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Towing capacity of a 4BT-powered SUV?

26K views 26 replies 12 participants last post by  Hickey 
#1 · (Edited)
Just trying to gather some info, I have a 4BTA and a '90's FJ80 Toyota Landcruiser. I'm planning on dropping the 4BTA into the LC this winter along with a NV4500. The Landcruiser has factory 4.10 gears and I'll be running 35's. The factory tow rating for the FJ/FZJ model Landcruiser has ranged from 3500#'s to 5000#'s as the engine size went up with the yearly model changes.

I'm planning on a decently built 4BT with the timing turned up, more fuel, a HY35 turbo, 3200 spring and worked-over injectors. I'm thinking I can get 400 ft/lbs out of the motor with that setup.

I'd like to be able to tow a tandem axle car hauler with another vehicle on it, perhaps one or 2 times a month. The car hauler with vehicle will weigh about 5500#'s and I'm curious how hard I'll be working the 4BT? Anyone else tow that much weight with a 4BT? How does it do with fuel mileage and that much weight?

(I'm well aware of factory tow ratings, don't want to get into that right here, right now. :happyfinger: )
 
#2 · (Edited)
I've towed a good bit with my 71 highboy. VE 4BT, M5R2, 4.10's, 35" tires. Truck weighs 5900, has great power empty and, powerwise, is comfortable towing up to 10K pounds. Last week I towed a tandem axle sealcoat pump rig trailer weighing 5000 pounds 450 miles up some moderate grades along the way. The truck easily held 60 MPH in 4th up 6% grade for 6 miles up cabbage hill. Did 65-70 most of the way loaded with 21.8 average. Got 23 for the return 450 miles doing 75-80.

I think you will have the power to tow far more weight than the landcruisers chassis can safely handle. If you plan to tow that regularly though you may want a transmission with better ratios than the NV4500 or a splitter.
 
#3 ·
I appreciate the first-hand info, sounds like the engine is more than capable of 5500#'s. Your truck weighs a bit more than a Landcruiser, so that's a good comparison. The mileage is very impressive, my Cummins Dodge is lucky to get 22 MPG unloaded.

As for the transmission, I'm not an auto fan and I need a manual I can adapt to a t-case with a rear offset, for the Toyota axle. Advanced makes a NV4500 to FJ60 t-case adapter. Do you think I'd need less RPM's for highway driving?
 
#7 ·
Front axle is an 8", rear is actually a 9.5". I would imagine there are different gear ratios available, but I was thinking 4.10's and 35's wouldn't be too bad.

That setup with a NV4500 would make 2200 RPM at 75 MPH. A gear splitter would be nice for those long freeway drives, but not required. Looks like a Ranger OD with the NV4500 would make 1600 RPM at 75.
 
#8 · (Edited)
It's a full-float axle with a 9.5" ring gear, it will be fine. A Dana 60 ring gear is 9.75" so the Landcrusier axle is quite comparable. :grinpimp: :happyfinger:


Its not going to be a question of the 4BT, it'll be a question of whether your suspension, diff's, and U joints like it. Dont worry about the engine...worry about the chassis. (You got the brakes to stop all that too?)
Like I said in the first post, I don't want to get into it here, that's not the purpose of this thread. I'm aware of what I'm asking here, but thanks for being worried.
 
#6 ·
Its not going to be a question of the 4BT, it'll be a question of whether your suspension, diff's, and U joints like it. Dont worry about the engine...worry about the chassis. (You got the brakes to stop all that too?)
 
#10 ·
The cruiser diffs are nothing at all like a dana 60. The bearings are considerably smaller. And the bearings are many times the weak link in a 30 spline 60 or light duty D70. Just a friendly note of caution, but I'd say towing what you plan to a couple times monthly will wear out/break your rear axle quicker than it should.

4.10's and 35" tires is a good combination. The NV4500 has a very steep overdrive. What I mean by poor ratios is that the NV4500 is functionally a 3 speed with overdrive. Granny gear is not used to accelerate, just to creep or get real heavy loads moving. You're not talking about weight that's anything the 4BT will struggle with, but don't plan on your engine with a stock 16cm H1C being a joy to pull that weight with those gear ratios.
 
#11 ·
Plenty of people tow 5000#'s with Landcrusiers quite often, this isn't something new that I'm thinking about doing. I understand I'll be pushing the limits of the factory parts. I'm alright with replacing bearings every now and again if I have to, but I believe it will be fine.

