Anyone offset ground a 3500 Crank?

betterthanyou · 11-04-2008, 01:47 PM

Has anyone gone through the steps of offset grinding the journals of a 3500 Crank? If so what did you achieve in terms of stroke and what rod and piston combination did you use?

I was pondering this last night at work. My goal is a high torque 3.2L for my Isuzu. I don't care at all about high end power. My goal is to turn big tires and crawl around the trails with the engine lumbering at low RPM. I also want to be able to drive on the highway and pull hills in 5th or 4th not 3rd and 2nd like I have do now with the 2.8L. The Cam will be a COMP 252 possibly advanced a couple degrease to increase bottom end. A couple dyno sims has already shown me 200lbs of torque by 2000RPM and up to 210lbs at just 3000RPM. If I could increase stroke by say another 4mm or more I could really make some torque gains.

If the cost is prohibitive or the retrofit proves too difficult I wont bother. But I don't have any concerns for crank sensor. All I need to worry about is the seals, the cam gear and the crank damper fitting on.

discostu · 11-04-2008, 02:42 PM

Displacement, compression, camshaft lift (more lift, same duration), better flowing heads and better flowing exhaust manifolds (or headers) are what will increase your low-end torque.

IMO you'll be throwing money away offset grinding a crank and changing your rods/pistons rather then going for more traditional methods of gaining power/torque.

I'd be building a 3400 if this was my goal. Have a cam custom ground from a stock 3400 cam that gives you near-stock duration, but increases the lift as much as you can, then throw on some 1.6 full roller rockers. 0.5" lift would be the minimum I'd be shooting for.

Leave the intakes alone (no porting), but port the heads a little, really just clean up the ports and bowl blend them, you don't want to enlarge them very much (keep your port velocity up). Throw on some 3500 valves for less valve weight and better flow, then some LS6 springs to handle the lift. Mill the heads a bit for compression. Shoot for 10:1 compression (can't do 11.5:1 with RWD pistons because you won't have the high duration to lower your DCR). Make sure your quench distance is .040" or slightly lower.

Look for 3500 manifolds and go with an exhaust that's slightly larger then stock, but not too big that it reduces your scavenging and kills your low-end torque.

ForcedFirebird · 11-04-2008, 03:44 PM

No one has offset ground as far as I know. Joseph priced it and it was about $600 because they have to grind 6 throws (vs 4 for a SBC).

You will need to use custom pistons/rods to get the deck height back. When we were discussing the strokers, the ideal situation would be to use a 3500 block/pistons, then going from the 3500's 5.9" rods to the classic 660 rods of 5.7" to get some of the deck height.

Since you are using an iron head, this all goes out the window.

betterthanyou · 11-04-2008, 04:06 PM

Alright that's going to be too much money then. Ohwell. The dyno sim showed a 25lb increase in torque. I will try and make it up in other areas as best I can. I will however give my uncle a call he may be able to hook me up with very cheep or free grinding. Then I would need pistons. I was going to use oversize pistons anyway I would just have to spring for the upgrade. But having custom parts means it will be hard to get if I have a break down for some reason. If I could get this cheep would there be enough room on the piston to move the pin up even more? I have not looked at a piston in about 6 years. Or did GM use up all they could when they stroked the 2.8L?

I wont be going with a 3X00 top end or any aluminum heads for that matter. This is a traditional budget build with off the shelf parts. A 3500 block/heads is appealing but I have no desire to make motor mounts or custom exhaust or retrofit 3500 engine controls in. I want this to be a bolt in project with parts available at the parts store should anything break down.

I will be shooting for about 9.5:1 compression on a 1mm over bore 3.1L. A Comp 252 Cam with 1.6 Com Pro Mag rockers (free and modified). The TBI intake will be bored for a 4.3L TBI unit (standard procedure) and the intake ports and heads will be gasket matched. The exhaust system will be what I have now which is stock down pipes with a 2.5" cat and muffler. The stock down pipes on the Trooper are not crush bent so they are not that bad. If I can score a DOHC windage tray I will put it on. I doubt I will see any power gains but with the off road driving it will stop sloshing oil from splashing on the crank. The block will be cleaned up and drain back improved in the lifter valley. A Snorkel Cold air intake will finish it off but that may have to wait until next summer.

I move into my new house next month and after that I will go pick up a Rodeo 3.1L From the junkyard to build. I already have a 3.1L Crank so I will just use the best one and sell off the other.

Thanks for the info!

ForcedFirebird · 11-04-2008, 04:23 PM

Wouldn't long headers help the tq a bit? Shaving the heads for more compression is another budget tq builder.

Joseph Upson · 11-04-2008, 04:29 PM

Quote:

Originally Posted by ForcedFirebird

No one has offset ground as far as I know. Joseph priced it and it was about $600 because they have to grind 6 throws (vs 4 for a SBC).

You will need to use custom pistons/rods to get the deck height back. When we were discussing the strokers, the ideal situation would be to use a 3500 block/pistons, then going from the 3500's 5.9" rods to the classic 660 rods of 5.7" to get some of the deck height.

Since you are using an iron head, this all goes out the window.

Actually that was for welding and grinding to increase stroke. There's Mike at a St. Pete Florida machine shop that for the second time in about a year has quoted me ~$200 for an offset grind. I just have to much tied up into the current build to take the extra crank down and have it done for a later fully forged build up.

Mike 727-323-4205

betterthanyou · 11-04-2008, 04:42 PM

Well I wont be shopping in Florida. But If I can get a price here in that ballpark I would go for it. Also I would be reducing the journal diam to meet up with stock Gen I rods and I can also use a cast crank which would possibly be cheaper than a forged one. I am not after any impressive power numbers.

Quote:

Originally Posted by ForcedFirebird

Wouldn't long headers help the tq a bit? Shaving the heads for more compression is another budget tq builder.

Yes it would but no one makes them for a Trooper. Hedman makes some for an S-10 but the trooper has the starter and e-brake lever on the drivers side which really makes a tight fit. I would love to do it but it would take a lot of mods to the headers. I am a welder/fitter and it would be quite easy for me to modify a set and TIG it up but then I have a time problem.

discostu · 11-04-2008, 06:03 PM

betterthanyou, since you live in BC, I might as well say that there's a great little place in Salmon Arm called Interior Cam Supply Ltd that will regrind 60v6 cams for dirt cheap, like $60 if you send them a core.

I got them to do my 3400 cam and it came back at 216/220 duration (276/280 adv) and .472/.498 lift. A good torque cam would be something like 200/204 duration and .490/.500 lift.

I went with a dual pattern cam because I thought I would be using stock type manifolds (to crutch the weaker exhaust system a bit). Then I ended up getting a great set of longtube headers, so now I'd like to have a single pattern cam, but whatever. I should have asked for more lift too.

betterthanyou · 11-05-2008, 02:25 PM

Well that's a little far for me. But I can pick up a COMP Cam and lifter kit for just over $100 including the break in lube. For that price a regrind just is not worth it if you have to buy new lifters. I am going to buy the whole COMP 252 K kit so I get a new timing set and valve spring too.

kwhauck · 11-09-2008, 11:44 PM

my friend in colorado springs offset ground to achieve a 3.7 stroker, with carrillo rods and custom pistons, never finished his build though so no solid evidence on the gains.....