1970 440 Piston Compression Height?

[BPBP440]

I am looking at putting some NOS pistons in my 440. They are NOS pistons, PN 3420214, correct for '70 (w) 4bbl......listed as 9.75:1 CR. I was told they are flat tops and the compression height is 2.000. However, when I run the CR calculations, I get closer to 9:1 with open chamber heads. I realize that there may be slight differences in assumed combustion chamber CC, crevice vol, etc, but not enough to explain a 3/4 point in compression. I thought 70 wore the 906 heads, but if they were closed chambers that would explain it.

Any insight would be appreciated.

 

[Meep-Meep]

I'm really sure the actual compression on all our era MoPars was less than advertised. Yes 70 had 906 heads and likely came with steel shim gaskets, which may be slightly less that 1/2 point of compression over the comp gasket. A zero deck piston (2.065") will yield nearly 10.5:1 on an early block, but on my late model block with huge bore chamfers and the big KB valve reliefs, I get 10.1:1. I'd say your numbers are pretty close with a piston nearly .100" in the hole.

 

[moper]

The modern equivilent is the Sealed Power cast - they have a compression height of 1.990. If you use inputs of '70 build specs (meaning blueprint deck height, steel head gasket, blueprint chamber size) it will come out around 9.5:1. If you go with reality using the available composite gasket, a deck height of 10.735, and chamber size of 88ccs (which I've found to be potentially smaller than what is in one's hands) it's closer to 8.6:1. Personally I would use a more performance oriented piston. The KB Hypers are great value provided you or your builder can follow directions.

 

[lewtot184]

2.03 for a 10:1 4bbl engine, 2.065 for 6paks. i agree with moper on the kb's. i use kb184's with open chamber heads. icon 836 for closed chamber.

 

[Cranky]

Yup...around .050 in the hole is what they were but with a closed chambered head and the factory style steel gaskets, 10.3-1 compression is more like it.

 

[RT K_line]

I'm also running the K B hypers for open chamer heads, they have a quench dome. I have about 11, 000 miles on the engine. The compression worked out to 10.6 : 1 have run the engine to 7200 rpm a few times, by accident with no problems. Normally I shift at 6800 to 7000 rpm. I also have shot it with 175 hp nitrous. Going to hit it with 300 hp hit soon. I'm hoping that the San Antonio race track will reopen soon. I would highly recommend them for a budget build that you can beat on occasionally. That's the fun of it. Good to luck with your build.

 

[69 GTX]

I thought Hypers & Nos were a no no?

 

[RT K_line]

I thought Hypers & Nos were a no no?[/QUOT
Before I Picked the Pistons I researched them.You do have to open up the ring gap, but the pistons come with intructions on calculating ring gap for different applications. Blower, Nitrous. ect. I even read an article on someone trying to blow them up with nitrous. they went up to a 300 hp shot, then they tore the engine down and inspected it.

 

[lewtot184]

nitrous will kill anything if not set up right. i've always felt the two keys are; plenty of fuel and not making maximum cylinder pressure too early in the power stroke.

 

[Garys1969RR]

nitrous will kill anything if not set up right. i've always felt the two keys are; plenty of fuel and not making maximum cylinder pressure too early in the power stroke.

We are putting nitrous on my sons 383 Super Bee. Anything to watch out for? We will put timing to 34 total advance.

 

[lewtot184]

We are putting nitrous on my sons 383 Super Bee. Anything to watch out for? We will put timing to 34 total advance.

i'm not an expert on the stuff. do a bunch of reading and asking questions to experienced people. you may need an extra fuel pump and a spark retard. too much cylinder pressure too early in the burn cycle can break stuff, not enough gasoline melts stuff.

 

[moper]

If the kits run rich - detonation can happen. If they run lean - detonation will happen. Hyper pistons will take lots of abuse - they won't take a lot of detonation well. Hence the standby of don't run them with NO2. Only the KB hypers need the special ring gap attention. The others use a different alloy and/or have the rings lower on the piston so they run cooler.
If it's a small kit, make sure to follow the jetting directions with it. Verify the fuel system can deliver the volume free flowing and that the presure to the fuel solenoid is steady and right. Take out 2° of initial timing per 50hp, and I'd run a plug one step colder for each 100hp of kit rating.