Stock M20 turbo - Maximum boost?

[Chuckcruzin1986]

How far to go with boost. I don't mind a slight risk of damaging the engine.

2.7 Liter
Super eta pistons
Balanced engine
Holset small HC1 turbo
Milled straight 885 head
Ground Top of block
Metric blue hex bolts
BMW OEM head gasket
9-1 compression
93 octane
Megasquirt
6500 max rpm

The max boost recommendation would assume that I tune the engine correctly :???:

Thanks,
Chuck

[Vivek]

yeah here is my new out look on the M20.

0-10psi=stock headbolts,can get away with WAR or other tuning methods
10-16psi=ARP head bolts+MS
17-20psi=+wasted spark
20-23psi=+welded coolant channels
23+psi=Build the snot out of it- ARPs,welded head,oring block and beefy lower end.

obviously there are exceptions, for example I got a away with 23psi on my stock head and 23yr old head gasket for several small pulls without issue. It is this new head and head gasket that blew on a more aggressive tune at 23psi within 2 very long pulls.

http://www.r3vlimited.com/board/showpost.php?p=3732621&postcount=1041

Check out kamotors build thread for more info:

http://www.r3vlimited.com/board/showthread.php?t=225271

[sayed ali]

9:1 compression is too high for boost, except if you're going e85 or similar ..

I suggest 1 Bar of boost

[e30 gangsta]

9:1 compression is too high for boost, except if you're going e85 or similar ..

I suggest 1 Bar of boost

Disregard this statement. Tons of people run higher than 9:1 compression and still boost their cars. Look at honda motors for example. Its all in the tuning.

[sayed ali]

Disregard this statement. Tons of people run higher than 9:1 compression and still boost their cars. Look at honda motors for example. Its all in the tuning.

but no way with 93 octane - high boost - 9:1 compression .. thats why I said around 1 bar

[bobross]

Its all in the tune op. Put a pro behind that megasquirt system and the sky is the limit.

Stock motor b25 here with MLS + Metric Blues, over 5 years of boosted life. The motor has seen ~25psi.

[TheTacoMan]

A general rule of thumb is the higher the compression the more difficult and more important tuning will be as well as the quality of fuel you run.

[sayed ali]

A general rule of thumb is the higher the compression the more difficult and more important tuning will be as well as the quality of fuel you run.

That's my point

[Q5Quint]

9:1 compression is too high for boost, except if you're going e85 or similar ..

You realize stock is 8.8:1 right? And you are saying .2 more is 'too much'?

The keyword is: effective compression ratio

Folks run 15psi on a mostly stock motor, which with a stock 8.8:1 static compression ratio gives you an effective ratio of 17.78:1

If you upd your pistons to 10:1 ratio, and ran 11lbs of boost, you would still be at 17.48 effective ratio, slightly less than stock compression +15psi.

Corvettes were running 10.7:1 ratio stock, and I think the new one with direct injection is running 11.5:1 stock from the factory.

If you push your effective ratio too high you will push the head off the engine and blow out your headgasket, hence why studs, welded heads etc are needed after a certain point.

The e46m3 has a 11.5:1 compression ratio. Look up turbo e46 m3s.... 500-600hp at 7psi max with stock engine. I am seeing some +700hp versions but at that point most everyone did have to lower compression.

What is the effective compression of a 11.5:1 3.2liter m3 engine at 7psi?
Boom~ 16.98:1

23 psi and stock 8.8 static moves you up to 22:1 effective.... hence why you need a lot of straps to hold the thing together. The cmopression ratio of my diesel truck is 17:1 stock, plus 20psi.... so the effective is 40:1.... sweet baby jesus.

http://www.gtsparkplugs.com/EffectiveCompressionCalc.html

With todays engine management you can run high static and high effective compression because you can dynamically pull timing with knock sensors, thus saving your engine from exploding. However, lower compression can still make more power but you will start to loose bottom end as well.

A m20 with 10:1 pistons and 10lbs of boost would be fun as hell, but might make less max hp than stock compression and 20psi. One would be better at the autocross, and one better on the drag strip. It seems the magic effective compression number is about 17:1 before you have to get weird with welded stuff.

[sayed ali]

^
Wow, very impressive!

[TheTacoMan]

One other thing, dont run metric blues yes they work but ARP is much much better.

[Northern]

I think we figured out a while back that metric blues had a lower rated tensile strength than oem head bolts. Not sure where the thread is, and it isn't like ARP studs are really expensive or anything.

[Q5Quint]

This would apply to smaller turbo and supercharger cars: you may get a faster 0-60 and quicker acceleration out of higher cr and lower boost. With super eta pistons and 9-1 compression you are still in the lower staticcompression range, and could still run a holset with 19psi and run ~400hp.

Here is a guy on a stock 2.5 bottom end and rebuilt/ported stock top end, running 19psi holset turbo with metric blue headbolts. Dyno at 380hp, here- eventually hit 400hp.

http://forums.bimmerforums.com/forum/showthread.php?1575491-Silly-Holset-M20-Dyno-Results