340 .040 over pistons for Zero Deck...Where to find?

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Propwash

Propwash

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Hey gent's....

Getting into the 340 build for my wife's '71 Dart. I'm building this motor for Quench. Along the way I decided to go with an Eddy Performer RPM Alum. head, 63CC closed chamber. The motor is getting punched .040 to eliminate some rust issues at the bottom of a couple cylinders.

Anyways, I'm trying to build for zero deck for my quench, with a stock stroke. One thing that is giving me grief is all the pistons I find are for the earlier high comp 340's with a compression height of 1.84, which puts the pistons above deck. I know there was the later 340 with a comp height of 1.74 (below deck pistons), but I can't seem to find pistons anywhere for that. The block will need the deck shaved a tad, so that put's a 1.84 piston even higher up.

Searching through the threads here I see folks have shaved the pistons to achieve a zero deck and then run a .039 gasket for their quench. With the deck coming down, i'm just hoping I can find a piston with a comp height more in the 1.70-1.74 range. I think if I found those piston's it would be easier to dial into zero deck than shaving the crap out of 1.84's. Any idea's or sources out there?

Thanks,

-Will


BTW, Pep boys has a sale going to the 24th, 25% off any order of $100 bucks or more, + free shipping. A set of assembled Eddy Performer RPM heads shipped to my door was $1050!
 
I like DSS pistons...1.802" CH

http://www.dssracing.com/6300X_p/6300x.htm

They're in the hole .020" by the math, but you can shave that off the deck.

There's also Ross pistons, and I bet Diamond makes a couple great sets.

EDIT: 1.70-1.74" CH would put you in the hole by .060-.100" depending on where your deck height is...
 
A few thoughts -
1. If the rust is low in the bore it's not critical. it may not ever even get near the rings. So you might not need to get anything funky unless you wanted to.
2. There are various ways to skin the quench cat... Most pistons are designed to come up proud of the deck when installed in a deck machined at blueprint height. But most decks are significantly taller than blueprint height. So unless you are instructing the shop to blueprint the deck height, or giving them a deck height to cut it to, then you really don't know where things are. If you are serious about building for quench, you need to have the deck square decked either to blueprint or to a height that works for your rotating assembly. Simply standard decking for flatness is not enough accuracy.
3. If the pistons you ultimately decide to use are proud, you can always run a head gasket that will set the quench you want. I only use FelPro 1008 with aluminum small block heads becuase of the pre-flattened fire ring. That's a .039 compressed gasket. IIRC 9.600 is blueprint. If you have the deck square decked to 9.6 then the pistons designed for +.018 above deck will come out around .016-.020 above due to stroke and rod variences. So you will have to have the pistons milled down by .015 to get the quench to .035 or so. If your deck is taller (and the shop that can square deck can also tell you this easilly) then have it square decked to 9.615.
 
Hey Thanks Fella's....I appreciate your input. I guess i'll wait to see how she sits after the deck is squared away. I do appreciate the link for the pistons. I sure couldn't find any with that compression height. Still nothing for the 1.74's. Starting to wonder if anyone makes them. I'd like to keep the piston shaving to null or minimal and that at least gives me options with the gasket & piston options.
 
I don't know of any OTS pistons with that CH with a SBM pin diameter...besides, if you need THAT much of a reduction in CH, the deck may've been cut a little more than normal, and dare I say too much. Like moper said, the blueprint deck height on a SBM is 9.6", and those DSS pistons I quoted above, even with the 1.802" height are .020" in the hole with a blueprint height...he also mentioned most uncut blocks are taller than 9.6" so unless the block has been cut--a lot--you probably don't need anything that short.

Working with your numbers, a 1.74" CH piston, with a stock 3.31" stroke crank, and a 6.123" stock rod, will put your pistons to 9.518" above the crank centerline at TDC...that's .080" in the hole for a blueprint cut block (9.6")...so, why are you particularly looking for 1.74"?
 
