Engine Masters DP VS test

[HQM383]

Could the difference simply be a mixture distribution issue?If the vacuum secondaries were not op÷n all the way vs the double pumpers that were?Air and fuel mixture direction into the plenum would be affected.

I think the secondaries of the vac sec is the key to the difference in power with this test. They have evaluated why the dp made more power but if it had both pri and sec throttle blades full open then that test is the baseline and the question then is why the vac sec made less. The secondaries not fully open was a known so to me it centers around that. They were thrown off by the flow meter saying the two different types of carb flowed the same. That means the turbine was spun to very similar rpm in the meter but that vac sec secondary blades not fully open must have created a disturbance somehow related to charge density in the manifold. An internal combustion engine depends entirely on AIR and FUEL MASS, never volume.

[Bigchief632]

These tests you have to take with a grain of salt. 3 carbs could have 3 different results. As far as the secondaries not opening fully, we usually use a zip tie to link the primaries and secondaries on the dyno when using a vacc secondary carb just to take that variable away so we know they open all the way. Then tell them you may need to work on the opening rate to suit your needs and or how you like it. I've done custom 750 vacc secondary carbs that have made more power than otb but jetted for the combo 850 carbs before, so, it's just a random test that is meaningless to most guys. Interesting, and whatever, but can't be taken as gospel.

[Bigchief632]

Freiburger said not a word about high speed air bleeds Certainly, the double pumper is the superior choice for street and track. Freiburger knows notta about how to calibrate a carburetor- beyond entry level tuning changes - giving false positive results or in this case not showing the true potential and gains one can expect.

I still hear people expressing concern about loosing low end torque on their 505 cid early Camaro with a 6 spd. as justification for running a dual plane and vacuum secondary carb or a stroked small block with a 5 spd. Really? I had a customer with a 502 Cid Boss 429 in a ‘69 Mustang worried about low end torque and another with ported (by me) ‘69 Boss 302 heads with great low end torque, but I digress.

Frieburger is an idiot, and not a real car guy. Dulcistch is though

[1980RS]

Freiburger said not a word about high speed air bleeds Certainly, the double pumper is the superior choice for street and track. Freiburger knows notta about how to calibrate a carburetor- beyond entry level tuning changes - giving false positive results or in this case not showing the true potential and gains one can expect.

I still hear people expressing concern about loosing low end torque on their 505 cid early Camaro with a 6 spd. as justification for running a dual plane and vacuum secondary carb or a stroked small block with a 5 spd. Really? I had a customer with a 502 Cid Boss 429 in a ‘69 Mustang worried about low end torque and another with ported (by me) ‘69 Boss 302 heads with great low end torque, but I digress.

Frieburger is an idiot, and not a real car guy. Dulcistch is though

[1980RS]

Here's my "real" world vs test from one intake to another with the same FST 850 vs nothing changed.

SBC 358 Air Gap with divider completely cut down
FST 850 vs stock of the box 1" open spacer with the sec pod turned in 2.5 turns in 11.30@118mph

SBC 358 with Ported Vic Jr. open plenum 1" open spacer
FST 850 vs carb the same no changes 11.54@114.5mph

Those guys are putzes when it comes to testing stuff like this and even just this year my really old 950hp took the honors busting better than expected numbers last month on my L-29 headed BBC.

[FC-Pilot]

Does the VS carb that was tested have the little brass tube in the primary side that helps one the secondaries fully? None of the VS carbs I have seen recently have had them, but I have not seen them all. I have modified a couple carbs while dyno testing with the tune and then I got the secondaries to fully open and was able to then tune for a better fuel balance between the primaries and secondaries. Not that I am anything special, but I have done it twice. (And no, I don’t remember the number improvement, I am 500 miles away from the computer that has the data. Also, we did not fully tune the carb with the throttles not opening fully.). Basically I used a zip tie on one and a bread tie on the other to see they were not opening fully, then modified them and finished tuning. That is one of my thoughts. Also, did they try leaning the primaries while richening the secondaries? As was also asked, air bleeds? There are a thousand more questions that can be asked that will never be answered. It fed/entertained the masses, and all of us skeptics will question it anyway. That’s what we are good at.

I guess I will have to waste some money and do the same test myself and address as many of these details that I can. I am sure I will get around to it sometime in the next 20 years.
Paul

[1980RS]

Does the VS carb that was tested have the little brass tube in the primary side that helps one the secondaries fully? None of the VS carbs I have seen recently have had them, but I have not seen them all. I have modified a couple carbs while dyno testing with the tune and then I got the secondaries to fully open and was able to then tune for a better fuel balance between the primaries and secondaries. Not that I am anything special, but I have done it twice. (And no, I don’t remember the number improvement, I am 500 miles away from the computer that has the data. Also, we did not fully tune the carb with the throttles not opening fully.). Basically I used a zip tie on one and a bread tie on the other to see they were not opening fully, then modified them and finished tuning. That is one of my thoughts. Also, did they try leaning the primaries while richening the secondaries? As was also asked, air bleeds? There are a thousand more questions that can be asked that will never be answered. It fed/entertained the masses, and all of us skeptics will question it anyway. That’s what we are good at.

