Octane rating vs CR

[frnkeore]

What is the highest, dynamic CR for 87 octane gas?

[travis]

Way too many variables to even make a half assed guess IMO.

Many modern engines run 12:1 or a little higher on 87 just fine.

[mopardave]

Don't know about dynamic, but my 511 has 12.5:1 static and runs safely with 100 octane. 36* total timing. 270@50 solid FT.

[David Redszus]

What is the highest, dynamic CR for 87 octane gas?

Which pump gas?

No two are the same.

[mt-engines]

What intake air temp? What elevation?

[frnkeore]

The criteria here is 2V wedge and heart shaped chambers, both aluminum and cast iron. Old school, if you will, not direct injection.

A safe guild line, in a loaded engine, with a .040 - .060 squish.

80 deg 800 ft elev.

[1980RS]

Don't know about dynamic, but my 511 has 12.5:1 static and runs safely with 100 octane. 36* total timing. 270@50 solid FT.

That 270°cam with the right timing events makes that happen, you sure would not want to do that with 12:1 and a 230°@ .050 engine would rattle itself to death.

[skinny z]

Well, if you believe what's printed in the car magazines of old, about 20 years ago Super Chevy put together a Vortec headed 355.
8.75:1 SCR and used Comp's XE268H cam (I believe on a 108 ICL).
Quench at .044".
87 octane fuel (from who's pump I can't say other than being California based) and netted peak TQ of 427 at 4000 and peak HP of 390 at 6000 on the magazine dyno.
DCR works out to 7.2:1.
Make of it what you will.

[frnkeore]

What is the highest, dynamic CR for 87 octane gas?

Which pump gas?

No two are the same.

I live in Oregon and we have both 87 & 92 oct, with ethenal in the winter months. But, to any that may post, assume it's your local pump, that you pull up to, when you need gas.

[NewbVetteGuy]

I remember the old version of PipeMax spitting out an actual fuel octane rating recommendation...

I don't have the newest version so can't comment on it.
DCR, squish / quench, IAT, chamber design, lots and lots of variables.

Many smart folks on here don't even want to make a call with DCR #'s... should possibly give you pause on accepting a simple answer to a complicated question.

David doesn't even want to make a call with RON/MON ratings of pump gas included.


Adam

[NewbVetteGuy]

Well, if you believe what's printed in the car magazines of old, about 20 years ago Super Chevy put together a Vortec headed 355.
8.75:1 SCR and used Comp's XE268H cam (I believe on a 108 ICL).
Quench at .044".
87 octane fuel (from who's pump I can't say other than being California based) and netted peak TQ of 427 at 4000 and peak HP of 390 at 6000 on the magazine dyno.
DCR works out to 7.2:1.
Make of it what you will.

And 160F dyno water, probably...

Even the # of variables is variable in these tests.

Adam

[skinny z]

And 160F dyno water, probably...
Even the # of variables is variable in these tests.
Adam

Undoubtedly.
Like I was saying...

Make of it what you will.

[Walter R. Malik]

What is the highest, dynamic CR for 87 octane gas?

At what temperature??? That has very much to do with, what will work.

[plovett]

Depends on the load on the engine as well, in my opinion. Is it a 500 cube motor pulling a 3000 lb vehicle with 4.11 gears or a 250 cube motor pulling a 4000 lb vehicle with 2.75 gears? One might detonate and one might not, with the exact same DCR and octane.

JMO,

paul

[frnkeore]

The criteria here is 2V wedge and heart shaped chambers, both aluminum and cast iron. Old school, if you will, not direct injection.

A safe guild line, in a loaded engine, with a .040 - .060 squish.

80F deg 800 ft elev.

Randy and Paul. Temp and Elev are as above. Loaded is loaded, no matter the weight. Consider it a steady dyno pull at 160 deg engine temp. The 80 deg is assuming air intake, out side the engine compartment.

I know by application, there are things that work. Such as 6.8 DC but, I would like a upper end number to build a engine to.

Will 7.5 do it, in those exacting numbers, supplied above?