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Upping the Comp ratio on a 400, engine builders please
#2106422
07/08/16 07:39 PM
07/08/16 07:39 PM
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Joined: Jan 2003
Posts: 2,345
west palm beach, florida
modelmakerinc
OP
top fuel
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OP
top fuel
Joined: Jan 2003
Posts: 2,345
west palm beach, florida
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OK SUPER LOW BUCK DEAL. basically stock '76 400, runs well, doesn't smoke but low on power. I want to do nothing more than swap out the low compression pistons for some KB240 ones, I do not want to do this if it needs to be bored oversize, I do not want to do any thing other than bump the compression.
QUESTION....when the heads come off, with a dial/bore gauge what is the maximum the cylinders can be to use standard bore pistons /rings???
If it has too much wear and needs to be bored, I will not take it apart father and it will go right back together.
If I can go the route of new pistons, I will mill the heads and deck the block only minimal to clean-up the surfaces, and be able to use fel-pro composite gaskets and gain cc's
Last edited by modelmakerinc; 07/08/16 07:40 PM.
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Re: Upping the Comp ratio on a 400, engine builders please
[Re: modelmakerinc]
#2106606
07/09/16 12:35 AM
07/09/16 12:35 AM
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Joined: Aug 2003
Posts: 43,228
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,228
Bend,OR USA
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If the bore tapered is over .003 from top to bottom I would bore it and replace the pistons and rings  That being said some old time mechanics back when I was young, right after dirt was invented  ,use to say if has over .015 taper bore it  
Last edited by Cab_Burge; 07/09/16 12:35 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Upping the Comp ratio on a 400, engine builders please
[Re: modelmakerinc]
#2106729
07/09/16 10:26 AM
07/09/16 10:26 AM
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Joined: Feb 2005
Posts: 4,316
Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,316
Prospect, PA
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What is your budget? IMO, it is really hard to tear into a short block, change a bunch of stuff, and come out on the cheep.
Also, in my limited experience, it seems that a really good set of heads on even a well seasoned short block, can give a big bump in performance.
If you sell what you have, and buy some aluminum heads, have them gone through, mill to 70 or 72 cc, you might not be into it for much more $ than what you are thinking now, with a more certain outcome. Just a thought.
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Re: Upping the Comp ratio on a 400, engine builders please
[Re: modelmakerinc]
#2106791
07/09/16 01:03 PM
07/09/16 01:03 PM
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Joined: Jan 2003
Posts: 14,506
So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,506
So. Burlington, Vt.
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What is your budget? IMO, it is really hard to tear into a short block, change a bunch of stuff, and come out on the cheep. This is my experience as well. Cheapest option in my mind is, mill the heads about .060-.070, steel shim gaskets, adjustable pushrods(if you don't have an adjustable valvetrain now). While the heads are off and apart, have them cleaned and do a quicky bowl blend.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
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Re: Upping the Comp ratio on a 400, engine builders please
[Re: modelmakerinc]
#2108057
07/11/16 06:44 PM
07/11/16 06:44 PM
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Joined: Jan 2012
Posts: 2,652
Stuttgart, Arkansas
rickseeman
master
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master
Joined: Jan 2012
Posts: 2,652
Stuttgart, Arkansas
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OK SUPER LOW BUCK DEAL. basically stock '76 400, runs well, doesn't smoke but low on power. I want to do nothing more than swap out the low compression pistons for some KB240 ones, I do not want to do this if it needs to be bored oversize, I do not want to do any thing other than bump the compression.
QUESTION....when the heads come off, with a dial/bore gauge what is the maximum the cylinders can be to use standard bore pistons /rings???
If it has too much wear and needs to be bored, I will not take it apart father and it will go right back together.
If I can go the route of new pistons, I will mill the heads and deck the block only minimal to clean-up the surfaces, and be able to use fel-pro composite gaskets and gain cc's The motor is 40 years old. I feel that is why it's down on power. Going thru all the work and expense you are talking about to only increase the compression, and nothing else, I feel will give you less than exciting results. The motor is tired dude. I recently tore down 4 1976 400's. It will need everything.
