When I bought my F-1 it had a 1985 302 with a 700 CFM Holley carb. and gas mileages is CRAP, what is the best size & make carb for good mpg, not looking for 40 mpg but would like to do better than 12-14
THANKS IN ADVANCE

John

 

It might not be the carburetor alone. What transmission and rear end does it have? Do you know the final drive ratio?

 

Everything being equal, for mileage and ease of tuning I prefer the Carter AFB (Edelbrock, Webber) style. I run these and Holleys and I have built and tuned just about any carb you can think through the years but these are one of the easiest for tuning, IMO.

 

I've just gone from a 750 holley to a 500cfm edelbrock on my 302 powered 47 ford coupe.
In now runs and starts better than it ever did , and MPG is now also much improved .
A 500 cfm is more than adequate if your 302 is basically stock .

 

If that carb has mechanical secondaries that could be part of the problem . A 500 CFM vacuum secondary carb may help . I agree the rear end ratio will make a big difference as will ignition timing and driving habits .

 

This is a reasonable choice: https://www.holley.com/0-1848-1.asp
The Holley 1848-1 is designed for Ford small-displacement engines. Prices vary, shop around.

 

Ya know, I once had a 75 3/4 ton Ford with a 460 in it. I put headers and wotnot on and a Holley 750 thinkin' this bad boy is gonna rock now. NOT. Ended up puttin' a 600 economizer on.Zoomazoom. Maybe the 302 was overcarb'ed. I was gettin' 10 to 12 with the smaller carb.

 

If you do the math, a 500 cfm carb is enough for any 302. The fuel metering is more consistent in the middle of the operating range rather than at the lower end of things. I have had both Holleys and AFBs over the years. Both are fine but I prefer tuning the AFB (Edelbrock) over the Holley. The needles and jets are easier to make small adjustments.

Dan

 

That is a pretty broad statement Dan and only true except in near stock configurations. But it is a good choice for a low RPM (>6000) engine with average volumetric efficiency.


Allan,
Just for info, the Edelbrock AFB style carbs are mechanical secondaries, not vacuum.

 

The Tranny is stock so is the 302 and the rear end is stock F-1

 

That being what you have a 500 CFM carb would be plenty good enough. Like I and some other have said the Carter/Edelbrock/Webber AFB style carbs are user friendly and easy to work on.

Good Luck, welcome to the forum and Merry Christmas.

(on a side note edit your info to include where you are and a first name, it is easier to respond to a name and somebody may be close to you that can help you out if we know where that is, I checked your info and see your in Wa, if you don't want to put your city maybe east or west as they are way differnt)

 

Hi Allan,

I'll stand by the math statement. Here's the way I figure it: A 302 ci engine turning say 7500 rpm would demand 302ci x 7500rpm....divided by 2 because it takes 2 full revolutions for the engine to demand 302 ci of fuel/air mixture

so.... 302ci x 7500/2 = 1,200,000 ci per min Divide that by 1728 cubic inches per cubic foot = 694 cfm.

Now take that number and factor in the volumetric efficiency. If you were able to get 75% you'd be doing great....so 694 cfm x .75 = 520cfm. Also note that as you get to the upper end of the RPM range, the volumetric efficiency will start to drop off due to the friction of the air flow in the intake. I will give in that you'll start to choke off a 302 at around 7000 RPM with that 500 cfm carb.

Given that jw-wa's 302 is in an F1 I'm guessing that he's usually going to be running is somewhere in the lower end of the RPM range.

I have had bigger engines set up with big fat carbs. My experience has been that the larger carbs are a little sloppy at the low end and things clear up in the middle of the RPM range. I put a 500 cfm Edelbrock on my 351w....it is essentially a stock engine with the cam timing set straight up. It idles well and runs clean through my typical driving range. When you get up around 80 mph in an F1 you really start to notice the wind resistance......so I've actually never had it over 6000 rpm. There are certain members here who have joined the F1 century club, but I chickened out....maybe that's a goal for 2014???

Dan

 

Are you sure this is an '85, with roller lifters? '85 was a changeover year, first year for rollers, and many models got TBI. If it is, you have a lot to gain by going to a non-smog cam and ignition curve, nothing wild, just not smog-oriented. Probably more to gain there than with a carb switch. Around here there are lots of later 5.0 EFI systems for sale on Craigslist, complete with manifolds and computers, for dirt cheap. Lots involved to changeover, but that's where you'd likely get the best performance and mileage.

 

Dan,
Allan is Old Merc an not the person who asked the question, John is the OP who had posted the question.

You said the same thing as I, on a basic stock 302 with average VE a 500 CFM carb is a good choice. I have learned on here that you can never assume anything about what someone is using or doing unless it is posted in writing so i try not to paint with a wide brush.

Have a Merry Christmas.