Demon vs Holley parts interchange

Demon vs Holley parts interchange

Joined: February 11th, 2002, 3:43 am

April 9th, 2011, 1:23 am #1

Hey all!

I should say right off the bat I don't have much experience tuning carbs. But I like to learn & can be pretty methodical when I have to.

My main question - does anybody have a link or know off the top of their head what parts will exchange between Holley & Demon carbs?

Basically I'm wondering if I'm going to be able to find all the parts I need to tune the Demon (Speed Demon 750 with vac. secondaries) correctly since Barry Grant is now defunct. I'd hate to spend $$$ and then have to turn around & buy a Holley anyway (although I have been eyeballing the Ultra Double Pumpers).

My other concern is whether the 750 Speed Demon is just too big for a 357" motor. It idles rich & occasionally will diesel a little at shut-down when it's hot. I didn't realize until after I bought it that BG rates their carbs differently because of the wet/dry flow differences. The only adjustments I've attempted so far are the 4-corner idle screws because we barely got the car on the road before time to put it up for the winter, plus I knew I'd be swapping the Weiand X-celerator out for an Edelbrock Performer RPM this spring.

In case it helps:
Aussie 2V heads
Comp 282S Magnum cam
MSD ignition
manual transmission

Thanks for any help - Doug
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Joined: June 12th, 2009, 1:31 pm

April 9th, 2011, 2:15 am #2

I dont know about what will interchange I only run Holleys, I think the 750 Demon carb should be fine, the cam is making the idle rich, you will just have to get used to it, and a high idle will make it run on after you shut off the engine, do you run premium gas? If you dont try it, it will help.
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Joined: December 16th, 2003, 1:59 am

April 9th, 2011, 2:39 am #3

BG recommends a 650

http://www.barrygrant.com/demon/default.aspx?page=11

Holley & BG are rated at different specs, a BG 750 flows a lot more than a Holley 750 at the same depression, Mighty Demon 750 is said to flow 952 cfm

you may have a hard time getting it tuned, if at all?

as you're saying idle will be rich and mid-full power will be lean due to poor signal. you'll have to lean the idle circuit at the idle restrictions and richen the jets until it AFR's right and even then you'll still have transition problems

pretty sure a good old 650 double pumper will rock

there'll be phantoms, there'll be fires on the road... and the white man dancing
Last edited by tinman351 on April 9th, 2011, 2:09 pm, edited 1 time in total.
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Joined: January 10th, 2002, 5:53 pm

April 9th, 2011, 3:35 pm #4

Hey all!

I should say right off the bat I don't have much experience tuning carbs. But I like to learn & can be pretty methodical when I have to.

My main question - does anybody have a link or know off the top of their head what parts will exchange between Holley & Demon carbs?

Basically I'm wondering if I'm going to be able to find all the parts I need to tune the Demon (Speed Demon 750 with vac. secondaries) correctly since Barry Grant is now defunct. I'd hate to spend $$$ and then have to turn around & buy a Holley anyway (although I have been eyeballing the Ultra Double Pumpers).

My other concern is whether the 750 Speed Demon is just too big for a 357" motor. It idles rich & occasionally will diesel a little at shut-down when it's hot. I didn't realize until after I bought it that BG rates their carbs differently because of the wet/dry flow differences. The only adjustments I've attempted so far are the 4-corner idle screws because we barely got the car on the road before time to put it up for the winter, plus I knew I'd be swapping the Weiand X-celerator out for an Edelbrock Performer RPM this spring.

In case it helps:
Aussie 2V heads
Comp 282S Magnum cam
MSD ignition
manual transmission

Thanks for any help - Doug
There is very little that interchanges. Time to shop for a new carb IMHO, or start buying up old Speed Demons so you have a parts pile to draw from.

1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.
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Joined: February 11th, 2002, 3:43 am

April 10th, 2011, 6:08 pm #5

I dont know about what will interchange I only run Holleys, I think the 750 Demon carb should be fine, the cam is making the idle rich, you will just have to get used to it, and a high idle will make it run on after you shut off the engine, do you run premium gas? If you dont try it, it will help.
Dan - I only run 93 octane in this one. Idles nice @ 800 rpm after it's warm, and will even go as low as 600. Just smells of unburned fuel & might make your eyes sting a little if you're in the garage & there's no breeze :o
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Joined: February 11th, 2002, 3:43 am

April 10th, 2011, 7:42 pm #6

BG recommends a 650

http://www.barrygrant.com/demon/default.aspx?page=11

Holley & BG are rated at different specs, a BG 750 flows a lot more than a Holley 750 at the same depression, Mighty Demon 750 is said to flow 952 cfm

you may have a hard time getting it tuned, if at all?

