3 7/8" sroke?
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Freshman User
Joined: Aug 2003
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3 7/8" sroke?
just measured the stroke for the first time on my engine and it is 3 7/8" what is this out of. i thought that is was a 390 .060 over but the stoke is to long for a 390.
got her apart to find the source of the wonderful metal shavings in the oil pan.
got her apart to find the source of the wonderful metal shavings in the oil pan.
Posting Guru
Joined: Nov 2003
Posts: 1,888
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From: Iowa
nothin has that stroke, not an FE anyway, id bet money on its a 390, when you measure with a dowel in the cylinder your not going to come up exact by no means. like i said before hers the stroke for FE's
352-3.5 bore-4.0
360-3.5 bore-4.05
390-3.78 bore-4.05
406-3.78 bore-4.13
410-3.98 bore-4.05
427-3.78 bore 4.23
428-3.98 bore 4.13
352-3.5 bore-4.0
360-3.5 bore-4.05
390-3.78 bore-4.05
406-3.78 bore-4.13
410-3.98 bore-4.05
427-3.78 bore 4.23
428-3.98 bore 4.13
Last edited by fordman428; Mar 1, 2004 at 04:40 PM.
FE "Freakin Expensive"
Joined: Dec 2003
Posts: 6,461
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From: Smith Mountain Lake, VA
Well we know its not a [454] that much we do know!!!! LOL!!
What did you measure it with??
Its a 390 with just super worn crank and rod bearings!! LOL!!
Just kidding!!! did you use a machinist scale to get to 100ths?
What did you measure it with??
Its a 390 with just super worn crank and rod bearings!! LOL!!
Just kidding!!! did you use a machinist scale to get to 100ths?
Lead Driver
Joined: Apr 2001
Posts: 6,175
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From: Texas
sounds like fuzzy math popping up again.
3 7/8" = 3.875" is almost exactly half way between the 3 3/4"=3.75" (3.78" may be the actual spec) of the 390/427 and the 3.98" stroke of the 428.
Either, you have a modified or aftermarket crank or you have a bad measurement.
My guess, you have an optimistic 3 3/4" stroke :-)
It is possible to get a stock crank ground for a slightly different stroke, as far as I understand.
3 7/8" = 3.875" is almost exactly half way between the 3 3/4"=3.75" (3.78" may be the actual spec) of the 390/427 and the 3.98" stroke of the 428.
Either, you have a modified or aftermarket crank or you have a bad measurement.
My guess, you have an optimistic 3 3/4" stroke :-)
It is possible to get a stock crank ground for a slightly different stroke, as far as I understand.
Postmaster
Joined: Nov 2002
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From: Littleton, CO
or are you measuring the distance from the top of the piston at BDC to the top of the deck surface? Since you have her apart, what is the crank number stamped in the second counterweight?
--Mike G
--Mike G
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Mountain Pass
Joined: Sep 2003
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From: Pulaski, NY
I just went through this. What I found to work was: take the heads off (I assume you already have) and pick a cylinder. Then bottom out that piston and measure distance to the deck of the block. Next, top out that same piston, and take another measurement to the deck of the block. The difference between the two measurements is the stroke.
Keep in mind that the first couple of times that I did this, I came out with some funky numbers, so I used a straightedge across the deck since the tops of the cylinders were worn enough to throw off my calibrated eye. Good luck!
Keep in mind that the first couple of times that I did this, I came out with some funky numbers, so I used a straightedge across the deck since the tops of the cylinders were worn enough to throw off my calibrated eye. Good luck!
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Posting Guru
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From: Iowa
i know this is off topic a bit but normally does a 390's pistons come just about level with the deck surface, i noticed when i was putting my 390 back togather my pistons just about come level with the decks surface.
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From: Long Island USA
Re: 3 7/8" sroke?
Originally posted by gunnabebad
got her apart to find the source of the wonderful metal shavings in the oil pan.
got her apart to find the source of the wonderful metal shavings in the oil pan.
Fordman428, when I did my 390, the block was decked a little bit, and my TRW flat-tops came right up to the top of the block. I'm assuming that that means that for a totally stock block, they should have been down in the cylinders .010-.020" ???
And, for gunnabebad, if you measured the stroke from the top of the block with the piston at BDC, this will give 3.78 + .010-.020 deck, makes your measurement almost perfect for a 390 if the deck height is .009".
Posting Guru
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From: yes
unless you specifically got car or high compression pistons your pistons sit that extra .125 (give or take more or less) in the hole at the top of the stroke too, you have a 390. you will not have 3 3/4" without bringing the pistons to zero deck height when you had the engine rebuilt. freakazoid came the closest, you really need to measure it with reference to the top and bottom of the stroke instead of just from the deck to the top of the piston
FTE Leadership Emeritus
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From: Long Island USA
Originally posted by FE427TP
unless you specifically got car or high compression pistons your pistons sit that extra .125 (give or take more or less) in the hole at the top of the stroke too, you have a 390. you will not have 3 3/4" without bringing the pistons to zero deck height when you had the engine rebuilt. freakazoid came the closest, you really need to measure it with reference to the top and bottom of the stroke instead of just from the deck to the top of the piston
unless you specifically got car or high compression pistons your pistons sit that extra .125 (give or take more or less) in the hole at the top of the stroke too, you have a 390. you will not have 3 3/4" without bringing the pistons to zero deck height when you had the engine rebuilt. freakazoid came the closest, you really need to measure it with reference to the top and bottom of the stroke instead of just from the deck to the top of the piston
A 390 with .125" deck clearance, with flat-top pistons, like the TRW's (with 9.7cc valve relief and a 67cc head, 10cc head gasket), gives a compression of 8.0645:1
My 360's had concave (dished) pistons, so did regular car 390 pistons, and the compression on those are 8:1. So, it sounds like you're way off... unless the 390 uses flat top pistons that are .125" down the cylinder? But, that ain't so...
Are you sure you're not thinking of the FT engines? They were pretty low, around 7:1 or so...
Posting Guru
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From: yes
My 360's had concave (dished) pistons, so did regular car 390 pistons, and the compression on those are 8:1. So, it sounds like you're way off... unless the 390 uses flat top pistons that are .125" down the cylinder? But, that ain't so...
well 390's in trucks did use 410 pistons that were .100 shorter than regular 390 pistons which would also make it .100 below deck, then they weren't level with the deck from the factory anyways this would make it more than .100 down from the deck, more like .115-.135 if using 410 and 428 specs for deck height, can you see the .010 or less difference on a tape measure? since the stroke is 3 7/8 which is within the tolerances I just mentioned he obviously doesn't have a 428 crank and it's not 3 1/2 so it's not a 360 so what else will it be?
