Carbruator for best gas mileage

[47coe]

we have had great success with the q-jets using the edelbrock SP2P manifold, It is a old intake but works from idle to 5500 rpm. this is where fuel mileage is made, also have your dist curved to match the rest of it..I run a q-jet now that has been sitting dry for over 5 years, put it on cranked it and no leaks...

[Denee007]

Not to change to subject (Rico forgive me for asking questions on your thread) , but Just out of curiosity, what is the high rise intake for? It looks neat! If my husband can buy boat loads of bullets, I can buy nicer looking bolt on parts! lol

[dyno]

Originally Posted by jackson

quadrajet. the end

I picked one up for 50 bucks and found the adapter (I think from Mr. Gasket) to bolt it up to my Edelbrock intake.

[Ricos54]

Originally Posted by Denee007

Not to change to subject (Rico forgive me for asking questions on your thread) , but Just out of curiosity, what is the high rise intake for? It looks neat! If my husband can buy boat loads of bullets, I can buy nicer looking bolt on parts! lol

No problem, I'm pretty sure the taller the intake is are the volume of air is going into your engine it changes the way it's delivered. It helps for power and helps to suck down the gas more. It definitely won't help with gas mileage, it should make it worse.

[gag1025]

What differential (ratio) are you running?

[mechanixman]

Dne' this should cover everything on intakes
http://www.enginelabs.com/engine-tec...or-dual-plane/

[Denee007]

Thank you! I think I'm going to print that out!!!

Originally Posted by mechanixman

Dne' this should cover everything on intakes
http://www.enginelabs.com/engine-tec...or-dual-plane/

[Ricos54]

Originally Posted by gag1025

What differential (ratio) are you running?

If that question was for me I'm running 300 gears with a posi 9" Ford.

[gag1025]

It was. What is the gear ratio for your differential? I use a Camaro differential with a 2.56 ratio (because I no longer care about what it will do in the quarter) which I figure will give me better mpg as well.

[Ricos54]

Originally Posted by gag1025

It was. What is the gear ratio for your differential? I use a Camaro differential with a 2.56 ratio (because I no longer care about what it will do in the quarter) which I figure will give me better mpg as well.

Yes, when I found out the 9" in the rear was 3.00 ratio I said perfect. Then when I put 20's all the way around that should make the it even taller. Not sure what the 20's will do with the 3.00. I was guessing it would move it around 2.90 ratio. I found a calculator on the net and I ran my setup and it said at 65 I will be running Round 1680 RPM's in overdrive.

[T-P Auto]

Ricos54;

You need to also think aboutthis;
If your rpm is that low at 65 your not reallyget the performance that would give you better gas mileage.
I how have a 96 chevy pu with 4.3 V6 n 700r4 trans.
just around town it does good in high at 45mph n about 1600 rpm.
running at 75-80 mph I turning 2200 rpm, which is still good for cruseing,just when I pull a hill it dropss into 3rd at 75 n 3000 rpm.
Just something to think about.

Tim

[Ricos54]

Originally Posted by T-P Auto

Ricos54;

You need to also think aboutthis;
If your rpm is that low at 65 your not reallyget the performance that would give you better gas mileage.
I how have a 96 chevy pu with 4.3 V6 n 700r4 trans.
just around town it does good in high at 45mph n about 1600 rpm.
running at 75-80 mph I turning 2200 rpm, which is still good for cruseing,just when I pull a hill it dropss into 3rd at 75 n 3000 rpm.
Just something to think about.

Tim

Yes, my buddy mentioned that and I've come to the realization that I won't have it all, but since my truck came with those gears I figured I would try it to see how it does. I'm sure there will be a few ways to go if I need to change something. Like putting in a RV cam or changing the gears. I was trying to find a happy medium which also lead me to the Carbruator. I figured the Q-Jet was the option for the best gas mileage I just worried about having power to turn those big 20's. Without having enough power especially getting that truck moving will also be hard on my gas mileage.

