300 with a 2bbl
Senior User
Joined: Apr 2003
Posts: 103
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From: Citrus County, Florida
300 with a 2bbl
Ideally a good set of headers would be the best but you can pick up a set of used EFI manifols and a Y pipe for less than half the cost of the header and you still would have to have the rest of the exhaust upgrade to match the header. I used the EFI manifolds and Y pipe and just cut the Y pipe right before the cat(junkyard wanted an extra$30 for the cat) and put on a reducer and it hooked right up and sounds great!
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Senior User
Joined: Jul 2003
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From: North of Toronto, Ontario
300 with a 2bbl
From the information that I've gotten from other users on this site, unless you plan on putting a cam in your truck, you won't see any real advantage of a header over the split manifolds. These manifolds are similar to a shorty header design, and will flow all the exhaust gasses that you are gonna make with a stock cam.
Post Fiend
Joined: Jun 2003
Posts: 8,209
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From: Black Hills of SD
300 with a 2bbl
I would think the 2 bbl adaptor will give better results on a newer truck. Some time between 76 and 79 the carb got bigger. I tried putting a 76 manifold on a 79 and found the hole and the bolt spacing to be considerably larger on the 79. I would think a 2 bbl. from a 289-302 would work ok since they are roughly the same size engine although you are restricting it some. You might also try opening up the hole in the manifold with a die grinder for a little better airflow.
Postmaster
Joined: Feb 2003
Posts: 3,441
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From: Muskegon, MI (home)
300 with a 2bbl
My 300 has been bored .040 over and it has a mild cam. It's mainly set up for torque, being it's in a 4wd truck. I frequently use the truck off road and tow with it occasionally also, so low end torque is most important to me. I am running 2.5 inch pipes into a Flowmaster 40 with 2.25 duals out the back, with no cats. So do you think the EFIs will help put out what I am looking for? I already ordered the 2 bbl adapter as well. Also before I forget, do you think the 2bbl on my 351m will be too much for my six? I am concidering just bolting it on, because my 77 will not be on the road for a while. Thanx!
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Senior User
Joined: Jul 2003
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From: North of Toronto, Ontario
300 with a 2bbl
Go for the 351M carb. Everybody says that the ideal 4bbl for this engine is a 390CFM Holly, but many people seem to bolt on 500's. If a 500 CFM 4bbl doesn't bog down and choke this engine, I don't think that your 351M carb will either.
I saw a 351M carb on a 79 F250 the other day, and it didn't look much bigger than the 302 2bbl.
I saw a 351M carb on a 79 F250 the other day, and it didn't look much bigger than the 302 2bbl.
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Joined: Apr 2003
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From: Citrus County, Florida
300 with a 2bbl
The difference between a 500 cfm 4 barrel and a stock 500 cfm 2 barrel off of a 351 big block is that when using the 4 you are idling and cruising with half of the carb and you can rejet the Holley to match your application (vehicle weight, tranny type,useage). With the 2 barrel you are stuck running the 500 cfm at all times hence giving you poor idle and part throttle performance due to the smaller air velocity from the 300 CI six. Also whenever you add height (spacers,adapters) to your carb you lose fuel atomization causing a LOSS in low end torque( think about a tunnel ram intake versus the low dual plane types). The only gain from a switch to a 500cfm 2 barrel from the stock 1 barrel might be in your upper rpm power and not where we need it the most with the big six.
Post Fiend
Joined: Jun 2003
Posts: 8,209
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From: Black Hills of SD
300 with a 2bbl
All that is good sounding theory and I even once cosidered using a small cfm spread bore just for that reason. A lot of other things also come into the muddle. Like the change in path of the airflow and some things that basic theory don't deal with. If you back up the thread a ways you will find a subscriber who put a 500 holly 2 bbl. on an adapter plate with pleasing results on all fronts. It would be interesting to compare the area of the openings in the manifold and carbs to see how much difference there is. Only so much air can get through and if you have your fuel jetted to that amount then you might just not have much of a problem. The 4bbl. should in theory work better than 2 bbl. of equal size due to port velocities ect. but those old motorcraft 2 bbl.s did get some great gas mileage on the 289-302s.
