mywhitewolf

I'm trying to work out if its worth while dropping the compression ratio on my maxima (VQ30DE). I've just recently blown a head gasket (was trying to diagnose a leaking injector, put in the stock injectors and accidentally hit boost while testing = blown head gasket).

I'm wondering what sort of HP i can run with a reduced compression ratio? i'm running between 12-14psi on a smallish T3/T4 currently. whats the limiting factor in our engines as far as boost is concerned? I've heard of people bending rods etc going higher than 14psi but is this because of Detonation (with stock CR) or is this just because the rods are at the limit?

Also, as far as reducing compression, as I'm very poor atm I'm limited to shaving the combustion chamber, shaving the Cylinders or getting a thicker head gasket.

It would be a shame to miss out on this opportunity to reduce CR while the heads are out and its significantly easier, but if the 14psi "safe" limit of the engine isn't due to the CR then i won't bother.

While the heads are out I would love to save up for a while and do the full forged / balanced crank/piston/conrods & revup oil pump & run some serious boost. but i need my car working as its also my daily and 13hour days including transit are starting to get to me.

Any input is welcome

Kevlo911

iTrader: (36)

Easiest thing:

Get a low mile DE-K and swap it in. Tuned properly, you should be able to reach 350ish hp on the stock 30.

Save money to build your current motor and you can take your time doing so.

mywhitewolf

currently running the 00vi from the DEK, so that doesn't really help, HOWEVER i do have a spare vq30de engine sitting in my parts car, but i don't have a good way of getting it out (its under the house and limited room, probably be able to drop it under the car though) even if i can get it out however i don't really have any way of getting it in the turbo maxima as the only place i can work on it is in the driveway which is not flat and level.

maxgtr2000

iTrader: (29)

Get with some org members if any are in your area, some one may be able to help. I know you can get lower compression pistons for the 3.0 but they are rare. You may want to consider a vq35 swap and build that with lower compression or maybe stock compression with performance rods. But your engine blew because of the circumstances, so it's really not a strength issue, it was a tuning and install issue.

mywhitewolf

I'm located in Australia so org members are pretty limited (everyone in Australia with a boosted max that i know about is about 2 days drive away :/). and if i was to reduce the compression i would look at upping the boost as well, (otherwise what the hell is the point?)

i just thought it might be worth looking at as it would be significantly cheaper to do while the heads are out.

streetzlegend

iTrader: (8)

It depends on how much power you are going for, what is your power goal?
In my opinion, no you should not lower compression, assuming you wanna be in the high 300 low 400 range, you should be fine with stock compression. Just need to have a real good tune. Good safe timing, if possible meth injection, enough fuel, up the boost, and your good to go. The next thing to go bad on the 3.0 would probably be the ring lands. My head gasket went first, then fixed. After, the rings went.

akurtzer57

iTrader: (4)

If really want to, make custom head gaskets or have them made if your not capable. Just have them made to whatever thickness you want. Might cost couple hundred. But id just run stock compression and tune well.

Nealoc187

iTrader: (23)

Weak points are head gaskets and ring lands on VQ30s. I haven't personally seen bent VQ30 rods, but I'm sure someone has. I have personally seen multiple blown head gaskets and cracked ring lands. I've also seen melted pistons, but those occurred when a boost controller was errantly turned up quite a bit higher than the car was tuned for (18psi).

My feeling is that with a proper intake manifold (MEVI or 00vi, not USIM) you should be able to run 450whp reliably on a well tuned VQ30DE. I don't know what octane ratings you guys have available down there (i think you have like 98 or something, but I believe it's measured differently than it is in the US). Methanol injection is a superb safeguard for pump gas cars. With MEVI or 00VI, meth, and a proper tune, 450whp is not a number that I feel is unsafe (your transmission on the other hand, you need to worry about). If I ever turbo a VQ30 again, meth and 00vi or MEVI are two things I'd most certainly have and I would be shooting for 450whp, and if things look good when I get there, maybe a bit higher.

Reducing CR would help of course, but I don't feel that it's a necessary expense unless you are shooting for the moon on otherwise stock internals.

BTW VQ30DET pistons are 9.0:1 CR, if you decide you really want to drop the compression. I think they're pretty easily available down there, no?

Sinturion

Whitewolf - I have some VQ30DET pistons if you are seriously interested in doing a high power build.