I understand what you're saying about the NV4500 now and I agree with you, but it's the most common transmission and will work with the Toyota t-case. I've had 2 Dodges with NV4500's and now an '03 with a NV5600, so I'm familiar with them. Like I said in the first post, I have a HY35 turbo with my 4BTA, hopefully that along with the other planned mods will help make up for the gear ratio spread on the NV4500.
 
#12 ·
It will be an interesting expiriment to see if they hold up. The 16 spline D60 rear is the only original running gear component under my '71. I didn't expect it to last forever, they broke under 2V 360 power, but I wanted to see how well it would hold up and it was in pristine condition when I frame-off'd the truck and installed the 4BT. The truck has just under 17K miles on it in the past 5 months with 4BT power. At 10K miles I changed the rear diff oil and found traces of metal, but all was tight. At 15K I opened it up again and found the carrier bearings smooth, but sloppy. I was going to rebearing the axle, but have since decided the D60 is an antique and not worth the effort. I'm going to replace it with a full floater sterling axle. They are much tougher, an absolute dream to work on and dirt cheap.

I want reliability more than factory appearance.
 
#13 ·
Don't know if this will help: I've towed once with my truck. It's a '67 Dodge now almost D-300 [one ton capacity], NV4500, 4.1 gears, 2WD, had 30" tires. Truck weighs 5,700, was loaded with machinery and several hundred lbs scrap steel, towing a '75 Chevy LUV [2,700 lb truck] loaded with scrap steel and more machinery. I'd guess I had a good 3/4 ton in back of Dodge, same in LUV, so 3,000, plus 5,700, plus 2,700: close to 11,500.

Traveled from far northern Cal to southern Cal, then up through Sierras on some fairly steep roads. Could hardly tell the LUV was behind, and truck ran almost like it was all level ground! It was comical it was so easy, just kept laughing to myself through the mountains, but I'm easily amused.

Since installed an compressor upgrade to HY35, 3,200 rpm governor spring: BIG difference, not even going to twist any screws.

By the way, all that was with a blown head gasket, didn't find out until a little over a month ago!!!!
 
#14 · (Edited)
Hey Greg,
Welcome to the forum!

The LC diff and suspension and all components will hold up just fine to the 4BT for general use, it is a good question when towing 1-2 times a month but it should be OK even with 400 ft/lbs. I figure I was at or close to that with my 4BT and it was just fine, zero issues at all...

I am using this chassis/axles under my FJ55 Land Cruiser with my 4BT/NV5600. I decided on the big, heavy, expensive NV5600 because I didn't like the shift patterns of the NV4500 the last round, it shifted/felt great but it is correct that it is a 3 speed with an overdrive and a granny below it.. But it is fine, just something you have to get used to.

The cruiser diffs are really strong, I towed with my FJ55 often (cars, etc), I have towed as much as 12K (which same thing, way way too much weight for the 55) but if you are careful. The biggest weakness will be the rear coil springs on that application. People do tow with 80 series Land Cruisers often. That is actually how I got my chassis, it was a wreck of a guy towing a FJ55 with the 80 that the trailer tongue broke looks (u-haul car hauler :eek:). I will not tow cars or things of that weight often but I want to have the ability as well. I mostly just want to reduce sagging in the rear.

I was planning on installing one of these (these are relatively nice and cheap as well):
http://www.suspensionconnection.com/cgi-bin/suscon/4124T.html

Should do the trick :)

Again hopefully the diff will hold up but my guess is it will be fine... :)
 
#15 · (Edited)
Good to hear you weigh in Andre! If you haven't heard, I picked up Kurts clean 4BTA and all the great parts he gathered. I've been wanting to do something like this for a long time and have been reading a ton on here. It's a great resource, thanks!!

Our FJ80 is planned to be a recreational exploration rig, but if I can use it to replace our Dodge tow rig, I'll be a very happy man. I fully understand they are 2 completely different vehicles, but I already had the plan to build the FJ with a 4BT, so I figure I may as well see how it will do pulling my rockcrawler around. If it's spooky, I'll concede and keep the Dodge. If it works decently, that would be great. I'm excited for the potential of this motor, it seems to do well in many different applications.

As far as the suspension, I'm going to use OME 4" J Springs which will be pretty firm. If I even attempted towing with the FJ80, I would at the bare minimum have; tandem trailer brakes, brake controller, equalizer hitch, rear air bags, larger front anti-sway bar and hydroboost brakes on the Landcruiser. Of course both front and rear disc brakes will be in tip-top condition. I'd like to add an exhaust brake for long downhill runs if needed, but I'd be keeping speed to a bare minimum.

