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Old 02-13-2012, 10:42 AM
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improving fuel mileage on 355, smog heads


I am not trying to win any races or build some thing that is not. I want to rebuild the stock engine that I have and see where I can improve on fuel mileage. This engine is just a stock , no frills, low maintenance , work horse, plain jane. Here is what I have.
1984 c-10 short wheel base truck
TH 350
31" tall tire
2:73 rear end gearing
4000 LBS
350 GoodWrench Crate
Engine Name: 350 LM1
Horsepower: 249 HP @ 5,000 RPM
Torque: 304 Ft/Lbs @ 3,500 RPM
Compression Ratio: 8.50 to 1
Block: 4 Bolt, 2 Piece Rear Seal, 4.000 Bore
Crankshaft: Cast Nodular 3.480 Stroke
Heads: Cast Iron, 76cc
Valves: 1.940 / 1.500
Camshaft lift: 0.390 / 0.410 Hydraulic
Duration @ 0.050: 195 / 202
Intake: Not Included

What can be done to improve fuel mileage? I am going to rebuild soon.
I asked on another forum about a rebuild, hope no one gets there feelings hurt.
Thanks

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Last edited by Catfish11; 02-13-2012 at 11:00 AM.
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Old 02-13-2012, 10:49 AM
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Best thing you could do to increase mileage is build the engine close to stock, but change the trans to a 700R4. The overdrive in the tranny will do more to boost your mileage than anything you can do to that engine.
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Old 02-13-2012, 12:09 PM
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Quote:
Originally Posted by Catfish11

I am not trying to win any races or build some thing that is not. I want to rebuild the stock engine that I have and see where I can improve on fuel mileage. This engine is just a stock , no frills, low maintenance , work horse, plain jane. Here is what I have.
1984 c-10 short wheel base truck
TH 350
31" tall tire
2:73 rear end gearing
4000 LBS
350 GoodWrench Crate
Engine Name: 350 LM1
Horsepower: 249 HP @ 5,000 RPM
Torque: 304 Ft/Lbs @ 3,500 RPM
Compression Ratio: 8.50 to 1
Block: 4 ? Bolt, 2 Piece Rear Seal, 4.000? Bore
Crankshaft: Cast Nodular 3.480? Stroke
Heads: Cast Iron, 76cc
Valves: 1.940? / 1.500?
Camshaft lift: 0.390? / 0.410? Hydraulic
Duration @ 0.050?: 195? / 202?
Intake: Not Included

What can be done to improve fuel mileage? I am going to rebuild soon.
I asked on another forum about a rebuild, hope no one gets there feelings hurt.
Thanks

X2 on 1971BB427's 700R4. The deep low in these boxes gets the truck launched without having to mash the pedal through the floor this will be a big help with your tall tires and high rear end ratio against 2 tons of truck. The Overdrive will cut highway revs way down allowing a fast cruise with hardly any throttle. The lockup converter alone is good for about a 10% improvement if you're on the highway a lot.

In the engine room the ubiquitous Vortec heads will pull up the compression and greatly improve the burn so you're getting the energy out of the gasoline you paid for. the cam you have is essentially the 300 horse, 327 cam. that was with 10.5 compression back when. Obviously you can't run that on an iron head today but you can run this more like 9 to 9.2. Given your big tires and high gear ratio the Swirl Port head from the TBI 350 would be a good choice, this tends to bump up the bottom end quite well and will fit conventional intakes where the Vortec takes a unique and somewhat pricey intake.

For a carb either the Edlebrock/Carter or the Q-Jet, the smaller primaries will help your low RPM cruise while keeping some big secondaries in reserve for when maximum flow is needed.

Unfortunately the pistons in the Goodwrench aren't the best configuration for chamber efficiency those circular dish pistons don't promote chamber turbulence. A change to D dish or flat tops would make an improvement but gets pricey since you have to get all the way into the engine.

Actually on a cost to benefit ratio these changes will take a long time to break-even on fuel savings.



Bogie
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Old 02-13-2012, 06:35 PM
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can't do much more than what you already have.

however......

Skinny tires would help. stock 4bbl intake and qjet would also work well.

headers are good idea.

make sure the carb is tuned well. Put in a 02 sensor so you can make adjustments

ignition timing is very important for good mpg. Use 15 initial, 37 total in soon as possible, plus 10 from the vacuum advance.

Use the stock thermal fan.

a tight convert will help too.

use a regular oil pump (not high volume)

you would be better off installing a late model 5.3, as it would be cheaper than to rebuild an old 350, makes more power, and gets better mpg.
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Old 02-13-2012, 07:32 PM
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Quote:
Originally Posted by 454C10
can't do much more than what you already have.

however......

Skinny tires would help. stock 4bbl intake and qjet would also work well.

headers are good idea.

make sure the carb is tuned well. Put in a 02 sensor so you can make adjustments

ignition timing is very important for good mpg. Use 15 initial, 37 total in soon as possible, plus 10 from the vacuum advance.

Use the stock thermal fan.

a tight convert will help too.

use a regular oil pump (not high volume)

you would be better off installing a late model 5.3, as it would be cheaper than to rebuild an old 350, makes more power, and gets better mpg.
Do you have any links for the 5.3 switch. Would I have to change the whole pulling system, brackets?
Edit: whew that a lot of work and money to put that in the simple truck. Not worth my time right now. I have to many other projects.

Last edited by Catfish11; 02-13-2012 at 07:56 PM.
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Old 02-14-2012, 06:00 PM
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You can get a complete 5.3 (fan to flexplate) with efi and all accessories fairly cheap. Prices will vary between 500 and 1000 depending on mileage.

Would need to fab in mounts, there are ways to uses your current trans, and some efi reprogramming to do also. Do some research when the time comes to rebuild the old 350.

If you have some skills and some time, you could so the swap very cheaply.

my 454/th400 gets 8 mpg around town and around 12 on the highway. When gas goes to 4 or $5/gallon. A 5.3 with od trans will paid for itself in short order! Only problem is I will need to change my name from 454c10 to 5.3c10 or maybe 6.0c10.
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