What Compression Ratio.....

[mclark]

are you UK guys running on your AS engines?

Really interested in the 5-550bhp engines and do you all run Shell Optimax to help?

Michael

[steve_D]

I built my own engine and it is to my own spec.
Compression ratio.... 10.32 Static. 7.9 Dynamic.

I run whichever fuel comes to hand at the pumps.

Steve

[G Man]

Shell Optimax where possible on a 10.5 :1

G MAN

[eclipsar]

My 427 has 550hp and a 9.6 comp, always runs on Optimax.

Regards
Chris

[mclark]

The reason I asked is that I have heard loads of people discussing (disputing) how high a compression you can run in the UK on Optimax.

The engine builder I intend to use runs a compression ratio of 10.8:1 (550bhp) and I felt this was quite high for UK petrol.

Michael

[G Man]

Mark

What is the spec, this seems right on the edge for a road going engine ..

Not that I know much about NA SBC ..

G MAN

[mclark]

Hi G-Man,

The spec is:

Chevy 70's era block high nickel thick wall .4 bolt mains full CNC machine
Crank Eagle 4130 forged 3.750 stroke internal balanced
Full CNC Eagle 5140 forged rods 6.00 long ARP cap screws,floating pins
Pistons JE forged 11.1 comp JE plasma moly file fit rings custom fit to piston & bore.
CL-77 -H series race brg Cam Isky Mega hyd.
Fast action .545 lift , 290 dur 108 C/L liftrers
Chain E/W full comp roller .250 pins 4130 forged gears.
Oil pump Melling HV 55 with ARP drive pan Kevko 6qt custom race pan
Heads are Canfields alum 200cc custom CNC
Rockers are E/W USA full comp forged rollers
Intake Power + polished air gap with Holley 750CFM carb fully recalibrated
Ignition is MSD 6-AL system , with Mega Fire 8.5mm wires into Bosh platinum rapid fire plugs.

If that helps....... it's all dutch to me.

Michael

[steve_D]

Most people here are talking about the static compression ratio which is not actually very pertinent.
The figure to consider is the Dynamic compression ratio.
This figure takes into account the valve timing. When the engine starts on its compression stroke the inlet valve has not yet closed and is taking advantage of the charge gases still rushing into the cylinder. Therefore compression does not start until the inlet valve is closed. Go here to have the whole thing better explained than I can. It also has a calculator so you can work out your own Dynamic ratio provided you know your valve timing data.

They talk of 7.5 – 8.5:1 DCR for pump gas which is why mine at 7.9 is happy with anything.

Steve