I'm Gonna Build A Dragster!

I put the original converter back in and it is 95% done. Waiting for 3" wheel studs and converter bolts. I ordered the Dutchman axles with 2" studs and now I've changed to aluminum wheels and they're too short.
I received the lower half of an EFI intake manifold from Old28 (thank you Tom). I'll build a plenum on it and add 2 Autolite two barrels . This will replace the single Holley four barrel later this summer.

Glad the dragster is getting back together. Those 3" axel studs will help keep NHRA Tech happy.[cl

Remember on the plenum build, lots of pictures to keep your followers happy. [P

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Got the 3" axle studs in and the slicks back on.
Started on the dual carb intake plenum. It is made from 14 ga. sheet metal and bolted to the aluminum base from an EFI unit. The top will be aluminum plate.

Don't build too much volume into the plenum. It'll make it lazy.

Will (can) having a low area in the bottom of the plenum box cause any issues. Seems like it could be a place for fuel to puddle. I know it is supposed to be vaporized in there, but...



NOTE: I know nothing of plenum building. Seeking enlightenment.

Race motors can handle 50% or more plenum volume than a street motor. With a 3500 leave RPM and 5500 finish line RPM motor never has a chance to get lazy.

My two cents only.

Thanks old28
I appreciate the info
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I made the plenum 300 cu. in., the same as the engine. Supposed to work good with a street/strip engine. I can add a spacer under the top plate to increase volume if needed. Added the end plates and the mounting flange for the top plate today. Also drilled and tapped the perimeter bolt holes. Will probably add an internal diagonal strip (as seen in one of the pics) to reduce liquid gas pooling. I share that concern with Skip.

Ok Bob I changed my mind, I would like my EFI tubes back and you can leave the plenum, I'll deal with it. You might just as well send the two 2100 1.14 carbs also.

Just kidding, make a few test passes to see how it works before
you send it off.

That is one real nice looking plenum and the EFI lower tubes make a good building platform. I think the top plate spacer idea is right on.[cl


Old Iron, Just another 2 cents from this old brain. A good rule of thumb for street motor 240 / 300 big block Ford L6 is plenum volume equal to cubic inches. On a race motor it may be 50-75% more volume depending on what parts are in the motor and how much air/fuel it can handle.


Sorry Bob for messing up your thread.

That's some good stuff there bobw, looking forward to seeing
how it works out....[cl[cl

bob w said:

I made the plenum 300 cu. in., the same as the engine. Supposed to work good with a street/strip engine. I can add a spacer under the top plate to increase volume if needed. Added the end plates and the mounting flange for the top plate today. Also drilled and tapped the perimeter bolt holes. Will probably add an internal diagonal strip (as seen in one of the pics) to reduce liquid gas pooling. I share that concern with Skip.

Click to expand...

Ford Autolite CFM by venturi diameter @ 3"Hg.

0.98 = 190 CFM
1.01 = 240 CFM
1.02 = 245 CFM
1.08 = 287 CFM
1.14 = 300 CFM
1.21 = 351 CFM
1.23 = 356 CFM
1.33 = 424 CFM

Remember that four barrels are flowed at 1.5 "hg.

So these flow numbers do not equate to 4V flow.

To convert divide by 1.41.


you may want to rethink this and make it a treesome of 1.14's

600cfm 2bbl / 1.41 = 425.5cfm 4bbl

900cfm 2bbl / 1.41 = 638.3cfm 4bbl

if I remember correctly you had a 750cfm 4bbl on there

and it worked pretty darn good.

Also because I am super paranoid about bolts inside of an intake system,

it would help me sleep better if Iknew you were planning to safety wire

those bolts inside the plenum, or better yet since they go all the way

through the aluminum base, you could put metal pinch type lock nuts

on the bottom side. that way if they should come loose, they would not

aerate one or more pistons.

aerate lawn = good. aerate piston= BAD.

Looking really "HOT DAMN". Keep at it!!!

BlueNorther, Lots of good information there. I didn't know the conversion for CFM from 2bbl to 4bbl. I already made the top plate for two carbs based on advice from a long time 300 Ford 6 racer. I put a tattletale on the secondaries on the 750 Holley and they open about 5/8. So not utilizing the full 750CFM.
Those internal bolts in the plenum are through bolts and will have lock nuts, not nylocks to secure them. Probably will use allen button heads for a bit of streamlining.
Do you have a recommendation for the radius on the runner holes in the bottom of the plenum? Same question to you old28 (Tom).
The spacer in the pics is from the slant 6 manifold I made. Will have to make a couple so the carb linkage clears. Consideering making them out of wood.

