I need to rebuild my engine and thinkin of goin to lower compression 8.5:1 Want to lower the compression because i want to run higher safer boost. Running mechtech turbo setup.

How reliable is lowering the compression? I will go with JE pistons and Total Seal rings. With out upgrading anything else but the pistons, will i be able the run higher safer boost? Will the crank handle the extra maybe 200hp?

In all i just want to know if lowerin the compression will I have a reliable engine.

Is 8.5:1 compression good or should i go with a different ratio?

Originally posted by guc32
Is 8.5:1 compression good or should i go with a different ratio?

8.5:1 is a number that AA uses when a customer requests it.

Jim Powell on this board has a mechtech setup and is also doing some internal engine work. You may want to ask or PM him what type of setup he's doing.

Lowering the compression ratio has nothing to do with reliability if you want to run higher boost. Remember that more boost means more exhaust backpressure and that equals heat! Its how much boost that will affect the longevity of the engine. Lowering the compression will also increase turbo lag... but since mechtech uses a smaller turbo, it wont lag as much as a larger TDO6 that AA commonly uses.

Your crankshaft will hold up. You might as well replace the rods if the engine is taken apart.

Someone mentioned, i think i may have mistaken, that the stock rods can hold almost 1000 hp. I dont want to replace the rods if i dont have to. Will it hold the power im goin to produce. I say about 200 hp more.

There is a car at AA right now putting 460ish HP to the wheels on stock internals.

460 x 1.31 = 602HP...

on stock internals.

Kevlar: Was the compression lowered with bigger headgasket? Is this on a 95 M3?

so your engine is jacked up guc? No simple head gasket probs? did paul show you it was broken? What caused the problem? You need to make sure your car is fixed in two weeks.

Originally posted by guc32
Kevlar: Was the compression lowered with bigger headgasket? Is this on a 95 M3?

Ya, they use a bigger gasket. It's on a 3.2L motor.

Cleo: head is cracked showed me the pistons were loose in the block. He said might as well go with lower compression when im at it. So dats what time goin to do so i can run higher and safer boost too. May need new head if this guy Paul is tryin to see if he could fix it. If not then i will need to get a rebuilt head. 2 half weeks to get pistons 2 half week for Paul to finish. So no go on Buttonwillow :chix :chix :dunno :dunno

Hmmm, that's not going to work for me E. YOu need to make it happen, maybe you and i should fix your engine. What's the worse we could do? Look how well we installed the turbo! Boy im sure you're all torn up inside, poor guy, engine all blown up and now you're forced to get awesome internals. Hey if you need a shoulder to cry on, im here!

This is a myth.

Lowering compression diverts energy from the crankshaft to the exhaust. Spool is actually better with lower compression. Same thing with retarding timing. - Beau

Originally posted by Jon Caldito
Lowering the compression will also increase turbo lag... but since mechtech uses a smaller turbo, it wont lag as much as a larger TDO6 that AA commonly uses.
[/B]

Do some research on 'quench' or 'squish'. - Beau

How much would be safe boost on 91 octane with 8.5:1 compression? Running 6 psi now with stock 10.5:1 compression.

A _general_ rule of thumb I've heard thrown around many times is 1 point of compression drop can allow an additional 2 psi of detonation free boost. - Beau

Originally posted by guc32
How much would be safe boost on 91 octane with 8.5:1 compression? Running 6 psi now with stock 10.5:1 compression.

Originally posted by Kevlar
There is a car at AA right now putting 460ish HP to the wheels on stock internals.

460 x 1.31 = 602HP...

on stock internals.


why are you multiplying by 1.31?? Seems like a nice exageration

should be like 1.17-1.21 at the most.

Originally posted by psk145

why are you multiplying by 1.31?? Seems like a nice exageration

should be like 1.17-1.21 at the most.

Dynojets use those numbers... Mustang Dynos use higher numbers... but whichever way...

460x1.17 = 538
460x1.21 = 556
460x1.26 = 579.6 (this is the number that I use most. When I multiply my base dyno number against 1.26, I get 246HP).
460x1.31 = 602

Originally posted by guc32
How much would be safe boost on 91 octane with 8.5:1 compression? Running 6 psi now with stock 10.5:1 compression.

Check out the Project M3 in European Car magazine. I think he's running that setup. 12psi of boost was the limit (the car had some occasional knock)... but I think the turbo was the problem. It was outside of it's efficiency range. I'm just guessing there...

The article...
http://www.europeancarweb.com/archives/tech/0502_tech01_2.shtml

From your sig:

Originally posted by Jon Caldito

Jonathan Caldito
'98 Active Autowerke Turbocharged M3
'02 M3 SMGII
"Boost... my anti-drug"

Lucky git ;) Too many toys to play with ;)

Originally posted by guc32
I need to rebuild my engine and thinkin of goin to lower compression 8.5:1 Want to lower the compression because i want to run higher safer boost. Running mechtech turbo setup.

How reliable is lowering the compression? I will go with JE pistons and Total Seal rings. With out upgrading anything else but the pistons, will i be able the run higher safer boost? Will the crank handle the extra maybe 200hp?

In all i just want to know if lowerin the compression will I have a reliable engine.

Here is the problem to your solution..

http://bimmerforums.com/forum/showthread.php?s=&threadid=25595

8.8:1 compresion. Je lowered comp pistons (ceramic coated), Pauter
Rods, Ceramic coated valves on head. blue printed motor..
blah blah blah.. your typical AA stage 3 motor.

Originally posted by Kevlar


Dynojets use those numbers... Mustang Dynos use higher numbers... but whichever way...

460x1.17 = 538
460x1.21 = 556
460x1.26 = 579.6 (this is the number that I use most. When I multiply my base dyno number against 1.26, I get 246HP).
460x1.31 = 602

Who's car is that? Last I checked the #'s were 471hp and 494tq
at the rear wheels on our stang dyno...

i luvved that 0-60 3.68sec run. i was watching the wheel spinning
like there was no tomorrow, when the run was over I realized I
was suppose to record it...

:dunno :dunno :dunno

New rods are not required although it will help the motor to lengthen the rod slightly and lower the wrist pin in the piston. This gives less angle on the piston.

The M3 rods will indeed handle 1000 HP. So if you aren't going to change rod angles and such, have the wrist pin bushings pressed out and replaced. You can also do yourself some good by having them lightened, sub-gram balanced and peened to remove stress and align the molecular structure of the rod.

Do not trust your gas. Especially with hot weather coming. The gasoline will lose octane sitting in the ground and in your tank. Always put in what you need to drive in the next couple of days only and buy premium at the busiest damn station you can find. It's gas will be freshest. Fresh 91 octane 7/11 gas is better than 2 week old Chevron.

Since boost is addictive, consider getting or making an alcohol injection system. I prefer these over water injection for a few reasons. First if the car does detonate, alcohol will not cause hydrolock from steam the way a water system will. Rare, but if it can happen in a Chevy, it can happen in a BMW. Second, occassionally people are idiots and drive their cars to the mountains in SoCal in the fall. Water will freeze alcohol won't. There's a couple more reasons. All of these are trivial but I still prefer alcohol.

I just use the water injection, right, but use more alcohol mix into it then water?

Looks like i dont have to work on my engine for now. Head is not cracked and pistons and rings are fine. Just need to replace head gasket. So im goin to hold off on the pistons for now. Save me lots of money.

Thx for the info from everyone.

juuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuc, any updates on the car today? I hope it can be ready for buttonwillow.

I doubt it be ready by then.

Just keep calling him, mechanics are lazy. Call him everyday

Bump!

Bob ///M3