351C 4V Spreadbore intake vs Squarebore intake

Charlie71 · Aug 19, 2024

Folks,
I'm updating my H code 351C-2V to a 4-V. I've purchased a set of D1AE-GA's from Valley Head Service in Chatsworth, CA. When searching for the intake, I've read that the spreadbore has better economy and better throttle response at lower RPM's and the squarebore if for higher RPM performance.
My Mach1 is a Sunday driver for me, mostly lower RPM driving with a few freeway WOT entrances and my Friday night hole shots in farmland Ventura.
I'd like some input from those that have experienced one or the either or both spreads vs. squares.
My car is a top-loader if that makes a difference.
If there are any pitfalls that I should be aware of when doing this conversion, I'd appreciate the input.

Thanks for your help,
Charlie B

Don C · Aug 19, 2024

Are you referring to OEM intakes or aftermarket?

Charlie71 · Aug 19, 2024

OEM intakes are my interest. I have several saved from Facebook Marketplace, eBay, etc. they all need refurbishing, and are about $100.
I am looking to save as much $$ as possible because I have many things to still buy. My wife is not pleased with my spending habits on my car

Certainly there is Edlebrock, but they are listing at about $400. If there are better alternatives, please let me know.

Don C · Aug 19, 2024

The only carburetor that will fit the OEM spread bore manifold is the Autolite 4300D. The 4300D carburetor is scarce and expensive and somewhat difficult to keep properly tuned. To use any other carburetor requires an adapter. This one is for a square bore:
https://www.summitracing.com/parts/trd-2199

Charlie71 · Aug 19, 2024

Are adapters not a good option?
I am planning on transferring the 1406 Edelbrock from my 2v.
Another question: are the Ford Cast Iron manifolds considered single plane? From my research Dual plane manifolds are best rated for street applications. Is this accurate?

73inNH · Aug 20, 2024

Note: Edelbrock intakes show up on Craigslist every now and then. Keep your eyes peeled. I'm not sure how much better they are then the cast iron originals, but they sure are lighter!

c9zx · Aug 20, 2024

All OEM intakes are dual plane. As far as OEM intakes, the almost square bore intake from 70-71 is the best option. Casting number D0AE-L. Chuck

Hemikiller · Aug 20, 2024

If you want to keep it interesting, get a square bore D0AE-L intake, add a spreadbore adapter and run a Quadrajet.

That'll keep 'em guessing.

Bobby · Aug 20, 2024

Are you interested in OEM period correct parts? eBay has a Buddy Bar Boss 351 spreadbore intake (aluminum) for $1600. That should give your wife a good fit! Also the Autolite 4300D when its available will run you about $1000.....another wife beater! The 4300D had issues back in the day but the problems were engineered out to provide a decent carb. Carburetorcenter.com sells them if they have stock. Attached is an article about the 4300D

https://www.carburetorcenter.com/pr...lite-cobrajet-4300d-carburetor-remanufactured

https://www.ebay.com/itm/3949863204...n31OSpaIEpzWmT2QN4wOzUxQ4=|tkp:Bk9SR8yHp4GuZA

darb_123 · Aug 20, 2024

Everything listed above is true. However, I am a diehard who likes the 4300-D and that is what I have on my H code 72 with 71 closed chamber heads. I have three, 4300-D's as spares. I have been picking them up as I see them at a good price over the past 20 years. I currently have a spare 4300-D original intake as well as an original 4300 square bore intake. You can also use the 4350 carb on a 4300-D intake. They are later model replacements for 4300-D carbs and usually sell at a much cheaper price.

Not mentioned in any other discussion is another option if you do not want to go after market is the AUSSIE spreadbore intake. Their advantage is they fit the 2100 two barrel heads without alteration but the spreadbore requires either the GM (QUADRAJET) spreadbore carb OR Holley spreadbore (4165 or 4175. I also have an AUSSIE intake I have been saving for one of my H codes for a future build. If you purchase an original cast iron intake, they are heavy and shipping gets expensive.

Mark Jones · Aug 20, 2024

I have an original cast 4bbl intake and the original Edelbrock 351C aluminum intake but i cant remember if they are for 2V or 4V heads. If you have any interest, I can take a look and post some pics.

Don C · Aug 20, 2024

Charlie71 said:
Are adapters not a good option?
I am planning on transferring the 1406 Edelbrock from my 2v.
Another question: are the Ford Cast Iron manifolds considered single plane? From my research Dual plane manifolds are best rated for street applications. Is this accurate?

Adapters are OK, proper fitting ones won't hurt power that much. The biggest drawback is hood clearance. If you have ram air you would have to modify the air cleaner housing. Check to make sure you have 1+" clearance above your existing air cleaner.

detritusmaximus · Aug 20, 2024

darb_123 said:
Everything listed above is true. However, I am a diehard who likes the 4300-D and that is what I have on my H code 72 with 71 closed chamber heads. I have three, 4300-D's as spares. I have been picking them up as I see them at a good price over the past 20 years. I currently have a spare 4300-D original intake as well as an original 4300 square bore intake. You can also use the 4350 carb on a 4300-D intake. They are later model replacements for 4300-D carbs and usually sell at a much cheaper price.

Not mentioned in any other discussion is another option if you do not want to go after market is the AUSSIE spreadbore intake. Their advantage is they fit the 2100 two barrel heads without alteration but the spreadbore requires either the GM (QUADRAJET) spreadbore carb OR Holley spreadbore (4165 or 4175. I also have an AUSSIE intake I have been saving for one of my H codes for a future build. If you purchase an original cast iron intake, they are heavy and shipping gets expensive.

