I have been considering adding a 4-barrel Offenhauser intake and 390 Cfm holley to my Duster. Will this be too much carb for a bone stock 225 slant? Which would work better, adding a super six or going 4-barrel? And by the way, how much does the front casting of a Dutra Dual cost? Where do I order them? I can make my own rear section of the manifold. I have lots of slant manifolds lying around.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Which carb is best for you depends what you are trying to get out of your upgrade. Installing the super six package is easier than installing the 4bbl option but will make a bit less power. You will probably have to do some jetting to get the best performance from a 4bbl carb. Since the Holley 390 CFM carb has vacuum secondaries, most of the time you will be using the primary barrels (195 CFM) and these have about the same flow as the Carter BBD (202 CFM). Only when you need the extra airflow will the secondaries open. If you rarely put the pedal to the metal, you wouldn't really notice the difference between the two carbs. The extra airflow of the 4bbl carb will allow you to pack more air molecules into the cylinders.

I'm not sure what is the flow rating of the dual Weber carbs that Proline has for sale but they seem to work great with stock engines. Those Weber carbs aren't staged so when you floor it, all the barrels (a total of 4) are open. I'm now using a 750 CFM Rochester Quadrajet with primary flow rating of 161 CFM. My engine is only mildly modified and runs great with this setup.

You have a lot of carburetion options available for your and it pretty boils down to how much do you want to spend and how you want your engine to look when you pop the hood. All will work fine once you get them set up properly. Obviously, the BBD would be the easiest to set up because it was a factory installation.

As for the Dutra Duals, send an email to Doug Dutra. As he is a regular poster here, you should be able to find him easily. Information about the manifolds can be found here:

http://www.dutra.org/doug/doug-sl6-exha ... -duals.htm

Frank Raso
Raso Enterprises

Yes.

D/W

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If it ain't broke, fix it!

I have heard that the sixties cams were more agressive and put out more power that 70's cams. Is this true, and will swapping a 60's cam into my motor enable me to add a 4-barrel?

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

I have a '64 Dart. I put an Offy intake with an Edelbrock 500 on. It was too much carb.
I did a new valve job and do-it-yourself port, and milled the head .060 with a Comp 252 cam, new chain and gears.

It's much better now.

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"Nothing in all creation is hidden from God's sight. Everything is uncovered and laid bare before the eyes of Him to whom we must give account."

I think I will go the super six route. If I find a complete Super six setup, linkages and everything, can I just perform the linkage/manifold swap and rebuild my carb and go? Will I have to change anything such as metering rods and such. Is the BBD an easy carb to rebuild. I have rebuilt two carbs before and they both ran like crap afterwards. How are remanufactured carbs when it comes to quality. I have heard that sometimes they come setup wrong for engine.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Sixty4dartgt, when you say that the Edelbrock 500 CFM was too much carb, what do you mean? What were the symptoms?

A few more questions:
* Were you also running headers with the Offy intake & Edelbrock carb?
* Did you make any changes to the metering rods and jets that came with the carb?

Frank

I think a 390 4bbl w/ vac secondaries should work very well on a stock Slant. You may have to adjust the secondary opening (spring kit) and jets and such, but it would work well.

Lou

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Home of Slant6-powered fun machines since 1988

Just the opposite for the run of the mill production cams.
The Slant Six Racing Manual (in the articles section of this site)
claims the best production cam to be the 71-77 grind. So
if you have a 60-70 slant you cam get a mild upgrade by getting a
71-77 cam.

I ran an Offy/390 combo on my Valiant last year with a stock '80 Volare motor. It actually ran really well. With a 3000 stall and 3.91 gears the car ran 16:20@80 mph, about a second faster than it should have.

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Official Cookie and Mater Tormentor.

Frank,
After reading the other post on tuning the carb with rods and jets, maybe I was wrong. But it was dead till about 3500 rpms when the motor was stock. The secondaries almost never opened and I was getting 10 MPG.
I admit that the head was in need of new valves and my chain was quite stretched, and my attempt to tune it was way off (I went lean instead of rich, figuring it was too much carb).
I will say also that some people on this forum said it would be too much w/o a new cam and head work. I put it on anyway, knowing I would do the additional work. It WAS an improvement to stock, but not as much as I thought. There is a noticable difference now.
And yes I have headers with dual 2" exhaust.
If I put Jeb off track, please set him straight.

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"Nothing in all creation is hidden from God's sight. Everything is uncovered and laid bare before the eyes of Him to whom we must give account."

That's pretty impressive. I bet the 3000 rpm stall and the 3.91 had a lot to do with being able to "use" that carb, don't you?

D/W

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If it ain't broke, fix it!

Yes, but with a stcok converter and gears a Slant will still work well with an Offy and 390 Holley. The one problem I did have with the Offy even on my good motor was when it got below 45* it would foul the #1 and 6 plugs. That was with stock Mopar Performance electronic ignition. I put an MSD box on and the problem went away. I even drove the car to work last winter when it was -7* with no choke and an open hood scoop.

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Official Cookie and Mater Tormentor.

Slantzilla, I couldn't help but notice that our cars have similar trap speeds in the 1/4 mile. I haven't spent a lot of time at the drag strip but the few times I did go several years ago, I got a best time of 17.078s @ 81.96 mph. Most of the runs I had that day were in the 17.1s to 17.3s range with a trap speed of around 80mph. I had a bit of a bog when I took off but the car really picked up (and still does) speed as the RPMs increased.

It seems to me I would be able to break into the high 16's with some improvement to my carb tuning. Mine is a highway cruising car so I'm planning to keep my stock gears. I shift around 5000 RPM, BTW.

Is it possible that something is holding your car back from getting a higher trap speed and possibly a lower time?

Does anyone have any experience with 1/4 mile times and trap speeds?

Frank

High numeric gear = lower trap speed.

D/W

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If it ain't broke, fix it!