JAH

I am looking for a 3.48" stroke crankshaft for a 6.0 block. I am limited to 360 cid.
If my calculations are correct, you can get a 3.48" stroke from the 4.8L, 3.268" crankshaft by offset grinding the rod journals to the honda 1.89" diameter. Then there is other issues with matching, connecting rod length, rod journal size, piston deck height and valve reliefs matching the LS3 cylinder heads that are planed to be used. I am trying to use as much off the shelf parts to keep the cost down.

Thank you!

SSCamaro99_3

iTrader: (1)

A 6.0 clock uses a 4in bore. General rule of thumb for displacment limited classes is more bore. You could run a 4.065 bore LS3 block and a 3.25 crank out of the 4.8, which would better pair with the LS3 heads you are planning. I would think stock rode/pistons may work here, but don't quote me on that.

If you have a few more dollars and wanted to stay with MG parts. You could always go with LS7 stuff.

4.125x3.25 = 347
LS7 heads/etc

JAH

Thank you for your response.

I am required to use a iron block. I have thought about using the GM LSX block, big bore 4.125, short stroke 3.268, like you suggested. I don't want risk a failure with the production 4.8 crankshaft in the GM LSX block. Maybe some body knows of an aftermarket forged short stroke crankshaft? I will have to do more research on the ls7 parts, like the crankshaft. I am trying to stay away of custom parts.

Scat will do a 4340 custom crankshaft for about $1500. Callies will do a billet crankshaft for $3000. I haven't checked into custom rods and pistons yet.

redbird555

iTrader: (14)

how much hp is the motor going to be pushing? The crank is actually the last thing you need to worry about in the bottom end of an ls. Stock cranks have routinely held 1000hp with no problem. Unless you really want a forged crank or special stroke I see no issue with the lsx block and a 4.8 crank

conan

iTrader: (5)

This thread might be some help to you...

https://ls1tech.com/forums/dynamomet...p-8000rpm.html

96capricemgr

iTrader: (1)

You concern over stock crank durability boarders on absurd.

JAH

Thank you for the video. That might be the way to go. It is down a little on cubic in displacement.

As the stock cast crankshaft holding up to the horsepower, that is not the concern I have, it is about holding up to the rpm cycles.

A forged crankshaft would allow lighting of the counter weights, to lower the rotating weight. Can the cast factory crankshaft have the counter weights machined to remove weight?

I am still crunching numbers on rod length, rod journal size, and piston compression deck height. If I could find a 6.200" rod with the honda journal, I could use the LS3 piston with the compression deck of 1.304".

Thank you for your responses.

JAH

I have an update. The machine shop says it will be about 8 hours of shop time. They are concerned about what they will find when removing the amount of material need to get the stroke. Pockets in the oil passages. If the crankshaft is undersized they can not get the stroke needed, there is not under sized bearings, they are a race only bearing.

Anyone have any experience with offset grinding the GM 4.8 crankshaft? What did you find out about grinding this much material off of the crankshaft? I can believe no one else has ever done this?

On a plus side, I found a LS (not a SBC) connecting rod, 6.200" with a 2.100 journal. Off the shelf LS rod, off the shelf LS piston, and a custom crankshaft, and it can be done.

Now it boils down to the $$$$.

BlwnLs1GTO

iTrader: (12)

I wish I could be more help. But it sound like a cool build and I'll be watching for updates.

JakeFusion

iTrader: (7)

Why not just leave the stock 4.8L crank alone, use the 6L block, bore it out to 4.060" and run the stock length 4.8L rods, 6.226" or whatever. Run a custom set of Wiseco Pistons for the 4.8L stroke and rod combo for the 4.060" bore with LS3 reliefs in them? That's a 338cid. You will be leaving some displacement on the table, but it would be the cheapest route.

LLLosingit

iTrader: (4)

On a small cube motor you're going to want to spin it hard to get the power out of it.
What is your budget? What is the engine going to be used for? Drag/circle track/ road course?

Rise of the Phoenix

iTrader: (27)

Curious too why you are limited to a certain size. Must be some kind of race application.

JAH

Pavement, circle track. Limited Late Model. They have 6 engine options, 3 are crates like the GM 604, Brodix spec head engine, with 2-barrel, iron head enginewith a 2-barrel.

Option 6, Open style engine, Gauge legal 4412 2-barrel with maximum 1" spacer. 360 cid, 10 to 1 compression, more weight and less left side %.

No computer or timing controllable ignition system will be allowed. No crank trigger allowed. No dry sumps.

I expect rules will be put in place to make the 3.48 stroke 6.0 block engine combination noncompetitive.

The budget I have for the complete rotating assembly, crank, rods, pistons, rings, wrist pins, bearings. I can see much of the rotating assembly becoming door stops. The budget is $3000. It is not as large as it should be, by a rule change it could be near scrap.

The rest of the parts can be used on something else.

Jenson

iTrader: (32)

If it were me, Id get the LS next block and go 4.185 bore with the stock 3.27 crank. That should net you 359.85 cu/in. Then your rotating assembly is really cheap just in case it is scrapped by a rule change. And you still have a nice block to use/sell/trade. With that bore you can also run stock LS7 heads with the GM carb intake and spin it to 8500+ no problem. If that 4412 2 barrel will do that...idk much about carb's.

A.R. Shale Targa

iTrader: (2)

By adding. stroke to your crank by offset grinding it, you're potentially weakening it and reducing it's max rpm. As other's have mentioned, the larger bore will breath better and the shorter stroke reduces linear ring travel which frees up power in restricted stock car classes. At 7200 rpms the crank is spinning 120 times/second. When you figure 8 pistons each traveling 3.27" per revolution times the 120/sec. you can see that equals 262 feet/sec. of ring friction. A 3.48" would be 278 ft./sec. or more than 6% more distance. Then you have the Total Seal ring spacers which allow you to put either .035" or .027" thick rings into the 1/16" piston grooves. This lowers the parasitic friction so much that shops are seeing in the neighborhood of 15-20 HP in back to back dyno testing. That's quite an advantage when you are making limited power because of the 4412 2bbl. Combine that with the definitive LS benefits and 300 cfm heads and the competition will quickly realize that 340 incher (4.065 X 3.27) gives up nothing to a gen I 360. The real key will be getting the correct camshaft timing events to make the short stroke LS torque band circle track friendly. The huge LS 3 intake runners are what add to that science. I've been messing with 4412 C.T. stuff for more than 20 years now and recently built a 353 (4.155 X 3.25) gen one for a .500" lift 10.8:1 dirt street stock guy with crappy 993 heads, EPS intake and headers. He also did not want to give up the cubes as the rules allowed 363, however the custom Bullet camshaft has this combo performing quite well. I've yet to put the ultra narrow rings in it or some nicely done EQ heads....next year it'll get that stuff.
Good luck on your combo !!