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440 compression ratio question #560427 12/23/09 01:59 AM 12/23/09 01:59 AM
Joined: Aug 2009 Posts: 135 Indiana O Osyman OP member
Osyman OP member O Joined: Aug 2009 Posts: 135 Indiana	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?

Re: 440 compression ratio question [Re: Osyman] #560428 12/23/09 02:03 AM 12/23/09 02:03 AM
Joined: Jan 2004 Posts: 27,347 Today? Who Knows? 1_WILD_RT Management Trainee
1_WILD_RT Management Trainee Joined: Jan 2004 Posts: 27,347 Today? Who Knows?	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..

Re: 440 compression ratio question [Re: 1_WILD_RT] #560429 12/23/09 02:06 AM 12/23/09 02:06 AM
Joined: Aug 2009 Posts: 135 Indiana O Osyman OP member
Osyman OP member O Joined: Aug 2009 Posts: 135 Indiana	i believe the heads are 72 or 75cc, ill check the piston depth. thanks

Re: 440 compression ratio question [Re: Osyman] #560430 12/23/09 02:15 AM 12/23/09 02:15 AM
Joined: Dec 2003 Posts: 5,314 Carstairs, Alberta, Canada dave571 master
dave571 master Joined: Dec 2003 Posts: 5,314 Carstairs, Alberta, Canada	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.

Re: 440 compression ratio question [Re: dave571] #560431 12/23/09 02:59 AM 12/23/09 02:59 AM
Joined: Feb 2003 Posts: 21,318 Manitoba, Canada DaytonaTurbo Too Many Posts
DaytonaTurbo Too Many Posts Joined: Feb 2003 Posts: 21,318 Manitoba, Canada	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.

Re: 440 compression ratio question [Re: Osyman] #560432 12/23/09 09:09 AM 12/23/09 09:09 AM
Joined: Apr 2003 Posts: 409 pa 7 73roadbird mopar
73roadbird mopar 7 Joined: Apr 2003 Posts: 409 pa	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...

Re: 440 compression ratio question [Re: 73roadbird] #560433 12/23/09 10:27 AM 12/23/09 10:27 AM
Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska	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. live every 24 hour block of time like it's your last day on earth

Re: 440 compression ratio question [Re: 73roadbird] #560434 12/23/09 10:28 AM 12/23/09 10:28 AM
A Anonymous Unregistered
Anonymous Unregistered A	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.

Re: 440 compression ratio question [Re: RapidRobert] #560435 12/23/09 12:41 PM 12/23/09 12:41 PM
Joined: Feb 2003 Posts: 21,318 Manitoba, Canada DaytonaTurbo Too Many Posts
DaytonaTurbo Too Many Posts Joined: Feb 2003 Posts: 21,318 Manitoba, Canada	If you're on a budget and want compression, do yourself a favor and buy the KB237's or even the TRW2355's.

Re: 440 compression ratio question [Re: Osyman] #560436 12/23/09 02:23 PM 12/23/09 02:23 PM
Joined: Jan 2003 Posts: 15,976 Chilliwack B.C. Canada R RUNCHARGER I Live Here
RUNCHARGER I Live Here R Joined: Jan 2003 Posts: 15,976 Chilliwack B.C. Canada	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

Re: 440 compression ratio question [Re: RUNCHARGER] #560437 12/27/09 06:46 PM 12/27/09 06:46 PM
Joined: Mar 2007 Posts: 181 Stow,Ohio RBSat66 member
RBSat66 member Joined: Mar 2007 Posts: 181 Stow,Ohio	If interested I am taking a set of TRW 2355 + .030 pistons with stock rods out of a 440.

Re: 440 compression ratio question [Re: 73roadbird] #560438 12/28/09 12:46 AM 12/28/09 12:46 AM
Joined: Feb 2007 Posts: 1,025 Las Vegas, NV dodgeboy11 super stock
dodgeboy11 super stock Joined: Feb 2007 Posts: 1,025 Las Vegas, NV	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).

Re: 440 compression ratio question [Re: dodgeboy11] #560439 12/28/09 12:48 AM 12/28/09 12:48 AM
Joined: Feb 2003 Posts: 21,318 Manitoba, Canada DaytonaTurbo Too Many Posts
DaytonaTurbo Too Many Posts Joined: Feb 2003 Posts: 21,318 Manitoba, Canada	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.

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