Warhead

Really, so they have been milled already?

Your stock #5 head will be around 68-69 cc's from the factory, it will take around a .030 cut to get the chambers in that ball park. It's a fact of life.

The #5 will flow a tad better than the #8, but not by alot. Performance will be aided by porting, but due to the bowl and intake port floor differences, you can not make them carbon copies of each other, for your test.

Jim

captjim

Please tell us how you get 10 to 1 compression on an Olds 355 with a 79 cc chamber.

MDchanic

• Deck head 0.100" (79cc - 22.7cc = 56.3cc)
• 0.014" steel shim gasket (3.18cc)
• piston 0.025" down in the cylinder (5.3cc)
• 14cc piston
• Swept area 717.1cc (stock bore)

should do it.

... But do the laws of physics allow it?

- Eric

cutlassefi

Sounds good except I think it takes about a .006 cut to equal 1cc. .100/.006=16.6, not 22.7. I wouldn't take that much off anyway.

MDchanic

Hmmmm...

4.057" bore ÷ 2 = 2.0285" radius
2.0285 x 2.0285 = 4.1148 x ∏ = 12.927"sq. = area of bore
12.927"sq x 0.100" = 1.2927ci = volume of 0.100" column of bore
1.2927ci x 16.387 = 21.18cc

Am I doing something wrong? (no sarcasm intended, which is unusual for me)

Why not? Structure? Valve clearance? Sealing area? Intake manifold fit? Giant pain in the a$$ milling that much off a big piece of steel?

I may be needing to do some similar work in a few months, so I figure I might as well learn a bit now.

Thanks,

- Eric

captjim

Guys, you kinda missed the point. I know he could mill the head, but he was asking about the chamber, just letting him know that without a domed piston, Cr maxes out around 9.2-.3 to 1 with that head. Why mill the crap out of a #8 when #5-#7a gets you there easily? Just making a point, but obviously not clearly.

He said "building" an engine so I assume a piston change.

I would not mill that much off when there are other very viable options. Furthermore, I was told by several Olds experts that the older 350 heads could be cut down to 58cc, I did mine to 60. No way can you cut that much off a #8 head, down to 56cc. The cost alone would be absurd, not to mention fitment issues and maybe hitting water. Piston to valve may be a problem, too. 10 to 1 is easy with flat tops or 6cc Speed Pros or 4cc Probes and older 350 heads.

MDchanic

Just asking...

And I think the priorities change depending on whether you've got a set of pistons from a swap meet stashed away somewhere, or a buddy who will let you in his machine shop to do a bit of work from time to time.

Personally, it's really just academic curiosity.

- Eric

captjim

That is fine, I enjoy the occasional theoretical discussion, but with the abundance of old 350 heads that flow better, messing with the #8s in that application is just not cost effective, IMO.

Kyle's 77 Cutlass

[QUOTE=captjim;241121]Guys, you kinda missed the point. I know he could mill the head, but he was asking about the chamber, just letting him know that without a domed piston, Cr maxes out around 9.2-.3 to 1 with that head. Why mill the crap out of a #8 when #5-#7a gets you there easily? Just making a point, but obviously not clearly.

He said "building" an engine so I assume a piston change.

I would not mill that much off when there are other very viable options. Furthermore, I was told by several Olds experts that the older 350 heads could be cut down to 58cc, I did mine to 60. No way can you cut that much off a #8 head, down to 56cc. The cost alone would be absurd, not to mention fitment issues and maybe hitting water. Piston to valve may be a problem, too. 10 to 1 is easy with flat tops or 6cc Speed Pros or 4cc Probes and older 350 heads.[/QUOTE



Guess I should of explained the question a little better.I can see 10 to 1 won't work. Lets say 9 to 1 than or what ever CR you want to use.Both engines have identical CR's , one will need flat tops and the other may be dished,but do forget just a theoretical question. The one engine will use #5 heads 64 cc's port and polish, no milling. And on the other # 8 heads 79cc's port and polish and no milling, so stock chamber size. Let say we up the valves 2 on the intake and exhaust 1.625 if possible. The heads are the same except chamber size is different. the one engine has flat top pistons with the # 8 heads, and the other has the dished pistons with the # 5's Now would there be a performance difference between the 2 engines because of the different chamber size but or yet the compression is the same that it wouldn't make any difference?? Now am I making sense.

captjim

The #5s are a better starting point, flow-wise. The #8s have larger ex valves and hardened seats already. The flat tops will give you better flame travel, though probably not noticeable at that power level, and a little more quench area. Coin flip, no real advantage, IMO.

cutlassefi

I'd go with the #5 head combo as well. Just an fyi, a couple of piston companies have changed their dish configurations to more resemble the Nascar stuff. Nascar engine builders are using smaller and smaller combustion chambers in conjuction with a soup bowl type dish in the piston for more hp. They contend putting the combustion process lower into the piston is more effective. The guys at Mahle piston confirm that, and it actually has less squish area too.

captjim

Interesting. Also, IMO quench (or squish) is pretty much a non-factor on olds engines, at least compared to the other guys.

cutlassefi

Jim, you never got back to me on your garage sale stuff.

380 Racer

Now that's interesting.

380 Racer

That's what my engine builder also told me a few years back.

tonycpe

How are you going to get 10-1 with a 79cc chamber ? i would like to see that custom piston.

MDchanic

As I noted above, it's mathematically obtainable (assuming a deck height of 0.025") by decking head 0.1", using a 0.014" shim gasket and a 14cc bowl piston, but I have no idea it it's at all reasonable or practical.

- Eric