Looking into converting 1990 c1500 383 MPFI/700R4 to 6.0 or 408/6l80e

Hey guys, I'm looking into the swap for the transmission and ease of tuning. My 383 is making about 430rwhp but the old OBD1 system is a PITA to tune bigger injectors. I have an aluminum radiator that i would like to reuse which i think possible if a coolant tank was built to handle it in the factory location. Has anyone installed a 6L80 or 90 into one of these trucks? I'm running a 4.30 gear as well which would work nice with the .67 gear but may mean I'll be shifting into 5th at the end of the 1/4 mile. I already have a Walbro 255 with hotwire kit installed.

Thanks for the info on this swap.

Anyone know if the 6L80 or 90e will fit?

I don't know of anyone who has swapped a 6 speed into an OBS. I know plenty have done 4L80e's into the OBS.

Yeah, I know people have swapped in the 4L80e but from what I understand the 6L90 is longer than the 4L60e but a bit taller than the 4L80e. But I dont have confirmation on that.

Quote:

---

Originally Posted by YenkoST

Yeah, I know people have swapped in the 4L80e but from what I understand the 6L90 is longer than the 4L60e but a bit taller than the 4L80e. But I dont have confirmation on that.

---

Its massive. And its garbage in a performance setting. There is a reason vette guys are spending 10-15k to swap to a 4l80.

Quote:

---

Originally Posted by pl4yboy

Its massive. And its garbage in a performance setting. There is a reason vette guys are spending 10-15k to swap to a 4l80.

---

And the fact that a 4L80 was never meant to go into a vette and it takes a lot of custom parts to make an engine mounted Transmission mount to a transaxle and work but none the less a much tougher transmission, but ANYWAYS who dafuq is buying an automatic vette? Lol

While I understand this, the truck is a weekend driver and the 6 speed in the right setting works well like in the G8. These are guys running 11s with cam and mild head work with 2.92 gears and the G8 weighs 4k lbs.

Quote:

---

Originally Posted by conekiller01

And the fact that a 4L80 was never meant to go into a vette and it takes a lot of custom parts to make an engine mounted Transmission mount to a transaxle and work but none the less a much tougher transmission, but ANYWAYS who dafuq is buying an automatic vette? Lol

---

My point is that the 6l80e isn't working in cars half as heavy as the trucks...

As far as who's buying one... not me. A powerglide fits right in place of a t56... ;)

Quote:

---

Originally Posted by YenkoST

While I understand this, the truck is a weekend driver and the 6 speed in the right setting works well like in the G8. These are guys running 11s with cam and mild head work with 2.92 gears and the G8 weighs 4k lbs.

---

If you say so. Just speaking from experience here.

Me too. I own a G8 for my daily driver and a tahoe with the 6L80e. If you are under geared like the G8 comes from the factory then the acceleration gained is great. While I'm not looking at this transmission to be a 9 second warrior, the truck sees city driving 95% of the time so the idea of the 6 speed in the OBS truck is different and would better serve this purpose in my opinion so this is the route that I'm goig with it. Also, a lot of G8 guys run 600rwhp with procharger and are on the stock tranny with an upgraded converter so its strong enough for my setup.

Quote:

---

Originally Posted by YenkoST

Me too. I own a G8 for my daily driver and a tahoe with the 6L80e. If you are under geared like the G8 comes from the factory then the acceleration gained is great. While I'm not looking at this transmission to be a 9 second warrior, the truck sees city driving 95% of the time so the idea of the 6 speed in the OBS truck is different and would better serve this purpose in my opinion so this is the route that I'm goig with it. Also, a lot of G8 guys run 600rwhp with procharger and are on the stock tranny with an upgraded converter so its strong enough for my setup.

---

Okay. What do I know? I just had a 600hp truck with one. Ask Allen Nelson how many 6l80s they have broken and ask him if he suggests it for performance in any way. Ask any reputable truck shop. This isn't a g8. It doesn't behave the same way. It doesn't transfer weight the same way. It has more drag in between shifts. Your stock Tahoe with a 6l80 is stock. You also arent undergeared like the g8.

They don't work in a truck. For performance anyway. I was a length or so behind Justin (pl4yboy) when his 6l80e decided it just didn't wanna shift with that much power going through it. Limp mode. Results? Two blown head gaskets and it could've been way worse.

Never said it was the best performance transmission. I just said that they have there place where they are undergeared like the G8 and where city driving will be 95% of the driving that it will see, it will make acceleration easy. Not trying to compare your truck to my truck or more importantly my driving style to yours.

And personally, I dont know you so how do I know what you know. Same can be said about me but back to the original question.

Has anyone done it and what can I expect? Dont want to go with the 4L80 due to the .75 4th gear and 2.48 first gear and the 4L60 is known to be weak unless to you want to spend 3k and have it built up by FLT, etc for a 600rwhp potential and even then they are suspect at times.

I know with the G8 at that power level that you have to make it start the shift at 5k instead where it should be but I wont be near 600rwhp but around 450-470 and again looking for more drivability then quarter mile times.

Quote:

---

Originally Posted by YenkoST

Has anyone done it and what can I expect? Dont want to go with the 4L80 due to the .75 4th gear and 2.48 first gear and the 4L60 is known to be weak unless to you want to spend 3k and have it built up by FLT, etc for a 600rwhp potential and even then they are suspect at times.

---

The 4l60e is weak and needs good parts to last, the 4l80e on the other hand takes more power than you will make more than likely in its stock form.

I highly doubt you will want to do the 6 speed. As far as I know you will need an entire TCM, separate from your existing PCM, to control just the trans. I guess if you want to do it that way then do it. If you're worried about gear ratio and shit like that, why not just do a t56 and have your 6 speed and not need to worry about all the other shit involved with the new auto?

Want to keep this one an auto for the wife as I have another project with a manual.