Ted, your exhaust test was very informative and I appreciate you providing that information.

I have a couple questions regarding the test engine itself, you mentioned using a 750 Holley and that the head porting was basically a stage 1.

1. Do you think there would have been any benefit from a smaller carburetor given the mid level build of the engine?

2. By stage 1 porting do you mean basically a bowl blend and flash cleanup?

Thanks, James

1962 Fairlane, 1954 Customline, 1949 IH Pickup

Based on the graph below, I’ll say No.

Yes.

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James.  Just prior to doing the actual exhaust test, a series of dyno pulls were made to get a good baseline for the engine combination to use for the exhaust test.  This involved a variety of carb spacers and different sized carbs.  One of those smaller carbs was an original 1957 Thunderbird L1273 ECZ Holley which is rated in the 390-410 cfm range depending upon the reference being used for the sizing.  Here’s the graph showing the T-Bird carb as compared to the 750 Holley that was ultimately used for the exhaust tests.  All other parameters on the engine were the same for both of these carb tests including the same 1” HVH dual oval carb spacer as well as the same Sanderson pickup 1½” tubed headers with 2½” diameter 22” long pipes with mufflers being used.

 

Lorena, Texas (South of Waco)

Ted, thanks for the response.  Folks usually recommend smaller CFM carburetors on Y-Blocks, but the "data don't lie".  The chart shows better torque and horspower, even at lower RPM where you would think that the smaller carburetor would have an advantage.

Thanks again for your work.

James

1962 Fairlane, 1954 Customline, 1949 IH Pickup

The carburetor test in Y-Block Magazine a while back illustrated that cfm alone has little to do with how the engine will respond. It has more to do with the overall setup of the carb.


Lawrenceville, GA

Ted:
On looking at the torque graphs the one for the ECZ Holley seems to be flat lining like running out of carburetor till about 2700 RPM then takes off like the secondaries cut in. Do you think different primary jets would have smoothed that transition out. The 750 carb seems to be doing similar except at a higher RPM where the velocity became sufficient to cut the secondaries in there also. I was wondering if a lighter secondary spring would have helped that carb kick the secondaries in faster for a smooth transition and helped that dip in the torque .

Very nice info there.
marv



 

Marv.  I can rule out that dip being secondary related as that particular carb was run on the dyno with and without the secondaries.  That same dip is present in both modes of operation.  Oxygen sensors were hooked up and air/fuel readings were in the ball park which puts the dip as a result of another tuning variable besides jetting.  Those other variables can include ignition curves, exhaust extensions, mufflers, and carburetor spacers under the carb among other things.  That’s a small dip compared to some that were present and getting all the dip out in that particular case still would not have improved the peak numbers.

 

Some information is obtained strictly by happen chance or accident.  A for instance is when that ’57 TBird carb was first put on the dyno engine, the secondaries were not functioning at all.  That ended up being an extra piece of data which answered the question “how much are the secondaries worth?”.  Here’s the graph of the L1273 carb comparing dyno pulls with and without secondaries functioning.

 

 

In the exhaust testing that was performed, dips in the torque curves could be very pronounced or non-existent with no other engine changes other than changing out the diameter or the length of the pipes behind the manifolds or headers.  That’s why the Sanderson Thunderbird headers were tested in eleven different configurations.  A considerable amount of effort went into the EMC engine to get a very pronounced dip out of its torque curve and most of that work concentrated on modifications inside the collector itself.  Getting that dip out helped out immensely in getting a higher score at the EMC competition as I saw several of the other competitors engines exhibiting the same dip that I had worked hard to eliminate.

 

Here’s the graph from page 3 of “the exhaust test to end all tests” with the Tri-Y headers demonstrating how the torque curves could be manipulated with a variety of exhaust extensions of the same size.  Experimenting with the pipe diameters also had similar results.

 

Lorena, Texas (South of Waco)

Ted:

Thanks for the detail and explanation.



marv