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25 MPG 327 possible?

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Melrose RS

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Discussion starter · #1 ·
Is anybody knocking down better than 20 miles per gallon with their 327?

I'm talking highway only. So far my best is 16 mpg staying out of the secondaries, and I want to see what I can do since my car is pretty much a highway car with 2.73's anyway.

If you are proud of your gas mileage let me know how you got there. Thanx.
 
#4 ·
With a good tune on a say 600 carb, OD trans man or auto and 3:08 gears, right cam, heads some of the other stuff mentions I think you can get in the 20's to mid 20's. That's what I am shooting for.

327, vortec heads, vortec optimized version of the 327 275 H/P cam from GM. Roller rockers, 200R4 trans, 3:42 gears, I hoping to get 20-22 or so I hope. I later plan to go FI but not sure what. I am thinking Retro Tech or the Edelbrock port injection set up for Vortec heads and roller cam. I would hope that gets me to 25 or better. I think a 327 can do it. I could be day dreaming also!!

Joe
 
#5 ·
Low duration cam, small carb 400/450 cast manifold headers, , small runner duel plane inlet manifold, low gearing, compression for the gas using, good wheel alignment and tyre pressures, and grany foot it, yes u can touch 30 mpg (4.54L/gal)

Change to LPG with full designed and dedeciated engine, convert cost LPG/miles to cost gas /miles u will get 33/35 mpg quite easy.
 
#6 ·
Back in the 1960's when I purchased my 65 Impala new I routinely got 22-23 MPG on the highway. The engine was a 327 w/ 300 hp, 4 speed and a 3.31 rear gear. That was a big heavy car that did well with mileage, then I installed an L-79 cam and I could never get over 15 MPG, but I loved the added performance. In a light car, driven right, with the correct engine and gearing combination I believe 25 MPG is possible.
Bill
 
Discussion starter · #7 ·
Joe Harrison said:
With a good tune on a say 600 carb, OD trans man or auto and 3:08 gears, right cam, heads some of the other stuff mentions I think you can get in the 20's to mid 20's. That's what I am shooting for.

327, vortec heads, vortec optimized version of the 327 275 H/P cam from GM. Roller rockers, 200R4 trans, 3:42 gears, I hoping to get 20-22 or so I hope. I later plan to go FI but not sure what. I am thinking Retro Tech or the Edelbrock port injection set up for Vortec heads and roller cam. I would hope that gets me to 25 or better. I think a 327 can do it. I could be day dreaming also!!

Joe
Click to expand...
Joe,
I'm really curious to follow your progress. I was wondering how much vortec heads(or Edelbrock) would help me.

Right now I'm running a new Jet stage 1 Q-Jet, pertronix ignition with crane adjustable vacuum advance, stock 275hp dual plane, 204/214 cam, stock manifolds and crossflow muffler. The powerglide kills me around town so I'm working with only the highway mileage. Plus that way I get to drive farther! :D

I'm also using the Innovate A/F meter and A/F cruise is about 15.2. I have not changed rods or jets in the QJ yet but this one is richer than the original. I'm trying to be scientific about this, making measureable changes only one at a time. I'll be jumping for joy if I hit 20 mpg! :hurray:

Anybody have good experience with the old Holley Economaster (450 cfm or so) carbs?
 
#8 ·
It's all about matching your gearing and RPM where you are making torque. The engine has to be able to over come the weight of the car with the least amount of fuel. I have gotten 23mpg staying at 60mph with my 383ci small block with a holley 780cfm vac sec carb, 3.73:1 rear gears and a 700r4 overdrive. That was driving a little over 1400 rpm in overdrive, if you don't make enough low end power to be able to keep the car moving at this rpm you will be giving it too much gas and won't get the mileage. I changed my rear gears and carb to 3.42:1 and an Avenger (holley) 670 cfm which dropped the RPM to 1300 at 60 mph and didn't see an improvement because there is less torque now at 60 mph. I need to be moving 65 now to be at 1400rpm, at 70 - 75 mph (1500-1600 rpm) I get 21-22 mpg so you can see how critical rpm and torque are to this fuel mileage equation.

A 327 is not known for low end torque and likes to be rev'd a bit. I think that will make it a little harder to pull the mileage out of it but it's not impossible. You could go electronic fuel injection, it can be more efficent and it might gain you a mile or two per gal but at what point do you recover the cost of the conversion. Even installing an overdrive trans means your mileage increase is really just bragging rights for a lot of miles before it pays off... Also note that even a modern LS1 that has been known to pull down as much as 27 mpg only does so when you can keep your foot out of it and you burn the whole tank with very few stops.
 
