283 270 horse pistons choices

[Philip M.]

What has anyones experince been using the 10.5 compression piston in the 270 horse 283

I have the heads the correct cam and of course the wickedly expensive carbs and I wonderd if anyone used the 10.5 in this engine was happy with the outcome as opposed to the standard 9.5 to 1

what i know is the book says they used 9.5 to 1 in the 270 horse with the high lift cam I'm looking to get this new engine running right and I find the original carbs as in the twin carbs have a lot of CFM for the 283 its nearly 800 cfm
I believe using the domed pistons may actulally help burn off some of this gas

I found the correct carbs and the correct cam so here's hoping, also after spending all this money it might be nice to have a little more power also I find it strange that the book says 270 horse vs 245 horse (hydraulic cam model) for the twin carbs on both these engines did GM actually create 25 more horsepower with only a solid lifter cam and some carb tweaking I have the correct 270 horse carbs that im sure of.
how could they get an extra 25 horse with just a cam or is the 270 horse actually a 10.5 to 1 and erverywhere I look is a misprint

the fuely specification (290 horse ) which in the fuely's case is 10.5 to 1 so i know they used them in a 283


Thanks to anyone who has an oppinoon or info on this

Philip mclachlen member 54904

[William C.]

Re: 283 270 horse pistons choices

OK, sad to say but the Chevy Parts book as well as all the other sources I've checked verify my memory from my racing days that the 270hp was a flatop piston engine with four valve reliefs, the exact same piston used in every other 283 except the FI ENGINES. The magic of the 270 HP was the extended rpm range at which the power was achieved, as opposed to the 245hp version with a 5000 rpm redline (approximately) The extra compression in the FI engine allowed Chevy marketing to advertise a higher HP for the (Higher cost) FI engine vs 2X4 when all things being equal in the compression department the difference would have been much less significant. An example of "apples to apples" would be the 245hp rating on the hydraulic cam flattop piston engine vs 250hp for the same identical engine with FI

[Duke W.]

Re: 283 270 horse pistons choices

With the OE pistons you can use regular unleaded - 87 PON. The "10.5" pons will require premium, but you should see at last 5 percent more torque and power across the range and 5 percent less fuel consumption in normal driving.

Google KB pistons and check their catalog for offerings. Also, Federal Mogul might still off the OE FI piston, and I think Danchuck does too, but I don't know who manufactures it.

Keep in mind that advertised CR always makes assumptions about deck height, head chamber volume, and gasket thickness, so actual installed CR requires knowing what you have and running the numbers through a CR calculator. See the Fall 2009 Corvette Restorer for detailed information on this important subject.

Regardless of what advertised CR piston you use, I recommend you limit actual installed CR to 10.25:1 with the Duntov cam.

Duke