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Ken had asked me if my 261 powered 51 PU can pull the Scotty trailer in overdrive, yes it can if the terrain is not too hilly.I put a A833 4 spd OD manual in awhile back, the truck has 3.42 gears in the rear so the OD overall ratio is 2.49, engine turns around 1800 rpm at 60.The Scotty weighs 1200 lbs, but has a big frontal area , lots of air drag.I think an ideal gear for towing a trailer like this would be 3.08,using a Saginaw 4spd or running in 4th with a T-5
My 94 S10 4.3 (262 cube) 5 spd will also pull the trailer in OD,(a 1.99 overall ratio with the 2.73 gears)on flat ground.Of course with the 2.73 gear, 4th is much better.If I liven in very hilly country,down shifting would be necessary .

yup,,,,,,,,,Fred

Tony, sorry but some how I got off the link, question, I may go to a taller gear instead of the 2:73 although it is ok, do I have to look for one that is specific to the 84 blazer rear end or will other gm's work, in other words will any taller gear from a gm worked regardless of year? thanks for your response and time,,,Fred

Tony, is your 261 completely stock? What is your timing setting and main jet? What kind of air cleaner are you using?

I was messing with mine last weekend and I had been running a bit rich with a #62 main jet in my Rochester B and I changed it to a #57 and it runs a lot better. The plugs were getting fouled out when I was going down long grades and it would run rough at the bottom. Now with the #57 and a slightly lower float setting the engine runs a lot better and the plugs don't foul. I had been getting about 15 mpg with the #62 jet, hopefully I will get 18 or 20 now.

I was going to put a 3.08 in with the SM420 I have now but I am kind of thinking of going with a 2.73. When you calculate out the gear ratios, 4th with a 4.11 gives you almost the same speed as 3rd with a 2.73. 2nd gear with the 2.73 falls between 2nd and 3rd with a 4.11, which is a pretty favorable place for my driving. 1st actually becomes useful, slightly below 2nd with a 4.11.

I think if I was going with tall tires I would use a 3.08 but with normal to low profile radials a 2.73 makes sense. I do haul loads occasionally but I only haul around town.

With the 2.73's and 28" tires a 2.73 would turn 2300 rpm at 75 mph in direct, 2800 at 55 mph and 1800 at 35 mph in 3rd, 2400 at 20 mph in 2nd, and 2500 rpm at 10 mph in 1st. There is a fair gap between 2nd and 3rd but I think it will be ok.

Four, the 261 is rebuilt stock except the block was milled .035 and the head milled about .020, #850 head.The B carb is the slightly bigger 261 model, runs a 57 jet. The air cleaner is the typical oil bath model,single exhaust,2-1/2 inch head pipe, turbo muffler and short tail pipe,used to get 18 mpg with the 3.42 gears, now with the OD, around 20 but I drive faster with the OD.The truck has 225/70-15 radials,suspension lowered about an inch. Gears in the 2.70 range do slow down the acceleration some, high gear acceleration in 3 rd direct is snappy,in OD,much less so.The truck always has 3 rd direct to use when the going gets tuff,2500 rpm at 60. With your 1.70 or so second gear,you may be caught between gears when hauling or driving in the hills with a 2.73 gear.But maybe you like the truck tranny and drive accordingly.
And this for us Chevy guys; I used to have a 49 GMC 3/4 ton with a good running 270 and a swapped in 3.73 14 bolt rear end.My brother in law owns the truck now, Joy's 261 truck will easily out accelerate the GMC in high gear. Yeah, I know it's a 3/4 ton against a lighter 1/2 ton, but a win is a win

Yeah, my truck is really snappy in 4th gear with 4.11's. It accelerates 45-60 just as well as my BMW in the same gear. It just sounds like an angry box of bees. Some shift boots might help that, I can hear all the underhood noise pretty good right now.

sorry, I won't ask again.........Fred

Fred, dah,I forgot your question, yes you need a gear set that is designed for rear end in the truck. Is the sheetmetal cover on the differential a 10 or 12 bolt, six lug axle flange? That's all you need to know.Or is yours an S10 Blazer rear?

Thanks very much, I believe that it is a 84 blazer k-5,,,,,,Fred

well i thinkzz and sez you don't want to use the overdrive when towing de scotty all loaded with twinkys ho ho and de stuff joy joy loads
tends to overheat de od/trans/engine and eng oil and ya go to de wrecking yard for one more 5 spd

now wind to your back and a down hill yea use it but all bullfoot aside loaded and pulling hills and a lot of wind use no higher than direct in most transmissions

a trans oil temp sender and gauge will tell you when your over working the overdrive heat kills