Discussion starter · #9 ·
DjD said:
It's all about matching your gearing and RPM where you are making torque. The engine has to be able to over come the weight of the car with the least amount of fuel. I have gotten 23mpg staying at 60mph with my 383ci small block with a holley 780cfm vac sec carb, 3.73:1 rear gears and a 700r4 overdrive. That was driving a little over 1400 rpm in overdrive, if you don't make enough low end power to be able to keep the car moving at this rpm you will be giving it too much gas and won't get the mileage. I changed my rear gears and carb to 3.42:1 and an Avenger (holley) 670 cfm which dropped the RPM to 1300 at 60 mph and didn't see an improvement because there is less torque now at 60 mph. I need to be moving 65 now to be at 1400rpm, at 70 - 75 mph (1500-1600 rpm) I get 21-22 mpg so you can see how critical rpm and torque are to this fuel mileage equation.

A 327 is not known for low end torque and likes to be rev'd a bit. I think that will make it a little harder to pull the mileage out of it but it's not impossible. You could go electronic fuel injection, it can be more efficent and it might gain you a mile or two per gal but at what point do you recover the cost of the conversion. Even installing an overdrive trans means your mileage increase is really just bragging rights for a lot of miles before it pays off... Also note that even a modern LS1 that has been known to pull down as much as 27 mpg only does so when you can keep your foot out of it and you burn the whole tank with very few stops.
Click to expand...
Dennis,

I hear what you're saying about the low torque of the 327. This is why the Glide and the 2.73's kill me around town. I'm thinking I may go to a TKO and had planned to earlier this year, but had to sort some other things first.

I'm not too worried about the time it takes for the cost of the trans to be recovered, because a large jump in gas prices changes that equation and I don't see prices going down in the long run.:noway:

I do plan to stay away from FI at this point just because I don't have the kind of time I'd need for the install and tuning.

Right now at 65 MPH, I'm at 2500 rpms with 235/60/15's.

Lately, I've heard from a few guys at shows that their 327's with more radical cams etc, are knocking down 16 mpg! That makes me feel frustrated with my progress!:mad:

Do you know your A/F ratio at cruise?
 
#13 ·
Anybody have good experience with the old Holley Economaster (450 cfm or so) carbs?
Click to expand...
yeah...very nice bottom end and cruise, foot hard in on a 350, strats to lean out around the 4500 rpm (thats about 120 mph) and seriously started to lean (damage potentual) at 5200 rpm but still pulls.
I have been running an impco 425 cfm for the last 25 yrs, and still run hi 13s/low 14s on 350 turbo/308 rear.

Canadian (imperial) gallon = 1.204 US gallon
Of course Canada is now on the metric system, so they don't get any MPG. Its liters per 100 K or Km per liter.
Click to expand...
NZ went metric in the 70s, I still think in mpg, mph AND lets face it there is no "milage" in metric lol
 
Discussion starter · #14 ·
Steptoe said:
yeah...very nice bottom end and cruise, foot hard in on a 350, strats to lean out around the 4500 rpm (thats about 120 mph) and seriously started to lean (damage potentual) at 5200 rpm but still pulls.
I have been running an impco 425 cfm for the last 25 yrs, and still run hi 13s/low 14s on 350 turbo/308 rear.

Back in the 80's a friend had the Holley economaster on a 350 Camaro. It had great low end and still did 120 on the top end. Don't know what the gas mileage was though. I may try one of these but first I'll work with the APT on the QJet and maybe go to some leaner primary rods. I've got the A/F meter so I can measure the changes.
Click to expand...
 
#16 ·
When I first bought my Camaro in 1980, it was equipped much like yours with a 327/275, PG trans, and a 10 bolt rear with 3.08 gears. The previous owner sold it because he couldn't get more than 14 mpg. I replaced the distributor which was toast and recurved it. After that it would do 17 mpg driving it around town if I drove it easy and 20-21 on the highway.

The next couple years saw a few mods- TH350 trans, HEI, Holley carb, water injection. None of these affected mileage much as long as I kept my foot out of it.

Then I decided I wanted some more power and built a 350 and swapped in a 9" Ford rear with 3.50 gears after which mileage took a hit, 13 city, 17 hiway.

