Block is in the shop and the guy was asking me what the stock number was on the pistons for the Rallye so we can cross reference them to order some. So.... does anyone know what the number was on the pistons? Did they use W-31 flat toppers or other?

Would love to get an answer soon so i can get them ordered

And as always TIA guys

 

No they used a 7 cc dish . I think the smallest dish you can get from speed pro are 3 cc. Or you can buy cast aluminum from egge they have the correct ones too.

 

Sicky, they used dished pistons as copper described. You can order a set of pistons from egge.

 

ok sweet. Is there any special parts i need to know about the engine before i go in tomorrow to talk to them some more?

 

i am far from an expert in this department but i used flat top pistons in my Rallye and it came to 9.94:1 compression if i remember right. i think original was 10:1. i know the original pistons had the small dish mentioned above but there was enough difference (deck height maybe) that the compression came out nearly the same.

 

So should i go with the flat pistons or the aforementioned small dish pistons?

 

Depends on the compression distance - check the specifications of both.

- Eric

 

How i do that lol

 

Well, look up the specifications of the original engine, and look up the specifications of the pistons you are considering buying to see whether the compression distance is the same or different.

Eric's (JensenRacing) experience may be because the new pistons had a slightly different compression distance, or it may be because he used a thicker head gasket.

It would be wise to calculate your actual static compression ratio with the original setup, and with the proposed new setup to be sure you are getting the compression that you want to have.

- Eric

 

uhhhhh what lol... So i am as you can tell not very good at this lol

 

Here's a reasonably well written explanation, and here's a calculator that saves you from having to multiply those nasty little numbers (Heaven forbid ).

- Eric

 

With stock deck height , and head volume and .040 head gaskets, with flat tops. You will be around under 10 to 1. Roughly depends on your variables.

 

. Originally would have been 10:25.1

 

350 Piston Set
350 68-70 10.25:1 comp. ratio. Standard bore. Set of 8. view photo 14-350 $399.95 350 Piston Set
350 68-70 10.25:1 comp. ratio. .030 oversize. Set of 8. view photo 14-350.030 $399.95 350 Piston Set
350 68-70 10.25:1 comp. ratio. .060 oversize. Set of 8. view photo 14-350.060 $399.95 350 Piston
350 68-70 10.25:1 comp. ratio. Standard bore. (Forged piston). 14-290 $99.95 350 Piston
350 68-70 10.25:1 comp. ratio. .030 oversize. (Forged piston). 14-290.030 $99.95
www.supercarsunlimited

 

Diffrences in today's thicker head gaskets . Original thickness is between .018-.022 if I remember correctly. New gaskets usually .040 also add volume which is why it would make almost the same compression as original maybe a little less with flat tops. I belive a .040 thick gasket add's 10cc's . You also gotta remember head volumes varied most people say 64 cc's but closer to 70cc's in a lot of cases. I ran flat tops with my heads milled .024 and a .040 head gasket and the pistons .025 in the hole I was fine on pump gas 93.

 

You could get a flat-top piston,massage the combustion chambers in the heads,and with the thicker head gaskets of today,you can still end up with the factory compression ratio,or something desirable,to run on today's pee pee gas.The original piston in the Ralle 350 engines was the common piston for the 350 4bbl applications of that year.The W31 was the only 350 to get the flat top,and they never made a Rallye 350 W31,but it never hurts to improve upon 40yr technology.

 

507olds the standard app. 350 piston was the 14cc dish for 9 to 1 compression.

 

The standard 1970 350 4bbl engines had the larger dish? Mine didn't.Maybe the 2bbls did.I haven't had too many 350's to compare,but the ones I had,came with the smaller dish,and my W31's obviously had the flat-tops.

 

The diameter is the same for the 7cc and the 14cc the 14cc is deeper. The huge 23cc dish didn't show up till 71.

 

Yes,the 71-up had the cereal bowls.All of the 68-70 350 4bbl engines that I have owned,came with the 7cc pistons.I have found the 14cc in some 2bbl engines.

 

All 68-70 factory 350 4bbl were 10:25.1, 310hp (excluding the W31), All factory 350 2bbl were 9:1.

 

So,back to my original post.The 7cc dish was the common piston for the 70 350 4bbl engines,and 68-69 for that matter.

 

i thought the 7cc dish only came in the 310 hp engine. i bought a 70 that had a 4 barrel original and it had the 14cc dish pistons. From what i read at the time it said that.

 

Is there any possibility that the intake/carb was changed many years ago,possibly from another 70 350?Anything is possible in 40yrs.

 

Sicky, What Brian is saying is correct. All 310 horse engines from 68 to 70 got the 7cc piston. Again, from speaking with you it sounded like you wanted to restore the car. Therefore, a set of cast replacement pistons would be fine. If it was mine I would use a set of flat top pistons from egge. They will yield a nice compression ratio as I am sure you will be using .040 gaskets.

Also, I have not seen a steel shim head gasket that was thick as .020. All of the steel head gaskets that I have are .015 to .017. However, more common in the .015 range. Also, it would depend if the head gasket was for a 350 or a 455. Again, the CC on the head gasket changed as the sealing ring was a different diameter.

 

I think i am going to stick with the 7cc pistons for 2 reasons: it is what it had originally and its cheaper (both gas and price lol)

 

Speed pro's aint that much more and with stock deck height and head volume ., your compression would actually drop and be even more pump gas friendly.

 

wasnt oldzy selling some 350 parts cam bullit pistions on High performance olds or real olds power