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K5's a dog up hill towing

brans87

brans87

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Well I was hauling around 2500 behind my K5 this weekend including my trailer and with the 350 TBI( only like 20k on it) and 700R4 when I hit a big hill it sucked and drank gas like no tomorrow!!!! I went like 35 miles and used a 1/4 tank gas. This trip was 90% interstate and was running on flats 70-75. Guess I really need to think about 5.3 swap or something if truck is going to drink this much gas.
Details: 87 K5 350 tbi with updated throttle body,injectors etc there but salad bowl,700R4 33x12.5x15's and 3:73 gears truck weighs as sits right now 4700 at scrap yard :D
 
2500 is not that much weight and I am being generous on weight actually
 
You said the engine only has about 20k on it, was it built for low end torque or was it just a stock rebuild?
 
How big a hill? My '90 K5 had a 350 TBI, 700R-4 and 3.42 gears with 35's. Lousy combo, I never used OD...but I towed a utility trailer with approx 3000 lbs in it, plus the weight of the trailer, so call it between 3500 and 4000 lbs and power wasn't an issue. Fuel mileage was still double digit too...pretty sure it pulled 10-5 to 11 most of the trip. this was through the mountains of BC on a 800 mile trip moving to Alberta. My only issue was an alternator that fragged a bearing, seized and blew the serp belt off the engine mid trip.

I've made the same trip towing with my '83 6.2 powered pick-up, again power wasn't an issue.

Towing with square bodies I've found once you hit about 5000 lbs and have significant aerodynamic drag is when I start wanting for more power.

2500 lbs, hell I don't hardly notice that even with some of the stock and anemic engines GM blessed us with.
 
just a crate motor from gm nothing fancy. Hill not sure of degree but wasn't a mountain lol probably takes 3 mins to get up and slow a tractort trailer down to 50 in right lane.
 
Stomis said:
For one 4.56s would be a good start with 33s.
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Gearing is at least part of your problem. Although with that light of a load I'd be checking everything out to be sure there wasn't an additional problem. I towed around a car hauler about that weight, and the truck didn't even know it was there, and that was when I had the anemic carbureted 350 with 882 heads and 3.08 gears.
 
brans87 said:
I went like 35 miles and used a 1/4 tank gas.
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That is simply not a very good indicator that something is wrong and a very inaccurate way to determine fuel economy. What was the overall MPG for the trip, assuming you kept track of total miles and the gallons required to fill up?

How long was the actual hill? Surely not 35 miles? I will say if you were pulling a 35 mile long hill steep enough to slow down most semis to 50 mph while pulling a trailer at 70+ MPH it will suck gas. Lets say the gas gauge and miles you gave are accurate. That would give you around 5 MPG on a hill where as the truck probably only gets 10-11 MPG on flat ground in those conditions. Not like you are going from 20 MPG down to 5.

Also keep in mind that while the trailer may not be that heavy you are increasing the overall weight by 50%. If a person weighs 200 lb. think of them walking up several flights of stairs....no big deal to the average person. Now put a 100+ lb. backpack on that same person and now those flights of stairs are something to think about!
 
so What if i do a 5.3 with 4l60/4l80 swap and 3/4 ton axle in rear with dana 44 hubs on factory 10 bolt and H2 wheels what gears then would you recommend?
 
brans87 said:
meant 3-5 minutes to get up hill.
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I can tell you that gears are not the problem if you honestly think the truck is using this much fuel. Everybody needs to back up and evaluate the original post and the accuracy of the observation. I'm not saying the OP is intentionally making it up or anything but rather is just mis-interpreting what is going on. 1/4 tank of fuel is around 7 gallons and you are saying the engine burned this much in 3-5 minutes? You would need a fuel pump capable of what, 80-100 GPH, which I believe is way past the capabilities of any production fuel pumps found in a Blazer. Of course that is even assuming you had an engine capable of using that much fuel without choking out.
 
no no no in a 45 mile trip mostly highway with 3 steep hills I burned up 1/4 gas.
 
35-45 miles speedo is off cause of tire size. the hills where probably 2-3 mins to get up doing 50 mph up them
 
brans87 said:
35-45 miles speedo is off cause of tire size. the hills where probably 2-3 mins to get up doing 50 mph up them
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You need to correct the speedo first thing, the ECM uses this for fueling and timing tables and if the speed reading to the ECM is off so is everything else.
 
brans87 said:
no no no in a 45 mile trip mostly highway with 3 steep hills I burned up 1/4 gas.
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brans87 said:
meant 3-5 minutes to get up hill.
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brans87 said:
35-45 miles speedo is off cause of tire size. the hills where probably 2-3 mins to get up doing 50 mph up them
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You are talking like there is some huge issue and contemplating major modifications and expense to the truck based on this? The speedo/odo is off some significant and unknown amount, and we all know just how accurate the factory fuel gauges are, but still that is reasonable fuel economy where you have some long and steep hills combined with pulling a trailer.

Don't get me wrong as I think a 5.3 swap and possibly gears (not sure what you currently have or really need) could really help the truck be a better highway cruiser and better MPG overall....but I just hope you are not basing the need to do this solely on one short stretch of road where you think it used a little more fuel than it should have.
 
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