I would never rev over 7k on a boosted application anyway. No need. I have a 7k limiter but typically shift at 6,500. And since when does compression ratio have anything to do with valve float?

 

it doesnt, and redssna i totally agree

 

So what's your opinion glen? Your pretty knowledgeable about these motors, 18 psi at 7000 fairly safe?

 

fairly safe, no lol

its all in the tune, 18psi is alot of boost, but in retrospec it all depends on how big of a turbo you go with, or if your supercharged etc etc

but 18psi on a 2.4 motor is kinda vauge

 

I'm only talking about valve float, not about boost.

 

well i got thrown off because you said 18psi, but 7000 isnt all that extreme, i run 7100 on the street tune

 

And you have no valve float?

 

nope, ill be getting the supertech springs as well as some other goodies next year though

 

Some good info.

 

Yea the application we're looking at here would be for my 2.4. I'm going to be doing a supercharger build in a couple months and would like to run a 2.75 pulley. But we were concerned with the ~17-18psi that would result from that and if the valves would start to experience float. The car would never be revved above 7,000 rpm though.

 

We were unable to run 15psi much past 7000 RPM. After a few trips to the track, the springs also seemed to get worse quickly. Eventually, power was falling off at 6500 RPM at 15psi and there was audible misfiring a little below 7k. When we swapped the springs out, we tested the old ones and found some in the 45-48lb range even though I believe they are supposed to be 60lb. With the new springs in, HP kept climbing to 7500+ RPM at 15psi and we had no problems at 17psi and 7900 RPMs.

As far as LNFs, the cam lobe shapes may be completely different. Either way, not too many people are revving them past 7k. They also have less miles on them in most cases.

 

We're not trying to run past 7000 at all. Any thoughts to why the LNF can run higher boost with similar cams and the same valve springs??

 

As far as LNFs, the cam lobe shapes may be completely different. Either way, not too many people are revving them past 7k. They also have less miles on them in most cases.

i don't know why i didn't think of / mention the RPM issue.. considering thats a key factor.. when i up the boost i'll be looking at a 7k redline and about 17 psi.. i'll find out how it is.. if there is an issue i'll pick up the zzp valve springs or the patriot 72lbs ones

 

You answered your own question. Not revving as high is the biggest factor.

I want to add that even when you can't tell that there is valve float/bounce, you may still be losing power. Many LNF power bands will carry out to higher RPMs with stronger valve springs.

 

Thank you sir!

 

what exactly does valve float look like on the tach?

 

you ignored the rest of it.. where he says with stronger valve springs you can extend the power band

 

I'm only asking with boost up to 7,000 RPM. I'm not talking about a higher redline then 7,000.

 

lnfs drop off at like 5800.. so if it extends the powerband till 7200 then that includes boosting up to 7k..

 

10.4:1 vs 9.2:1 CR, and while i dont know if the cams are the same between the LE5 and LNF (likely just timed different or just minor changes), but things like ramp rate will also be a factor. Also, that does the LNF redline at, and what does the LE5 redline at?

Symptoms of valve float are really just a loss of power assuming its not floating enough to cause the valves to hit the piston.

 

I guess it is worth noting RPM. Maybe an over looked detail of LNF vs LE5 valve float debate. LE5 is 6750 from factory and the LNF is 6300. 6300 might be ideal redline for higher boost numbers.

Wonder what RPM tuned guys are pushing?