First ever multi-carb draft!

cr_bobcat

cr_bobcat

Famous Member
Supporter 2018
Supporter 2021
It's the "fantasy football draft" for multi-carb setups. Who would you draft and in what order? This is a hyphypothetical situation so consider ability to eek out power the top characteristic, followed by ease of tuneability, then finally cost. Anything carburated goes!

Consider how different areas of the log run rich vs lean. We're looking for all outperformance, not necessarily a matched set!
 
I always liked the idea of two of the Weber 32/36 on a well built 250 for a street rod. I think they are available in a 235 cfm version so 470 cfm total should be reasonable for a 250. Simpler and less parts and clutter than three carbs and performance may be at least as good plus you get to enjoy the secondaries kicking in. Not easy to tune from what I have heard but the 32/36 seem reasonably priced.
 
I thought about that too. Wonder if that would be a scenario where the original boss is blocked off with a plate and then the webers are mounted near 2 and 5. Those two would run a little richer but i doubt too much worse than 3/4 with the stock setup.
 
I was also thinking how a triple SU HS4 would play out. I've read they can be troublesome to synch tornhough
 
:unsure: My vote goes for triple set (3 x 2) of 40 or 44 Weber IDF's carbs or the DOHC carbs if you have a low hood clearance. :nod:
 
I've seen a couple posts on here where folks have talked about motorcycle carbs being used. Does anyone have pictures of what that would even look like? Sounds wild to me. It being -15F here makes me wonder if there is a snowmobile carb (if they are any different from a motorcycle ) that might be an interesting application. Those things can scoot and i only have to imagine that they run at an RPM that would be sporty.
 
Years ago did the Alk Miller 4 honda carb set up. Worked great. Later started a 6 carb version using at that time the newly designed Quick Silver motorcycle carbs but sold the head. Still have 4 carb setup was going to use on my 2.3 Pinto engine only got the maniflod about half done. been thinking about a motorcycle carb set up on my 250.
 
If you'd asked me before Hanuka, I'd have said three IDA Webers or three 500 cfm Holley 2300's on an POPIR intake (Port O Port, Independent Runner) intake manifold. Think early Ford GT40 Windsor 289 or Kar Kraft FE 427 induction system.

Then I rediscovered the restrictor plate two cylinders per venturi (RP2CPV) engines, such as what NASCAR used to use till 2011, and what the Austin Healy Sprite and Mini Cooper and Cooper S 1097, 1098, 1275, 970 special engines ran, Fisa Group 2 were normally trying to go back from Port On Port to something less to restrict performance. So were the power boat and Hydrofoil engines, the racing powers that be always tried to go back from Port on Port.

When you down grade from POPIR intake to NASCAR style RP2CPV With the right cam, you can drop the carb size down, and still get great power.

I'm thinking that Ak Miller actually understood the over carburation as he didn't do many POPIR engines. I know that there is a 15% peformance growth using POPIR, but with an optimized cam, you can get close to matching Port on Port, but with less fuel consumption.

The true masters of the RP2CPV carburation cam timing were American...Clay Smith, Ak Miller, and to another extent, Endyns Larry Widmer, were able to see the concept of fuel delivery differently to the classic Weber port on port Engine cubes verses rpm peak formula.

Those little Tri-Power Ford sixes, a classic restrictor plate two cylinders per venturi (RP2CPV) engine, shouldn't ever have made 220 hp as a 250 or over 180 hp as a 200 cube engine. But they did, and there was some kind of excellence going on in the way they were set up.

They did so with total carb size area and cfm rates half the amount that a Weber engined Port on Port car would need
 
IR setups have the fuel stand off issues at high RPM .They need some sort of a containment air box for safty as a stray spark or such could cause a fire. Ditched a webber set up on my friends Pantera when I BUILT HIS ENGINE TO CRANK 9000+ RPM.
tHE 6 motorcycle carb set up I was planing to do, was to cut openings in the log insert tubes close to the port but leave a gap inbetween the port opening and the tube. This would allow some comunication between cylinders, reduce reversion, use of a bit smaller carbs, floored more direct shot at the port. Along with the use of CV carbs should be about like the best of FI today.
 
cr_bobcat":24gqc4ot said:
...so consider ability to eek out power the top characteristic, ... We're looking for all outperformance..!
Click to expand...