as you're saying idle will be rich and mid-full power will be lean due to poor signal. you'll have to lean the idle circuit at the idle restrictions and richen the jets until it AFR's right and even then you'll still have transition problems

pretty sure a good old 650 double pumper will rock

there'll be phantoms, there'll be fires on the road... and the white man dancing
tinman posted:
"Holley & BG are rated at different specs, a BG 750 flows a lot more than a Holley 750 at the same depression, Mighty Demon 750 is said to flow 952 cfm"

Wow - I knew there was difference in the ratings, but 200 cfm is quite substantial! Before I found out BG went under, I was looking at their 650's.
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Joined: February 11th, 2002, 3:43 am

April 10th, 2011, 7:46 pm #7

Hey all!

I should say right off the bat I don't have much experience tuning carbs. But I like to learn & can be pretty methodical when I have to.

My main question - does anybody have a link or know off the top of their head what parts will exchange between Holley & Demon carbs?

Basically I'm wondering if I'm going to be able to find all the parts I need to tune the Demon (Speed Demon 750 with vac. secondaries) correctly since Barry Grant is now defunct. I'd hate to spend $$$ and then have to turn around & buy a Holley anyway (although I have been eyeballing the Ultra Double Pumpers).

My other concern is whether the 750 Speed Demon is just too big for a 357" motor. It idles rich & occasionally will diesel a little at shut-down when it's hot. I didn't realize until after I bought it that BG rates their carbs differently because of the wet/dry flow differences. The only adjustments I've attempted so far are the 4-corner idle screws because we barely got the car on the road before time to put it up for the winter, plus I knew I'd be swapping the Weiand X-celerator out for an Edelbrock Performer RPM this spring.

In case it helps:
Aussie 2V heads
Comp 282S Magnum cam
MSD ignition
manual transmission

Thanks for any help - Doug
I've done quite a bit of reading here on the forum over the last few days, searching through a lot of the 'carb recommendation' threads, and my head hurts!

I've seen some people say Clevelands like more carb than your typical small block, and others say most people over-carb. The 'carb chooser' on the Holley site picked me out a 650 VS, yet I've seen it posted by a respected contributor here that a 700 DP was too small for an engine very similar to mine (same displacement, cam, & aussie heads).

I think the bottom line is I'm asking a question that has no clear answer. Since I don't own a speed shop & a dyno, it looks like I'm just going to have to wait until I get the intake & dizzy swapped, and then let the engine tell me what it wants. Which means I'll probably have a couple of hundred invested in an Idle-Eze baseplate, power valves, and jets... and still end up needing a different carb. Or just spend the $$$ on a new carb & wonder if I really needed it :P
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Joined: November 26th, 2003, 2:49 am

April 10th, 2011, 9:09 pm #8

Bottom line is it is not too much carb for what you got,just tune it for your combo and run it.would a 650 work a little better on the street only car, sure but run what ya got it'll be just fine.
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Joined: June 12th, 2009, 1:31 pm

April 10th, 2011, 9:12 pm #9

I agree, a 950 HP works very well on mine, a lot better than the 850 that was on it.
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Joined: March 9th, 2004, 3:37 pm

April 12th, 2011, 2:21 pm #10

Hey all!

I should say right off the bat I don't have much experience tuning carbs. But I like to learn & can be pretty methodical when I have to.

My main question - does anybody have a link or know off the top of their head what parts will exchange between Holley & Demon carbs?

Basically I'm wondering if I'm going to be able to find all the parts I need to tune the Demon (Speed Demon 750 with vac. secondaries) correctly since Barry Grant is now defunct. I'd hate to spend $$$ and then have to turn around & buy a Holley anyway (although I have been eyeballing the Ultra Double Pumpers).

My other concern is whether the 750 Speed Demon is just too big for a 357" motor. It idles rich & occasionally will diesel a little at shut-down when it's hot. I didn't realize until after I bought it that BG rates their carbs differently because of the wet/dry flow differences. The only adjustments I've attempted so far are the 4-corner idle screws because we barely got the car on the road before time to put it up for the winter, plus I knew I'd be swapping the Weiand X-celerator out for an Edelbrock Performer RPM this spring.

In case it helps:
Aussie 2V heads
Comp 282S Magnum cam
MSD ignition
manual transmission

Thanks for any help - Doug
>The only adjustments I've attempted so far are the 4-corner idle screws because we barely got the >car on the road before time to put it up for the winter

It takes a while to get the carb set up on a cleveland. There are a bunch of things that could be giving you the rich idle. Not enough initial advance, power valve opening at idle, leaking accelerator pump discharge nozzles, etc.

I don't think the carb is too big, it just needs tuning. That's the fun part

Good luck,
James P.
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