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Old 04-18-2012, 07:08 PM
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350 build for MPG?

Hey guys,

Over the summer, I plan to build a 350 engine as my project to install in a GTO im getting from a neighbor. Question is, im interested in buying this engine for $100, but the guy said he got a quote to machine it and rebuild it for $600 with all these high performance parts. As of now, im more focused on fuel economy. What type of parts should i get to improve mpg without breaking the bank? Ive asked this before but for a 305 in my Bird, but for this engine, the block will be stripped so i can install whatever i feel is better for mpg. What carb? Camshaft? Piston type? Heads maybe? Also what transmission would go well for this. A 350 or 700? What ideal rear ratios?

Thanks alot!!

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Old 04-18-2012, 09:54 PM
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Go back and read the responses for the 305. What kind of mileage are you thinking you want? $600 won't do much for updating internals. As far as trans, 700 hands down over the 350 for mileage.
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Old 04-19-2012, 04:11 AM
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Fuel injection always helps.
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Old 04-19-2012, 07:35 AM
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Quote:
Originally Posted by 79bird
Hey guys,

What carb? Camshaft? Piston type? Heads maybe? Also what transmission would go well for this. A 350 or 700? What ideal rear ratios?

Thanks alot!!
QuadraJet Carb.
Talk to a few Cam grinders, mild, low-mid torque cam.
18cc D-Dish Pistons, 9.0 Compression.
Vortec Heads.
X2^^, 700R4 or 2004R Trans.
3.23 - 3.42 rear Gear.
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Old 04-19-2012, 12:10 PM
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if u want the best mpg u can get i would go with fuel injection over a carb.
not saying a carb cant work very well but with fuel injection u could cruise on the highway with afr's in the 16's without any problems

of course the fuel injection would cost more to start over a carb setup

but the parts can easily be sourced from the junkyard or ebay for not to much money

the simplest way would be to get a tpi intake off a 80's camaro or vette and use a factory 7730 ecm and harness,
the 7730 ecm is well documented and is simple to tune only requireing a laptop and a prom burner. the burner will run about 50-80 bucks and a handfull of blank chips which i belive are around 5 bucks each

only problem is the tpi intake wont bolt onto vortec heads unless u buy a vortec tpi base which is in the 400-500$ range.


if u want to get really involved with it u could do a turbo on the 350, with aproperly sized turbo and proper turbo system u will actually gain mpg and not lose it

on my v6 camaro i went from 27-29mph on the highway n/a to 36+mpg highway after my turbo install, and thats with a 3.1L v6 with a 700r4, 4:10 gears and 4,000 stall converter, going that route takes alot of research and carefull planning though to do it right
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Old 04-19-2012, 12:53 PM
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Anything you do to the engine to increase mileage wont come near the savings you'll get with an overdrive trans and a lockup converter. But you also wont save much money going economy build vs. moderate performance build. The mileage might be better, but the cost of the build will be basically the same.
Electronic fuel injection will help, but the cost is greater vs. buying a carb. A properly built and tuned 350 with a small 4 barrel, decent heads, and not too high compression, can give decent mileage if tuned right. Be sure to also go with an HEI type distributor to help with good spark. Headers and dual exhaut will also help mileage.
I'm running a 350 with Edelbrock Performer, headers, small 600cfm Holley, HEI, and a mild cam in my '69 Suburban. Not a lightweight vehicle by any means, but I get around 18-19 mpg at 60 mph with a TH400. I'm planning on changing to an OD trans sometime to increase my mileage on the highway.
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Old 04-19-2012, 01:40 PM
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Quote:
Originally Posted by 79bird
Hey guys,

Over the summer, I plan to build a 350 engine as my project to install in a GTO im getting from a neighbor. Question is, im interested in buying this engine for $100, but the guy said he got a quote to machine it and rebuild it for $600 with all these high performance parts. As of now, im more focused on fuel economy. What type of parts should i get to improve mpg without breaking the bank? Ive asked this before but for a 305 in my Bird, but for this engine, the block will be stripped so i can install whatever i feel is better for mpg. What carb? Camshaft? Piston type? Heads maybe? Also what transmission would go well for this. A 350 or 700? What ideal rear ratios?

Thanks alot!!
Fuel economy is the result of a system that includes the engine to the tires.

