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400 motor

Posted By: DusterKid

400 motor - 12/28/08 09:50 PM

I know the stroke of a 400 is slighty less than a 440 (4.375 vs 4.750 I think), but the pistons are also .020 larger in size. Would taking a 400 motor, and having it bored out .010 and use a 440 .030 piston help bring up the compression? I know 400 lack compression because the pistons are so far in the hole, so would using a 440 piston help bring up the piston any? or is the wrist pin in the same position on each of the pistons? also i'm assuming you can use a 440 rod in a 400 since they take the same rod bearing, so would a 440 rod work with either a 400 or 440 piston? also if you can indeed use a 440 rod and bring the piston (either 400 or 440 if either can be used) flush with the top of the block, how would that motor run compared to a 440 with the same compression and setup? would the different stroke of the crank make that big of a difference?
Posted By: CompWedgeEngines

Re: 400 motor - 12/28/08 10:09 PM

OK, I'm going to try and help you out here without making this too long. You have said a lot, but its not all correct!

The stroke of a 400 low deck motor is 3.38" and a RB ( 440) is 3.750. The deck heights are 9.98 vs 10.725 respectively.

A typical 440 piston is 2.061 inches. Take that, add it to the stock 400 stroke, add for crank travel and add in the stock 440 rod length and you'd arrive at 10.511 inches. That means the piston would be above the block over .500 inches.

Take your scenario and use the 400 rod ( 6.358, add for crank throw, and add in the height of a stock 440 piston and you would arrive at 10.109, which means the piston is still .11o above the deck surface.

What you are ultimately asking for is a 451" or 470" type of stroker motor, very very common.This would be a 440 crank in a 400 block, with changes made to the crank, piston and rods. The pistons need to be custom ( there are some stocking part numbers now however) because of the difference in compression height.

Adding stroke will have more of an impact on compression that will the larger bore. The larger bore helps in other areas however.

The stroker motor will certainly run better if cammed properly and especially in a heavy car. The addition of the cubic inches alone doesnt amount to a hill of beans. Its the additional stroke that creates the torque, which moves the vehicle. There are many other factors, but this is a quick explanation.
Posted By: Sledge_57

Re: 400 motor - 12/28/08 10:25 PM

Sounds to me what he's looking to do is increase the compression without breaking the bank.

Doesn't someone, KB maybe, make a higher compression piston for a 400?

Of course if you got the money a stroker is the way to go with that 400, a 470 is lots of fun, trust me
Posted By: Blown61

Re: 400 motor - 12/28/08 10:27 PM

Quote:

Sounds to me what he's looking to do is increase the compression without breaking the bank.

Doesn't someone, KB maybe, make a higher compression piston for a 400?

Of course if you got the money a stroker is the way to go with that 400, a 470 is lots of fun, trust me




How does one make a 470??
Posted By: 440Jim

Re: 400 motor - 12/28/08 10:34 PM

Lots of details in the 440 crank into a 400 block swap, but it is very common. As stated the matching piston compression height and rod length to achieve the piston to deck distance is the key.

A 3.750" stroke in a 4.375" bore is a "451 CID".
One way is a piston compression height (CH) of 1.320", rod length of 6.76". The compression ratio will depend on the head chamber volume (cc), the valve relief size (4cc), and the block deck height (piston to head).
Posted By: DusterKid

Re: 400 motor - 12/28/08 10:57 PM

Thanks for the info guys. Reason I asked is I have a 400 block that was bored .010 over and has .030 440 pistons in it and they come flush to the top of the block. Not sure what part # the pistons are but remember that they were purchased and once received noticed that they were designed to lower the compression in the motor to be capable of running "todays gas". So I'm guessing they are .030 replacement pistons for the newer 440 motors (76-78) that only had 8:1 compression or so. I can't remember what rods were used in the combo and I don't want to tear the motor apart as it is complete, so I'm thinking I must have used the 400 rods and with the 440 pistons being (I don't know the correct term, but have the wrist pin higher up in the piston to lower compression) made it come flush to the top of the block.
Posted By: Sledge_57

Re: 400 motor - 12/28/08 11:21 PM

Quote:

Quote:

Sounds to me what he's looking to do is increase the compression without breaking the bank.

Doesn't someone, KB maybe, make a higher compression piston for a 400?

Of course if you got the money a stroker is the way to go with that 400, a 470 is lots of fun, trust me





How does one make a 470??







Some answers here:

http://www.moparts.org/Tech/Archive/bb/38.html
Posted By: challenger73400

Re: 400 motor - 12/28/08 11:23 PM

Quote:

Thanks for the info guys. Reason I asked is I have a 400 block that was bored .010 over and has .030 440 pistons in it and they come flush to the top of the block. Not sure what part # the pistons are but remember that they were purchased and once received noticed that they were designed to lower the compression in the motor to be capable of running "todays gas". So I'm guessing they are .030 replacement pistons for the newer 440 motors (76-78) that only had 8:1 compression or so. I can't remember what rods were used in the combo and I don't want to tear the motor apart as it is complete, so I'm thinking I must have used the 400 rods and with the 440 pistons being (I don't know the correct term, but have the wrist pin higher up in the piston to lower compression) made it come flush to the top of the block.





That's what I did. My pistons ended up .008 in the hole for a 9.3:1 CR. Stock 400 rods but I don't remember the part no for the pistons. I went with a .038 over bore and .060 over 440 pistons.
Posted By: 440Jim

Re: 400 motor - 12/29/08 12:21 AM

Quote:

Would taking a 400 motor, and having it bored out .010 and use a 440 .030 piston help bring up the compression?


I see you are asking about using a 400 crank and 440 pistons in a 400 block. There were several variations, by year, in 440 piston compression heights (pin to top of piston). Even some replacement pistons had variations from factory specs.

I have no idea what you have. But for example, I measured:

440 piston: 1.924" CH
400 piston: 1.826" CH

The block height can also easily vary 0.030" from the factory.
Here is an example, put in your numbers:

1.69 Stroke divided by 2 (3.38/2)
6.358 Rod length
1.926 Piston Compression height
------
9.974"

If the block was 9.980", the piston would be 0.006" down the hole.
Posted By: forphorty

Re: 400 motor - 12/29/08 12:33 AM

yep, 440 pistons in a 400. done it. the late 70s replacement piston. i think the pn for trw forged was 2388. i just used a cast piston, badger i think.no mods. was down in hole about .010. i think someone here used a 2266 but had to modify it to clear the head as it was positive deck. was once probably the cheapest way to get compression in a 400. there are probably better options now.
Posted By: Blown61

Re: 400 motor - 12/30/08 04:51 PM

Is this doable with a 383 and a standard bore 440 piston?
Posted By: 440Jim

Re: 400 motor - 12/30/08 08:24 PM

Quote:

Is this doable with a 383 and a standard bore 440 piston?


The 383 bore is 4.25", while the 440 bore is 4.32". Too much to bore, the cylinder walls would likely be too thin, IMO.

The 400 bore is 4.34" to start with.
Posted By: Glen440

Re: 400 motor - 12/30/08 11:00 PM

I looked into the 440 piston in a 400 a long time ago. The biggest drawback is those cheap pistons have no valve reliefs. It was cheaper for me to just put cheap KB's in it.
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