wills30

who makes decent piston for a 65 400 olds . i plan on gutting a 66 425 ,and i need some decent piston for a street motor ,and i really don't need to bore,so standard size would be nice if possible?

61reoldsman

Have a look on Summit Racing they have a huge selection of pistons ,any bore size you may need.You may want to go with better pistons than what came from the factory ,but it at all depends on what you have planned for your motor;stock rebuild ,mild perf,etc.

joe_padavano

I'd be amazed if Summit lists a piston for a B-block 400 with the correct bore, compression height, and pin diameter.

Note that the Olds 350 uses the same compression height and pin diameter as the short stroke 400 motors. While it requires an overbore, many folks use standard bore 350 pistons in the early 400s. The 4.057" piston diameter results in a 0.057" overbore in the 400. The result is 412 cu in.

wills30

thats what i seen, maybe i can come across a good used set, some where really don't need a custum piston for this build , just useing it for a driver. and i really dont want to use the 425 piston .in case problem occur later,.thanks for the reply

joe_padavano

Good thing, because that's a 0.125" overbore.

wills30

ive got the room in the block , its a soild block , just too many chances , for a long term

61reoldsman

http://www.summitracing.com/parts/cnn-bo7000-008 ,like I said Summit has lots of pistons available ,this one is Oldsmobile specific, 4.065 bore,add a 7 '' rod and a 1.625 C.H and half the distance of the stroke @1.9875 ,the piston will be .012499 below the deck.Just saying you can find them.

wills30

.The 65 400 has a 4.000 bore actually 65 66 67 . They change the bore in 68 69

joe_padavano

Correct, and the O.P. originally asked for standard bore pistons. Again, good luck with that. The 68-69 G-block motors used the 4.250" stroke crank from the 455, so bore was reduced to 3.890". The longer stroke also necessitated 6.7" rods and a different compression height.

chadman

Not really an issue with the early 400's. I have one that is .155 over.

chadman

Here is an option but only available in .060 over.

http://highperformanceolds.com/phpbb...php?f=1&t=4315

wills30

thanks for the reply , and i seen those and i was hopeing not to bore ,but may become the option i have for the build ,thanks

joe_padavano

Good to know. Do you happen to have wall thickness measurements at that bore? Was this a B-block or an E-block 400?

aliensatemybuick

Use 350 pistons and bore the motor .057

Walla.

While this was already said (!), I recall reading that using W31 pistons will result in high compression (comparable if not the same as the motor had originally), if that's what you are looking for.

Also, I know of two people who overbored B block 400s .125 so they could use 425 pistons without a problem.

joe_padavano

Correct, the W-31 used flattop pistons also. Of course, today one would likely be buying aftermarket, so you can get whatever piston shape you like.

Voila!

("Walla"?? )

wills30

i seen some on ebay , i do not know how to down load, or show ad
Item number:
150690265710

Oldsmobile Olds Flat Top Pistons Set/8 400 1965 1966 1967 Cutlass F85 442 any body use these?

chadman

65 B block. I have the sonic test results somewhere. I will try and look them up. It was plenty thick though. Currently in my '65 in my avatar. Been beating on it at the track weekly for 2 yrs. now plus a few thousand street miles.

aliensatemybuick

Just being intentionally silly. Like exclaiming "Eurethra!" upon discovering something.

They can't all be gems.

chadman

OK, I looked up the sonic test card. The thrust side walls measure from .240-.300 thick and the thinnest spot is .180 on one wall between two cylinders where water passes between them.

joe_padavano

That's great info, thanks.