So I'm screwing together this fuzzy-kitten little 454 for street duty that I picked up cheap. It should make a little over 500HP on motor (pump gas, modest flat tappet mechanical cam) and then another 200HP worth of nitrous on top of that. No big deal for a big block.

I'm looking at the really excellent selection of aftermarket heads available these days (wow! Nothing like this available 20 years ago that I could afford). Just STUNNING flow numbers for out-of-the-box heads. One problem.... everyone seems to be using what we used to call "open chamber" head design. BIG chambers, especially on a wee little 454. Around 120cc is typical. I guess they need the room around the valves to help get those flow numbers which is cool, but causes other problems.....

It takes some serously domed pistons just to get compression up into the mid 9s (assuming no block decking or milling of the heads). On the order of 25cc domes with a typical .040" thick head gasket (11cc).

Yeah, I know, zero deck the block, mill the heads and use a smaller dome, right? Well even if I zero deck the block and mill the heads down to 114cc I still can't get into the mid 9s with a more reasonable 12cc dome. Plus I hate milling the crap outta good virgin castings for no good reason. Game over, right?

I'm staring down the barrel of some serious piston domes unless somebody's got a better idea. As always, thanks in advance for any help.

 

Well first of all, you can buy a Mahle piston pack.
Mahle designs their pistons to sit higher in the block so you get a psuedo "zero-deck" by using them. Plue they really are nice products.

As to heads, lemme whip out my handy dandy scoggin-dickey catalogue...

Then you can use a set of GM aluminum oval ports from scoggin-dickey.
110cc chambers and hardened seats. 290cc intake ports. Supposed to have good velocity.

PN: 12363399 - Bare -------- $660ea
PN: 12363392 - 2.19/1.88 --- $890ea
PN: 12363390 - 2.25/1.88 --- $890ea


OR...

I don't know if this might be too small for you or not...


You can use the L29 Vortecs.

99cc Chambers. That's not a typo. Ninety Nine CC chambers.

PN: 10141280 - 2.065/1.725 --- $430ea

They even had a flow chart in the catalogue:

.200 = 121/91
.400 = 198/133
.600 = 242/142


Oh....

Edelbrock has some 110cc heads too. About $940-950ea.
Supposedly good for 540hp, according to edelbrock.

 

even though they arent the greatest heads on the market, edelbrock is a good answer for your situation. thier oval ports come in both 110cc and 100cc chambers out of the box, and dont have raised exhaust ports in case you have a tight header clearance issue. i still recommend zero decking the block or at least shaving it .020 to try and get some sort of decent quench. with the dope i'd be shooting for forged pistons. also if you dont want to mill the crap out of the heads probe and wiesco make pistons with about an 18cc dome so if you get down to 119cc chambers or so you'd be hitting mid 9's. i know where you're coming from on piston selection being crappy for a 454 bbc though. i recently dealt with that myself, ended up taking 50 off the heads and zero decking the block so i could get by with ~12 cc dome, all in the name of a 9.5cr.

also... as i've said a few times before... go for a roller in a bbc, it beats the hell out of taking it apart and cleaning it out after a cam fails. also keep an eye on what the head makers have done with the ex port some of those companies like to raise em up quite a bit which is good for flow but in some cars can push you into custom header terretory real quick.

 

With a 200 shot of giggle-gas, you need some strong pistons and proper ring gap....I don't know if the mahle's can take that kind of abuse with their 1.5mm ring sets....havent gotten to try it yet.

My recomendation would be avoid the nos, go roller cam, use a 13cc dome piston with the trick flow 320cc R series heads.

 

1.5 mm is .059". That's just .003 thinner than a standard 1/16" ring package. Many nitrous combinations use .047" top rings, durability on nitrous with the 1.5 mm ring is not an issue. The 5 liter Ford used 1.5mm top rings since the mid 80's with a ton of nitrous/forced induction usage.
The power level you are shooting for is easy to obtain with less than exotic parts. Factory oval ports from the late 60'swill get you there or you can use an aftermarket head. I would consider a forged Federal-Mogul piston with a factory casting. They will hold up to aggressive nitrous use and the availability and price is good.
If you use an aftermarket head with a revised chamber check out the SRP line of JE pistons. They have good fitments and the price is right.
The TrickFlow 320s are choice heads and are a high quality casting, but they might be tricker heads than what you really need.

 

The intake ports are a bit on the large side at 345cc, but if you want small chambers you might consider the Merlin X 16° heads. 80cc chambers on top of 454ci shouldn't need much of a dome for 9.5:1.

 

You are right - I wasnt thinking when I typed that.

We just did a roller 489 BBC mild street motor that made 500rwhp on pump gas, used the bigger trick flows(340/2.25"int). If you want the basic receipt i can tell you the cam and other basic specs, its not to expensive of a build. You can also pick up late model 454 roller blocks for cheap, and they are all 4-bolt main

 

I know how domes are out of style and all, and probably for good reason. But there are plenty of big block Chevy's around running domes without a problem and making hp. I would zero deck it and use the dome needed to get the desired CR. Just IMHO.

Rich

 

Thanks, guys, you've certainly given me a lot of options to look into here and that's exactly what I was looking for.

T3RROR also raises another good point which I have considered but didn't bring up in this thread- lots of the aftermarket BBC heads have the exhaust ports raised by A LOT! .300-.375" being typical. I'm researching header clearance right now BUT that's a little tough to do since I don't know what car I'm putting this motor in yet!

Roller cam? Eh........ maybe later. It's just not in the budget right now. All the serious money is going to be plowed into the heads for round 1 which is why I'm concentrating on that for now. Flat tappet mechanicals have worked for me many many times over the years, including big blocks, and while a wiped cam can happen it's really very rare in the grand scheme of things.

 

Uh oh, you just struck a bundle of nerves there... run for cover!

 

Hell that's ok. I said .047" when I should have said .043".

 

Flat tappet will work for the next 20 years also.
Just not the fashionable thing to do.

 

I looked in some of my catalogs for you today, and wiseco makes one of their Pro-Tru pistons that would work well with a 120cc chamber... I think it was a 16-20cc dome...let me know if you are intrested I can confirm a part number.

 

Because of the valve orientaion, a dome piston for a BBC works fine. My old 781 casting oval port heads and my aluminum Canfield rectangular port heads have the open chamber 119cc. The open chamber allows room for bigger valves and it unshrouds the valves. If you want to make the chamber smaller, you can always have the heads milled down.

Because mine is a race engine running on alcohol, I want as much compression as I can get. My old 469 (+.070 454) was around 13:1. My new 540 has an even bigger dome and works out to around 14.2:1 with the open chamber heads. I only use JE race pistons and not the cheaper SRP ones. The lighter the piston, the better. When I had my 540's rotating assembly balanced, they still had to add weight to the crank because the pistons weren't light enough. If I had a smaller dome, the weights on the crank would have probably been a lot closer to perfect.

SBC engines normally want a flat top design but BBC can easily use a dome piston to bump up compression.

www.jepistons.com

 

Yes, any part numbers would always be appreciated. I like things nice and specific when it's time to actually put it together and make it all work. Which should be around the middle of next month.

Stephen- I was wondering about that. I can't recall putting together a big block WITHOUT domes in the past (I don't do a lot of big block Chevys, though). I suspected something like that might be going on. Certainly the head manufacturers don't seem to have any problem forcing their customers to use heavily domed pistons or they wouldn't all be making heads with humongous combustion chambers.