I have an opportunity to purchase a 377 SBC with a reported 11.5 to 1 compression ratio, Motown 220 heads, Holley intake, and a crank trigger ignition. I know that there is a big difference between static and dynamic compression, but am wondering how to tell. I am not sure if I can take enough timing out to run premium pump gas on this motor- and that is my biggest concern. No way am I paying $7 a gallon for race fuel on a street car. It really looks like a stout motor that could pump some hp, but it is not a race car. Am I dreaming? Any suggestions?
377 small block
SS69Cam
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I have an opportunity to purchase a 377 SBC with a reported 11.5 to 1 compression ratio, Motown 220 heads, Holley intake, and a crank trigger ignition. I know that there is a big difference between static and dynamic compression, but am wondering how to tell. I am not sure if I can take enough timing out to run premium pump gas on this motor- and that is my biggest concern. No way am I paying $7 a gallon for race fuel on a street car. It really looks like a stout motor that could pump some hp, but it is not a race car. Am I dreaming? Any suggestions?
You need to know when the intake valve closes. Ask the seller for a copy of the cam card. Or ask him for the brand and part number of the cam. You can then look it up on the internet.
Take all the information about the motor and use a calculator like this one: http://www.kb-silvolite.com/calc.php?action=comp to determine the SCR and DCR. Regardless of what the SCR is the motor doesn't start compressing the air fuel mix until the intake valve closes.
So he tells me the only thing he knows is that its a Comp Cams with 630/630, 254/264@.050 and lobe separation at 106 degrees.
I could not find that exact cam. I looked at a couple cams on the Comp website that were close and made some assumptions on the parts in this motor. I came up with 8.7 to 9.2 DCR depending on which cam specs I used. Both of those are too high for pump gas. To be absolutley sure you need all the details on this motor so you can calculate the SCR and DCR. The current owner could be guestimating on the SCR. It may be 11:1 instead of 11.5:1 or it could be 12:1.
I ran 13:1 on pump gas but my cam closed the intake valve a lot later.
If the builder built it to run on race gas, chances are slim you will get it to run on pump gas.
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Did you buy it? If so pull the heads and see what you have. I am sure you can sell the "race" parts and replaces for street parts and break even or come close.
How about AV Gas? About $1 or $2 more than premium pump gas and have run 13:1 on it before. 100LL Av gas
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Aviation fuels can be tricky because they are designed to burn at higher alitudes where there is less oxygen so you may have to jet to compensate. Aircraft have mixture controls that allow you to compensate from inside the plane. Which when you think about it pretty cool...but the engines are air cooled so they are more sensitive to rich/lean condidtions.
Not saying the fuel will not work....you could just have issues and not know what they are due to using it.
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The other thing is, is he SURE it's 11.5:1 or is that just assumed? If you don't measure everything there is a good chance the compression could be much lower.
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:yes:
AV fuels are being reformulated as we speak
The GA community is under very serious pressure to 'get the "Lead" out' ...
All TEL blends are highly reduced at this time and more restictions are on the way Jan. 1, 2012.
Soooo - if you do decide to go this route then be sure you can reconfiqure for these changes as they continue to occur.
Some interesting reading in some past threads, like this one - http://www.camaros.net/forums/showthread.php?t=185805&highlight=Aviation
Planes do take off at sea level, and end up at how many feet in the air?
Summer time temps here at sea level, are calculated at 2800' to 3200' above sea level
And to also not, I had the 100LL tested, and I have the sheets some where, the Sunoco Blue race fuel was a copy of the 100LL with the 100LL having one additive to prevent vapor lock and cold start issues
On the automotive scale they were tested, octane numbers within a point or so (MON) and identical specific gravity, in the end, 100LL ran the same ET's as Sunoco Blue Race Fuel
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Uhmmmm - don't take this wrong - but ... you need to 're-test'
Here is actual published data* for the two (2) fuels you stated;
Sunoco “Blue” SUPREME Racing fuel;
Specific Gravity - .713
Lbs/gal. - 5.94
Pump Octane (R+M)/2 - 112
RON - 115
MON - 109
Vapor Pressure - 6.3 (Reid)
Boiling Point/Range: 10% - 143°F
Boiling Point/Range: 90% - 233°F
Boiling Point/Final - 253°F
Leaded - yes, TEL - varies by distribution point
Color - Blue
Ethanol, volume % - 0.0%
Oxygen, wt% - 0.0%
Stoichiometric A/F 14.9:1
(this is not to be confused with the 260 GT Plus fuel - it's also 'Blue' but intended for very high [15:1+] CR ... main difference is C2H6O %wt.)
