92.8mm Crank for stroker

[PRY4SNO]

I have a 92.8 stroker in an AAT tall deck.

After much research, I decided it was the way to go (largely) based on its favourable rod ratios. If I decide to rev high and often, it should (in theory) be reliable. However, by all accounts, the 95.5 crank is good up to 8,000 rpm.

Considering the stock oil pump is good to 8,500 rpm, you're not gaining much with the unicorn crank. For me to consistently rev over the oil pump's capacity, I'll need to revisit the head with solid lifters, full valve train and go to dry sump for the oiling.

[JariP]

What limits the 95.5 crank to 8000rpm?

[diesel des]

What limits the 95.5 crank to 8000rpm?

Piston speed. The longer the stroke the faster the pistons move at any given rpm. 8 K rpm is around the limit on a stroker though the odd buzz past that is ok. A stock crank reaches the same limit at 8800 rpm. The 92mm crank is about 8280 rpm.

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[JariP]

Piston speed doesn't mean anything. It's all about accelaration rates (or G's) and weight of moving parts. Force = Mass x Accelaration. The force acting on crank (due rpm) is greatest on TDC when piston changes it's direction, piston actually slows down to zero speed to change direction and reaccelerate. F= ma. From this equation you can see, that if the acceleration rate (=rpm's) goes up, to keep the force the same all you have to do is make the mass smaller. So just by using a lighter piston you can turn up the rpm's without changing the forces acting on the crankshaft.

[FCP-ENGINEERING]

For this reason we offer 159mm rods and low pistons with CH29mm.

[rynaqui]

What are the benefits or otherwise of keeping the stock block and with shorter 144mm rods with the 92.8 crank?

[rxl]

You don't have to modify the block just do a rebore. Everything is just plug and play. No custom belt tensioner required, engine mounts also don't require a modification as tall block has issues with the hood clearance.

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[rynaqui]

That was my biggest reason for keeping the stock block as I've heard of problems with the hood especially on custom intake manifolds.

[diesel des]

Piston speed doesn't mean anything. It's all about accelaration rates (or G's) and weight of moving parts. Force = Mass x Accelaration. The force acting on crank (due rpm) is greatest on TDC when piston changes it's direction, piston actually slows down to zero speed to change direction and reaccelerate. F= ma. From this equation you can see, that if the acceleration rate (=rpm's) goes up, to keep the force the same all you have to do is make the mass smaller. So just by using a lighter piston you can turn up the rpm's without changing the forces acting on the crankshaft.

Excessive piston speeds cause ring and bore damage. Its a well known and understood issue in all engine designs.

But obviously lighter reciprocating parts reduce other stresses. I think it's fair to say any continual over 8 k rpm use on a stroker will shorten its life. Any continual use in a stock stroke engine over 8.5 k rpm will do the same.

At these rpms a dry sump and solid lifters should be used as has already been stated.

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[diesel des]

What are the benefits or otherwise of keeping the stock block and with shorter 144mm rods with the 92.8 crank?

This is generally a bad idea. The rod to stroke ratio is poor compared to 159mm rods in a tall block and so peak piston speeds are higher as are cylinder thrust loads.

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[FCP-ENGINEERING]

Normal combination as such goes from factory.
All 2.0 engines, also 2.5 5cylinder USA version.

What are the benefits or otherwise of keeping the stock block and with shorter 144mm rods with the 92.8 crank?

[diesel des]

That was my biggest reason for keeping the stock block as I've heard of problems with the hood especially on custom intake manifolds.

Just drop the engine on its mounts with spacers.

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[Error404]

Then you have the space the subframe down, which dumps your roll centre towards the ground.

[diesel des]

On my Urs4 i used 10mm spacers and had no issues. But at that point you should have a dry sump pan and so have loads of room... 😀

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[urs4guy]

I have a 92.8 crank for sale.



I've sold the rods so they are not for sale. Freshly polished journals by Jeff Gerner. Price is $1500 plus shipping.

Hap Maguire
303-475-6760
captmagu@gmail.com