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Need some more hp from a 350 in a 85 suburban towing a trail

General engine tech -- Drag Racing to Circle Track

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drifter
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Need some more hp from a 350 in a 85 suburban towing a trail

Post by drifter »

What should i do to get some more power from a 350 engine in a big 85 carburated suburban and towing a 6000# trailer anyone know of a good cam to use? he dosent want headers and right now its only getting about 9mpg towing his trailer what do you guys suggest?
dan miller

Post by dan miller »

I would suspect that not many things will be cost effective. Nine mpg isn't all that bad.

A cold air intake MIGHT help a little, as will a good exhaust system. Maybe 1 mpg between them. Of course, 1 mpg is 10%, so that might be worth a try. But, truth be known, the only usual change is more noise.

The camshaft change would probably not increase the mileage.

About the only meaningful way to increase mileage in a case like you mention is by driving habits. Drive at a moderate pace, accelerate slowly, and (very importantly) pay attention to what's ahead and plan your moves accordingly. Probably worth an honest mile per gallon.

Tires inflated a little on the high side might be worth something, but probably not enough to measure.

Danny
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Post by lasermike »

The total package probably weighs a good 10,000 lbs., so 9 mpg isn't too bad. You might try advancing the spark timing? Dual exaust for sure. An EFI would probably make a difference but the cost is high. Make sure the carb has a large (clean) air filter.
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Re: Need some more hp from a 350 in a 85 suburban towing a t

Post by Keith Morganstein »

drifter wrote:What should i do to get some more power from a 350 engine in a big 85 carburated suburban and towing a 6000# trailer anyone know of a good cam to use? he dosent want headers and right now its only getting about 9mpg towing his trailer what do you guys suggest?
I used to build these all the time for that purpose. An economical towing engine build

Flat top pistons and an MTC-1 Camshaft (204/214 .420 /.447)
Edelbrock performer manifold and Dual exhaust.

Makes a big improvement over stock in terms of pulling power. Maybe better mileage because you can pull some hills without down-shifting.
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Post by drifter »

What is a mtc camshaft? who makes it?
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Post by drifter »

Keith have you used Engine Tec kits? Are there bearings and pistons ok for a build like this or should i go federal Mogual?
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Post by Keith Morganstein »

drifter wrote:What is a mtc camshaft? who makes it?
MTC-1 is a melling cam #. (MTC = Melling Torque Cam)

It is a basic garden variety torque cam that has been around for a long time and works in those types of applications. An extra point of compression from the flat tops helps too.

This cam is sold under many brands and labels. MTC-1 is the best known. I have it in Engine-Pro brand. Just look for specs (204/214 .420 /.447)
drifter wrote:Keith have you used Engine Tec kits? Are there bearings and pistons ok for a build like this or should i go federal Mogual?
Engine Tec kits are likely o.k.

I buy from an Engine Pro warehouse that has name brand components and a few of there own label. All good parts.

You can PM me if you need more info on Engine pro kits
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Post by drifter »

Keith i checked for that cam today my book says the mtc-1 is 204/214 with 420 & 433 lift is this the same one you use? I also checked federal mogual and they list one called performace cam with those same specs.What about valve guides for a hauler like this would you use k-line bronze liner type or a 1/2 od cast iron? And are the alun. bearings any better then the regular bearings?
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Post by Keith Morganstein »

drifter wrote:Keith i checked for that cam today my book says the mtc-1 is 204/214 with 420 & 433 lift is this the same one you use? I also checked federal mogual and they list one called performace cam with those same specs.What about valve guides for a hauler like this would you use k-line bronze liner type or a 1/2 od cast iron? And are the alun. bearings any better then the regular bearings?
My mistake 204/214 .420 /.443

Choice of guide is personal and depends on equipment. I use 1/2" cast iron guides in heads like that. A decent valve job and resurface the head. If I'm motivated enough I will also clean up the big ugly ridge in the valve bowl before the valve job.

Both types of bearings are fine for that application.
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Post by CamKing »

If you want to run something designed after 1960 :wink: , you could go with my towing cam.
Part# H65295-66299-112
260/264 @ .006"
204/208 @ .050"
.443"/.449" Valve Lift w/1.5 rockers
112 LSA

This will increase the low-end torque, and he won't have to put his foot down as much when towing. He'll see a noticable difference in both power and fuel milage.
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Post by randy331 »

Camking, will that cam really improve mileage, or just power?

