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4 Barrell Conversion

dvalentine

dvalentine

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I have a 70's era 307 in my 64 C10. I know little about the moter but I suspect, except for a HEI distributer, its' stock.
The truck originally had a 283. When the 307 was installed they used all parts they could scanvage, like water pump and intake manifold from the old motor.

I suspect it's the original 2 barrell and intake on it now.
I'm wondering what would be the impact on milage and performance if I switched to a 4 barrell. (?) General numbers please.

Thanks!
 
Howdy:

I've done this conversion many times with good results. Look for a divided plenum low rise intake manifold at a swap meet. You can usually find one for $50-60, if you look around. Watch for welds and make sure the bolt holes are not stripped out. Also check for milling on the head surfaces, you don't want a manifold that's been milled.

What you are looking for is a square flange manifold, not a spread bore manifold with different size holes in the rear. A square flange manifold will accept new aftermarket carbs made by E-br**k and H***ley. I would especially recommend a 600 cfm E-b**k carb for your application. You will get better gas mileage because the primary venturis on a 4-bbl are smaller than the venturis on a 2-bbl. Use a vaccume gauge to tune it. Performance will also be a pleasant surprise.
 
Thanks Junkman. I had my suspisions about a milage improvement.
Craig, What Happened? Got shy on us ?
 
Mr. Valentine:

To follow up, you should see about a 2-3 mpg improvement, on a 1966 Impala with a 283, I was getting 19 mpg on the highway consistently (3.36 rear end). The Impala weighs over two tons, and is comparable to a truck in weight. But of course, if you drive a full size pickup, gas mileage is really not your primary concern anyways? Save your Rochester 2 barrel and take it to a swap meet, maybe you can get a few bucks for it if it's in good shape. Most common problem besides accelerator pump piston wearing is leakage around throttle body where shaft goes thru. If you see gas dripping around the shaft & throttle linkage, you will experience poor idle and vaccume, which will cut down on your mileage as well.

Be patient with Craig, he undoubtedly has many irons in the fire.
 
I'm here-Dennis,you will actually see a decent improvement in gas mileage .The two barrel is a old design,when swapping out for a four barrel,I would recommend a modern Edelbrock Quadra-Jet or something similiar.We have come along way in carb technology.You might check Ebay for a good cheap intake.The four barrel carb will have two side idle mixture screws,fine tuning your idle mixture will be simple when you switch.The throttle response will also be crisper,and you will get more power,(thats what we all what).
Craig Hager
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Craig ! There you are ! If you remember mine is a 64 panel. Gas milage is in the 6 to 9 MPG range (!) and is not going to cut it. I have other contributing factors to the problem like 3.70 rear end and Granny 4 speed. The trans is comming out shortly for a 700R4. My thinking was it would be easier to adapt the trans to carb linkage with a modern 4 barrel. Loads of aftermarket adapters for the conversion from folks at Lokar, etc.
I just missed a Edlebrock carb, intake etc on e-bay that went for $100 under retail. (dang!)
Thanks !
 
You will pick up a couple of miles when you do the tranny swap.The 700r4 is great for highway use.It still would be great if you could switch rear-end gears,but the tranny will be a big drop in rpm's.It should drop about 900 to 1000 rpms at 60 mph.You are correct in your thinking about the four barrel carb,it will be much easier to do if you have a four barrel.Lokar makes some nice(pricey)stuff.High quality and easy to use.Let me know if you don't find any carbs or intakes.I will see what I have.
Craig Hager
[email protected]
 
[font size=1" color="#FF0000]LAST EDITED ON Aug-31-00 AT 12:07 PM (CST)[/font][p]One important thing to keep in mind about the 700R4 is that it really is not made to do any pulling or towing in 4th gear. Two people I work with have newer trucks, and both of them burned up the tranny towing boats or fifth wheels.

If you intend on using the truck to tow anything, a much better way to go would be with a turbo 400. If you are not towing anything, a turbo 350 with a 3.08 rear end gear swap may be the way to go if you want to replace the manual transmission. Why not just change the rear end gear and keep the 4-speed? Would be less expense and hassle. If you want better gas mileage, a manual trans gets better mileage, and is more durable. (easier to change a clutch disc vs. rebuilding the automatic)

My $0.02 worth
 
Junkman, "Preciate" the comments. I won't be towing anything and plan on crusing to swapmeets, rod runs etc. I WAS planning on the rear end at a 3.08 ratio. As for holding onto the 4 speed, It already has problems that are just a matter of time before they become terminal and I can't see droppin a load-o-money into a trans, ( and while I'm down there) clutch. Additionally, in my younger years I too would have kept the 4-speed, preferring to crunch gears rather than sit back and relax. In my new life as a somewhat older, and lazier, person I've become accostomed to gettin it rollin, turnin the tunes up and set the cruise control.
Just a matter of taste and life styles I guess. Thanks for the suggestions they are welcome.
 
The 700r4 is a reliable transmission.They had a bad rep years ago with people that didnt understand them.I personally know one that is a early model(the bad years)that has been rebuilt and withstands a 500 ft.lbs. small block.And it has done it for 75,000 miles.If you are going to tow a heavy load then go with the modern 4L80e(its a 400turbo with a overdrive).With today's good automatics the gas mileage difference is down to nothin.Also the reliablity of a new automatic vs. old manual transmission has greatly improved to where the old isn't so good anymore.
Craig Hager
[email protected]
 
How about going with a T56 six-speed manual?I have been wanting to swap one into something.Dennis you up for that project?Your funding it of course.Ha ha
Craig Hager
[email protected]
 
Craig , Since I'm funding it, well...... NO !
See my message from the 31st? I ain't gettin any younger Pal.
Last week was the 16th anniversary of my 35th birthday!
 
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