4300 Carb Replacement Advice Needed

[The Big One]

Hi- I'm not very knowledgeable about carburetors and need your advice. I have a 1974 Ford pickup with factory 460 and original 4300 4 bbl carb. Because the carb continues to have issues, I have decided to replace it with a Street Demon #1901 625 cfm unit :http://www.demoncarbs.com/1901.asp. My question is: Since the Motorcraft 4300 is a spread bore carb on the factory iron intake, will I need an adaptor to fit the new carb to the factory spread bore manifold? Summit has an adaptor set from Edelbrock
http://www.summitracing.com/parts/ed...commendedparts. I was also considering installing a 1/2" phenolic spacer to address heat rise issues like this set: http://www.summitracing.com/parts/sum-g1405-1. I've done some research and a lot of folks seem to say that the adaptors don't work and you are better off changing out the intake manifold to avoid problems. I was hoping to keep the original iron intake but if necessary, I could swap it for a new aluminum intake. I'm not all that familiar with these square bore, 4-hole, spread bore, etc. issues and I want to make sure I do this right.

Thank you and any advice will be greatly appreciated!

[cletus66]

I can understand not wanting to spend the money on an aluminum intake for a pickup truck. If you don't mind changing the intake, they were available from the factory with the Holley pattern. I would try to find one locally, because shipping might suck. If you don't want to change the intake at all, I don't know, but maybe somebody will.

[The Mad Porter]

Originally Posted by The Big One

Hi- I'm not very knowledgeable about carburetors and need your advice. I have a 1974 Ford pickup with factory 460 and original 4300 4 bbl carb. Because the carb continues to have issues, I have decided to replace it with a Street Demon #1901 625 cfm unit :http://www.demoncarbs.com/1901.asp. My question is: Since the Motorcraft 4300 is a spread bore carb on the factory iron intake, will I need an adaptor to fit the new carb to the factory spread bore manifold? Summit has an adaptor set from Edelbrock
http://www.summitracing.com/parts/ed...commendedparts. I was also considering installing a 1/2" phenolic spacer to address heat rise issues like this set: http://www.summitracing.com/parts/sum-g1405-1. I've done some research and a lot of folks seem to say that the adaptors don't work and you are better off changing out the intake manifold to avoid problems. I was hoping to keep the original iron intake but if necessary, I could swap it for a new aluminum intake. I'm not all that familiar with these square bore, 4-hole, spread bore, etc. issues and I want to make sure I do this right.

Thank you and any advice will be greatly appreciated!

Using an adapter will kill total airflow. Don't do it.

Find an early square bore intake or a later truck intake with the holley pattern locally. It should cost almost nothing. OR... Find a used eddy performer.

For best economy an eddy 1411 carb will offer better power than a 625 cfm carb.
If mileage is not as big a concern the 3310 holley 750 vac sec with elec choke and ford kick down is a great choice. The universality of this carb has the idle and transition circuits pretty fat. It will make the best peak HP.

Having a properly curved dizzy and free breathing exhaust will help significantly as will the installation of an early straight up timing set.

[MrScharfenberger]

I know you don't want to change intakes but bite the bullet and find a used Edelbrock performer out there. You will be glad you did...

Here are a couple. The first one looks real promising:

http://www.460ford.com/forum/showthr...rock+Performer

http://www.460ford.com/forum/showthr...rock+Performer

[DanE]

The 625 cfm Demon is a relatively new carb and is designed to work on both spread bore and square bore intake manifolds. According to Demon, it will support 350 hp. How much HP do you have? As for intake manifolds, the stock factory manifold will outperform the others at RPM's of about 3500 rpm or less. At what RPM range do you use your engine in that truck?

[D Pope]

Like Scotty said!

[rmcomprandy]

Originally Posted by The Big One

Hi- I'm not very knowledgeable about carburetors and need your advice. I have a 1974 Ford pickup with factory 460 and original 4300 4 bbl carb. Because the carb continues to have issues, I have decided to replace it with a Street Demon #1901 625 cfm unit :http://www.demoncarbs.com/1901.asp. My question is: Since the Motorcraft 4300 is a spread bore carb on the factory iron intake, will I need an adaptor to fit the new carb to the factory spread bore manifold? Summit has an adaptor set from Edelbrock
http://www.summitracing.com/parts/ed...commendedparts. I was also considering installing a 1/2" phenolic spacer to address heat rise issues like this set: http://www.summitracing.com/parts/sum-g1405-1. I've done some research and a lot of folks seem to say that the adaptors don't work and you are better off changing out the intake manifold to avoid problems. I was hoping to keep the original iron intake but if necessary, I could swap it for a new aluminum intake. I'm not all that familiar with these square bore, 4-hole, spread bore, etc. issues and I want to make sure I do this right.

Thank you and any advice will be greatly appreciated!

You won't need an adapter for the bolt pattern; just for the secondary barrels.
Just use a 1/2" thick three barrel type plate; (a four hole plate with the secondaries opened to one another), between the carb and the manifold. Be sure it covers the open barrel holes of the present intake manifold, on the sides.

