Any idea on what the compression would be for a 78' 440 using L2355 forged pistons (Compression Height 2.061) and a 78cc closed chamber head?

Thanks.

http://www.csgnetwork.com/compcalc.html

About 10.6, give or take a .1.

I'm having my machinist get back with me on how far the new pistons are in the hole. This morning when I was tearing the motor down, the stock cast pistons looked to be about a 1/16 to 1/8th of an inch down the hole, just below where the tops of the piston chambers tapers. Don't have a depth gauge so can't give exact numbers on that.

I think the CH of the stockers is like 1.9 so the new 2355's should put it close to zero deck. I was aiming for 9.5 CR, would I run into problems with a CR that high? Would it be best to go with an open chamber design to drop the compression back down?

Below is a pic of one of the cylinders at the top of its stroke.

what is bore size? gasket thinkness and type? heads milled? deck milled?

pump gas? quench? iron or alum?

Don't have heads as of this moment. Just got my 452 heads back from the machinist and the valve seats have cracks showing after the magnaflux.

I'm going to buy a set of heads from aeroheads and have a choice of either open chamber 452-906 style or 516-915 style. Going with iron heads and pump gas.

The head gasket I'm looking at is the steel shim style with .040 thickness or maybe a standard felpro replacement.

So no on heads being milled, the block has not been decked as I think the higher CH with the forged 2355's will compensate for how far the stockers were in the hole.

That calculator you put up daytonaturbo is showing me almost at 11:1.

What are the benefits to quench or no quench?

Did you get that engine from a motorhome? The extra cooling passages between the lower head bolt holes gave it away. I am rebuilding one like it that's a 74 engine for a pickup for towing. Compression isn't real high in stock form probably between 8 and 9 to 1.

Those TRW's felt to be just slightly heavier than the cast ones but not that heavy.


Let me give you guys some more specs on the overall car.

- 71' Roadrunner
- 4 speed
- EZ-EFI Fuel Injection Kit
- 3.55 rear
- Plan on going with Hughes Cam

With the fuel injection, the lowest I want to go on the LSA on the camshaft is 110. What I'm lost about is these 2355's are basically "6 pack" pistons, so how am I hitting close to 11:1 with stock style heads and 6 pack pistons in a 78' 440 when they supposedly had a taller deck?

I plan on aeroheads simply for just the heads themselves. I'll be swapping all the hardware anyways to match what Dave or Kevin over at Hughes Engines recommends.

Good quench will also let you run pump gas with higher comp then you can run without quench and not have pinging or detonation. The camshaft selection will also help at controling cyl pressure as to high a cyl pressure will want to let it detonate more. Ron

82Ram,

Yeah I pulled it out of a 78' RV at pick-n-pull with only 30k miles on it. Paid 220 for the complete long block.

I never understood what people meant by those extra passages. They kept calling them "peanut" something passages.

From what I've read on other forums (should have taken that info with a grain of salt) the later 74-78 440 blocks were slightly taller and used a short piston in order to achieve 7.5 to 8:1 compression.

I'm getting 78cc because that is what aero heads advertises there closed chamber heads while the open chamber heads run larger chambers.

I'm re-using the stock LY rods that came in the 78 440 since they were in excellent shape.

The reason I asked that is because the stock 440+6 had compressions advertised at 9.7 to 10:1. That's why I asked because I was having an "o sh**" moment. So without decking the block I should be fine on pump gas and compression.

What heads did the majority of 440+6 motors use? 915 or 906? I know the last ones used the 346 heads.

you want to have the block squared at minimum. closed chamber heads are over 80cc stock so I would specify to aerohead that you don't want a set cut a bunch . Seriously there is nothing special about the head from aero , you could spend your money elsewhere more wisely.

440-6pks used 906's or the 346 in 71, 70-71 , which is the piston you are using , was rated at 10.5 , 69 was 10.0 and used a different piston. Both used a head with about 90cc or as much as 92 ...

I know there is nothing special with aero. I'm just looking for good cast iron replacements. Don't want to go with aluminums and deal with that. Just my preference.

I would like to just get a bare set from them rather than complete.

Are big block mopars really that prone to detonation? I know that working on a sbc that I never considered quench into the equation when I was building it and I've only ever heard the term with mopars. Did the factory ever utilize quench in most engine builds? Can you utilize quench without getting into high compressions?

First of all with a B or RB engine the steel shim head gaskets are available so having a piston 0.020" down in the hole is all right. Squish with a closed chamber head will be at the optimum 0.038".
Second, I do not believe the RB deck of 10.725" was changed from 1958 to 1979. But those motors' decks are all over the place and famously not square, tilted front to back or even side to side. So spend the money and get the decks squared and you can set your piston depth at the same time.
Third, the Speed Pros are meant to be a stock weight replacement.
Fourth, the closed chamber heads are better and of the two, 915s are the best. They usually came with 84cc chambers, so a 78cc head has been cut a bit. However, the newest of them is 45 years old and things happen.....
Fifth, you should know that MOPAR engines of that era usually came with real compression ratios about one point lower than the advertised compression. So any 10.5:1 engine was really closer to 9.5:1, etc. If you build an engine to the published compression ratio it will have a hard time on pump gas. So I'd say run an honest 9.5:1 with the closed chamber head, , which means a total of 107.5 cc above the piston. With an 84cc head and 0.039" squish distance that means you remove an additional 5.5 cc from the chamber, probably can be done by unshrouding the intake valves a little. For a 78cc head you take off something like 11.5 cc which I would do by cutting a little off the top of the piston in the non-squish area. If you were to use an open chamber head I'd run no more than a real 9.0:1 so you'd have metal to move in that case as well plus a much worse combustion chamber. There's a reason that the new heads for most every engine everywhere have squish, you need it too.

All in all it's not that bad a situation in which to find oneself.

R.