Inliners International Forums General Discussion Hi Performance 250 Pistons

This is my first post just found this site. I was wondering if you guys know if someone still makes a piston for a 250 with a 4 inch bore. i know back in the 70s on the round tracks around here they used to bore them out to 4 inches. i am looking for a set with 6 cylinder specific dome configuration for the 6 cylinder head. don't really want a v-8 piston. also whats the deck height on a 250 and 292.


thanks,
mike

Mike:

According to Leo Santucci's book "Chevrolet Inline Six-Cylinder Power Manual" (you really need to own a copy!) the block deck heights are as follows:

Standard Duty/Low Deck (230/250) is 9.150 inches +/- .007

Heavy Duty/Tall Deck (292 only) is 10.875 inches +/- .007

I suspect several of the good piston manufacturers can provide the proper pistons for your application with domes to match the Chevy inline head. Ross is one manufacturer that comes to mind. Of course, these are not what you'd call cheap . . .

Hope I have this right and that it's of some help.

JE & others will make you what ever pistons you want. Approx $100.00 each or a bit more.

As far as a V-8 piston,,,,it's been a while IIRC,you would use a 327 piston for a 4" bore for a 250 L6
People,, correct me if I'm incorrect.

Not sure why you would not want to use a V-8 piston?

SBC pistons are cheap.

What kind of compression are you looking to get?

W/a 4" bore, flat top & small chamber 194 head ,I would guess you can make 14:1 compression.

I had .030 307 forged flat top pistons w/4 valve reliefs & a 194 small chamber head & had 12:1 compression w/220 psi cranking compression.

Douglas, has a 4" bore 250 L6 in his race car,high compression,& it will over heat in about 5 minutes of driving on the street.


MBHD

For the record, a 250 bored to 4.000 will use a standard 327 piston. You probably need to sonic check your block first, and consider a short fill.

thanks for the answers guys! i have not been around these engines since the early 80s so i may be a little behind now. but i was thinking with a 194 head after you put .194 valves in it the intake was very shrouded by the combustion chamber. thats why i wanted to use a 250 head. as far as pistons go do the v-8 pistons have the valve relief in the right place for a six if i use a flat top? i know you can flat mill the head to get some compression back. i was looking for around 14 to 1 or so.

Mike, you will need to use an application specific piston for your 250 to get the valve reliefs in the correct location for your engine. But only if you are running a huge enough cam that will need reliefs to begin with. The SBC pistons are not the same valve angle or valve centerline relative to the cylinder bore. Venolia offers a piston forging specific for Chevy 6's. Even if you can get your cylinder head down to 50cc's, you still will need a dome of around 3cc's to get 14-1 compression with a 4" bore. You still should unshroud the chamber for the installation of 1.94" valves. Don't forget to open the intake bowl area up as well, installing the larger intake valves without doing so won't be of any benefit to you, especially with this much compression. IMHO, 1.94" is still too small for the compression you are trying to run....What will you actually be doing with this engine, street/strip, circle track....

On my old 17yr plus 250 I ran a 194 head 1.84 valves with a .030
pop-up 307 piston and was pushing somewhere between 13.9-1 to 15-1 compression according to the guys over at Glen Self racing when i gave them the specks of what was left of the dome to clear a 583/607 lift. And the CCs off the 194 head at that time.

Now the same psitons are being used and have been remilled to clear a 700 lift and with the head work the should?? be at about 13-1.Also in your case I'd have the block O ringed.