What thickness of head gasket?

What thickness of head gasket?

Author
Discussion

jetx

Original Poster:

5 posts

140 months

Friday 22nd April 2016
quotequote all
I wonder if anyone can help me calculate what thicknes of head gasket I require for max compression?
The engine is a BMW 6cyl 3.0 twin turbo diesel M57 with a 8mm long throw crank short rods the pistons protrude @ 2.5mm from the block. Head is flat, decked 6 thousanths?
how do I calculate the thickness of head gasket required? with maximum compression ratio possible.
Thank you.

stevieturbo

17,229 posts

246 months

Friday 22nd April 2016
quotequote all
That will be entirely dictated by piston to head contact by the sounds of things ?

Not sure on diesels, but generally 1mm is taken as a safe clearance from top of piston to cylinder head...so if your pistons are already 2.5mm proud, then that would suggest 3.5mm as safe.

Or is there some sort of round recess in the head that allows the piston to protrude so far ?

CrutyRammers

13,735 posts

197 months

Friday 22nd April 2016
quotequote all
It also depends on what "max compression ratio possible" means, since it depends on the octane of the fuel you are intending to use, and what sort of boost the turbos will be running, and whether you have intercooling and how good it is. You'd need to determine the size of the combustion chambers then, and work back from there, taking all the rest into account.

A book like Corky Bell's "Supercharged" will have all the info in it.

Or just add 6mm to the thickness of a standard one, since that's what's been removed?

227bhp

10,203 posts

127 months

Friday 22nd April 2016
quotequote all
CrustyRammers said:
It also depends on what "max compression ratio possible" means, since it depends on the octane of the fuel you are intending to use, and what sort of boost the turbos will be running, and whether you have intercooling and how good it is. You'd need to determine the size of the combustion chambers then, and work back from there, taking all the rest into account.

A book like Corky Bell's "Supercharged" will have all the info in it.

Or just add 6mm to the thickness of a standard one, since that's what's been removed?
If you read his post properly it contains the words 'Diesel' and 'Turbos'.

Boosted LS1

21,167 posts

259 months

Friday 22nd April 2016
quotequote all
I agree with Stevie but where can you find a gasket that thick? Mls would be good, maybe Cometic can offer something. If not, could you skim the pistons as it seems there's an awful lot of piston above the deck in the first place? I imagin the top ring land is substantial and strong. Skimming would save weight to.

stevieturbo

17,229 posts

246 months

Friday 22nd April 2016
quotequote all
If I'm reading right...or misreading.

The post almost implies he's added a longer stroke crank ? Which clearly you cannot just do alone, it will need pistons with a lower compression height, or shorter rods.

Boosted LS1

21,167 posts

259 months

Friday 22nd April 2016
quotequote all
^ I think he's done a stroker conversion with parts from a similar engine family. It could be that his pistons have huge bowls in them in which case things may work but not with his pistons embedded in the head wink

helix402

7,832 posts

181 months

Friday 22nd April 2016
quotequote all
CrutyRammers said:
It also depends on what "max compression ratio possible" means, since it depends on the octane of the fuel you are intending to use, and what sort of boost the turbos will be running, and whether you have intercooling and how good it is. You'd need to determine the size of the combustion chambers then, and work back from there, taking all the rest into account.

A book like Corky Bell's "Supercharged" will have all the info in it.

Or just add 6mm to the thickness of a standard one, since that's what's been removed?
It's a diesel, cetane not octane. Have a look on TIS re the gasket, there is a choice of thickness (indicated by the no of holes at the edge) depending on the piston protusion.

