Yep, the more the dome, the more you should pay attention to quench. Its relevant on all wedge pistons (Dont matter on the hemi heads). I'd keep it under .060 and thats the absolute max I'd consider using to prevent detonation and promote flame travel. I think .038-.045 is probably safest and what I would shoot for. Some guys like less all the way down to zero but I 'd pass on that set up if you're into reliability.

Reference off of the flat part of the piston furthest from the plug. Dont forget to figure gasket thickness in there as well.

 

hope it will run on pump gas

Yep, the more the dome, the more you should pay attention to quench. Its relevant on all wedge pistons (Dont matter on the hemi heads). I'd keep it under .060 and thats the absolute max I'd consider using to prevent detonation and promote flame travel. I think .038-.045 is probably safest and what I would shoot for. Some guys like less all the way down to zero but I 'd pass on that set up if you're into reliability.

Reference off of the flat part of the piston furthest from the plug. Dont forget to figure gasket thickness in there as well.

I hope it will run on pump gas. I am running a cam with quite a bit of duration. I think it will bleed off some of the comp at lower speeds. thanks philr

 

A .125 dome piston with 64cc heads will yeild a pretty stout compression ratio for pump gas. Do you have access to super high octane gas if you need it?

I hope it will run on pump gas. thanks philr

 

At the risk of sounding like a dink, this aint the time to be "hoping" it will, and "thinking" it will. There is basic math available to put your compression ratio exactly where it needs to be. Thinking and hoping usually results in wishing you'd done it right. Wishing it was right always costs more then doing it right.

So, I am "hoping" that you're "thinking" that you're "wishing" to build it right the first time and enjoy it without doing it twice.

 

do you have the formula?

I based this piston combination on a another thread advice. He had about the same combination 10.75 comp and 292 dur. and 488 lift and he said it worked fine.If you have any ideas tell me I havent even taken the engine apart yet. thanks philr

 

compression

I prefer flat top pistons with low cc heads. This combo seems to alleviate quench questions. I try to hit anywhere below 11 to 1 using this combo.

The .100 dome piston, also known as the 11 to 1 piston used in the Corvette LT1 motor, ran on pump gas with no problem. Maybe you should go that route.

I just built a 400 sb, zero deck, .030 flat tops, Edel 70cc heads. This puts me at 10.8 to 1. Since I am using aluminum heads and a fully adjustable distributor. I have better heat disapation and can lower my static time and raise my total. There is also the option of recurving the dist to stronger springs. Regardless, I am not worried about 10.8 to 1 compression.

 

If your heads are aluminum, 11:1 and below should work.

Adam

 

camel 202 heads

they are cast camel 64cc heads. thanks philr

 

I had a 355 with 64cc Vortec iron heads with flat top pistons with dual reliefs. That motor measured at 9.98:1 compression. It ran well on 93 octane, but it dieseled when you shut it off unless you left it in gear. I think that was on the edge for pump gas. My cam was the XE268H.

Adam

 

Very good advice already offered. I agree a flat top piston is a far better way to go. Domes are "old school" only needed in very high compession engines that you can't get there with smaller chambers. You will make more power with a flat top.

You will have "issues" trying to run that much compression with iron heads.

Might be time to re-think the combo a little. Hopefully you haven't bought any parts yet. If you have a goal in mind and specific use of the car as well as, as many details as possible about the car (weight, tranny, stall, rear gear ratio, etc..) There are a lot of wise/smart guys here that can help you reach your goal. If you learn one thing from this thread listen to what Maynard said "It's cheaper to do it right the first time" Almost all of us have learned that the hard way (me included). Save a dime now spend $100 later.

Royce

 

already bought pistons

I have already bought pistons and I am going to have to use the pistons.I have exhusted my budget.I was going to get flat top pistons but changed my mind.I bought a good set of 345 pistons off ebay but they are .020 in hole pistons and I didnt want to use them.I am going to rethink this thing anybody else got any comments or answers welcome thanks phil

 

That's going to have some compression for sure!

Maybe you can polish the combustion chambers & piston tops to gain some CC's in addition to running a
circle track style cam with a 104*-106* lobe seperation that will bleed off some of the gasses at lower speeds. {Not too good for bottom end power or gas mileage mind you but hit 4000 rpm and it'll pull like there's no tomorrow!}.


-or-
use the NP345's with a .026" or .015" steel shim head gasket and eliminate the quench & compression worries you have using those pistons...the correct solution to this financial situation

 

do not care about gas mileage

That's going to have some compression for sure!

