440 Compression
#1158815
01/16/12 07:53 PM
01/16/12 07:53 PM
|
Joined: Feb 2009
Posts: 583 San Antonio, TX
CurYellowBird
OP
mopar
|
OP
mopar
Joined: Feb 2009
Posts: 583
San Antonio, TX
|
Any idea on what the compression would be for a 78' 440 using L2355 forged pistons (Compression Height 2.061) and a 78cc closed chamber head?
Thanks.
Project War Bird:
1971 Plymouth Roadrunner
383 4 speed with air conditioning
GY3 Curious yellow
All original
|
|
|
Re: 440 Compression
[Re: DaytonaTurbo]
#1158817
01/16/12 08:40 PM
01/16/12 08:40 PM
|
Joined: Feb 2009
Posts: 583 San Antonio, TX
CurYellowBird
OP
mopar
|
OP
mopar
Joined: Feb 2009
Posts: 583
San Antonio, TX
|
I'm having my machinist get back with me on how far the new pistons are in the hole. This morning when I was tearing the motor down, the stock cast pistons looked to be about a 1/16 to 1/8th of an inch down the hole, just below where the tops of the piston chambers tapers. Don't have a depth gauge so can't give exact numbers on that. I think the CH of the stockers is like 1.9 so the new 2355's should put it close to zero deck. I was aiming for 9.5 CR, would I run into problems with a CR that high? Would it be best to go with an open chamber design to drop the compression back down? Below is a pic of one of the cylinders at the top of its stroke.
Project War Bird:
1971 Plymouth Roadrunner
383 4 speed with air conditioning
GY3 Curious yellow
All original
|
|
|
Re: 440 Compression
[Re: RapidRobert]
#1158820
01/16/12 09:17 PM
01/16/12 09:17 PM
|
Joined: Feb 2009
Posts: 583 San Antonio, TX
CurYellowBird
OP
mopar
|
OP
mopar
Joined: Feb 2009
Posts: 583
San Antonio, TX
|
Don't have heads as of this moment. Just got my 452 heads back from the machinist and the valve seats have cracks showing after the magnaflux.
I'm going to buy a set of heads from aeroheads and have a choice of either open chamber 452-906 style or 516-915 style. Going with iron heads and pump gas.
The head gasket I'm looking at is the steel shim style with .040 thickness or maybe a standard felpro replacement.
So no on heads being milled, the block has not been decked as I think the higher CH with the forged 2355's will compensate for how far the stockers were in the hole.
That calculator you put up daytonaturbo is showing me almost at 11:1.
What are the benefits to quench or no quench?
Last edited by CurYellowBird; 01/16/12 09:21 PM.
Project War Bird:
1971 Plymouth Roadrunner
383 4 speed with air conditioning
GY3 Curious yellow
All original
|
|
|
Re: 440 Compression
[Re: RapidRobert]
#1158823
01/16/12 09:47 PM
01/16/12 09:47 PM
|
Joined: Feb 2009
Posts: 583 San Antonio, TX
CurYellowBird
OP
mopar
|
OP
mopar
Joined: Feb 2009
Posts: 583
San Antonio, TX
|
Those TRW's felt to be just slightly heavier than the cast ones but not that heavy.
Let me give you guys some more specs on the overall car.
- 71' Roadrunner - 4 speed - EZ-EFI Fuel Injection Kit - 3.55 rear - Plan on going with Hughes Cam
With the fuel injection, the lowest I want to go on the LSA on the camshaft is 110. What I'm lost about is these 2355's are basically "6 pack" pistons, so how am I hitting close to 11:1 with stock style heads and 6 pack pistons in a 78' 440 when they supposedly had a taller deck?
I plan on aeroheads simply for just the heads themselves. I'll be swapping all the hardware anyways to match what Dave or Kevin over at Hughes Engines recommends.
