Draw through turbo - triple carb intake manifold - Ford 300

[Bradz]

Hey guys. Long time no speak.

I've been working on a project which involves converting a stock log intake into a triple carby manifold. As you can see in the photos Ive simply welded on 2 additional carb mounts between the runners for 1 and 2 as well as 5 and 6. The plenum is completely open. No segregation.

Here you can see it fitted with 3 single barrel Stromberg carbs (1 1/32 venturi) which flow about 162cfm at 3"Hg or if converted to compare to 4-barrel carbs, which are measured at 1.5"Hg 1 1/32" = 114cfm. Either way it provides a total of over 340 cfm. I havent run this set up yet.

Now to the purpose of this post.

My actual question......If I decide to go down the turbo route, could I effectively use this manifold with a single carby (ie 600 holley) draw through turbo and have the pressurised air from the turbo split into the 3 ports? Effectively creating a new "plenum" which collects the pressurised air/fuel and then feeds the 3 intake ports.

Would it work much worse than using my Offy intake?

For now I'd rather not debate the pro's/cons of draw thru versus blow thru.

 

[pmuller9]

Nice job on the intake manifold!
The 3 carburetors give you very even distribution. If you connect the 3 inlets with a single plenum you would lose the even distribution while also adding 90 degree turns. You would be better off using the Offy.

 

[pmuller9]

Are there turbochargers available that have the correct seals for draw thru?

 

[Bradz]

Yes, you can get carbon seals for some turbos. I'd be particularly looking at the Garrett. I don't believe you can get carbon seals for the Holset turbos (HX35 etc).

Can I ask why you'd lose the event distribution if the air is actually pressurised compared to N/A?

 

[powerband]

Oh boy, a favorite subject, from the wayback machine :

Unlike a blow-thru setup where you may actually need a carb with less CFM than in NA operation, a Draw-thru setup requires the upstream carb to go from idle cfm to a much larger CFM under boost than in NA operation . The draw-thru turbo I used from a carbureted early 80's Buick 231 V6, used a specially designed Quadrajet with external Power Valve port for switching under boost and a WOT rating of 850 CFM while in boost... .

MacInnes makes no statement as to which method is best in his "TURBOCHARGERS" , the bible of forced induction. The problem with early draw -thru setups wasn't lack of performance as much as a warranty nightmare for the mfg. . With only enthusiast/light use of a homebrew draw-thru carbd' setup, there is not a real issue with MTBF for the setup.

The BOP 231 V6 turbo setup was simply adapted to my Ford inline 250 six. It made great power and I incrementally upped boost until @ 15-20 PSI when it lost power, the stock piston lands cracked off and a blue mist covered my windshield .

( PS - no need for return / referenced fuel supply as the carb bowl always is at atmosphere.)

have fun

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After the draw-thru Buick turbo project on the Ford 250 six, now the Maverick 250 runs a Vortech SC with a Blow-Thru modified Holley 2 Bbl carburetor. With available 'reverse' power valves, modifying a Holley 2Bbl carb for blow-thru is simple...

 

[powerband]

250 small block six with large plenum on top of Tri-Port Offy adapter manifold was fabbd' to proof for a forced induction setup .
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It was surprisingly well tempered with a large 2Bbl with excellent response and consistent idle. Unfortunately that tri-forced induction project was suspended but I believe the Plenum on top of Tri-Port is a workable option.

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[drag-200stang]

I does not matter, Air is naturally pressurized on earth, at about 14.7 lbs. per square inch, boost is just more of it. 14.7, plus lets say 8.3 lbs. boost =23 lbs. of air pressure in lbs. PSI the engine will see, roughly.
Think of air as the roadrunner and fuel as the coyote. When the roadrunner comes to a turn, he makes it, the coyote does not and runs off the cliff. Fuel is heaver than air. Regardless of that they say , '''the turbo will completely mix the air/fuel'', it will separate at sharp turns. Well that is my story and I am sticking to it.

 

[pmuller9]

Can I ask why you'd lose the event distribution if the air is actually pressurised compared to N/A?

If you make a plenum that is bolted across all three inlets on the intake manifold, the outlet tube from the turbocharger will enter the plenum at the center of the plenum directly over the center inlet that services cylinders 3 and 4.
Cylinders 3 and 4 will get a direct feed while the air/fuel mixture going to 1, 2 and 5, 6 will have to make a 90 degree turn and travel down the plenum before having to make another 90 degree turn to enter the inlets.

One option would be to have 3 separate equal length runners coming from the turbocharger that go to each of the 3 inlets on the intake manifold.

 

[drag-200stang]

That will help.