Topic: Riddle me this, riddle me that, a four into one carb could it do that!!

[kos]

It can be done, It WILL BE DONE and YOU CAN ALL EAT YOUR WORDS WHEN I TARE ASS THOUGH MY CITY!!! ))))

   You know, this sounds a lot like the bar drunk picking a fight with the biggest guy in the bar.
Ignore physics at you own peril. 

I mentioned inlet pulses in an early post.
The inlet flow is not a constant.  It only flows when the intake valve is open, which is, at best, 1/4 of the time per cylinder.  Worse, once all the flow gets up to speed, the intake valve slams shut, producing a reflected wave.  Ever been to the ocean and see a wave hit a barrier wall?  Didn't the water then move back toward the ocean?  Same thing occurs in an inlet tunnel to the intake valve and is called reversion.  These reversion pulses have a frequency, and are timed differently, as in staggered, for each cylinder.  A single carb venturi will see four of these reversion pulses, and this will effect the a/f mixture delivered.  Even with a two carb log manifold, the reversion pulses from one inlet will arrive back at the venturi when the other inlet is drawing fuel at some RPM(s) and this timing will depend on runner length between the venturi and the intake valve.  Then there is the firing order to consider, which for the SOHC4 is 1,2,4,3.  In real time, to make the reversion and flow pulses equidistant, you need to pair the 1 and 4 cylinders with each other, to make any kind of even, average flow, as with this pairing, they are timed 180 degrees from each other.  Pairing 1 with 2 gives a 90 degree phase separation of pulses, which gives some rather "interesting" modal aberrations/interactions over an applied varied RPM range.

Four carbs and independent runners for four cylinders allow one to ignore all the adjacent cylinder inlet and reversion interaction physics.  Log manifolds do not.

Cheers,

Ken over at Cycle X has a pair of carbs that work just fine replacing  4 individual one...pulses are not what you think they are.  No problems between 1 & 2 and 3 & 4.

KOS

[cobrajunkie]

Well, according to the "theory" presented here, that intake will lean out the two outside cylinders and you'll get "puddling" which I think is complete hogwash and I've never heard of "reversion intake pulses".   Reflection pulses in the exhaust when tuning an exhaust system perhaps but any such reflections in the intake are negligible with the amount of air velocity in such a short runner.  If this reversion pulse theory or the lean/rich cylinder theory had any legs, then the single plane manifold below would be downright dangerous.  Cylinders 1,4,5,8 runners are twice the length of 2,3,6,7 and it's a straight shot for the "reversion pulses" to upset the emulsified fuel from the four barrel carb to those same cylinders.



 

[TwoTired]

Ken over at Cycle X has a pair of carbs that work just fine replacing  4 individual one...pulses are not what you think they are.  No problems between 1 & 2 and 3 & 4.

Thanks for the technical and quantifiable, ...er opinion.

Its a fine day, too.

[Pinhead]

When citing the useof a single plane manifold on a V8, consider that the real professional engine builders very loudly complain about uneven cylinder distribution. David Vizard, Larry Widmer, and others have written articles on this very subject.

[TwoTired]

Well, according to the "theory" presented here, that intake will lean out the two outside cylinders and you'll get "puddling" which I think is complete hogwash and I've never heard of "reversion intake pulses".   

Love the argument.  Since you've never heard of it, it must not exist?

I can recognize "hogwash", too.

Cheers,

[cobrajunkie]

Well, according to the "theory" presented here, that intake will lean out the two outside cylinders and you'll get "puddling" which I think is complete hogwash and I've never heard of "reversion intake pulses".   

Love the argument.  Since you've never heard of it, it must not exist?

I can recognize "hogwash", too.

Cheers,

Didn't say it doesn't exist.  I just don't think it has any consequence to what it is trying to be accomplished by the OP.

[anthony]

i think this will work with a 28 mm carb. only one cylinder is in the intake stroke at a time. it most likely be harder to start due to longer travel in 1-4 . I would go for a straight tube meeting in a collector at the carb with the outside tubes on the top. just my $0.02

[Terry in Australia]

Not sure if this alread posted....

I have a Posa 4 into 1 that I probably don't have time to work on...

Woohoo! How much do you want for that thing mate? Is it for a 750? Cheers, Terry. (thanks for the tip off FFJ!)

[BeSeeingYou]

Posting while drunk again, eh?
It's OK, I've done it myself on more than one occasion.