I'm not sure what that means, but if you intend to do 9000RPM in the neighborhood of 600-700 HP normally aspirated, then a manifold like this with three split Dominators instead of the three 540s shown will do you fine.

 
cr_bobcat":9n8x6rcw said:
....

so consider ability to eek out power the top characteristic,
followed by ease of tuneability,
then finally cost.
Anything carburated goes!

Consider how different areas of the log run rich vs lean. We're looking for all out-performance, not necessarily a matched set!
Click to expand...


I still think the NASCAR style RP2CPV, or some halfway house between that an POPIR, withh the right cam is the only way to go.

Think the least cfm at 1.5"Hg for the most performance as a measure of efficency.

Faron made 220 hp with just 446 cfm on a 250.
In Australia, one 650 cfm 4-bbl double pumper can make a 350 to 425 hp x-flow 250 engine
Holden made 230 hp with the 58 DCOE's and 1.85" venturis, so that's like 938 cfm at least a t 1.5"Hg, and on a 202.
Holman Moody, according to Six Gun or FrenchTown Flyer, might have been trying to do the same thing...

http://fordsix.com/forum/search.php?aut ... 1&sr=posts
http://fordsix.com/forum/viewtopic.php? ... 56#p535256


The one above had a halfway house 4-bbl In line six intake that was supposed to be a transitional intake, using elements of 180 degree intake, with a degree of port on port inertial ramming.

Somewhere, the tri power three 1-bbl downdraft optimization or a 4-bbl on an I6 , can yield pay-dirt.

As I've said, Point is, There is nothing in between a pure IR system with 1452 cfm or more, and the 255-446 cfm 1-bbl per 2 cylinder item

In Australia, the 350 to 425 hp 250 X-flows are using 650 4-bbl double pumpers. What does a log I6 guy to get 650 cfm? Three 350 cfm Holleys is 742 cfm, and three DGAS38's is 679 cfm.


Its time to try an intermediate step, a semi Port on Port Independent runner set up.

And spend time creating the right cam to make it behave like its got 1500 cfm.

Fuel containment. A 3-bbl In line six, with a Restrictor plate cam.

The specific hp per rpm can go up.

I've heard so much from GT40 racers who found they lost rpm when the carb venturis were dropped below the idealized Weber Port on Port size verses cubic centimeter engine capacity, but none of them ever changed the cam to suit a smaller venturi size. IR systems need the idealized venturi size to work, but NASCAR and Historical C racing has been stuck with non IR systems, and developed cam strategies to make up for the loss of peak rpm.


What I am saying is don't go IR, go back a step, and copy NASCAR's 3'c's, the ability to Cheat on Carburation, Compression and Cam timing.


If IR sizes are taken to there expected requirements, then you'll end up with a Mini Prostock triple 650 cfm Z28 302 Cross Ram carbs and 12 throats like the three 4-bbl 250 in line Six Chevies with a 700 tho lift roller cam like used to rule the drag strips in the late 70's , CNC-Dude pit crewed with people like that.

The best Ford dual quads weren't strictly Independent Runner, they were a blend.

I'd start with downgrading a Double Pumper 4-bbl 650/351 combo into a 3 bbl 250, and work the a$$ out of the cam and legs to the pais of cylinders, making an HS Mikuni Flatside style system. Like the 1973 Circuit racing 202 xu1 Holdens ran.

So that's where it is for peak performance, not IR, because you can't package and feed it properly.

viewtopic.php?f=5&t=71515


This is where Holden was in 1973...Chrysler with there E49 was using independent Runner Aston Martin DB6 Vantage Weber DCOE45's with 40 chokes to get 295 HP net (306 HP Gross rated), while Holden was able to use Mini A series style Weber Splits, 3 56 DCO carbs with each second barrel deactivated to copy the triple CDS175 intake 190 hp gross rated engine into 230 hp net.

viewtopic.php?f=1&t=72684&p=559201#p559201

xctasy":9n8x6rcw said:
The topic is side mounting a plenumb., and log kit modifications or changes that allow this to take place. If you are using draft carbing, here is how it can work.

