5.13s and 39'' Boggers

[BOWTIE]

5.13s and 39\'\' Boggers

I have a mildly built 350 with a 700R4 and np208 transfer case. Currently I'm running 4.56s with 39'' Boggers and in third gear at 70mph I'm cruising at about 28-3000 rpm. With over drive I'm at 24-2600 rpm. I want to know if anyone is running 5.13s with this setup and can tell me if this will be too low of a gear to run on the highway. Keep in mind that any highway driving that I do is just to get to the trail and back...at the most maybe 100-200 miles one way. I'm planning on an axle change and trying to deside what gear ratio to go with.

thanks for your help.
Ric

MY K-5 DOESN'T LEAK... IT JUST MARKS ITS TERRITORY.

 

[Zepplin]

Re: 5.13s and 39\'\' Boggers

That sounds like a good number to shoot for. I have a set of 38.5 TSL waiting to go on, after I get my engine and other projects done. I think I will get 4.88's for my 14 bolt. I don't do alot of highway driving so I think these would work for me. Plus, your gas mileage, if you care, will suffer more with the 5.13's.

74 Blazer
Kashmir
Zepplin

 

[Emmettology 101]

Re: 5.13s and 39\'\' Boggers

Well if you are running 28-3000 in third with 4.56's and 39's, then with 5.13's you will be running 3177rpm in tird and 2166 in OD.
According to Randy's ring and Pinion calculator, with 4.56's you should be running: 2824 in D and 1925 in OD... (@70mph)

His recomended RPM range for 60mph for a SBC is 1800-2800....

Mike

See <font color=green>EMMETT</font color=green> -&gt; <A target="_blank" HREF=http://emmett.coloradok5.com>http://emmett.coloradok5.com</A>

 

[bigerik]

Re: 5.13s and 39\'\' Boggers

Definitely go w/ the 5.13s! I have 5.13s on both my trucks (1 has 38.5X14.5 TSL/SX and 1 has 39.5X18 Boggers), and I have a Turbo 350 and Turbo 400! AND these are my daily drivers!! I love my low gears!! An old redneck once advised me, "When selecting gears, pick the lowest that are available." With a 350 and those big Boggers, you definitely need 5.13s for acceleration and (I'm talkin' safety, now) steep downhill descents. Even w/ your 2.61 t-case ratio, 5.13s are not at all extreme. Your 350 is fine up to 4000-4500 rpm no matter what. I have been running this combo for 3 years (w/ 3 speeds, remember), and the only bad thing is the 8 mpg and the fact that the 350 engines will need rebuilding as early as 150K miles. As an aside, I had to do MAJOR fender trimming for the 39.5X18 Boggers w/ my 9 1/4" lift on the fullsize Chevy '76, '81 trucks.

 

[6.2Blazer]

Re: 5.13s and 39\'\' Boggers

You shouldn't have any problem with the 5.13's since you have the OD transmission, however your rpms don't quite sound right as Emmetology already pointed out. The OD gear in the 700r4 is around 0.70:1, which should reduce the rpm by 30% from the rpm when in drive, so if you are running 2800 in drive, shifting into OD should lower it to around 2,000.

 

[BOWTIE]

Re: 5.13s and 39\'\' Boggers

Thanks guys for the help.

6.2Blazer,

I was wrong about my OD rpms. I'm running at about 2100-2200 rpm. Just checked it out today.
thanks,
Ric

MY K-5 DOESN'T LEAK... IT JUST MARKS ITS TERRITORY.