going to be vulnerable compared to the 8v, but there are enough examples of people who have had very good success with the 16v heads. I don't think anyone is uncovering any secrets in here. 'Caveat Emptor' as such...
968 head seems to be very good turbo candidate and If I got one I would go ahead and CNC my pistons to 16V spec and try to achieve working variocam.
ramius665:
This is what I think, could be wrong.
- You must use heavier valve springs in a 16V turbocharged application
(If stock redline is retaned I think heavier springs are not necessary)
- You cannot turbocharge a 16V motor with the stock pistons
(you can but you have to retain balance of boost and CR to not go overboard with cylinder pressure and temperature. The higher the CR the less boost can be safely used)
- Stock S/S2/968 rods will not support turbocharging
(They will, stock sintered rods will hold ~350 crank hp just fine, anything over that is asking for troubles)
- 16V heads flow so much they kill the low end torque
(air speed is lower if ports are wider and slower air speed means less torque. That is the reason porsche used variable lenght intake manifold on 968)
Low static CR has its good sides too.
One of the better ones is related to heat caused by compressing air.
If most of compression is done by the turbo, heat can be taken away by the intercooler(s), if most of it is made in head by high CR it can not be cooled.
04-01-2015, 05:12 PM
#127
Three Wheelin'
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Back to the head:
The Vario-Cam system changes lobe separation angle which helps gain some low end torque back.
Having cams made that are more tailored for turbocharging will help as well.
Last edited by fortysixandtwo; 04-01-2015 at 06:14 PM.
04-01-2015, 10:02 PM
#128
Rennlist Member
I've got a question that maybe you guys can answer now that this thread has so much attention.
Can the S2 cams and tensioner assembly be swapped into a 968 head? I have a 968 head with no cams and an S2 head with cams. It's sounding like the best option is to run the 968 head with S2 cams and variocam delete with the S2 cover.
Can the S2 cams and tensioner assembly be swapped into a 968 head? I have a 968 head with no cams and an S2 head with cams. It's sounding like the best option is to run the 968 head with S2 cams and variocam delete with the S2 cover.
Note the S2 has one more tooth on the chain sprockets than the 968. The smaller gear on the 968 is to allow more room for the big VarioCam tensioner.
You won't have VarioCam if you do this, but mechanically it will work fine.
04-01-2015, 10:37 PM
#129
Rennlist Member
I was going to say that potentially those that are seeking some serious hp out of the 16v motor would look to rework this tensioner issue.
04-02-2015, 01:13 AM
#130
Three Wheelin'
Regarding valve temp issues on 4v cars (not referring to 944 16v head), most of the time the reason for too high temps is too thin contact area betweeen seat and valve resulting in too little heat transfer during operation.
For turbocharged track applications it is advised to leave a bit wider contact surface than factory recommended. When I had my 16v head done, I asked for it from the machinist. Totally worth sacrificing few hp for better valve cooling.
For turbocharged track applications it is advised to leave a bit wider contact surface than factory recommended. When I had my 16v head done, I asked for it from the machinist. Totally worth sacrificing few hp for better valve cooling.
04-02-2015, 02:21 AM
#131
Burning Brakes
Another way to help keep the exhaust valves cool is to run a shorter duration cam. I'm sure most of you know that the stock 8V turbo cam has shorter exhaust duration than the 8V NA cam.
02-17-2023, 08:44 AM
#132
Rennlist Member
Regarding valve temp issues on 4v cars (not referring to 944 16v head), most of the time the reason for too high temps is too thin contact area betweeen seat and valve resulting in too little heat transfer during operation.
For turbocharged track applications it is advised to leave a bit wider contact surface than factory recommended. When I had my 16v head done, I asked for it from the machinist. Totally worth sacrificing few hp for better valve cooling.
For turbocharged track applications it is advised to leave a bit wider contact surface than factory recommended. When I had my 16v head done, I asked for it from the machinist. Totally worth sacrificing few hp for better valve cooling.
What contact width did you use? Or is there a minimum that should be used in high temp applications?
04-30-2023, 12:09 AM
#133
We have built a few 3.0ltr 16v turbo engines now and while i would consider them on the cheaper side of the 3.0ltr build. Reason i say this is that for all of them that we have done the only changes internally have been con rods and pistons. In our case Wossner rods and pistons. All other moving parts have been factory. In the case of the head it gets new chain and tensioner pads. Standard cams, valves and springs. From this we have had great longevity with the 3.0ltr block and 16v setup. Our own car has over 75,000kms on it a 1.5bar boost running E85. Driven everyday and also competes in our state supersprint/motokhana season.
At the end first year we pulled the pan to insect the big ends, which happened to be as good as when they went in. On the boost we run we have now seen double the amount of track days per cometic head gasket as we were using on the 2.5 8v setup. Blow by is almost non existent compared with the 2.5 block and 8v head. Im not sure exactly why but the 8v setup does throw a lot more oil through the catch can system. Lastly the 16v setup has a larger power band gavin similarly sized turbos for both 2.5 and 3.0ltr. On the 2.5 we would reach 1 bar by 3200rpm and it would seize to make power past 5600rpm even with the 9r camshaft. On the 16v engine we see 1 bar at 3000rpm and continue to make power through to 6500rpm.
With all of these positives its hard to go past a 16v setup if you can afford them, And on that end they really do not cost much more then a 8v build. Just get yourself a S2 or 968 donor engine.
Regards
Sean
At the end first year we pulled the pan to insect the big ends, which happened to be as good as when they went in. On the boost we run we have now seen double the amount of track days per cometic head gasket as we were using on the 2.5 8v setup. Blow by is almost non existent compared with the 2.5 block and 8v head. Im not sure exactly why but the 8v setup does throw a lot more oil through the catch can system. Lastly the 16v setup has a larger power band gavin similarly sized turbos for both 2.5 and 3.0ltr. On the 2.5 we would reach 1 bar by 3200rpm and it would seize to make power past 5600rpm even with the 9r camshaft. On the 16v engine we see 1 bar at 3000rpm and continue to make power through to 6500rpm.
With all of these positives its hard to go past a 16v setup if you can afford them, And on that end they really do not cost much more then a 8v build. Just get yourself a S2 or 968 donor engine.
Regards
Sean
04-30-2023, 09:08 PM
#134
Drifting
Sorry to join the grave dig but do you run the stock head and main studs Sean? Just starting a 16V street built, and this is the one point that's causing the most anxiety. I know most of these engines are 30 year old but I have a new 968 block with new studs sitting in the garage ready to go.
Regards
Sean
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333pg333 (05-01-2023)
05-01-2023, 06:09 AM
#135
Rennlist Member
That was interesting to re-read. So...Duke has gone from 16v Porsche motor to 16v billet Honda motor. Thingo has gone from 3.1lt 16v Porsche motor to insane billet 4lt 16v Thor creation. Thom has gone from 3lt 8v to 3lt 16v. successfully. I went from 3.1 8v to 3.2lt 16v. (The only thing that didn't crack on that was the head). I just received a newly MiD sleeved S2 block and had the head virtually completely rebuilt due to all sorts of problems from previous builder. By the time I get this back in the car it will be right up the very top of the most expensive Porsche i4 motors. Shawn and Sid are mostly out of the game. Guess the only constant is JET951 who continues to have success with their numerous 16v builds with to my knowledge NO failed heads. Obviously there are many more out there running non stock i4 motors. People seem to mostly be communicating via FB pages. Despite some of the disagreements in here from time to time, it's a shame that this forum has fallen away so much. There were some heady days in here and I still enjoy going back in the archives to see who was doing what and when. May it continue...
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Rob 3 (05-08-2023)