440 compression ratio question

Posted By: Osyman

440 compression ratio question - 12/23/09 05:59 AM

does anybody know the c/r of the 75 440 police interceptor? I ordered .030 over pistons with the same c/r that was in the interceptor, then put the '67 closed chamber heads on it. do yall know my new c/r?

also anyone know the specs of a stock 426 hemi cam?

Posted By: 1_WILD_RT

Re: 440 compression ratio question - 12/23/09 06:03 AM

To get an acurate number you would need to measure how far the piston is in the hole @ TDC & CC the heads... Without that info I'd guess roughly 8.5-9.0 to 1..

Posted By: Osyman

Re: 440 compression ratio question - 12/23/09 06:06 AM

i believe the heads are 72 or 75cc, ill check the piston depth. thanks

Posted By: dave571

Re: 440 compression ratio question - 12/23/09 06:15 AM

with a standard deck they typically cc around 78-80 cc's.

Aftermarket pistons, it's anyones guess as to the ratio.

Plug the measurements into a comp ratio calculator, like the one at www.kb-silvolite.com

The numbers are usually surprising, and not in a good way.

Posted By: DaytonaTurbo

Re: 440 compression ratio question - 12/23/09 06:59 AM

75 police 440 was just a 440HP which featured a whopping 7.8:1 (calculated) compression from the factory with stock 452 heads. With your smaller closed chambered heads that's more like 8.4:1 compression, assuming those are stock replacement mid 70's 440 pistons and assuming you didn't mill your block or heads to increase cr. If those are truly the pistons you bought, those are basically the least desirable 440 piston out there.

Posted By: 73roadbird

Re: 440 compression ratio question - 12/23/09 01:09 PM

I don't know if this will help you or not, but I'm working on a 75 440 that's out of a truck, and the pistons measured .0160 to .0162 down, so compression would be quite low from factory. Not to hijack this post, but could I deck the block and re-use the factory pistons or get earlier year 440 pistons to get a better compression ratio. Looking to do a budget build, Thanks...

Posted By: RapidRobert

Re: 440 compression ratio question - 12/23/09 02:27 PM

Quote:

could I deck the block and re-use the factory pistons or get earlier year 440 pistons to get a better compression ratio.

You're too far in the hole. I'd get some KB's to get .040" Quench and a higher CR and you'll be MUCH more satisfied w the outcome.

Posted By: Anonymous

Re: 440 compression ratio question - 12/23/09 02:28 PM

i think you meant .160 & .162 down in the hole. .0160 & .0162 actually isn't that bad. would give you around 9.2:1 CR. with open chambers.

Posted By: DaytonaTurbo

Re: 440 compression ratio question - 12/23/09 04:41 PM

If you're on a budget and want compression, do yourself a favor and buy the KB237's or even the TRW2355's.

Posted By: RUNCHARGER

Re: 440 compression ratio question - 12/23/09 06:23 PM

You should stop the order for those replacement pistons, I agree that you will have less than 8.5-1 compression with those pistons and 915 heads. I would order some TRW 2355 pistons at the very least, that will get you between 9 or 9.5-1 compression.

Sheldon

Posted By: RBSat66

Re: 440 compression ratio question - 12/27/09 10:46 PM

If interested I am taking a set of TRW 2355 + .030 pistons with stock rods out of a 440.

Posted By: dodgeboy11

Re: 440 compression ratio question - 12/28/09 04:46 AM

Quote:

I don't know if this will help you or not, but I'm working on a 75 440 that's out of a truck, and the pistons measured .0160 to .0162 down, so compression would be quite low from factory. Not to hijack this post, but could I deck the block and re-use the factory pistons or get earlier year 440 pistons to get a better compression ratio. Looking to do a budget build, Thanks...

You can buy new KB hyper pistons from summit for 310 bucks with a .075 quench dome or 320 for flat tops (I have no idea why the flat tops are 10 bucks more).

Posted By: DaytonaTurbo

Re: 440 compression ratio question - 12/28/09 04:48 AM

Quote:

You can buy new KB hyper pistons from summit for 310 bucks with a .075 quench dome or 320 for flat tops (I have no idea why the flat tops are 10 bucks more).

Yes the only downside being you have to have your rotating assy rebalanced. With the TRW's they're made so their weight is 'close enough' to stock pistons that many guys run without a rebalance.