Topfuel67

I made a mistake on my tire size. They're 265/75/16. I did not do any tire size calibrations with the Diablo. Just tweeked the tune a bit and made it richer as I have dyno'd lots of cars in CA. Our gas is ethanol high and requires a richer tune than other states. I'll GPS my truck next time I drive it on the Freeway. Maybe several days as I am using it to move my car hauler around town for the next few days.
As the trans goes, when I bought her a year and a half ago, she had a slipping trans. I rebuilt the 4L80 and did not get something right. I don't think I set the pin to the right height for the reverse band. When I installed it she would only go into first. Wouldn't go into reverse or any other gears. Anyways, I bought a new stock spec TC and then bought a used 4L80 from a 2005. It was rebuilt with a few upgrades. I see it has the valve body mod where one of the passages is drilled and a plate is installed over it. This trans feels really good for what it is. Shifts are crisp and it really does tow great. I just feel with the power of the big block it is lacking with that 2.48 1st. I've read about the TCI kit where they made a 2.97 first gear and a better 2nd. I have searched and searched for that, but it is discontinued. I get that this is a close ratio trans. Drag racers love it. People use these behind high hp applications and even complain about how the 4L60 has too much gear drop between first and 2nd.
My point about the manual trans and changing the rear gears is I can still have superior starting gear with the NV4500 5.2x3.21 starting, far better than 3.73 or even 4.11x2.48. Then if the 3.21 is too low, especially towing, for the o/d I can simply down shift into 4th and be at 1:1. 4.11x.75 o/d would be equivalent to a 3.08 rear at 1:1. So 3.21s with a 1:1 4th would be even more gear than the 4.11s in a 4L80. With how much torque she has I don't think she will be struggling even with a 3.21 and .71 o/d. I do understand lowering the rear to a 3.21 and keeping the 4L80 would not make sense. That would put too much strain on starting off and would greatly reduce her towing capacity. All your points above really only apply to only changing the rear to a 3.21 and leaving the 4L80. I was hoping that there would be some other 6 speed out there with better ratios that I could leave my 3.73s, have somewhere in the 3-4:1 1st gear ratio and a .6 o/d. Unfortunately one doesn't exist from my research and what others have chimed in.
I bought another stock intake manifold and am going to open up the bottom and gut it. I'm also going to plumb in a better PCV system than stock and a catch can. I've seen countless articles about that is a choking point and the stock pcv system floods the intake with oil vapor gumming up the rings. I'll probably do 1.8 RRs as well. Plus the electric fans. I know these basic mods will help with her efficiency as well. Last thing is I am looking for headers and other exhaust mods. I'll post back once all this is done and see where the MPGs end up.

Topfuel67

Thanks for that excel sheet with the rpms. I am really liking the idea of the nv4500 and the 3.21s more now. That puts me right at 1750 RPM in 5th doing 70. That is of course not towing and just cruising down the highway. Up a steep grade or if I have a bit of a load I can easily downshift to 4th and be at 66 doing 2250. Or towing in 4th at 66 doing 2250. I wonder if my speedometer is off that much. My wife always comments that it feels like we're going way too fast towing.
So with towing the Expedition my friend got it for free (2004 Eddie Bauer edition). PO drove it into a ditch, and wasn't even that drunk. It sat for several years at someone else's house. It had a broken A-arm, broken shock, hub etc. So we spent several hours changing the new parts in the dirt and were exhausted when we finally finished pushing that beast out of the dirt, with flat tires onto a too small u-haul trailer. We threw all the tools, spare parts, floor jack, spare tire/rim etc. in the rear of the loaded expedition and got out of there. Yeah, we realized our error and pulled over and moved everything from the back of the expedition into the sub. It was better, but still squirrely over 55. Also more evidence that my speedometer is off.

Fast355

My 99 Tahoe has an 8.1L with the 425 hp marine cam and headers. 4L80E with a stock B82 small block converter that stalls 2,500 rpm behind the 8.1L. Rolls on P305/50R20s and has 3.42 gears. It will boil the 305s from a stop and rolls down the highway at ~1,850 rpm at 70 getting ~18 mpg. As I said previously added stall speed gets it rolling from a stop without a cruising fuel economy penatly. Lug the 8.1L too low under load and it is in power enrichment, dumping fuel which tanks the mileage despite being at lower rpm. I have towed my travel trailer a few times with it on shorter more local trips but the vans added weight and longer wheelbase give more control. Both the Van and Tahoe have the manual mode enabled and a momentary switch to enable it. The result is you can put the shifter in whatever gear you want the transmission to be in and it will stay in that gear. Can do a 2nd or 3rd gear start if you want to.

dantheman1540

Fairly certain a stock 22r can burnout on 32”s.

adriver

iTrader: (1)

I know there are two different NBS tahoes in here that have the NV4500 swap. One responded and not sure if he has the 2wd or the 4wd, or if that even matters. I think one of em needed the slightest massaging on the trans tunnel, (but only to give some transmission (case) shifting clearance).


The NV4500 came behind the 6.0, 8.1 and 6.6 diesel in the 2500 and 3500. The 6spd was only an optional upgrade.


I've got a NV4500 out of a 2000, (with the lower top) sitting 50 ft away, if measuring anything on it might help.

wretched73

iTrader: (1)

What fantasy world do you live in where your 8.1 gets anywhere near 18 mpg? That is a blatantly obvious lie.

Topfuel67

I'm still several months to a few months from doing this. I'll wait until the weather gets cold in December/Jan when its in the 60s. I did just find a 1995 NV4500 from a 10,000 mile truck complete with bellhousing and hydraulics for 1000.00. I also watched a youtube video on rebuilding them. Doesn't seem too difficult. I've rebuilt Muncies and it seems like pretty much the same process. Just slightly bigger gears and clips.

Topfuel67

That Tahoe could get 20-30k on BAT if that MPG could be validated/documented especially making 425 hp. That is Diesel power efficiency with gas. Might even bring $40k.

adriver

iTrader: (1)

I bought a complete truck at auction with a 6.0 and a NV4500 for that. It may seem easy, but I'm pretty sure there are a few specialty tools you need, or need to make. I want to say the cheapest rebuild kit I've seen, where nothing is broken is about $400. Price out the rebuild kits, and then go a price one that is already rebuilt. Your call, but $1,000 and a rebuilt should be right about what a rebuilt unit is to buy outright.

Topfuel67

Only special tool is a 2 3/8" socket with 4 teeth to remove the input shaft nut. About $250 for a rebuild kit. I always like going through trannies before installing them. It is such a PIA to pull and install one. Plus the fab I'm going to have to do. It would be like finding a needle in the haystack to find a 6.0 with a nv4500 at auction. They didn't make many. That would be such a huge find for me as I have my Silverado with a 4.8l that has some mystery vacuum leak. Finding a 6.0 for that and a nv4500 in one shot would be nice. Plus all the other donor parts I need.