2011 Drag Pak Challenger
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Re: Upping the Comp ratio on a 400, engine builders please
[Re: lewtot184]
#2108095
07/11/16 07:42 PM
07/11/16 07:42 PM
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Joined: Jan 2003
Posts: 25,881
Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,881
Rio Linda, CA
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my experience with the kb's i've used is that the bore size needs be on the money to achieve recommended clearance. .001"-.002" larger and they're pretty noisey, in fact they're a little noisey cold at .002"-.0025". Better to hear 'em than to smell 'em. 
The INTERNET, the MISinformation superhighway
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Re: Upping the Comp ratio on a 400, engine builders please
[Re: modelmakerinc]
#2108735
07/12/16 02:37 PM
07/12/16 02:37 PM
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Joined: Jul 2008
Posts: 610
Boise
Moparteacher
mopar
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mopar
Joined: Jul 2008
Posts: 610
Boise
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Run a ridge reamer on the top of the cylinders prior to piston removal. Ball hone with an appropriate grit to match the rings, and put it together. If you're worried about piston slap you may consider knurling the pistons and then use a flat file to size the pistons to the individual cylinder. You'll have to check with a machinist as to whether a hypereutectic will take a knurl the same as a cast piston. Stock bore is 4.342. Rings are available in 4.350 for $40. That's .008" over. File fit the rings. Run the steel shim gasket sold through Summit for $25. https://www.summitracing.com/parts/dcc-4286754/overview/It'll use a little oil and make a little noise, maybe, but it'll run, just don't expect to get 200k miles out of it.
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Re: Upping the Comp ratio on a 400, engine builders please
[Re: modelmakerinc]
#2109332
07/13/16 01:06 PM
07/13/16 01:06 PM
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Joined: Jan 2003
Posts: 75,058
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,058
U.S.S.A.
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If I can go the route of new pistons, I will mill the heads and deck the block only minimal to clean-up the surfaces, and be able to use fel-pro composite gaskets and gain cc's
Where is Dan when you need him ?? You are going to do ALL that and you can't come up with MAYBE another $300 to BORE it ... seriously ??? Ignore the ridge reamer recommendation , if you don't know what you are doing with it then you will do more HARM than good to the block. I have personally been burned by someone that didn't know how to use one ... had to sleeve a block because it took .075 overbore to get a clean pass, top to bottom, on one cylinder , .040 on the one next to it , the 2 next to those at .030 , the other side would have cleaned at less ...
running up my post count some more .
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Re: Upping the Comp ratio on a 400, engine builders please
[Re: JohnRR]
#2109430
07/13/16 04:03 PM
07/13/16 04:03 PM
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Joined: May 2008
Posts: 5,399
Aurora, Colorado
451Mopar
master
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master
Joined: May 2008
Posts: 5,399
Aurora, Colorado
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If I can go the route of new pistons, I will mill the heads and deck the block only minimal to clean-up the surfaces, and be able to use fel-pro composite gaskets and gain cc's
Where is Dan when you need him ?? You are going to do ALL that and you can't come up with MAYBE another $300 to BORE it ... seriously ??? Ignore the ridge reamer recommendation , if you don't know what you are doing with it then you will do more HARM than good to the block. I have personally been burned by someone that didn't know how to use one ... had to sleeve a block because it took .075 overbore to get a clean pass, top to bottom, on one cylinder , .040 on the one next to it , the 2 next to those at .030 , the other side would have cleaned at less ... I agree. Usually if the ridge is that bad, the block needs an overbore, and most people usually take too much out with a ridge reamer making things worse. Been there and done that and learned from my mistake. A friend raced a low compression 400 engine with decent results. It had a decent sized cam and ported heads, with 6-pack intake and headers. He just used a high stall converter and higher gears to get past the weak low end torque.
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