Can anyone give me an idea of what the dish (in cc) is for these pistons? I'm guessing -27cc, but I slept through math classes!

http://store.summitracing.com/defaul...22410%20301507

 

The math doesn't exist to figure the displacement of the dish, from the info given. Give Summit a call. Caution! There is no quench surface on those pistons.

RACE ON!!!

 

Why the caution?

 

"There is no quench surface on those pistons."

RACE ON!!!

 

Just in case you are still lost as to what CFI-EFI is saying here is a little tid bit about what quech does.
The quench area is the flat part of the piston that would contact a similar flat area on the cylinder head if you had .000" assembled quench height. In a running engine, the .035" quench decreases to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity through the combustion chamber. This movement tends to cool hot spots, average the chamber temperature, reduce detonation and increase power.


Jason

 

Tnx for the explanation. I won't know for sure until I pull the heads, but I believe those are the pistons I have. My plan is to replace the heads this winter from the stock 76cc to 64cc to increase compression to be more suited to the cam. What are the chances that an increase in compression with those pistons will lead to detonation or other problems? The motor runs surprisingly strong as it is, no detonation, 87 octane, steady 180 degrees, but I know there's lots more to be had, especially down low, by getting closer to the right combination. I was thinking of some 292, 041, or similar heads. May also consider Dart, but don't want to spend much dough on this motor.

 

No surprise, there. With 76 cc chambers and a .160 dish piston, it probably wouldn't knock on kerosene. A tight quench area promotes faster more efficient combustion in any engine, but as the compression is increased, so is the need for a good quench area. With the piston, selected, there is almost no flat area on the piston to match up with the flat portion of the head. Even with a properly designed piston, it is likely you will have to have the block decked to get the piston to head clearance down to the minimum preferred, .035"-.040". The head gasket, compressed thickness, is an important factor in this. It takes a little planning, to do it right. You shouldn't just slap an engine together with what is readily available.

RACE ON!!!

 

If you are planning on pulling the motor down and upping the compression I would look to flat top pistons to achieve the desired compression ratio and maybe some simple porting of the heads you already have to improve on flow #'s... I really think that would give you the most bang for your $$. The investment in new heads while using those dish pistons sounds like a less desirable path to performance to me.

Hey if you don't plan on boring out the block I have some stock cast Flat top pistons out of my 1992 LT1 I'd be willing to sell. email me if that sounds interesting to you..
jswooldridge@verizon.net

 

Good comments, guys. I wasn't planning on pulling the motor, and the existing heads are really in sad shape and would need to be reworked anyway. That would pretty much mean a major rebuild. I'm not crazy about the cam I have, so if I was going that far, I'd swap that out as well. If I just replaced the pistons, I'd still have lousy heads, and I don't think they're worth the effort or $$ to rebuild. I have a tendency to catch the 'while I'm it' virus, so I'd probably end up just reusing the existing throttle cable!

I'm guessing that my compression is pretty low. Static is 135 psi with the .228@.050 cam. I was guesstimating #'s with the online calculators, and come up with 7.9 - 8.1 with the 4.155 bore. I don't have enough info to get it right, though. If you want to take the time to figure it out, I can list all the specs I have, but you'd still be missing some info, such as deck height.

If my only option for now is to swap heads, what would you replace them with? I was going for 64cc to up the compression, which may still be lacking, but wouldn't I still realize an improvement? I figured bringing the compression up a point or so, plus better heads would wake this thing up a bit.

 

Those pistons are going to be too loose in his bores. Your LT1 has a 4.000" bore. The pistons in the link are for a 4.125" bore, IF he doesn't bore it.

It is already .030" over? If so, why the new pistons? You weren't going to bore the block "in the car", where you?

To figure your compression ratio, use a deck height of .025". It may be greater than that, but it will get you pretty close. That is why I said you will want to deck the block to get a good quench. Also, regardless of what piston you select, look, closely, at the compression height. A replacement piston, like you linked, often has an additional, .010"-.020" deck clearance. Know what you are doing, before you have the block decked... in the car???

RACE ON!!!

 

The motor was already rebuilt when I bought the car. Bored to a 4.155 406 with those pistons installed, along with the Crane 284 cam. The receipt shows the pistons to be TRW 400NP-30, which I'm assuming is the same as the STL in the link. Won't know for sure until I pull the heads. No indication that the heads were rebuilt - and they look it. It's not the way I would have built the 406, but I have what I have....for now...

 

[QUOTE=CFI-EFI]Those pistons are going to be too loose in his bores. Your LT1 has a 4.000" bore. The pistons in the link are for a 4.125" bore, IF he doesn't bore it.
QUOTE]


Sorry My fault I wasn't paying attention... I do have some Flat tops for the engine but I'm not ready to give those up just yet..