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Old 09-06-2011, 02:05 PM
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Better mpg from 350 small block Chevy ?

I was hoping to get some feedback from you master mechanics here on this fabulous site. I was wondering if there where some modifications I could do to my Chevy engine. to gain better MPG'S. Here in Iceland a gallon of regular 91 Oct gas cost's 7.68$ so it's important to get good milage.

The engine is in a fairly heavy 4x4 vehicle 4000 lbs. The transmission is TH700R4 with lock-up. And S-10 converter (around 1800 stall, Would there be a good choice going with converter from Diesel engine) ?

The engine is 350 Chevy, very freshly rebuilt (maybe ran 2000 miles) it's bored 0.030" over.
it's got flat top pistons (10:1) compression
but otherwise stock bottom end.
The heads are aluminum from corvette, 113 casting if i'm correct. 58cc camber and 1.94"/1.5" valves.
Intake is an old Edelbrock unit called Street Master (It's a single plane intake) from some old article I read it was built for economy and idle - 4500 rpm range.
The carburetor is 670 CFM truck avenger from Holley, it's mostly stock. 68 Jet's front 89 rear 6.5" Hg power valve and 31" squirter.
Distributor is new MSD street fire HEI. All plugs and wires are new.
Ignition timing is 14 at idle 34 @ 3000-3200 rpm w/o vacuum adv. and 48 with vacuum advance connected (not sure if i can run more vacuum advance)
Vacuum advance is connected to a full timed vacuum port.
Crane Powermax camshaft # 113942. 216/228 dur @ 50. 272/284 adv dur. 454/480 Lift and 112 LSA. 1800-5600 rpm range.
Exhaust system is combined with 1.5/8" long tube headers and dual 3" exhaust with 4 glass pack mufflers.

If you need some more information please ask.
Best regards from Iceland

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Old 09-06-2011, 04:19 PM
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Change the cam to an economy cam or put fuel injection on it and ditch the carb.
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Old 09-06-2011, 05:08 PM
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I think that going with different camshaft is the more realistic choice here, But what kind of cam would be more economical, I need to have a good low end power.

Best regards.
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Old 09-07-2011, 04:22 PM
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Quote:
Originally Posted by cool rockin daddy
Change the cam to an economy cam or put fuel injection on it and ditch the carb.
From what I gather, a very well tuned carb can offer much the same fuel economy as almost any EFI set up.

The hard part is knowing exactly how to tune it, and so that it works with everything else as efficiently as possible. If you really cared, you can buy a book on Holley/Edelbrock carb tuning. I just bought one for Holley carbs, and.... holy **** cakes its a science within itself. WOW. SO much stuff to consider that I didn't even know about.

But if you're kind of lazy like me, EFI is the way to go. The 700R4 is a good tranny for fuel economy though, so short of really fine tuning your set up, I think given the 4x4 situation you're doing almost everything you can.
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Old 09-07-2011, 05:26 PM
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You can come close, but you can never achieve the same power and efficiency with a carb as you can with fuel injection. If you could, car companies would still be using carbs .

As it is now, "modern" fuel injection is becoming outdated as companies like BMW are going to direct injection and shooting the fuel directly into the cylinder.

What is your MPG now and what are you hoping to get? Can't really say you can improve if we don't know where you're at. For all I know you could be getting 20+mpg, in which case I'd say you're about tapped out lol.
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Old 09-08-2011, 10:35 AM
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JMO but I would ditch the outdated intake for an Edelbrock Performer and a Q-jet. Don't misunderstand- I love Holleys but think that Q-jets get better mileage even though they can be a booger to fine tune. I really don't have a prob with the cam because I used that cam on a couple 350s years ago with good results.
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Old 09-08-2011, 11:05 AM
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Most important info for fuel mileage not listed.
What gearing are you running with the 700R4?
700R4's like 3.42 or 3.73 gears, although have seen a few people with 3.23 gears that said they got good mileage.
Also what is your tire size, not just rim size but actual tire size?
A higher stall converter will give you worse fuel mileage.

