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Discussion Starter · #1 ·
OK, this is not a typical topic on this forum, but...

I have searched threads and have not really found any good info on this...am wondering if anyone is able to get 25+ on their Chevelle. If so, what combo do you run.

Long story short, I need another car...one with decent mileage...and I don't want to spend a ton. I have the never ending daily driver Chevelle project and thought I might be motivated to go ahead and finish it if I could make it work for this particular need. I have already started out pretty good setup for mileage I think...327, with Edelbrock Performer cam/intake, 3.36 gear, HEI, headers and Q-jet. Tranny is up in the air, but I know it will be OD of some sort.

Trying to decide what to do...I fully expect to be able to pull down 20 mpg highway (I got that on a similar setup in a 66 Chevelle w/o OD). But am curious how much better I can do than that.

Thoughts???
 

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one of the car mags had an ongoing articule on this back in the 80's.
it was a 70's monte.carlo with a 350 rv-cam and very long tube headers, no overdrive.
if i remember correctly they were able to get 23-25mpg in this heavier unit.
 

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I got 22-24mpg on 87 octane with mine, and ran a traction-limited 13.82 :) Should have been about a 13.5 or 13.6 with better tires.

Combo was a mostly-stock '95 LT1 out of a Caprice, 4L60e, and 3.08 gears. I've since swapped to 4.10s though, and mileage has dropped to ~18mpg.

Fuel injection and overdrive :thumbsup:
 

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Probably not a likely goal for those of us running the older engines, but 25mpg is definitely obtainable if you have an LS1 transplant with everything else to make it work efficiently.
 

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That was PHR's Project Econo Performer. I used to follow that monthly in the early 80s. It was a 350 block w/ TH350 3-speed. The magazine staff would play around with headers (long tube and Cyclone anti-reversion) as well as carbs, torque converters and cams. I think they even did an engine based on Bruce Crower's high mechanical compression ratio / low pressure efficiency engine too. Anybody recall that engine theory??

The PHR theme: Mileage was all about creating low-end torque.

Imagine what could be done with a 305 (same 3.48" stroke as a 350) and one of those new 6-speed trannys. PHR would be the magazine to do it again. Maybe with an A-Body this time. High 12s & 35 MPG. Who knows. Okay 30 MPG.
 

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I got 22-24mpg on 87 octane with mine, and ran a traction-limited 13.82 :) Should have been about a 13.5 or 13.6 with better tires.

Combo was a mostly-stock '95 LT1 out of a Caprice, 4L60e, and 3.08 gears. I've since swapped to 4.10s though, and mileage has dropped to ~18mpg.

Fuel injection and overdrive :thumbsup:
Fuel Injection will give an automatic 7-10% increase in mileage because FI can be run leaner than carbs to come up with the same results. With a carb, you have to jet for the leanest running cylinder, because cyl-cyl distribution is never even with carbs through the entire RPM range as it is with FI. You have a lot more pulse-induced unevenness with carb manifolds.

With a carb, forget about main jets. They control mostly WOT mixtures. You have to concentrate on the transfer slots, because that is where most of the cruise gas comes from. In other words, you cruise, mostly, on the idle circuit. That is why it is so important to have the transfer slots look like little squares when your idle speed is right. After you get those right, you can start tuning for cruise. The idle screws, the idle jets, and the idle air bleeds, and sometimes, idle emulsion tubes, are the things you need to adjust to get good mileage.

If you can turn the idle screws all the way in, and nothing happens, the transfer slots are too far open. If screwing the idle screws in kills the engine, you are halfway there. The first thing I do is, find some small pieces of wire to block off some of the flow to the idle jets. (Most aftermarket Holleys have rich idle circuits.) This is where 8th grade math comes in. Measure the idle jet and square the diameter. Measure your wire and square that dimension. Subtract the wire number from the jet number. You want to start with plugging about 10-15% of the flow through the idle jet. You dont have to figure the area of the jets because the squares of the numbers will give the same results. I have found that the wires in wire brushes are sometimes workable diameters.

You can use wires in the idle jets, and the idle air jets, depending on whether it is rich or lean.

Next thing is to make sure you have 48 to 55 degrees timing advance at cruise: somewhere in that area. You want to make your engine lean-surge, or lean stumble, with that timing. If it doesn't surge or stumble, lean it out some more. And this is where the hard part is: sometimes, you will only have to turn in your idle screws to get lean surge; sometimes, you will have to reduce the flow through the idle jets; sometimes, you will have to increase the size of the idle air jet; sometimes, you will have to drill holes in the idle jet emulsion tubes.

