What do you think our engines can rev to? I've got a set of SR 268 cams laying around which are for NA supposedly. I know for turbo setups you're supposed to minimize overlap, but a lot of the DSM's run high duration cams on their turbo setups. I'd have to upgrade to Ferrea valve springs etc, but wonder if we could rev to say 8500-9000?



If I go GTX3582 I'd almost have to rev it that high to keep it in boost for a decent time period. I won't make 30+ PSI until 4800-5000 RPM.



My other option is a GTX3076 which will result in a very similar spool time and capability of running 35 PSI efficiently. However I'd like to go big or go home so to speak. With the crazy tall gears and wide tires I think I'm in need of a solid 600 whp, which I think would be the limit of the 3076. The 3582 however would be nice and comfortable at that power level...



Here is a very valuable review thread that I found regarding the GTX turbochargers:



http://blog.perrinperformance.com/ga...turbo-comparo/



Keep in mind they are running a Subaru WRX Sti engine which has 2.5L of displacement vs. our 2.0...

 

I know the DSM/Evo valve springs fit. Brian Crower valve springs set are around $75-$80. I don't know for sure how high you can rev with them though.

 

You need to compare the spring rates. I have a set of Crower springs, but I don't plan to rev out over 8k. And when I do, it will be for seconds while crossing the finish line.



You could get a set of high pressure springs, but then you run the risk of breaking the valves when they hit the seat. That's when you need upgraded valves. Ferrea is our only off the shelf option, but they too have been known to break. This is on Hondas though who constantly rev to 9k. So, as racing goes, nothing is indestructable no matter what you get.

 

Thanks for the information guys. I've already got custom .5mm oversize Manley stainless steel intake and exhaust valves. So that part is covered. My main concern is will the engine continue to make power above 7500 RPM with factory cams? Looking at my 425whp dyno graph, the power curve remains flat from around 5500 to 7000 RPM where he stopped the pull. I know I've rev'ed the engine up to 7800 with factory valve springs and the 268 cams back when I was NA. There were not issues with valve float. I need to find the dyno sheet from when I was running that setup to see the power curve. The issue is with the car being turbocharged now, there is no guarantee the power curve will be a similar shape as it was when the car was NA.



Back to trial and error, I guess I'm used to it at this point .

 

You wouldn't have valve float on an n/a car. It comes into play during high boost levels.

 

Float can happen when the spring can no longer adequately close the valve fast enough. That typically means the spring pressure needs to be upgraded whether by new springs or shims on the OE springs. Either too high an RPM or too high a boost pressure or both can contribute to valve float. Heck even springs that have lost their 'spring' can float valves at stock RPM

 

Yes, it CAN happen on an n/a car, but we're talking about 7-8k rpm. I've seen a SCCA Beta rev to 8k locally without any problems. I would agree that it can come into play around 9-10k though.



Dave, weren't you getting valve float at 25psi and 7krpm?

 

nope, no floaty valves here. Now spark flame out..that's a different story. MSD ignition helped with that.

 

Well, in that case I don't know of anyone who's experienced it. I would just go with the Crower springs and leave it at that. A member on NT is pushing a little over 500 with just the springs. You don't want super heavy springs or you'll risk damage due to the added strain on valves and retainers.

 

Great information guys, thank you. I imagine I can keep the stock retainers and bottom seats if I go with the Crower springs? I'd like to be able to rev the engine to 9,000 RPM if I decide to upgrade the springs and pull the head again to do so. The Ferrea springs and retainers on IPP.net are around $600. I'd have to compare the factory valve spring pressure to the Crowers. I know the dual Ferrea springs are much higher pressure than the stock ones (200 lb. @ 22mm). Their single spring option is only 150 lb. @ 24mm. I'd assume the mm listing is how far compressed the spring is from its rested position? So 24mm is almost 1" compressed being that 1" is equivalent to 25.4mm.