Technical section T/A details

[gt350shelb]

[gt350shelb]

[propayne]

Detail from Shelby's "How To Sharpen A Cougar's Claws" brochure.

- Phillip

[shelbydoug]

Those are the "special" mechanical secondary TA Holleys but what cfm are they? Aren't they called 625's somewhere?

[pbf777]

     If they are not actually very early experimental ("special") TA" example carbs (seems like the side levers might be later?  ) then they would be the Holley List 4224, 660 C.F.M. "Center-Squirter"  carburetors.

     Scott.

[98SVT - was 06GT]

Sometime you just need to mount them sideways......

[98SVT - was 06GT]

Sometimes 1 is enough

[gt350shelb]

no there are not period  they are newer 660 center squirters

[shelbydoug]

I went a different route. This is a set of BC-BD, 427 Hollies. The car likes them the best so far.

Presently there are 1850-1's on it, facing forward. That linkage is simpler but the original 427 linkage works as well but does have a tendency of occasionally binding up

To me the BC-BD set up is like a 700DP with afterburners and the 1850's like a 600DP with a lot of extra top end. The sound of the secondaries opening with a womp is worth the cost of admission alone. The set up is a monster and understated at that.

I haven't decided on which is better yet but I'm still trying.

The bores in the manifold actually are the same diameter as the 427 carbs.

One would think either is drastic overkill but oddly enough it isn't. Both are very streetable too.

How anyone could determine that something like a pair of 1848's is what to use is beyond me?

[gt350shelb]

I dont think i will use the 660s  / but  all your  R&D is  helping another 68 Gt 350 

[TA Coupe]

shelbydoug, what's wrong with 1848's? I've been running them for years.

       Roy

[shelbydoug]

shelbydoug, what's wrong with 1848's? I've been running them for years.

       Roy

I don't know? Considering what I've run so far, smaller doesn't seem likely to be the solution for me?

I would have to try a set and see if they work for me?

I may be wrong but it seems illogical that they would work better then what I've tried? If you are happy with them, leave it alone. That's ok.


This was really an unknown category in the beginning. I had four sets of carbs. The first set was a pair of 84-85 Mustang GT carbs that I converted to 1850's. I was concerned that the idle of any standard Holley would be way too rich.

The GT carbs are designed to idle at a stoiochemic ideal of 14.6:1. What happened was that they were so lean that the exhaust manifolds were glowing red in the dark.

Did they work? Yes. The annular discharge really helped with the sensitivity to the throttle opening but glowing red was not good. It melted/burned the ceramic coating off of the first set of headers which got returned under warranty. Those were JBA's.


I had the BC-BD's that were fresh from restoring from Holley (not Drew) and needed to be set up. Those are my '67 GT500 carbs. Sure I know they are not "correct" for the car. You don't need to mention that. 

Installing them first accomplished two things. First, it would set them up for running on my 67 GT500 in the future. Second, it would likely eliminate that much carb for my set up as ridiculously over carb'd. Little did I suspect that they would be the best match?

Now I first had them installed with 427 linkage, i.e., backwards, and had to listen to Randy (and others) that WTF are you doing, that's wrong? OK. Eventually I found that the 427 linkage, although INSTALLED FOR YEARS ON PRODUCTION 427's, had issues with twisting and binding up, sometimes at WOT, so reluctantly I went to the T/A front mounting throttle linkage.

That works predictably and is much simpler. I was concerned initially with the change of where the engine would idle, i.e., the design of the intake manifold itself, which carb location was it intended for, since the T/A setting really had no or little concern for that and there really had been no Ford regular production cars ever made like that and to me, there likely was a reason. One serious enough to go with a radical design like the reversing the carbs and using the 427 linkages?

As it turns out, it doesn't really matter a hill of beans but simpler is better so the T/A linkage and forward mounted carbs is really the better solution. It would certainly make more sense for a flat out race car.


It struck me that the BC-BD's on a 347, didn't make sense on paper? That couldn't be right? So there were two more sets sitting here to try. A pair of 1848's and 1850's. All were the Ford version throttles.

So I flipped a coin and on went the 1850's. What were the results? Actually little change from the 427 carbs at idle but noticeable less top end. Less whomp when secondaries open but still making people turn on their wipers to get the cloud off of their windshields.

So in my seat of the pants dyno, it was already noticible that the bigger carbs were better, so even for me, there is a time limit, this isn't Dyno Masters where "we" can try every combination available. There are no "sponsors" to foot the bill. The 1848's got 'nixed'.

I think a large portion of the answer to this is that all of these carbs that I used/am using, are vacuum secondaries. That allows the engine demand to control the secondaries. Then what I am feeling is just essentially either a 600 double pumper or a 700 double pumper with "secondary" demand controlled throttle boosters.


On the subject of secondaries, I'm as subject to information coming from "Automotive Journalists" of the time as everyone else is and at some point in covering the T/A cars one mentioned that initially the engines uses vacuum secondary carbs (size wasn't mentioned) but the drivers complained that the secondaries didn't close fast enough under race conditions and the center squirters were developed as a result specifically by Holley for Ford. Randy said he had a set of them and they were all hand made secondary linkages.

Keeping in mind that center squirters are largely thought of as 660's, and they directly derived from Ford's T/A car application (on 289/302's)  that's not a bad place to start and not a bad guess point but I'm not sure on a street car if all that pump shot is really what you want?



That is where I am at. So that is what I know. It may in fact be incredibly limited and feeble, but that is how I roll here and maybe it's just a '68 GT350 thing, and incidentally, the '68 Shelby hood actually "whistles" at speed with the ducting connected so "the ram air" may actually be doing something? You need to go fast enough to hear it. It is very audible but that is just unique to us '68 guys? Apparently we are "very special people"?  I'm pretty sure others have noticed that as well but keep it to themselves? 

[TA Coupe]

Pictures of original TA carburetors which I believe are 525C. F. M which John Slack now owns. It also shows the special linkage.
Scott, Do you have any comment on the exhaust flow on 68 hypo 289 heads? Which I read or was told flowed better than the other Exhaust ports because of the D shape.

       Roy

[shelbydoug]

Great pics. Thanks for posting them.

[gt350shelb]

damn doug did you sleep last night