I guess I will have to waste some money and do the same test myself and address as many of these details that I can. I am sure I will get around to it sometime in the next 20 years.
Paul

I know my FST one did not have the brass tube but opened well on the SBC dual plane intake, but the sec side did not do well on SBC with the Vic Jr or the BBC Vortec engine with a dual plane intake. Best part is I can add that little tube in any day of the week to fix it if needed.

[Tom68]

My only VS experience was a 600 on a 327, C3BX, 230 230 112 TRW Cam, in the 80s, dug a deeper groove under the ball bearing in the secondary housing. Bought the Holley spring kit and ended up linishing the wire on the softest spring. With a powerglide and 3.08 diff she was a big drift show when you kicked it down on a wet road.

Pretty sure I confirmed full opening, there was no stumble even though they opened quickly, you could actually get them to open a bit on a free rev throttle blip.

[skinny z]

As a carburetor tuner, engineer, designer I have done back to back testing with different intake styles such as your example and necessarily had to alter the calibration and fuel curve in the carburetor. In these cases I have never seen a dual plane out perform a good single plane, and a Victor Jr. is a good single plane.

"Out perform" in what metric? Drag strip performance? I can see how the carb involved can be game changer. Absolutely.
But from another performance measure, what are your thoughts on how they stack up at cruise RPM?
I ask this legitimately as I'm on the cusp of needing that single plane performance but wanting the dual plane lower RPM efficiency.
I guess that would be to ask if your carb calibrations could make the single plane effective outside of it's traditional comfort zone.

[Tom68]

I ask this legitimately as I'm on the cusp of needing that single plane performance but wanting the dual plane lower RPM efficiency.
I guess that would be to ask if your carb calibrations could make the single plane effective outside of it's traditional comfort zone.

Average horsepower for intended rev range applies here, we know the single plane will make the bigger peak number.

[HQM383]

I ask this legitimately as I'm on the cusp of needing that single plane performance but wanting the dual plane lower RPM efficiency.
I guess that would be to ask if your carb calibrations could make the single plane effective outside of it's traditional comfort zone.

Average horsepower for intended rev range applies here, we know the single plane will make the bigger peak number.

And the right annular can help extend lower rpm torque and still be efficient with a single plane.

[1980RS]

Here's my "real" world vs test from one intake to another with the same FST 850 vs nothing changed.

SBC 358 Air Gap with divider completely cut down
FST 850 vs stock of the box 1" open spacer with the sec pod turned in 2.5 turns in 11.30@118mph

SBC 358 with Ported Vic Jr. open plenum 1" open spacer
FST 850 vs carb the same no changes 11.54@114.5mph

Those guys are putzes when it comes to testing stuff like this and even just this year my really old 950hp took the honors busting better than expected numbers last month on my L-29 headed BBC.

What your “test” revealed was the native fuel curve and tune in your carb was better suited to the dual plane intake. Now, if you were a great carburetor tuner, like me you would have set about recalibrating the fuel curve for the DIFFERENT metering signal characteristics of the single plane intake. The reason the two intake manifolds perform differently is because the (metering) signal they deliver to the carburetor across the rpm range is different. I should add that how your engine was built, transmission, gearing, headers and exhaust system, valve job, your driving style, etc. are all variables in your test. One of the first things I learned when doing research and development is that even though I thought I was making one change only, that one changed altered a number of other variables which all required being zero’d out or returned to baseline before an accurate evaluation could be performed. Nothing against Freiburger, I do enjoy his shows and am glad he covers many of the things he does, but he never does that and he never talks about it either leaving the average viewer to draw erroneous conclusions.

As a carburetor tuner, engineer, designer I have done back to back testing with different intake styles such as your example and necessarily had to alter the calibration and fuel curve in the carburetor. In these cases I have never seen a dual plane out perform a good single plane, and a Victor Jr. is a good single plane.

Now while I am not a great carb tuner, I do know one thing about that test. I only had 1 run that day to try the 850 out, that's what happens when your stuck on a day with no time trials and the test day gets rained out. I have several 750 vs that I added the little tube to make work right, my Street 750HP and my 770 Avenger were good examples of both working fantastic after just one little tube to make so-so stuff into 3310-1 performance.

[FC-Pilot]

Alright, my “mad hatter” brain has decided on my plan of attack. I will take a DP carb and modify it to take a vacuum advance diaphragm on the side and a base plate swap only. (I will make sure the base plates are as identical as can be, that way the only real difference will be how the secondaries are opened, and I will plug the secondary squirter when running as a VS). That way it can be as equal of a test as possible. Yep, probably get around to it in a decade or so.

Paul