Carburetors...

[lsrjunkie]

Just fishing around for input. Things are progressing nicely on my project, and I'm trying to decide what I will be running for a carb. I am leaning toward a Holley style mechanical four barrel, such as a Mighty Demon, Quick Fuel, or a Pro Form. What have you guys run and what do you like the best?

[Harold Bettes]

Please consider that all carburetors are merely organized leaks and as such, it is up to the individual using them to make sure the things work correctly. The result is not brand loyal nor type dependent. The higher the density altitude, the more importance is the circuit that controls droplet size.

Everybody that has a set of screwdrivers and a numbers drill set (including miniatures) does not a carburetor tuner make.  8-)

If you can get on a dyno over there in Grand Junction, you might be surprised how close to Bonneville conditions you might get during the tuning process.

Regards,
HB2

[Leadfoot]

Holley Dominator works for me.

[kiwi belly tank]

The fact you are asking for input on carbs tells me you are not a carb guy & like Harrold just said, they are only as good as the tuner. I have no idea of what you're building but if you can run a self learning TBI, do it.
  Sid.
 

[fordboy628]

What is it going on?

[Milwaukee Midget]

I'm only somewhat familiar with the Holley offerings, but what I would be looking for is the choice that gave me the quickest and easiest route to rejetting and adjustment. 

We were fortunate, in that we used a Weber, and Mark had a boatload of jets and emulsion tubes at his disposal.  During dyno work, we were able to rejet and test in less than 5 minutes between pulls.  It's my understanding that turnaround on a Holley is somewhat s l o w e r than that.

At that point, anticipate what you're likely to see at Bonneville and limit the number of choices.  I want to say we saw adjusted air densities from 6000 to 7200 feet on any given day. 

I expect Harold is right - you should be able to get a pretty close dial in at 4500 feet.   

[lsrjunkie]

Sid, my carb experience has been limited to mostly daily driver applications and a few warmed over hot rods. I'd love to run any type of EFI, but my understanding is that class rules won't allow it. My biggest concern will be ease of tuning, hence my leaning towards the Holley type of carb. In my experience any adjustments on that style of carb aren't terribly tough with the carb installed. FYI, I plan on running XO/GCC.

Fordboy, I am building a 320" GMC six cylinder. Stock cylinder head with some port work, and a plenum type intake.

There's a couple of pictures, http://www.landracing.com/forum/index.php/topic,12252.330.html towards the bottom of the page.

MM, I agree 100% Tuning the carb in the shop or on the dyno is one thing, but I want the same ease of tuning on the salt.

[fordboy628]

Fordboy, I am building a 320" GMC six cylinder. Stock cylinder head with some port work, and a plenum type intake.

There's a couple of pictures, http://www.landracing.com/forum/index.php/topic,12252.330.html towards the bottom of the page.

There are more knowledgeable carburetor guys on the board, than I am.    Especially for modified Holley stuff.    But having said that, some advice:

A)    If you are going to dyno test, weld small 1/8th NPT bungs in the top of your intake runners.    Being able to record vacuum during "pulls, (even 1 tap at a time) may prove "insightful".     BTW, do not presume 3 separate vacuum gauges will read identically, if you go that route.    Pay to have any you use, calibrated.

2)    Choose your carb size based on measured flow of the carb, Vs theoretical engine air capacity * x % Volumetric efficiency, in the rpm range you intend to use.   This will give you a low/high number to select a carb.    You will need someone experienced with your engine to suggest a probable V/E %.   Or, you will need to flow the whole inlet tract, and then run a computer simulation based on the flow/displacement/geometry.

d)    If you don't know how to do the above, BUY & READ "Performance Automotive Engine Math" by J Baechtel.    Also BUY & READ "Engine Airflow" by Harold Bettes.

HB2 or Dynoroom may be able to recommend a carb size from their experience.    But be prepared to do the math on your own anyway.     That way you learn something.

Fordboy

[lsrjunkie]

Fordboy, As always you have the information inquiring minds want to know. Thank you very much! You're recommended reading has been purchased and is en route. Here's to hoping I can learn a little about this whole going fast business. 

[1leg]

Stick with the traditional Holley in the race models. The proform and quickfuel are made in china and seem to have out of the box performance issues. Would be a good idea to check out the offering of some carburetor shops that work on NHRA stock and super stock car carbs they also hot rod the holley carbs.

[wobblywalrus]

Vizard wrote a book on tuning Holley carbs.  It is in print.  I saw a new one on the book shelf a few days ago at Barnes and Noble here in Oregon.   

[lsrjunkie]

Thanks 1leg, That's good information to know.

WW, I'll keep an eye out for that book. I'm all about learning something new. Thanks for the tip.

[WOODY@DDLLC]

Amazon or http://www.cartechbooks.com/david-vizard-s-how-to-super-tune-modify-holley-carburetors.html

[Leadfoot]

Call Patrick at Pro Systems Carburetors.

[Stan Back]

Well, hope I don't step on my . . . , whatever here.  I believe you can run a self-adjusting throttle body f.i. in XO/CC.  You're not running Classic, as there are no Classic Comp Coupes.  You're not running Vintage -- as you've stated.  Maybe DW will confirm this for you (us).