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Author Topic: WARNING ! "stock" 440 Piston Selection...  (Read 28104 times)
Challenger340
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« on: June 09, 2015, 04:23:13 PM »

I am wondering if there needs to be a "sticky" of some sort about the pitfalls in rebuilding a 440 Engine ?

One of the biggest mistakes out there ? and one which I had thought was common knowledge enough nowadays, but apparently is NOT, is the mis-information regarding actual real-world compression ratios of stock rebuilder style cast pistons ?

The problem in a nutshell, is that contrary to published data in the counter catalogs,there is no such thing as a 9.5:1 stock cast Piston available for the open chamber cast iron BB Mopar heads, anywhere in the marketplace ?
At least NOT that I can find anyways ?
A Piston that would provide an actual 9.5:a C.R. with any of the O.E.M. open chamber iron cylinder heads, using a .039" thick head gasket, would require a Piston "C.D." or "compression distance"(the distance from the center of the wrist pin to the top of the piston), of around 2.025" to 2.035".
so,
when rebuilding your 440 Engine, do not believe your Engine machinist if he says there is.... especially if you are thinking about any kind of "performace" whatsoever in your build..... you have to educate yourself first, and be smarter at piston selection than they are !

Here is some handy information to that educational end:
1.) An un-milled "stock" 440 Engine Block.... requires a Piston Compression Distance spec of about 2.085" to reach "TDC".
6.76" Rod Length + 1.875"(1/2 Stroke length) + 2.085" height Piston = 10.720" 440 Block Height.
2.) Each .010" less than 2.085" of Piston Spec Compression Height.... ADDS approx 2.4 CC's of Volume to the Final Clearance Volume for calculating actual static Compression Ratio.
3.) Most, if not all "open" Chamber BB mopar cast iron heads after rebuild, will come in around the 88 CC mark. Again here.... actual CC'ing to verify is always best, but 87-88 CC's  is a good base assumption without milling.
4.) pretty much all "composition" style Head Gaskets are approx 10 CC's of Volume.

From the above....
it is pretty easy to see, that a Piston with a 1.969" Compression Distance like even the "high" offering from Silvolite(the HIGHEST stock cast piston I can find in the marketplace)
see here:
https://www.uempistons.com/index.php?main_page=product_silvolite_info&cPath=6_25_27&products_id=1643&zenid=86510ba966b1a2d67c36e77071ecd75a
 will be,
 about .110" DOWN the hole at TDC on an UN-milled 440 Block, good for about 11 X 2.4 CC's or about 26 CC's of Volume

Now add 10 CC's for the head gasket, and 88 CC's for the Head to the above 26 CC's, and PRESTO !
We now have a TOTAL Clearance Volume for calculating static Compression Ratio of 124 CC's

(Swept Volume PLUS Clearance Volume) divided by (clearance Volume) = Compression Ratio
.030" Overbore 440 = 914 CC's
(914 + 124) divided by 124 = 8.4:1 Compression Ratio.
and that's using the HIGHEST compression height stock cast Piston I can find !

* please feel free to post up a higher stock cast Piston available anywhere..... maybe I missed it ?

Morale of the story.... DO NOT let your engine get rebuilt using 'stock' cast pistons for ANY of the open chamber cast iron heads, unless you WANT to have a 1972 to 1978 smogger terd engine for some reason ?
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cdr
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« Reply #1 on: June 09, 2015, 04:43:43 PM »

thanks Bob for taking the time to TRY & educate people on proper engine building   2thumbs
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« Reply #2 on: June 09, 2015, 06:58:55 PM »

 coolgleamA thanks for sharing this info , interesting  yesnod  cheers cheers
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« Reply #3 on: June 10, 2015, 10:02:51 AM »

are the Speed-Pro 2355's a decent alternative? they are actually a bit cheaper, 2.061 compression height and forged. However I think they could be heavier? I can't find decent information on what the stock sets weigh.

KB237KTM's also have a 2.067 Compression height and a decent price point, however they are Hypereutectic which adds other considerations.