To show you what possible without even a turbocharger, but just a great cam and a nine port head nigh on over40 years ago.

The 202 cubic inch L6 Holden XU1 GTR 3300's in 1972 made 216 hp flywheel hp is race trim with this Three side draft Stromberg Zenith CDS175 carb set up. It was good enough to win a 6 hour, 500 mile road race in Bathurst Australia





from http://www.partscloner.com.au/homephotoone.jpg

The next year, the 1973 Bathurst Torana XU1 GTR 3300 used triple 2-bbl 58 DCO carbs with half the barrels inactivated for about 230 HP flywheel net hp.

(Note, the description is wrong, its certainly a triple 58DCO set up from memory)



The 14 hp boost came solely from the use of those huge 1.85" 47 mm chokes in the 2-1/4" throttle carbs, and reliability from special Cologne Capri V6 style solid skirt cast pistons.
Click to expand...
 
Would 3 side draft Weber 40's work? I may be able to get my hands on them cheap. I also have an EFI lower to work with.
 
I wanna see one of the Autolite Inline 4 barrel carb used on a 300. Preferably the 1400cfm version so it better be a beefy six! I would think that would give good fuel distribution.

Of course i dont have the skills or money for one of those carbs...
 
GPGoverMPG said:
Would 3 side draft Weber 40's work? I may be able to get my hands on them cheap. I also have an EFI lower to work with.
Click to expand...
No. Talking just 200 and 250 here, the Carb Size is critical. Talking 300 Fords, that size is super critical and all your cost savings on a Tri DCOE40 on an EFi intake will vaporize because the effective Rev range where peak power occurs will be at about 3800 rpm. You won't get more than 180 hp with 32 or 34 mm chokes on any 4.9 liter engine with 681 cc cylinders...absolute fact borne out using the PMO and Weber Independent runner graphs. As with the log head six, the much better Big Six still has a heat sink from the non cross flow head, which doesn't work well with a triple or six side-draft system. Which is what a DCOE Weber system is. A port on port 6bbl carb, basically.

Going back to our 200 and 250 engines, with triple side drafts or 6bbl six carb systems.:-

Port On Port and Independent Runner 6 bbl carbs with 40 mm throttles need 32 to 34 mm chokes and on a Log head, DCOE 40's will "Heat Soak" and have a splayed "roosters tail". On a 200 engine, the peak power rpm range will sit at just 4800 rpm, maybe not enough to give any more than 180 hp. You'd get that result with just three Weber ICT 34 1 bbl carbs, and a lot less outlay. Due to simple physics that the likes of David Vizard and Richard Holdener could go into if you took a night out superchatting one of there YouTube sessions.

All that "probably" means three 105 mm spacing DCOE carbs might not mix well with six variable inlet spacings if the Falcon Six . I can say....One guy here has done a six Mikuni 40 Flat side 2V 250/Classic In Lines head with great results using some K&N Mini 1275 air cleaners...so if you want to...Engineer and Kill and Conquer.

For everyone else, I'd advise three 1bbl or 2bbl downdraft carbs. Carter YFA or Carter BBD's. The work done by Ak Miller included Weber DCOE45's, fuel injection, turbo and propane, but by 1981, he came back to triple carbs or a nice 2bbl Motorcraft 1.08/1.14/1.21 or the 5.0 HO 2V, a 1.23 carb. Full circle happens when the scienced responses to injection of cash and development failed to pay off in terms of performance on the 200 or 250 log head engine.
 
Last edited:
I know, it's an old thread.. 390 on a EA Falcon cfi manifold.. to an 89 crossflow motor. It works, haven't properly tuned it yet, very time poor atm.. J.
 

Attachments

  • 20221011_085245.jpg
    20221011_085245.jpg
    1.7 MB · Views: 16
  • 20221011_085258.jpg
    20221011_085258.jpg
    1.4 MB · Views: 16
  • 20221011_084843.jpg
    20221011_084843.jpg
    2.2 MB · Views: 16
You must log in or register to reply here.
Back
Top