Moparts
stock 440 pistons, how far down in the hole?
Posted By: VITC_GTX
stock 440 pistons, how far down in the hole? - 07/03/08 02:52 PM
Trying to figure out the compression in my '70 GTX with original 440 (without tearing the motor apart). I'm getting tired of fighting pre-detonation and want to try and do something. First thing I want to do is figure out my CR.
I have ported 906's that are shaved .006" (assuming 78 cc's), .030" over bores, stock replacement forged pistons. If I can find what the average depth of the pistons are (and look at compression thickness of my head gaskets) I can closely estimate my CR.
What's the average depth in the hole for a '70 440?
Posted By: DaytonaTurbo
Re: stock 440 pistons, how far down in the hole? - 07/03/08 03:46 PM
If it's a factory 1970 6 pack motor, your pistons should be about .02 in the hole. If it's not a factory 6 pack motor from 1970, then your pistons should be about .09 in the hole. That is assuming your block's deck, pistons, rods and crank are all exactly to blueprint spec.
906's with a .006 shave are nowhere near 78cc. Stock open chamber heads are closer to 90cc and you can start working backwards from there based on how much you shaved off. I forget the formula that shows how much to shave off heads to get a 1cc reduction. Stock steel shim head gasket thickness is around .022, but that's no guarantie that's what you are running now.
Posted By: Anonymous
Re: stock 440 pistons, how far down in the hole? - 07/03/08 03:46 PM
There is no way to tell without pulling heads and measuring.
They were all over the place when new so I don't think there was an average.
This why you hear stories about certain cars running so hard back in the day.
In the town I lived in the 60s-70s there was a 1968 383 RR bought new there with an auto trans, 3.23 rear, and only non stock item was a set of headers hooked to the factory exhaust. People would come from several towns away to race this car with there 440 Magnum cars, Charger and Coronet R/Ts and GTXs. 9 times out of 10 he would beat them in the 1/4 mile street race. It was just one of those cars.
I would bet if it had been torn down and checked closely you would have found that the compression was at or above the factory stated rating and that the tolerences were closer to a blueprinted engine than the typical factory engine.
These engines were put togather quickly, by humans, and with whatever part came next out of the bin. It was a crap shoot and some times you got lucky and everything in a particular engine was just right.
Posted By: Classof70Chally
Re: stock 440 pistons, how far down in the hole? - 07/03/08 04:53 PM
The guy who restored my car used 6 pack rods and cast TRW pistons. When I pulled a head off I found the pistons to be about .170 (that's one hundred-seventy thousandths) below deck. That, combined with the 906 open chambered heads gave me a whopping 7.5 to 1 CR more or less.
I guess he wanted to make sure it would run on regular!
Posted By: JohnRR
Re: stock 440 pistons, how far down in the hole? - 07/03/08 05:38 PM
Quote:
If it's a factory 1970 6 pack motor, your pistons should be about .02 in the hole. If it's not a factory 6 pack motor from 1970, then your pistons should be about .09 in the hole. That is assuming your block's deck, pistons, rods and crank are all exactly to blueprint spec.
.090 for a non 6pk ? whats the compression ratio that the factory stated in 1970 ? if its the same as 69 on the HP 440 it would be 10.0 , that piston will be .040 in the hole at blueprint .
oh , and yes a 906 is assumed at 86-88cc but its more like 90-92cc , general rule of thumb is you remove 1cc for every .005 you cut off a 906
Posted By: VITC_GTX
Re: stock 440 pistons, how far down in the hole? - 07/03/08 06:23 PM
Yeah, you guys are correct about the head cc. I mistyped, I was assuming 88 cc's not 78.
I was hoping to get a ball park CR so I could estimate what some changes may do (thicker head gasket for example).
Posted By: Anonymous
Re: stock 440 pistons, how far down in the hole? - 07/03/08 06:49 PM
My stock Pistons were .120 in the hole and my 906's were 90cc.
Posted By: JohnRR
Re: stock 440 pistons, how far down in the hole? - 07/03/08 07:01 PM
Quote:
My stock Pistons were .120 in the hole and my 906's were 90cc.
what year short block ?
Posted By: Anonymous
Re: stock 440 pistons, how far down in the hole? - 07/03/08 07:03 PM
Quote:
Quote:
My stock Pistons were .120 in the hole and my 906's were 90cc.
what year short block ?
68
supposedly a 10:1 motor
Posted By: JohnRR
Re: stock 440 pistons, how far down in the hole? - 07/03/08 07:09 PM
Quote:
Quote:
Quote:
My stock Pistons were .120 in the hole and my 906's were 90cc.
what year short block ?
