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Discussion Starter #1
Newbie here, I dont have a 4x4 but a 1968 GMC swb, 2wd that Im rebuilding right now. I have purchased a crate 8.1L engine to swap in this truck but Im now finding out that this is not a popular swap. After seaching around I found that alot of folks here on this site have done the 8.1L swap and seem really knowledgable on this engine....

So here goes- if you want to pm with your comments me thats fine....

1. Who did you harness, how much and are you happy with it?

2.Have someone rework a stock harness or start from scratch?

3.Is it better to leave in the O2 senors? I have 2 different answers on this from 2 different harness makers.

4.Are you happy with the performance? Other than a custom tune, any other suggestions other than maybe a regap of the plugs, and the 180 thermo swap?

5. I really want this truck to be a good driver, not another hotrod, something I could drive out of town with. That being said, I really want to go with a 4l80eHD, trans. But from what I have read I have to cut up the cab floor and make a new trans tunnel. Not a big deal but just one more thing to do. But the question is: If I go with some 3.08 rear gears or higher, would I be happy on the hwy with a th400? (already have the th400) Or stay with the 3.73's (in the truck now) and go with the 4l80e?
If you went with the 4l80e what shifter did you use?
Im sure the later is the better answer, but in terms of money, its getting thin. And this dilima is the problem I need to resolve first before I do the harness and tune and put the interior back in...

6. What kind of gauges are you using? Dont really want to spend $1000.00 on gauges if I dont have to.

7. As far as the front of the engine, all the accessories, alt, powersteering, ect-- What did you use? The stock mounting bracket or custom fab some brackets up?


Im sure I will think of something else... But thanks in advance for any help or suggestions you may have.
 

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Hello TonyPaul
I am running a 502 HT in a 86 K30. I love it lots of torque and power. My motor has a carb. I used the stock wireing and gauges. You also can use sock BBC Acc. Mounts. I use a mechanical fan with a 4 core radiator. with a 195 thermostat. Hope this helps any other questons just ask.
 

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I did an 8.1 swap in my blazer, I have learned alot throughout this process to say the least. To answer your question about harness yes you can get the harness re-worked but there are several problems you have when re-working a harness. First is the quality of the harness is there any problems the were pre existing prior to the the removal of the motor. I would contact the guys at www.pacificfab.net. They sell complete stand alone harnesses which are all new and I would highly recommend going that route rather than having the computer flashed, harness re-worked and still have problems. As for the O2's since you want to have reliability I would suggest keeping them. If you go stand alone then its just plug and play with at two wire hookup system.

Tell them Jeremy sent you.
 

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If its going to be a "good driver" you will want the overdrive! The TH400 even with 3.08's will suck gas. The 4l80 isn't realy that much bigger than the th400 anyway (longer though) I doubt you would have to to much if anything to the trans hump.

Also you will need to keep the front O2's if you want any kind of gas mileage!

Regapping plugs does nothing but fuck them up, at least the stock iridium delco ones. The lower themo isn't really worth the trouble.

A custom tune and cam would be best.

For gauges just get something off ebay and install in the dash.

The 8.1L is a Gen (whatever???) big block with LS injection and coil pack ignition. So some of parts of the earlier big blocks may fit.

Good luck! A 6.0L or 5.3L would be cheaper and easier IMO.
 

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I agree with Bo, I would do the 6.0 or 5.3. Either can be made to have a good amount of power and torque. A local guy around me has the 6.0 in all of his cars. He runs carbs and swears by them.
 

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Running a carb on an LSx is a step back IMO not really worth it, unlee looking for maxpower! The EFI will get way better MPG vs a carb on a normal motor. Both will make power, but which is more effecent, EFI. Not to mention more expensive as well.
 

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Discussion Starter #7
Thanks for the replys. I already have the 8.1L sitting in my garage, brand new with only GM run time on it only. I got too sweet of deal on this to go to a differnt engine. Im going to get a new stand alone harness, but the question was more from whom, and whom not to get a harnesse from. I have spoken to a few companys that build harness and they all seem to have a little difference in them. But wasnt sold over the phone by none of them. None of them had 8.1L knowledge, they just build off blueprints. I was kinda wanting to find a company that really knows what there selling.

I have a couple leds on some 4l80e's, which brings me to a question- I ran across one that has somekind of brake on the rear of the trans, like a drive shaft brake... Anybody every heard of such a thing?
Thanks again!
 

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There were some 4l80e trannies behind 454's in motorhomes that used the brake on the back of the tranny for the e-brake. I'd run an allison behind the 8.1 if one came around at a good price.
Good luck on the swap, post up some pics and tech when you do it. I'd like to put on in my blazer.
 

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The allisons are fucking HUGE! Thats why the 8.1l's in the avalances had the 4l80's in them to clear the body. It won't fit without cutting the tunnel for sure.

Street and perfromance is another company for the harness, kinda of high.

Not alot of demand for 8.1l stuff so not alot of companies mess with it. And since its not used in the HD's anymore its getting hard to find complete decent motors.
 

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Allison would be my choice for tranny if you can fit it. Other than that I would either go with the 4l80 if you can build it right or nv4500. I know Kevin stands behind his company and work, you won't be disapointed with Pac fab.
 

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I put an 8.1 out of an 02 Avalanche in my 84 trail truck and it was prety painless. My engine came with the stock harness and computer, which I sent to Jim's Performance. He got rid of all the emissions bullshit and unnecessary leads as well did a computer reflash. He did a kickass job, I highly recomend him. I am running a TH400 but I dont drive it on the street much. I am VERY happy with the power. I had been running a 6.2 diesel. When I swapped in the 8.1 I doubled my torque and trippled my horsepower. I dont have any phyiscal mods done to my motor, just the computer tune. Putting the sensors for the truck's stock gauges on the new motor shouldnt be hard. Since my engine was a take-out, it came with all the accesories. Since it is a tall deck block, I dont think normal BBC accesory brackets will work, but I'm not positive about that.

Fuck all the smaller engines, big blocks rule!
 
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