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Mechanicall VS dynamic compressio ratio and fuel ?
#1680531
10/01/14 01:06 AM
10/01/14 01:06 AM
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Joined: Aug 2003
Posts: 43,157
Bend,OR USA
Cab_Burge
OP
I Win
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OP
I Win
Joined: Aug 2003
Posts: 43,157
Bend,OR USA
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I'm putting together a 440 block 505 C.I. bracket motor(4.350 bore x 4.300 stroke) that has a mecahical compression ratio of 12.60 with a dynamic compression ratio fo 9.08 to 1 according to United Machines on line calculator. The customer wants to mix 110 octane race gas with non ethanol pump gas that has 92 octane here in OR, my question is what percentage would be better for this motor, 50/50 (2.5 gallons of each) or 3 gallons race gas to 2 gallons pump gas for a 66.6 percent of race gas to pump gas  I've never heard or paid any attention to dynamic compression ratio before coming onto this site many years ago   This is a bracket car only, not street raced   The solid roller cam is 108 LSA in at 106 on the intake and it has 269 @ .050 on the intake and 276@ .050 on the exhaust side, ported 440-1 with no flow numbers, single 1050 dominator on a 440-2 intake modded to fit the dominator carb. pattern. I am planning on dyno testing it next week on the local Studka dyno that has been calibrated recently, I'll ask to have it recalibarted for this motor, it has had a bunch of SB Chevys on it and may have been tweaked for those tests  Just kidding on the tweaking 
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: Cab_Burge]
#1680533
10/01/14 09:34 AM
10/01/14 09:34 AM
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Joined: Jan 2003
Posts: 9,996
Frostbitefalls MN (Rocky&Bullw...
gregsdart
master
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master
Joined: Jan 2003
Posts: 9,996
Frostbitefalls MN (Rocky&Bullw...
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The fuel octane will be in direct proportion to the mix.(Edit; I stand corrected, non leaded only) No expert hear, but would think 50/50 should work. It would be nice to have a knock sensor on that dyno, just in case there was a hint of trouble. It would be good to have the extra octane in the tank though. Like for when my electric pump quit in the staging lanes just before the burnout! I didn't see it till the return road.
Last edited by gregsdart; 10/01/14 04:55 PM.
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: Cab_Burge]
#1680535
10/01/14 10:59 AM
10/01/14 10:59 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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I've never played with the dynamic pressure to octane to see what will work and be safe... plus different fuels will knock at different rates so start on the safe side... but I always try to reduce octane a little at a time... I see the engine running better and quicker with a lesser octane thats ends up being correct.. I wish there was a quick chart to use for a relation of dynamic to octane(and be close)... when I was talking with Dan on my SB he gave me a number for the dynamic that I should stay under for pump gas but I would have to find it 
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: Cab_Burge]
#1680536
10/01/14 11:20 AM
10/01/14 11:20 AM
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Joined: Jan 2003
Posts: 12,068
Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
Joined: Jan 2003
Posts: 12,068
Benton, IL.
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Will the dyno graph show detonation? A local racer told me a while back that he could identify detonation on the dyno by comparing the graphs. He said detonation makes the line much choppier. Any truth to that?
And have you thought about water/meth injection? It would be a lot less trouble than mixing and may save some money in the long run with the cost of race gas today.
Master, again and still
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: dogdays]
#1680538
10/01/14 03:57 PM
10/01/14 03:57 PM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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Quote:
The 110 race gas is rated by the Research method.
The 92 pump gas is rated by the (R+M) / 2 method. Rated by the Research method it'd be around 97 RON.
If the 110 has tetraethyl lead in it, adding the unleaded to it will not change the octane rating in direct proportion to the mix, because TEL follows the law of diminishing returns. So, the first gram changes the octane more than the second gram, which is more than the third gram, etc. This means that the last gram in the race gas turns into the first gram in the unleaded and the result is higher octane than you would expect, although lower than 110.
If the 110 is unleaded, then the octane changes in direct proportion to the mix. So 50/50 would get 97/2 + 110/2 = 103.5 RON.
R.
I believe 104 is as high as you can go without lead. And 104 is full of ethanol, way more than 10% to get it to 104. So I'm sure 110 is leaded.
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: Challenger 1]
#1680539
10/01/14 04:33 PM
10/01/14 04:33 PM
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Joined: Jan 2003
Posts: 8,164
Plymouth, MI
Blusmbl
master
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master
Joined: Jan 2003
Posts: 8,164
Plymouth, MI
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You can buy 110 unleaded all over town here in Detroit.
'18 Ford Raptor, random motorcycles, 1968 Plymouth Fury III - 11.37 @ 118
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: Blusmbl]
#1680540
10/01/14 04:43 PM
10/01/14 04:43 PM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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I said I believe. I think you should look closer, Here's Sunoco's list of unleaded fuels which I have been selling for years. Does not mean someone else is not selling 110 unleaded but I have never seen it. Show me some proof. Here's sunoco list. web page
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: MR_P_BODY]
#1680541
10/01/14 05:07 PM
10/01/14 05:07 PM
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Joined: Nov 2007
Posts: 21,822
Kirkland, Washington
Pacnorthcuda
Too Many Posts
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Too Many Posts
Joined: Nov 2007
Posts: 21,822
Kirkland, Washington
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Quote:
I've never played with the dynamic pressure to octane
to see what will work and be safe... plus different
fuels will knock at different rates so start on the
safe side... but I always try to reduce octane a little
at a time... I see the engine running better and quicker
with a lesser octane thats ends up being correct..