68
supposedly a 10:1 motor
i just checked a 68 350 HP 440 motor i have , it's got its original flat tops in it , it's a 10.1 rated , and its STOCK pistons were not .120 in the hole .
Posted By: Anonymous
Re: stock 440 pistons, how far down in the hole? - 07/03/08 07:12 PM
Quote:
Quote:
Quote:
Quote:
My stock Pistons were .120 in the hole and my 906's were 90cc.
what year short block ?
68
supposedly a 10:1 motor
i just checked a 68 350 HP 440 motor i have , it's got its original flat tops in it , it's a 10.1 rated , and its STOCK pistons were not .120 in the hole .
How deep are they, John?
Posted By: John_Kunkel
Re: stock 440 pistons, how far down in the hole? - 07/03/08 07:59 PM
A '70 440HP piston should be .090" in the hole (same as the '67), '68 and '69 should be .050" down.
'70 was the first compression reduction for the 440-4, they went from 10.1-1 advertised to 9.7-1 advertised; they used the shorter '67 closed chamber pistons with the open chamber 906 heads to reduce the compression.
The TRW 2266 piston is the same 1.991" compression height as the original factory '67 and '70-'71.
Posted By: DaytonaTurbo
Re: stock 440 pistons, how far down in the hole? - 07/03/08 08:31 PM
Yes all other years but 68-69 should be around .09 in the hole. 67, 70-72 ran a piston with a compression height of 1.991. That CH is commonly available on the aftermarket in everything from forged to cast to hyper pistons. The 68-69's used a compression height of (I think) 2.031, giving you a piston that's around .05 in the hole. The 70 6 packs(pistons with valve reliefs) got the 2.061 compression height piston for a piston that sits around .02 in the hole.
But like I said, that's best and I mean BEST case scenario. There was an acceptable variance in size in the block's deck height and specs of the crank, rods, pistons, so it's possible any of those motors could in theory be off by as much as .01-.02. I'm sure some 6 packs left the factory with dang near zero deck pistons, and some 440hp's probably left the factory with a piston .1 in the hole. Engines did not roll off the assembely line built to blueprint spec, so like was said, you really have to take a head off and measure the depth of your pistons and measure the CC's of your combustion chambers. Make sure to check several not all were created equal either.
Posted By: JohnRR
Re: stock 440 pistons, how far down in the hole? - 07/03/08 09:26 PM
Quote:
Quote:
Quote:
Quote:
Quote:
My stock Pistons were .120 in the hole and my 906's were 90cc.
what year short block ?
68
supposedly a 10:1 motor
i just checked a 68 350 HP 440 motor i have , it's got its original flat tops in it , it's a 10.1 rated , and its STOCK pistons were not .120 in the hole .
How deep are they, John?
.040-.050 , i have then still i'll measure the CH of them over the weekend
Posted By: JohnRR
Re: stock 440 pistons, how far down in the hole? - 07/03/08 09:30 PM
Quote:
But like I said, that's best and I mean BEST case scenario. There was an acceptable variance in size in the block's deck height and specs of the crank, rods, pistons, so it's possible any of those motors could in theory be off by as much as .01-.02. I'm sure some 6 packs left the factory with dang near zero deck pistons, and some 440hp's probably left the factory with a piston .1 in the hole. Engines did not roll off the assembely line built to blueprint spec, so like was said, you really have to take a head off and measure the depth of your pistons and measure the CC's of your combustion chambers. Make sure to check several not all were created equal either.
i'd have to touch and feel these supposed engines with deck heights that are as much as .040 OVER factory blueprint as i have yet to find one, though i SEEN a number of people CLAIM this with NOTHING to back it up ...
edit ...
I just looked at NHRA blueprint for a 1970 440HP , advertised compression is 9.7, and the blueprint spec is .051 in the hole. As far as I can tell on the chrysler engines I have checked into NHRA blueprint is usually .020 HIGHER than the ACTUAL CH (the highest over being the 68-69 383 HP at .024 over actual). I would SURMISE that the CH of an ACTUAL 440 HP 1970 piston is 2.010 and the available pistons across the board at 1.991 by the AFTERMARKET is allowing for decking . The ONLY MAINSTREAM BB aftermarket piston that I have found to date that is the SAME as the factory PISTON it replaces is the 1970/71 6 PACK piston ...
YMMV
Anyone have an ACTUAL 1970 440HP std. bore CHRYSLER ORIGINAL piston they can measure the CH of , I would really like to know what it is ?
