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General Metal spacer gasget for head gasket (low comp)

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General Metal spacer gasget for head gasket (low comp)

gazzaman2k

gazzaman2k

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going for the cheaper option to make my engine a hi boost turbo so wanting to lower the compression by getting a thick aluminium spacer made up for the head and turn boost up on the turbo using a electronic boost controller.

i saw a while back a website on here that someone posted that make these, but cant find it anywhere now been searching for past hour but no luck

anyone help?

cheers

gaz
 
Have a chat with richcinq. I think he knows an engineering company that will make a (copper?) decompression plate for around 100 quid. Frankly I don't see why more don't do this. Cheaper than getting machined pistons, easier to fit, cheaper to fix if it goes wrong and you get a stronger headgasket :confused: .
 
IIRC correctly (beers swilling aorund :rolleyes:) Dave the trike has had something similar made for his punto, check his supercharging thread in the punto section.
 
CaneyJ said:
Have a chat with richcinq. I think he knows an engineering company that will make a (copper?) decompression plate for around 100 quid. Frankly I don't see why more don't do this. Cheaper than getting machined pistons, easier to fit, cheaper to fix if it goes wrong and you get a stronger headgasket :confused: .
Click to expand...

Copper is the material to go for.

It's regarded as a bodge when used as a substitute for forged pistons (the problem with stock pistons is generally their composition and that the ring lands are too thin -- machining doesn't improve this, so machined stock pistons are also a bodge.) You can't address issues of squish with a decompression plate, either, and can still run into sealing issues with the oil and water passages.

The way to go is (progressively)

forged pistons
head studs instead of bolts
'O' ringed block with stock HG
copper gasket
dry decking

AFAIK, no-one has tried a decompression plate on a high boost turbo (Cinq). I'll await the results with interest.;)
 
If you you put a spacer plate in do you need 2 headgaskets to seal the head to the block?:confused: If so, do you then need to account for the thickness, compressed, of 2 headgaskets and the spacer to work out the CR?
 
gazzaman2k said:
yes i have also wondered this do i need 2 headgaskets? one to go either side of the metal block one?
Click to expand...
Speak to Ferriday (from Tom's post) they are experts at this and will tell you all you need to know about material, thickness, head prep and gaskets.
It may be considered a 'bodge' but IMHO fitting a turbo onto a car that was originally N/A is also a 'bodge' :D so i don't see a problem with either method of reducing CR.
 
balidey said:
Speak to Ferriday (from Tom's post) they are experts at this and will tell you all you need to know about material, thickness, head prep and gaskets.
It may be considered a 'bodge' but IMHO fitting a turbo onto a car that was originally N/A is also a 'bodge' :D so i don't see a problem with either method of reducing CR.
Click to expand...

Ferriday

have a range of gaskets from0.6 to 1.1mm if you tell him your bore and current compression ratio he'll tell you what gasket you need.


In copper or aluminium

We chose aluminium for mine because, oddly, its not quite as good as copper - although expansion rates match the head better than copper . With 10psi running (maybe more) constantly in an unkown situation I'd rather an aluminium gasket let loose than pistons.....



You do not need two head gaskets, the spacer mates to the cylinder head using hylomar or equivalent.

As an aside.
With regards to the mating of the two surfaces without a gasket.
Hylomar sounds bodgy but, it was a common method of raising the compression ratio on fast road/race 2 strokes where the head and the barrel were skimmed flat and mated together with hylomar (no head gasket was used) to raise the compression. Worked well never had any problems with blown headgaskets after that! Lots of melted pistons (too fast, too lean) but, the non existent head gasket was fine!
 
Worked well never had any problems with blown headgaskets after that! Lots of melted pistons (too fast, too lean) but, the non existent head gasket was fine!
Click to expand...

On 2 strokes -- in particular -- it's usually detonation which eats pistons (too much ignition advance). Even Yamaha had an issue with this with the RD350.