Project War Bird:
1971 Plymouth Roadrunner
383 4 speed with air conditioning
GY3 Curious yellow
All original
|
|
|
Re: 440 Compression
[Re: 82ramIndy493]
#1158824
01/16/12 09:52 PM
01/16/12 09:52 PM
|
Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
Too Many Posts
|
Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
|
Good quench will also let you run pump gas with higher comp then you can run without quench and not have pinging or detonation. The camshaft selection will also help at controling cyl pressure as to high a cyl pressure will want to let it detonate more. Ron
Last edited by 383man; 01/16/12 09:53 PM.
|
|
|
Re: 440 Compression
[Re: 82ramIndy493]
#1158825
01/16/12 09:54 PM
01/16/12 09:54 PM
|
Joined: Feb 2009
Posts: 583 San Antonio, TX
CurYellowBird
OP
mopar
|
OP
mopar
Joined: Feb 2009
Posts: 583
San Antonio, TX
|
82Ram,
Yeah I pulled it out of a 78' RV at pick-n-pull with only 30k miles on it. Paid 220 for the complete long block.
I never understood what people meant by those extra passages. They kept calling them "peanut" something passages.
Project War Bird:
1971 Plymouth Roadrunner
383 4 speed with air conditioning
GY3 Curious yellow
All original
|
|
|
Re: 440 Compression
[Re: CurYellowBird]
#1158827
01/17/12 01:02 AM
01/17/12 01:02 AM
|
Joined: Jan 2003
Posts: 75,282 A gulag near you.
JohnRR
I Win
|
I Win
Joined: Jan 2003
Posts: 75,282
A gulag near you.
|
Quote:
so how am I hitting close to 11:1 with stock style heads and 6 pack pistons in a 78' 440 when they supposedly had a taller deck?
What leads you to believe that the block you have has a taller deck , no such animal exists for B or RB blocks .
Also where are you getting 78cc number when you don't even have the heads yet ?
The 2.061 piston will be roughly .020 in the hole on a blueprint spec block of 10.725 using factory 6.768 rods, aftermarket rods are usually .008 shorter and it seems that the block could be a little taller than spec, maybe .010 ...
|
|
|
Re: 440 Compression
[Re: JohnRR]
#1158828
01/17/12 01:16 AM
01/17/12 01:16 AM
|
Joined: Feb 2009
Posts: 583 San Antonio, TX
CurYellowBird
OP
mopar
|
OP
mopar
Joined: Feb 2009
Posts: 583
San Antonio, TX
|
From what I've read on other forums (should have taken that info with a grain of salt) the later 74-78 440 blocks were slightly taller and used a short piston in order to achieve 7.5 to 8:1 compression.
I'm getting 78cc because that is what aero heads advertises there closed chamber heads while the open chamber heads run larger chambers.
I'm re-using the stock LY rods that came in the 78 440 since they were in excellent shape.
The reason I asked that is because the stock 440+6 had compressions advertised at 9.7 to 10:1. That's why I asked because I was having an "o sh**" moment. So without decking the block I should be fine on pump gas and compression.
What heads did the majority of 440+6 motors use? 915 or 906? I know the last ones used the 346 heads.
Project War Bird:
1971 Plymouth Roadrunner
383 4 speed with air conditioning
GY3 Curious yellow
All original
|
|
|
Re: 440 Compression
[Re: JohnRR]
#1158830
01/17/12 02:48 AM
01/17/12 02:48 AM
|
Joined: Feb 2009
Posts: 583 San Antonio, TX
CurYellowBird
OP
mopar
|
OP
mopar
Joined: Feb 2009
Posts: 583
San Antonio, TX
|
I know there is nothing special with aero. I'm just looking for good cast iron replacements. Don't want to go with aluminums and deal with that. Just my preference.
I would like to just get a bare set from them rather than complete.
Project War Bird:
1971 Plymouth Roadrunner
383 4 speed with air conditioning
GY3 Curious yellow
All original
|
|
|
Re: 440 Compression
[Re: CurYellowBird]
#1158831
01/17/12 03:35 AM
01/17/12 03:35 AM
|
Joined: Feb 2003
Posts: 21,318 Manitoba, Canada
DaytonaTurbo
Too Many Posts
|
Too Many Posts
Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
|
Quote:
What heads did the majority of 440+6 motors use? 915 or 906? I know the last ones used the 346 heads.
