Head Gasket - Compression

[revingtosh]

Hi,

Assuming an A Series of the following spec, what sort of CR should i be looking at aiming to achieve?

I have no idea on the current CR is so i would like to at least know what im aiming for when putting the motor back together!

Also, can i ask for a recommendation on a suitable Headgasket please? I would also need the "compressed height" on the gasket too if possible.

Cheers,

Mike

1380cc A Series
Nitrous
Weber 45 DCOE
Mini Sport Weber Inlet Manifold
12G940 Oselli Big Valve Head
Piper 285 Cam
Double Valve Springs
Aldon Contactless Ignition System
Polished Alloy Rocker Cover
LCB Exhaust Manifold
Twin Box Rally Exhaust System
Kenlowe Electric Fan
Quick Shift Gear Linkage
4 Speed Gearbox
Boot Mounted Electric Fuel Pump
Mocal Oil Cooler

[FWDRacer]

Not dificult to source - Payen AF460 - 2.8cc Compressed.

[Cooperman]

I had been a bit wary of the gasket volumes quoted in various places, so I measured a BK450 head gasket that had been used, i.e. it was the correct thickness. It came out at a compressed volume of 3.9 cc, so that's the figure I now use. Is the 460 a thinner competition gasket of another variant of the 'black' composite gasket like the 450?

[FWDRacer]

The 460 is a Copper/Steel item, hence the recommendation for the use on the OP's 1380 unit. Bit more robust with the thin cylinder wall thicknesses (2-3).

[Cooperman]

Thanks, Gareth. That accounts for the lower capacity than the BK450, which is what I normally use on a standard bore, up to +0.060", 1275 lumps.

[Phil Hill]

Guys, the OP asked what compression he should aim for ??

For the spec advised I'd be thinking somewhere in the 10.5 to 11 region would be about right.

Phil.

[FWDRacer]

Oooppps, your right Phil - thread deviation . CR is dependent on fuel. If he is happy to run on 98 octane all the time (£) - then 11 to 1 isn't an issue with the Aldon set-up. 95 octane would limit CR to 10:4 - 10:5 to 1.

It'll be important to get the advance curve sorted by rollering with an A-series specialist.

[revingtosh]

Yes, the cylinder head im running dictates that i need lead additives so i might as well run an Octane Booster at the same time.

The car will only be a weekend warrior so annual mileage would be relatively low anyhow.

Does the the use of Nitrous not affect the CR you wish to use? What pistons would you guys recommend for an engine of this spec?

Mike

[Cooperman]

If you can find a set, the Karl Schmitt pistons are fantastic. Fantastically expensive as well! If not, try an Omega 1015 with a 10 cc dish. You'll probably need to deck the block a bit if you go to the Omega as I think they sit a bit lower down the bore.

[rambax777]

bga gaskets are twice as thick as a copper one on a small bore engine,,makes a 850 really slow,
good if u want to drop your compression ratio a bit tho,not good on a a series 850--ha ha