davepl

Long story short, I wound up with 122cc chambers on a ZZ502 short block because I planned to add a blower but decided against it. So now I have somewhere between 8.5 and 8.75 to 1 compression.

To bring that up to 11:1 I would need a 36cc dome. A 30cc would put me at 10.5:1, which is the range I want to be in.

I need a standard bore ZZ502 piston (4.470) with a dome in that 30-35cc range, then, but can only find 17 and 41cc.

I'll throw out the numbers in the hopes someone can suggest an off-the-shelf piston or some other solution (milling the heads?) to improve the compression ratio. It's all because of the 122cc chambers but they're great heads already port-matched to a Hogan sheet metal intake, so I sort of want to keep them.

Bore 4.470"
Stroke 4.000
Chamber 110cc (stock) 122cc (now)
Piston to Deck 0.015
Piston Dome (-1cc stock)
Gasket 0.039"

That yields 9.5:1 for me with the small chambers, as low as 8.48:1 with the 122cc chambers and a fatter 0.060 gasket.

I'd like to bring the compression ratio up and change the cam out to a 214/220 to really bring up the static AND dynamic compression, shooting for around 160lbs cranking.

Thanks for any advice!

Dave

mikem350

Super flowing heads, sheet metal intake....with 214/220 cam, on a 502??
Am I missing something? Like a bigger cam?

How about cutting the 41 cc domes down to what you want?

68post

Call RaceTec/AutoTec Pistons 714-903-4362 , or email them :
http://www.racetecpistons.com/pages/contact.php

I'm pretty sure their custom pistons are the same price as their shelf pistons.

davepl

Yeah, at this point I don't care how fast it is (my '15 Z07 is almost certainly faster) so I'm really trying to get the street manners right. I realize that large heads with a sheet metal intake and a smaller cam don't make a lot of sense.

I want it to drive well. Then what "bonus" power it makes on the top end due to good parts is, well, a bonus. Someone said put a Cadillac 472 in it, which isn't far off. But clearly I'm fighting some low velocity issues, complicated by cam and compression. I can't fix the velocity without epoxying the heads.

I could just stick a set of square-port Edelbrock RPM heads or similar on it, but that's probably even more money.


Cutting the domes is something I considered, I just don't know much about it (how to get them all equal, not weaken the piston) but I'll check with my machinist.

MotorHead

Get a good machinist and cut the domes down, easiest and most inexpensive route to go.

Jebbysan

Get the 41cc dome and fly cut/radius the top....4cc is not a lot of material. Have the manufacturer of said piston pin gauge it first for deck thickness.
Venolia, JE and Diamond will make what you want but $$$$$$

Jebby

GOSFAST

Hi Dave, take the bore to 4.500" (block-plated), use a 6.385" rod, and use a 17 cc dome piston. Not sure if your pins are "floated" from G.M., but if not, I would definitely change the rods either way.

Bring the heads back to 118/120 and you should be in decent shape?

Thanks, Gary in N.Y.

P.S. We've done a couple similar builds (on that block) back in the past, should be near 10:1 with the right pieces?

toobroketoretire

Can you use .035" head gaskets?

cv67

Assuming these are GM rect iron heads?
11:1....short cam;do you know how much overlap it has or grind #?

davepl

I'm using aluminum Trick Flow 340cc (Intake) rect port heads. Big heads. The cam is currently the stock ZZ502 cam, which is

224/234 @ 0.050"
.527/.544 w/ 1.71 rockers
on a 110 degree centerline

I might stick with that cam when I bring up the compression, as it's not that lumpy. But with 8.5:1 and a huge plenum intake and those big heads, it's not that smooth either!

MotorHead

If you stick with that small cam and raise the compression you are looking at detonation problems.

Pop Chevy

Look at Mahle pistons. That's what I am using for my 540 build. I too had trouble finding a mid dome.

MotorHead

Mahle pistons are getting very popular, I have them in my 427ci small block. They are forged and have small skirts but they don't rattle around when cold, I would go with them again. And they come with a ring pak.

MotorHead

41-39=4cc, yeah that will solve all his problems

davepl

I was thinking about that, but at what RPM/load range would that happen?

My theory is that a shorter cam would increase low-rpm cylinder pressures, but that they're low anyway due to the lazy runners and big plenum. So it brings up cylinder pressure down low but actually would build less at high RPM.

If I went the other way, putting a short cam and high compression on a motor that had good VE down low, that'd do it.

c6silver

Be careful of removing material from the 41cc dome...if the domes are hollow the pistons could be junk....it's not like the old days when TRW sold solid dome pistons, everyone wants lightweight parts.

davepl

Per the other thread, for now, replacing the motor with an LS3.

427Hotrod

Well...that will take care of the smooth issue! Looks nice!

JIM

davepl

Yep, even stuck with the 430hp cam instead of the 480hp cam for now!