You might consider switching to LPG or Propane like the Auzzies and New Zealanders do.
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Old 09-13-2011, 02:01 PM
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Sorry for this late reply, Have been using this Jeep for daily driving for some time now. It seems I'm getting between 10-12 MPG's in city driving. haven't gone highway yet. And yes. The Jeep is on 4.56:1 gears and 38" tires (actual height is 36.5")

Best regards.
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Old 09-13-2011, 03:01 PM
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Quote:
Originally Posted by TroyBoy
JMO but I would ditch the outdated intake for an Edelbrock Performer and a Q-jet. Don't misunderstand- I love Holleys but think that Q-jets get better mileage even though they can be a booger to fine tune. I really don't have a prob with the cam because I used that cam on a couple 350s years ago with good results.
No offence to TroyBoy,but when the Streetmaster was introduced it came out during the Jimmy Carter "gas crisis" in the 70's when TroyBoy was about 6 years old, the development by Edelbrock at the time was based on using the Quadrajet and the Carter AFB's with these intakes and there are two series of Streetmaster intakes for SBC's.The premise of the Streetmaster was by using smaller runners you would increase port velocity and thereby save on fuel in the low and mid range power bands.Crower had also developed camshafts for low end torque and fuel economy which are still available today.My 1965 El Camino "test mule" with a 283 Muncie 4 speed and 3:73 posi would pull 26 MPG highway with a 500 CFM AFB and 1 1/2" primary headers and still run low 15's at Sacramento Raceway.The Streetmaster is a better intake than the Performer in my opinion,the Streetmaster will fall off in power past 5,000 RPM so the components need to match like small runner heads,free flowing exhaust,RV mileage cam and a smaller CFM carb.Holleys 450 CFM Economaster was capable of 2-3 MPG over the factory Quadrajets.To achieve your mileage goals you need a cam swap and a 500-600 CFM carb.
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Old 09-14-2011, 05:46 PM
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Quote:
Originally Posted by Icejeep
I was hoping to get some feedback from you master mechanics here on this fabulous site. I was wondering if there where some modifications I could do to my Chevy engine. to gain better MPG'S. Here in Iceland a gallon of regular 91 Oct gas cost's 7.68$ so it's important to get good milage.

The engine is in a fairly heavy 4x4 vehicle 4000 lbs. The transmission is TH700R4 with lock-up. And S-10 converter (around 1800 stall, Would there be a good choice going with converter from Diesel engine) ?

The engine is 350 Chevy, very freshly rebuilt (maybe ran 2000 miles) it's bored 0.030" over.
it's got flat top pistons (10:1) compression
but otherwise stock bottom end.
The heads are aluminum from corvette, 113 casting if i'm correct. 58cc camber and 1.94"/1.5" valves.
Intake is an old Edelbrock unit called Street Master (It's a single plane intake) from some old article I read it was built for economy and idle - 4500 rpm range.
The carburetor is 670 CFM truck avenger from Holley, it's mostly stock. 68 Jet's front 89 rear 6.5" Hg power valve and 31" squirter.
Distributor is new MSD street fire HEI. All plugs and wires are new.
Ignition timing is 14? at idle 34? @ 3000-3200 rpm w/o vacuum adv. and 48? with vacuum advance connected (not sure if i can run more vacuum advance)
Vacuum advance is connected to a full timed vacuum port.
Crane Powermax camshaft # 113942. 216/228 dur @ 50. 272/284 adv dur. 454/480 Lift and 112? LSA. 1800-5600 rpm range.
Exhaust system is combined with 1.5/8" long tube headers and dual 3" exhaust with 4 glass pack mufflers.

If you need some more information please ask.
Best regards from Iceland
Lots of less than ideal parts selection but I'll give that where you live doesn't provide the parts choices of the San Fernando Valley.

