increasing compression

it will bring up ur comp, but not very much, vs is 9.4:1 i think it will take it to about 9.6:1 9.7:1. you will feel a lil more power, but it wont be WOW this is the best thing i've ever done, if you up it to 10:1 u'll feel it more.
RE: tune, i would get it retuned, and i think u'll have to run minimum 95ron fuel just so she doesnt ping, maybe 98 with the cam

 

well the highest i;ve ever seen is 10.5:1 on the emotec, i think anything over that, u gotta watch the valves hitting the pistions.. really its a strip down, new higher comp pistons and rods while ur there.

umm cost of shaving i think is around 500-1000 depending on where u go, and how good ur heads are, see u may have to face em first get em flat, then shave. n if u can rip the heads off n take em in, or whether they do it for you.

i would love 10.5:1 comp, n with the combo that u have so far, u'd be doing urself a favour, n would turn have into a beast of an engine

 

i think my figures n what-not are round the mark, but i know theres a few that can either vouch or correct what i've said.

yea i recon they'd still be in fair condition, u know if u got a decent price for the work, maybe go with 3 seat cut valves too. dont know how much but whilst the heads are off might be worth looking into

 

shaving heads for a c/r increase is ok for small amounts like a 1 to 0.5 increase is safe enough just by shaving a few thou off (going to the trouble of taking the heads off - shaving then re-installing, with paying for labour and new head gaskets aswell, makes it hardly worth it at all though).
for a really substantial increase in comp then the pistons themselves need changing to high comp ones - especially for a 10:1 + c/r where the pistons would want to be alot better than stock, either hyperuetectic or forged. so really you need to build the engine to run as a high comp n/a engine, with the right piston and rod combo so its all safe and the engine will last.
you could go higher that 10:1, but i wouldnt recommend it, the engine probably wont last more than a few years, even if it is build right. alot of high comp engines, which are used in racing and such are stripped down regularly and rebuilt, which is ok for them, but not really the best for a street car.

 

umm, yeah pretty much mate. looking at a few grand minimum, really depends on labour cost - which is the killer for things like engine rebuilds.
basically you could go with shaving the heads and increase from 9.4:1 to 9.5:1/9.6:1 safely enough that way for probably just under a grand (going off your $440 cost to remove and re-fit heads + the head shaving + gaskets).
or any more than that (more is possible, but on stock pisons is a bad idea in my opinion) you'd probably want to look more at changing the pistons, which would require a rebuild.

the small c/r increase from shaving the heads would be pretty un-noticable in the scheme of things, bit more torque, tiny bit more top end. quality fuel would always be needed and your tune checked over (in particularl the timing) so you dont have any detonation/pinging issues.

 

haha, i just dont wanna see you disappointed after spending heaps of money, or worse, blow up your engine. to my small knowledge of these things you cant just change the pistons over without taking the bottom end apart - but checking with someone else cant hurt incase im mistaken.

edit - forgot to answer one of your questions - yes, the engine wouldnt last too long with stock pistons and high comp. stock pistons wont take too much abuse, so if you happen to get some pinging happening they'll be screwed in no time.

 

Nope....

aZk.

 

on a stock motor there is no need for such a large exhaust (bar 2.5), There isnt any flow restricitons at 2.5"... the stock motor isnt making enough power to warrent any bigger.

If you go larger youll just loose back pressue and low down torque. You might gain some noise but thats about it really....

For a stock V6, 2.5" is ideal.

aZk.

EDIT: Just relised you have a cam, even then, you said it yourslef that its a mild one. The only reason a six needs to be bigger is if its pulling horses now thats through either boost (+6psi) and/or serious NA work (storker, massive compression increases and extensive porting + cams)

Stocky on here is(or maybe not, but he was) going to be getting a 2x2.25, but hes running 8pound of boost...

You see VL turbos running 25pound and running 9sec passes, with a 3", do you really think your gonna match that sort of flow?

 

read my above edit

aZk.

 

I've had a few exhaust on my car and I would say that the best system I have ran was twin 2 1/4" pipes coming off the extractors into twin 2 1/4" cats then a Y merge into 2 1/2" pipe, muffler and resi. simular to the factory exhaust system for the Supercharged 3.8L.

The good thing about this setup is 2 1/4" cats come standard on VR commordores which you can pick up from a wrecker at a reasonable price. They will flow more then enough for the 3 cylinders each.

My mate had the same thing on his car but put 3" pipe and muffler after the merge but that was just for noise.

Jezz