THANKS
Posted By: maximum entropy
Re: stock 440 pistons, how far down in the hole? - 07/03/08 09:35 PM
Quote:
The guy who restored my car used 6 pack rods and cast TRW pistons. When I pulled a head off I found the pistons to be about .170 (that's one hundred-seventy thousandths) below deck. That, combined with the 906 open chambered heads gave me a whopping 7.5 to 1 CR more or less. I guess he wanted to make sure it would run on regular!
the ironic thing is even with that low compression it would still be prone to detonate because of the huge cylinder, chamber, and total lack of quench. i had an 8:1 440 that pinged like a mutha because of pistons in the hole and open chamber heads. now it's a 496 with closed chamber heads, 10.33:1, pistons .002 out o' the hole, and no detonation. ever. me thinks quench is more important than compression ratio. btw, my 440 was .090 in the hole. more or less. alot more or less.
Posted By: JohnRR
Re: stock 440 pistons, how far down in the hole? - 07/03/08 09:42 PM
Quote:
Quote:
The guy who restored my car used 6 pack rods and cast TRW pistons. When I pulled a head off I found the pistons to be about .170 (that's one hundred-seventy thousandths) below deck. That, combined with the 906 open chambered heads gave me a whopping 7.5 to 1 CR more or less. I guess he wanted to make sure it would run on regular!
the ironic thing is even with that low compression it would still be prone to detonate because of the huge cylinder, chamber, and total lack of quench. i had an 8:1 440 that pinged like a mutha because of pistons in the hole and open chamber heads. now it's a 496 with closed chamber heads, 10.33:1, pistons .002 out o' the hole, and no detonation. ever. me thinks quench is more important than compression ratio.
Posted By: John_Kunkel
Re: stock 440 pistons, how far down in the hole? - 07/03/08 10:49 PM
Quote:
67, 70-72 ran a piston with a compression height of 1.991.
'72 was the first year of the really lowered compression (8.2 advertised), the compression height on those is 1.926" which puts it close to .150" down.
Posted By: dave571
Re: stock 440 pistons, how far down in the hole? - 07/04/08 01:56 AM
Quote:
I just looked at NHRA blueprint for a 1970 440HP , ....and the blueprint spec is .051 in the hole. ....
Anyone have an ACTUAL 1970 440HP std. bore CHRYSLER ORIGINAL piston they can measure the CH of , I would really like to know what it is ?
THANKS
I think your number is pretty close.
I've never measured one, but I think I saw a post on here where someone had.
I measured a virgin 67 hp engine and found that they were about .070 in the hole.
Since 67 had closed heads, the newer ones would have needed to be a little higher to maintain any kind of decent compression with the open 906 heads 
Posted By: DaytonaTurbo
Re: stock 440 pistons, how far down in the hole? - 07/04/08 04:19 AM
Either way, at the end of the day, what does it really matter? Nobody builds a performance engine with stock pistons these days and no two engines were built exactly the same. Go with your aftermarket pistons, have your block decked to get zero deck and call it a day.
Posted By: Anonymous
Re: stock 440 pistons, how far down in the hole? - 07/04/08 04:33 AM
Quote:
Quote:
67, 70-72 ran a piston with a compression height of 1.991.
'72 was the first year of the really lowered compression (8.2 advertised), the compression height on those is 1.926" which puts it close to .150" down.
cept' for the 72 440+6. that big dog still had 9.5-10.0:1 cr.. depending on who you believe.
Posted By: 440beep
Re: stock 440 pistons, how far down in the hole? - 07/04/08 06:54 AM
70 440 4bbl hp are 9.7l flat tops
71 440 4bbl hp are 9.5 l flat tops
71 440 4bbl lp are 8.8.1 flat tops
70 440 6bbl hp are 10.5
71 440 6bbl hp are 10.3
Posted By: Mr.Yuck
Re: stock 440 pistons, how far down in the hole? - 07/04/08 01:35 PM
My 440 has TRW forged "6-pack" pistons. They are .020 in te hole. W/ a 74cc head and the FAT fel-pros I should be at about 10.82:1. My 67 Coronet had a 70 440 w/ stock Speed Pro relacements they were way down in the hole (I don't remeber how far) but we figured w/ the steel shim head gaskets and stock 906's it was about 9:1
Posted By: stumpy
Re: stock 440 pistons, how far down in the hole? - 07/04/08 02:15 PM
A lot of the factory compression ratings were blue sky and no where near close. If the engines were blue printed rather than mass produced they would have been right.