The intake is a poor and obsolete selection for mileage and improved bottom end torque there's nothing like a Performer for almost as good but with a bit more top end the RPM Performer is an excellent choice.

Your cam is on the hotter side and will demand to be fed. The rather wide LSA of 112 degrees makes for a nice idle but it pushes the intake valve into staying up late which creates a lot of reversion problems which a 180 degree intake like the Performers do a good job of damping out where the single plane you have can't. I didn't look to the cam specs on overlap but overlap while good for top end power simply throws mixture unused right out the exhaust pipes.

Your exhaust is much too large this causes the exhaust to stall in the pipe and reduces the temp which could have been used to help pull the exhaust from the engine. As it is the engine is having to do all the work to get that stuff out.

Aluminum heads are not a good choice for mileage, they give up the heat of combustion too quickly to the cooling system. This is effort that could have been used to push the piston rather than trying to create a balmy climate for Iceland. To go further into the heads while the chambers are small GM specifies a very thick head gasket around .053. This makes the chambers a lot bigger reducing compression. You have a cam that needs quite a bit of compression. A thin MLS gasket would solve the many problems of these heads. These type gaskets allow the shear of thicker OEM gaskets o seal isn't lost and wear doesn't occur to the aluminum casting from the effects of different rates of expansion of the aluminum heads and iron block. Further, the thinner gasket reduces the volume above the piston increasing compression and reducing the distance between the head's squish/quench deck and the piston making the squish/quench more effective which improves combustion efficiency and detonation resistance. Running the thermostat temp up to 210-220 will healp with the thermal efficiency problem of these heads but make make the motor ping more. cold air intake and lack of exhaust heat to the intake mainfold are also things that reduce mileage.

Yes a properly set up Qjet or Carter/Edlebrock would provide a bit better mileage than the Holley. But the Holley will operate better than these carbs when set up reasonably close, where the Qjet and Carter/Edlebrock won't perform any better, if as well, than the Holley if the set up and tune is an approximation rather than dead-on and dead-on is the realm expert tuners with high knowledge of these beasts.

Your weather is pretty cold, this affects the rolling resistance of tires to pavement, and bearings, and certainly the lubrication resistance in the engine, transmission and differential(s). Using a more modern radiator with an engine oil to coolant heat exchanger will get the engine and transmission warmer faster reducing oil resistance losses and getting the engine off the choke a lot sooner. The differentials ca run a lighter grade and multi-weight weight oil to reduce resistance. Lucas sells some hypoid oil including the words Shock Proof which in my experience covers low temp resistance reduction and continues to protect the gears in mesh.

While EFI is very nice, unless you get a system at an amazing price it's unlikely you will ever see a mileage return big enough to pay for the systems cost. That may be true of these other tricks as well if not as individuals certainly as a complete systems cost.

Bogie
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Old 09-15-2011, 07:17 AM
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@ Jeff- no offense taken,lol . Although I was 12 when Carter was elected and the fuel crisis crap started years earlier,lol. Your 283 experiment (while certainly cool ) can't be considered relevant to the 350 the OP is using-apples and oranges. If the street master was still a great intake, they would still be making it IMO. But thats not to say that there are not design featured from it that have been incorporated into the Performer. @ Bogie- I have to disagree with your statement about the Q-jet vs Holley-JMO. Also, the Crane catalog reccomends 8:75 to 10:75 comp, so the OPs comp is right in line . After more thought , I might reccomend the Performer cam that I am using in my 1/2 ton GMC with a 350 right now. It makes a ton of low end torque but I really have no idea about the fuel mileage because of a broken speedo cable that I haven't got around to fixing. I use my TomTom for my MPH. I use approx 1/8 of a tank of gas for approx 30 round trip to work doing 60-65 mph. I am using the Q-jet from the 4.3 that was orginally in my truck.
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