2bbl to 4bbl
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
2bbl to 4bbl
Yeah Dude, Please do if you really can find any. 
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John
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In the cool still quiet of night, you can hear chevies rusting away.
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John
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In the cool still quiet of night, you can hear chevies rusting away.
Elder User
Joined: Aug 2001
Posts: 962
Likes: 2
From: Collierville, TN
2bbl to 4bbl
It is unlikely that the conversion will gain you any noticeable power. In fact, it'll probably hurt your low end torque and throttle response. The only improvement, if any at all, will likely come at 4000 rpm and above. I don't know about you, but I don't operate my truck much in that range.
All respect to DF, who knows his stuff as well as anyone here, there are two "tricky" parts to the conversion. First, those manifolds weigh a frickin ton. Getting your loose and off won't be fun, especially if you don't have a cherry picker. Getting the second one on and sealed properly -- especially at the back of the block -- can be a nightmare, too. Second, tuning that carb will be some work.
Good luck, but I think you're asking for several weeks worth of headaches, backaches and frustration just to end up with a motor that doesn't perform as well as the one you started with.
All respect to DF, who knows his stuff as well as anyone here, there are two "tricky" parts to the conversion. First, those manifolds weigh a frickin ton. Getting your loose and off won't be fun, especially if you don't have a cherry picker. Getting the second one on and sealed properly -- especially at the back of the block -- can be a nightmare, too. Second, tuning that carb will be some work.
Good luck, but I think you're asking for several weeks worth of headaches, backaches and frustration just to end up with a motor that doesn't perform as well as the one you started with.
Thread Starter
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Senior User
Joined: Feb 2002
Posts: 465
Likes: 0
2bbl to 4bbl
no performance increase? . Lifting those things (manifold)
is a bit akward but not all that tough. on performance
a 390 from a car w/2bbl has 265hp w/4bbl it has 300-325hp
so...
Fe power
is a bit akward but not all that tough. on performance
a 390 from a car w/2bbl has 265hp w/4bbl it has 300-325hp
so...
Fe power
Cargo Master
Joined: Jul 2000
Posts: 2,281
Likes: 18
From: Northern California
2bbl to 4bbl
The intakes are heavy, but just be careful and it's not a problem. It's really going to depend on the tuning of the carb, With smaller primaries and the ablility to custom tune the kick in point of the secondaries, you should be better off.
I don't know that carb off hand, but IF it doesn't have custom tunable vac secondary springs (like the Holley) then I'd give the holley a try.
Sealing the intake can be a trick, but I haven't had a problem. Just use a bit extra sealer and clean it REAL good, then use some carb cleaner to check for leaks when it's running.
Most FE's had 1 of two cast iron 4v intakes, the T and the S (found on the #1 runner behind the water neck) The S is for higher rpm and has different runners that don't go down like the T does.
If it doesn't give the power you want, you've only lost some gaskets and 2 days work, not a bad trade off.
I don't know that carb off hand, but IF it doesn't have custom tunable vac secondary springs (like the Holley) then I'd give the holley a try.
Sealing the intake can be a trick, but I haven't had a problem. Just use a bit extra sealer and clean it REAL good, then use some carb cleaner to check for leaks when it's running.
Most FE's had 1 of two cast iron 4v intakes, the T and the S (found on the #1 runner behind the water neck) The S is for higher rpm and has different runners that don't go down like the T does.
If it doesn't give the power you want, you've only lost some gaskets and 2 days work, not a bad trade off.
Elder User
Joined: Aug 2001
Posts: 962
Likes: 2
From: Collierville, TN
2bbl to 4bbl
>no performance increase? . Lifting those things (manifold)
>is a bit akward but not all that tough. on performance
>a 390 from a car w/2bbl has 265hp w/4bbl it has 300-325hp
>so...
>
The 2 and 4bbl 390s in cars were different in more ways than just the intake and manifold. The 4 bbl engines typically had higher compression ratios, which account for most of the power gain. More importantly, power is the product of torque and rpm. Torque is what is important, not power -- especially in a truck. Lots of HP don't mean squat if it doesn't occur in the rpm band you run your motor at. A bigger carb and more runner volume help the engine breathe at higher revs, but also slow down intake charge velocity at lower revs and depress throttle response.
Don't get me wrong -- if building a 390 from the ground up, you might as well go with a good 4 bbl manifold and carb (so long as they're not oversized). But if you have a 390 with a 2 bbl that is running well, I don't see the point in changing it to a 4 bbl.
>is a bit akward but not all that tough. on performance
>a 390 from a car w/2bbl has 265hp w/4bbl it has 300-325hp
>so...
