Hi, I'm having some trouble calculating compression ratio. I'm missing dome volume I think? Please help, here are my specs:

- SBC 350 from 1972
- Bored 0.020"
- Pistons: Mahle 224-3547WR-020 (link)
- Edelbrock top end kit 2038 (link to components)

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Generally 4 valve relief pistons are minus 9-10 cc. Your head's are 64 cc. You have what ever thickness of the head gasket. Bore of 4.020 and stroke of 3.48

Personally I would never install hyper pistons in any motor exceeding 300 hp. They are a great idea for piston to wall clearances, but they have no detonation resistance and feet per minute limitations

 

Here's a compression calculator that I used with gkull's numbers and some guesses at deck height and gasket thickness:
https://www.summitracing.com/.../compression-calculator

 

Even if you use 8 cc pistons number and and use a .027 head gasket you get a little more C/R

 

I can see you're looking to get more bang out of your 350.It's a good idea to get those better pistons. As far as hyper vs forged..I've been using hypers for well north of 400HP at 6200 RPM for over 10 years without any issues. I do stay away from detonation, but would in any case regardless of piston material.
I for one do not like the way those top end kits are put together. That kit is for top end power while sacrificing all street driving performance. The @.050 cam specs are good, however advertised is a long slow ramp and makes for lots of overlap making the power lazy at lower RPM's. My roller cam as an example is 270 advertised with 219@.050.

I know the kits make it sound easy and fast. Understand the risks involved with going with a flat tappet cam vs a roller cam. The heads are meh, ok I guess for 300ish or a little more power. The head gaskets are too thick unless you've had your block zero decked. Too much squish/quench promotes detonation. If your deck is stock then figure .025" in the hole plus the head gasket thickness. Felpro makes a .015" shim head gasket that I use which added to the stock deck gives a nice .040" quench.

My recommendation would be to buy the components separately optimizing them for your intended use. A retro roller cam adds about $1000 dollars to the build. Up to your budget. You will not have to be concerned with a flat lobe at any time in the future however.

I know that was not your question, just though I'd throw a little info in, in case you are doing this for the first time.
This is a good CR and DCR calculator:

https://www.jeepstrokers.com/forum/calculator/

 

I too would like to see you go to forged pistons.
For the detonation resistance alone.
Think of it as cheap insurance.
There are a lot of 350 pistons that will give you low 10:1 CR with 64cc heads and a .040" quench:

You just need to manipulate the block deck height and the gasket to get .040" quench height.


On the cam it has decent .050 specs 218/224*, but I do not like the 309* advertised. That is a very lazy ramp old school cam, with low TQ output.
You can do much better with this Howards: Same .050 but 50* wider on advertised. Fast enough to improve low speed TQ but still gentle on valvetrain.


Here is a Howards Hydraulic Roller which will make more TQ, and more power:

The red one will drive like a ***** cat, but be stronger than the flat t cam. The blue one will snort or lope a little at idle. And is about as big as you should go for a good driving street cam.

I like Howards cam specs and cam cores better than many of the other guys, for longevity (first) and power (second).

All of the cams mentioned should pull real hard between 1500 and 6000.

 

Rabbit trail: why would you choose a longer rod & shorter compression height (or vice versa) when everything else above is the same? Is it merely accommodating one of two rod lengths a customer may already have?

 

Maybe.
Some guys are convinced long rods are better.
But look at the difference in piston weight with the longer rod.

 

I have 4 relief speed pro (united) 6cc relief pistons in my 355 they are the hypers. I use them in an undecked block but use them with .015 steel shim gaskets and aluminum heads so the quench is around .040 and the compression is around 10.2:1. My engine is not a drag or race build so the hypers offer more advantages for my than forged. I run a 270/276 comp retro roller with 1.6 RRs I'm happy with the performance but decided since im swapping transmissions to install the 400 Ive always wanted to build.

I decided on the Keith black (also United) supposedly 30% stronger hypers for my 406 build im about to install as well. (I went with 5.7" rods in the 406 but in that engine the longer rods have more advantages). Forged pistons are good for performance but have other things like higher cost and piston slap that often come with them. It really depends on what type of use the engine will really see IMO. and where do you stop.. Then you might as well look for a forged crank and the roller cam.

 

I am awaiting on a Summit order of pistons for my stock build 427/390. I almost pulled the trigger on KBs that matched the GM specs, but was pointed to the same spec Speed Pro forged by folks on the C1 & 2 forum. The KBs are actually $80/set more.

 

It really depends on how big or should I say deep are those 4 valve reliefs are. So it sounds like 10.2 c/r is a good number or approximation