The V8 Owners Forum -

Hello. I'm rebuilding RV8 4.6 Top hat linered block, deck skimmed->stock pistons 0.2mm above deck at TDC. 4.6 heads with stage 3 valves and some porting. Hedman hedders and single exhaust. MS2 v2.2 for 98 octane petrol delivery with wasted spark ignition. Looking for bottom and mid range torque.

Any experience here which cam to use from realsteel? Any cam specs to calculate dynamic CR? Am i trying to built engine with too high CR. I send query to realsteel about week ago but no reply so far.

Crower 50232 (or something similar) is one option but it is recomended to light vehicles and RRC is not i think.

Personally I never like to push my luck when it comes to CR, I would not take a RV8 over 10:1, I think that 10.25:1 is pushing your luck! 10.9:1!!...Tell me where you are getting your pistons from, I think that I'll buy shares in that company!

Of course the dynamic CR is what really matters and things like the camshfat are going to effect that.

No reason to buy shares. If detonation is a problem i can use RE85 (85%ethanol15%petrol) but i prefer 98 octane

Hi
you are asking a very complex question here, however there are ways of making this work, in fact some cams will require a high CR it is a tricky one.
10.9:1 isn't that high on some cams, however on a 4.6 rover you are going to create an engine with a relatively narrow power band if you are not careful. basically 10.9Cr will work with a cam with more that about 235 degrees of inlet timing at .05 inches of lift, however that is a very approximate statement and if you have too aggressive a ramp on the inlet lobe you may still have problems. If you go 235+ degrees of lift with only about .5" lift maximum on the inlet, you are aiming to have a volumetric efficiency of about 90 to 95% at peak torque but have it roll off very slowly to give you the top end power and keep the power band as wide as you can, very "old school" tuning.
Really this is going about the thing back to front, decide what power band you want (where is peak torque to be where peak power), look at the cam/heads combination that will deliver that and then match the CR to the cam, really where the inlet valve closes.
There is a very rough calculation to compare "dynamic CR" for a given cam, take a combination of cam/CR that you know does not detonate and take the mechanical CR, divide it by 1+ cos(angle after BDC the inlet valve reaches .05")/2 and that should give you a number to compare the new cam to (it is the mechanical CR after which the air effectively stops moving back out the inlet valve. Now do the same calculation for your new cam and CR combination and if they look similar or the new number is smaller then there is a good chance the new combination will not detonate, however this all assumes you have everything else the same!
Best regards
Mike

Difficult question...yes it is. I'm looking any experience / knowledge about this. Trying to avoid mechanical/hydraulic race cams. Maybe i play safe and use "stump puller" cam and RE85.