New Motor Doesn't Want To Rev
 

Just got a new motor in my car last week.

The old set up was a 4.8 with LS9 cam
The New set up is a 5.3 with LS2 cam

Same 241 heads and Lunati valve springs, same S475 (1.10 83mm), same LS1 intake. Same TH400 and Circle D converter.

The 4.8 would rev to 6800rpm all day long. The new set up feels much better all around but it just does not want to rev. It will go 63-6500 in 1st then about 58-6000 in 2nd then 3rd gear will just hang around 5200rpm and not move much. It doesn't feel like its slowing down but I know something has to be off.

It doesn't break up or miss, the tune up looks pretty good. Running E85, 12psi and 14-15* timing.

Main difference between the two set ups are the cam and displacement. My initial though is that cam timing. What are some other things I should check? I am debating just tossing in another LS9 to see what that does.

This is a 2nd-3rd pull.
http://i68.tinypic.com/2likgfa.jpg

Sorry if this sounds random, but did you check your bearing clearances?

Dial bore gauge and a micrometer. 0.0022"-0.0025" on the rods, 0.0027"- 0.003" on the mains. It does make more oil pressure than I expected. With the 10296 pump its around 40-45psi hot idle goes up to around 75 psi with Rotella 10w30.

All standard Clevite H series bearings in the rods, a mix of standard and X bearings on the mains.

Ok cool. I really wouldn't expect it to be ar high rpm screamer with an ls2 cam either. It seems like it's right on par to me. Smaller motors tend to rev a little better than larger displacement motors.....usually. Other than that, I'm stumped.

Yeah I am kind of with you. It runs too well for there to be something majorly off. I know the motor is bigger, the compression is high and the cam is smaller that my 4.8. So all of that combined it shouldn't rev as high. The car runs strong for sure. But I was just expecting a bit more revs.

Take it to the track, and see what it runs like. That will let you know whats up for sure.

I would suspect the post-turbo exhaust. I also think the timing may be a bit low for e85 at 12psi. I am neglecting the fact that the same turbo will choke lower on larger displacement, because I seriously doubt that an s475 will be any where near a problem on your setup.

The exhaust is just a 4" dowpipe right off the turbo, and its only 2' long at best.

http://i133.photobucket.com/albums/q...809_183734.jpg

Can you elaborate. What do you mean 'kinda stays' that sounds like it has a dead leg (do a compression test). It shouldn't stop revving with 12psi of boost, even if it was a stock engine the thing should shoot to 8k 9k without a limiter and explode parts and oil everywhere, showering the road.

Its just slow to rev in high gear. It will take a few seconds to gain 2-300 rpm in 3rd.

Check cranking compression. Did you degree the cam?

I have yet to check compression, I will do that tonight. When installing the cam I found true TDC, the just lined the dots up.

maybe retarted cam timing or back pressure issues

Pushrod length?

could engine management be detecting knock and pulling out timing? You're timing is lower than what I'm used to seeing at 12 psi of boost. Do you have a way of logging knock and timing?

This is a little off topic, but if I were you...I would put a blanket on your turbo. Probably has nothing to do with your issues, but I believe you will see some benefit.

I am going to see what an LS9 cam will do in it. That way the only real difference between my two set ups will be 4.8 vs 5.3. The car still runs great, has plenty of torque down low but is just lacking up top.

And I did order a turbo blanket.

Why keep messing with these stock cams if you want the car to rev? Why not put in a good size cam made for a turbo car? How about a tu1...or tu2.

I am certainly going to get a real cam. I mainly just want to try the LS9 for comparison purposes. There is an event I am going to run this Friday so I didn't have much time to order a real cam.

For reference, degree the current cam and see where it is before you pull it out and degree the LS9 so you know where it is when installed. You'll save yourself lots of time and uncertainty when installing a cam to simply degree it and know where it's at.