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Old 03-15-2000, 08:10 PM
Duster440 Duster440 is offline
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how can u tell if your engine's deck height is too high and is causing bad compression ,without hauling the heads off?i havve a 76 440 and wanted to know if the deck height is too large and would i get it milled off? would heads and stuff still fit fine? thanks.
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Old 03-15-2000, 10:45 PM
Chris A Chris A is offline
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The deck height is set by the factory and won't cause "bad compression". It may be lower than you like but it is the stock ratio. If your rings are worn or your valves aren't sealing, this is when you have bad compression.

The stock compression ratio on your motor is probably around 8.5. Has your deck or heads ever been cut? If not you can raise your compression by cutting the heads .050, but I would recommend also cutting the intake face to copensate, so .0123 for every .010 decked off the heads, total of .061 on intake face, ( My intake didn't fit after i cut my block/heads .030) Also you will have to check your lifter preload and adjust accordanly with rocker shaft shims.

If the motor has a lot of miles on it and compression is lowered because of poor ring/valve seating, decking the heads will not solve your compression problems. Otherwise good luck.



[This message has been edited by Chris A (edited March 15, 2000).]
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Old 03-16-2000, 12:35 AM
Duster440 Duster440 is offline
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could i just put higher comp pistons and a cam or somthing like that? what would i have to do to get around 375 hp?
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Old 03-16-2000, 04:23 AM
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440 Jim 440 Jim is offline
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Just to be sure everyone is talking about the same thing, a few definitions are in order. I will attempt to get things started, if I am wrong please post.

Deck height: The distance from the center of the crankshaft to the top of the block cylinder (deck). Typically 10.725 for RB blocks, 9.980 for B blocks.

Compression height: The distance from the center of the piston pin (rod small end) to the top of the piston (for flat top), excluding any dome. i.e. the dome extends above the top of the piston for this definition.

Rod length: the distance between the center of the big end of the rod and the small end. Typically 6.768 for RB, 6.358 for B engines.

Compression ratio: too many details to post here...



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440 Jim
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Old 03-16-2000, 09:26 AM
BB 70 Challenger BB 70 Challenger is offline
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Yeah, 440 Jim has it right on. Those were the facts on right terms.

Duster440: sure you can change the pistons to get more compression. The biggest problem with cheap smog 440´s is that in order to get them to run on low octane fuel the factory put such pistons inside, that at TDC the piston is still some 0.15-0.175 of an inch down the bore.

That´s around 4mm, and it sure kills compression. And makes future performance upgrades either difficult or expensive. Or both. Trust me, been there done that :-(

The problem when changing pistons is that if the new pistons weight less or more than the ones installed at the factory (they normally do), the crank, damper, flexplate, one rod and piston with rings has got to be balanced at a pro shop. Otherwise there will be an annoying vibration in around 3500-4000 rpms. And that all costs: new rings, pistons, pressing them to rods, new bearings, gaskets... no wonder many guys just skip the expensive balancing act.

And because most guys don´t know this so most self built engines vibrate = are out of balance. And they say "it doesn´t matter", or "these things always shake a bit" or something like that ;-) And I have to admit again: been there, done that myself :-(

Well, those were just my opinions, I may be wrong. Keep up the good work, guy
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Old 03-16-2000, 01:42 PM
DartGT66 DartGT66 is offline
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The factory balance is way off in many cases, so I suggest a balance job even if doing just a basic rebuild. If you have a '76 440 with 8.5:1 real CR, you have a good starting point. However, they tend to be well in the 7's rather than 8's. Switching to other pistons, like TRW '10:1' L2266F's will propably take your CR to high 8's without milling. Don't bother using the MP 9:1 cast pistons, the 9:1 is bull. So to get the CR where you want it to, you have to measure everyhting first and then choose the pistons with the correct compression height to take you where you want to, and maybe do some finetuning with milling. To get 375 real hp out of a 440, use a cam with about 280 degrees and .48" lift, 9.5:1 CR, performer rpm intake with a 3310 holley and headers, and you should be pretty close.
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Old 03-16-2000, 09:08 PM
Duster440 Duster440 is offline
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would that engine in a duster just be extra weight the way it is now? should i just leave my 318 or 360 in until i get some milling done to the 440?
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Old 03-17-2000, 07:41 AM
DartGT66 DartGT66 is offline
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No, you can't even talk about a 360 and a 440 on the same day. While you can make a 360 a good runner, it can't match the 440's low end torque. Even in stock form you will ahve a great driver. I drove many years with a 360 Valiant, and it run pretty well, 13.2's at 106 mph with 3.23 gears and street tires. However, the engine needed a big stall converter and liked rpm. I replaced it with a pretty stock 8.7:1 magnum with a stock converter, and with the torque the car run 12.9's at 109 mph wiht the same gear ratio and tires. A lot more fun.
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