Lower Compression H/G

[Mador 0]

Im having to post here as I cant find anything in the search,

Does anyone have a chart or a formula to work out compression vs head gasket thickness?

for example: on an M50, 1mm H/G = 10.5:1 and a 3mm H/G = 9.0:1

am going to laser one out at work but want to know which thickness material I will need to get desired C/R

also anyone recommend what material I should use? I was thinking copper but a guy at work made one for his friend out of steel

Cheers

Ben

[*Glenn* 854]

This might help you

http://www.johnmaherracing.co.uk/enginecalc.htm

[thorburn 120]

I'll do the maths for you if you cut me out one as well

What pistons crank and rods are you using?

I've got an m50b25 vanos head I can cc for you.

I'd recommend going for an iron block. Mostly only found in m50 form

You could just copy the mls gaskets that come out of the states from cometic

.120" seems to be the usual thickness. I'd of thought a copper gasket of that thickness wouldn't take the beating

Edited January 25, 2012 by bbs

[Mador 0]

Thanks will stay away from the Ali blocks then

Was hoping to get away with just the head gasket to lower compression and use B28 Crank and Pistons but havent looked into that yet as still acquiring an engine

and thanks for that page Glenn seems to do the trick! It suggests 3.25mm for a CR of 9:1

[thorburn 120]

Sounds about right

Can you say more about the headgasket making process?

These engines seem hard enough to seal with the 'proper' cometic head gaskets

[Mador 0]

glad you didnt have any problems with the B28 gear was cringing when I saw a post thinking I was going to be told it wouldnt work,

Gasket making process, I plan on buying a sheet of copper and using the laser to cut it to specs of oem gasket but at the thickness I choose of course, anneal it professionally in an oven, head and block machined flat and when it comes to install ive got a can or 2 of that spray on copper gasket stuff by CRC (shouldnt even need that though)

Heres a read if your interested in it

http://www.headgasket.com/faq.html

Also found this paragragh on a Nascar site

"Copper gaskets are popular with top fuel drag racers because the gaskets are available in a wide range of thicknesses, which can be changed to alter the compression ratio and "tune" the engine to changing track conditions. Different thicknesses can also be used to accommodate different piston and deck clearances. As a rule, every .010" change in the thickness of the head gasket will change the combustion chamber volume about 2.5 cc."

let me know if your interested in one as id have to buy a sheet anyway unless I can find an offcut big enough somewhere (but thats another hunt I havent started yet)

[Ben 0]

Im keen on a .120" gasket as well M50B25 non vanos

[No name user 379]

I know not everyone do things the same way but big thick head gaskets is a very bad way to drop comp, it increases the flame pattern across the piston causing the top ring to bite and can increase detonation as there is very little control over flame travel across the piston also your increasing the squish band hurts power, my m50 i had custom pistons made and retain the fire ring/squish but increased the bowl area to reduce comp, before you get too carried away 10-1 with the correct tune can run 20psi on pump gas can make you 500hp when you drop comp too much you'll lose boost response and thermal bang for you dollar.

Another way to reduce effect comp is bigger cams or on stock increasing overlap, the guys i deal with in the land big hp BMW's are running over 500hp easily on a stock m50 with only 1bar, as Ive always said just cause its a BMW you don't need to do anything different than any other engine brand all common engine building principals apply.

if your going to make a copper head gasket you have to use the correct material type and it has to be soft as butter and 100% annealed they also tend to leak around the water ways also o ring the block using 1mm stainless wire sticking up no higher than 7-9 thou or it ll push the head, also use cap screws if you cant afford studs.

[thorburn 120]

If you increase the dynamic compression ratio on a turbocharged car are you wasting more air(and fuel)?

I suppose you could say the same about that for dropping compression when you aren't on boost.

I'll have to do some maths to find out what sort of overlap difference is needed to drop the dynamic compression to what it is with a lower compression m50

Cheers for the brain bump

[No name user 379]

If you increase the dynamic compression ratio on a turbocharged car are you wasting more air(and fuel)?

I suppose you could say the same about that for dropping compression when you aren't on boost.

I'll have to do some maths to find out what sort of overlap difference is needed to drop the dynamic compression to what it is with a lower compression m50

Cheers for the brain bump

By increasing the dynamic/effective comp ratio you don't waste more air a turbo engine of any sorts is load dependent thus no load no boost that's how trucks work and they don't run boost control the turbo is sized to suit but when carrying a load or under load up hill boost comes on so no you don't waste air or fuel plus anything off boost its tuned to suit and becomes n/a as such.

and again dropping comp is giving protection against det if there's an issue but you do lose thermal bang for money off boost,again not wasting.

You'll never find a math calc to know how much overlap is effective that's not how you pick a cam but the bigger the cam the greater the effect, again you dial a cam based on center line as per spec but that's a starting point as long as you have safety clearance of .100" exh and .080" intake piston to valve on overlap you can more the center line to find the sweet spot but that must be checked when putting it together.

