FRporscheman

Rich, yeah, that was my thinking. Looks like I'll have to factor in the cost of a custom 6th gear into my project budget. I might have to cut back on some power mods to afford that... but it's OK. I must have speed.

notthd

Though I'd jump in--I've seen over 180 in my modified turbo. Exhaust, T3T4 hybrid, injectors, remapped at 14psi. you get the picture.The Rev limiter was increased to 7400rpms and I had no problems with the car for over 170K miles. Approaching the top end aerodynamics really start to come into play. Any large upset of the suspension and I felt like the car would of gone airborne. May have been able to get close to 190 but I will never get that car up that high again....

A actual snap shot with speed and RPMs. There is more left than in this photo.



Regards, Mike

RajDatta

I plan to do an NA modded 968 soon. The redline will be increased to 7200rpm. The valvetrain will be appropriately modified to handle this.
Raj

968turbos2

Hey notthd, that is the kind of info I was looking for. Thanks. Did you do any valve train mods to do this? I was thinking about where I should set the redline for speed given our tranny gearing.

luckett

I think these engines would run great tuned at a narrow high RPM band, but my concern is oiling of the con-rod bearings at that high of an RPM. I've blown an engine in a 944 with a high RPM chip coming down the esses at Road Atlanta. Coming out of #4, which is a long, high G-load turn, and after making the next right hander that drops down, I was running at redline ready to shift and it let go. Infamous #2 failure. I attribute the failure to oil starvation from the high G-load turn exacerbated by the high RPMs it was running at the moment it let go.

I'd love to squeeze some more RPMs out of my car, but now I'm scared to run it that high.

Do you know when the OEM valves begin to float?

notthd

Autothority mapped my chip and has done many modified 968s/ 951s. They picked the redline which I stayed under all but 3rd gear and topend which is where I felt I most effencently used the extra rpms.

Oil Starvation in high G situations at the higher RPMs is exactly what I read here. Could be trouble. I am not sure but I though my car had additional oil pan reserve with baffles to help with this. I remember it taking an extra quart after the mods were done. 7200 "safer" side 7400 asking for trouble if you go there often or track the through the Gs. Anytime you up the RPMS could be certain death... My motor had no high performance valve train mods and stock gearing 5 spd. We felt the pinion gear in the 6spd could not handle the extra horsepower. From memory... plus or minus- 1st to 40mph, 2nd to 95/100, 3rd to 130+, 4th I do not remember but top speed was in 5th.

Regards,Mike

luckett

At these speeds aero is the most important factor. In terms of attaining a high speed and making the vehicle stable at those speeds. Just taking the mirrors off could easily gain you 5mph as evidence by the top speed testing of the Carrera 3.2 body with flag mirrors vs racing style mirrors.

Racers driving 917s back in the day were afraid to drive certain early iterations of the car due to the horrible aero charateristics that gave the car a mind of it's own on the Mulsanne at 250mph. There were stories told of the cars jumping left/right by about 10ft as the cars made their way down the straight. Many considered them "undrivable" and some drivers refused to race the car.

luckett

If I was going to try those RPMs I would go a full dry sump system straightaway. Not cheap up front, but cheap insurance relative to a blown high dollar motor.

notthd

Very True both in the sump and in Aero.. This car was street dress with a larger wing and a lip spoiler. Over 160 it felt like it was "lightening up" I kept thinking of that mercedes flipping into the woods in one of those Lemans races not too long ago- and it was designed to go that fast. I wanted to see if I could bounce it off 200mph once to say we did it but I felt it was not safe as I approached 180... talk about pucker factor. I started thinking of what safety gear I WASN'T wearing and backed off....

RajDatta

Chris, this would be an engine for street use so the high G loads will not be seen. I don't expect to any oiling issues. Also, I doubt the redline would be hit as often on a street car as a track car.
Raj

luckett

What about valve float? Any info on that one?

RajDatta

Chris, with the proper valve springs and cams, its not an issue.
Raj

luckett

I meant, do you know at what RPM the stock valves begin to float? Or is it at such a high RPM to not be an issue?

Some of the racing rules allow you to change the rev limit, but not the internals of the head. If the stock valves begin to float at a low RPM, there is no reason for me to raise the rev limiter.

RajDatta

I will have to ask and get back to you on that. The package I was looking at involved HD springs so I never asked the question on stock springs.
Raj

edco

H2 you should come on down and run an open road race, there a few new guys coming down from Washington state for the 08 season. Nothing like running the car all out! Keep in mind your running at an altitude from five to seven thousand feet.

It’s a blast no matter what speed class you run, we ran 150+ for almost 50 miles in the PE130. Seriously you should consider running one of the MKM events in “June or August” We are getting the car ready for the NORC in May

Matt