Maybe you can polish the combustion chambers & piston tops to gain some CC's in addition to running a
circle track style cam with a 104*-106* lobe seperation that will bleed off some of the gasses at lower speeds. {Not too good for bottom end power or gas mileage mind you but hit 4000 rpm and it'll pull like there's no tomorrow!}.


-or-
use the NP345's with a .026" or .015" steel shim head gasket and eliminate the quench & compression worries you have using those pistons...the correct solution to this financial situation[/QI UOTE]

 

thats all I can afford for now

Just something to consider. With that much compression and cam, those heads are going to be the weak link in making any power. In there day, they were good heads, but now days they are old hat. You might want to consider some better flowing heads to go with all your other upgrades.

Mark

I hope I can make some decent power with these heads.This is not a daily driven car and ocassinal strip for fun. Anybody else running anything like this? Thanks philr

 

quench

Yep, the more the dome, the more you should pay attention to quench. Its relevant on all wedge pistons (Dont matter on the hemi heads). I'd keep it under .060 and thats the absolute max I'd consider using to prevent detonation and promote flame travel. I think .038-.045 is probably safest and what I would shoot for. Some guys like less all the way down to zero but I 'd pass on that set up if you're into reliability.

Reference off of the flat part of the piston furthest from the plug. Dont forget to figure gasket thickness in there as well.

what would the quench be with.025 deck,64cc heads,.125 dome.What head gasket would you use?

 

quench

Yep, the more the dome, the more you should pay attention to quench. Its relevant on all wedge pistons (Dont matter on the hemi heads). I'd keep it under .060 and thats the absolute max I'd consider using to prevent detonation and promote flame travel. I think .038-.045 is probably safest and what I would shoot for. Some guys like less all the way down to zero but I 'd pass on that set up if you're into reliability.

Reference off of the flat part of the piston furthest from the plug. Dont forget to figure gasket thickness in there as well.

what would the quench be with.025 deck,64cc heads,.125 dome.What head gasket would you use? thanks philr

 

your quench is the gap between the flat part of the piston top and the flat part of the chamber at TDC (top dead center). Example if your piston is .010 in the hole and the head gasket is .035 thick you have a quench of .045.

You want to keep the quench .035-.045 anything tighter and you run the risk of the piston kissin the head. Anything more and you really no longer have a quench.

A good quench will help you fight off detonation. I still think you are going to have problems with that much compression and the old school chamber design. What good is the engine if you can't drive it? Put the pistons back on e-bay and try to get your money back out of them. Find a decent set of flat tops and save up for some decent heads. You will be glad you did.

Royce

 

maybe I missed something? You said you bought a set of these>
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33623&item=7985053950
off eBay?

They say "9.4" with a 64 cc head.

but they are .020" in the hole you say?

drop the GM .026" steel shim head gasket on it.

your quench will be:
.026 + .020" = .046"

and your compression ratio will be about 10:1.

Just about perfect!

 

I bought a good set of 345 pistons off ebay but they are .020 in hole pistons

I thought 345 was "345np", a TRW part number for a 4-valve relief flat top.
does the 345 come in a dome also?

 

345np pistons off ebay were used

The speed pro 618 pistons are new.thanks philr

 

You could run the combo with a larger cam, the 292/.488 is a very old school grind and has a fairly wide Lobe Seperation Angle-probably 112. I ran the same cam back in the late eighties. If you do the math and chose the cam acordingly shoot for a dynamic compression ratio of about 8-1.

 

290 duration and 488 summit hyd cam

That is what cam I will be running. 64cc camel heads, 618 speed pro pistons .125 dome thanks phil r

 

The summit cams are for lower compression engines. the lobe sep is too wide for that kind of compression.

 

probably in trouble

I thought these pistons would work with this much duration but I didnt know for sure.I have had a lot of suggestions and I appreciate all of them.I just wished I would have posted some questions first.I was going to put flat top pistons in it but I probably went overkill. I should have stuck with the flat tops. Thanks philr

 

Phil, A good friend of mine built a 350 that was bored .060" and ran those pistons with a set of the 64'cc 186 casting camel hump heads. He used a generic hydraulic cam from PAW with an advertised duration of 300 and .500 lift. His engine ran fine on premium pump gas and would run OK on regular unleaded if he pulled some timing out. The car made plenty of power and started out as a 4 speed then later switched to an automatic. You can build with those pistons if you choose the proper cam, what you want is a cam with enough duration so that the intake valve closes late enough that the actual running compression ratio will be 8-1ish. Is this an automatic car? Bob