Hi all,
I know this has probably been brought up in the past but my situation is a little different. I have an extra 400 setting in the garage, and I have a brand new set of TRW forged pistons (standard bore)installed on reconditioned rods with ARP rod bolts. I also have a set of rebuilt heads bronze guides,3 angle valve job, and adjustable rocker arm kit.I also have all necessary items too complete the engine except the cam. I will be installing this engine with a 4 barrel carb and headers into my 79' F-350 4x4. question #1 how much can the block be decked and /or the heads milled to bump up the compression ? Is this a good route to take? 8.25 : 1 seems awful low. My main concern is torque and drivability.

Thanks,
solidaxle

 

>question
>#1 how much can the
>block be decked and /or
>the heads milled to bump
>up the compression ?

solidaxle,

You can mill the block down to zero deck clearance. If you want to mill the heads after milling the block down to zero deck clearance, I'd recommend using clay to make sure you don't crash the piston into the valves or spark plug.

If you have the specs for the pistons, you can use this calculation to determine deck clearance.

deck height - (stroke/2 + rod length + piston compression height)

Stock 400 numbers are:

deck height = 10.297"
stroke = 4.0"
rod length = 6.580"
compression height = 1.650"

10.297 - (2.0 + 6.580 + 1.650) = 0.067"

You can calculate the static compression ratio with the formula

SV/CV + 1

SV = swept volume
CV = clearance volume

swept volume = ((bore/2)*pi) * stroke

clearance volume = (deck clearance volume + gasket thickness volume + combustion chamber volume + piston top relief volume)

If you have the specs for your piston compression height and top relief volume, you can calculate the CR.

To determine the effect of milling the block/heads on CR, just subtract the proposed milling amount from the deck height number in the formula above.

>Is
>this a good route to
>take? 8.25 : 1 seems
>awful low.

I would recommend increasing compression by using different pistons rather than milling the block/heads. You can get inexpensive cast pistons to increase CR to around 9:1. You can mill the block/heads a little to get some more CR, or if you want a lot more, you can use 351C pistons. To use the 351C pistons, you'll have to bush the top end of the rods to accept the slightly smaller 351C pins, and then you can use just about any 351C piston you want.

If you want to keep your forged pistons, you'll have to mill the block/heads to increase CR.

Don't forget, you'll have to get the intake manifold milled to fit if you mill more than about 0.050" total from the block/heads. You might also have trouble with the valley pan intake gasket if you do much milling.

>My main concern
>is torque and drivability.

The cam is a big factor in getting power out of an M-block. I built a 400 for a guy with the same truck ('79 F350 4x4) and used the Comp Cams 265DEH. The specs for that cam are 265 adv dur, 211/223 @ 0.050", 0.484"/0.510" gross lift. The engine had about 9.4:1 CR using Keith Black 351C hypereutectic pistons and it's still going strong at about 60K miles. The power is good (485 ft/lb and 388 hp), but it could be better.

Next time, I'll use a cam with a little more duration and lift (about 215/225 @ 0.050" and 0.510"/0.530").

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.

 

 

10:1 BADGER pistons part # 400-100f ordering info: 1-626-869-0270

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77'FORD F150 XLT 400