305 & Th 700 good combo? Reliable? mileage?

[bavarian_blazer]

Hi folks,

I got me a 86 Jimmy with a 305 and a th700 acouple months ago. it has all the goodies like trans oil cooler, quad shocks etc.
As I'm not able to afford a fancy AMG 6500 optimizer the next 4 years, I have following drivetrain-options for my truck(s)


1. keep my old 6.2

-unknown mileage
-several oil leaks
-hacked wiring harness
+good mileage

2. keep the 305

-minor oil leaks
+only 80 000 miles
+one owner truck, everything works/all original
+transmission oil cooler

I read somewhere that the 305 is a quite reliable engine. It seems (can this be real?) that the truck gets about 18-19 mpg. Besides that, I just like the idea to swap the bodies without the need for installing new wires/redoing the electrical components...
(I'm planning to keep one frame to build up a solid drivetrain (repaint the frame/new or rebuilt engine and transmission and a 4''lift)

Well, what do you think?
-are 19mpg actually possible for the 305?
-how reliable is that engine/combo? (the truck always got good care and regular oil changes)


Greetings

Flo

 

[andyblack]

My dad had a 2 wheel drive with a 305/700 that he was able to get 19 mpg out of, but in a 4X4, I doubt you could.

I have a 305/TH700R4 in my K1500 and it gets me around fine on 35s with a heavy winch/bumper and 4 inch lift. I have 4.10s in the axles. The engine and trans are stock. I usually get about 10-12 mpg though. All 305s leak oil, I think. I'm pretty happy with mine - not the most powerful, but among the most reliable for a mildly built truck. I say keep it.

 

[dyeager535]

Best I ever got with the 305/700 combo was 17MPG. I was able to do that a few times, so it wasn't a fluke. Depending on how light the vehicle got, that could probably go up. That truck had a complete interior, no idea what it weighed.

6.2 is going to net better mileage than the 305.

 

[andyblack]

Best I ever got with the 305/700 combo was 17MPG. I was able to do that a few times, so it wasn't a fluke. Depending on how light the vehicle got, that could probably go up. That truck had a complete interior, no idea what it weighed.

6.2 is going to net better mileage than the 305.

Wow. What size tires and what gearing were you running to get that mileage? It was a 4X4, right? The truck I was talking about of my dad's that he could get 19 mpg out of was a long bed 2WD with a 2.73 rearend.

 

[scrappyk5]

I ran my blazer with a 305/700r4 , for 7 years and 87,000 miles. only problem i had was the ignition module wnet bad. I think the 305 is a very reliable motor. the last 4 years I was running 35s and the last two the 305 was hooked up to a th400.

 

[dyeager535]

That was either 235/75R15's or 31x10.5R15's. 3.08's, 4WD. 60MPH.

I got 18 with my next K5, 350/3.42/33" combo, but that one was stripped inside and quite a bit lighter. No OD either. Big factor here IMO is that the best economy recorded was at 50MPH.

 

[AJMBLAZER]

Stockish truck with highway oriented gear/tire combo? You might see 19mpg on the freeway if you keep your foot out of it.

I had a '92 Blazer K1500 4x4 that when it was stock with the 265/75R16's and 3.73 gears got me 19-20 on the freeway. TBI 350 and 700R4.
Hard to say if an older Blazer with a more square body could do it, especially with a carb.

 

[andyblack]

I ran my blazer with a 305/700r4 , for 7 years and 87,000 miles. only problem i had was the ignition module wnet bad. I think the 305 is a very reliable motor. the last 4 years I was running 35s and the last two the 305 was hooked up to a th400.

Yeah, my ignition module went out too. Also the timing chain streched out and slipped off the cam shaft once. Other than that, I've had just a few carb issues. The odo read 53,000 when I got it and now it's showing 71,000. I'm not sure if that's actually 171,000 or 271,000 actual miles.

You guys are getting excellent gas mileage from your rigs. I guess the Blazers get way better mileage than the trucks do. I'm going to start hitching a ride with one of you.