350 crate HP vs. '85 350 L Series

[krcaddis]

I'm just installing a low mileage crate engine to replace my grossly overheated original 350 /turbo 350 trans '85 2WD C-20 Scottsdale.

The specs on the factory (14010207) is 165 HP @3800 rpm, 275 FT LB @1800 rpm
The crate as spec'd (1066036) is 249 HP @ 4300 rpm and 275 FT LB @ 3600 rpm
They share the same comp. ratio, so the difference is likely due to the cam. Gas mileage was a poor 10 mpg, although better when I bought the truck I had the Holley 4BBL rebuilt by a specialist, which was overdue. It has a 4.10 14 bolt diff. All the other parts were switched over or replaced in kind. It's a ranch truck used or hauling larger loads- I now use a Taco' for running around as we're 20 miles from town.

Will my MPG likely improve with higher HP engine? Will I seriously miss the low end torque? Or will they perform about the same?

 

[4WDKC]

I'm just installing a low mileage crate engine to replace my grossly overheated original 350 /turbo 350 trans '85 2WD C-20 Scottsdale.

The specs on the factory (14010207) is 165 HP @3800 rpm, 275 FT LB @1800 rpm
The crate as spec'd (1066036) is 249 HP @ 4300 rpm and 275 FT LB @ 3600 rpm
They share the same comp. ratio, so the difference is likely due to the cam. Gas mileage was a poor 10 mpg, although better when I bought the truck I had the Holley 4BBL rebuilt by a specialist, which was overdue. It has a 4.10 14 bolt diff. All the other parts were switched over or replaced in kind. It's a ranch truck used or hauling larger loads- I now use a Taco' for running around as we're 20 miles from town.

Will my MPG likely improve with higher HP engine? Will I seriously miss the low end torque? Or will they perform about the same?

I believe it will be the same maybe even worse, hp isnt what gets the truck moving torque does, your old engine had peak torque at 1800 rpm which means it would work less and the new one makes the same amount of torque but at twice the rpm.

 

[bucket]

I believe it will be the same maybe even worse, hp isnt what gets the truck moving torque does, your old engine had peak torque at 1800 rpm which means it would work less and the new one makes the same amount of torque but at twice the rpm.

Torque peak is only part of the story. It could have nearly as much torque down low too. It's hard to guess economy changes without knowing the entire torque curves of both engines.

 

[4WDKC]

Torque peak is only part of the story. It could have nearly as much torque down low too. It's hard to guess economy changes without knowing the entire torque curves of both engines.

If that engine has a torque graph like a picnic table I will be surprised.

 

[Honky Kong jr]

I believe it will be the same maybe even worse, hp isnt what gets the truck moving torque does, your old engine had peak torque at 1800 rpm which means it would work less and the new one makes the same amount of torque but at twice the rpm.

Horsepower gets you to the wall torque gets you threw it.

 

[rpcraft]

Most of the power numbers listed were always skewed towards EPA regulatory stuff and consisted of the truck being laden with smog equipment that really capped the power output. I'd say there is nothing wrong with the Targetmaster type budget block that a good set of heads, cam, and intake can not solve, but I doubt it will get much better than the current mpg's you are getting. Meanwhile, as far as the motor goes... It'll never be a fire breather on the strip, but it should definitely provide you the upper range of horsepower you seek. The key here is you want to get Vortec heads to match that motor, and you can do it relatively cheap, so no reason to skimp and buy the short block version unless you really can find a great deal on just the short block. A lot of the performance is also going to depend a great deal on how you drive your truck, what gearing you have (and tires), as well as the current Torque Converter you have if you are using an automatic.

Remember on the L31 block and heads even the best the General often got was around 14 to 16 mpg on the early Vortec trucks (21 on highway sometimes with a 700R4 or 4l60E depending on the year)...

 

[bucket]

I remember the window stickers of the '97 4x4 Suburbans, they were rated for 13 city and 17 highway. It's why dad couldn't bring himself to buy one and bought another GM minivan for work instead.

 

[4WDKC]

Horsepower gets you to the wall torque gets you threw it.

I like the one.

You must be registered for see images attach

 

[rpcraft]

Well, I never could imagine a suburban getting good mpg's. 17 seems like wishful thinking in a tank like that, lol. I know my 1977 JImmy with a Goodwrench 350 got 10 on a good day, the upside is the only time it got worse was when i was in 4-lo and I drove it pretty normally unless we were offroading. Glad that thing had a 30 gallon tank.

I figure a truck, like the early Vortec's not loaded, with a tonnue cover, might stretch it out to 18 or 19, especially if you drive miserly.

 

[4WDKC]

Well, I never could imagine a suburban getting good mpg's. 17 seems like wishful thinking in a tank like that, lol. I know my 1977 JImmy with a Goodwrench 350 got 10 on a good day, the upside is the only time it got worse was when i was in 4-lo and I drove it pretty normally unless we were offroading. Glad that thing had a 30 gallon tank.

I figure a truck, like the early Vortec's not loaded, with a tonnue cover, might stretch it out to 18 or 19, especially if you drive miserly.

Thought I read the cam wasnt installed straight up on these from GM.

 

[rpcraft]

It was pretty vanilla but from some research I gathered when making choices for my engine stuff there was one that gave a lot of life back into the "stock L31" I can't recall the specific cam but it's probably documented on this story somewhere. http://www.fourwheeler.com/how-to/e...6-to-2000-350ci-chevy-vortec-5700-v-8-engine/

 

[Jrgunn5150]

The difference is the cam, the heads are the same. I'd imagine the difference between a fresh engine a little warmed over and the older one you had would make up for any negligible difference in low end.

 

[rpcraft]

The Goodwrench 350 motors pretty much suffered from every problem the smog era had except for one and that is they did not have the boat anchor "swirl port" heads that the TBI setups had in the late 80's to early 90's. A cam swap, good intake and carb definitely made a difference without even using the heads, but the Vortec heads definitely helped step it up a notch and the nice thing is now days you can go get a dirty set out of a pick-n-pull for less than 75 bucks and if they are in good shape you can do a good clean-up and valve lap, and even in mediocre condition It'll probably give you a huge ROI.

 

[bman1985]

Gas mileage probably won't change a bit..its still the same size motor. If.mpg is what you're after put in an overdrive transmission and different gears out back.

 

[rpcraft]

Might change some overall but not a lot. Maybe the difference between 12 mpg vs 10