Long before I bought another Mustang,
I was in a local junkyard poking around. Always look inside trunks and hatches, you never know what is lurking there waiting to be picked up.

I was rummaging thru an old VW Microbus and found a decent Holley 4175 just laying there.
I asked, "How much for carbs?"
"$15."
"Eh, yeah, okay."

It's in a box somewhere. But now I have a Cleveland powered Mustang again and factory squarebore and spreadbore intakes as well as Edelbrock 4V intakes for 2V and 4V heads.
Someday I'll have to decide what I'm going to use....

Charlie71 · Aug 23, 2024

Folks,
I think I’m changing directions. I have a strong feeling that going with Aussie 302 /2V heads is the correct choice. I’ve been talking to “my guys” in CA and they question changing out of the 2V has it delivers good street performance. It is the opinion that the 4V heads I’ve bought are too high in the upper RPM range to be noticeable by me and the Sunday driving that I do.
Linking posts by @Spike Morelli explaining how he is going with Aussie heads. @Spike Morelli has a great reputation in So. Cal as an engine builder.
As it seems, converting an H code into a breathing and HP machine using the Aussie heads is viewed by many as the most efficient modification to an H code engine for increasing HP at the street level.
So, I’m investigating, wanting to find the correct casting numbers for the Aussie Heads. There are aftermarket options that are really expensive.
I committed to buy the 4V heads from Valley Head Service and I’ll do that, but they may be up for sale soon. It’s been explained to me that using camming to keep the torque at a lower RPM level using 4V heads is tricky.
If there is an argument, I’m very open to listen. I’ve just spent $1,100 on the 4V heads.

Sheriff41 · Aug 23, 2024

Don't overthink it. Build your engine with proven parts and drive line combination and enjoy.

Q1SVT · Aug 23, 2024

Charlie71 said:
Folks,
I think I’m changing directions. I have a strong feeling that going with Aussie 302 /2V heads is the correct choice. I’ve been talking to “my guys” in CA and they question changing out of the 2V has it delivers good street performance. It is the opinion that the 4V heads I’ve bought are too high in the upper RPM range to be noticeable by me and the Sunday driving that I do.
Linking posts by @Spike Morelli explaining how he is going with Aussie heads. @Spike Morelli has a great reputation in So. Cal as an engine builder.
As it seems, converting an H code into a breathing and HP machine using the Aussie heads is viewed by many as the most efficient modification to an H code engine for increasing HP at the street level.
So, I’m investigating, wanting to find the correct casting numbers for the Aussie Heads. There are aftermarket options that are really expensive.
I committed to buy the 4V heads from Valley Head Service and I’ll do that, but they may be up for sale soon. It’s been explained to me that using camming to keep the torque at a lower RPM level using 4V heads is tricky.
If there is an argument, I’m very open to listen. I’ve just spent $1,100 on the 4V heads.

... Larry's shop, Valley Head Service has done my 4V heads and my set of Aussie heads [one of Spike's threads shows some pictures of my Aussie heads]... Rubin [Alex too] is the man. Personally I would go 4V they can handle ALL RPM ranges given the build is correct! Open chambers heads need popup pistons to get the needed compression. The cam sets the performance range ... NOT TRICKY...

edit: just checked your head D1AE-GA are CC... JE pistons work with those

Your 2V and Aussie heads are the SAME just open or closed chambered.. performance/Air flow is the same... Finding/ordering pistons for Aussie 56-58 cc heads is $$. Cheaper to use your 2V's with pop ups ...

Larry was long time friend of the owner of Bullet Cams and I have a couple of specifications you might like.

Intake for 4V is the 1970 L Mustang/Cougar, and several years from Torinos/Montergos just need to be opened up a little see my old post. I have the tooling Larry's shop can used, problem is Larry just past away and ??? not sure what's next.
https://7173mustangs.com/threads/new-intake-manifold.37894/#post-386157

If you go Aussie or 2V, I have a new in box Edlebrock 4V/2V intake. 2665. I live very close to you.

c9zx · Aug 24, 2024

I find it hard to understand why the "2V is better for street use." tale is still alive. For optimal performance, getting the cam right is tricky on anything, so many variables. Chuck

Hemikiller · Aug 24, 2024

Since you're committed to owning the 4V heads, why not use them? As Chuck noted, the majority of issues with 4V heads can be traced back to poor cam choices or an unsuitable application to begin with.

Charlie71 · Sep 7, 2024

Folks,
Sorry for the delay, family issues...
Ruben at Valley Head Service is working on the 4V heads, I need to select the cam and the springs. Ruben found a pair of Aussie Heads, they are on Larry's Ranchero. I'm working with Kim (Larry's wife) to purchase the car, but right now, I'm committed to the 4V heads.

@Q1SVT "Larry was long time friend of the owner of Bullet Cams and I have a couple of specifications you might like." I'd like to talk with you about your experience in the cam choice.

Also, I believe that my Mach1 has a 5/16" fuel line supply to the pump. If that is true, is upgrading to the 3/8" necessary?

Thanks,
Charlie B

Hemikiller · Sep 8, 2024

71-73s had a 3/8" line from tank to pump, 5/16" from pump to carb. It's plenty of capacity for what you're building.

I'd recommend a call to Lykins, Bullet or Schneider for cam recommendations. Get the cam, lifter and valve springs/retainers from them as well.

351C 4V Spreadbore intake vs Squarebore intake

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