I would find an 80's OEM Holley 4180 carb if I could with the Ford electric choke; it will bolt right on.

[The Big One]

Originally Posted by DanE

The 625 cfm Demon is a relatively new carb and is designed to work on both spread bore and square bore intake manifolds. According to Demon, it will support 350 hp. How much HP do you have? As for intake manifolds, the stock factory manifold will outperform the others at RPM's of about 3500 rpm or less. At what RPM range do you use your engine in that truck?

It's a completely stock/original F350 2WD, C6 tranny, 4.10 axle truck with 43K original miles. It's really a show truck that I tinker with and my son and I take to local car shows. I am trying to keep it as original as possible but I am going to have to make a few upgrades with the carb, ignition. I don't know the stock HP but I'm not interested in gaining a ton of HP as I don't race it but some increase is always nice but not a priority. As far as RPM's, the range would be relatively low due to the type of use. I'm also not concerned with fuel economy as this is not a daily driver. The price of a new alum intake isn't my main concern, again just trying to keep it as stock as possible. Thanks!

[The Big One]

Originally Posted by The Mad Porter

Using an adapter will kill total airflow. Don't do it.

Find an early square bore intake or a later truck intake with the holley pattern locally. It should cost almost nothing. OR... Find a used eddy performer.

For best economy an eddy 1411 carb will offer better power than a 625 cfm carb.
If mileage is not as big a concern the 3310 holley 750 vac sec with elec choke and ford kick down is a great choice. The universality of this carb has the idle and transition circuits pretty fat. It will make the best peak HP.

Having a properly curved dizzy and free breathing exhaust will help significantly as will the installation of an early straight up timing set.

Thanks Scotty. What you have said is along the lines of the research that I have found, regarding the adaptors and intake. I was very intrigued by the Street Demon carb because of the polymer bowl and the design. I've read some good things about it but not opposed to the Eddy or Holly. I do plan on upgrading the Distributor at some point and ICM to a Duraspark II. Thanks!

[The Big One]

Originally Posted by rmcomprandy

You won't need an adapter for the bolt pattern; just for the secondary barrels.
Just use a 1/2" thick three barrel type plate; (a four hole plate with the secondaries opened to one another), between the carb and the manifold. Be sure it covers the open barrel holes of the present intake manifold, on the sides.

I would find an 80's OEM Holley 4180 carb if I could with the Ford electric choke; it will bolt right on.

Thanks Randy. So if I were to consider the route you've suggested, would this barrel type plate be custom made or do these already exist?

Thanks everyone, this is all great information and very helpful! Please keep your opinions and advice coming.

[429TORQ]

Originally Posted by rmcomprandy

You won't need an adapter for the bolt pattern; just for the secondary barrels.
Just use a 1/2" thick three barrel type plate; (a four hole plate with the secondaries opened to one another), between the carb and the manifold. Be sure it covers the open barrel holes of the present intake manifold, on the sides.

I would find an 80's OEM Holley 4180 carb if I could with the Ford electric choke; it will bolt right on.

Absolutely, the 3 bbl thing will get it done.
If it is an actual early generation 4300 pad intake (car 68-73, the motorcraft spreadbore generation where the secondaries are only like 1/16" larger than the primaries), the demon should bolt right on if I am not mistaken.
I know for sure that a holley 600 4bbl will bolt right on to these oem iron intakes (the holley 1 9/16" butterflys will clear all 4 holes).
Edit- a Holley 3310 750 will not clear on the primaries on a 1st gen iron bbf 429-460 intake without a 4-hole or open spacer The oem intake will clear 1 9/16" on the primaries and 1 11/16" on the secondaries.

[DanE]

The 625 Demon has 1.375" primarys with triple stack boosters. The carb is a modified 3 barrel where the secondarys flow more than twice what the primarys flow. It is a carb worth looking into. I am going to run two of them on a Blue Thunder, dual plane, CJ intake manifold on P51's on a 483 cubic inch 460. (4.44 x3.9 with a 7.1 rod and 11 to 1 compression.) The carb comes with the necessary gaskets ( paper and metal ) to take care of the issues with the spread bore intake manifold sealing issues.

[68xr7cat]

Was just reading the instructions for that new Demon carb.

http://www.demoncarbs.com/Assets/doc...LIT701rev7.pdf

From what the manual states it will fit a spread bore intake, just tells you to use the gaskets and plate that come with the carb. It does mention that you may need to use a thick spacer for the throttle linkage to clear some intakes.

Don't know anything about this new carb, the looks reminds me of a thermoquad, but chromed. Does seem to have some nice features and if you don't mind trying something new I would say go for it.

Steve

[429TORQ]

Just looked at the carby, it looks like it will only fit the 68-73 bbf intake with a 1/2" or 1" open spacer(or the 3v spacer Randy mentioned). I had no idea that it had that "married" style secondary plate. If his '74 460 has the "big" ford spreadbore pattern(4350 style) I don't know what the deal will be.

[D Pope]

I think my Holley 3 barrel looks better than the Demon.