Gearing is perhaps as important in economy as the engine perhaps more so. The OEMs tried for years to get away with very high ratio rear ends behind the 3 speed automatics of the 1960ís. This worked on the Federal fuel mileage tests till the feds figured out that most cars donít spent their lives traveling at 55 to 60 miles an hour for hours on the freeway. When the mileage tests were changed to cycle representing something closer to the 25-35 mile an hour stop and start reality of life suddenly the OEMs could meet the fuel economy standards. So some real engineering had to be done which in many ways took transmission design back to the 1930ís, 40ís into the mid 50ís where lower ratio rear ends and overdrive transmissions were the norm as a means to improve engine fuel economy. The modern implementation took some different turns than back to the manual 3 speed gear box with an electric overdrive. Instead automatics got a deeper low, an overdrive high, and a lock up converter while rear axle ratios were lowered a bit from the 1970ís and 80ís 2.73 to a 3.08. Manual gear boxes received deeper lows with an overdrive 5th or even 6th. These changes improve mileage by:

1) Addressing the slippage losses of a torque converter (whatís more innocuously revered to as torque multiplication) by locking it up under cruise conditions. This typically reduces cruise RPMs by about 200, this varies somewhat from light load on flat ground to the heavy load of pulling a hill where the slippage may be 300 or more RPMs that donít translate into road speed for the fuel burned.
2) The deeper low ratio provides greater leverage from the power output of the engineís crankshaft as itís transmitted to the rear axle. This makes launching from a stop possible with less throttle and therefore less fuel burnt.
3) The overdrive highs drop the engine speed at cruise making it work harder on less throttle, this raises the thermal efficiency which translates into less fuel burnt for miles traveled. To a large extent electronic fuel injection and ignition controls make it possible to operate the engine in an area that was defined as lugging back in the carburetor days. If your using a carburetor you probably canít configure the car to get all of this advantage. This is also an arena of modern lubrication where lighter viscosity oils that have stronger molecules and additive packages will tolerate the higher loads being imposed at slower engine speeds with out the oil film failing. Certainly the synthetics are great at this but all the major branded mineral oils are much better at it Chevron DELO ISO-SYN comes to mind but all the other majors are making mineral bases that perform closer to the synthetics than the mineral base oils of a couple years ago for considerably less money.
4) Rear axle ratios have been raised a little, typically 2.73 to 3.08. This helps get launched better with stop and go traffic and builds a better torque profile on the tire in the mid gears which also helps in traffic while using the overdrive ratios to drop engine RPMs at high speed cruise. One could argue the case for staying with the higher ratio rear (2.73) lower the transmissionís low and adding 4th or 5th or 6th as a direct drive with the additional gears filling more and closer ratios between low and direct drive. This discussion rages at Harley Davidson sites over the merits of the Harley 6 speed with the top gear being an overdrive and the Baker 6 speed with the top being direct drive. But this discussion gets into the motorcycle unique situation of having a primary reduction between engine and transmission, the transmission, and the final drive reduction. For automobiles there isnít a primary reduction between engine and transmissions so if youíre aware of or accidentally tune into this discussion in the motorcycle press youíll find it is interesting but not applicable.

So as usual I beat around your question but unless you think about the engine in the larger context itís most difficult to extract much in the way of mileage improvements. Typically looking only at the engine the choices run to mild cam timing with no overlap and low lifts .4 inch or less. Put on a small carburetor and run lots of advance, use shorty headers of rams horn style manifolds into dual exhaust of moderate size. In your case I probably select Swirl Port heads over Vortecs to place more emphasis on building bottom end torque, though either is probably not far from a toss up in terms of mileage. The Swirl Ports build a little better torque but donít burn as well. The Vortecs trade a more efficient burn for a small loss of bottom end torque. The end result where mileage is concerned is probably 6 of 1 a half dozen of the other. Compression is all important for mileage you need to pick the grade of fuel youíre willing to buy and push the compression just to that fuelís edge of detonation. This gets to needing to compute the Dynamic Compression Ratio (DCR) before buying parts like pistons and heads. The OEMs tried this back in the latter part of the 1950ís where you could option a large size, mildly cammed engine with massive amounts of compression. That was something they could do when 100 plus leaded fuel was available, but even then without improvements to manifolds, fuel delivery, combustion chambers, and transmissions this never improved mileage enough to justify the expense of premium fuel. Today there is a similar problem with diesels, the price difference between regular gas and diesel fuel is greater than the improved mileage of the diesel. So the diesel costs more to buy, as much or more to operate and while with a minimum of care it will last your life time, most people trade the vehicle before the up front investment is paid for by the savings of fuel cost. Which is a big answer to question of why these things arenít more popular in America where we put a lot of miles on a vehicle in a fairly short time compared to the rest of the planet. We wear out the body, paint and interior well before the fuel savings repays the additional upfront purchase cost.

Frankly for the money you have to spend on this project, you might just as well devote it to buying gasoline for what youíve got. Mileage improvement projects are very frustrating because the rate of payback from the improvements is so small that it takes a long time to get to the breakeven cost let alone get ahead. Because of this, the subject is full of charlatans selling stuff that promises a lot of improvement for what appears to be reasonable prices which donít perform anywhere close to their expectations. Or use the cash toward a new small car, not cool but they do deliver a low cost of operation for real.

If you just gotta spend your savings on the GTO, a 700R4/4L60 transmission with a lock up converter, a set of shorty headers or rams horn manifolds either with dual exhausts would make the best improvement for the buck spent. After that better heads with more compression over flat top or D dish pistons. Compression is dangerous too much causes you to have to back down the timing that will quickly cost more fuel than the higher compression saves. This is a tough dance to get all this stuff to work effectively.

Bogie
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