Drifter, I guess this engine is coming apart for an overhall?
I'd look first at things that gain power, and mileage.
Increase compression,
Get some quench in the chamber with a flat top, and decking the block, thinner gasket etc.
Probably most important, good valve, and ring seal.
Good working small carb,
and Ignition.

If a daily driver, (short trips) getting to operating temp quickly.
Thermostate, heat crossover in manifold, hot air intake from ex manifold working properly, thermostaticly controled electric fan.

A mild port job will add power, maybe mileage.

Randy
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Post by MadBill »

dan miller wrote:...A cold air intake MIGHT help a little...Danny
A cold air intake definitely adds power, but it actually hurts fuel economy. At cruise, the hot, less dense air means more throttle opening is required to produce the same power, and the resultant lower manifold vacuum reduces the pumping losses within the engine.

Ideally, something like the old "Thermac" intake system used on carburated GM engines in the seventies and early eighties engines would be best. It utilized a vacuum operated flapper valve to pick up hot air off the exhaust manifold during cruise and cold air at WOT.

He might gain more via aerodynamics though. A fairly deep front air dam reduces the turbulent flow under the vehicle and can substantially lower drag.
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Post by randy331 »

MadBill wrote:
A cold air intake definitely adds power, but it actually hurts fuel economy. At cruise, the hot, less dense air means more throttle opening is required to produce the same power, and the resultant lower manifold vacuum reduces the pumping losses within the engine.
There would be a trade off here. If the wider throttle setting lowered manifold vacuum to the point of power valve opening, or other mixture enrichment method, the mileage could suffer.
I'd tend to lean towards warmer air, it should help fuel atomization.

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Post by MadBill »

Overlooked that this was a carb application! It should already have a Thermac system. Presumably a Quadrajet? If so, a couple more tips:

o These carbs have a cruise AFR adjuster which can make quite a difference to economy. There is a 5/16" aluminum plug on the top surface, just ahead of the air cleaner gasket. If you drill a shallow hole in it, thread in a sheet metal screw and pull out the plug with a slide hammer or vice grips and hammer, a brass fitting with a male tang protruding can be seen. This is an adjustable stop which determines how deeply tapered needles extend into the primary jets during cruise, when manifold vacuum holds a piston/needle carrier down against it. A 5/16th bolt can be slotted (~double the width of a hacksaw cut, ~1/4" deep) and used to turn this stop down 1/4 turn at a time until the point is reached where a slight surge can be felt at a steady 40 -50 MPH cruise on a smooth level road. From this point, back the screw out ~1/4 turn and the AFR should be very close to optimum. A piece of tape can be used over the hole while adjustments are being made and the plug tapped back in when they are complete.

o Also, as randy says, there's certainly a trade off re power enrichment. If you know or determine the vacuum at which the power valve opens, and fit the truck with a vacuum gauge, the driver can work to stay out of power enrichment. Once the load demands it though, it's usually better to use more throttle in a higher gear (or as permitted by an automatic) than to down shift for higher RPM and more vacuum.
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Re: Need some more hp from a 350 in a 85 suburban towing a t

Post by Keith Morganstein »

Keith Morganstein wrote:
drifter wrote:What should i do to get some more power from a 350 engine in a big 85 carburated suburban and towing a 6000# trailer anyone know of a good cam to use? he dosent want headers and right now its only getting about 9mpg towing his trailer what do you guys suggest?
I used to build these all the time for that purpose. An economical towing engine build

Flat top pistons and an MTC-1 Camshaft (204/214 .420 /.447)
Edelbrock performer manifold and Dual exhaust.

Makes a big improvement over stock in terms of pulling power. Maybe better mileage because you can pull some hills without down-shifting.
The real world experience was this.

Customer would have the stock 350 4bbl in his Chevy or GMC with 70-100k on it. Would be trying to pull a good size trailer and be downshfting on highway hills, pulling them at 45mph.

Rebuild it as above and he would pull the same hills at 55mph without downshifting. Usually reporting better MPG.

It's nothing special and I'm positive there are better cams, but It worked, customer was happy and told some friends and so on. I saw no reason to change.

Built plenty of these, but most of this vintage truck have rusted away in the northeast and haven't had one to do in a couple years.
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