35 replies to this topic

[minivanman8]

Evening all,

 

I seem to be blowing head gaskets like its going out of fashion - fresh build 1293, sw5 cam, vmax m45 blower, omega 18cc pistons, bk450 head gaskets, new head studs, the list goes on.

 

Its blown 2 head gaskets and spewed coolant out of a fresh third. A compression test prior to removing the head reveals 160-165 psi across the board - I'm told I should have 150 psi tops.....What do you guys run? Should I be concerned with 165psi?

 

Compression ratio is unknown.

 

Block has been skimmed and head skimmed twice in the time I've had it.

 

Any thoughts?

Edited by minivanman8, 17 April 2014 - 08:23 PM.

[Gremlin]

Thats a disaster waiting to happen, forced induction + unkown CR + skimmed twice = dangerous unkown. Do you know what boost pressure your running, and get that compression ratio measured!

[minivanman8]

No idea of boost pressure. I've never had it running long enough to find out! Does anyone have a dummy's guide to working out cr?

I had to have it skimmed twice - once during initial build and again when warped head following blown head gasket!

[cal844]

Thats why you've blew head gaskets

[minivanman8]

What's why? Dodgy tongue wrench, dodgy gasket, not knowing cr, not knowing boost? Any remote direction would help! ;)

[Gremlin]

Because the pressures and temperatures are possibly much higher than the gasket is designed for, there are various online guides for measuring compression ratios, the head will need to be removed if it isn't already

[minivanman8]

Head is off as I've got to change the gasket. I don't see why temps would be higher than any other engine?

Any links to a cr calculator online?

[Turbo Phil]

Are there any signs of detonation ? Have you any pictures of the gasket ? Has it blown in the same place each time ?

There are so many unknowns here. You need to know how much boost you're running, what your ignition timing was under boost, what the fuelling is like & what your compression ratio is.
Without knowing the above there's no way you should even contemplate running an engine under any kind of boost.
To work out your compression ratio you need to know, head chamber cc, head gasket cc, piston dish cc, how far the piston sits down the bore at TDC & engine cc {in your case 1293cc}
You need to measure the above requirements then its easy to work it out. I can do it for you if you let me know the above.

Phil.

[coopdog]

There's also an app on the apple store called mini head

[Mini 360]

There's also an app on the apple store called mini head

Thought that was a joke but I'm now downloading it.....

[coopdog]

 

There's also an app on the apple store called mini head

Thought that was a joke but I'm now downloading it.....

 

hahaha it just makes it easier, you just put the values in and it works it out

[Gremlin]

Yeah but it's rubbish, don't rely on it completely

[coopdog]

Yeah but it's rubbish, don't rely on it completely

Why is it rubbish?

[Gremlin]

I had it ages ago and I seem to remember it wasn't very clear what they were asking you for and it came out wrong

[coopdog]

I had it ages ago and I seem to remember it wasn't very clear what they were asking you for and it came out wrong

I've found it very clear, there's a description on it telling you what it needs for each part