BlueNorther said:

Also because I am super paranoid about bolts inside of an intake system,

it would help me sleep better if Iknew you were planning to safety wire

those bolts inside the plenum, or better yet since they go all the way

through the aluminum base, you could put metal pinch type lock nuts

on the bottom side. that way if they should come loose, they would not

aerate one or more pistons.

aerate lawn = good. aerate piston= BAD.

Looking really "HOT DAMN". Keep at it!!!

Click to expand...

I had the same thought. I would tack those bolts in and then put a small plate or tab over them and tack that on as well, so none of it can go anywhere. That's just my thinking.

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bobw -- keep in mind what FRENCHTOWNFLYER told me and I passed on to you. Three 2100 on a race motor is a major headache in trying to get all three working together. Easier to tune a dual carb setup on a race motor that uses straight linkage. His words of wisdom to me was if you need more CFM get two bigger 2100 carbs.


I ran two Autolite 1.08 on a plenum with my Chevy 292 L6 drag race motor that had more cam & CR than your current motor. I really think the dual 1.14 carbs will work out fine on your mildly wormed over 300. You can upgrade to a pair of 1.21 or 1.23 if you do a cam change later on.


As for the radius on the runner holes in the bottom of the plenum I really did not put a lot of thought into it. I just made sure there was a nice smooth tapper. My feeling was that the plenum with the intake tubes was so much better in air & fuel flow over a 4V intake that it would not matter. Because your bottom is on an angle just make sure it will not puddle on the low side.


Not trying to jerk anyone around, just some vintage L6 drag race experience.

Post on. I'm here for the educational opportunities [cl
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Old Iron said:

Post on. I'm here for the educational opportunities [cl
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Click to expand...

Oi, I could learn more from you about fabrication than you could ever learn from me, about anything.

OK I understand the simple is better concept, but I always preferred more cfm than was typically arrived at by so called "formulas" which are based on the lowest rpm that would be seen at full throttle. on my sbc 338ci in a 3200 pound car I ran a worked over 3310 that flowed north of 900cfm, and it ran 11.6 at 121mph very consistantly.

on that straight 6 i would prefer 3 300cfm 2bbls which would be equal to 638cfm 4bbl.

and remember that a 300ci 6cyl moves 33% more air flow than a 300ci v8 per cylinder stroke. that 300 6cyl has a cylinder size of a 400ci v8.

Now, about the wood spacers, a lot of them are used in all forms of racing, to insulate the carbs from the heat of the engine, mostly on closed engine compartments, on an open air motor I don't think they make a ton of difference, but they can't hurt.

I would shoot for a 1/4" radius on the entry to each runner, same thing on the bottom of side of the carb outlet holes.

also those carbs along with holleys do not like side ways air flow across the tops of the venturies, they like straight down air flow, a forward open scoop covering both carbs, with a 4 to 6 inch tall, funnel shaped air horn for each carb, will do a lot to make them easier to tune.

also machine off the choke horns flush with the top of air filter gasket flange, leaving the inner gasket vertical wall intact as a guide to hold the scoop in place, and leave the part of the choke horn where the center stud to hold an air cleaner on stays intact, then with a die grinder clean up the inside of the remaining base of the horn to a 1/4" to 3/8" radius, no sharp edges there.

my 2 cents.

Some good information & I built an air scoop open in front about like BlueNorther talked about.

I ran dual Autolite 1.08 on a plenum intake much like bobw has been building for my 1450# vintage dragster with a L6 292 (bored to 310"). Dual 1.08 worked out to 574 cfm (407 V8 cfm). This motor had a big solid cam & 1.7 rockers. The dual 1.08's pushed the dragster to a best of 10.37 @ 131 and was still pulling through the lights, never ran out of carbs.

As I understand bobw is not wanting to run the motor on kill and is just looking to get the dragster into the 10.75 - 10.99 range. I really feel like the dual 1.14 on the EFI plenum will put the dragster in that range, might be wrong, but some all out passes will tell the story.[cl