piston ?
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From: kansas
piston ?
Will 302 pistons fit in a 351 with stock rods and crank? I know the bore is the same but what about comp height and pin size. I,m in process of building backup motor for next seasons fun on the dirt.
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As an example, trick flow offers pistons of the 302 variety and list them as having 1.6 compression height and 351 as having 1.785. They list the stroker 393 pistons as having 1.61 which is why you can use the 302 pistons on a 393 stroker kit. later
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From: Still under the hood in O
If you use the 302 pistons with the stock length stroke and the rod of the 351W (9.503 deck height) without decking the block, the piston would be .19 down in the hole.
Yes, you could use it. But, with it that far down you would have severe detonation.
Deck height equation;
(DH - stroke/2) - (CH + Rod Length)
Using the 302 pistons - (stock 302 from factory has 1.605 CH)
(9.503 - 3.5/2) - (1.605 + 5.956)
7.753 - 7.561 = .192
Using stock 351W pistons (stock 351 from factory has 1.769 CH)
(9.503 - 3.5/2) - (1.769 + 5.956)
7.753 - 7.725 = .028
Notice the 351W has a stock piston to deck clearance of .028, this results in a fairly poor quench right from the factory (.028 + head gasket thickness/ .028+.039=.067 quench). This is the reason we always should consider having the block zero decked to improve the quench when doing a rebuild. But the difference with the 302 piston is night and day.
Yes, you could use it. But, with it that far down you would have severe detonation.
Deck height equation;
(DH - stroke/2) - (CH + Rod Length)
Using the 302 pistons - (stock 302 from factory has 1.605 CH)
(9.503 - 3.5/2) - (1.605 + 5.956)
7.753 - 7.561 = .192
Using stock 351W pistons (stock 351 from factory has 1.769 CH)
(9.503 - 3.5/2) - (1.769 + 5.956)
7.753 - 7.725 = .028
Notice the 351W has a stock piston to deck clearance of .028, this results in a fairly poor quench right from the factory (.028 + head gasket thickness/ .028+.039=.067 quench). This is the reason we always should consider having the block zero decked to improve the quench when doing a rebuild. But the difference with the 302 piston is night and day.
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90f150moneypit
You state the 302 piston would be .19 down in the hole and the 351 would be .028 which would mean there is more space between the piston top and deck surface that would equal more cc with the 302 pistons which would equal a lower compression ratio. How would that equal severe detonation, I would think it would equal a sad motor with no power? Lemme know. later
You state the 302 piston would be .19 down in the hole and the 351 would be .028 which would mean there is more space between the piston top and deck surface that would equal more cc with the 302 pistons which would equal a lower compression ratio. How would that equal severe detonation, I would think it would equal a sad motor with no power? Lemme know. later
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From: Still under the hood in O
It would result in low compression. But with the piston that far down, by the time the motor fires, the fuel mixture is no longer in the combustion chamber (actually as soon as the fuel mixture enters the chamber it drops down into the hole). The heat from the cylinder walls detonates the remaining fuel, after the initial combustion. It's pretty hard to explain without a visual of the process. Another way to look at it - all of the A/F mixture isn't burned in the combustion chamber, the rest is burned after the fact by means of detonation.
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Well I get what your saying, kinda. IF on the compression stroke it doesn't fully burn it won't really generate enough energy to cause a detenation (ping), if it continues to burn on the combustion stroke it will go out the exaust port in the form of a backfire, wouldn't it? Trying to calibrate my mental picture to yours. haha Later
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From: Still under the hood in O
Think of it as a secondary explosion. On the power stroke, after combustion takes place the piston is moving down. Then the hot spots in the cylinder ignite the unburnt fuel. On the compression and power stroke both valves are still closed, so there's no where else for it to go. This is the detonation that you can't hear like pre-ignition (ping), although pre-ignition can be caused by this as well except on the compression stroke as the piston is on the way up.
Like I said it's pretty hard to describe, you may be able to find in depth articles by doing a search for 'quench and detonation' or something similar.
Like I said it's pretty hard to describe, you may be able to find in depth articles by doing a search for 'quench and detonation' or something similar.
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From: Still under the hood in O
Because some of the fuel is farther down in the hole, away from the combustion chamber. There is no way for the ignition to be able to light off all the fuel that far down.
One other cause is, the fuel can and will light off before the ignition from the hot spots in the cylinder. Remember, the piston would be over 3/16" in the hole, exposing a lot more cylinder area to fuel than it normal would instead of just the combustion chamber.
One other cause is, the fuel can and will light off before the ignition from the hot spots in the cylinder. Remember, the piston would be over 3/16" in the hole, exposing a lot more cylinder area to fuel than it normal would instead of just the combustion chamber.
