The V8 Owners Forum -

Been looking at the engine today, and what to do with it, and as the pistons are at 0 to the deck height, I was going to use tins, whats the opinion on coating the tins with some soert of sealent, Ive heard of Allumnium Paint, also blue and red hylomar
I am thinking skimming the heads as well, but I need to calc the comp ratio, before I start, can I find a calculator, can I heck, so can some nice person have a quick calli, for me,
Bore; 93.5 x stroke at 71.7
pistons, Flat top, and level with the deck, small eyebrows cut, of unknown capacity,
Heads are 4.6 UBVs with 36cc chambers, and I was looking to reduce the chamber size to around 30cc using tins again,
please can some nice person get their calculator out for me,
Ian

Yes but my spreadsheet is at work - you'll have to wait till tomrrow unless someone else answers first.

UBV's ? ? ?

Russ

Ultra big valve

for jointing compound lookup Wellseal.

brilliant stuff mate, get the one in the tin with the brush applicator.

Too many variable such as pistons dish and inlet closing but I'd guess at around 11:1

I ran my 3.8 with supercharger at 13:1 on tins coated with Blue Hylomar. No sign of leaks when I removed the heads after 20K

I must admit my heads before were given a smear of Blue Hylomar, I could just detect a slight compression blowby more like a silght brown/grey feathering going away from one of the bores, not looking like it was a serious problem, ---------------------YET

I calculated my comp was around 11-1 some time ago, but when I compared my heads against some early heads, I could not remember what heads I had used for the calcs

Ian,

Total Capacity 3936cc.

Cylinder swept Volume (SV) 492cc
Deck 0cc
Gasket 3cc.
Head 36cc.
Cutout 2cc.
total 41cc.
SV. 492cc
Total. 533cc divide by 41cc = 13/1

Composites would reduce compression, to 12.18/1

I checked my figures three times but it's the flat tops and zero deck that are doing it.


Kevin.

Don't forget that you make no compression until the inlet valve is closed.

So if you run a wild cam you can have a static comp of 13:1 but a dynamic comp of 9.5:1

and dont forget I do run a cam with a lot of O/lap, so I probably run a compression of 8-1, I may add 1.7 rockers as well to compound the loss of compression, I have seen some flame reversion on the bodies at steady speeds.

when I built the engine with oiled bores, I was getting 225-230PSI

Rossco wrote:Don't forget that you make no compression until the inlet valve is closed.

So if you run a wild cam you can have a static comp of 13:1 but a dynamic comp of 9.5:1

I thought that the static would be the lower figure - and the dynamic getting higher as the effect of ram charging due to gas mass and velocity filling chamber when piston rising and inlet still open.

Hence with wild cam you raise the compression ratio.

Andrew

Darkspeed wrote:

Rossco wrote:Don't forget that you make no compression until the inlet valve is closed.

So if you run a wild cam you can have a static comp of 13:1 but a dynamic comp of 9.5:1

I thought that the static would be the lower figure - and the dynamic getting higher as the effect of ram charging due to gas mass and velocity filling chamber when piston rising and inlet still open.

Hence with wild cam you raise the compression ratio.

Andrew

Andrew, Hi

No, all that has little effect on the compression ratio.

Mainly it serves to scavenge the cylinder and ensuring a good fresh charge in the cylinder.

Until the inlet valve is closed the engine makes no compression at all as despite what you say all that the piston does is push the charge back out of the inlet valve.

I may be being a thicko here but isn't a 20 thou squish clearance a bit too tight? I used to work on race tuned bike engines and we ran 40 thou. (They did rev to 12.5k but then again the pistons were a lot smaller and lighter).

Sidecar, Hi

Rover heads are not 'squish' heads.

The chambers are open unlike Chevy.