BP GA (AV) 100LL;
Specific Gravity - .682
Lbs/gal. - 5.83
Pump Octane (R+M)/2 - 101
RON - 104
MON - 94
Vapor Pressure - 5.5 (Reid)
Boiling Point/Range: 10% - 75
Boiling Point/Range: 90% - 301°F
Final Boiling Point: - 338°
Leaded - yes, TEL = <0.13pwt (2010 reg. - 2012 reg. will be lower)
Color - Light Blue
Ethanol, volume % - 1.5%
Oxygen, wt% - 7.6%
Stoichiometric A/F 11.7:1
And ... given the delta of these two fuels tested and the inherent BTU values of the two fuels - there's no way the "ET's" were the same" :noway:
Unless of course something else was changed for the two runs - or that vehicle just can't use a 'better fuel' efficiently to begin with
As always - not trying to confuse an issue with facts, just trying to help
* = I have the data for all 11~12 current formulations for Sunoco fuels (including the current 'Green' and 'Yellow' special formulas), if you think you got the wrong one ...
Along with 20+ other specialty fuels commonly used in 'racing' applications - I'll be glad to cross-reference those with any GA 'Av' fuel you'd like :thumbsup:
GA fuels are formulated for something totally different these days that land based performance fuels - these are not the same 'Back-in-the-Day' formulations, that all the old stories of "fantastic performance" were based on
This includes completely 'disassembling' the HC molecules to re-structure them for increased efficiency in low-pressure/high alt. operation in a completely different engine designed to run a constant speed at constant cool temps. ...
I love watching those engine tests though :yes:
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No matter the alt a plane takes off from the ground at the pilot adj the mixture for optium performance prior to take off.....it's called a run up area or they may do it on the flightline. Richer settings are the norm for takeoff but once in the air the settings can change to lean out the engine. The engine is air cooled and when your flying you just don't sit behind the stick like you would behind the wheel of your car. You look at and maintain your alt, RPM performance, direction and engine temps that all vary with the alt your at, head winds, tail winds or cross winds.
this is a very stout motor--is it 350 stroked to 377 or 400 destroked to 377--i ran this cam in both set ups at 11.7 but on race fuel--106 LS and close to this compression(no way on pump gas)--aviation fuel is run alots down here but it builds up heat and is a dry fuel--when we run it down here on the street , we add marvel mistry oil to the fuel and seems to work fine
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And that all important Exhaust Gas Temp. (EGT)
Lean to a given EGT % for best operation at cruise vs. climb ...
Heat is most likely due to leaner A/F with the AV fuel
The 'Marvel' most likely adds quench and slows flame propagation in chamber effectively masking the lean mixture - but this hinders BTU conversion and negate any 'benefits' of running AV ...
Matching the fuel composition and performance design parameters should always be a consideration in operation of any high efficiency engine :thumbsup:
It's how you win "heads up" races
In my Opinion a 327 has to be at least 10.5 to 11.5:1 Static Compression with about a 280 to 298 Intake Cam Duration pushig 450+Hp @ 8000rpm - If you're interested: PM Me and I can Tell you How to do It on Pump Gas.
Warning - You might not like the Initial Cost.
If you want a a Car by all means pick a 327 but if all you want to do is DRAG forget about me.
Warning - You might not like the Initial Cost.
If you want a a Car by all means pick a 327 but if all you want to do is DRAG forget about me.
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