6 pack engines never used a closed chambered head. They ran an open chamber head closer to 90cc's. For the 10.6 CR quote I gave, I assumed a 4.35 bore, .020 steel shim head gasket and the 2355's sitting about .020-.025 in the hole, which is a fair guess assuming a stock deck at or a little taller than the 10.725 blueprint spec. Also the 2355's have a 6cc valve relief in them so factor that into play as well. With the 90cc open chamber, compression drops down to about 9.5 which is more realistic for a stock 1970 6-pack. However with the open chamber you lose quench so what you gave up in compression you lose in quench so I don't know how much better off you really are in terms of detonation resistance.
|
|
|
Re: 440 Compression
[Re: DaytonaTurbo]
#1158832
01/17/12 02:07 PM
01/17/12 02:07 PM
|
Joined: Feb 2009
Posts: 583 San Antonio, TX
CurYellowBird
OP
mopar
|
OP
mopar
Joined: Feb 2009
Posts: 583
San Antonio, TX
|
Are big block mopars really that prone to detonation? I know that working on a sbc that I never considered quench into the equation when I was building it and I've only ever heard the term with mopars. Did the factory ever utilize quench in most engine builds? Can you utilize quench without getting into high compressions?
Project War Bird:
1971 Plymouth Roadrunner
383 4 speed with air conditioning
GY3 Curious yellow
All original
|
|
|
Re: 440 Compression
[Re: DaytonaTurbo]
#1158833
01/17/12 02:17 PM
01/17/12 02:17 PM
|
Joined: Jan 2003
Posts: 16,376
dogdays
I Live Here
|
I Live Here
Joined: Jan 2003
Posts: 16,376
|
First of all with a B or RB engine the steel shim head gaskets are available so having a piston 0.020" down in the hole is all right. Squish with a closed chamber head will be at the optimum 0.038". Second, I do not believe the RB deck of 10.725" was changed from 1958 to 1979. But those motors' decks are all over the place and famously not square, tilted front to back or even side to side. So spend the money and get the decks squared and you can set your piston depth at the same time. Third, the Speed Pros are meant to be a stock weight replacement. Fourth, the closed chamber heads are better and of the two, 915s are the best. They usually came with 84cc chambers, so a 78cc head has been cut a bit. However, the newest of them is 45 years old and things happen..... Fifth, you should know that MOPAR engines of that era usually came with real compression ratios about one point lower than the advertised compression. So any 10.5:1 engine was really closer to 9.5:1, etc. If you build an engine to the published compression ratio it will have a hard time on pump gas. So I'd say run an honest 9.5:1 with the closed chamber head, , which means a total of 107.5 cc above the piston. With an 84cc head and 0.039" squish distance that means you remove an additional 5.5 cc from the chamber, probably can be done by unshrouding the intake valves a little. For a 78cc head you take off something like 11.5 cc which I would do by cutting a little off the top of the piston in the non-squish area. If you were to use an open chamber head I'd run no more than a real 9.0:1 so you'd have metal to move in that case as well plus a much worse combustion chamber. There's a reason that the new heads for most every engine everywhere have squish, you need it too.
All in all it's not that bad a situation in which to find oneself.
R.
|
|
|
Re: 440 Compression
[Re: CurYellowBird]
#1158834
01/17/12 02:48 PM
01/17/12 02:48 PM
|
Joined: Feb 2003
Posts: 21,318 Manitoba, Canada
DaytonaTurbo
Too Many Posts
|
Too Many Posts
Joined: Feb 2003
Posts: 21,318
Manitoba, Canada
|
Quote:
Are big block mopars really that prone to detonation?
Yes and no. Depends on the build and fuel quality. Many of us are trying to squeeze performance to the ragged edge, ie run as much compression as we can get away with, because compression + cam =
Quote:
Did the factory ever utilize quench in most engine builds?
No. But like said already, the factory built to a lower compression ratio that was actually advertised, and leaded fuels back then were better than the garbage we have today.
Quote:
Can you utilize quench without getting into high compressions?
Yes! With a closed chambered head, you can run a piston with a D shaped dish. So one side of the piston gets nice and close to the closed part of the chamber, the .040 or so clearance, and the dish is under the open part of the chamber. This allows you to run quench and get the compression ratio you desire. This is the only way you can get quench in a stroker without running 12:1 pistons!
|
|
|
|
|