95 ZJ Turbo Boosted Stroker

[SilverXJ]

Why is the desk clearance so large?

[beiwulf]

If I am understanding this right about deck clearance. It's the actual number taken from when the piston is at TDC to the cylinder the gasket on. Things that will affect it's number will be if the crank casing was machined or if changing pistons. 2 of 3 of those are certain and have yet to be done. I am not sure a conservative number to assume on this one. Would taking .020 off the default on calculator be a safe assumption? .010 from each surface area?

[beiwulf]

Right now i'm reading a few books for this build and forums for information other then just here. I've got "Street Turbocharging" by Mark Warner, P.E. - & I was on the supra forum earlier. I reading up on the turbo setup and lag vs. spool time with engine loading (vehicle weight, gearing, tire size). Looking for the learning curve information to help me over the hump. Considering the build and trying to find the right setup to start looking for a turbo that will provide early spool up without winding out before 5300rpm. Any input links, experience, formula's feel free to jump in please anyone.

[SilverXJ]

If I am understanding this right about deck clearance. It's the actual number taken from when the piston is at TDC to the cylinder the gasket on. Things that will affect it's number will be if the crank casing was machined or if changing pistons. 2 of 3 of those are certain and have yet to be done. I am not sure a conservative number to assume on this one. Would taking .020 off the default on calculator be a safe assumption? .010 from each surface area?

Deck clearance is the amount the piston sits below the deck surface, the surface the head gasket lies on. The quench is the deck clearance + compressed head gasket thickness. I would either go slightly in the hole, like .005" or zero deck and let the gasket set quench.

Considering the build and trying to find the right setup to start looking for a turbo that will provide early spool up without winding out before 5300rpm.

Are you switching to a turbo now?

[beiwulf]

Yes, going turbo since issues with where I had invested some moneys before going south (and i'll leave it at that-still hasn't sorted out). Depending on how sorts out maybe I will consider other options at that time.

[beiwulf]

Does anyone know the formula(s) used for figuring out tensile strength of a given material? I am looking to find out the given strength of our cast nodular iron journals. Considering reducing journal size for offset on stroke. Curious to know what the rating for trq/hp would rate for.

thank you

[beiwulf]

So talked with Joe Castillo of Castillo's Crankshaft in La Mirada, CA and his balance guy. Gave me some information regarding offset grinding on the 258 crankshafts. Doing a 1.8885 / 1.8890 would make a large selection of bearings available to me and get my longer stroke. Allowing a 4.00-4.10 (.135-.205) stroke off a 3.895 crankshaft with that undersize/offset grind. Talking with the balancing guy he uses he mentioned that the reason for that higher counterbalance crankshaft throws gives better stability for more force at higher rpm range and less flex on the crankshaft. Instead of the welding on the crank to add size just offset grinding it seems to be a better idea after looking through our forums and the web.

He also mentioned going with a 1.90 puts it close to what bmw is running on some of there engines and a lot higher cost of bearings ($45 per bearing cost vs. a set for that cost)

Came across this article when researching tonight.
http://www.hoigto.com/tech/crankgrind.htm

[I6FAN]

Does anyone know the formula(s) used for figuring out tensile strength of a given material? I am looking to find out the given strength of our cast nodular iron journals. Considering reducing journal size for offset on stroke. Curious to know what the rating for trq/hp would rate for.

thank you

Tensile strength is defined by how much load per cross sectional area (lbs/in2 or psi) is required to break something. There are two strengths to consider in materials design; ultimate strength and yield strength. The terms tensile strength and ultimate strength are used synonymously, whereas yield strength is simply yield strength. The biggest unknown in wanting to determine these strengths is the actual numbers for a Jeep crankshaft. Ductile cast iron is anywhere from 60,000 to 100,000 psi, and the yield strength is 40,000 psi. So just using 60 ksi, a 2.1" cross section would require a load of 207,816 lbs (103.9 tons) to break with a yield load of 138,544, lbs (69.3 tons). A 1.9" section would have an ultimate load of 170,117 lbs (85.1 tons), and a yield load of 113,411 lbs (56.7tons). Engineering design uses yield strength when designing with a certain percent of safety margin added. Basically, by going from a 2.1" to 1.9" diameter is an 18.1% reduction (original minus new divided by original times 100), so that's what you give up in tensile loading. A tensile test is in perfect tension, so determining what a crank can handle is much more complex than just tensile strength; probably a combination of shear test of sorts also. The biggest hurdle for the cranks in these engines is a harmonic that occurs at ~5,400 rpms where the crankshaft "corkscrews" wildly. If you are planning to run much past 5,000 rpms, use the twelve weight crank, and the four weight for under that. The twelve weight is stiffer. There were also solid main caps on 258 engines (I think in the 70's) at some point that are good to have.

[I6FAN]

Not to get to far off topic, but could you take a close-up picture of the inside of the crankcase of one of those 258s your breaking down? I've heard that the one superior thing that the 258 block has over the 4.0 block is the bottom of the cylinder hangs down farther into the crank case than the 4.0 which better supports the piston when it's at BDC lowest point. There is a "rocking" element that worsens when using the 258 crank in the 4.0 block; more reason to use the longer rod. The VAM (Mexico) blocks had this feature and the larger bore already which made them very desirable.

[beiwulf]

1973 232 block cylinder wall height 6 1/4 inch
cast # 3218618


1984 258 block cylinder wall height 6 1/8 inch
cast # EF3235444


1995 242 block cylinder wall height 5 3/4 inch
cast # 53008405

[beiwulf]

btw great question -

appreciate the reply and the information.

[I6FAN]

btw great question -

appreciate the reply and the information.

I actually wanted a picture of the inside of the crankcase, but your measurements really tell the story better as the deck heights are not a whole lot different, yet the cylinder wall heights are way-way different. Thanks!

[I6FAN]

What is your intended usage for the vehicle?

[beiwulf]

I'll verify deck heights in the next day or so also for academic purposes

The build is currently going to go into a Daily Driver. Next after engine will be the 5 or 6 speed transmission most likely. Been looking at the 6L80 and running it with a PCS unit. We shall see what this manifest into over the next couple years as money permits tho. I am not looking to put a Huge lift on it and not be able to park in structures. I'm shooting for a long arm kit with about 4" lift with my body spacer lift. Flared fenders to allow for more clearance with larger tires. Extended axles looking at either custom spidertek or ford super duty 65" axles 10.25-10.5 or dana 60 depending on year. Will also allow for newer and larger factory rims from newer jeeps among other vehicles with a 5 on 5 or 5 on 5.5". Just to mention a couple things.

[beiwulf]

Here's the pics for you I6FAN

84 block




95 block