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Hi guys,

I was given a used Holley 4780 by my father over the weekend. From what I can find out, it's a street/strip 800CFM double pumper carb. Given that this thing doesn't have a choke or a kickdown setup on the throttle lever, I'm thinking this is mainly intended to be a strip carb.

My question is, would you spend the time setting this thing up for a mostly street 340+hp 355 to see what it'll do with this motor at the track. I've got someone interested in it if I decide I don't want to play with it.

I know I'll lose some low-end drivability by even bolting this thing on, but would you play with it anyway to see about picking up a 10th or two at the track?
 

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Based on what your mods are and converter, I would say that it's probably too much carb. We'll see what others say.
 

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Maybe someone will trade a smaller carb for it, that's if you need a carb. Prices around here range from 50 to 100 for a used stock carb in decent shape. Seems like the smaller carbs sell for more than the big ones around here anyway. RM
 

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Discussion Starter #8
Real McCoy said:
Maybe someone will trade a smaller carb for it, that's if you need a carb. Prices around here range from 50 to 100 for a used stock carb in decent shape. Seems like the smaller carbs sell for more than the big ones around here anyway. RM
Interesting idea. I wouldn't mind trying out an appropriately sized DP at some point to see how it compares to the 750 vacuum secondary carb I'm running right now.

Thanks for the info guys.
 

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800 holley

the 800 double pump holley would be an increase in hp and torgue, and alot better throttle response when slamming pedal to the floor!
 

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I doubt if you would see a difference. A 750 vac secondary with the secondaries tuned correctly will run fine. A 350 doesn't need more than a 750. I can tell you I never tried an 800 on a 350, but I ran a 700, 750 and an 850 on a 450 hp 350 and the 750 killed the 850 hands down. The 700, ran great too, but it was old and that was what started the carb swapping.
 

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Keep it & try it!

* At your power level you only need maybe 600cfm or 650cfm
* So its too big, and the mechanical secondary makes that worse
* It will be a BOWOW DOG unless you have a really high stall (like 3000 or more) because-
* If you floor it off the line it will just bog out like you have the brakes on
* If you get into it gently, it will launch ok but you cant open the primaries all the way else those big secondaries will dump in.
* A 780 vac sec is actually the same carb and much better for your combo, you can floor it right off the bat. Still a little big though.

So why keep it?
1. It was free and from your dad.
2. The 800 is a nice setup, good throttle response on a bigger motor, good downleg boosters.
3. In the right engine it will run with or outrun just about anything.
4. You will probably get bored and want a bigger motor/converter soon. Then you already have the right carb.

I'd test it out at the strip if you go. Just make sure to bring another carb, one thats the right size. That way you can see how much SLOWER it is. I'd guess you will be at least 0.2sec (2 carlengths) slower with that big 800 on there.

But, dont drive it to the strip with the 800 on there, you will run out of gas!

They do come with a choke, but I dont ever remember using it even in the winter, they are set up pretty rich. Just right for open headers but too rich for street use.

I would only swap it for a known good carb of the size you need. But if youre just starting your carb collection, its a keeper.:devil:
 

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Hi guys,

I was given a used Holley 4780 by my father over the weekend. From what I can find out, it's a street/strip 800CFM double pumper carb. Given that this thing doesn't have a choke or a kickdown setup on the throttle lever, I'm thinking this is mainly intended to be a strip carb.

My question is, would you spend the time setting this thing up for a mostly street 340+hp 355 to see what it'll do with this motor at the track. I've got someone interested in it if I decide I don't want to play with it.

I know I'll lose some low-end drivability by even bolting this thing on, but would you play with it anyway to see about picking up a 10th or two at the track?
What kind of air density do you have usually? IF it is close to 300ft. then the larger carb might work. Jet it with 72's on all 4's. read the plugs and go from there. IF you have high density altitude, it is probably too much carb. (just my opinion)
 

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I don't get it? :confused:
How did a 7 year old thread get resurrected?
 
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