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351c Cast Iron Intakes

10K views 15 replies 11 participants last post by  Precision Transmission 
#1 ·
Howdy,

Currently running my OEM cast intake on my 70 M-Code M1. Noticing the 71 intake for clevelands have larger secondary ports.
Why? any performance difference? Both accommodate 4150 type carbs. I know the spread bores are different.

would the 71 intake.. If better mount to my 70?

attached are a couple links to some sales on ebay.

71 intake
1971 72 73 FORD MUSTANG CJ Q CODE COBRA D1ZE 351C CLEVELAND 4V INTAKE MANIFOLD

70 intake
1970 FORD MUSTANG MACH 1 TORINO COUGAR 351C 4BBL FACTORY INTAKE MANIFOLD 9L24

thx for your help/responces

PJ
 
#2 · (Edited)
You would have to change to a proper spreadbore carb to take advantage of it. They were trying to improve driveability/throttle response. Unless you drive in city traffic a lot I can't see the point.


 
#3 ·
carb pad

PJ, you want the square bore. The 71 manifold was intended to fit some weird carbs Ford was trying to run. They aren't well though of. If you want a spread bore, get a regular Thermoquad / Quadrajet style. If I had the strange spreadbore you're showing as the '71, I would remachine the pad for a regular square bore carb. LSG
 
#6 ·
the spread bore intakes were for the 4300 autolite carb. it was supposed to be a better carb than the 4100 "cracker box" carb, it wasnt. there are also holley carbs that have a spread bore design as well that use the original holley carb bolt pattern, a friend of mine has such a carb for his corvette.
 
#7 ·
Keep the 70 intake. The PO had a 71 intake on my 70, with a 4100 carb. I constantly had drivability issue. Swapped to the correct 70 intake with a 4100 with no further issues. The 4100 will fit on the 71. But the base of the carb covers part of the secondary holes. Therefore reducing those big secondary holes to smaller openings than the base of the 4100. The base of the 4100 fits perfectly over the 70 intake secondary holes. If you doubt it, just place a 4100 base gasket over the base of a 71 intake and you can see how much of the secondary holes are covered.
 
#9 ·
Well.........I've seen many Quadrajets that totally "haul" when tuned right. They ARE different from a Holley so........holley "tricks" won't work. GM had pretty good luck with'em too.
Tiny primaries and HUGE secondaries! What's not to like. Check Youtube for tuning tips. Still many dirt track classes that run quadrajet carbs and they flyyyy!
6sally6
 
#10 ·
There is nothing wrong with a properly set up Quadrajet. I ran one on my 460 for several years. I think Woodchuck''s point was the Autolite/Motorcraft spreadbores are different than the Rochester (GM) Quadrajet and are not interchangeable. The Q-jet is a symmetrical spreadbore meaning primary and secondary bores share the same center line. The Ford spreadbores are asymmetrical. The primary and secondary bores have different center lines.


To add to the confusion the Ford 429 CJ engines in 70/71 used a Quadrajet carb as Woodchuck has already stated.

To the OP, the bolt pattern on the two manifolds are the same for the Ford and Holley carbs but you won't be able to run a Holley on the spreadbore intake without an adapter.

It should also be noted that the primary and secondary holes in the M code squarebore intake are not the same size. The primary bores are only about 1.5" and will only accommodate a 1 9/16" throttle blade which is typical of the 600 cfm Holleys. If you want to run a 750 or larger you will need a short spacer to prevent the throttle blade from binding on the intake bore.
 
#11 ·
Nothing wrong with a spreadbore carburetor, but I doubt the OP would be happier if he swapped out the intake and carb for a spreadbore setup. If they OP is looking for better performance and driveability, I would suggest a "Super Holley" like something from Quick Fuel. I've never been impressed with Ford's 4V carburetors after the 4100.

The best Cleveland 4V intake would be a Blue Thunder, but those are pretty expensive. Otherwise, an Edelbrock Air Gap would work well. But no need to go to a spreadbore.
 
#12 ·
Thank you very much gentlemen.. I don't post much out here but when I do.. Responses are very helpful...I'll stick with what I have currently.. I'm using a 680vs quickfuel black diamond on it. Mach is Running fine.. But always looking for a little more.. getting bored and looking for small projects.
I've had my eye on the Scott Cook aussie intake and then maybe step up to a 750/780... Big $$. So HP to $$ amount may not be worth it.

But a nice set up and conversation piece...

I guess I can't leave well enough alone ;`)

Thanks again!
PJ
 
#13 ·
Sounds like you've got a perfect carb. I doubt you'd be happier with a bigger carb. What cam are you running? If it's not a custom grind, I would suggest one. Try a small vendor like Bullet Racing cams. That will get you a lot more than a bigger carb.

Also, consider what's behind the engine. A Cleveland 4V likes a big rear gear. What about an overdrive trans? Yeah, this stuff is a lot more expensive than a new carb and intake, but it will also get you a lot more performance.
 
#14 ·
Thx Klutch. My Cleveland looks stock. Wanted to keep it that way. It's actually stroked to 408. FPA headers. 3in exhaust etc. Cam is a comp. Don't have the specs in front of me. But nice lope and vacuum. PS,PB..The rear is a 3.50 Trac loc. 4sp close ratio. It's an all #s matching car. Shaker,etc. Fun to drive.
 
#16 ·
I modified a 1970 style intake to take a Holley List 7010/ 780cfm carb . The 7010 has primaries the size of a 600cfm, and secondaries the size of an 850cfm. The primary holes in the intake were a perfect fit for the carb, and a short bit of time on a mill had the secondary holes opened up enough to match the carb secondaries. The nice thing about the 7010 is the primary and secondary bores are on the same longitudinal centreline.

I only did this because the D1ZX aluminum manifold was unobtainable. Now, thanks to Blue Thunder, it is.

Don
 
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