Hemi Compression Ratio You've Used

[Nxcoupe]

9.5-1 but not on the road yet........ @ 5800 hydraulic lifters.... dynoed

A fun car with worrying about doing any higher end issues.

still yielded 580 and 555. plenty for me

A good mid-range... cam.

36 degrees total
View attachment 1393223

Any idea on the cam specs?

 

[Bold & Old]

Sorry .......A miscalculation on my part the compression is 10.25 @175 PSI and not 9.5

if this helps... my paper work is not in my file

 

[diesel_lv]

The couple cam grinders I've talked to have said that they like to see 195-200psi cranking pressure on 93 octane w aluminum heads and 175-180psi on 91 octane. Didn't ask about iron heads as I don't have them. Here is a calculator that you can plug in numbers to get the cranking pressure you need to keep detonation down. I was way up at 196psi on 91 octane. Ordered new cam and will hopefully be better when it's back together.
Cranking Pressure Calculator

 

[Nxcoupe]

Sorry .......A miscalculation on my part the compression is 10.25 @175 PSI and not 9.5

if this helps... my paper work is not in my file

View attachment 1393404

My butt calculator says that's prob in the upper 230, lower 240 @.050" lift duration. I'm leaning towards 11 to 1 on mine, jetting it a bit rich or just backing timing out.

 

[Bold & Old]

The couple cam grinders I've talked to have said that they like to see 195-200psi cranking pressure on 93 octane w aluminum heads and 175-180psi on 91 octane. Didn't ask about iron heads as I don't have them. Here is a calculator that you can plug in numbers to get the cranking pressure you need to keep detonation down. I was way up at 196psi on 91 octane. Ordered new cam and will hopefully be better when it's back together.
Cranking Pressure Calculator

93 octane cast iron heads
39 degrees BTDC @3000 RPMS

My butt calculator says that's prob in the upper 230, lower 240 @.050" lift duration. I'm leaning towards 11 to 1 on mine, jetting it a bit rich or just backing timing out.

I had my carbs completely redone, tested and dialed in on a hemi mule by Scott Smith.


Just dropped them on my motor an some minor adjustments then dynoed it.

 

[Bold & Old]

Sorry .......A miscalculation on my part the compression is 10.25 @175 PSI and not 9.5

if this helps... my paper work is not in my file

View attachment 1393404

removed the dyno due to personal info on the dyno.

 

[INTMD8]

The couple cam grinders I've talked to have said that they like to see 195-200psi cranking pressure on 93 octane w aluminum heads and 175-180psi on 91 octane.

Some kind of guideline is good but I think can vary greatly depending on many other factors.

Vehicle weight, gearing, driving style, converter, altitude/etc. Everything needs to be considered.


RPM range as well.

For example you could build a big cube engine that cranks 200 that makes peak hp at 6k or a smaller one that cranks 200 and makes peak hp at 7k+ and requires shorter gearing.


I think every combo should start with a goal. Whether it be HP or ET/MPH. Decide what fuel, then build it to match.

 

[hashmaker]

With an Aluminum block and heads mine is 11-1, solid roller 6.13/6.40 cam. Runs great on pump premium. I don't race it, just cruise around.

 

[Nxcoupe]

With an Aluminum block and heads mine is 11-1, solid roller 6.13/6.40 cam. Runs great on pump premium. I don't race it, just cruise around.

Any idea on duration of your cam?

 

[hashmaker]

I would have to dig up the cam card but as I remember it was in the 290ish area. It idles around 950.

 

[6PKRTSE]

Mine is a custom nitrous grind 55MM roller bearing with a 4/7 swap over .800 lift. Idles at 1200 and street driven on 93 pump gas.