wcourt3010

Hi, so i had a leak down test down on my tired old 350 and the results came back negative, a lot of leakage on the passenger side cylinders 30-50% and two cylinders on the driver's side over 20% so I've decided to do a rebuild. The car is fun to drive now with all that leakage so i'm staying with my current setup and figure things can only get better (or worse if I choose poorly).

What I need is piston recommendations based on the following (which i'm not changing). I figure my compression goal is 8.5 to 1. Car is street only, light to light fun. no track.


Edelbrock Performer intake
Edelbrock Performer Carb (600 cfm)
lunati voodoo cam adv 256/262, 213/219 @ .50, .485/.499 lift, 112/108 LSA
hooker long tube headers
1973 block (removed #8 heads)
7a heads installed (3 angle cut and mild port and polishing already done)
3:42 posi rear gears

wcourt3010

just let me add that I'm assuming the car has never been bored over so I'm guessing that will need to be done. .30 over. I'm getting a shop to do the rebuild, just want to go in with knowledge on what pistons i should go with.

I'm refreshing the motor mounts and wiring harness (painless) while the engine is out of the car.

olds 307 and 403

Go with the Street Demon 625 for a carb, just a better carb all around. 8.5 to 1 is tough. Get the LF2321 pistons for low 9 to 1 compression, depending on your specs.

Sugar Bear

Where was the leak? Valves and/or rings?

Indy_68_S

Just FYI...

Another member has these LF2320 -F30 (same as 2321 but flat top instead of 6cc dish) for sale
https://classicoldsmobile.com/forums...s-pistons.html

...but that might be a little hot for your application

mech199

you may want to double check your engine because that year had a couple different compression ratios one is 8.5 to 1 the others are 10.25 to 1 or 10.5 to 1 depends which car you had and options on that car the 10.5 to 1 is a different stroke than the other two I think but best to use in any of them forged pistons and flat top I would have to check my books to certain on the stroke

Fun71

That is correct for the 1968-1970 350 engines but note that he said he has a 1973 block and he has a 1971 car. The 350 had 8.5:1 compression from 1971 onward and had the same stroke as all the other SBO engines.

mech199

sorry about that had a phone issue anyway you are correct on the 73 block I missed that and there is two sbo engines that are different the 400 and a version of the 330 the 400 has same bore as 350 just different stroke and that 330 that has a different angle on the cam and valves and the best piston I have found has been forged flat tops

coppercutlass

The 400 was never a small block that is a big block. The 403 is a smal block all small blocks had the same stroke. The 400's had 2 diffrent bore sizes. But im pretty sure the bore ws not the same as the small block. But guys will use a 350 piston for their 400's due to availability issues. 68-69 400's had a 3.875 bore stock sbo was 4.057 I think the 65-67 was a 4 in. so if you bore .057 you can stuff a std. 350 piston.

Fun71

Again, all small block Olds engines have the same stroke (3.385"); the displacement changes due to the bore diameter.

260 = 3.500"
307 = 3.875"
330 = 3.938"
350 = 4.057"
403 = 4.351"

mech199

wcourt3010

rings.

cdrod

Kenneth:
FYI, the stock bore of a 403 block was 4.351, not 4.385. Just keepin' the info correct.
Rodney

cdrod

wcourt:
Are you planning to rebuild the engine yourself?

Fun71

Thanks for the number check! I am very well aware of the 4.351" bore size so what the heck was I doing when I typed that? Looks like I had the 3.385 stroke length on the brain and entered part of that for the 403 bore diameter.

wcourt3010

no, delivered it to an engine rebuilder in Toronto yesterday. we're going to talk today hopefully to discuss what needs doing.