Posted By: JohnRR
Re: stock 440 pistons, how far down in the hole? - 07/04/08 02:21 PM
Quote:
Either way, at the end of the day, what does it really matter? Nobody builds a performance engine with stock pistons these days and no two engines were built exactly the same. Go with your aftermarket pistons, have your block decked to get zero deck and call it a day.
what matters is there is some potential misinformation in this thread . too many times i have seen people that haven't researched the combo they want get STUCK with a low compression PIG because they either assumed that they were buying correct replacement parts when what they were really buying was the aftermarkets COMPROMISE to having to carry an EXACT replacement for every model year , at least thats how it works with big block MOPAR engines .
take the 383 for example , 2 or 3 basic compression ratios built over multiple years with first a closed chamber head then an open chamber head , dicounting a DOMED piston, both TRW/SPEEDPRO and KB carry ONE piston to cover ALL those variations 
Posted By: JohnRR
Re: stock 440 pistons, how far down in the hole? - 07/04/08 02:25 PM
Quote:
Trying to figure out the compression in my '70 GTX with original 440 (without tearing the motor apart). I'm getting tired of fighting pre-detonation and want to try and do something. First thing I want to do is figure out my CR.
I have ported 906's that are shaved .006" (assuming 78 cc's), .030" over bores, stock replacement forged pistons. If I can find what the average depth of the pistons are (and look at compression thickness of my head gaskets) I can closely estimate my CR.
What's the average depth in the hole for a '70 440?
Van lets try to actually ANSWER your question instead of GUESSING what you have .
heads shaved , by you ? if so what head gasket did you throw it back together with ?
Posted By: stumpy
Re: stock 440 pistons, how far down in the hole? - 07/04/08 03:57 PM
If you are having detonation trouble try retarding your timing a little.
Posted By: VITC_GTX
Re: stock 440 pistons, how far down in the hole? - 07/04/08 05:58 PM
Quote:
Quote:
Trying to figure out the compression in my '70 GTX with original 440 (without tearing the motor apart). I'm getting tired of fighting pre-detonation and want to try and do something. First thing I want to do is figure out my CR.
I have ported 906's that are shaved .006" (assuming 78 cc's), .030" over bores, stock replacement forged pistons. If I can find what the average depth of the pistons are (and look at compression thickness of my head gaskets) I can closely estimate my CR.
What's the average depth in the hole for a '70 440?
Van lets try to actually ANSWER your question instead of GUESSING what you have .
heads shaved , by you ? if so what head gasket did you throw it back together with ?
I did not put the motor together. I have all receipts showing parts and head machine work. The receipts shows that the heads were shaved .006". I know I can't count on everything I read (or believe everything Ma Mopar said) but I was just trying to see if I have a compression problem, quench problem, or another problem.
Posted By: 1_WILD_RT
Re: stock 440 pistons, how far down in the hole? - 07/04/08 07:11 PM
Useing 906 heads you can count on it not having any quench effect...
Posted By: JohnRR
Re: stock 440 pistons, how far down in the hole? - 07/04/08 07:52 PM
Quote:
Quote:
Quote:
Trying to figure out the compression in my '70 GTX with original 440 (without tearing the motor apart). I'm getting tired of fighting pre-detonation and want to try and do something. First thing I want to do is figure out my CR.
I have ported 906's that are shaved .006" (assuming 78 cc's), .030" over bores, stock replacement forged pistons. If I can find what the average depth of the pistons are (and look at compression thickness of my head gaskets) I can closely estimate my CR.
What's the average depth in the hole for a '70 440?
Van lets try to actually ANSWER your question instead of GUESSING what you have .
heads shaved , by you ? if so what head gasket did you throw it back together with ?
I did not put the motor together. I have all receipts showing parts and head machine work. The receipts shows that the heads were shaved .006". I know I can't count on everything I read (or believe everything Ma Mopar said) but I was just trying to see if I have a compression problem, quench problem, or another problem.
do the receipts show what pistons were used ? i just noticed you said its .030 and stock replacement pistons , which could be anything and will effect the compression ratio greatly .
unless its got KB step heads you can rest asuure that you have NO quench
Posted By: GTX70sixpack
Re: stock 440 pistons, how far down in the hole? - 07/04/08 08:32 PM
When I rebuilt my GTX engine I used TRW forged pistons for a 71 440 4 barrel application and Felpro head gaskets. It runs fine on pump gas but does have a noticable power loss, does not pull hard on the big end.
Posted By: VITC_GTX
Re: stock 440 pistons, how far down in the hole? - 07/04/08 10:04 PM
Quote:
Van lets try to actually ANSWER your question instead of GUESSING what you have .
heads shaved , by you ? if so what head gasket did you throw it back together with ?
I did not put the motor together. I have all receipts showing parts and head machine work. The receipts shows that the heads were shaved .006". I know I can't count on everything I read (or believe everything Ma Mopar said) but I was just trying to see if I have a compression problem, quench problem, or another problem.
do the receipts show what pistons were used ? i just noticed you said its .030 and stock replacement pistons , which could be anything and will effect the compression ratio greatly .
unless its got KB step heads you can rest asuure that you have NO quench
The part number for the pistons is SPE 2286P .030. I was told these were Speed Pro forged replacements for the '70 440, but have nothing to back that up.