I am beginning of 350 build. Block needs to be bored to 4,125". I am going to use reasonable priced (read: cheap)sbc aftermarket rods. Need flat tops and close to zero deck.
Any suggestions wht pistons and rods to use?

 

Are you going to offset grind the crank to add a little stroke or keeping stock stroke of 3.385"?

 

Cranck is already 010 ground and needs to be grinded 020 under. Not much stroke potential left, probably keeping the stock 3.385 stroke. Even like this, the piston/crank combo seems not easy to choose without going custom? Pistons for 4.125 bore aren't easily available for sbo compr. height.

 

That's diameter piston in a SBO-friendly 1.615" pin height is hard to find. It's a stock 425 size, and there is almost no availability these days. You can get close with a Pontiac 428 piston, so look into that as a possibility.

 

The way to go it to use SBC 400 pistons, they have a 4.125" bore. Then, use a SBC rod to match with the pin height and get what you need with the crank cut down to 2.10" (which is .025 off stock SBO rod of 2.125") Choices then become plentiful.

 

Stroke it to 3.5 and use the CP Bullet piston.

 

That's an expensive piston, just sayin. There are other good choices out there for less money.
I'd look for a Scat or Eagle 6.00 or 6.125" length small journal Chevy rod. From there you can either use a 1.425 or 1.550 compression distance piston to complete the combination.

 

Yes, the SBC 400 pistons are something to consider. As a downside, they all seem to have valve reliefs(of some kind), and of course in the wrong Place/angle concidering the SBO. I don't know if I should worry about these or not?
The SBC 2.100 dia 6.2"long rods combined with SBC 400 1.425" Compr.Height would be close to perfect match with original 3.385" stroke. But those valve reliefs.......?

 

By going for small 2.00" journal, I could only achieve 3.49"stroke with existing crank. Well, I have to make some calculations, sure it's still an option.


6.125" rod and CP Bullet pistons with 1.550c/h with stock stroke is an option also. Just have to mill about 0.04 from piston tops for a zero deck. Probably doable.

 

I just did a quick search on this combo, 3.5" stroke 4.125" bore 6.125" sbc rod. Looks like a good way to gain cubes for cheap, 374ci. I'm sure you can throw more money at this, but I'm a cheap bastard and can't justify it for a grocery getter. Here's what I found, maybe others have some better options.

http://www.summitracing.com/int/part...make/chevrolet

http://www.summitracing.com/int/part...bblw/overview/

 

Very attractively priced pistons! Just too much dish, unfortunately. Hmm.. wonder if there is enough meat in top of those to mill them to flat tops and then use 6,2" rods..... I like to travel in cheap side also!

 

If compression is of importance couldn't you get thinner head gaskets , smitty offers the shims, and you can get the corteco .028 from rocket racing perfromance. The dishes\valve relief aren't much. I had some probes with 3cc's .

 

How much compression are you looking for? That piston should give you a little over 9 to 1 with a 68 cc head. Probe pistons will give you more for more money.

 

I believe Dick Miller carries the Diamond 425 piston in standard bore. A nice, modern, forged piston in the proper compression height. Of course using decent rods will require crank and pin work. Just another option.

 

Look for that rod in a 2.00" journal instead.
Don't worry about the valve reliefs. Valves won't even be close to hitting the pistons.
I'd shoot for about 9.5:1 if possible. There are also some alternative forged pistons available that have a better ring pack but are cheaper than the CP stuff.
Hope this helps.

 

About compression, I am aiming to 9,5:1. But with #8heads, so, I really need zero deck and flat-tops. 3 or 5cc valve reliefs are still acceptable.


Asked about DMR, they do not have suitable pistons, at least for now. Also, their price level is too much for my budget.


About sbc valve reliefs, I am not worried about my pistons to hit the valves, just annoyed about un-needed extra holes stealing the compression ratio.


But if I really want to keep the costs reasonable, have a modern ring pack, forged pistons, the SBC 400 ones are maybe the only off the shelf choice. And I just have to live with valve reliefs.


http://www.summitracing.com/int/part...-std/overview/


http://www.summitracing.com/int/part...bblw/overview/

 

You're using #8 heads and you're worried about the effect those two little valve reliefs are gonna have? Really? I wouldn't be.
And I wouldn't use that rod. Use something made from 4340, not 5140. They'll be just a few bucks more but worth it.

 

As cutlassefi pointed out, thanks, you need a rod to fit the 2" journal size after the offset grind.
I don't see any cheaper options under $300, but this should work.

http://www.summitracing.com/int/part...2520/overview/

This piston has a 6cc reliefs.

http://www.summitracing.com/int/part...16cp/overview/

The costs are adding up. You might be better off finding another block.

 

Exactly! it is my bad habit to get stuck in to minor details! Anyway, I try to avoid other factors than #8 heads from lowering the cr.


I don't really see big difference in using#8 heads, if you just can get the cr right. After pocket porting, they are very similar to earlier castings, exept bigger ex. valves.


And thanks for the rod tip.

 

If you are going to port and do big vlaves why not cut down the heads to ge the compression you need ? Won't cost much more.

 

Yes, #8 heads will be milled to about 70cc. This means about 0.06 cut.

 

Why not just start with the better, old 350 heads? Cores are abundant. Better flow and with a small dish or relief, you are at 9.5 to 1, perfect for a street car, IMHO.

 

It is understandable that you ask this question. Here where I live (Finland) the Olds heads are not so easy to find. On the other hand, I do have #5 heads in my -69 Cutlass. But it is a good running stock engine, and I would not like to take those heads in to this build.


I understand the differencies between, let's say #5 and #8. Small chamber vs. big chamber. Also, in the unported condition #5:s exhaust sure flows much better, but when ported, the difference is not big, if any? Intake side is actually quite similar, even unported.


I'm building the short block anyway, so it doesn't rise the costs signifigantly to zero deck with flat top pistons.


So, when zero decking the sbo, what is the minimum thickness for head gasget? In other words, what is the minimum distance you can build between the piston top in tdc to the head?

 

What compression ratio are you looking for? You can easily get 9.5:1 without cutting that much off the head by using the right piston. Plug your numbers into the calculator.

http://www.summitracing.com/expertad...ion-calculator

 

Most agree that .040 is about optimum. I did not realize you were in Finland, i woud definitely not tear apart a good running engine. Use the #8 heads, flat tops, and go conservative on the cam and you should have a good runner.

 

So the thickness of regular Fel-Pro will be just good.



Yeah, not going to get grazy with the cam. My plan is Comp XR262HR.

 

Yes I have played with these calculators, also with dynamic compression one.
I prefer to mill the heads bit more and go with 0.04 gasget. Dont want my pistons to hit the heads Other thing the thick ones are cheap and easily available.

 

Nice article about #8 heads:


http://www.members.shaw.ca/gregtsmith/Head_Porting.htm

 

VERY good read, lots of practical advice. Spend your time and money on the chamber and bowl, including a quality valve job, and a little bit goes a long way.

 

That is a good article. The #8 heads are much better than a 4A or J head on the exhaust side. My 4A heads are just plain awful on the exhaust side. A low roof and just plain restrictive.Just a few hours opening up the bowls with a big intake valve will be a huge improvement. I don't why Olds restricted just under the valve and left the rest of port quite decent.