New stroker option (5.0L)

[CW]

I was talking to a few guys at an engine shop today and they told me they were putting together a stroker kit for the 258ci. That immideately got my attention for obvious reasons. The crank they use has a 4.145" stroke, that gives us 4.0L guys a displacement of 297.9 at .030 over. Running the numbers on dyno 2000, with a CR of 10.5:1, crane 753941, ported big valve heads, yields 352hp @ 5500 and 361lb-ft @ 4000. Obviously custom pistons are needed to get everything right but this setup would probably cost no more than my AP stroker I built a couple of years ago. Does anyone see any potential problem with going this route? I am going to get into the math and get piston height and quench in the next few days.

 

[CW]

Also, I am thinking about making this build carbuerated with HEI ignition instead of fuel injection because this engine may end up in an Eagle. I am also considering a 4.00" bore bringing the displacement to 312.5ci and making 393hp and 393 lb-ft. Does anyone have any experience with the carbed 258 that may prove usefull?

 

[Kittrell]

A 5.0L stroker is nothing new. Look around a little bit.

 

[CW]

I wasn't implying that the idea was new, but typically is focused on a 4" bore and not on a production 258 stroker crank that a few shops make, that retains the block strength. With a 4" bore and the 282 stroker crank it would make a 5.2l engine. 258 stroker kits are out there for around $1600 making this build not so "high buck".

 

[Dr. Dyno]

The 4.145" stroke crank (Flatlander Racing) will work in a 4.2 block but I'm not so sure that there's enough clearance inside the 4.0 block for it to work there. The other problem is that such a long stroke would cause the piston pin to come out of the bottom of the cylinder at BDC. If you did combine that stroke with a 4.00" bore in a 4.0 block, you'd end up with a displacement of 312.5ci or 5121cc (5.1L) but that's academic 'cause I don't think it's feasible.
Even if you use the 4.0 rods (rod length/stroke ratio would be 1.48 and using shorter rods would be plain stupid), the piston compression height will only be a measly 1.255". You'd certainly need custom pistons with the pin placed as high as possible, so the piston rings and ring lands would be rather thin and prone to breakage if the engine detonates.

 

[CW]

What would you say the maximum feasable stroke would be for the 4.0L block? I hadn't thought about problems with the piston coming out of the bore. What is the ideal rod length/ stroke ratio?

 

[Dr. Dyno]

I know Jakes Racing Engines (before they went out of business) used to build a 5.0L stroker long block with a 4.00" bore and 4.06" stroke based on the 4.0 block. The crank was an AMC 258 unit that had the rod journals offset-ground. They used 6.00" long Cunningham rods and Ross custom forged pistons.
Using the '96+ main bearing cap girdle wasn't an option because even if you raised the girdle enough with spacers to clear the rod pins of the crank, you couldn't get the oil pan on. Essentially you had to make do with an '87-'95 style block. If you had a '96+ block, you deleted the main cap girdle and used the main cap bolts from earlier blocks.
The bottoms of the cylinder bores needed to be notched to clear the rod bolts of the offset-ground crank.

 

[75SV1]

Dino,
Someone mentioned using a 258 oil pan on a 4.0L. Suppose to give a bit more pan depth. I haven't looked into this myself. I want to, as I am thinking of a windage tray. Might this be worth looking into for this situation? Or taking two 4.0L oil pans and cut and weld a bit deeper pan?
Tom

 

[ChevelleSSLS6]

Check bolt pattern, and axle/suspension clearance with the pan. I don't think there's anything else that would interfere with a deep-sump pan. Wouldn't a deeper oil pump pickup be a good idea to take advantage of the greater capacity in terms of being on an incline and not starving the engine of oil (never heard of a situation like that, but oil starvation is a good thing to prevent)