With its current drivetrain (same rear end), which includes a 210/224 Crane cam and headers I've been getting 16 city and 20 hiway but it has a bunch more power than either of the previous engines.

I was pleasantly surprised last February when I took a 500 mile trip to visit my daughter and meet my new grandson. On the way there I got 20.1 mpg. While there, it was decided that my daughter and the baby would ride back with me so we proceeded with the three of us and the car loaded to the windows with luggage. We got 20.2 mpg.
 
#17 ·
DjD said:
I have gotten 23mpg staying at 60mph with my 383ci small block with a holley 780cfm vac sec carb, 3.73:1 rear gears and a 700r4 overdrive. That was driving a little over 1400 rpm in overdrive, if you don't make enough low end power to be able to keep the car moving at this rpm you will be giving it too much gas and won't get the mileage. I changed my rear gears and carb to 3.42:1 and an Avenger (holley) 670 cfm which dropped the RPM to 1300 at 60 mph and didn't see an improvement because there is less torque now at 60 mph. I need to be moving 65 now to be at 1400rpm, at 70 - 75 mph (1500-1600 rpm) I get 21-22 mpg so you can see how critical rpm and torque are to this fuel mileage equation.
Click to expand...

Sorry, I messed up using the tire and gear calc when I posted above. I thought the rpm seemed too low :clonk: It should read...

I have gotten 23mpg staying at 60mph with my 383ci small block with a holley 780cfm vac sec carb, 3.73:1 rear gears and a 700r4 overdrive. That was driving at 2000 rpm in overdrive, if you don't make enough low end power to be able to keep the car moving at this rpm you will be giving it too much gas and won't get the mileage. I changed my rear gears and carb to 3.42:1 and an Avenger (holley) 670 cfm which dropped the RPM to 1850 at 60 mph and didn't see an improvement because there is less torque now at 60 mph. I need to be moving 65 now to be at 2000 rpm, at 70 - 75 mph (2150-2300 rpm) I get 21-22 mpg so you can see how critical rpm and torque are to this fuel mileage equation.
 
Discussion starter · #18 ·
red67camaro said:
When I first bought my Camaro in 1980, it was equipped much like yours with a 327/275, PG trans, and a 10 bolt rear with 3.08 gears. The previous owner sold it because he couldn't get more than 14 mpg. I replaced the distributor which was toast and recurved it. After that it would do 17 mpg driving it around town if I drove it easy and 20-21 on the highway.
quote]

Thanks-that's good to know. My recent increase from 13 to 16 mpg was due to recurving and the adjustable vacuum advance canister. I'm not sure I have it right yet but I've got a long drive coming next weekend and I'll have time to tweak it.
Click to expand...
 
#19 ·
I got close with a Q-jet very mild cam set of 220 HP heads and a 4spd. You are right about the Glide hurting you. Get something with a lock-up convertor or a manual trans and you can do it or get awful close.
 
#20 ·
Melrose RS said:
Right now I'm running a new Jet stage 1 Q-Jet, pertronix ignition with crane adjustable vacuum advance, stock 275hp dual plane, 204/214 cam, stock manifolds and crossflow muffler. The powerglide kills me around town so I'm working with only the highway mileage. Plus that way I get to drive farther! :D

I'm also using the Innovate A/F meter and A/F cruise is about 15.2. I have not changed rods or jets in the QJ yet but this one is richer than the original. I'm trying to be scientific about this, making measureable changes only one at a time. I'll be jumping for joy if I hit 20 mpg! :hurray:

Anybody have good experience with the old Holley Economaster (450 cfm or so) carbs?
Click to expand...
Actually with 2.73 gears and a Powerglide, you should do pretty good around town. The Powerglide has either a 1.76:1 or 1.82:1 low gear final drive and a 1:1 high gear final drive so you should get great mileage. May I ask why you went with the Jet Performance stage 1? A richer carb is for performance, not economy. Why not go back to your original Q-jet? I have a Powerglide, but I have 4.10's. Most definately not the thing for economy. I also have a Pertronix dizzy. I am going to be switching to Sean Murphy's stage 2 Q-jet just as soon as it gets here. I am also going to be switching to a Performer RPM Q-jet manifold instead of the RPM Air Gap, per Sean's suggestion. I am anxious to see how his Q-jets perform.
 
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Joe Harrison
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