750CFM vs 600CFM
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Senior User
Joined: May 2003
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From: Omaha, NE
750CFM vs 600CFM
When we bought our truck last year, I had problems with leaks on the
factory Holley 4180 carb. I fixed a few but more were appearing...
So I decided to buy a new carb... a nice new Holley 4160 universal,
electric choke carb (insert Edelbrock comments here).
Only problem is, I found out after the fact that the 4180 is a 600 CFM
carb where the 4160 is a 750 CFM carb.
I figured big block (460) - big carb... but given Holley's CFM formula,
my needs are only in the 600 CFM range...
The truck seems to run okay, but I'm wondering if I hurt my low end
torque some by stepping up to the larger carb.
Also having a bearcat of a time setting up the choke on the 750 -
truck seems to load up on fuel and never really seems to run at
fast idle.
The new carb is still pretty much "out of the box" save the choke and
idle adjustments I've made.
Also wondering if it would benefit me to rebuild the original 4180 carb
and put it back on or even maybe get a new 600 CFM carb.
This is on an 86 F250 equipped with a 460/C6 combo...
Thoughts, suggestions, concerns?
Thanks!
Scott
factory Holley 4180 carb. I fixed a few but more were appearing...
So I decided to buy a new carb... a nice new Holley 4160 universal,
electric choke carb (insert Edelbrock comments here).
Only problem is, I found out after the fact that the 4180 is a 600 CFM
carb where the 4160 is a 750 CFM carb.
I figured big block (460) - big carb... but given Holley's CFM formula,
my needs are only in the 600 CFM range...
The truck seems to run okay, but I'm wondering if I hurt my low end
torque some by stepping up to the larger carb.
Also having a bearcat of a time setting up the choke on the 750 -
truck seems to load up on fuel and never really seems to run at
fast idle.
The new carb is still pretty much "out of the box" save the choke and
idle adjustments I've made.
Also wondering if it would benefit me to rebuild the original 4180 carb
and put it back on or even maybe get a new 600 CFM carb.
This is on an 86 F250 equipped with a 460/C6 combo...
Thoughts, suggestions, concerns?
Thanks!
Scott
Senior User
Joined: Nov 2003
Posts: 284
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From: Beaverton, Oregon
I have a 625 CFM Road Demon on my 460. It took some jetting and secondary spring changes to get it tuned right (Most 600CFM carbs are set up for a 350 out of the box), but it runs great.
You should be fine, but expect to do some jetting changes to get optimal power. I installed an air/fuel meter (o2 sensor and gauge) in my truck which made it super-easy to tune the carb.
Dan Martin
86 F350 Crewcab Dually, 460, C6
You should be fine, but expect to do some jetting changes to get optimal power. I installed an air/fuel meter (o2 sensor and gauge) in my truck which made it super-easy to tune the carb.
Dan Martin
86 F350 Crewcab Dually, 460, C6
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Senior User
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From: Omaha, NE
That's just it, I have a 750 now and I'm wondering if I should go back
to a 600-650 CFM carb.
I talked with Holley tech support and they told me that the jetting
was probably okay (I'd be losing low end torque, but that would be
mainly due to the larger CFM of the carb).
The main thing the Holley tech told me to do was change out the
secondary spring - he told me that I should go with the heavyest
spring (the carb should have the middle spring now).
So do I keep my 750 or go back to a 600? If I go back, is the factory
4180 worth rebuilding (with all the emissions), or should I look at a new
universal 600 carb?
Thanks!
Scott
to a 600-650 CFM carb.
I talked with Holley tech support and they told me that the jetting
was probably okay (I'd be losing low end torque, but that would be
mainly due to the larger CFM of the carb).
The main thing the Holley tech told me to do was change out the
secondary spring - he told me that I should go with the heavyest
spring (the carb should have the middle spring now).
So do I keep my 750 or go back to a 600? If I go back, is the factory
4180 worth rebuilding (with all the emissions), or should I look at a new
universal 600 carb?
Thanks!
Scott
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From: GANS
I don't think you'd lose enough power to notice; you'll probably gain a few ponies up on top.. The holley tech was rite, if you put the strongest spring on the secondaries, you effectively reduce the CFM (by keeping onlu 2 barrels open) until you punch the gas, which is where you need the extra CFM anyways..
The only thing I'd worry about is gas mileage... notice any difference?
The only thing I'd worry about is gas mileage... notice any difference?
Thread Starter
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Senior User
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From: Omaha, NE
I don't really notice any change in MPG... heck, when you have the
460, you only get about 6 MPG towing or not!
The main problem I'm really having is setting the electric choke.