[oldman3]

Hey Rico, Jim here. Don't want to step on your thread, but wheel dia. has nothing to do with changing the rear end ratio. Tire size does. A 245/40/20 tire is 27.6" tall. A 305/45/17 tire is 27.8" tall and a 235/70/15 tire is 28" tall. All are almost the same, but you have 3 different wheel sizes. Depending on the tire you select for your wheel, will make a difference. Based on my limited knowledge of overdrive trans normal 3rd or drive is a 1/1 ratio and 4th or overdrive is a .7 to 1. So your 3:00 ratio is now changed to 2:10, then your tire could change this up or down depending on how tall. Based on a formula from Hot Rod mag. years ago. It said MPH is equal to RPM times tire dia. divided by 336 times gear ratio. So 1680 times 27.6" (20" tire above) equals 46,368 then 336 times 2:10 (final drive) equals 705.6 So 46,368 divided by 705.6 equals 65.7 MPH. Almost the same as the one you found on the net. Hope I didn't mess things up for you..Jim

[Ricos54]

Originally Posted by oldman3

Hey Rico, Jim here. Don't want to step on your thread, but wheel dia. has nothing to do with changing the rear end ratio. Tire size does. A 245/40/20 tire is 27.6" tall. A 305/45/17 tire is 27.8" tall and a 235/70/15 tire is 28" tall. All are almost the same, but you have 3 different wheel sizes. Depending on the tire you select for your wheel, will make a difference. Based on my limited knowledge of overdrive trans normal 3rd or drive is a 1/1 ratio and 4th or overdrive is a .7 to 1. So your 3:00 ratio is now changed to 2:10, then your tire could change this up or down depending on how tall. Based on a formula from Hot Rod mag. years ago. It said MPH is equal to RPM times tire dia. divided by 336 times gear ratio. So 1680 times 27.6" (20" tire above) equals 46,368 then 336 times 2:10 (final drive) equals 705.6 So 46,368 divided by 705.6 equals 65.7 MPH. Almost the same as the one you found on the net. Hope I didn't mess things up for you..Jim

You can always give your opinion Jim, lol. I want to here from anyone that has knowledge so I can make an educated guess on what to do. According to that same site I found my tire hight will be 28.5"

[T-P Auto]

Ricos54:

Just something else to add to your gas mielage.

Back a few years ago I had this set up in a car.
1- 1973 chevy caprice(big boat)
2- 350 V8 2bld
3- 400 trans
4- 273 gears
5 - 235 70 15 tires
6 - At 60 mph I was turning 2100( would run all day at that speed)
7 - never had a problem on take off
8 - got around 20 mpg on the open road.

So just some more info for you to think on.
It can get very scary when you try to figure out how to get mpg n performance together.

Wish I still had that eng trans n rear end set up! !

[mechanixman]

That's awesome!
Every time I tell someone I'm running a small block 327, they always tell me to expect 10 to 15, 15 if I'm lucky.

[Ricos54]

Originally Posted by T-P Auto

Ricos54:

Just something else to add to your gas mielage.

Back a few years ago I had this set up in a car.
1- 1973 chevy caprice(big boat)
2- 350 V8 2bld
3- 400 trans
4- 273 gears
5 - 235 70 15 tires
6 - At 60 mph I was turning 2100( would run all day at that speed)
7 - never had a problem on take off
8 - got around 20 mpg on the open road.

So just some more info for you to think on.
It can get very scary when you try to figure out how to get mpg n performance together.

Wish I still had that eng trans n rear end set up! !

So what Carbruator were you using?

[oldman3]

Rico, I'm sure you've heard the old saying " figures never lie, but liars figure". Anyhow my formula was when we used adding machines, so I would probably go with the newer computer one. Also wanted to add that on my truck I have a 350 (325 hp), 350 turbo and 2:56 Nova rear axle. I run an Edelbrock 600 CFM carb and have 235/55/17 tires that are 26.7" tall. Running at 70 MPH (GPS) I pull around 2400 rpm and get 17 mpg with the AC on (and really watch how I accelerate, going up and down hills) . The only time I check it is going to the Nats in the summer, otherwise its just gas and go. I've been told that a 350 best performance and gas milage is between 2000 and 2200 rpm. So if you could get your set-up in that range at 70 mph, you might get close to 19 or 20, just a guess. I'll keep my mouth shut for awhile now..Jim

[T-P Auto]

Ricos54;

The 350 was set up with rodchester 2bld from the factory,I got the whole engine assy from a 76 chevy Nove that had been hit in the rear end.

I also know that sometimes you can over do the carb n that is when you get in to trouble with gas mileage.
Cams, heads n carb all make it run right n perform.

I working on a 305 V8 sbc for the project that I'm working on.
I'm also trying to work out a 350 V8 sbc(76 yr) going to try to put votex heads,stock 4bld intake, Q-jet carb with HEI dist.

Have always been a SBC person.
First car was a1959 chevy biscayne 6 cly 3 speed,just back from viet nam n needed a car. yr was 1970.

