Hi all,

Just a quick question. I've been searching around for pistons for a 400 sbc that will have a 64cc chamber head. Problem is, the lowest inverted dome piston that I can find is -22cc which is advertised at a 9.8 compression ratio. Also, this is an SRP forged piston which is pretty pricey. Can anyone give me a reference to where I could find a hypereutectic piston that would yield a 9.5 compression ratio with a 64cc head? Preferablly Speed Pro? Thanks for any input.

Keith Black (Silv-O-Lite) has a 30cc D-cup Hypereutectic for a 400 with 5.7" rods that will put you at 9.3 with 64cc heads. It's part no. K126. Probably not cheap but I haven't found an inverted dome of any depth that was. I'm in the same boat on a 350/383 I'm trying to build except I have 58cc chambers and I'm trying to limit it to 9 to 1. So far all I have found are the SRP's but I'll probably bite the bullet and fork over for a set.

 

I think it would be better to run a flat top or smalll dish with a larger cc head like a 72 or 76 cc. This will allow for unshrouding of the valves plus you'll have a stronger piston(or at least a stronger piston $ for $).

 

I think it would be better to run a flat top or smalll dish with a larger cc head like a 72 or 76 cc. This will allow for unshrouding of the valves plus you'll have a stronger piston(or at least a stronger piston $ for $).

All other items being equal the "closed" chamber 58 and 64cc heads with D-cup pistons have been shown to produce more TQ and HP than the larger chambers with a shallow dish or flat tops due to quench area and swirl. Shrouding is not as much of an issue ( NOTE: I said "not as much".) because effectively the total combustion area does not expand beyond the perimeter of the cylinder head combustion chamber. The head chamber and piston cup come together to form a sort of flattened egg shaped chamber rather than the conventional wedge shape and with a traditional dished piston it isn't even a true wedge as it has area beyond the combustion chamber that is partially blocked off from the combustion flame travel. The D-cup pistons are just as strong as any other.

I believe it was John Lingafelter that did a comparison several years ago of a 355 SBC with small chambers and D-cups vs. a 383 SBC with flat tops and 76cc chambers. He tried to make the heads as similar as possible, of course there was some variation in flow but otherwise they were identical in every detail, compression, cam, etc. The 355 significantly outpowered the 383 at every point in the RPM range both in HP and TQ. How much of it was the port configuration of the heads is hard to say but he believed the effect was minimal. He then built the 383 with the same small chamber heads and D-cup piston design and the increase over the earlier set up was substantial. Enough to justify the added expense of the pistons.

I guess it's a matter of the specific application and the builder's needs as to which is better dollar for dollar. Large chamber heads with conventional dished or flat top pistons are definitely cheaper and will still make decent power but there is more to be had it's just a matter of how far you want to go to get it. I was going to build a mild 383 with 76cc heads, dished pistons and 400 rods but then I started crunching numbers and I can build a 355 with small chamber heads and D-cups running the same compression ratio and cam for about the same money that makes a little more power in the same RPM range give or take a couple hundred RPM. That tells me the 355 is more efficient so therefore should give me the same performance on less fuel. I'd build a 5.7 rod 383 with the small chambers and D-cups but the added stroke puts my CR over the edge with available pistons. If anyone sees an flaws in my logic holler, I'm open to all input.

 

Hippie,
your killing me here, with all this anti 76cc head stuff :sweat: i need a 76 cc 400cid motor combo thats gona move my 63 Nova, 350 375 HP range. i bought the 76cc heads to put on a 383 i was gona build, butt got a 400 SBC for a fair price, and plans changed, and with all the car build stuff i need, (you know drive train & body work ect. gota try to use whats paid 4) i want/need to use them.


Mustangsaly

 

The 76cc heads will do what you need no sweat. It's just that you can squeeze a whole lot more out of a SBC with the same cam and compression using the small chamber/D-cup combo but it does cost more. I built a 76cc/flat top 383 back in '82 and it ran great, I was thrilled with it but I now know I could have gotten a lot more out of it with different heads and pistons.

 

i found some of the stuff i need here at a reasonable price www.cnc-motorsports.com

just trying to help a little

J

 

Im using Mahle's

I just trashed the new hypertec pistons that i bought, for a new set of mahle pistons with a -20 dish for my 383, I had the machinist order em so I dont have a distributor name for ya but Im sure you can find em. Also they were 540.00 a set and their coated
Hope this helps
PS thats complete w/rings

 

Mahle's

I forgot to mention that their also forged

 

In my situation, I have to use a dish type piston cuz I already had the vortecs worked over and the intake to match. I have checked out that cnc-motorsports before and they seem to have pretty good deals on rotating assemblies. I think with all forged parts and dished SRP pistons, you can get it for something like $1575. Or you could go down to the street/strip assembly for like $1100 something, but hell for another $500 I would go all forged. That way I have room to grow in the future. Is a 9.8 compression ration going to be suitable to drive on the street without any detonation concerns?