I've been working with it for a while and have gone to both ends of
the spectrum and found the "happy medium", but the truck still has
a rough idle while the choke is on and no fast idle (I might have to
double check the fast idle cams - aren't these interchangeable?).
It just acts and smells like the engine is loading up on fuel, then
once the choke comes off, the idle is normal again.
I didn't have this problem with the factory 4180 carb - just one press
of the gas pedal to set the choke then hit the key and the engine was
off an running on high idle, wait a minute or two, kick the throttle and
it would come down to the second notch of the fast idle cam, a minute
more and it's ready to go.
Now I do the same as before - one press to set choke and hit the key...
truck starts right up abut then starts running rough cause it's loading up.
Can I change to a less aggressive fast idle cam? Think this would cure
the problem?
Thanks!
Scott
460, you only get about 6 MPG towing or not!
The main problem I'm really having is setting the electric choke.
I've been working with it for a while and have gone to both ends of
the spectrum and found the "happy medium", but the truck still has
a rough idle while the choke is on and no fast idle (I might have to
double check the fast idle cams - aren't these interchangeable?).
It just acts and smells like the engine is loading up on fuel, then
once the choke comes off, the idle is normal again.
I didn't have this problem with the factory 4180 carb - just one press
of the gas pedal to set the choke then hit the key and the engine was
off an running on high idle, wait a minute or two, kick the throttle and
it would come down to the second notch of the fast idle cam, a minute
more and it's ready to go.
Now I do the same as before - one press to set choke and hit the key...
truck starts right up abut then starts running rough cause it's loading up.
Can I change to a less aggressive fast idle cam? Think this would cure
the problem?
Thanks!
Scott
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From: Beaverton, Oregon
Originally Posted by bremen242
dan, does you gauge show how much you are lean or rich, or just that your are lean or rich?
I bought the Autometer one...ran about $150 all-told, but it works great and I'm sure I've saved at least that in gas since I've installed it (milage went from 6.8 to almost 10 by getting it running efficiently).
Hope that helps!
Dan Martin
86 F350 Crewcab Dually, 460, C6
Senior User
Joined: Nov 2003
Posts: 284
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From: Beaverton, Oregon
Clifford,
I have the same issue with the fast idle and choke, and have the same solution (get it close and live with it). I never could get the fast-idle to work properly on that carb, but I haven't really given it my full attention either.
On the coldest of days, It'll start up and idle with a single press of the throttle to set the choke, it'll run rough for about 1-2 minutes (loading up I'm sure) but smooths out when the chocke opens and all is well...then I can drive off.
All told, I think it's doing pretty well for a carbed big-block, so I'm not looking a gift horse in the mouth over this...
Dan
I have the same issue with the fast idle and choke, and have the same solution (get it close and live with it). I never could get the fast-idle to work properly on that carb, but I haven't really given it my full attention either.
On the coldest of days, It'll start up and idle with a single press of the throttle to set the choke, it'll run rough for about 1-2 minutes (loading up I'm sure) but smooths out when the chocke opens and all is well...then I can drive off.
All told, I think it's doing pretty well for a carbed big-block, so I'm not looking a gift horse in the mouth over this...
Dan
Postmaster
Joined: Jul 2003
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From: iowa
I would keep the 750 and adjust it accordingly. It won't have the lowend torque of a smaller carb but will have midrange and top end. The 4180 emissions carb is a pile. They work but are like tamper proof. I bought a new street avenger and have choke problems. And thats with Holleys so called no trouble choke. And i have a edelbrock and its choke never worked the greatest. It would come off too fast all the time when you needed it.
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Joined: Feb 2003
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From: Spokane WA
try setting the choke with a 1/8" drill bit keeping the choke from completly closing.
1/8" gap should help the loading up issue. if it isn't enough choke to start it easily, try setting it with a 1/16" drill.
most universal carb are set up for chevies and chevies are cold blooded needing a really tight choke to start .
1/8" gap should help the loading up issue. if it isn't enough choke to start it easily, try setting it with a 1/16" drill.
most universal carb are set up for chevies and chevies are cold blooded needing a really tight choke to start .
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From: Omaha, NE
Originally Posted by fordeverpower
I would keep the 750 and adjust it accordingly. It won't have the lowend torque of a smaller carb but will have midrange and top end. The 4180 emissions carb is a pile. They work but are like tamper proof. I bought a new street avenger and have choke problems. And thats with Holleys so called no trouble choke. And i have a edelbrock and its choke never worked the greatest. It would come off too fast all the time when you needed it.
The main task of this truck is to pull our 2003 27ft Four Winds travel trailer.
I need all the low end torque I can muster...
Thanks!
Scott