Mr2Mike

20,143 posts

254 months

Friday 22nd April 2016
quotequote all
helix402 said:
Have a look on TIS re the gasket, there is a choice of thickness (indicated by the no of holes at the edge) depending on the piston protusion.
The OEM gasket for the M57 engine ranges from 1.47mm to 1.77mm, about half what the OP is going to need. Typical head clearance is about 0.6mm minimum.

jetx

Original Poster:

5 posts

140 months

Friday 22nd April 2016
quotequote all




Thank you for all your input
Here are the pics of the head and block the pistons protrude 0.95mm not 2.5 as first stated sorry typo, yes it is Diesel with 2 hybrid turbo's the crank is a one off 8mm long throw with shorter rods this is why we are looking on how to calculate the gasket thickness, it also runs a 300 jet dry nitrous just short of 700bhp, this engine is fitted in a 120d baby bmw that currently runs a 11.62 1/4 mile we are trying to get it in the 10's.
Mr2Mike your right just after you posted this BMW told us the gasket sizes they supply, we are going to try the 2 notch gasket I believe is a 1.67mm fingers crossed.

Edited by jetx on Friday 22 April 20:38

jetx

Original Poster:

5 posts

140 months

Friday 22nd April 2016
quotequote all
I also forund this calculator which says a 2 notch will be fine.

http://www.summitracing.com/expertadviceandnews/ca...

stevieturbo

17,229 posts

246 months

Friday 22nd April 2016
quotequote all
With 0.95mm protrusion and a 1.67mm gasket...I'd be expecting the pistons to hit the head when it's running.

stevesingo

4,848 posts

221 months

Friday 22nd April 2016
quotequote all
I run 0.80mm clearance on my engine which revs to 8k rpm. Endoscope inspection shows no touching.

Mr2Mike

20,143 posts

254 months

Saturday 23rd April 2016
quotequote all
stevieturbo said:
With 0.95mm protrusion and a 1.67mm gasket...I'd be expecting the pistons to hit the head when it's running.
0.6-0.7mm clearance is about the minimum. Don't forget this is is a diesel so no silly RPMs and huge rods and bearings to minimise "stretch".

stevieturbo

17,229 posts

246 months

Saturday 23rd April 2016
quotequote all
Mr2Mike said:
0.6-0.7mm clearance is about the minimum. Don't forget this is is a diesel so no silly RPMs and huge rods and bearings to minimise "stretch".
yes, but it still has pistons that may rock at TDC etc, depends how tight bore clearances are and piston skirts etc.

Not really sure stretch itself is a huge factor even with high revving engines ?

And an iron block will expand less than an alloy block, so that tolerance will remain tight.

It's a ballix to have to take it all apart again if they do hit, although it might sound normal on a diesel lol

Mr2Mike

20,143 posts

254 months

Saturday 23rd April 2016
quotequote all
I mean 0.6mm is about what the BMW specification is.

One hole gasket: 1.47mm, Piston protrusion <= 0.92mm
Two hole gasket: 1.57mm, Piston protrusion 0.92mm to 1.03mm
One hole gasket: 1.67mm, Piston protrusion > 1.03mm

Boosted LS1

21,167 posts

259 months

Saturday 23rd April 2016
quotequote all
It's also about expansion of the rods as well as stretch. Stretch would be minimal. Cranks flex, pistons rock and blocks get taller. I think expansion and rock are the main issues.

chuntington101

5,733 posts

235 months

Saturday 23rd April 2016
quotequote all
Regardless of the gasket issue can we please get a build thread as a 700bhp diesel sounds pretty cool! smile

jetx

Original Poster:

5 posts

140 months

Saturday 23rd April 2016
quotequote all
chuntington101 said:
Regardless of the gasket issue can we please get a build thread as a 700bhp diesel sounds pretty cool! smile
Thank you all for your comments, If you would like to see the build follow us on Instagram BMW135D lets see if we can get this Diesel in the 10's.

This is the 11.62 run on street tyres https://www.youtube.com/watch?v=nhTfkcSAr2g&fe...

stevieturbo

17,229 posts

246 months

Saturday 23rd April 2016
quotequote all
jetx said:
Thank you all for your comments, If you would like to see the build follow us on Instagram BMW135D lets see if we can get this Diesel in the 10's.

This is the 11.62 run on street tyres https://www.youtube.com/watch?v=nhTfkcSAr2g&fe...
What sort of 60fts are you getting now ? 700hp should easily get you into the 10's unless traction is very bad