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2BBL to 4BBL

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78FordLtd2 View Drop Down
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    Posted: 02-May-2021 at 8:28PM
After discovering a vacuum leak where the intake meets the head on the passenger side of the engine, I'm considering swapping out the stock 2bbl carb and manifold for a 4bbl carb and manifold set up. Is the power gain worth the extra cost in doing the swap or just pull off the old manifold and install new seals? This would be the best time to make the swap, but is it worth it?

The engine is a 351 Modified with about 85k miles. It has descent power...for what it is,  with economy gearing, but more would be nice. It's completely stock.
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Steve M. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve M. Quote  Post ReplyReply Direct Link To This Post Posted: 03-May-2021 at 1:57AM
There's some power gained and a little better fuel economy with that change. Granted, the changes are small but they are noticeable. Get a good set of Headers with a 2 1/2" duel exhaust. That will allow your engine to breathe. That is probably the most bang for the buck.
Steve M.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 03-May-2021 at 2:13AM
The carburetor is the key point, whichever carb is tuned better to the engine, the better the power and fuel economy it will have. So if you the old carb is working well and you swap to a common Holley, it will use a lot more fuel. Whichever is the better carb will be the best choice, it's that important.

The 351M is an under developed engine, emissions and smog junk, the big block weight, so the potential is not that high. Improving the carb and intake, exhaust, and tune up items, those would be your best things to work on.
Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 03-May-2021 at 2:55PM
I did the 4bbl swap on my 400 before I built it and it made a noticeable improvement. If you do that along the dual exhaust and waking up the ignition timing a bit, it will surely make it more lively. Edelbrock and Weiand make an intake for the 351M and 400, but they are more pricey than a small block Ford intake. All you'd need for a carb would be something around a 600 CFM carb, which are pretty cheap.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 03-May-2021 at 3:08PM
What does a high quality carb cost these days? I rarely see mention of any pricing, and those are always some large 800cfm or bigger race style. I have an Edelbrock on my latest 351C-4V engine, and it needs rebuilding. That's what most people would look to I'd guess. I have an old first version Holley 4-hole TBI I may try to replace this thing with, it shouldn't be worse.
Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 78FordLtd2 Quote  Post ReplyReply Direct Link To This Post Posted: 03-May-2021 at 3:28PM
I think for now I'll stick with the 2bbl. I still need to swap the exhaust...I was never happy with it when it was replaced 2 years ago...still single and emissions required I had to replace the cats. I can't wait to get a proper 2 1/4 set of pipes on it.
I agree, the 335 engines were under developed. Ford really could have done something with this series of engines. The heads were still decent and the block was pretty beefy. Instead of making an existing engine meet the new '75 emission standards, Ford could have gone the other route and redesigned the 335 series and the 302 the same way Chevy did for its LM1 350, and make the most out of these engines and be emission compliant.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 78FordLtd2 Quote  Post ReplyReply Direct Link To This Post Posted: 03-May-2021 at 3:39PM
A high quality 4bbl carb and manifold is pretty pricey. A lot depends on which side of the border you are on. Lol!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 78FordLtd2 Quote  Post ReplyReply Direct Link To This Post Posted: 03-May-2021 at 3:45PM
First version of Holley 4 hole TBI?? I remember seeing adds for those in Hot Rod and Car Craft magazines! I've always wondered how well they worked. Both Ford and GM TBI units worked great but never saw a Holley unit used ever. I think they were very expensive at the time.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 04-May-2021 at 8:18AM
The early Holley TBI has a bad reputation now, it's not very able to adjust to changing combinations or conditions. The newer EFI systems put the old kinds to shame, so everyone talks it down if you dig for reviews. I got it for what then was a good deal, about $500 for an unused still in the box unit. Now it may be similar in performance to a nice carb. I don't have the original project car and the 400 engine isn't that viable given I have my old 72 351C-2V to build with, and 4V heads. I was going to put the 4V heads on the 400, with a Torker intake, for a 70 Mustang I had briefly. Things change and time flies.
Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Big Bird Quote  Post ReplyReply Direct Link To This Post Posted: 04-May-2021 at 10:32AM
The early Holley Pro-Jection 2 and Pro-Jection 4 weren't bad for their time.
Ever driven a Ford with CFI? 84-85 Clown Vic/Grand Monkey/Lincoln ClownCar and a lot of the Fox-based cars used it. That's the basic Holley Pro-Jection 2. Controller for the Pro-Jection was somewhat flexible/adjustable, but Holley was using their paying customers as a test group.
"What we do in full frontal view, is more honest than your cleaned-up mind."
Randy
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How the Heck does a REGULAR CAB SHORTBED weigh over 5200 pounds?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 04-May-2021 at 1:29PM
Originally posted by Big Bird Big Bird wrote:

The early Holley Pro-Jection 2 and Pro-Jection 4 weren't bad for their time.
Ever driven a Ford with CFI? 84-85 Clown Vic/Grand Monkey/Lincoln ClownCar and a lot of the Fox-based cars used it. That's the basic Holley Pro-Jection 2. Controller for the Pro-Jection was somewhat flexible/adjustable, but Holley was using their paying customers as a test group.


That sounds more promising than the EFI forum I was reading on a month ago. Mine is the Pro-Jection 4 and I should use it and see how it does work.
Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Big Bird Quote  Post ReplyReply Direct Link To This Post Posted: 05-May-2021 at 2:31PM
If you already have it, what do you have to lose? You gain fun time in the garage whether it works or not.
"What we do in full frontal view, is more honest than your cleaned-up mind."
Randy
1979 T-Bird
2005 F-150 STX RCSB 4.6, 3.55 LSD
How the Heck does a REGULAR CAB SHORTBED weigh over 5200 pounds?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve M. Quote  Post ReplyReply Direct Link To This Post Posted: 06-May-2021 at 2:10PM
Fun time in the garage!  Love it.
Steve M.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 07-May-2021 at 6:13PM
Originally posted by Steve M. Steve M. wrote:

Fun time in the garage!  Love it.
learning new cuss words too LOL
JOHN
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