These of course are other lower budget options, because those are the people considering cast are most likely looking for low budget. The proper way is a quality forged piece which are readily available from many places.

Hypothetically speaking, wouldn't a hemi length rod 6.86" with a 1.094" pin be an option if it was available? if priced like 440 sources stock replacement rods it would be fairly affordable. Of course nothing like this exists and never will.
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66FBCharger
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« Reply #4 on: June 10, 2015, 10:23:19 AM »

Great info! This should be a sticky.
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« Reply #5 on: June 10, 2015, 11:51:03 AM »

3.) Most, if not all "open" Chamber BB mopar cast iron heads after rebuild, will come in around the 85 CC mark as a minimum, again.... actual CC'ing to verify is always best, but 85 CC's  is a good base assumption without LOTS of milling.

I've CC'd a bunch of open chamber BB heads and never had one under 88 CC's.
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« Reply #6 on: June 10, 2015, 03:38:15 PM »

3.) Most, if not all "open" Chamber BB mopar cast iron heads after rebuild, will come in around the 85 CC mark as a minimum, again.... actual CC'ing to verify is always best, but 85 CC's  is a good base assumption without LOTS of milling.

I've CC'd a bunch of open chamber BB heads and never had one under 88 CC's.

Same here.  Original from factory may have been as low as 88cc.
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« Reply #7 on: June 10, 2015, 03:45:25 PM »


are the Speed-Pro 2355's a decent alternative? they are actually a bit cheaper, 2.061 compression height and forged. However I think they could be heavier? I can't find decent information on what the stock sets weigh.


Yes, they are an alternative, but their quality is not what it once was.

They weigh about the same as the factory and in theory can be replaced without balancing.  The piston goes about 870 gm.  pins about 225 gm.  They make the "LW" version of the 2355, it is about 50 gm lighter
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firefighter3931
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« Reply #8 on: June 12, 2015, 05:49:35 AM »

The Speedpro 2355's are an excellent budget option. Yes they are heavy but the weight is very close to a factory cast piston (within a few grams) which makes balancing easy. I ran those in my old 446 with reworked factory LY rods & ARP bolts. That engine made very good power on pump gas (535hp/540tq)

As long as you keep the rpm's in check it will live a long time  yesnod


Ron
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« Reply #9 on: June 12, 2015, 07:30:47 AM »

3.) Most, if not all "open" Chamber BB mopar cast iron heads after rebuild, will come in around the 85 CC mark as a minimum, again.... actual CC'ing to verify is always best, but 85 CC's  is a good base assumption without LOTS of milling.

I've CC'd a bunch of open chamber BB heads and never had one under 88 CC's.

I haven't done a bunch, but the four engines worth that I've done were all 88+.

I agree that there is a lot of mis-information out there about piston heights and compression ratios. However, the attention to the details in making good parts selections is what separates good engine builders from the catalog browsing, bolt together builders. IMO, why anyone would want to exactly duplicate a stock build from 40 years ago is lost on me. There are parts out there that are much improved that achieve better results than the original stuff that was developed almost half a century ago. Not only that, but the opinion of a stock rebuild can have as many different connotations as car that is "restored".
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Challenger340
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« Reply #10 on: July 12, 2015, 07:06:39 PM »

Which brings up a second consideration for anyone considering, or looking to purchase a "performance" 440 powered car if "restored" and/or with a "rebuilt" 440 Engine ?
WHAT Pistons were used, when the so-called "numbers matching" 375hp 440 Engine was rebuilt ?

My point being....
you see so many factory Mopar musclecars advertised as "numbers matching this".... "numbers matching that"... worn like some holy grail of originality
when really...
what the fawk is the point being "numbers matching" anything.... because when they rebuilt the 375hp 440 they used 8.5:1 rebuilder pistons and de-nutted the engine into a 230hp smog motor that can't get outa it's own way !