EXACTALLY what to do is the part I can't give advice on, because so many combos act so different. The main thing is to get the timing where it needs to be, and jet for lean surge. After you get the surge, richen up slightly until it quits. If you step on the gas and get hard pinging, you need a vacuum can with a stronger spring in it, so it will reduce the advance quicker. Or less vacuum advance. (Or ported vacuum. Cruise is where it works best.)

Also, the tune will be dependant on your rear gear ratio. If you change gears, you will have to change jetting. Get the gears right first.

It is simpler than it sounds. It only takes a little time. Keep notes on sizes you change so you can go back to them. Keep the fire extinguisher handy when working on carbs.

Years ago, many carbs were jetted so the ends of the tail pipes were white inside. You never see white pipes anymore. I'm not sure why that is. We used to set the lean stops on the Rochester injectors so the pipes ran white, and never had any engine problems caused from leanness. But we had real gas back then. A fuel injected 283 Corvette would get road mileage in the low 20's with the 097 cam and a 3.70 rear gear. Not bad at all.
 

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65 Vette with 4.11 and FI would get over 20

Same guy built a 454 for his bud's work DOZER-Puller 4x4 PU, early 80s.
IIRC, Streetmaster intake, Q-Jet, 9.5:1, Isky 'Mile-a-More' cam.
All in the tune and calibration. They would make changes, drive the truck from SoBay Los Angeles area to Palm Springs each weekend.....They were up to 16mpg in a big-a$$ truck.
 

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i once had a 76 Monte Carlo that got an honest 30 mpg if i drove it nice.. 25 if i drove it like a 19 year old kid that loved doing burnouts.
the combo was as follows:
stock 1976 350 with a $150 Northern rebuild kit- i just put the new bearings in the stock rods and i didn't own a cylinder hone, so i just threw the new rings on the stock pistons. i sold the pistons that came with the kit and bought a pair of used rear tires to burn off..
i used the.390/.410 lift cam that came with the kit.
i never did anything to the stock 882 heads, since i was young and poor and the springs still worked.
intake manifold was an old Weiand from the 80's or so that looked like an older version of the Stealth intake, and i rebuilt the stock qjet carb and bolted it on with an adapter plate. i made a dual ram air setup by riveting a second snorkel on the stock air cleaner, and adding a stock air scoop out of a Caprice or something on top of the rad support like the stock scoop was mounted.
i had some rusty old 1 5/8 primary headers with 3" collectors, with 4 feet of 2.5" straight pipe leading to a pair of cheap Thrush turbo mufflers held up by coat hanger wire..
stock HEI with an old cap and rotor and some old crappy wires and the AC 4R45TS plugs the book called for.
stock TH350 trans and stock 2.56 gears.
don't ask my why it worked as good as it did- but it would go just over 300 miles on 10 gallons of gas- and, yes, the speedo was dead on. it weighed in at just over 4000 pounds with 1/4 tank of gas and no one in it. i even beat up on a friend's 79 Mustang that had a 351W in it with 3.42 gears and my cousin's 280Z on a very deserted straight back road..
 

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Discussion Starter · #9 ·
That was PHR's Project Econo Performer. I used to follow that monthly in the early 80s. It was a 350 block w/ TH350 3-speed. The magazine staff would play around with headers (long tube and Cyclone anti-reversion) as well as carbs, torque converters and cams. I think they even did an engine based on Bruce Crower's high mechanical compression ratio / low pressure efficiency engine too. Anybody recall that engine theory??

The PHR theme: Mileage was all about creating low-end torque.

Imagine what could be done with a 305 (same 3.48" stroke as a 350) and one of those new 6-speed trannys. PHR would be the magazine to do it again. Maybe with an A-Body this time. High 12s & 35 MPG. Who knows. Okay 30 MPG.
Wow! Thx for the walk down memory lane MALIBRU. I believe that car in PHR was a Monte? I'll have to see if I can scrounge that series up.
 

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Discussion Starter · #10 ·
All, thanks for the replies. GREAT stuff on the carb setup!

I was wondering about fuel injection...7-10% increase, huh? Even with a TPI unit? That seems like the most practical way to convert my old-school motor. That may be worth doing since I believe those old TPI units are pretty affordable these days.