I'll add - it's usually minimal $$ to have them wing off a little from the piston tops with a Bridgeport. It's super-easy and normally less than an hour's labor.
 
Only thing I saw that was close also is SRP-310725. They are a .040 piston with 1.804". I use the same piston in a .030" over version and mine sit .020" in the hole.
 
Thanks guys! Before your enlightenment, I was going off the standard train of thought of the all high compression pre '72 pistons always rise above the deck and the 1.74's from '72 up (low comp) are the ones that sit a tad below deck. My ignorant/simple line of thinking was I need to find the 1.74's to get close to that zero deck, especially considering the deck needs to be shaved. Now that you guys took the time to explain the geometry/dynamics of it all, 1.74's are not the ticket. So I appreciate you clearing that up for me.

The engine is in a bit of limbo with the machine work right now. Still waiting on the bore to get done as well as a line hone below. I know the deck will be coming down, but still unsure how much (not a whole lot). This motor will be in the 400HP range, so i'm guessing it's safe to say I'll need to run a decent forged piston? One more question for you guys if you have time...Would it be safe to say I could probably go with the 1.84's with the possibility of just shaving the pistons a tad? Those pistons I see all over the place.
 
Would it be safe to say I could probably go with the 1.84's with the possibility of just shaving the pistons a tad? Those pistons I see all over the place.
Click to expand...


Answer:

moper said:
I'll add - it's usually minimal $$ to have them wing off a little from the piston tops with a Bridgeport. It's super-easy and normally less than an hour's labor.
Click to expand...

Yes...like the man said. It really depends on what you want to do with the engine. The KB hyper pistons are good units, and readily available along with Speed Pro forgings (both of them would need a quick mill to zero in a 9.6" blueprinted block). The DSS and SRP ones mentioned above are typically available--a quick call to a distributor could clear that up. The advantages of running forgings are simply that you can put them through more abuse...but the Speed Pros mimic the original 68-71 forgings, and therefore are pretty heavy. Other brands are up to a couple hundred grams lighter and use a lighter and low friction ring pack, but typically cost a little more.

Also with the DSS and SRP slugs you'd be milling the decks to zero the pistons...which arguably should be squared and equalized during a good rebuild anyway.
 
Thanks Tx! Much appreciated sir. Just getting back into small blocks and it's nice knowing folks like yourself, moper and duster360 that have the knowledge & experience to get me dialed in. Thanks for your input & time!

-Will
 
I run the KB Hyper .40 over, only off the shelf pistons i could find, they sit .022 out of the deck, and i run a .066 head gasket for 10-1 with the eddy heads and the 63cc chambers
 
Take a look at Mahle forged pistons ,they have taken a beating in my car for 5 years , no problems . Decent price as well
 
cometic will make any gasket thickness you want....research the pistons and rings and find what you like. a set of custom gaskets are about $175...and are reusable according to cometic....
 
65Vsignet said:
I run the KB Hyper .40 over, only off the shelf pistons i could find, they sit .022 out of the deck, and i run a .066 head gasket for 10-1 with the eddy heads and the 63cc chambers
Click to expand...

Thanks for the heads up '65! I'll be shooting for around 10:1 as well

jerry6 said:
Take a look at Mahle forged pistons ,they have taken a beating in my car for 5 years , no problems . Decent price as well
Click to expand...

Thanks Jerry! I'll definitely check'em out sir.

abody said:
cometic will make any gasket thickness you want....research the pistons and rings and find what you like. a set of custom gaskets are about $175...and are reusable according to cometic....
Click to expand...

appreciate it abody! I've heard of those.
 
While I greatly appreciate the accolades, I deserve no thanks here, man-moper and many like him on this site have legitimately been building engines for years...I've just been workin' for Uncle Sugar's AF for about 18 years now. In my off time, I've assembled parts together than ran pretty well in a few instances (mostly SBFs and a couple SBCs), but those guys will steer you straight.
 
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