Thread: 512/514 CR for 91/93 pump gass

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Planning a build of a 514ci using SRP pistons with 28cc dish and Edelbrock 60679 75 cc heads is that a good combination for 91/93 oct. pump gas ?

Depends on what the configuration of the piston dome and compression height is on the piston Bob..... If you're ordering it as a stroker kit then the company selling it will have a chart saying what the CR will be with different CC heads. Or, you can run the whole formula for CR and see if yours comes out at a number commensurate to run pump gas on. My engines were either on race gas and then on E85 which allows the engine to have a whole bunch more compression!!!! Aluminum heads are generally good for 10:1 CR on pump premium, as long as you don't get too crazy on the timing!

Generally speaking, aluminum heads will allow up to 10.5:1 static compression ratio on pump gas, provided everything else is chosen to compliment the build for pump gas, like the camshaft intake closing point. For a street motor though, there would not be enough difference in power for me to choose 10.5:1. I would be very happy with 9.5:1 to 10.0:1 with aluminum heads because I could choose a shorter cam that would be more street-friendly. More SCR will require more cam, more torque converter, more rear gear, ad infinitum, until you have a combination that won't work well on the street anymore. Let's run the numbers with the 154167 piston.....

.7854 x 4.44 x 4.44 x 4.14 x 16.387 = 1050.4 cc's in the cylinder
combustion chamber = 75 cc's
piston deck height = 0 (stack of parts is 10.290", so cut block decks to 10.300" for use with a 0.041" head gasket to make a 0.051" squish)
piston crown = 28 cc's
head gasket = 11.2 cc's (I would use this head gasket for its pre-flattened steel fire rings that will be compatible with aluminum heads and will minimize brinelling).
http://www.summitracing.com/parts/fe...view/make/ford
Total cc's 1164.6
Subtract cylinder cc's from total cc's (1164.6 less 1050.4) and find 114.2 cc's.
Divide total cc's by 114.2 (1164.6 / 114.2) and find 10.2:1 static compression ratio with a 0.051" squish.

A retro-fit Howards hydraulic roller cam (part number 243745-10) and lifters (part number 91169) will close the intake valve at 40.5 degrees after bottom dead center and will produce a 8.7:1 dynamic compression ratio, just right for aluminum heads, pump gas and zero detonation with the tight squish. (well, tight for a big block).
http://www.summitracing.com/parts/hr...5-10/overview/
http://www.summitracing.com/parts/hrs-91169

Use a minimum 800 carb on an Edelbrock 7166 intake manifold. Use long-tube, tuned headers and cobble up an H or X pipe immediately after the collectors. Use a 14" x 4" air filter assembly so the motor can breathe. The cam will want a large dose of ignition timing. I would begin with 16 at the crank and 16 in the weights, then begin adding more at the crank, 2 degrees at a time, until power falls off. Experiment with vacuum advance to see what the motor wants. I would use a quality 10", 2500 stall torque converter. I always made it a rule to use quality parts in any location that was hard or difficult to get to for repairs, so I would also recommend that an SFI 29.1 flexplate be used, doesn't matter who the manufacturer is as long as it's tagged. Here's a converter I stumbled across.....
http://www.bmracing.com/products/404...5-crank-pilot/

If the motor kicks back against the starter due to the agressive ignition lead when firing it up, splice in a 15 amp (NC) push-button switch to the coil hot wire. Mount the push button switch on the left of the steering wheel to operate with your left hand. Push the button with your left hand to disable the coil and turn the key switch with your right hand. The motor will begin winding up with no strain on any parts. Release both switches at the same time and the motor will be idling.

OK, that's all the damage I can do.....

.

Thanks, You really laid out a great plan of what will work for my application. Now I have got to get over this knee replacement and back to work for some money for parts. The bills have drained my money that I had for this project. Seems that Insurance doesn't pay all the bills !!!!!!!! But again I thank You !!! Bob

Originally Posted by Thunderhorse

Planning a build of a 514ci using SRP pistons with 28cc dish and Edelbrock 60679 75 cc heads is that a good combination for 91/93 oct. pump gas ?

Assuming your 514 will have a 4.14" stroke then you compression ratio should come in at about 10.2:1. Depending on the rest of of the engine combo, 10.2:1 may be pump gas friendly but in most cases I tell customers over 10:1 is pushing it.