306.5in stroker

[heartlandoffroad]

I'm building a 306.5in stroker for a customer to take to the King Of The Hammers race in Feb. so I came up with this unique build.

I am using a JE custom piston and a Pauter custom rod. Then I had 258 crank offset ground out to 4.200 ( did not weld it just offset ground ), bored the block .060 over . I'm using a .051 head gasket, 67cc chamber and 18cc dish (max dish for the piston) trying to keep compression down so he can run it on pump gas. Using a 7120 head with Ls1 stainless valves, beehive springs, ported and polished (flo bench #'s .55 280 in, 200 ex) MP 1.6 roller rockers. Bullet made me a custom grind using a Johnson lifter.

My customer is sponsored by Painless so he is running there stand alone ECM, harness and distributor so there shouldn't be any problem tuning

When I get it assembled I'm going to be taking it down to Ranken Technical College and put it on there DTS dyno the Tech teacher is a wizz with standalone ECM's so I'm going to let him tune it.

This motor should be a beast and very reliable.

5.0L jeep stroker 2.JPG

[Mgardiner1]

over 3/4" extra stroke is very impressive! But whats reliable about taking over a 1/4" off of the rod journal? especially in a high HP motor? Rod journal size is going from 2.095 to 1.790....

[heartlandoffroad]

Actually having a big rod journal doesn't add much strength to any crank. The journal size I went with is a journal size from a 90-92 Eclipse, Talon, Laser that people are making 500hp on a cast crank and 1200-1400hp with a steel crank and that's a 4cyl. Heck even NASCAR is using journal sizes in the 1.7-1.8 range. I'd call that pretty reliable. Besides that I'd much rather do this than have any cast crank welded and offset ground.

[dwg86]

COOL! Are you using a heavy or light crank?

[heartlandoffroad]

I went with a light one

[Mgardiner1]

The difference between a crank designed around that size, and one ground to that size, is A LOT! You are now bringing the oil passage that much closer to the surface of the journal, which is drilled on an angle to begin with.

I love the specs, and i do hope its a real strong engine! I just wouldn't feel comfortable spec-ing out my own engine (which is usually a DD) like that. But i realize this is not a DD, and a high performance vehicle.

Good luck! keep us updated!!

[heartlandoffroad]

Actually that was a big concern of mine when I looked at this configuration but if you look at oiling port on the 258 crank it's at the tall end of the crank so there is really very little material that gets taken off that side of the crank.

[Plechtan]

Using a 7120 head with Ls1 stainless valves, beehive springs, ported and polished (flo bench #'s .55 280 in, 200 ex)

What size valves did you go with? stock or 2.02 and 1.60? I would like to see some pictures of the head. did you open up the combustion chamber as well?

[heartlandoffroad]

I used 2.02 and 1.60 and yes I opened it up to a 67cc chamber.

Sure I'll get some pics up as soon as I get time to take a couple I'm assembling it rite now.

[Flash]

Vary cool!
So what are you going to set the rrev line on this race truck?


Flash

[heartlandoffroad]

6000 will be the limiter it is set up to run strong at 5600

[Plechtan]

The eight counterweight crank and 5600 rpm? Maybe you should read the "max rpm of jeep engine" thread.

[Mgardiner1]

The eight counterweight crank and 5600 rpm? Maybe you should read the "max rpm of jeep engine" thread.

I think the light crank is 4 counterweight.


What kind of cam drive do you plan to use? Any kind of special harmonic balancer?

[Plechtan]

You are correct, i got confused with the 4.0 stock crank which is 8 counterweights. 4 counterweights still does not sound like the best idea for a high performance engine.

[1bolt]

Well instead of poo poo ing him... man that sounds gay, okay instead of doubting on him, lets see what it does in that competition and on the dyno.

I for one will be real interested to see the torque curve of such big ports. 280CFM is 30 more than I've seen from any other head porter on an iron head, and 200 CFM exhaust is just insane... Did you get into the epoxy to get that kind of flow? Did you hit any water jackets?

I can't wait to see the Dyno graph.

If the crank stays together up in those RPM's then I could see offset grinds becoming all the rage around here.

One last thought... the 8 CW 4.0 crank is said to have the bad harmonic and the 12 cw is said to not have it, but no one at all has said whether the 4 CW crank is prone to it or not... Considering it is (give or take) 15 pounds lighter and with weights in different places the 4 CW crank will have all sorts of different dynamics than the 4.0's 8 CW.

I'm not dogging on you Plechtan, I just think we need to not start our very own misconceptions, when the only thing we seem to have confirmed is that Lee Hesco says the 4.0 crank has the harmonic and the 258 12 CW crank may not. He didn't say anything about the light 258 crank. Even if it was implied by omission Hell it may have the worst harmonic of them all, but there's no evidence of that either.

This build is certainly going to find out one way or another, and if it survives or not we'll all learn something new.