I thought about a NV5600 but they're too much $$! I'm trying to keep this semi-cheap and I've liked the 2 NV4500's in the Dodge trucks I've owned. I'm willing to test out the towing capacity of rear axle, I also think it will be just fine with the right precautions. By my calculations I'll be 500#'s over factory towing capacity. I'm not planning on hauling my Jeep to the Rubicon, just to Moab, Montrose, etc. All places within a couple hours, no big mtn passes, etc.

I need to start a build thread on here, it's going to be slow at first. I want to try gather all the parts for the 4BT swap before I tear down the Landcrusier. We're having too much fun with it running!
 
#16 ·
Very cool Greg... Yes I knew he sold the 4BT, just wasn't sure to who. When I finally get mine done $5 says he'll regret selling it. :) Or yours :)
 
#18 ·
I agree, Kurt has a full plate 24/7/365, I think this was just too much of a distraction for him. We'll have to let him drive our rigs once they're done! Even better, we'll have to get together for a trail sometime.


Towing that much with an NV4500? yea, it will be fine. Mine's a bit slow waiting for the turbo to spool up, but does just fine overall! i'm close to 7k towing and i'm betting my tow rig is around 5 or so, maybe more loaded with camping gear and tools.

the 3-4 shift WILL kill you on steep hills. maybe with the HY35 will be a little bit better, i'm looking to possibly switch down the road for a little faster spool up.

I haven't met a hill i couldn't get up, maybe slow, but i get there. I get pretty darn good mileage doing it too :D

Good info, thanks for sharing. Mabey I'll have to add a 75 HP shot of NOS to build momentum for the 3-4 shift. :happyfinger:
 
#17 ·
Towing that much with an NV4500? yea, it will be fine. Mine's a bit slow waiting for the turbo to spool up, but does just fine overall! i'm close to 7k towing and i'm betting my tow rig is around 5 or so, maybe more loaded with camping gear and tools.

the 3-4 shift WILL kill you on steep hills. maybe with the HY35 will be a little bit better, i'm looking to possibly switch down the road for a little faster spool up.

I haven't met a hill i couldn't get up, maybe slow, but i get there. I get pretty darn good mileage doing it too :D
 
#19 ·
The FJ80 and HDJ80 landcruisers here are all rated at 3500kg towing on a fully braked trailer.
This tow limit is the same regardless of the engine fitted, 3500kg is the limit of commonly available towing couplings here (until you step up to ring-feder types).

IMO the US trend of changing tow ratings with engine power is simply marketing, trying to upsell people to the bigger engines etc.
The towing capacity of a vehicle is set by the chassis, suspensoin, brakes and couplings. Engine size is almost irrelevant.
 
#20 ·
i think it is done to help save components too.

for example, in my durango, the 360 v8 with 3.55's is rated for a good bit less than the 360 v8 with 3.92's and the towing package. this is i'm sure to help save the craptastic transmission chrysler fitted them with :beer:
 
#22 ·
I would think 400 ft lbs of tq would be suffice, That is probably what my 02 Dodge was puttin out on the ground in stock form and it pulled my old stock trailer with 2 horses just fine, and probably about the same trailer weight to. I know your not askin but I feel complled to tell you how I feel about pullin with that much weight with that lc, don't do it, espically on the rocky mnts. hwys.
 
#23 ·
Not planning on towing in any mountains, I live 90 min from Moab and it's more or less flat ground there and back. I'll probably tow on occasion to Montrose, CO also, which is about 2 hrs and also flat ground. But yeah, I know what you're saying. I'm going to try it and if it's slightly sketchy, I'll keep the Dodge.
 
#24 ·
Wow, this thread is frustratingly degraded from the original question....so, I will add to that :D.

My opinion on occasional towing is that you can live with a less than perfect tow rig if you are careful. Keep speeds down and drive conservatively. I have towed 6K many times with a little half ton truck. I would not run 70MPH down the freeway, but at 60MPH it is completely tolerable. The great thing about ratings is that there are always safety factors built into engineering projects. Typically every component has some margin or error which is many times 50% or better. With this in mind you can usually go over the rated capacity without fear of catostrophic failure....which is a good thing.

I would not do this for a planned tow rig, but once in a while in my book is okay.
 
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