high compression 7M

[jimmmayyy]

Hey all,

After getting my MZ20 soarer just a couple of weeks ago, a dodgy batch of fuel has screwed it and now has a slight rattle... time for a new bottom end.

My question is has anyone here had any experience with using the GE bottom end for higher compression? With the GTE at 8.4 vs the GE at 9.1, there isn't really a great difference. I have done this before with an RB30, (7.8 vs 9.0), with really decent results, better off boost response etc. Is there really any possible major issues with a setup like this?, ie differences between blocks possibly?


I'm not set either way as yet and nor have i gotten any prices yet, but i'm assuming that a GE bottom end would most likely be cheaper. Anyone know a good place where I could hopefully just source a short motor in SA?

Would just like to hear anybody's thoughts/opinions/experiences with this. Would I be better off with a GTE bottom end?

cheers, -jimmy

[haison]

From memory the GTE bottom end has oil squirters and the GE doesn't. You'd be better off getting the GE pistons into the turbo bottom end. Are you still going to be running a turbo? Cause it'd probable ping it's head off with out a decent ecu and very good fuel.

[stradlater]

yeah, mate, 8.4 vs 9.1 is a fair jump. It ain't insignificant like you suggest.

[Kyosho]

I beleive you'll be fairly surprised at how cheaply you can pick up whole 7M-GTE.

[Hibba]

Jin~Jah is running a GE bottem end in his GTE cressida. Runs perfectly fine. no pining. have ran up to about 12psi on it.

Computer is the factory 7MGTE one with a HKS VPC.

[jeffro ra28]

there is no problem with 9:1 and boost.

Numerous production engines these days are running over 9:1 and some even over 10:1 and boosted. As long as the ECU will cater for the needs.

[jimmmayyy]

ahh ok oil squirters. i wasn't aware that GTE's had them.. thats a good enough reason to stick with that.

strad i'm not suggesting its insignificant, just that there is much better fuels available now than there was back when they were made.

yeah i know they aren't too expensive, but prices in SA are rather inflated over prices in the east. i had good results with a higher comp RB30, so i was just considering the same with this motor. being twincam and better chamber design than the RB30 with less of a difference between GE vs GTE, i'd have thought that it could be a worthwhile thing.

[30psi 4agte]

Are the pistons the same in the GE as the GTE

Ie: does the GTE have forged pistons or a stronger designed piston to cope with boost ?

[jimmmayyy]

as far as i know they are both cast... so besides the different height i think they may be the same. can anyone confirm or deny?

[jeffro ra28]

Fuel qaulity and detonation resistance has actually gotten worse over the years.

[Hibba]

30psi: they are both cast. But the GTE pistons are dished on the top.

[Hibba]

ahh ok oil squirters. i wasn't aware that GTE's had them.. thats a good enough reason to stick with that.

There were 3 gen's of 7MGTE's

Gen1: 6M Crank. No Squiters.
Gen2: 6M Crank. Oil Squiters.
Gen3: Double Counted Waited Crank. Oil Squiters.

[o_man_ra23]

I can think of a reason that this might go sour... the head gasket

What are you doing to counter the infamous 7MBHG when you put more compression with boost there?? Also I would be seriously considering an aftermarket ECU with this (as suggested, fuels have gotten worse over the years, and with global worming ambients are up )

[Norbie]

We have 98 and 100 RON fuels available today, neither of which were available when the 7M was released, so I don't see how fuels have gotten worse over the years? Sure we had high octane mega-leaded fuel in the 70's but that's hardly relevant here.

IMO high-compression turbo engines are an awesome idea but good engine management and a top-notch tune are a must.

[o_man_ra23]

Sulpher content has gone up, as have other impurities. It negates the improved octane. Basically we are getting dirtier fuels these days.