2bbl to 4bbl

[OVERKILL]

How much power do you want to make? Lots of good advice in the thread, we all have our own preferences. I've built a few small Windsor's (302's) and I prefer a roller conversion with the readily available link-bar lifters and a decent cam. For OTS a TFS #1 would be really mild, has a wide LSA so the idle is good, nice split-pattern profile, I made 270RWHP (around 320HP flywheel) out of a mild 302 with some ported GT40's with that camshaft. Ran the Crane/Cobra 1.7 radio roller rockers to add some more lift.

Car had a perfectly flat torque curve too, which made it a great driver.

For the intake the Weiand X-Celerator is a good choice unless you prefer a dual-plane. My cam grinder preferred the X-celerator, and we even ran a Victor Jr. on the last carb build my buddy and I did, but that was a 7,000RPM engine.

Carb choice, a vac sec Holley 650 is easy to setup.

Ignition, I'd go with the Duraspark dizzy with an MSD digital box or find a used Crane HI-6. I've used the latter on a couple of cars and it is FANTASTIC. The soft-limiter feature is beautiful and works extremely well.

You WILL need new valvesprings if you intend on retaining those heads. Trickflow will be able to tell you what to run with that cam if you go that route.

For exhaust, I'd do longtubes. Not sure what your budget is but stainless is nice. You want 2.5" collectors into an H or X-pipe. 1 5/8ths primaries should be more than big enough for those heads.

Also, don't forget the little stuff. A 3G alternator and electric fan conversion will make the engine more free-reving and is a cheap upgrade.

 

[userfriendly]

Would that Cougar have a 9" rear end?
What would be the gear ratio?

 

[TFB1]

Originally Posted By: NHGUY
The only good thing about the Ford 2 barrel is ease of servicing,otherwise they are about as "performance" as a 1 barrel.Notice why Ford went to MPI seemingly before anybody else did and the 302/351 went Holley 4 barrel in the 1980s.Shame they put that 2 barrel in engines from 221 V8s thru 390s/400s....
Yeah but are far from being same carbs, looks ain't everything...

The little 221 used a .98" throttle bore and size progressed upward dependent on engine size... Were also 1.08", 1.14", 1.21" & big a boy 1.33" used on 2bbl big blocks... At one time the 1.33 were in demand for some of the stock classes at the amateur roundy-round tracks, sold the only one I had probably 10 years ago...

Originally Posted By: used_0il
Would that Cougar have a 9" rear end?
What would be the gear ratio?

Everything with 351 & up got the 9" as did Hi-Po 289, Boss 302, etc... Full size models used 9" behind every engine, incl 6cyl till approx '67...

Ratio would have been something between 2.75 & 3.25 for a non performance engine...

 

[turtlevette]

Originally Posted By: tomcat
is there enough benefit to just switching the carb and intake first?


Yes the intake is really easy. Try and find a stock setup on eBay for cheap. I was able to get an 81 vette stock al intake for 25. A qj could be had for around the same.

The 2 to 4 barell swap will be the biggest step in HP. Headers and exhaust make things too loud for what it gains. And its all at the top end.

 

[Kruse]

Originally Posted By: Chris142
A 351w can't breath well.


The argument to your statement is....it depends.
The '69 and '70 351W heads breath okay. Back in the day, Hot Rod magazine took some '69 351W heads, dropped in some Chevy valves and made them comparable to some of the best Chevy small block heads from that era.
AFR, as well as some other aftermarket manufacturers make some very good, high flowing 351W replacement heads. That, along with some aftermarket cranks to bump the displacement to 393, 406, or even greater can really make the 351-blocked engine a real sleeper.
But the OP really didn't say what type of 351W heads he was going to install, did he? There truly are some 351W heads out there that are dogs.
BTW, I've got a '71 Cougar 351C/C6 with ~70K original miles.

 

[Merkava_4]

What works really good on those is a Holley 2bbl rejetted to 500 cfm.

 

[TFB1]

Originally Posted By: Merkava_4
What works really good on those is a Holley 2bbl rejetted to 500 cfm.

And just how does one re-jet a carb to a different CFM rating??

 

[Robenstein]

Originally Posted By: Merkava_4
What works really good on those is a Holley 2bbl rejetted to 500 cfm.


