looking for the closest to original pistons for 71 440 Six pack

[Fm3 Dart]

I'm rebuilding a 71 440 Six Pack. Completely stock. I would like to use pistons that match the original specs for compression. I see the Keith Black KB 237 pistons appear to have the same compression height. Anyone have experience with these pistons? Other than the modern head gaskets being thicker, everything will be stock specs

 

[BSB67]

Sealed Power/Speed Pro 2355

 

[BSB67]

On second thought, the 2266 might be the right piston for 1971.

 

[Gunner1]

I have the 2355 pistons in my uncut block. Came in at .017 down the hole.

 

[Fm3 Dart]

my factory installed 440 Six Pack pistons are zero deck.
Edit: Close to zero deck. I have it all apart, and did not measure before pulling it apart, but they were visually very close to zero deck.

 

[Curiousyellow71]

I have not been in a 71 six pack, but I have been into a low mileage 70 which I can verify the 2355 is real close, usually the oem piston has a slightly higher compression height. The compression was only .2 lower in 71. I don't know what they did (or if) they lowered it. The advertised compression seemed to be very subjective, most of the six pack engines were actually mid 9's for compression. I would use the 2355. It may be correct?..and if it isn't it will be closer then anything else.
Since I have never owned a 71 six pack, I am not sure what heads a 71 had? 346 or 906. A 346 usually has a a couple more cc chamber then a 906, which would lower the compression slightly.
Possibly someone can chime in on what heads a 71 six pack ran?

 

 

[Fm3 Dart]

I just compared the Speed Pro pistons, and the 2355 looks closest in compression height and it has 4 valve reliefs like the factory pistons have. But if it is .017" down in the bore like Gunner1 says above, then its lower compression than stock. The 2266 looks very low compression

 

[RemCharger]

Not a 6 pak expert, but I thought the 71s had 346 heads, and all 6 packs had the 6 pack pistons..

 

[Curiousyellow71]

I just compared the Speed Pro pistons, and the 2355 looks closest in compression height and it has 4 valve reliefs like the factory pistons have. But if it is .017" down in the bore like Gunner1 says above, then its lower compression than stock. The 2266 looks very low compression

Speedpro/trw forged replacement pistons are typically shorter to compensate for the extra compression gained from the larger overbore. Their pistons are also comparable in weight to the oem.

 

[Fm3 Dart]

Yes, 4 valve relief Six Pack pistons, and 346 heads in 1971

 

[33 IMP]

I doubt that a 71 sixpack motor was zero decked from the factory, at least not intentionally. And you are looking at forged pistons, sixpack pistons were cast. Frankly, I would build it for the compression you want, without worrying a minute if the pistons were anything like the stockers, or not.
I would use the 2355 "sixpack" forgings, and leave em a little down in the hole for better s#!t gasoline tolerance.

 

[Fm3 Dart]

at this moment, It's a toss up between the Speedpro 2355 forged pistons, which have a 2.061 compression height, and the Keith Black Silvolite 237 Hypereutetics, which have a 2.067 compression height. Both are close to the factory specs, although the 237's have only 2 valve reliefs, which isn't a problem.

The 2266 has only a 1.991 compression height, so that one is out of the question.

 

[Curiousyellow71]

A hypereutectic is just a cast piston made w a stronger alloy. Forged is considerably stronger, the 2355 is nearly 200 hundred grams heavier then a 237... a 2355 is a drop in replacement piston for what you have. My preference would be neither of those choices for performance if you are having it balanced. I would look at a icon, wiseco or srp. Depends on what you want from it. I have seen forged pistons take a beating...and a cast piston literally shatter. If this is a original engine use a forged piston...imo.

 

[BSB67]

Technically, the 69 6 Pack did not have the commonly referred to “6 Pack” pistons. They had the std. 4 bbl pistons.

The 2355 forged is the replacement piston for the factory cast. It’s the same in every meaningful way. Piston with pin will be within a few grams of the factory original and the CD within a few thousandths. They were approved for NHRA stock and Superstock back in the 1970s.

The factory pistons are typically 0.015” to 0.020” below the deck. Blueprint spec is 0.001” below.

If all you are looking for is a 2.06”-ish CD piston, there are a bunch available, most of which are better than the KB or the Speed Pro, IMO

 

[toolmanmike]

Forged would be my choice.

 

[Master Gunner]

Unless you change your cam to something with a little more duration than the stock cam, you're going to have to be carefull with compression with todays gas. Call the Hughes tech line, tell them what you're building, what you want to do with it, and they'll give you a good recomendation on what cam will work best.
Personally, I used the KB236 pistons, for mostly street with some strip use.

Mark

 

[Cranky]

my factory installed 440 Six Pack pistons are zero deck

Only doing the math will tell you if your deck is at blueprint height....and like someone has said already, factory engines usually ended up at .015 to .020 down.

 

[RJRENTON]

A hypereutectic is just a cast piston made w a stronger alloy. Forged is considerably stronger, the 2355 is nearly 200 hundred grams heavier then a 237... a 2355 is a drop in replacement piston for what you have. My preference would be neither of those choices for performance if you are having it balanced. I would look at a icon, wiseco or srp. Depends on what you want from it. I have seen forged pistons take a beating...and a cast piston literally shatter. If this is a original engine use a forged piston...imo.

Regarding pistons.....FYI..
Although not as strong as forged pistons, hypereutectic pistons offer increased strength that raises piston reliability at a lower cost. Hypereutectic pistons also don't experience as much thermal expansion as forged units, which means they can be mated to their respective cylinder bores with tighter tolerances.
A hypereutectic alloy is metallic alloy with a composition beyond the eutectic point. A typical alloy may have a substrate and a primary alloying element. Typically, the alloy is silicon carbide and aluminum and the silicon carbide alloy is added to the molten aluminum to the saturation point (where no additional alloying material will be absorbed) called the eutectic point.
Which is best????...I vote for the tried and true FORGED PISTON......just my opinion of course....
BOB RENTON

 

[1968rt]

This is what I have on TRW/Speedpro. The piston weights are close to factory pistons


Part# CH Weight Pin Wt CCs Deck Ht

L2266F 1.991 876 225 0 flat top .090
L2355F 2.061 872 225 -7cc .020
L2388F 1.926 819 225 0 flat top .155
L2295 2.029 817 250 13.1cc .140 dome .051
7025P 2.050 815 250 13.1cc.140 dome .051

 

[lewtot184]

so, why a factory 10.5:1 piston? is this a 100% restoration only? does it make any difference about what kind of gasoline will be used?