So sad.... to see these beautifully restored examples, and they are just fawking DAWGS !
Now you know WHY !
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« Reply #11 on: July 12, 2015, 08:45:40 PM »

Sounds like my car... rotz
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« Reply #12 on: August 05, 2015, 03:00:49 PM »

Which brings up a second consideration for anyone considering, or looking to purchase a "performance" 440 powered car if "restored" and/or with a "rebuilt" 440 Engine ?
WHAT Pistons were used, when the so-called "numbers matching" 375hp 440 Engine was rebuilt ?

My point being....
you see so many factory Mopar musclecars advertised as "numbers matching this".... "numbers matching that"... worn like some holy grail of originality
when really...
what the fawk is the point being "numbers matching" anything.... because when they rebuilt the 375hp 440 they used 8.5:1 rebuilder pistons and de-nutted the engine into a 230hp smog motor that can't get outa it's own way ![/b]

So sad.... to see these beautifully restored examples, and they are just fawking DAWGS !
Now you know WHY !

Please explain how you came up with 230 hp as a result of lower compression pistons.

These calculators don't come up with that number.


* mickhpconversion1.jpg (110.83 KB, 933x582 - viewed 8884 times.)

* mickhpconversion2.jpg (61.18 KB, 821x331 - viewed 8609 times.)
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69wannabe
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« Reply #13 on: August 05, 2015, 07:55:14 PM »

The Speedpro 2355's are an excellent budget option. Yes they are heavy but the weight is very close to a factory cast piston (within a few grams) which makes balancing easy. I ran those in my old 446 with reworked factory LY rods & ARP bolts. That engine made very good power on pump gas (535hp/540tq)

As long as you keep the rpm's in check it will live a long time  yesnod


Ron

I agree!! These are very good performance replacement pistons. They will not give you 10 to 1 with an 88cc head but should give you a good 9.5 to 1 with an open chamber head. That's not proper for an exact from factory rebuild but are alot better than the cast replacement's that are out there. I can't remember the last time I even bought a set of cast piston's, even my 4.0 jeep engine's get the hypereutectic piston's which are not that much more expensive than the cast replacement's.
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« Reply #14 on: May 23, 2016, 09:01:37 PM »

I always ran 2355s at the very least for a B.S. street car
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« Reply #15 on: January 04, 2018, 09:47:29 AM »

Great info C340!

Would only use 70/71 SixPack four notch pistons if I had to use cast myself.
Other than that its a forged piston every time, ROSS are my favourite.

Low comp is fine for most Folks who like to go to Car-shows only!
The infamous 1972/1976 Jensen Interceptor hipo 440 motors were 8.2 to one and were less powerful that the 383 they replaced. (Basically a steel crank truck engine.)

Easiest way to check piston height is a quick assembly and 'down the bore' measurement.
Anything more than 40 thou and you can run cheapo GAS! (depending on head spec of course)

Real racers use ZERO DECK pistons, KOFFEL spec lol...
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« Reply #16 on: January 07, 2018, 08:49:26 AM »

Instead of rebuilding the dawg 440 on my 68rt...
Im just going to put a big inch Hemi in her!
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« Reply #17 on: March 18, 2018, 10:31:14 PM »

  Thanks for the education as I'm just about to start building an old 440. I'm looking for big horse power so if anyone wants to send me their "recipe" for their build I'd appreciate it.
  Chris
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Challenger340
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« Reply #18 on: March 19, 2018, 08:56:25 AM »

 Thanks for the education as I'm just about to start building an old 440. I'm looking for big horse power so if anyone wants to send me their "recipe" for their build I'd appreciate it.
  Chris

It's a long read, but here is a link to a KISS(keep it simple stupid) regular old 440 recipe we did in the past, with Dyno Sheets on both as we did 2 at that same time, basically the same shortblocks but with different Cams, and slightly different Head work.
It may be worth a read for ideas...
http://www.dodgecharger.com/forum/index.php/topic,106687.0.html

The common advice from many these days, seems to be that by the time you spend building a regular 440 ?    that a guy might as well just go buy a "Stroker Kit" instead ?
THAT.... depends on a ton of things ? but I would tend to disagree along a number of criterion I won't get into here and now.



