Compression Ratio Help!

[tdstuart]

Check again. I cropped the first one

On the summit calculator, you use a negative number for the dome. On the calculator you used, you use a positive number.

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[K4fxd]

So what’s your recommendation?

Same as before, use what Ford uses. 10 or 10.5 if going FI for best longevity.

 

[K4fxd]

On the summit calculator, you use a negative number for the dome.

I tried it both ways, that is why I posted 2 screen shots.

The Big Boyz calculator is pretty accurate it even shows dynamic compression if you know the cam specs.

 

[tdstuart]

Yea, I'm not trusting this calculator. 1.24 to 1

You put 15 inch not 0.015 inch

 

[tdstuart]

Same as before, use what Ford uses. 10 or 10.5 if going FI for best longevity.

What about for N/A? I can always pull the motor if I want to do FI or just throw in a thicker head gasket to lower compression.

 

[tdstuart]

 

[K4fxd]

You put 15 inch not 0.015 inch

LOL another senior moment.

Again follow what Ford Dodge GM ect. Port fuel injection 11 to 1. DI raise to 12.

This is for a daily that will see some WOT blasts.

If you are building a race engine go 14 and E85 or 110 octane race gas.

Pulling it down for thicker gaskets is a PIA. 10.5 to 1 is a good happy middle ground.

 

[K4fxd]

Yes saw that but didn't link it because you figured it out on my summit mistake.

 

[K4fxd]

We have 93 and I can only get 24 degrees of advance before knock sets in. Probably only get 20 on 91. MBT table says 29 is best torque.

This is an 11 to 1 gen 2 with 1 heat range colder plugs.

 

[tdstuart]

We have 93 and I can only get 24 degrees of advance before knock sets in. Probably only get 20 on 91. MBT table says 29 is best torque.

This is an 11 to 1 gen 2 with 1 heat range colder plugs.

Like I said I plan to run e85 most of the time just need 91 support for casual long drives if I ever travel.

Do you recommend 1 heat range colder plugs?

 

[K4fxd]

Do you recommend 1 heat range colder plugs?

For my car I do. If you are mostly using E85 I would not. I run mine pretty hard on gas and do what I can to prevent pre ignition and detonation.

If you really are going to use E85 then 12 to 1 is fine. But when you do use 91 baby it.

 

[K4fxd]

I've got true E85 close to me, pump is labled E85 and tests at 85%. I ran it for a couple of months and switched back because I was at the pump every other day. It works well in my P/U which has a 36 gallon tank.

 

[GregO]

@tdstuart
Any more 170+ mph runs planed for the replacement motor ?
Was that last 176 mph pull on gasoline or E85 ?

Any other engine assembler fretting over a couple 1/10’s of CR would cc the motor. You might have more fun cc’ing it than playing CR calculator shuffle board with more than a few obscure values.

 

[tdstuart]

@tdstuart
Any more long 170+ mph runs planed for the replacement motor ?
Was that last 176 mph pull on gasoline or E85 ?

Any other engine assembler fretting over a couple 1/10’s of CR would cc the motor. You might have more fun cc’ing it than playing CR calculator shuffle board with a few obscure values.

Maybe a 180+, but I think I will wait till I am able to upgrade the cooling. I got the motor too hot last time, and don’t want to do that again.

The 176 was on e85 if I remember correctly. And ya I would like to cc the motor but I don’t have the heads :(

 

[tdstuart]

I've got true E85 close to me, pump is labled E85 and tests at 85%. I ran it for a couple of months and switched back because I was at the pump every other day. It works well in my P/U which has a 36 gallon tank.

Ya I ran e85 straight for a couple months or e54 mix. I used a full tank in one day of driving around town. My MPG is seriously impressive.

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