Inliners International Forums General Discussion Engines Cast 307 Pistons in 250 L6 swap

I am starting a motor build for a vintage 6 cylinder dragster and would like to get some information on using cast 307 pistons in the build. Trying to keep cost down so I won't be using $500+ race pistons. I am using a 230 block as it tested thicker on cylinder walls, 250 crank, 5.7 rods, 64cc 194 head milled .060, I plan on -0- decking the block for a CR of 10.75-11.00.

Heads already have been modified in the chambers and run sbc 1.94/1.60 valves with Z28 springs and BBC 1.7 roller rockers.

Any one out there tied a similar setup? How did it work?

Any one know were to find stock 307 pistons without the big cut on top edge?

What kind of RPM are you planning on running? What camshaft are you going to run?

I will be running a Clay Smith Cam around 560 lift and RPM around 6800-7200. Motor will run the same SFI 7" Fluiddamper I run on the 194 in the car today. Will run a vintage Cliford Ram Intake with 3 94's.

I ran a similar set-up.

I used forged 307 TRW pistons,(currently still in car) I have a positve deck of .002- .004 my 194 head was milled a lot, cannot remember the current cc's but I had 12.0:1compression camshaft ,,,, (going from memory) .560 lift 238 intake 248 ex. degrees duration @ .050 & all cylinders cranking compression was 220-230 PSI range.

I ran 3, 48 MM DCOE sidedraft Webers & it was by far the fastest & most torque my 250 engine ever made.
Really put a smile on my face & surprized many guys on the street.

This was my daily driver & I enjoyed this combo the best for overall driving experience. When I used a Paxton supercharger blowing through the same 48's, it was faster, but not from the start.


MBHD

Then cast pistons shouldn't even be a consideration, you need to run forged.

CNC-Dide -- I agree if forged TRW's in a 3.935 (.060) over are still avalible.

MBHD -- Were did you purchase the TRW Forged pistons from?
Sounds like a real solid motor with tons of power. The vintage class this dragster runs in only allow normal asperated carbs and I am running two 94's on a home made intake at present. The Clifford Ram Air intake has 3 seperate 10" runners (one per 2 cylinders)and I am going to start with the 3 94's (160 CFM) each and may go to Rochester small base at 210 CFM each if needed.

Did you take more than .060 off the head surface? I want to keep CR in 11.0 range. Your cam is almost the same as I am currently running.

I bought the forged TRWs years ago.

Only way to get them now is if someone has some new old stock NOS.

I have not looked @ the compression heights of the Chevy LS pistons, but they have the same bore size.
Anyone know here?

MBHD

MBHD -- LS pistons have a CH of 1.328, to tall. I am going to post on a couple of other sites and see if I can find some NOS forged 307 that may be out there.

CNC-Dude -- Do you know how much the heavy chamfer at the top edge lowers the CR? With my block -0- decked, a .020 copper gasket, head milled .060 with 62cc 194 small chambers I still think I could get 10.50 - 10.75 CR.

You need to re-think the gasket thickness, .040" is the minimum you can safely use with zero deck.

THATS TOO MANY RPM,S FOR CAST PISTONS, YES THEY WILL DO IT BUT NOT FOR LONG. THERES TOO MUCH $ ON THE LINE TO NOT RUN FORGED . ALSO BUMPING UP THE COMPRESSION WILL ALSO SHORTEN THE LIFE. JMO
P/S
I HAVE A SET OF NEW OLD STOCK 307 .030 TRW FORGED PISTONS ON GM REMAN RODS, ARP BOLTS AND CANT REMEMBER THE RINGS BUT THEY AINT CHEAP. BOB
423-384-8938

CNC-Dude -- The .020 was just an idea as I run a .042 crushed in the 194 motor currently in the dragster. All valve clearances will be run to make sure I have the clearence with the FT pistons, -0- deck and a 560 lift cam.

Do you have a feeling on the CR loss with the big chamfer on the current 307 cast pistons?

Not really, I know it is a pretty big chamfer though, plus the 4 valve reliefs they have also. Each valve pocket is going to be between 1 to 1-1/2 cc each plus i'd add an additional 6-8 cc's for the chamfer, so you'd be looking at a value of 10-14 cc's to factor into the compression ratio formula. I would expect to lose 1/2 a point minimum because of it.

tom, welcome to inliners int`. you have been racing to long not to know what the damage will be when those cast pistons let go. these guys really know their stuff as i have been gently told what they think of my ideas. nobody is more into keeping costs down than me but it`s more cost effective to put good parts together than the alternative. i, myself am going to buy the tlowe pistons for my build, partley because of the quality and the peace of mind. see you at the march meet where i`ll be stuck doing the clutch again.

CNC-Dude -- Thanks for the cc information.

sparks -- Dan it is good to hear from you. Ya I know forged is the best way and I do have a lead on some NOS forged 307 FT pistons that I hope will work out. If not maybe you can pick up another set of those tlowe pistons for me and I will pay you back out of any winings I make with the "Juice Bucket", no that will not work as our races don't pay that much. See you in March.