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Re: Mechanicall VS dynamic compressio ratio and fuel ? [Re: Crizila] #1680551
10/02/14 10:34 AM
10/02/14 10:34 AM
Joined: Oct 2003
Posts: 11,684
W. Kentucky
justinp61 Offline
I Live Here
justinp61  Offline
I Live Here

Joined: Oct 2003
Posts: 11,684
W. Kentucky
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You can buy 110 unleaded all over town here in Detroit.




Same here, says right on the pump "unleaded".


Trust me, Sunoco 110 is leaded fuel. Don't are what the pump sez. Look on their web sight.




I don't see Sunoco mentioned in my post or the one I quoted. There are no Sunoco stations here.


Ok. So, what 110 unleaded fuel is available all over Detroit?




You'll have to ask Blusmubl, I live in KY.

Re: Mechanicall VS dynamic compressio ratio and fuel ? [Re: AndyF] #1680552
10/02/14 03:29 PM
10/02/14 03:29 PM
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Posts: 15,439
Val-haul-ass... eventually
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BradH Offline
Taking time off to work on my car
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Dynamic compression doesn't mean anything on a race engine. Once the engine is up on the cam you'll have 100% compression if not more due to the ram tuning.



This also means that the crutch of using a "big" cam to bleed off cranking pressure to run lower octane w/ a higher CR only works up through a certain RPM range before the engine's static CR is driving the WOT octane requirement.

That's not my opinion, that's info that came from both a successful cam grinder and an engineer for a race fuel company.

Re: Mechanicall VS dynamic compressio ratio and fuel ? [Re: Cab_Burge] #1680553
10/02/14 06:18 PM
10/02/14 06:18 PM
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organ
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maximum entropy Offline
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cab, i've found those dynamic c.r. calculators to be inconsistent, depending a lot on what they consider the closing of the intake. the best way to determine actual dynamic c.r. (in my humble opinion) is to measure cranking compression. if you've got zero deck, closed chambers, aluminum heads, you can get a way with quite a bit. the specific numbers escape me, but you know that engine better than we do. if you nailed zero deck, it will be a lot more detonation resistant. personally, i would run 110 in that thing.
karl


for what is the good life if not doing things thoughtfully?
Re: Mechanicall VS dynamic compressio ratio and fuel ? [Re: maximum entropy] #1680554
10/02/14 06:57 PM
10/02/14 06:57 PM
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Im probably wrong here but.


Doesn't the longer duration camshaft events lessen the effective stroke (where both valves are closed)? And this is where the motor hits it powerband?

So with less effective stroke don't you have less air to compress and is why some cars run so well with a lesser duration camshaft because they do have a much longer effective stroke which increases cylinder pressures.

So wouldn't a deciding factor be how much cranking or running cylinder pressure a setup could handle without popping a head gasket.

Small blocks I know are different.

Im a bit confused on the "If" you nailed zero deck? With the proper tools or a good moch up checking each end of the deck then deck the block to achieve a zero deck "with consideration to piston rock" its easy to achieve zero deck.

I see many just taking a block in to have it square decked and cut to the oem deck height which to me is hit or miss at times.

.032 on a true zero deck small block has worked well for me to 7200 area.

Id think a BB has a bit more piston rock and would not go that tight on quench.

Its possible at least on a small block zero deck with a modern domed piston to still hit a good quench # on the pad.

Factor in the al. head aspect and the heat lost couldn't you run 110 or better on track and at times if needed non eth. premium?

And does that seem reasonable as when running on spray, some have a separate cell with the C116 to handle the increased cylinder pressures that nitrous produces

Re: Mechanicall VS dynamic compressio ratio and fuel ? [Re: BradH] #1680555
10/02/14 07:27 PM
10/02/14 07:27 PM
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Oregon
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AndyF Offline
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Quote:

Quote:

Dynamic compression doesn't mean anything on a race engine. Once the engine is up on the cam you'll have 100% compression if not more due to the ram tuning.



This also means that the crutch of using a "big" cam to bleed off cranking pressure to run lower octane w/ a higher CR only works up through a certain RPM range before the engine's static CR is driving the WOT octane requirement.

That's not my opinion, that's info that came from both a successful cam grinder and an engineer for a race fuel company.




If you run the numbers you'll see that most race engines have dynamic compression ratios down around 9:1 or so. Even Pro Stock engines. They certainly don't run those on pump gas.

The dynamic compression ratio doesn't mean anything when picking a fuel for racing. Once the engine speed gets into a range where the cylinder is getting a full charge of air then you need good gas.

Call any race fuel engineer and ask them or look on their websites. Nobody picks fuel by dynamic compression ratio when racing, all of the charts are static compression ratio.

Re: Mechanicall VS dynamic compressio ratio and fuel ? [Re: AndyF] #1680556
10/04/14 01:23 PM
10/04/14 01:23 PM
Joined: May 2008
Posts: 1,131
Thigh-Gap Junction
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Quote:


The dynamic compression ratio doesn't mean anything when picking a fuel for racing. Once the engine speed gets into a range where the cylinder is getting a full charge of air then you need good gas.

Call any race fuel engineer and ask them or look on their websites. Nobody picks fuel by dynamic compression ratio when racing, all of the charts are static compression ratio.





There's nothing 'dynamic' about the so-called Dynamic Compression ratio. It's just Static compression based on intake valve closing point instead of BDC. A true Dynamic Compression Ratio would include Volumetric Efficiency and the Thermodynamic conditions inside a running engine. Unfortunately, you can't calculate that kind of stuff on a calculator or spread sheet, it's just too complex. However, if you just substitute 100% Volumetric Efficiency and calculate you're right back at the good old (volume@BDC)/(volume@TDC) compression ratio of old. (That's me agreeing with Andy)

It sounds like a good E85 build to me but it seems that the owner has an aversion to Ethanol, at least as a fuel.

Re: Mechanicall VS dynamic compressio ratio and fuel ? [Re: @#$%&*!] #1680557
10/04/14 01:36 PM
10/04/14 01:36 PM
Joined: Nov 2007
Posts: 21,822
Kirkland, Washington
Pacnorthcuda Offline
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Quote:

Quote:


The dynamic compression ratio doesn't mean anything when picking a fuel for racing. Once the engine speed gets into a range where the cylinder is getting a full charge of air then you need good gas.

Call any race fuel engineer and ask them or look on their websites. Nobody picks fuel by dynamic compression ratio when racing, all of the charts are static compression ratio.





There's nothing 'dynamic' about the so-called Dynamic Compression ratio. It's just Static compression based on intake valve closing point instead of BDC. A true Dynamic Compression Ratio would include Volumetric Efficiency and the Thermodynamic conditions inside a running engine. Unfortunately, you can't calculate that kind of stuff on a calculator or spread sheet, it's just too complex. However, if you just substitute 100% Volumetric Efficiency and calculate you're right back at the good old (volume@BDC)/(volume@TDC) compression ratio of old. (That's me agreeing with Andy)

It sounds like a good E85 build to me but it seems that the owner has an aversion to Ethanol, at least as a fuel.




Agreed. Volumetric efficiency plays a BIG part, and is incredibly complex.

Regarding cranking compression, I am in the middle of a head-replacement project on a 440. Before tear down the cranking compression was 188-200! Much higher than expected.9.25 iron heads. Now going to 10.2 aluminum, with quench, but I am concerned what the cranking psi will be. I was going to go to 10.5 before I did the compression test...

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