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Senior User
Joined: Jul 2003
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From: North of Toronto, Ontario
300 with a 2bbl
On the old carbed 6's, that 1bbl is as restrictive to air going in as the stock manifold is to air going out. I can't help but think that a larger onening would mean more air in, resulting in more power. There are a few people that claim that they DID experience more power with the 2bbl.
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Postmaster
Joined: Feb 2003
Posts: 3,441
Likes: 5
From: Muskegon, MI (home)
300 with a 2bbl
Well I have 3 stock 2bbl carbs. off a 302-not sure about working condition, 400-also not sure, and a 351m which I know runs. I will probably use the other 2 carbs to build one good 2 bbl. Thanx!
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
300 with a 2bbl
It is a question of balance. The smaller openings will give more low end while more airflow is needed to make more power and higher revs. I have, however went to more carburation and got noticable results right off idle.
One time I installed a stock rebuild 350 in a 66 chev c/10. The owner wanted to use the stock 2 bbl/ intake and carb off the original 283. It ran real nice, up to about 32-3500 rpm and then just started to flatten out real bad. It also got kindof poor mileage. A classic example of a mismatch.
This is why so many of the aftermarket people now offer package deals, so you will get a cam, intake and carb that are proven to work good together.
One time I installed a stock rebuild 350 in a 66 chev c/10. The owner wanted to use the stock 2 bbl/ intake and carb off the original 283. It ran real nice, up to about 32-3500 rpm and then just started to flatten out real bad. It also got kindof poor mileage. A classic example of a mismatch.
This is why so many of the aftermarket people now offer package deals, so you will get a cam, intake and carb that are proven to work good together.
Junior User
Joined: Aug 2002
Posts: 67
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From: Irvine
300 with a 2bbl
I say forget this 2 and 4 bbl nonsense. I have a 240 and I put a Rochester BV on it (smaller carb than the carter YF). The Rochester gave me a noticiable low end torque increase. These engines were optimised by Ford for low range torque; why not exentuate the positive and modify/tune for low end torque? Bump up the compression, get a smaller carb, increase fuel atomozation, Increase cam lift slightly and leave the duration alone, advance spark timing, advance cam timing, get overdrive/aux transmissions, switch ring and pinion ratios according to your driving style. Sorry so long; just thought I might suggest something a little different.
Thanks
Thanks
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
300 with a 2bbl
My 68 F-250 is a 240 C4. with a 4:10 gear. It runs perfect and has plenty of power but gets horrible mileage, like maybe 10 at best. It will run 70 but is starting to complain a little after 65 so I don't like to take it on the interstate. Alot of our secondary roads here in East Texas are also posted at 70 and if you can't run with the big dogs you are considered a menace and get ran over. I have towed my 16 ft. car hauler with about 1000# load effortlessly with her though. ( I stayed on the service road since it has non-power drums and no trailer brake provision )
Senior User
Joined: Jan 2002
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300 with a 2bbl
I don't know about the technical flow characteristics of the one brl manifold with a two brl carb attached via an adaptor but I do know that there is a big difference, in my case, between the stock 1 brl and my Holley 500 2 brl. My power gain is noticeable and the engine runs, starts easier. I would have thought that a 500 2 brl would cause me to run very rich especially at low rpms, idle etc... but my plugs look excellent and my exhaust smells as good as carbon monoxide can smell. I am guessing that a 4 brl might do even better due to not running 500 cfm ALL the time but right now I am too satisfied to buy a 4 brl and swap intakes. I don't think I will ever be as happy with this 6 banger as I was with a mildly warmed up 360 in my '73 high-boy but it works for now.
Postmaster
Joined: Feb 2003
Posts: 3,441
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From: Muskegon, MI (home)
300 with a 2bbl
I am going to run the 2bbl with an adapter, but will keep my 1bbl carb if I decide to switch back. Currently the 1bbl runs flawlessly, I just want a little more under the pedal for when I need it.