Moparchat - Home of MOPAR enthusiasts worldwide!



Go Back   Moparchat - Home of MOPAR enthusiasts worldwide! > Technical Forums > Performance Talk

Click here to search for Mopar cars and parts for sale.


Reply
 
Thread Tools Display Modes
  #1  
Old 05-25-2010, 08:53 PM
bwake bwake is offline
Inactive User
 
Join Date: May 2010
Location: Goodlettsville Tn.
Posts: 15
Default Why different compressions?

Why are the 440 compressions prior to 73 higher than those after 73? Is it because of the different head cc volume or are there other factors?
Reply With Quote
  #2  
Old 05-25-2010, 08:57 PM
rampage_82 rampage_82 is offline
Inactive User
 
Join Date: Dec 2007
Location: Mountainair NM
Posts: 657
Default

pistons...
Reply With Quote
  #3  
Old 05-25-2010, 09:20 PM
bwake bwake is offline
Inactive User
 
Join Date: May 2010
Location: Goodlettsville Tn.
Posts: 15
Default

Rampage, you are quick on the reply. I guess my question is how can I get my low compression, low HP 73 440 to match the higher compression, higher HP of a 1971 440? What's the difference in the pistons? What makes them higher compression?
Reply With Quote
  #4  
Old 05-25-2010, 09:47 PM
rampage_82 rampage_82 is offline
Inactive User
 
Join Date: Dec 2007
Location: Mountainair NM
Posts: 657
Default

Compression height... you'll need to get some six-pack replacement pistons or the equivalent.. Such as.. http://www.summitracing.com/parts/TRW-WL2355F30/
Reply With Quote
  #5  
Old 05-25-2010, 11:03 PM
cudabob496 cudabob496 is offline
Inactive User
 
Join Date: May 2007
Location: Richland, WA
Age: 71
Posts: 2,018
Default

why not try thinner head gaskets?
Also, compression ratio is not a big factor in making power, as compared to other means, such as cam, head, exhausts, intake, etc. changes The 11.5/1 CR 413 Super Stock engines in the early 60's only gained 20 hp when CR was bumped to 13.5/1. In the 50's and 60s compression ratio was a way to make power, but now a days cam technology and head technology far outweigh the compression ration factor.
Reply With Quote
  #6  
Old 05-25-2010, 11:17 PM
rampage_82 rampage_82 is offline
Inactive User
 
Join Date: Dec 2007
Location: Mountainair NM
Posts: 657
Default

Well I kinda concur, however the higher compression will always give more power up to the point of detonation... But if we are talking about the difference between 10.5.1 and 12 to 1, there isn't that much in terms of power... But the difference between 7.5.1 and 10.5.1 is drastic.... also this is a great article on engine building from speed-o-motive... just go under the fill in the blank form for the article..

http://www.speedomotive.com/t-showbymodel.aspx
Reply With Quote
  #7  
Old 05-25-2010, 11:20 PM
dodger1 dodger1 is offline
Inactive User
 
Join Date: Feb 2004
Location: Princeton BC
Age: 85
Posts: 2,648
Default

Quote:
Originally Posted by bwake View Post
Why are the 440 compressions prior to 73 higher than those after 73? Is it because of the different head cc volume or are there other factors?
Reason is mainly - cats + unleaded fuel. Catalytic converters (being phased in at the time) will not tolerate lead. Unleaded will not tolerate high compression. So we got low(er) compression engines, (bad) hardened exhaust valve seats (good) and cats (bad then, not bad now) via low comp. pistons and heads. This got so ridiculous that the stock 318 in my Mirada was rated at 135 HP - about the same as a /6 in the late 60's. It took computers and fuel injection to get around the problem, not to mention 25 years. But hey - 425 NET H.P. out of a current 371 cu. in. Hemi ain't too shabby, either.
Reply With Quote
  #8  
Old 05-25-2010, 11:33 PM
bwake bwake is offline
Inactive User
 
Join Date: May 2010
Location: Goodlettsville Tn.
Posts: 15
Default

Guys I appreciate the info! The compression on this engine is listed around 8:2:1 with a Horsepower rating around 220. It just seems to me that the compression has got to be raised if I'm gonna get any power out of it.
Reply With Quote
  #9  
Old 05-26-2010, 12:25 AM
cudabob496 cudabob496 is offline
Inactive User
 
