Visit The Dirt Forum for More Information

Author Topic:   does anyone make these pistons?
dode
Dirt Freak

Total posts: 417
posted July 11, 2002 03:57 PM UIN: 13209501
I am looking for an off the shelf flat top piston that will yield a 9:1 compression ratio with a 64 cc head. Does this exist? I am not even concerned about rod size at this point. Thanks.

John

6pack
Dirt Maniac

Total posts: 128
posted July 11, 2002 08:45 PM
With a 64cc head you'll probably need a dished piston to get 9 to 1, unless you have considerably more than zero deck clearance.

BayouGent
Dirt Forum Racer

Total posts: 87
posted July 12, 2002 01:24 AM
Oops I missed in one of your earlier posts that you are running flattops already. Stock chevy 4 eyebrow pistons with a 76 cc chambered head yielded 9.5:1 compression in 1970, according the the books. Just out of curiosity...why are you wanting to stay with a low compression ratio? The 64 cc heads with flattops should give you at least 10.5:1 compression which that cam you are wanting to use would like MUCH better. Just my opinion.

dode
Dirt Freak

Total posts: 417
posted July 12, 2002 08:16 AM UIN: 13209501
**** rules...9:1 comp ratio rules suck (and they do check). I would love to run higher, but I can't. Our rules read that we can run any cast iron OEM head. Says nothing about not running vortec or anything. However, we must run flat tops (it also says nothing about rod length, and I know a lot of them are running 6" rods). I am just trying to find a better set of heads than 882's or 993's that will work. Surely there is some way to do this without paying Ross or JE like $1000 for a set of custom pistons. Thanks.

John

Monster
Dirt Maniac

Total posts: 135
posted July 12, 2002 05:22 PM
Do you have to run flattops AND 9:1, or does the rule say 9:1, with no mention of pistons? Even if you have a custom flattop made, if it is too far down in the hole, very bad things can happen. Once deck clearance starts to get much over .075 total, the whole bore starts to act like a huge inefficient chamber, and will tend to detonate very easily. Another option is to get a set of inexpensive flattops of adequate strength, and have the tops machined down, or have a dish put in. Pretty quick and simple operation, IF the shop is equipped for it. I believe even TRW does this on some of their own pistons.

dode
Dirt Freak

Total posts: 417
posted July 12, 2002 05:36 PM UIN: 13209501
The rules say flat tops AND 9:1. They suck. Cast iron manifolds too. Is there any way around this? There has to be something...It wouldn't have to be that far down in the hole...I mean I only need to get an additional 12 cc, which would be like .06" less compression height. Could I mill pistons to get this? Anyone have any ideas?

Monster
Dirt Maniac

Total posts: 135
posted July 12, 2002 10:18 PM
OK, here are some more ideas if you need 12 cc's. I don't know how much they'll each give you, but should not be too hard to figure out. Turn some material off the deck of the piston. I made a set of aluminum lathe jaws that hold a piston by the oil ring groove, and make this a simple operation. As per my last post, I would not make the total deck clearance more than .065, but this is just me. Others who have run them way down in the hole like this would have a better feel for what you can get away with. I usually set them the other way, like REEAALLYY close! Make the valve notches absolutely huge, and put more than one set in, maybe more than 2 sets, all under the head's chamber! Borrow a trick from Chevy(and others), by machining a very large(we're talking about 1/4" or so) 45 degree chamfer around the outer edge of the piston top. This will give a lot of cc's without the bad effects of the large deck clearance, and it will also give in effect, a much higher top ring placement, in which area most economical pistons are lacking. High top rings are good for power. The particular piston will dictate the angle and depth. This and the deck cutting would be first on my list, then the valve notches. By the time you do all this work to a set of pistons, that custom set will look a whole lot better to you, hang the cost! They also could be about 150 grams lighter. Each! Get a copy of a TRW/SpeedPro catalog, all kinds of piston sets and info in there. I'm sure you will find something that will work.

Flatlander
Dirt Freak

Total posts: 310
posted July 13, 2002 08:05 PM
try to find some Dcup pistons I think that they make some that will bring it down for you

dode
Dirt Freak

Total posts: 417
posted July 15, 2002 08:45 AM UIN: 13209501
Those D-cups won't meet the flat top rule though will they?

John

Flatlander
Dirt Freak

Total posts: 310
posted July 16, 2002 03:45 PM
I would argue that point all flattops have indentations some 2 some 4 When we get checked they shine a light and use a feeler and if there is a flat surface and no dome it's considered a f/t in my feeble mind

Racer14K
Dirt Freak

Total posts: 247
posted July 20, 2002 01:06 PM
John, in the Sealed Power catalog a flat top piston with a .025" deck height,compression rates at--
64cc head
STD.--9.61
.020--9.69
.030--9.73
.040--9.77
.060--9.85
68cc Head
STD.--9.21
.020--9.29
.030--9.33
.040--9.37
.060--9.45
72cc Head
STD.--8.85
.020--8.93
.030--8.97
.040--9.00
.060--9.08
76cc Head
STD.--8.52
.020--8.60
.030--8.63
.040--8.67
.060--8.74
It does not say what head gasket thickness was used for these figures but most ratings are done with a .042" to .045" head gasket. These ratings would be higher if you use the steel shim head gasket which is .020" thick.

Back to the Archives