CFM refers to the amount of air it can flow, has nothing to do with the jets which control the fuel side of things.

If it DID refer to fuel, no one would ever make it out of the driveway before the tank ran dry.

 

[userfriendly]

One has to be careful who they take advice from these days.

 

[Merkava_4]

Originally Posted By: TFB1
And just how does one re-jet a carb to a different CFM rating??


- Change main jets from #57 to #65
- Change throttle bore size from 1.500'' to 1.750''
- Change venturi size from 1.187'' to 1.376''

 

[TFB1]

Originally Posted By: Merkava_4
Originally Posted By: TFB1
And just how does one re-jet a carb to a different CFM rating??


- Change main jets from #57 to #65
- Change throttle bore size from 1.500'' to 1.750''
- Change venturi size from 1.187'' to 1.376''


Assuming you've actually checked flow for the given dimensions fair enough, though the $$$ for machine work is going to be steep, no doubt better to buy another carb...

 

[Shannow]

Keep in mind that the CFM ratings between the Holley 2BBls and 4BBls are different, as they are done at different manifold depressions (3" Hg for the 2 barrels versus 1.5" Hg for the 4s)...so a 500CFM 2BBL if flowed on a bench with the 1.5" Hg of the 4 barrel should really only indicate 500*SQRT(1.5/3), or about 350CFM in 4BBL equivalent.

Go the 4BBL, vacuum secondaries.

(Although yours is a Ford, I've had QJets on Holden 253s before...yeah small V-8, and the small primaries are great, and the super large secondaries didn't affect driveability)

The 2BBLs did OK if I put an open spacer under them so that both planes had access to the full carb.

If swapping intake, you make as well do the cam at the same time...you've only got to take the intake off at cam time anyway.

 

[HangFire]

Originally Posted By: Merkava_4
Originally Posted By: TFB1
And just how does one re-jet a carb to a different CFM rating??


- Change main jets from #57 to #65
- Change throttle bore size from 1.500'' to 1.750''
- Change venturi size from 1.187'' to 1.376''


Uh, that's quite a bit more than a "re-jet"!

 

[Silverado12]

I would do a Carter AFB, Edelbrock intake, dual exhaust and leave the rest alone.

 

[tbm3fan]

Originally Posted By: tomcat27
I've got a 1970 Cougar with a stock 351W with a 2bbl carb. I'd like to eventually replace the heads, intake, carb, and cam. but, if I do this in phases (father/son project) is there enough benefit to just switching the carb and intake first?


You would be better off going to here:

http://www.mercurycougar.net/forums/forum.php?s=63d7337bcb54157b39d7db2e6b85b27a

 

[Garak]

Someday, I'll have to post some pictures of my F-150's 300 straight six conversion to a 4 barrel and dual exhaust. Some of those forums, such as the one tbm3fan mentioned, can be great resources.

 

[Trav]

Originally Posted By: Shannow
Keep in mind that the CFM ratings between the Holley 2BBls and 4BBls are different, as they are done at different manifold depressions (3" Hg for the 2 barrels versus 1.5" Hg for the 4s)...so a 500CFM 2BBL if flowed on a bench with the 1.5" Hg of the 4 barrel should really only indicate 500*SQRT(1.5/3), or about 350CFM in 4BBL equivalent.

Go the 4BBL, vacuum secondaries.

(Although yours is a Ford, I've had QJets on Holden 253s before...yeah small V-8, and the small primaries are great, and the super large secondaries didn't affect driveability)

The 2BBLs did OK if I put an open spacer under them so that both planes had access to the full carb.

If swapping intake, you make as well do the cam at the same time...you've only got to take the intake off at cam time anyway.


The Qjet was always my favorite 4bbl carb, the Holly IMO was way overrated for street engines. I had one on a big nail head Buick and it couldn't touch the Qjet for fuel economy and power when it needed it.

Course with big carb you need to get the air/fuel mix and and the exhaust gases out or its a waste of time.
I had a Ford 429 CJ that had factory Qjet on it and it ran well. I had another holley carb on a BBC that was quite good and efficient for its huge size, it was 3 bbl, that was a good one but long obsolete and scarce today.