I'm looking into buying an engine kit and it comes with 10.3:1 pistons. My question is can I run this compression on pump gas? or what is a good ratio to shoot for?

 

that is getting near the upper limit most people consider for pump gas and iron heads. each engine is differant and has differant needs but you shouldn't have any problems with that set up.

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ICON Motorsports

1st & 3rd

 

That is about as high as I wouold go even with aluminum heads. Some go higher. Like Ede said, each engine is slightly different too.

Timing (base, rate of advance, etc) has a big influence on detonation too...

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in...

-=ICON Motorsports=-

 

If you go with that kit get the Fel-pro teflon head gaskets or a premium quality heat gasket thats a little "fat". Agree, 10:1 is about the limit for the street but small blocks heve a lot of leeway depending on the rest of the set-up. Get the best ignition you can afford. This will pretty much assure an occasional fill up of bad gas won't hurt much.

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Kenney
82 Trans Am WS7 notchback
83 Trans Am WS6 T-tops
72 Vista Cruiser 455
90 Olds Trofeo
80 K-10 w/snow plow
Painter @ Chevy dealer
GM junkie

 

Where you live also plays a part in the compression limit. A car that pings with the best pump gas at sea level will run fine at a higher elevation like Denver.


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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

The compression ratio you can run without problems also ties in to your camshafts duration figures. The longer the cams duration numbers, the higher static compression you want to run. That's because the valve opening and closing events create a "dynamic compression" ratio which is somewhat lower than the static compression normally calculated by the standard formulas. Essentially, if the intake valve is still open when the piston begins it's upward compression stroke, you really don't get all of the full compression on the gas mixture. Dynamic compression ratio is typically calculated from the intake closing point on an engine, and this point depends on the camshaft's duration.

If your camshaft has high duration numbers, you can run higher static compression. If your camshaft has low duration numbers, you need to stick with lower static compression.


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89 IROC with lots o' stuff

-=ICON Motorsports=-