625 Road Demon to be happy or replace?

[MUST 25]

Hi,

 

I´m Tom from Germany. I am proud to drive a 69' mustang coupe J

 

Please, I would like to ask you of a clear advice about the following issue or consideration.

 

 

My topic is the carburetor and the fuel consumption and the "quieter and more cultured engine running".

The motor is a 302 with a sharp camshaft (not shown which) 2.5 H-pipe, Hooker header, and auto transmission c4.

 

Currently, a 625 Road Demon is installed. No idea how or what he has needles.

 

The 625 Road Demon setup, for me is very complicated. I have a spend a lot of time, money and nerves..

Many friends have tried it.

 

For me the question is, should I keep the 625 Road Demon or another fits better for my engine?

Is the 625 Road Demon too big, too complicated, more for more power, etc. intended?

 

Shout I bye a 1404/1406 500/600 edelbrock, a smaller Holley, or perhaps another form you "recommended" carb?

 

With which carb I'll be happy?

 

 

Thank you guys

[barnett468 418]

hello;

 

the std holley is a bit easier to tune/adjust.

 

no way to tell how big of a carb you need unless we have a lot more info.

 

how many rpm does it rev to?

 

does it idle smooth or rough.

 

exactly what is your ignition timing at the following with the distributor vacuum disconnected:

 

idle

 

1800 rpm

 

what is maximum/total timing?

 

what rpm is total timing reached?

 

have you tried increasing the amount if timing to see if it will idle smoother and run better?

.

[Max Power 74]

Ignition timing really has nothing to do with carb sizing.

 

For out of the box drivability, Edelbrock is hard to beat. You provided no real cam specs, or maximum RPM specs, but a 500cfm would be good for regular street driving on mild to medoum cams, and 600cfm for more agressive cams and higher rpm use.

[barnett468 418]

Hello MUST;

 

I get the ignition timing curve close first. Incorrect timing can cause hesitation upon acceleration and poor performance that some might confuse with being a carb issue. Also insufficient timing can cause an engine to run hotter than it normally would.

[sportsroof69 13]

I've never had much luck with the Demons.

[juit 34]

Edel are easy to set up,

 

Holley are awesome i just got a 4160 600 cfm and the car drives smooth, i had some trouble with the install but here are a lot of folks willing to help you out

 

My engine was rated for a 570 holley but i think you will be fine with the 600

 

Read my sig

Edited October 10, 2014 by juit

[RPM 1,190]

Hey Tom, the Demons are based on the Holley. Many were shipped out without cleaning and still have trash inside.

 

Bob

[Jimjific 23]

Copied from a previous post of mine.

 

What is your target top RPM?

 

Engine Size - 302

RPM - ??

Vol. Efficiency = ~.85

 

Use this equation:

((Engine Size x RPM)/3,456)/Vol. Eff. = CFM

Or in your case:

((302 x RPM)/3,456)/.85 = CFM

 

So if you are going to spin your motor up to 5K rpm then:

((302 x 5000)/3,456)/.85 = 514CFM

 

Jim

[juit 34]

https://www.holley.com/products/fuel_systems/carburetors/avenger/street_avenger/parts/0-80570

 

Or the 4100 clones from summit they are having great reviews

 

http://www.mustangandfords.com/parts/mump-0908-street-and-strip-carburetor-performance/

Edited October 10, 2014 by juit

[juit 34]

heres a great article in over carbing

 

http://www.badasscars.com/index.cfm/page/ptype=product/product_id=79/category_id=13/mode=prod/prd79.htm

[MUST 25]

Hi @all

thanks for the many tips!

 

Unfortunately I have no exact data from the engine.

Adjusted is everything but he running too fat.

I think the Demon 625 just does not fit well with the engine.

 

I would like to change the carburetor.

Which is the best choice?

 

The 570 CFM Street Avenger looks good. but what does mean "Ford A/T kickdown, does not work with A.O.D transmission) Does it not work with my 4C automatic?

 

BR

Tom

[shaun071 62]

Hi, I have a 570 street avenger on a mild 302 and it works well. The A/T kick down will work with your C4 auto. It's the same gearbox I have.

[juit 34]

http://www.quickfueltechnology.com/carburetors-slayer-series/slayer-series-600-cfm-single-inlet-fuel-bowls.html

 

Thisones work like the holleys but they have anular boosters instead

[barnett468 418]

http://www.quickfueltechnology.com/carburetors-slayer-series/slayer-series-600-cfm-single-inlet-fuel-bowls.html

 

Thisones work like the holleys but they have anular boosters instead

 

hello;

 

are you sure?

