Trade? GBR 4.71

Drea

Well-known member
Jun 20, 2007
182
6
I have set of GBR 4.71 R&P that I'm potentially interested in trading for a higher gear set. At least I think they are GBR 4.71...identification help is appreciated.

I got these in a parts truck and was thinking they could be used on my RRC but I fear the rpms may be too high at highway speeds for the tired 4.2L.

I'm not sure how high, maybe a 4.1x or even 4.43? One if the ring gears has a little surface rust but nothing on tooth faces or anywhere else. Very good condition overall. I have no idea of mileage.

If you are interested in ac trade let me know.
 

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Drea

Well-known member
Jun 20, 2007
182
6
Ashcroft calculator press the rpms at 2800-3000 from 60-80. Seems excessively for long trips.

I guess I don't mind paying for more gas, I just don't want to ruin the motor running that high on road trips to the trail.
 

Harv

Well-known member
Your gas mileage might be a little worse at higher RPM, but not necessarily. Lower RPM may have the engine at a poorer efficiency speed. Some say that peak torque RPM will give you the best fuel economy, but I haven't seen that documented.
 

bri

Well-known member
Apr 20, 2004
5,733
34
US
I have had 6 3.9 to 4.6 rover engines. All made it to at least 170k and were still going.r

I have never attributed a problem to running 3000 rpm for extended periods, but also don't put 20k miles a year at that rate. More like 3 to 5k.

I ran at least 3k rpm on my 160,000 mile 98 disco for about 700 miles a month ago. 235/85 w/ 4.11 GBR. Still running fine.

I run mine up to 4000 and 4500 for 20 miles weekly on purpose.

Dumb, perhaps but I like to know my engine is reliable at high rpm for hours.

Quite frankly with a decent 3.9 to 4.6 , my only concern is overheating.
 

Drea

Well-known member
Jun 20, 2007
182
6
Although different, worth mentioning. I run 4.1 on the 04D24.6 with 315/75 and it motors. Nice low end torque on the trail and cruises on the highway at 80/~2800. Easy.

I don't mind getting 8-10mpg. Pay to play. But I do worry about driving long distances running at 3000+ in a slightly tired 4.2 that's also giving me misfire issues(electrical?, Not sure yet).

I've come across a few things lately that have slightly changed my mind. Not the the numbers, but free 4.6 short block and donor truck for D2 crash has a decent 4.6. so now I've got parts if something catastrophic happens. I'd just hate to kill the 4.2 and find out later it was a completely bad decision to test the 4.7's on that platform