Example: with stock cams around 218@50 you may get 180-200 psi with compression test using say 225@50 youll drop down to around 140-160psi but changing centre line you gain or lose accordingly again calculator wont tell that number.

theres free hp in any cam timing including stock,

At the end of the day the motor will decide what you get not the calculator......

[Mador 0]

So you think I should scrap the idea all together?

Work wont let me use the laser to cut the copper, dont want to risk sending a 3 - 5k watt beam back into the machine due to the reflective properties of the copper

Would have to get it turret punched or choose a different material, but I dont want to risk spending alot of coin on a 3mm copper sheet just to find the punch rounds the edges of the cut and leaves nasty burs and tits

Just to understand your idea of using a Cam to lower compression, use a longer duration cam to allow the piston to follow the closing valve to release pressure out the exhaust? Or decrease the time the intake valve is open to allow less gasses in to compress?

Off topic, I have an E34 with M20b25 that has been through 2 heads, have now parked it up and am tracking down an M50 to turbo, have a garret T3/T4 and megasquirt sittin around and ability to fabricate almost anything at work and do the machining of the engine, you say you can get 20psi/500hp out of a complete stock unit as long as detonation is controlled through a tune? id be more than happy with less than 500hp

What would you suggest Crunchy since you have just completed or near completion of your build?

How much HP is your goal for what you have done to yours?

[Ben 0]

If you get an M50NV you can adjust the factory cam gears for overlap

but only a limited amount (about 4 deg either way I think)

[Mador 0]

Originally was wanting to get a vanos engine, lower Comp with HG, Boost the hell out of it and control the Vanos through the megasquirt for "Cool" factor

Is Vanos controlled electronically, or some sort of mechanical regulator that opens to allow the high pressure oil feed to engage the Vanos?

edit: Great name by the way Ben

Edited January 26, 2012 by Mador 525i

[No name user 379]

Off topic, I have an E34 with M20b25 that has been through 2 heads, have now parked it up and am tracking down an M50 to turbo, have a garret T3/T4 and megasquirt sittin around and ability to fabricate almost anything at work and do the machining of the engine, you say you can get 20psi/500hp out of a complete stock unit as long as detonation is controlled through a tune? id be more than happy with less than 500hp

What would you suggest Crunchy since you have just completed or near completion of your build?

How much HP is your goal for what you have done to yours?

i cant tell you how yours will come out unless im tuning it im sure nzefi or whoever down your way will fit the bill, you cant compare with my build with components im using over a thicker head gasket im after a tad more than 500

[CamB 48]

Surely a T3/T4, at least most of the ones you see, is too small (exhaust and compressor) for that sort of power, especially at 20psi and without detonation.

500hp at 20psi would need a freeflowing exhaust, big turbo (both sides of it) and good tuning.

[polley 916]

Surely a T3/T4, at least most of the ones you see, is too small (exhaust and compressor) for that sort of power, especially at 20psi and without detonation.

500hp at 20psi would need a freeflowing exhaust, big turbo (both sides of it) and good tuning.

500hp at the wheels or crank? I think 500 crank hp is realistic on 20psi.

[No name user 379]

t3/4 is like saying you own a Toyota Honda BMW etc but not saying what model, there's over 2500 combos you can have with them rated from 80hp to 650hp so can be done but not with Chinese knock off versions.

500 at the flywheel would be correct cant say i would push it any further on stock internals and 400 is safe still cheap engine you can just chuck another in if its not happy or build a strong one from the start.

[CamB 48]

t3/4 is like saying you own a Toyota Honda BMW etc but not saying what model, there's over 2500 combos you can have with them rated from 80hp to 650hp so can be done but not with Chinese knock off versions.

Yeah that's what I meant - its possible he has a big (and $$$) T3/T4 but more likely those middle sized chinese ones.

[No name user 379]

Yeah that's what I meant - its possible he has a big (and $$$) T3/T4 but more likely those middle sized chinese ones.

pretty much everyone of those Chinese crap turbos ive seen and what advertised are the same spec,you would think if anything is worth coping you would at-least be more creative or improve on the original.

[Mador 0]

The T3/T4 I have lying around ran 21psi in a 3sgte, should be able to get something of the same from 2 extra cylinders, see how it goes if it shits itself ill get a bigger one, just using what I have lying around

T88-34D is big on both sides

[No name user 379]

The T3/T4 I have lying around ran 21psi in a 3sgte, should be able to get something of the same from 2 extra cylinders, see how it goes if it shits itself ill get a bigger one, just using what I have lying around

T88-34D is big on both sides

ah yes the trusty t88 go on put it on you know you want to

[Mador 0]

ah yes the trusty t88 go on put it on you know you want to

Yeah right I wish! doesnt look like theres much room between the exhaust and that stupid RHD steering

[Guest Ari Gold]

Yeah right I wish! doesnt look like theres much room between the exhaust and that stupid RHD steering

Spool it off the driveshaft don't be soft.

[Mador 0]

Spool it off the driveshaft don't be soft.

Lol huuuh?!