[DKJones96]

going from stock 8.8:1 to 10,10.5, or 11:1.

which one would be best? i know 11 offers more power but if i went that high would i be using octane booster? i'm thinking 10.5 like the new celicas run.

i want to do this by using a thinner headgasket and shaving the head.

anyone else done this for power? how did it turn out?

also thinking about a 3-angle valve-job and p&p while it's in there they'll only charge 100 more for it.

 

[MK2Racer]

For the money to power ratio, not really worth it. The only way to make any real power with these engines is turboing, and its not really worth it to turbo a 5m. For price of a rebuild and turbo, it would be far more economical to get a 7mgte, then there is also more aftermarket for that motor.
As far as raising your compression, I dont think you are going to be able to raise it that much by shaving the head, you will need new pistons.

 

[DriftMe]

If you increase your compression and don't change the motor's breathing habits then you won't see much gain. Raising the compression isn't just a quick fix, for the best results you should tinker with the timing, intake temp., and fuel injector mapping. The injector pulse time doesn't need to be changed, but the pressure should be increased on stock injectors, if you're looking at 11:1 then I recommend you use larger injectors.

Of course, you'd run into more issues as well but I won't get into all of that. Unless you feel like putting several hours into perfect tuning then don't go up by more than 1 point of compression.

 

[Dave A.]

High compression pistons are available for the 5M and would be your best bet , but unfortunately they don't come cheap! :? Plus, you would need to have the reciprocating assembly rebalanced due to the difference in weight of the new pistons. Higher compression would result in higher cylinder and combustion pressures as well, which would put more strain on your bearings, rods, and so on, and thus facilitate the need for stronger rods, a change in oil pressure, and possibly bearing clearances. IMHO, Toyota engines just aren't designed to be modified internally and remain reliable unless you go full bore and build a complete race engine. A 10:1 compression ratio on the 5M would probably push the limit of the octane rating of todays high octane pump gas as well. It all adds up real quick! The 7MGTE can give you plenty of power and torque without having to dish out a huge amount of cash, and reliabilty would be much less of a concern.
HTH!

 

[Black Dawg]

Do it! I'd say 10.5:1 should be good. Get the head ported as much as possible, and the largest valves crammed in there as possible. Also probably need a larger throttle body. Make sure you have a header and 2.5" exhaust. Good luck!

 

[Dave A.]

A 3-angle valve job....plus porting and polishing the head....all for $100.00 No offense, but you must have friends in high places or can get some serious discounts on machine work and flow testing. 8)

 

[SilverMk2]

You don't want to use a thinner HG on a M series engine. The headgasket thickness is the actual clearance between the piston and the head. 1.2 mm stock is already pretty thin for this. The 5/6M runs plenty fine with increased compression on regular octane gas. I run about 10.5:1 on CAs 91 octane just fine. Personally I'd leave the compression stock and turbo the motor. NA mods aren't very cost effective for the small gains you get. You can spend mucho dollars and still not make a fraction of the power someone will get off a $50 j-yard turbo.

 

[cheappower82]

If this is the 5M-GE, just swap in a 6M-GE. Easy and fairly cheap swap (cheaper than what you'll have after machine work and new pistons). I probably gained 35 - 40 RWHP for less than $800 with the swap.