I had entertained the notion of an LS motor or even an LT-1...but the only way for right now I can justify this project is to roll with what I've got.

I'm trying really hard to figure out a way to justify this being my daily driver!!! Way more fun than driving an econobox...even if I do dial it back for mileage. :)
 

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That was PHR's Project Econo Performer. I used to follow that monthly in the early 80s. It was a 350 block w/ TH350 3-speed. The magazine staff would play around with headers (long tube and Cyclone anti-reversion) as well as carbs, torque converters and cams. I think they even did an engine based on Bruce Crower's high mechanical compression ratio / low pressure efficiency engine too. Anybody recall that engine theory??

That was the energy engine that Crower built for them. It was like 16.1 static compression with a cam that had extreme overlap pushing the gases back into the intake and a final dynamic fo 8.5.1. I have asked if they still made that system and nobody even knows about it.
The best way to get fuel economy is a fuel injection unit added on. Grab a TBI system off a 305 or 350 or bite the bullit and bye a new FI system. With O2 sensors these units can get the fuel economy you desire.
 

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"Years ago, many carbs were jetted so the ends of the tail pipes were white inside. You never see white pipes anymore. I'm not sure why that is. We used to set the lean stops on the Rochester injectors so the pipes ran white, and never had any engine problems caused from leanness. But we had real gas back then. A fuel injected 283 Corvette would get road mileage in the low 20's with the 097 cam and a 3.70 rear gear. Not bad at all."


The white pipes came from the lead in the gas of the old days. My son was mowing the yard with the riding mower and ran out of gas. I had some AV gas in a container and he poured that in instead of going and getting gas. As soon as I looked at the tanish color in the exhaust I knew what he had done. It took a couple of questions but he admitted to putting the 100LL in the mower. I have never seen the exhaust color anything but sooty black with unleaded gas. It is much harder to read plugs with unleaded also.
 

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SSBUMS wrote:

"I'm trying really hard to figure out a way to justify this being my daily driver!!! Way more fun than driving an econobox...even if I do dial it back for mileage. :)

Hello, I missed what heads you have, but a set of Vortecs off of a 96 or later small block would probably be helpful in the torque/ mileage department. After reading many mileage threads over the last 2 onths, I think you can get close to your goal. Lots of great info on this forum.

Bob
 

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If you do go carb, a properly tuned QJet maybe the choice. Assuming you are driving primarily on the highway, 2.56s or 2.73s would be a good choice if an OD trans is not on the table.

Alum intake, headers instead of manifolds, alum wheels, and any thing else to shed weight is helpful.

Does lowering a car help for mileage? Maybe not measurably on these cars....?
 

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Everybody needs two cars and a moped.
 

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x2 on the small scooter, for putting around. This is going to get more popular if your not faced with being run over by a jerk in a pickup truck. At six to eight dollars a gallon the big pickups are eventually going to dissappear as daily drivers. We may all be peddling bicycles soon. A friend of mine rides to Reno, Nevada every year on his 250 cc Honda scooter with friends. This bike has over 80K miles on it without any repairs. He says it gets from 60-80 mpg and runs comfortably at 60 mph. They thought they would be lucky to make 300 miles a day but got nearly 500 after the first 8 hours so they stopped and saw the Grand Canyon and other sights.
 

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Ken, you could not have said it any better on the carb tune..get to where you know it is lean and work from there,,,

We just bought my son his first bike a 2004 rebel 250..73mpg
I built a windsheild Lexan and brackets $15 and a luggage rack...it'll cruise at 65-75mph..

I find myself riding it more than him..and i have an 87 magna that gets 38mpg

The Q jet will pull great mileage. set the APT at 2.5 turns out for starters, i beleive that is on the 170 series, then do what Ken said.

high compression allows more mileage, if you can keep preignition at bay.

going with a smaller chamber is the best way ,and blend all sharp edges on chambers and pistons.
piston to head .035-.045

I will have one engine together this summer 350 with 10.7 comp. and a 218 218 cam shooting for 25 average mpg with no OD..I will tell what happens in a couple of months
 

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I got 22 mpg in a 76 Chevelle running a 327, stock 305 heads,the 151 corvette cam,Performer intake with Q-Jet and .......don't laugh 2.73 gears. Thing couldn't spin the tires if you tried, but felt like a rocket going into second.Overall, not a bad combo.
 
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