Engine swaps, bigger tires and gearing

[Greg]

Just putting this out there for discussion...

My FJ80 has 4.10 gears stock, I'm planning on swapping a GM 5.3l V8 and a 4L60e into the Land Cruiser and eventually run 35" tires. The 4L60e has a .70 overdrive ratio and the GM 5.3 has a pretty high peak torque and horsepower curve. I'm trying to determine what axle gearing would be ideal for fuel mileage and driveability.

I'm thinking that the stock 4.10's combined with that high OD ratio and 35" tires will lead to lugging the engine. I'm not really concerned about offroad gearing or around town, I think I'll be fine for the most part. Freeway speeds are my concern.

Using the gearing calculator at 4lo.com, that combo ends running the engine at 2066 RPM @ 75 MPH.

If I need a gear swap, I'd probably go with 4.88's. I don't think 4.56's are enough of a change to justify the upgrade and any deeper than 4.88's would be too much.

So 4.88's with 35's and a .70 OD ratio will turn the engine at 2460 RPM @ 75 MPH.

So any thoughts on the ideal freeway RPM for a GM 5.3? Will 4.10's be cause the engine to be running outside of ideal speeds while running down the freeway?

 

[I Lean]

EZ has 5.13's and 37's with his TBI 350/700R4, and it's superfantastic. Got him 17 MPG's driving to Moab, and that's in a Scrambler. Without checking, I'm thinking his 37/5.13 is probably roughly your 35/4.88?

 

[billylight]

4.88s for sure it will get you into a little more power without over doing it. unloaded it may be a little low but with a few people and some gear in there you will be dead on. i have had a suburban with 5.7 700r4 and 4.10s 35s the over drive was only good on absolute flat ground with no wind at 75. it just seemed to kick down alot. i have always preferred to be on the little low side then a little high. with those calculators you have to take into account more than just rpms cause bigger tires weigh more and lift creates more drag so you never want your rpms to be at the stock spot. always a few higher

 

[Greg]

EZ has 5.13's and 37's with his TBI 350/700R4, and it's superfantastic. Got him 17 MPG's driving to Moab, and that's in a Scrambler. Without checking, I'm thinking his 37/5.13 is probably roughly your 35/4.88?

That sounds about right, the transmissions are about the same, just updated differences. I do remember that his Scrambler got pretty good mileage.

 

[Greg]

4.88s for sure it will get you into a little more power without over doing it. unloaded it may be a little low but with a few people and some gear in there you will be dead on. i have had a suburban with 5.7 700r4 and 4.10s 35s the over drive was only good on absolute flat ground with no wind at 75. it just seemed to kick down alot. i have always preferred to be on the little low side then a little high. with those calculators you have to take into account more than just rpms cause bigger tires weigh more and lift creates more drag so you never want your rpms to be at the stock spot. always a few higher

Thanks for weighing in, I totally agree. Our Land Cruiser will usually be loaded down with gear, people, etc as well as lifted on big tires, so deeper gearing will not hurt at all. I just don't want to be getting poor mileage and be lugging the engine with the 4.10's. Sounds like the best thing will be to regear after the engine swap.

I would like to hear from anyone that has a truck/SUV with a 5.3l engine and what RPM it runs at doing 75 MPH with stock tires and gearing.

 

[crawldaddy]

Give Ken @ Novak adapters a call. I think he put this same engine in his fj 80.

 

[Rot Box]

I'm wierd but I prefer to keep my RPM's up I would go with 5.29's (2600 @75mph) without hesitation. I like the mechanical advantage, but I usually drive 65mph on the freeway.

That being said you'd be better off finding another 4BT and lugging it with the 4.10's

 

[1\4elliptic toy]

I would like to hear from anyone that has a truck/SUV with a 5.3l engine and what RPM it runs at doing 75 MPH with stock tires and gearing.

Greg, I have that exact setup in my 95 GMC truck (350/4L60E). Running down the highway at 75 I would say your about 2600-2800 RPM's if I remember correctly. Do you need a doner vehicle? That truck is for sale..

EDIT: Sorry I have a 5.7(350)/4L60E not the 305/5.3 4L60E

 

[Greg]

I'm wierd but I prefer to keep my RPM's up I would go with 5.29's (2600 @75mph) without hesitation. I like the mechanical advantage, but I usually drive 65mph on the freeway.

That being said you'd be better off finding another 4BT and lugging it with the 4.10's

I hope the 4.88's will be more than sufficient, I really think 5.29's would cause the engine to drink more fuel with 35's. 5.29's would be great for the stock engine and 35's though.

I would like a diesel of some sort, but I'd rather drop in a Cummins 5.9 than a 4BT. Either way, the expenses add up quickly and it's not the simplest swap. IMO the 5.3 is the simplest, with the most available parts and damn near the least expensive.

Greg, I have that exact setup in my 95 GMC truck (350/4L60E). Running down the highway at 75 I would say your about 2600-2800 RPM's if I remember correctly. Do you need a doner vehicle? That truck is for sale..

EDIT: Sorry I have a 5.7(350)/4L60E not the 305/5.3 4L60E

Good to know, thanks Tracy! Seems like that's surprisingly high RPM's for a Chevy V8.

I don't need a donor, I'm sticking with the GM Gen III engine and I will need a 2WD 4L60e to adapt to a Land Cruiser t-case. Thanks anyhow.