lart951

Not a tech here but Chris advice sounds good to me. Give it a try Jim you can go back to the dyno Sunday morning and make the year end a little brighter to all of us, your fans.

Laust Pedersen

Hmm, I’ll stay out of this discussion, except just adding a generic graph of combustion (and compression) pressure as a function of crank angle in the compression-combustion stroke.

The graph is lifted from Aquamist and mostly intended for showing the benefits of water injection, but the effects of varying timing with knock as a result can also be seen.

Laust

special tool

All input is appreciated as usual, guys.
Thanks.


By the way - I won't be quitting on the 600 wheel 2.5 8 valve much too long before I am dead.

tedesco

OK, so what about this one:

If I remember well, during your first attempt you made max power at something like 5000+rpm. I think this is a result of a small turbo combined with stock or close to stock valve events.
Normally maximum volumetric efficiency of the engine is around 4000rpm which would mean that naturally aspirated you would make max torque at this rpm. If you want to have a turbo with good spool up you size it to run though its max eff roughly in the middle of your desired power band. This on the other hand means a dropp of eff towards higher rpm.
If you now combine both you arrive at an engine that has massive torque compareably low down but loses torque significatly towards max rpm (engine and turbo work worse at high rpm).
The design principle of virtually all race engines is to increase max prm as much as possible and to try to maintain torque until this point. Long story short: Go for a bigger turbo. This way at low rpm you are getting good VE due to the basic engine design (NA). The bigger turbo compensates for the loss of VE at high rpm due to increasing its own eff (big turbo=>max eff close to max rpm). This way the torque curve would be more straight. Max torque will be less than for your current engine concept but due to making more torque higher up max power will be higher.
This way you would also avoid head lifting until higher rpm as torque directly relates to combustion pressure.

sweanders

ST, remember to strap the car down or this might happen:

http://www.youtube.com/watch?v=ftk6OOMO6MA&eurl

toddk911

Would releasing any backpressure help with this?????

Time to go to 4" down pipe back????

toddk911

I'm starting to thing people should not ask why one should use water injection but why we are NOT using water injection. The benifits just seem to be non stop.

I will do it this summer!!!!!

special tool

Todd - reverse your thinking.
My head lifts from TOO MUCH airflow into the cylinder head during the intake stroke.
This is why I don't use a 16 valve head, and also why I never had a problem with the tiny #8 exhaust housing.

toddk911

So the head lifting has nothing to do with backpressure in the head/motor???

toddk911

if I blow on a straw that has a hole covered with tape and the straw is flowing fine, the tape will not lift/leak.

If there is an obstruction (NOT good airflow), or some increase in back pressure in the flow of air, the tape will lift/leak.

Please edubacate me

hot-J

OMFG!!!!!!!!!!!LOL.......

Tms951

none of that made any sense to me. The head is lifting because of stock head studs plain and simple. At this point I am only trying to make 450whp at 23psi on race gas. I just put race ware head studs a few weaks ago, I picked raceware because they have done so much porsche stuff, other than that I don't think they are that different from the ARP.

I would say going from a 3" to 4" down pipe would make no difference with out a big T4 (.96a/r or Bigger) hot side and at least a p-trim wheel.

special tool

interesting viewpoint.

Porsche-O-Phile

Eventually you're going to get to a point where the limiting factor of how much flow (air-fuel mixture being crammed into the cylinders) is the strength of the threads holding the head studs. If the threads start ripping out before the studs elongate enough to allow head movement and relieve the pressure, it's going to result in the same problem. You can have an uber-hard head stud but if the threads in the block aren't strong enough to keep it in place under super-high compression of the pistons, it's going to fail - badly.

Porschefile

Dude, your logic just doesn't make any sense. The combustion stroke contains a significant amount more cylinder pressure compared to the other 3 strokes. You are most likely to see head lifting on this stroke. If you are seeing it on the intake stroke then you can be darn sure you're getting lifting on the combustion stroke. Cylinder pressures on the combustion stroke can reach as high as ~600psi. There's no way you'd see that kind of pressure on the intake stroke. A 16v would only help combat against these problems due to the more efficient combustion chamber design.