1992 302 V8 Smaller Carb Opinion

[92FiveOh]

I have a 1992 Ranger 302 V8 I was wondering if I should switch to a smaller carb because the truck seems like it should be going way faster than a 14.1 in the quarter also I receive horrible gas mileage. Would switching to a smaller carb like a 600 CFM or 650Cfm give my better gas mileage than what I am already receiving. My Set up is below.

Quarter Mile 14.1 Best Time 8-10 MPG Highway Cruising 55Mpg 2300Rpm

5.0 Roller Dish Top Pistions 9:1 ? Commpression
X303 (Big Cam)
World Senior Heads
Holley 750 Vacuum secondaries
Edelbrock Performer RPM Intake
Full MSD Ignition
C4 Transmission 3200 Stall Manual Valve Body.
7.5 Locker 3.55 Gears
Drag Radials

 

[baddad457]

That 3200 stall converter certainly isn't doing you any favors. I get 16 mpg @70-80 mph with a Z303 cam in the 331 in mt 77 Comet. Same gear raio (3.50's with 26.5 tires) The stall in it is something around 2000. What size chambers do the heads have ? And what exact pistons are they ? The pin height varies enough between part numbers to make a half point difference in the ratio. The carb is on the big side, but shouldn't affect the mileage that much, as long as it's tuned for the motor (jetting and the sec's coming in late) The MSD was a waste of money.

 

[droptopfox]

id recomend you put it up on a dyno get it tuned in mint its like 100 bucks at my local dyno to have a carbed truck dynoed and why is msd a waste in my old mustang i picked up 15 hp buy going with a msd set up also a 3200 is a good convertor thats what i run with an aod not a good for a daily driver but i think its a perfect street strip convertor if you know who to launch it good luck it definitly should do better tyhan a 14.1 my bone stock 89 mustang went 14.4 on street tires

 

[RangerSVT]

EFI fixes all those problems and the guess work, and makes cold morning starts a breeze. No need to keep adjusting the carb for changing temps...And if yo want better mileage, get an AOD
SVT

 

[847b]

Yes, switching to a smaller carb will most certainly help gas mileage. Good rule of thumb is nominal carb cfm should be about twice the cubic inch. For a 302: 302 x 2 = 604 cfm, so 600 cfm carb is a good place to start. Motors that do their deep breathing at higher rpm's (>6500) can tolerate/benefit from more carb. On a full race motors, venturi size is more important than an advertised cfm rating.

The most important factor in the intake system is velocity. High velocity keeps the fuel in suspension. High, uniform velocity will essentially ram the greatest amount fuel/air through the head ports, around the valve, and into the cylinder. By choosing a smaller carb for this 302, we are attempting to increase velocity without hurting overall flow.

I think you might benefit from a carb spacer as well. If you have the hood clearance and the linkage is not too much of a pain, try a 1/2" or 1" four hole plastic spacer. I have seen this help on most motors. Low end torque and throttle response improves, as well ET. They fairly pretty cheap too.

And yes a loose converter will not help gas mileage. I would be hesitant to say that it is severely hurting ET though. If I recall, stall speed should be within 400 rpm of where the engine makes peak torque.

 

[92FiveOh]

Yes, switching to a smaller carb will most certainly help gas mileage. Good rule of thumb is nominal carb cfm should be about twice the cubic inch. For a 302: 302 x 2 = 604 cfm, so 600 cfm carb is a good place to start. Motors that do their deep breathing at higher rpm's (>6500) can tolerate/benefit from more carb. On a full race motors, venturi size is more important than an advertised cfm rating.

The most important factor in the intake system is velocity. High velocity keeps the fuel in suspension. High, uniform velocity will essentially ram the greatest amount fuel/air through the head ports, around the valve, and into the cylinder. By choosing a smaller carb for this 302, we are attempting to increase velocity without hurting overall flow.

I think you might benefit from a carb spacer as well. If you have the hood clearance and the linkage is not too much of a pain, try a 1/2" or 1" four hole plastic spacer. I have seen this help on most motors. Low end torque and throttle response improves, as well ET. They fairly pretty cheap too.

And yes a loose converter will not help gas mileage. I would be hesitant to say that it is severely hurting ET though. If I recall, stall speed should be within 400 rpm of where the engine makes peak torque.

Thanks for the help, I think I am going to tune the 750 for now because backfires threw the carb on occasion. Which I know is not good. I believe this is because the secondaries are kicking in way to early also could account for some of the poor gas mileage. So I will tune it see where I am at then. As far as ET, and performance. I know I have been told the stall is on the high side but I was thinking of a mild stall like around 2500.

 

[superdave1984]

Backfiring through the carb is typically a timing problem. You have more carb than you need IMO.

 

[85_Ranger4x4]

Will help to read through a Holley book, been using that, this site: http://www.bob2000.com/carb.htm, this site, and searching on helping tweak my Holley 4160 600CFM in versus how the engine is behaving. It's been a basket case so far LOL, but I have been learning a lot about these carbs. I definitely want to add an o2 sensor like what is described in the link at some point in the future.

My 302 will have an 02 senser for just that reason.

Backfiring through the carb is typically a timing problem. You have more carb than you need IMO.

+1 to both counts.

 

[baddad457]

id recomend you put it up on a dyno get it tuned in mint its like 100 bucks at my local dyno to have a carbed truck dynoed and why is msd a waste in my old mustang i picked up 15 hp buy going with a msd set up also a 3200 is a good convertor thats what i run with an aod not a good for a daily driver but i think its a perfect street strip convertor if you know who to launch it good luck it definitly should do better tyhan a 14.1 my bone stock 89 mustang went 14.4 on street tires

Are your sentences always "paragraph" in length ?

 

[baddad457]

EFI fixes all those problems and the guess work, and makes cold morning starts a breeze. No need to keep adjusting the carb for changing temps...And if yo want better mileage, get an AOD
SVT

If you constantly keep adjusting a carb for different temps, you don't know how to tune an engine or a carb.

 

[baddad457]

Backfiring through the carb is typically a timing problem. You have more carb than you need IMO.

It can also be a lean condition too, causing this. Both need to be checked.

 

[droptopfox]

Are your sentences always "paragraph" in length ?

hey im not an english major but ive built 3 mustangs and 1 of them was well over 500 rwhp and ran 11s. efi is easier but naturally asperated a carb make more power, i have a 670 street avenger on my truck works good but even its kinda big