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Old 05-18-2010, 02:33 PM   #1 (permalink)
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Building a SBC for both POWER AND MPG

Judging by the other posts here this might be a first! I have posted this in other "muscle car" forums and basically everyone knows how to make a car get 400horsepower and 8 MPG, but NOBODY knows how to make a muscle car that is a good balance of Horseys AND Not a total hog.

I am looking into changing my green-unfriendly muscle care into a "greener" car. My goals are to get the MOST "bang for the buck" out of every Cubic inch of the SBC 350. The car was never a computer controlled car and never had an o2 sensor. It was the LAST of that type of car from GM in 1980 sold outside of CA. Where I live now there are no smog regulations and zero testing, so whatever I do is safe as far as "legal", but I want to get the max fuel MPG and also cut down on Co2 emissions. P.S. My Daily Drive is a 2009 Jetta with 34MPG. This is just a project car!

Mission Objectives:
1. Use existing GM 350 Hencho En Mexico short block with no modificaitons
2. Use existing 600 CFM Edelbrock 1406 carb and Performer EGR Intake (currently plugged with included cap as I dont think my heads have the needed crossover?), flowtech headers, dual exhaust, MSD pro billet distributer (no multispark setup....yet)
3. Still use 87 octane gas
4. Idle smooth, not wake the neighborhood, be useful around town and get reasonable MPG of 12+ city, 17ish Highway (or better)
(i have a TH350 tranny (tranmission, not cross dresser!) and 3:42 rear gears)


Preliminary research:
1. Edelbrock heads and CAM seem to be a good deal.
Question: Do I go with the 50 State Legal heads? Or the E-street series? The 50 state ones allow EGR, i.e. will that help increase mileage and smooth idle? OR do the newer style heads burn less fuel more efficiently for a more complete burn thus making ERG on this type of engine obsolete? or overkill?

2. I am sitting at 76cc heads and 8.5:1 compression. I am Thinking of using 70cc heads. That should be around 9:1 compression. I think...
Question: Can I still run 87 Octane? if so what do I have to look out for to avoid detonation? Will running higher octane help or change nothing?

3. Comp Cams has nice Ultra Gold rockers at stock ratios for much more reasonable price than Edelbrock, AND lifetime warranty.
Question: Will those mate up nice on the Edelbrock heads and increase horsepower? or should I stick with Stock rockers? Is 1.5 or 1.6 the correct stock ratio that the Edelbrock head require?

4. go with a matched Double Roller timing chain
Question, will that fit on my Hench En Mexico block without modification?

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Old 05-18-2010, 03:20 PM   #2 (permalink)
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Hi, welcome to ecomodder. I don't have any answers to the questions posed, but hopefully do have something to think about.

Probably the biggest returns would be to put a stick shift in there and a kill switch on the shifter and pump up the tires and learn to pulse and glide (the nascar guys do it under yellow FYI). A lower rear end and advancing the cam a few degrees to give move the torque band towards the low end might prove beneficial as well.

I put a stick shift and a kill switch in my saturn and went from 25mpg to 45 mpg with proper stick technique.
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Old 05-18-2010, 03:32 PM   #3 (permalink)
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With the higher compression, you might have to adjust cam timing a bit, as well as ignition timing, and possibly run slightly colder spark plugs. It'll probably be fine, however, and can definitely be made to work, although 89 might be a little closer to optimal.

If you want to keep your TH350, being that it lacks torque converter lockup, build the engine to have the power band down low, and run the lowest stall torque converter you can.

Even with the non-lockup 3 speed auto, I could see your MPG goals happening. Of course, a 5 speed or a newer 4 speed auto w/ lockup (beefed up 700r4 maybe?) would help a good bit. With your current tranny, I'd consider dropping to 3.23 gears to get the highway RPM down a bit, although the 3.42s aren't terrible. Depending on how extreme you get with the mods, I could see anywhere from 17 - 24 mpg on the highway being possible.

Regarding the current carb, being that it's square bore, it's not optimal for MPG. A switch to a Quadra-Jet or other spread bore 4 barrel with good flexibility for tuning will give better mpg under light acceleration and when cruising at light throttle. A good, well tuned spread bore setup can come close to EFI for fuel efficiency.

Not waking the neighborhood is a function more of the muffler you choose than anything else.

Your goals sound similar to what I'm planning with my Jeep, except that I am willing to use 93, as it already needs 91 minimum, and it's EFI. Of course, my Jeep is as heavy or heavier than your car, and far less aerodynamic. Plus, the 360 isn't known for mpg in any form, but I still get about 12 - 12.5 mpg around town and 19 - 21 driving slow on the highway stock, so I figure I can probably improve on that a little. Of course, once it's retired from DD duty in a few years and gets a (possibly twin turbo) 408 stroker, all bets are off for mpg.
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Old 05-18-2010, 03:53 PM   #4 (permalink)
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First off... thanks for not yelling at me for having a PIG I was expecting everyone to shame me for having something other than a VOLT, or Prius! hahahaha.


A Stick would be nice if I lived in the country still. I live in a City with stop and go traffic. Plus I just spent $2600 on a totally rebuilt tranmission and some otehr work about 3 months ago when the 350 gave up at about 200,000 and 30 years old!!! So...I would LOVE a 700r, but not in the near future...

As for a Spread Bore Qjet, that is certinally an option. Edelbrock makes a lot of refurb souped up ones OR I can buy one of Autozone, without a core to exchange. I already have problems tuning my Edelbrock properly so Im worried I might have problems tuning a Qjet.

