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Carb Selection

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    Posted: 24-March-2015 at 11:58AM
Since my last thread about the carb and intake went to being only about the intake, I figured I'd start a new thread.
 
I am looking to swap a aftermarket 4bbl carb on my 1972 400 soon.  I was thinking of running a Street Avenger 400, as this was the carb that Holley recommended.  Holley has aluminium and zinc carbs in this line.  Is there any advantage to running one over the other, besides weight and the shine?
 
I am open to any suggestions, advice or opinions of the carb.  I am basically looking for a street car, vacuum secondaries, that will work well on a stockish engine, but will also be tunable when I do the cam, heads and bump the compression later on when money allows for a full rebuild.
 
Thanks
 
 
Vince

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Post Options Post Options   Thanks (0) Thanks(0)   Quote OleDutchD Quote  Post ReplyReply Direct Link To This Post Posted: 27-March-2015 at 4:53AM
Carb preferences are like opinions and a**holes... everybody has one. That said....

The motor in our '72 is a 351W w/ TF heads, Comp Cam XE274, headers 3" exhaust... yadda, yadda, yadda. I've run Holleys on several motors, but the most satisfying experience with an out-of-the-box carb has been the unit I'm running, now. It's a QFT 735SS with vacuum secondaries and an electric choke. It runs crisp and clean and the wideband O2 tells me it's a damned sight better than the Holley 750DP that came off. Very happy with it. QFT's are aluminum. The SS and HR series carbs each have secondary metering blocks, 4-corner idle and are very tuneable. The SS are calibrated for a little more cam and the HR's are for more stock(ish) applications.

As for sizing, the formula on top is the one that's been trotted out for 40 years:

CID x RPM x V.E. / 3456 = CFM
400 x 5500 x .9 / 3456 = 573 cfm

THIS formula helps picking a carb with a lower pressure drop/higher performance:

CID x RPM x V.E. / 2820 = CFM
400 x 5500 x .9 / 2820 = 702 cfm

The VE (volumetric efficiency) varies depending on build, I just plugged in the .9 as a middle of the road starting point for comparison. You can see how the same engine, different application can have different size requirements.

Pretty sure you'll get plenty of feedback on this one....
Just an analog guy stuck in a digital world!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 27-March-2015 at 12:15PM
Thanks for the feedback.  I forgot to post Holley recommended the 670 SA carb, which I think should be sized alright for my car.  It also features secondary metering block, 4 corner idle and vacuum secondaries.
I have heard good things about quick fuel.  Are they not based on a Holley 4150 design?  What about the QF carbs is different from a Holley?  I was leaning toward Holley for the carb because I have a local dealer that's also a good carb tuner.  I'd definitely consider a QF if I could get one locally at a decent price.  The exchange rate to Canada is too poor right now to order from the USA.
 
Anyone have any opinion on Zinc vs Aluminum? 
Vince

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Post Options Post Options   Thanks (0) Thanks(0)   Quote OleDutchD Quote  Post ReplyReply Direct Link To This Post Posted: 27-March-2015 at 12:55PM
I won't say one brand is necessarily superior to the other. Holley has been around for decades. A proven product that works (or can be MADE to work). You need to Google various Holley products for reviews. It can be very enlightening. Holley offers zinc and aluminum carbs. Most of their metering blocks are cast with fixed bleeds. The higher end stuff is more tuneable with replaceable bleeds, etc,... but still cast blocks, for the most part. The shortcoming with castings being occasional porosity issues.
QFT's are exclusively aluminum and parts are interchangeable with Holley. Aluminum is lighter, obviously. It's also prone to corrosion from alcohol content in blended fuels. 90/10 blends are likely safe. E85? Don't know. I bought one, so we'll just wait and see if it becomes an issue in the long haul. QFT's use billet metering blocks in all but the lower end stuff, which nearly eliminates porosity, They're supremely tuneable, as well. All circuits are adjustable using screw in bleeds. Their throttle base plates are billet, as well, on all but the lower models. One key difference between the two, as it pertains to vacuum secondaries, is that the Holleys use springs in the diaphragm housing to adjust the opening rate, whereas the QFT's utilize a needle valve (no springs) in the housing to tailor the vacuum opening rate.
Just use your best judgment. If your tuner can work on a Holley, he can work on a QFT.

Good luck!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nomadlife Quote  Post ReplyReply Direct Link To This Post Posted: 08-April-2015 at 10:59AM
My answer has nothing to do with my knowledge but from when I was still DD'ing my 72 and was trying to decide what to do when I placed a Cleveland in it. I found myself talking with aN old timer (60's in the 90's). His opinion (he was a Ford man and had raced and run them) was if it was to be a race -drag- engine, then run the Holley, if you wanted a street motor that could wake up, then the stock 351C Ford 4 bbl carb was a great setup(Autolite 4300).
Marilyn - '72 Ranchero 500 - known her since I was born, and traveled across the states in her; first in the back, then as the driver. Under restoration (and a little modification)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 08-April-2015 at 1:20PM

I decided on the Street Avenger 670.  I looked at the QFT HR 680.  It looks very similar to the SA 670, but it does have screw in air bleeds and the vacuum secondary control without the springs.  It looks like the HR series carbs don't come with billet metering blocks or base plates.  The price difference is well over $100 for me up here in Canada, so those extra features aren't worth the price difference.  Too bad, the online US prices were pretty much the same, and if that were the case I probably would have went with the QFT.

I also decided on aluminum.  I figured it seems all the other "Holley" based carbs seem to be aluminum and I see no advantage to going with zinc.
 
Hopefully I will have the carb and intake soon and have the car on the road before the end of the month (once the streets have been cleaned up).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Regul8r Quote  Post ReplyReply Direct Link To This Post Posted: 09-April-2015 at 4:13PM
http://www.4secondsflat.com/Carb_CFM_Calculator.html
 CFM calculator to help you and others figure what size you might need.
Look forward to seeing you driving and enjoying her!
 
Carl Corey (Moderator/Event Coordinator) Contact ANYTIME!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Eliteman76 Quote  Post ReplyReply Direct Link To This Post Posted: 10-January-2016 at 2:34PM
Keep in mind the calculators are basic. A cleveland needs more fuel than the basic calculators call for. But the trick is not going overboard with it.

I'm by no means an expert and I'll be the first to admit I have a 1971 351c 2V that's been punched .030" over. My rear tire is a 28" tall tire, 2.75 gear, with a 4 speed.
My carb has been a 600 CFM #1406 Edlebrock performer carb on a performer 351 2v intake.

Make sure you look at everything as a package and build around that accordingly.

I will say that once I get my TKO600 this year, and switch back to 3.50 gearing I will be looking to a RPM Air Gap intake and something a little bigger for carb.

I can say that the 600 is probably too small and lately it seems like the GTS has gone from a mild thirst to downing go go juice like a frat kegger.

Andrew:GTS.ORG admin, '72 Q code 5 speed Restomod
Pondering: #99Problems
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