Join Date: May 2007
Location: Richland, WA
Age: 71
Posts: 2,018
Default

I disagree. Even without increasing CR, you can probably add 50 rear wheel horsepower with a good tuneup, new plugs and plug wires, synthetic oil in engine, tranny, rearend, a quality ignition system like MSD, electric fan, etc etc. Just shaving spark plug electrodes is good for 5 hp. Cold air intake is worth 10 to 20 hp. Reduced diameter pulleys. I'm sure guys can add to the list of ways to increase power output!! Headers, free flowing exhaust (20hp), K&N air filter, etc etc. Then of course, if you want to be even quicker, start to lighten the car, new rear gears, etc.
Reply With Quote
  #10  
Old 05-26-2010, 12:41 AM
Ray Bell's Avatar
Ray Bell Ray Bell is offline
Registered User
 
Join Date: May 2005
Location: Dalveen, Queensland
Posts: 3,236
Default

A compression bump with a bit shaved from the heads isn't going to hurt, though...


.
Reply With Quote
  #11  
Old 05-26-2010, 01:00 AM
cudabob496 cudabob496 is offline
Inactive User
 
Join Date: May 2007
Location: Richland, WA
Age: 71
Posts: 2,018
Default

Quote:
Originally Posted by Ray Bell View Post
A compression bump with a bit shaved from the heads isn't going to hurt, though...


.
Generally no, but depending on the combustion chamber design of the heads, and the cam, you may not be able to raise it that much, before you exceed design peak cylinder pressure, when detonation occurs. And, if you shave heads, you may mess up air flow around the valves. Pocket porting is generally good for 30 to 50 hp. Just seems there are 50 things to do to make power before raising CR. I've also heard that on older engines, due to carbon buildup, your CR can be .5 higher. YOu wanna get the most bang for the buck. After a good tuneup, that would be a cold air intake, which give 1.5% power increase for every 10 degrees you lower air temp to the carb! Lower it 50 degrees, and on a 400 horse engine you add 30 hp!!
Reply With Quote
  #12  
Old 05-26-2010, 09:51 AM
JVMopar's Avatar
JVMopar JVMopar is offline
Senior Member
 
Join Date: Feb 2000
Location: Mellen, WI
Age: 42
Posts: 2,524
Default

You can't compare the HP ratings from the late 60's to the ones of '72 and up. They aren't measured the same so the HP difference is rather dramatic.
Reply With Quote
  #13  
Old 05-26-2010, 10:04 AM
rampage_82 rampage_82 is offline
Inactive User
 
Join Date: Dec 2007
Location: Mountainair NM
Posts: 657
Default

Well it is a general consensus that there is a 4% gain for every full point of compression gain.. So that being stated, if you jump from 8.0.1 to 10.0.1 and the 8.0.1 starts off with 300 hp, then doing nothing but a compression jump would give you 324hp. However the higher compression will also allow for a bigger cam, without the associated hassles. Such as if you put a .509 cam with 8.0.1 compression, it will be a doggy, soggy, pig. Put the same cam with 10.5.1 compression it will run very hard, and act much nicer...
Reply With Quote
  #14  
Old 05-26-2010, 03:41 PM
John Kunkel John Kunkel is offline
Registered User
 
Join Date: Nov 2001
Location: NorCal
Age: 80
Posts: 10,059
Default

Quote:
Originally Posted by cudabob496 View Post
why not try thinner head gaskets?
It's pretty hard to get much thinner than the original .020" steel shim gaskets the factory used.

Like JV said, in '72 they changed the way HP is measured; so you can't directly compare old/new HP ratings.
Reply With Quote
  #15  
Old 05-26-2010, 07:25 PM
cudabob496 cudabob496 is offline
Inactive User
 
Join Date: May 2007
Location: Richland, WA
Age: 71
Posts: 2,018
Default

Quote:
Originally Posted by rampage_82 View Post
Well it is a general consensus that there is a 4% gain for every full point of compression gain.. So that being stated, if you jump from 8.0.1 to 10.0.1 and the 8.0.1 starts off with 300 hp, then doing nothing but a compression jump would give you 324hp. However the higher compression will also allow for a bigger cam, without the associated hassles. Such as if you put a .509 cam with 8.0.1 compression, it will be a doggy, soggy, pig. Put the same cam with 10.5.1 compression it will run very hard, and act much nicer...
Iron heads limit you to 9.5 CR.

No one should ever put a 509 on an 8 CR engine. Each cam has a minumum CR/peak cylinder pressure it is designed to work at. On my 496 Cuda, the CR is 10.5. My cam is a 254/258 duration at .050. I'm probably right on the limit of maintaining enough cylinder pressure for the cam to function as designed.