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« Reply #19 on: July 17, 2018, 08:08:58 AM »

Easiest way to check piston height is a quick assembly and 'down the bore' measurement.

Wouldn't a compression test tell you all you need to know? I.e. a PSI reading of xxx should indicate the compression ratio as the PSI should be consistent if the ratio stays the same no? (assuming the amount of air/fuel mixture and the temperature do not change)
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« Reply #20 on: July 17, 2018, 08:30:27 AM »

Easiest way to check piston height is a quick assembly and 'down the bore' measurement.

Wouldn't a compression test tell you all you need to know? I.e. a PSI reading of xxx should indicate the compression ratio as the PSI should be consistent if the ratio stays the same no? (assuming the amount of air/fuel mixture and the temperature do not change)

The camshaft specs change the cranking pressure, intake valve closing events, also cranking rpm & altitude will have an affect.
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« Reply #21 on: July 17, 2018, 09:18:27 AM »

The camshaft specs change the cranking pressure, intake valve closing events, also cranking rpm & altitude will have an affect.

Ah, yes. We are not talking about a fixed system because those elements effectively create dynamic initial gas/air volume conditions from one engine build to another.  2thumbs
 
  • Camshaft will change volume compressed due to grind (letting air escape based on lift/duration).
  • Cranking RPM will have effect with the dynamics of the valve springs.
  • Altitude because the local air pressures are different (that's just like a change in temp or weather for that matter).

So with that in mind I note that the CR is not taking into account the losses mentioned above (thus the name Static Compression Ratio and its formula above).  And as such the CR is the best case compression because the above factors all act to effectively REDUCE the actual CR when the engine is running, correct?
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Challenger340
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« Reply #22 on: July 17, 2018, 09:26:54 AM »

Easiest way to check piston height is a quick assembly and 'down the bore' measurement.

Wouldn't a compression test tell you all you need to know? I.e. a PSI reading of xxx should indicate the compression ratio as the PSI should be consistent if the ratio stays the same no? (assuming the amount of air/fuel mixture and the temperature do not change)

A Compression Test will only tell you it builds "this" much psi, but not "how" it is delivering that psi or under what Intake Valve Closing point for example ?
For example only,
you could have an 8:1 Engine show 160 psi if the Intake Valve closed right at Piston BDC ?, but conversely, same Engine may only show 115 psi with an aftermarket Cam that doesn't close the Intake Valve until 65* after Piston BDC.

The difference when running, the "0" BDC Cam/Valve Closing event Engine, although very "responsive" off idle, might make diddly for power much past 3,500 rpm, whereas, the 65* Intake Closing Engine may power right through to 6,000 rpm, but alas, NO power down low whatsoever.

I'm just trying to point out the difference between what's called "Static" or "theoretical" Compression Ratio which assumes a complete Compression of all gases from Piston BDC right to TDC
versus,
"Dynamic" Compression Ratio, which is the actual Engine "running" Compression Ratio, because the Piston can not begin to compress anything in the cylinder, until both Valves are closed, which, the Cam event relating to where the Intake Valve actually closes after the Piston is past BDC and heading back up determines cylinder filling @ rpm.  (Cam is like a "program" in a computer)

That said,
If you know where the Intake Valve Closes ABDC, and the ambient elevation, etc., etc. it is possible to then reverse Calculate a somewhat close "static" C.R. from a psi reading(Ring Losses, etc will deviate)

On a side note,
the early factory 440 Magnums were IMO, a very well balanced Pkg in terms of trade offs in power, drive-ability, and C.R.
I have great respect even today, for what those guys did "back in the day" with C.R. and Cam events.
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« Reply #23 on: July 17, 2018, 09:33:22 AM »

Yes, thanks for elaborating on the finer points. This all makes sense I just never really had any in depth discussions with anyone about it. This helps (me anyways) a LOT with understanding!  cheers

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