>
The 2 and 4bbl 390s in cars were different in more ways than just the intake and manifold. The 4 bbl engines typically had higher compression ratios, which account for most of the power gain. More importantly, power is the product of torque and rpm. Torque is what is important, not power -- especially in a truck. Lots of HP don't mean squat if it doesn't occur in the rpm band you run your motor at. A bigger carb and more runner volume help the engine breathe at higher revs, but also slow down intake charge velocity at lower revs and depress throttle response.
Don't get me wrong -- if building a 390 from the ground up, you might as well go with a good 4 bbl manifold and carb (so long as they're not oversized). But if you have a 390 with a 2 bbl that is running well, I don't see the point in changing it to a 4 bbl.
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Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
2bbl to 4bbl
I am building a new 390 for my truck, and it is going back in with the 2 barrel and log manifolds. I have a S manifold and a 1406 Edelbrock but not in my truck. I think this engine will out perform the other truck with the 4 barrel and headers.
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John
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[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NCFTO] North Carolina Ford Truck Owners Group
In the cool still quiet of night, you can hear chevies rusting away.
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John
jowilker email me
[link:www.ford-trucks.com/users/jowilker|My Club FTE Page] Member since 01 01
[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NCFTO] North Carolina Ford Truck Owners Group
In the cool still quiet of night, you can hear chevies rusting away.
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Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
2bbl to 4bbl
Barry, Do you want me to time mine from one gas pump to the next?
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John
jowilker email me
[link:www.ford-trucks.com/users/jowilker|My Club FTE Page] Member since 01 01
[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NCFTO] North Carolina Ford Truck Owners Group
In the cool still quiet of night, you can hear chevies rusting away.
http://www.clubfte.com/users/jowilker/USFlag.gif
John
jowilker email me
[link:www.ford-trucks.com/users/jowilker|My Club FTE Page] Member since 01 01
[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NCFTO] North Carolina Ford Truck Owners Group
In the cool still quiet of night, you can hear chevies rusting away.
New User
Joined: May 2002
Posts: 1
Likes: 0
From: Memphis U.S.A.
2bbl to 4bbl
>the improvement will be posted,it has dual 2-1/4" dual
>4 foot straight pipes w/glass so the flow will definitly
>go up.I hope...
>
>
>
>Fe power
The question of power from 4b over 2b carbs is more than compression ratios. You will see improved power at higher rpms as stated above, but he key to getting the most out of the swap is changing cam and lifters. A cam with lift and duration (Lift is the amount of opening of the valve and duration is the length of time it remains open) is the key to utilizing the extra fuel mixture. I say go ahead anyway, just keep this in mind for future upgrades.
Hunter34
>4 foot straight pipes w/glass so the flow will definitly
>go up.I hope...
>
>
>
>Fe power
The question of power from 4b over 2b carbs is more than compression ratios. You will see improved power at higher rpms as stated above, but he key to getting the most out of the swap is changing cam and lifters. A cam with lift and duration (Lift is the amount of opening of the valve and duration is the length of time it remains open) is the key to utilizing the extra fuel mixture. I say go ahead anyway, just keep this in mind for future upgrades.
Hunter34
Elder User
Joined: Aug 2001
Posts: 962
Likes: 2
From: Collierville, TN
2bbl to 4bbl
Scott, you are absolutely right that a bigger/hotter cam (more lift and duration) is required to take advantage of a larger manifold and carb, and the combination of the right cam and induction will generate a lot more power. Again, though, the intended use is critical. A long duration cam will allow more air and fuel into the cylinders, which in turn will generate more power, but it also means lower cylinder pressures and, accordingly, less torque. That's why long duration cams typically don't start making serious power until much higher in the rpm band. It's also why longer duration cams typically make poor choices for trucks. Trucks are heavy vehicles that need a fair amount of twist just to get moving, and they are often used for towing or hauling heavy loads. A truck motor that has to be spun up to 4000 rpm to get it into the power band is a bad idea. That's why I'm using a fairly moderate dual pattern cam in my current rebuild, and wouldn't recommend anything more radical for a truck motor.
Post Fiend
Joined: Feb 2001
Posts: 6,624
Likes: 8
From: Missouri
2bbl to 4bbl
My friend at work went from a 2 bbl to an Scode intake and a 600cfm edelbrock. He said there was a more than noticeable improvement in low RPM response and had more top end improvement. His '70 truck is completely stock except for that.
Elder User
Joined: Aug 2001
Posts: 962
Likes: 2
From: Collierville, TN
2bbl to 4bbl
That's quite possible, rs, especially if the 2 bbl he replaced wasn't tuned well. A poorly tuned or oversized 2 bbl carb will easily be outperformed even at low revs by a new moderately sized 4 bbl. I think most of the guys who swear that a 4 bbl did wonders for them would have seen 95% of the improvement just by rebuilding and tuning their existing 2 bbl carbs.