4.75.stroke

Will a 4.75 stroke scat crank fit in a D1 block?

Yes

Wil it fit ...? Yes
Will it pull the piston way out of the bottom of the bore, even with a really long rod ...? YES

Will it run reliably?

stanger68 wrote:Will it run reliably?

Define reliable ... How often do you wish to take it apart and put new rings in it and maybe new pistons; down a drag strip 40 times a summer, a once in a while cruiser, 10,000 or more miles, RELIABLE means a lot of different things to different people.

It probably will not blow-up ... that is considered reliable to many.

LOL, You are correct reliable is a relative term. I should've been more specific. This is for a tube chassis 1/8 mile drag car. Maybe I should elaborate. When weighing out options on crankshafts I noticed there really isn't much difference in cost of a 4.5 vs. 4.75 especially if you step up to the lightweight or super light models. Before doing any calculations on pistons I just thought I'd ask if it was a yes, yes with notching, or a hell no don't even go there.

Stanger68; The D9 block has a slightly longer bore. (+- .2")

Yes but I have two D1's on hand.

Why put that much stroke with a little bore in a factory block?

4.5" should be the max in a factory block. Beyond that, you should consider an A460 block or an Eliminator block.
The 4.75 will fit and work in a production block, but the piston comes out the bottom of the bore a little too much, and can cause a lot of wear and possibly galling of the piston skirts because as the rod changes direction, it 'rocks' the piston in the bore to one side. As the piston moves upward for the first few degrees, its not "straight" in the bore until probably after the wristpin travels back into the cylinder bore, past the bottom edge...thus it has to straighten itself out somewhere in the bottom half of the cylinder bore.

The longer cylinder bores of the aftermarket blocks will keep the piston straight in the bore all the way at the bottom.

The longer rod you can run the better. Putting the pin as high in the piston as possible helps with the rocking. Personally I wouldn't even bother with the 4.5 stroke.

BBFTorino wrote:4.5" should be the max in a factory block. Beyond that, you should consider an A460 block or an Eliminator block.
The 4.75 will fit and work in a production block, but the piston comes out the bottom of the bore a little too much, and can cause a lot of wear and possibly galling of the piston skirts because as the rod changes direction, it 'rocks' the piston in the bore to one side. As the piston moves upward for the first few degrees, its not "straight" in the bore until probably after the wristpin travels back into the cylinder bore, past the bottom edge...thus it has to straighten itself out somewhere in the bottom half of the cylinder bore.

The longer cylinder bores of the aftermarket blocks will keep the piston straight in the bore all the way at the bottom.

The D9 blocks do have similar cylinder lenghth compaired to the A460 blocks.

Yes. Are'nt they like a 1/4" (.250) inch longer or thereabouts??

Scott Foxwell wrote:The longer rod you can run the better. Putting the pin as high in the piston as possible helps with the rocking. Personally I wouldn't even bother with the 4.5 stroke.

Meaning?
Would not want to use 4.5 in factory block or go straight to 4.6 or 4.75?

Thanks,,
Sheldon G

I have built several 4.500 inch stroke D1 block engines and have had no problems. These were drag and mud truck engines.

I wouldn't want to try and get 100,000 miles out of it.

IDT-572 wrote:I have built several 4.500 inch stroke D1 block engines and have had no problems. These were drag and mud truck engines.

I wouldn't want to try and get 100,000 miles out of it.    

Mostly drag use, also have at least 2 D-9 blocks, a Dove A and some others I need to check casting #'s on.  Maybe just stick with 4.5" as to cylinder head limitations and being able to use the 6.8 rods I already have.
Thanks,,
Sheldon G.

STR-LGL-70 wrote:

Scott Foxwell wrote:The longer rod you can run the better. Putting the pin as high in the piston as possible helps with the rocking. Personally I wouldn't even bother with the 4.5 stroke.

Meaning?
Would not want to use 4.5 in factory block or go straight to 4.6 or 4.75?

Thanks,,
Sheldon G

I look at stroke from a piston speed view point, then look at the induction. The more stroke, the more demand on the induction because of increased piston acceleration (not necessarily mean piston speed). You also have to look at the mechanical issues with increased stroke like others are mentioning. Increased cylinder side loading and friction, increased piston rock, and pulling the piston out of the cylinder at BDC and this condition gets worse the closer the wrist pin is to the bottom of the cylinder. A long rod becomes mandatory and still, these issues persist.
I would not arbitrarily go to anything over 4.5" stroke unless the application absolutely dictated it. We had the choice when I built the 611 puller motor to go whatever stroke we wanted. We intentionally stayed with a shorter stroke (compared to others in comparable classes) and longer rod (4.5 x 6.8 ) and it is a very successful combination. Bigger is not always better.
JMO