I wish there was a quick chart to use for a relation
of dynamic to octane(and be close)... when I was
talking with Dan on my SB he gave me a number for
the dynamic that I should stay under for pump gas
but I would have to find it
I hear to stay under 8.5 dynamic for pump gas (92 here). On my motor thats 10.2 static--I was going to shave the AL heads to 10.5 but decided I better not.
My Voodoo cam intake closes at 60, thats pretty early, not too forgiving to high compression ratios.
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: Blusmbl]
#1680542
10/01/14 06:37 PM
10/01/14 06:37 PM
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Joined: Oct 2003
Posts: 11,684
W. Kentucky
justinp61
I Live Here
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I Live Here
Joined: Oct 2003
Posts: 11,684
W. Kentucky
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Quote:
You can buy 110 unleaded all over town here in Detroit.
Same here, says right on the pump "unleaded".
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: justinp61]
#1680543
10/01/14 06:47 PM
10/01/14 06:47 PM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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Quote:
Quote:
You can buy 110 unleaded all over town here in Detroit.
Same here, says right on the pump "unleaded".
What does a gallon of 110 unleaded cost?
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: Crizila]
#1680545
10/01/14 06:54 PM
10/01/14 06:54 PM
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Joined: Oct 2003
Posts: 11,684
W. Kentucky
justinp61
I Live Here
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I Live Here
Joined: Oct 2003
Posts: 11,684
W. Kentucky
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Quote:
Quote:
Quote:
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.
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: MR_P_BODY]
#1680546
10/01/14 06:55 PM
10/01/14 06:55 PM
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Joined: Oct 2003
Posts: 11,684
W. Kentucky
justinp61
I Live Here
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I Live Here
Joined: Oct 2003
Posts: 11,684
W. Kentucky
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Quote:
I've never played with the dynamic pressure to octane
to see what will work and be safe... plus different
fuels will knock at different rates so start on the
safe side... but I always try to reduce octane a little
at a time... I see the engine running better and quicker
with a lesser octane thats ends up being correct..
I wish there was a quick chart to use for a relation
of dynamic to octane(and be close)... when I was
talking with Dan on my SB he gave me a number for
the dynamic that I should stay under for pump gas
but I would have to find it
Mike if you find the number Dan gave you can you post it? 
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: Challenger 1]
#1680547
10/01/14 06:57 PM
10/01/14 06:57 PM
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Joined: Oct 2003
Posts: 11,684
W. Kentucky
justinp61
I Live Here
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I Live Here
Joined: Oct 2003
Posts: 11,684
W. Kentucky
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Quote:
Quote:
Quote:
You can buy 110 unleaded all over town here in Detroit.
Same here, says right on the pump "unleaded".
What does a gallon of 110 unleaded cost?
The last time I bought any was six or so years ago and it was $6 a gallon then.
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: justinp61]
#1680548
10/01/14 06:58 PM
10/01/14 06:58 PM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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Quote:
Quote:
Quote:
Quote:
You can buy 110 unleaded all over town here in Detroit.
Same here, says right on the pump "unleaded".
What does a gallon of 110 unleaded cost?
The last time I bought any was six or so years ago and it was $6 a gallon then.
Thanks.
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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
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Joined: Oct 2003
Posts: 11,684
W. Kentucky
justinp61
I Live Here
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I Live Here
Joined: Oct 2003
Posts: 11,684
W. Kentucky
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Quote:
Quote:
Quote:
Quote:
Quote:
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.
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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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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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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.
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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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Joined: Feb 2007
Posts: 5,080
organ
maximum entropy
master
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master
Joined: Feb 2007
Posts: 5,080
organ
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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?
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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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Joined: Jun 2014
Posts: 5,183
Porter67
master
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master
Joined: Jun 2014
Posts: 5,183
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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
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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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Joined: Jan 2003
Posts: 31,021
Oregon
AndyF
I Win
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I Win
Joined: Jan 2003
Posts: 31,021
Oregon
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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.
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: AndyF]
#1680556
10/04/14 01:23 PM
10/04/14 01:23 PM
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Joined: May 2008
Posts: 1,131
Thigh-Gap Junction
@#$%&*!
New user name, Same old jerk!
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New user name, Same old jerk!
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. 
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Re: Mechanicall VS dynamic compressio ratio and fuel ?
[Re: @#$%&*!]
#1680557
10/04/14 01:36 PM
10/04/14 01:36 PM
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Joined: Nov 2007
Posts: 21,822
Kirkland, Washington
Pacnorthcuda
Too Many Posts
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Too Many Posts
Joined: Nov 2007
Posts: 21,822
Kirkland, Washington
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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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