The nice thing about copper is that it's a bit tougher and (much) easier to anneal than aluminium. If you're careful,you can re-use the gasket.

IIRC, hylomar was developed in conjunction with Rolls Royce for a similar application (copper head gasket).

Historically, lots of bike engines run with copper head gaskets or no gaskets whatsoever (Ducati, etc), relying on a lapped finish. Hart got round the HG problem by casting the heads and barrels in one peice (expensive!) while Porsche have been known to weld heads to barrels (which sort of dates back to Mercedes' pre-war practice of welding the whole thing together from fabricated peices). The Hillman Imp (IIRC) used a gasket less design initially and then switched to Wills rings.

But then, 10psi is pretty close to low boost territory.....................;)

I don't think the results of a gasket letting go are necessarily going to be less extreme than a piston.
 
fingers99 said:
AFAIK, no-one has tried a decompression plate on a high boost turbo (Cinq). I'll await the results with interest.;)
Click to expand...


I have on mine ;)

Has run 18psi before with no problems... even went up to 26 by accident a few weeks ago and not one problem with that other than cracking the manifold which has nothing to do with that.

Personally I would recommend it over the 400quid for pistons (y) if money is a issue obviously
 
jamie86 said:
I have on mine ;)

Has run 18psi before with no problems... even went up to 26 by accident a few weeks ago and not one problem with that other than cracking the manifold which has nothing to do with that.

Personally I would recommend it over the 400quid for pistons (y) if money is a issue obviously
Click to expand...

That's good! Did you have to fit a vernier pulley (I've an idea that gazzaman has one anyway)? Did you have the block skimmed? Copper or aluminium?
 
what thickness would i need? havent got a clue to what bore stroke and compression ratio is on my engine? nor to what compression is best for it?

its just a 1.1 sporting engine with a turbo bolted on and uprated fueling bits :\

also whats a safe limit to crank the boost upto? at the mo its doing 0.5-0.6

gaz
 
Last edited:
OK standard engine is 9.6:1
VAD hi-boost in general are meant to be 8.6:1, though on taking my engine apart it was found to be about 8.15:1.

As for other turbo cars here's some of there ratios

Uno turbo 90-92 OE ratio 7.7:1 Wossner forged piston ratio 7.7:1
Uno/Punto turbo 93-97 7.8:1 Wossner forged piston ratio 7.8:1
Fiat Coupe 20VT OE ratio 8.5:1 Wossner forged piston ratio 8.0:1
R5GT Turbo OE ratio 7.9:1 Wossner forged piston ratio 7.9:1 though offer competition spec 7.5:1
Lancia integrale 16V OE ratio 8.0:1 Wossner forged piston ratio 8.0:1
Lancia integeale 8V OE ratio 9.0:1 Wossner forged piston ratio 8.0:1
Ford Fiesta/Escort RS Turbo OE ratio 8.3:1 Wossner forged piston ratio 8.3:1 though offer competition spec 7.5:1
Sierra/Escort Cosworth OE ratio 8.0:1 Wossner forged piston ratio 8.0:1
Ford 2L Zetec E turbo conversion OE ratio 10.0:1 Wossner forged piston ratio 8.5:1

all data lifted from http://www.forgedpistons.co.uk
 
also whats a safe limit to crank the boost upto? at the mo its doing 0.5-0.6
Click to expand...

The real answer is, it depends.........

It's not really about boost, but about detonation (after all, there are plenty of NA motors in these here pages that have blown head gaskets).

If you had an ECU which could control fuelling and ignition and which could adjust boost if it detected detonation, you could set the max boost to 3 bar and all you'd have to worry about is the bottom end and the head gasket (and the gearbox ;) ).

With piggy back systems there's no real way of relating ignition to boost or fuelling, so (IMHO) something bad will happen sooner or later. If the fuelling is right, 10psi should be safe enough, but there are no guarantees.
 
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