I can definatly change my rear gears at some point too....

for now though this engine work is a definate as I have a busted Head gasket that is burning water. So while the engine is all tore up fixing that problem I want to put it all back together MEANER AND GREENER
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Old 05-18-2010, 03:55 PM   #5 (permalink)
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Actually stick and p&g are at their best in the city. I can get 60mpg around town and it still beats walking You can't hardly tell the difference, a quick blip of the throttle and a coast to the next stop. Takes a lot of thinking and strategy though.

As we like to say, the best mod is to adjust the nut behind the wheel
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Old 05-18-2010, 03:59 PM   #6 (permalink)
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While you have it apart, it would be a good opportunity for a cam swap. Go for whatever gives the most low end power. Being that the tranny is a recent rebuilt, unless you can sell it and get/rebuild a 700r4 for very little overall cost, then keep it and put in a lower stall torque converter, if possible. A low stall converter and 3.23 rear gears would do decently for MPG with your current tranny. 3.42s and a 700r4 would probably be a bit better on the highway, however, with little difference between the 2 around town.

I fully understand not wanting a stick in city traffic. Every time I drive through downtown, I'm glad my Jeep is an auto.

As far as tuning the Q-jet, it's not too bad. There are lots of good guides out there.

Also, once it's all back together, run the timing as advanced as possible without pinging for best power and mpg. On my Jeep, at the factory, to squeeze out all the possible performance, they simply took a regular 360 Magnum, tweaked the cam and cranked the timing. Good for +15 hp and +10 ft. lbs over the standard 360 of that year. Plus, it gets about the same, or a little better mpg than the 318 powered version of the Jeep.

Anyway, the site isn't about 100mpg cars, it's about getting the best mpg from what you have.
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Old 05-18-2010, 04:09 PM   #7 (permalink)
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I'm just sayin that assuming city therefore not stick might be a mistake. Plenty of cities full of stick shifts in the world.

You might be leaving gobs of performance and mpg on the table at fairly low expense. I've never spent more than $300 on a stick conversion (I'm not real picky though)
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Old 05-18-2010, 04:34 PM   #8 (permalink)
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My 2c

-forget the Edelbrock heads, too expensive-find some '96+ vortec truck heads, some of Edelbrocks heads are pretty much exact copies of these they are so good, and much cheaper (I see them on craigslist for less than $300 a set often). The small Edelbock cam (204/214) is a good choice, I've had one in a 1970 truck with a 305 and it worked well, if anything you could actually go smaller if you were to change the rear gear for lower RPM cruise speeds.

-Don't worry about the compression, the 96+ heads have a MUCH better chamber design and detonation won't be a problem with flat top pistons or less.

-Personally I stay away from aluminum rockers, they will break eventually. Stockers suck too, and avoid those gimmick roller "tip" rockers, most of the friction is at the pivot. That leaves the steel roller rockers as the best choice but they are expensive. Maybe as a compromise buy some cheap aluminum one and get a couple extra to have on hand/ in the glove box for when the time comes, probably Speedway Motors would be my choice for good quality/ price combo. And you might as well go with the 1.6 ratio with such a mild cam.

-Any good double roller chain will do the job, assuming it's not a roller cam block they are really common and inexpensive. I'd probably advance the cam 4 degrees as others have mentioned as well.

-the Q-jet recommendation is a good one but not a deal breaker, an Edelbrock carb tuning for mileage instead of performance (they sell them both ways) wouldn't give up much.

Not sure what kind of car you have but I had a 1980 malibu with a 350/350 and 2.29 gears and it got a little better than your goals with absolutely no thought given to economy, and the motor was completely wore out.

If you were to switch trans, and stay with an auto, I'd recommend a 200R4 over a 700R4, they have a much better gear spacing (700R4 has too low of a 1st gear).
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Old 05-18-2010, 04:58 PM   #9 (permalink)
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Yup, I have a 1980 Olds Cutlass.

I will look into Vortec heads, problem is that requires a new intake.
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Old 05-18-2010, 05:09 PM   #10 (permalink)
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Ok here is the Vortec setup going for NEW (i have had BAD luck with used items from Craiglist). Its a Kit from Jegs. I can reuse my 1406 Edelbrock carb, and I can use an matched CAM to the Edelbrock manifold this ket comes with.

America's favorite high performance cast iron small-block cylinder heads offer big power and bigger value. The GM (Chevy) Vortec cylinder heads fast burn combustion chamber and high velocity ports combine to produce big horsepower out of the box. Vortec heads can be mildly ported for additional performance and can be milled up to .040'' for increased compression ratio. The Vortec head uses 1.94'' intake valves and 1.50'' exhaust valves to compliment the high velocity port design. The Vortec head out-flows the bow-tie head out of the box and is a 20 to 40 horsepower bolt-on increase over earlier cast iron small-block heads. Vortec Heads require a Vortec style intake manifold due to its improved manifold mounting flange and gasket design and raised intake ports. It is not recommended that the heads be modified to accept early design intake manifolds. Vortec heads fit all small-block engines produced 1955 to present, excluding LT1/LT4 reverse coolant flow engines and current LS1 style engines. Heads come completely assembled with valves, springs, retainers, and 3/8'' rocker studs. Requires the use of self-aligning rocker arms.


# Material: Cast Iron
# Intake Port Volume: 170cc
# Combustion Chamber Volume: 64cc
# Vale Diameter: 1.94'' Int./ 1.50'' Exh.
# Spark Plugs: Straight
# Special Note: Valve Springs - .475 Max Lift



With the 64cc chamber can I still run 87 octane?

Also, I notice this is not "50 state legal"meaning no heat cross over for EGR. So any idea if the fact this is a more efficient head design makes EGR obsolete?

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