To increase compression ratio on an engine from 8 to 10, would require probably thousands of dollars in parts changes. On a 400 horse engine, that would be a gain of 32 hp. Not worth it! For a $100 ram air box, you would gain 30 hp.
Reply With Quote
  #16  
Old 05-26-2010, 07:52 PM
rampage_82 rampage_82 is offline
Inactive User
 
Join Date: Dec 2007
Location: Mountainair NM
Posts: 657
Default

Well I guess we're just insane, We run true 10.5.1 compression on iron heads all the time, but then again we are at 6500ft of elevation, which makes a huge difference evidently. Thousands of dollars to change from 8 to 10.1 compression, what world are you in? Speed-Pro pistons 2295F30= $430 Felpro 1009 head gaskets = $80, ARP head Bolts = $70 = $580 by my count. The machine work is going to be the same regardless, as well as the price of the camshaft and lifter's and springs, which will work on either motor... And while compression all by itself will only gain some power, when you put the other parts to work with it, then the power goes up exponentially.... Believe me I spent too much time trying to get smog motors to run with engines with compression, heads, and real cams... It is way easier to go with what actually works, and yes the cold air boxes and heads do help with the lower compression engines, but think about how much better they are as a complete package....
Reply With Quote
  #17  
Old 05-26-2010, 07:58 PM
bulldog426's Avatar
bulldog426 bulldog426 is offline
Registered User
 
Join Date: Apr 2008
Location: sippi
Age: 37
Posts: 868
Default

Quote:
Originally Posted by rampage_82 View Post
Well I kinda concur, however the higher compression will always give more power up to the point of detonation... But if we are talking about the difference between 10.5.1 and 12 to 1, there isn't that much in terms of power... But the difference between 7.5.1 and 10.5.1 is drastic.... also this is a great article on engine building from speed-o-motive... just go under the fill in the blank form for the article..

http://www.speedomotive.com/t-showbymodel.aspx
i agree, and most cams that have any kind of power-making duration, lift, etc require at least 10;1 or higher compression to make the cam work, even my litte cam requires 10:1 compression
Reply With Quote
  #18  
Old 05-26-2010, 08:57 PM
dodger1 dodger1 is offline
Inactive User
 
Join Date: Feb 2004
Location: Princeton BC
Age: 85
Posts: 2,648
Default

Quote:
Originally Posted by JVMopar View Post
You can't compare the HP ratings from the late 60's to the ones of '72 and up. They aren't measured the same so the HP difference is rather dramatic.
You're right, I should have mentioned that in my post. Went from "gross HP" (on the dyno, no accessories such as alternators, water or power steering pumps, etc.) to "net HP", measured with all std. equipment attached and under normal load. I'm not sure if one can find a standard conversion factor for comparison's sake, as different engine combos probably had different results. The change to unleaded low-compression specs did co-incide witrh the change in advertised HP, however.
Reply With Quote
  #19  
Old 05-26-2010, 11:59 PM
cudabob496 cudabob496 is offline
Inactive User
 
Join Date: May 2007
Location: Richland, WA
Age: 71
Posts: 2,018
Default

Quote:
Originally Posted by rampage_82 View Post
Well I guess we're just insane, We run true 10.5.1 compression on iron heads all the time, but then again we are at 6500ft of elevation, which makes a huge difference evidently. Thousands of dollars to change from 8 to 10.1 compression, what world are you in? Speed-Pro pistons 2295F30= $430 Felpro 1009 head gaskets = $80, ARP head Bolts = $70 = $580 by my count. The machine work is going to be the same regardless, as well as the price of the camshaft and lifter's and springs, which will work on either motor... And while compression all by itself will only gain some power, when you put the other parts to work with it, then the power goes up exponentially.... Believe me I spent too much time trying to get smog motors to run with engines with compression, heads, and real cams... It is way easier to go with what actually works, and yes the cold air boxes and heads do help with the lower compression engines, but think about how much better they are as a complete package....
I think I'm in the world of reality. I suppose if you do all the work, and own your own machine shop, and have a lot of free time, you could do it for
$580. But as you state, you up the compression, you would obviously make other changes to the engine to go along with the compression increase.
And a lot of us, due to lack of space or time, might pay someone else to do the work. I installed my own engine, but I had a professional build the short block for me. You also
have to decide how much your time is worth.

