5M Pistons in an 6M

[RPMsOnHigh]

Before I get flamed for this, I'll explain. At the moment, I have a JDM 6M block. I've been doing reasearch and I found that it is possible to put high compression piston in a 6M. I plan on taking 7M rods and coupling them with high compression 5MGE pistons. I want to confirm if this will actually work, and will I have to do anything else such as balancing, getting better fuel injectors, an aftermarket computer(megasquirt) etc. Or am I going overboard? Please let me know I'm completely new to this and this is my project car. Thanks in advance!

Also about how many horses would I be looking at with the higher comp pistons, 6-2-1 headers, 2.25 straight pipe, and cold air intake.

[SilverMk2]

I've done the later 5M pistons in my old 6M. It works fine probably the only downside would be a low octane gas tolerance due to the higher compression ratio. I always ran 91 octane in my car with 4AGE 210cc injectors. If you're not going turbo the 7MGTE rods are just overkill and probably will hurt more than they help.

[RPMsOnHigh]

I am using regular 7MGE rods, not 7MGTE, not sure if there is a difference. Dont 6M and 7M rods have the same length?

[SilverMk2]

The 7MGTE rod is a little thicker with larger bolts etc. Again if you're not going turbo you're just wasting your time. If nothing is wrong with the rod or crank I'd keep the matched set together and use the factory bearing size. For your power question you'll probably be in the 155-165rwhp range.

[Road Ripper]

My hybrid 6M in my black car is just a 7MGTE bottom end with the higher compression later 5M pistons and everything else is just 5MGE stuff (no injectors, computer, etc). I put 87 octane in it and it never pinged, but I never got to daily drive it. The previous owner loosened the AFM spring 1 tooth to make it run richer.

If you look up Tanya's build of her black car, you'll find a real high compression engine because she had the head shaved. She burned through a cheap Ebay head gasket in 500 miles and then went with a metal HG and ARP studs. Probably overkill for a regular hybrid 6M, so just use a good name brand head gasket like Beck Arnley, Toyota, Victor, etc.

[Tanya]

If you look up Tanya's build of her black car, you'll find a real high compression engine because she had the head shaved. She burned through a cheap Ebay head gasket in 500 miles and then went with a metal HG and ARP studs. Probably overkill for a regular hybrid 6M, so just use a good name brand head gasket like Beck Arnley, Toyota, Victor, etc.

My cylinder head was milled just to clean it up, nothing crazy, think the # was .005" taken off. At any rate my cylinder pressure is 230psi with the metal (1.2mm vs OEM 1.47mm) head gasket and the .030" oversized, high top pistons.

Roughly 10:1 compression, maybe a little more but runs FINE on pump gas. I run 87 octane here in South Florida when temps are steady under 80 degrees, and 89 octane when 80 and higher.

Also, I am running a 6MGE ECU with the AFM leaned out about 6 turns with an idle AFR of about 15:1. Stock 30 year old injectors (which are probably clogged to hell) and I get on average 25mpg both city and highway.

You won't get much horsepower out of this setup, but you'll get a lovely amount of torque. My motor, last dyno'd, made 165rwhp and 188rwtq
http://www.celicasupra.com/forums/sh...ight=6MGE+dyno

If you want more power you will need a standalone or piggyback to get rid of the bottleneck AFM and go MAF sensor.

[RPMsOnHigh]

My cylinder head was milled just to clean it up, nothing crazy, think the # was .005" taken off. At any rate my cylinder pressure is 230psi with the metal (1.2mm vs OEM 1.47mm) head gasket and the .030" oversized, high top pistons.

Roughly 10:1 compression, maybe a little more but runs FINE on pump gas. I run 87 octane here in South Florida when temps are steady under 80 degrees, and 89 octane when 80 and higher.

Also, I am running a 6MGE ECU with the AFM leaned out about 6 turns with an idle AFR of about 15:1. Stock 30 year old injectors (which are probably clogged to hell) and I get on average 25mpg both city and highway.

You won't get much horsepower out of this setup, but you'll get a lovely amount of torque. My motor, last dyno'd, made 165rwhp and 188rwtq
http://www.celicasupra.com/forums/sh...ight=6MGE+dyno

If you want more power you will need a standalone or piggyback to get rid of the bottleneck AFM and go MAF sensor.

All I have is the 5MGE ecu. So can I use that? Also will I have to balance the engine?

[D-cat]

All I have is the 5MGE ecu. So can I use that? Also will I have to balance the engine?

Yes you can use the 5M ECU. As far as balancing, unless you are going to do a whole lot more to your set-up, it isn't needed. There are dozens of posts on here about building 6M engines, I suggest you read them, a lot of good information.

[Tanya]

Yeah you can use a 5M ECU just fine. I balanced my motor at the suggestion of Aaron garney @ RabidChimp and it was a VERY good decision. The engine revs as if it has a light weight fly wheel, smoother and quicker than a 5M. My only regret is not getting the crank knife edged.

[RPMsOnHigh]

Yeah you can use a 5M ECU just fine. I balanced my motor at the suggestion of Aaron garney @ RabidChimp and it was a VERY good decision. The engine revs as if it has a light weight fly wheel, smoother and quicker than a 5M. My only regret is not getting the crank knife edged.

Thank you Tanya, the reason why I was asking about the balancing was because my Mechanic suggested it. He is helping me with the engine build and he knows a thing or two about the "M-series." He also said the engine would rev faster as well. I will be adding a light weight flywheel to my set up so I'm sure I'll be able to rev it up really quick. I already have injectors that can handle up to 300hp, headers, a 2.25 inch straight pipe and intake. I'm sure this will be a very enjoyable car when I'm finished Any other suggestions?

I also will be making a build thread when things really get rolling.