dynoed hp for a 289 hipo with dealer option dual quads ?

[shelbydoug]

Although I have no way to definitively prove it, the dual quad update to 6S1575 was supposedly done at the selling dealer on day 1.  The original owner told me this in 1987, the year after I bought the car and started contacting the 2 previous owners and diving into its history.  He said he added the lemans cam and hurst shifter the following year, which are still also installed.  He had many great stories to tell which I have documented but unfortunately he did not keep one piece of documentation from his term as owner between 1966 and 1971.  I have no reason to believe he would make up that story, so that's just one of the reasons I've left it as is.  He was quite a gear head, worked at various automotive jobs, was a manager at Roush Racing when we first talked and went on to be President of TRD - so you would think a credible story teller.  Fortunately the second owner was opposite in disposition and kept every receipt other than gas receipts.

With that date code on the carbs, that is entirely possible and the carbs do fit the story. Now if the carbs were dated 1969 or something later that wouldn't have been possible.

[1967 eight barrel]

Thanks for the great replies.  My car has the Holley 2 x 4bbl OTC setup (List 3360 and 3361 dated 634).  It also has a Lemans cam and tri y headers.  I've always really liked the way this setup worked but never knew how much extra hp this setup made vs stock vs the ad claims way back when.  I've driven a stock 66 GT 350 as well.  It seemed to me that my 2 x 4 setup was a little slower out of the hole, but pulled much stronger above 3,500 rpm.  And the sound at high rpm with side pipes is heavenly!

Those carbs are 427 carbs and are rated at 710cfm each. That's kind of big for just a 289. I can believe the throttle response could be described as lacking crispness off of idle?

The carbs on the 67 GT500 are rated at 652 cfm each and have been criticized by some for being too large for the street.


Actually the BJ-BK are rated at 580 CFM, not 652.

For a 289 I'd guess that 1848's would be about right for that set up.

I'm using two 85 Mustang GT carbs. They have been converted to 1850 bowls. The idle bypass has been increased to .028 and the primaries have annular discharge venturies which help throttle response immensely over the 1850's. It's a 347 with AFR 1388 heads.

Those carbs are generically a 600cfm carb but because of the annular ventuies I think are rated at 595cfm each? They idle very very clean.

I have run a single 715, 780, 750 and 600 double pumpers. This set up is more responsive then even the 600dp is by far. The 780 was used stock on the Boss 302, and the 715 on the 65-66-67 GT350. They are about equal response wise and I would describe as being a bit sluggish off of idle.

[gt350hr]

    The 3360 and 3361 were recalibrated 1848's so they were 465cfm and noted that way in many period ads and paperwork. They were very good and with the progressive linkage could perform AND have fuel economy.
    The '67 T/A cars built by SAI featured the C6ZZ "style" updated dual four and the BJ-BK carburetor set up. For THAT engine combination the carburetion was near ideal. Other sizes were tested and the BJ -BK was the best.
     Randy

[Dan Case]

This was one version of the 1967 Group II induction system for 289 engines. This one includes a preproduction hand numbered intake manifold serial 4 and the R-2804/R-2805 carburetors converted from vacuum secondaries to mechanical secondaries. Factory systems started the season with vacuum secondaries.  Shelby Mustangs and Moore Cougars used these type systems.

The person we obtained this from had the complete engine but wanted to use modern aftermarket cylinder heads, intake, and carburetor in a vintage racer. He claimed that the Group II engine had not been run since the 1967 race season.

[gt350hr]

   Thanks for the picture Dan. Those carburetors are some of Holley engineer Harold Droste's (rip) initial reworks and still have the primary only "squirters". It is as you mentioned a 2804 and 2805 ( BJ-BK) 427 carburetor that  was also used on '67 GT500s in stock form. The last change he made was going to the "center squirter" design and mill off the air horn. Those were the for runners of the 660 center squirter carbs released to the public in late '68 .
      Randy

[427heaven]

Randy- What is the benefit of milling the air horn off do?

[shelbydoug]

I think that it's important to remember that these changes to the carburetors are for racing needs. Even the orientation of the carbs and the throttle linkage used is involved in that. So one needs to determine which is better for a street car.

Some things like a T/A manifold are very streetable but carbs are a different situation. Two double pumpers or center squirters on a street car might be and probably are a little much to handle on a street car? The carb modifications were made to make running at WOT 99% of the time.

In many respects what makes this 2x4 set up streetable is the vacuum secondary carbs and the 427 street linkage.

[Dan Case]

I think that it's important to remember that these changes to the carburetors are for racing needs. Even the orientation of the carbs and the throttle linkage used is involved in that. So one needs to determine which is better for a street car.

Some things like a T/A manifold are very streetable but carbs are a different situation. Two double pumpers or center squirters on a street car might be and probably are a little much to handle on a street car? The carb modifications were made to make running at WOT 99% of the time.

In many respects what makes this 2x4 set up streetable is the vacuum secondary carbs and the 427 street linkage.

+1

[gt350hr]

    The "small block" carburetor orientation was always the same as the pictures Dan posted above. "Ford" did not use the FE style linkage on them.

   The purpose of milling off the air horn or choke housing was to reduce air flow restriction on a race only carburetor. With an "air box" or short air cleaner element , the air is restricted a bit with the full height air horn. "Most" racing carburetors are modified like this today. There is no real benefit on a "street" performance application. Same for mechanical secondaries.
   Randy

[shelbydoug]

    The "small block" carburetor orientation was always the same as the pictures Dan posted above. "Ford" did not use the FE style linkage on them.

   The purpose of milling off the air horn or choke housing was to reduce air flow restriction on a race only carburetor. With an "air box" or short air cleaner element , the air is restricted a bit with the full height air horn. "Most" racing carburetors are modified like this today. There is no real benefit on a "street" performance application. Same for mechanical secondaries.
   Randy

The heat choke in the manifold  design provides for the primary carb sitting over it like the 427 street cars. To say it was never put into production that way is irrelevant. It was never a production set up.

The forward facing linkage is because the reverse 427 street linkage has the tendency of locking wide open under certain circumstances.

On a race car it doesn't matter which is primary and secondary. A street car has different requirements.