 

i don't see them listed. i know they make an ss model with annulars but its mechanical secondaries.

 

the holley 670 low rider carb us annular as well as both summit shoe box carbs.

[juit 34]

QFT™ now offers a Slayer Series carburetor that is designed for use on stock replacement to mildly modified engines.

 

Key features:

 

Single inlet, side hung fuel bowls.

3-Stage emulsion circuits.

Changeable idle air and high speed bleeds.

Secondary metering plate with changeable jets.

Electric choke; Fully adjustable, one-wire hookup.

Universal throttle linkage.

QuickSet™ adjustable vacuum secondary.

Ford A/T kickdown linkage included.

Polished finish for superior appearance.

 

 

 

quick fuel its vac sec and includes ford kick down plus you can change the jets on the back plate

 

changable speed bleeds are a plus

 

universal throtle likage you will save 30 bucks there

 

this one you can adjust tension from the cap no need to change springs like in holley

 

670 cfm its too big for ya, stay in 500 600 CFM range

 

also summit carb has anular boost and its vac sec, its a bastard son from holley and a 4100 autolite

Edited October 14, 2014 by juit

[Max Power 74]

Hi @all

thanks for the many tips!

 

Unfortunately I have no exact data from the engine.

Adjusted is everything but he running too fat.

I think the Demon 625 just does not fit well with the engine.

 

I would like to change the carburetor.

Which is the best choice?

 

The 570 CFM Street Avenger looks good. but what does mean "Ford A/T kickdown, does not work with A.O.D transmission) Does it not work with my 4C automatic?

 

BR

Tom

 

That would be a good choice, or an Edelbrock. As stated, the kickdown will work with C4 transmissions, AOD transmissions have their internal pressures controlled to some extent by throttle position, and the linkage for that transmission is completely different.

[juit 34]

Quick fuel or summit both can take your trans

[jholmes217 65]

I had one of the Summit 600 cfm carbs on a mild build 302, and I put it on after running a Holley 1850 600 cfm. The Summit had crisper throttle response and seemed to make the same or more power through the gears. I think it had slightly better mileage also.

[shaun071 62]

I've been looking at the Summit carbs too for the 351C I'm building for my coupe. Nice to hear some real world experience with them. I'm undecided on the 600 or 750 though.

Edited October 17, 2014 by shaun071
added info

[juit 34]

Milds 300 to 400 ci 600cfm is enough

[barnett468 418]

I've been looking at the Summit carbs too for the 351C I'm building for my coupe. Nice to hear some real world experience with them. I'm undecided on the 600 or 750 though.

unless that is a box stock 2 barrel you need at least a 670 cfm and for a moderate or higher hp 4 barrel you need a 750.

[jholmes217 65]

I've been looking at the Summit carbs too for the 351C I'm building for my coupe. Nice to hear some real world experience with them. I'm undecided on the 600 or 750 though.

 

Ya, I've been eyeballing the 750 for my 428. My thinking is take the original Holley 735 carb off to preserve it and run a 750

[Max Power 74]

Ya, I've been eyeballing the 750 for my 428. My thinking is take the original Holley 735 carb off to preserve it and run a 750

 

That would be a good plan. Numbers matching carbs are getting pretty rare.

[barnett468 418]

Ya, I've been eyeballing the 750 for my 428. My thinking is take the original Holley 735 carb off to preserve it and run a 750

you can buy a new holley down leg booster carb then buy new float bowls and cross over tube from holley so it will look similar to stock. the lettering on the front of the new bowls is slightly different and the needle and seat might sit a hair higher possibly requiring a 3/16" spacer under your air cleaner.

[jholmes217 65]

you can buy a new holley down leg booster carb then buy new float bowls and cross over tube from holley so it will look similar to stock. the lettering on the front of the new bowls is slightly different and the needle and seat might sit a hair higher possibly requiring a 3/16" spacer under your air cleaner.

 

Sounds interesting, but I have more carbs floating around than I know what to do with. I have the stock 735 cfm Holley carb, I have a "U" replacement 735 Holley carb, I have a 750 Holley mechanical secondary that was on the car when I got it. I have a 700 cfm vacuum secondary that was on an intake manifold I bought, I have a Holley 1850 600 cfm, I have several Autolite 4100s, including one of the rare 1.19 venturi, and probably a couple more I forgot about that are buried on a shelf in the garage. Doesn't keep me from saying "hmmm" to the Summit, Demon, Quick Flow, etc., or the carb your talking about. Always in the search for better throttle response and power! Too bad the wife doesn't understand that!