But I did mis-speak. I meant to say doing all the work would be in the thousands. In my case, I could not do it all, and I'm using expensive JE slugs which bring the price up.

found this on the web:http://www.youtube.com/watch?v=QR7iB...eature=related
http://www.youtube.com/watch?v=ZVv4_...eature=related
Reply With Quote
  #20  
Old 05-27-2010, 12:39 AM
DartGT66 DartGT66 is offline
Inactive User
 
Join Date: Sep 1999
Location: vantaa,finland
Posts: 4,622
Default

The 8.2:1 is advertised compression ratio, real world compression ratios aren't usually even close. But lets do the math aasuming other factory blueprint specs are correct (which they propably aren't) Deck height 10.725"- rod length 6.766" - half stroke 1.875" - piston compression height 1.912" = 0.172". That's the amount the pistons are in the hole at TDC. Now, typically the open chamber heads have88-92cc chamber size, if we use 88cc and calculate the CR we end up with 7.7:1. Because of the variations in deck heights etc, the true ratio may be even lower than that. Now, if you think milling is the key, what would for example milling .040" do? IT would bring the CR to 8.2:1. And if you consider that these calculations are with the currently unavailable factory steel shims, and hte commonly available head gaskets are over .020" thicker, the situation gets even worse. .040" from the factory height is about all you can do without compensating it somewhere else. So, there really isn't any other reasonable method to raise the CR in the low compression engines than to change the pistons. The factory six pack pistons (trw/speed pro L2355F) have a compression height of 2.061", and they will bring the CR up to where you propably want it to be, about 9.3:1 with .040" thick head gaskets. That is a figure you can easily adjust with minor milling where you want it to be.
Reply With Quote
  #21  
Old 05-27-2010, 01:01 AM
rampage_82 rampage_82 is offline
Inactive User
 
Join Date: Dec 2007
Location: Mountainair NM
Posts: 657
Default

Also if you get zero deck and proper quench/squish with the proper chamber and the proper pistons (such as the KB piston... http://www.summitracing.com/parts/UEM-KB184-030/) then you can have a compression ratio of 10+to1 and have less problems (even with an iron head) with detonation that you will have with 8 to 1 and the piston being .180" down the hole..
Reply With Quote
  #22  
Old 05-27-2010, 02:52 AM
rampage_82 rampage_82 is offline
Inactive User
 
Join Date: Dec 2007
Location: Mountainair NM
Posts: 657
Default

Quote:
Originally Posted by cudabob496 View Post
yes that is one way to cure the low compression problem, is forced induction, however I wouldn't want to try it on the stock 900 gram cast pistons reinforced with iron struts.. LOL

Also to think, that is a 383, which everybody poo-poo's because of the valve shrouding, and the short tiny stroke.. HAHAHA Well I guess imagine what he could have done with a correct motor like a 474? haha

I myself like my short stroke 383, sure it lacks the punch of a 440 off the line, but after you get them moving they pull like little freight trains... well not the one in the video but you get my drift...
Reply With Quote
  #23  
Old 06-06-2010, 10:47 PM
ehostler's Avatar
ehostler ehostler is offline
Registered User
 
Join Date: Jan 2000
Location: Annandale, VA
Age: 57
Posts: 15,212
Default

Larger valves and the correct cam will make a world of difference.

As far as the 383 goes, I've always liked that engine. I just fired up my old 383, after sitting for 18 years. Once I replaced a failed coil, she started and idled easier than my 440 that runs on a regular basis. This 383 is bone stock and has a rather mellow idle. I didn't know how much I missed the purr of that engine, until she fired up.
Reply With Quote
  #24  
Old 06-07-2010, 11:07 PM
bulldog426's Avatar
bulldog426 bulldog426 is offline
Registered User
 
Join Date: Apr 2008
Location: sippi
Age: 37
Posts: 868
Default

Quote:
Originally Posted by cudabob496 View Post
Iron heads limit you to 9.5 CR.
really??? my dad's cuda with a magnum 360 block with r/t iron heads is running 12:1 compression

and with my low compression 440 it costed only a few hundred bucks for a set of kb pistons and a balance job
Reply With Quote
  #25  
Old 06-08-2010, 03:16 AM
cageman's Avatar
cageman cageman is offline
Inactive User
 
Join Date: Dec 1999
Location: Bismarck ND
Age: 46
Posts: 5,544
Default

so when I drive my 273 when it is -40 degrees I have an 800 hp motor? sweet.
A tune up gains hp?, hmm sweet again.
I have never owned a motor that had carbon, what am I doing wrong.
If your looking for more HP, than carbon probably isnt there, as you are flogging the heck out of it.

I think I need to drop a grand or so on go fast parts. I can get 8,000 hp if I add em all up.
insert sarcasm here.

Since when doesnt unleaded like high HP?
A head gasket that is thinner isnt going to help much on a 7 1/2 to 1 comp motor. New pistons is all it takes to get it to the prior years HP.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump




All times are GMT -4. The time now is 03:25 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
. . . . .