3.1 upgrade rebuild?

[Reckone]

I recently aquired a rod knock in my 91 Isuzu. I have been looking to rebuild the 3.1 that is in it. But I would like to get a bit more power out of it if I could. Any suggestions on what I could do to it during the rebuild? Or other parts I could swap on to it to gain more?

I am totally new to these motors

[torq455]

It would would be worth it to swap to a 3400 SFI. The cost would be comparable and you have more options to build with--not to mention more power to start with. Check out this site: http://wot-tech.com Ben is the owner and knows his stuff!

[geoffinbc]

No it would NOT be cheaper or the same price to swap in a 3400 SFI. A strict rebuild with a nice cam, 4.3L Throttle Body on a bored intake and some 1.6 ratio rockers would benefit you quite nicely. You would be looking at an engine capable of 200LBS of torque which would move your Rodeo along well. If you doing a rebuild I would look into a COMP Cams full K kit which would get you your entire valvetrain in one shot. The get a junkyard 4.3L throttle body and clean it up and swap in your injectors. Then get your intake bored out by a machine shop to match the larger throttle body. Check with a local supplier and pick up some bearings and pistons.

[923.4v6]

If it's a 3.1 isuzu truck they have the starter on the drivers side like a fwd engine, which he might could do a 3x00 swap into it with some custom motor mounts. If its a rodeo I don't know much about them.

[torq455]

OH duh! I was thinking cavalier. Geez.... Sorry for the misguided info. I thought 4.3 TB's were 70mm.

If it's a 3.1 isuzu truck they have the starter on the drivers side like a fwd engine, which he might could do a 3x00 swap into it with some custom motor mounts. If its a rodeo I don't know much about them.

Even so, someone would have to fabricate mounts with the vehicle present. I agree in rebuilding the 3.1 with mods. Grab more compression while you are there. Me in a mild/moderate build would shoot for 10:1. You will need the ability to tune when you are done. Ostrich 2.0 will be good for that. http://www.moates.net/product_info.p...roducts_id=169

[Reckone]

Thanks for the info fellas. I would like to stick with the 3.1. I swapped it into my 91' Amigo. It was originally from a 91' Isuzu pickup.

The motor is TBI, so I am not to sure what other TB would fit. Where would you suggest to get top end parts at?

[geoffinbc]

Rebuilding your 3.1L is the quickest and most budget conscious decision. If the motor is currently stock then it still has some of the factory short commings. The biggest ones being the stock cam, compression ratio and throttle body. I am guessing you plan to just pull the whole motor, rebuild it and drop it back in, correct?

If so I would first get it out and check the damage. If you are mechanically inclined then tear the motor down and send it to a machine shop if you wish or measure everything out yourself if you have the tools to do so. If the knock is just damaged bearing inserts and the crank is not damaged and the journals are not out of round or tapered then I would not machine it and just get some new bearings. The pistons will most likely be fine but you will need new rings and if the block needs honing or boring beyond what a ball hone on a drill can take care of then you will need new pistons. Mahle makes a selection and GM Performance may have some suitable replacements too. At this point I would get compression up a bit into the 9.5:1 range. I would not go up to 10:1 or more unless you cam choice is going to be a Crane or Comp 260 or better. But since this is a truck I would suggest something that will give you more bottom end grunt. Comp sells a 252 Cam in a K kit which gives you the Cam, Lifters, Valve Springs w/retainers and a timing set. You can't really beat a package like that. So with some bearings, pistons, rings, and valvetrain taken care of your rebuild is under way.

The heads will most likely need the valves done and the guides but that's about it. Don't forget new stem seals

Now for the mods. I have already written a how-to for a 4.3L TB swap and how to adjust the minimum idle along with the TPS.

http://members.shaw.ca/betterthanyoutoo/how-to/28to43tb/28to43.htm

http://members.shaw.ca/betterthanyoutoo/how-to/TBI%20Idle/tbiidle.htm

These next 2 are optional.

http://members.shaw.ca/betterthanyoutoo/how-to/gtvcovers/gtvcovers.htm

http://members.shaw.ca/betterthanyoutoo/how-to/tbicai/tbicai.htm

[Reckone]

Thanks for the tips. I did just plan to take the motor out and drop it back in. Figured I might as well do somehting to get a bit more power of it during the rebuild.

[torq455]

If my calculations are correct, the 2.8 TBI has 2 - 54mm openings. The others are 2 - 66mm openings. That's not enough air flow?? I mean a stock 2.8 needs the airflow of a 350? This is a wet flow intake which you can over do on TB size. If it's too big, the velocity slows and the fuel begins to fall out of suspension. Granted, I'm not Mr. knowitall when it comes to this particular build, but I have dealt with wet flow systems for a few years. The saying was that if you are unsure what you engine needs, pick the smaller size, you'll be happier.

[geoffinbc]

Uh I don't know where your numbers came from but the 2.8L TBI has 2 34.925mm (1 3/8") openings and the 4.3L 5.0L and 5.7L all have 46.8625mm openings (1 11/16") Hell the 7.4L Big Block only had 2 50.8mm (2") openings.

[torq455]

ROFL! I'm a dumbass! I did the conversion backwards. That's what I get for thinking before noon! Usually GM undersizes their TB's. I thought that was kinda weird.

[geoffinbc]

It would be bad ass if the openings we 2 5/8" though LOL

[torq455]

you'd have to have a 650 CI motor and twin turbos the size of Fat Bastard's ass to utilize that TBI!

[Reckone]

Ok getting back on topic here.

I pulled the 3.1 from the truck a few days ago. I stripped the motor down to a short block as of right now. I know it will need a least new crank and rod bearings. Topend wise though. It will need new lifters, pushrods, valves, etc... I was going to just buy new rebuilt heads for it instead. The pistons look to be in pretty rough shape as well with over 200k on them.

I have been trying to look for a cam, but Crane doesn't list anything for the 3.1 on there site. Anyother options? I can't find much of anything aftermarket wise. I have been looking for a et of headrers for the longest now.

[torq455]

here's what Crane listed for the 2.8/3.1:

http://www.cranecams.com/index.php?show=browseParts&lvl=2&prt=5&Vehicle_Type=Auto&Cylinders=6&Engine_Make=CHEVROLET&Year=1991&Engine_Size=2.8-3.1%20L

i've heard to not waste money on anything less than the 260. the 272 has a lopy idle, makes lots of power, and with the small intake runners, has surprisingly stout low/mid torque. however, without a 3x00 top end swap, you can't take advantage of the cam. without headers, a street port, and gasket matching etc, the powerband runs out at about 4500 rpm.