Tim

[low54panel]

Originally Posted by mr48chev

I'd have to first ask if you have run the 670 or if it is still in the box and you can return it.
With some careful jetting and some other tuning such as picking the right accelerator pump cams to help mileage you might get reasonable mileage with it.

Any carb has to be tuned to the engine it is on and the type of driving that the car or truck it is on is going to do. Many of us put up with a box stock carb that has little more than the idle speed set and the Idle mixture screws set for the highest vacuum reading and little else and don't get too carried away with trying to get the best performance and or mileage out of the carb.

You need to tune your carb to your motor. I putan edelbrock on an 81 blazer I had years ago right out of the box, set idle and mixture screws and it ran great. However where a tank of fuel used to last a week and a half or two I was filling up every 4 days. A jet kit and some fiddling and I had it getting better mileage than with the original carb.

[1project2many]

The Quadrajet is a staged carburetor with a fairly small diameter primary venturi. Air passing through does so at high velocity and fuel is drawn into the venturi with a strong vacuum signal. This does a better job of shearing the fuel as it's introduced into the incoming air. Once fuel is introduced into the air it must be heated before it will turn from small droplets (atomized) into combustible vapor (vaporized). The smaller the drops to begin with, the faster they will vaporize. Unlike Holley or Edelbrock carbs, Q-jets have several additional features which attempt to compensate for some temperature and / or airflow variations as the throttle opening changes. Q-jets were OEM and needed to meet emissions and fuel economy standards where the others were performance replacement versions. Non-electronic carbs from the late '70s to early '80s are usually my choice when retrofitting as after about '83 or '84 GM was really trying to make the Q-jet do more than it was designed to do.

There are huge amounts of data around for the Q-jet carb. If you're going to get into tuning one for mileage, an excellent reference book is Doug Roe's "Rochester Carburetors." Although many of the part numbers listed are NLA, there's still a ton of wealth for a guy wanting to make a good carb work well. And these carbs can be tuned well. I had a Buick 455 in a '79 Monte that would pull 18 mpg on the highway. It took a bunch of work and the car was a long way from stock, but we're talking about an engine that normally got 8-12 mpg. I used 2.26 rear gears, 235/75 15 tires, a switch pitch 400, and a low end cam to make that combination.

EFI has upsides and downsides. I tend to recommend using stock GM parts for a conversion because you can usually find them cheap at wrecking yards, on CL, at swap meets. But unless you have a stock engine that's similar to the one the EFI came from, chances are you'll end up getting a custom tune to get best performance. When combined with electronic spark control EFI gives a whole new level of performance if properly tuned. EFI can be better than a carb for being able to deliver exactly the amount of fuel needed at exactly the right time even with temperature and weather changes but there's more complication and there can be more frustration during the tuning process. There are plenty of guys on gearhead-efi that have done EFI retrofits including a guy putting TBI and distributorless ignition on a Corvair and a 4.3 Vortec engine installed in a VW Vanagon.

The Holley spreadbore carb was a decent unit but I don't believe it was designed as a stock replacement for emissions applications. It was larger and provided slightly better response than the Q-jet although I never tuned one for economy and don't know if it was very flexible that way. I've worked on a couple of them and even owend one but ultimately once I learned to tune a Q-jet that was my preferred street carb.

Cylinder heads and compression play a huge part in getting good economy. TBI truck heads are not great for performance but they'll do 200+ hp and have special ports designed to get better mixing and combustion. Vortec heads are even better by a long shot. Combining either of these heads with an aftermarket aluminum intake and a Q-jet can give a decent response and economy. Pick a cam that makes peak power at low rpm with the 700R4 and a set of numerically lower rear gears and you'll have good acceleration and acceptable performance while retaining good fuel economy. The stock cams from the '70s often liked to run at 2800-3200 rpm while a low end grind can have a peak from to 2200 - 2600 rpm.

[skip99]

,I've used q jets , and Holley , liked them both, I have an edelbrock that I'm hoping to try on the 51....
Qjets are awesome, had them on a 454 vette, and a 455 olds jet boat, even though the small primaries, get good mileage, it was too much fun keeping all four flowing ! Pretty easy to adjust and rebuild, but watch out for old carbs cheap, usually the throttle shafts wear, and you suck air around there, ...but here is something I've run across, and would use in a second...
http://www.ebay.com/itm/Holley-Reman...item20dca4757a

Holleys are good, easy to adjust, never had any problems, but ,,I never cared about mileage...