In your other thread entitled the same thing, I made a quick drawing of what might work better in your single carb situation.

Your current design will not feed equal amounts of air and fuel across the cylinders. You'll also be dealing with very different intake velocities, and restrictions, on the outside cylinders.

You can laugh at me all you like, but your design will continue to be horrible regardless.

You mean this one???

Back to this design for a moment.  While a definite improvement it has one inherent problem.  The design incorporates two nipples (not shown but we know they are there) and this can lead to a phenomenon known as "fuel splatter".  Often the operator will try and jerk the throttle rapidly to relieve the effect that the nipples can cause.  While this can be gratifying to the operator it can be annoying to those nearby.  It is possible to minimize "fuel splatter" by the proper placement of some type of filter medium (like tissue paper).  Adding more nipples only compounds the problem.

[mlinder]

When each cylinder on a 750 is trying to suck in over 600 litres of air and fuel per minute at 7k rpm through a 6 inch long pipe that averages about 1" in diameter (and not even evenly, only when the intake valve is open, and after it closes, you are dealing with reversion) , you better bet that difference in intake runner length make a difference, on many levels.

[Flying J]

No way. Its going to work! and better then the 4 carbs. What did Soichiro and the rest of the people on that island know anyway? Cant even build a nuclear reactor that can withstand a 9.1 earthquake. Do it! Build the intake. No more talk, lets see prototypes.

[scottly]

What did Soichiro and the rest of the people on that island know anyway? Cant even build a nuclear reactor that can withstand a 9.1 earthquake.

(I believe the reactors were designed in the USA by GE. High-jack over)

[scottly]

8 carb's V8s: this was never done due to complexity and expense on a mass produced vehicle.

Lots of production vehicles had one carb bore per cylinder, such as Porsche 911 six cylinders, that used one 3 barrel Weber on each side, as well as Ferrari and Lotus, although the latter might not qualify as "mass production". 

[splitt]

One of the problems that was noticed on the Posa carb/intake systems was the lag in throttle response. This was due to the distance of the carb from head. Another strange phenomenon exhibited by them was that the intake would frost over, freezing the fuel pooled in the intake runner, leaning the mixture out. I read the physics behind why this occurred one time, but can't for the life of me remember it. I do remember that the pooling of fuel in the intake was partly due to the insufficient intake vacuum of the SOHC engine throughout the rpm range. If the engine was run WOT (like in drag racing), the puddling & lag was non-existent. There have been some who have built there own intake manifolds with a rubber liner to combat the frosting/freezing problem with some success. If you can also alleviate the runner length & pooling issues & build a streetable single carb/multi-cylinder system, you would have something that could be used by many different bikes.

One carb per cylinder is still the most efficient system.

[oldhondarider]

Not sure if this alread posted....

I have a Posa 4 into 1 that I probably don't have time to work on...

Woohoo! How much do you want for that thing mate? Is it for a 750? Cheers, Terry. (thanks for the tip off FFJ!)

It's for a cb750... At least that's what I'm told... it matches up to the 750 4 set up.
I bought it for 85.00... LOL.. now it sits on the shelf... I was thinking of trying to put on an SU Carb.... but life happens..yadda yadda...    I'd sell if for what I paid + shipping.

[Hondell]

I imagine these would scare the shat out of you !!! Just don't go planning a single carb setup for my CBX. The Honda gods would rain Amal carbs upon you !!!!!!

[anthony]

I've been BACK & FORTH with this....  

I got this bright idea to do 1 34mm Mikuni on a 71 CB500

My guru of a friend an bike tech & racer of almost 35 years swears up & down it will work......

Yet everyone I told doubts this.... Some say it won't start, some say it won't rev over 4K....

But FTW Who's right???

Im dying to know if it will work & have the "I TOLD YOU SO" moment when it does......  Or just punch & scream and cut the plenum in half & add a second carb..... But its 1 for now.....

What say you??? There's gotta be more then one of you out there has a background in this.........

he has a 500 not a 750

[splitt]

Just an fyi so you can figure carburetor size for your experiment here.

This is the carb size equation that I have always gone by to determine maximum carb size: CID x max rpm / 3456 = CFM

1 Cubic Centimeter = 0.0610237441 Cubic Inches

[scottly]

This equation assumes a given pressure drop across the venturi at WFO to determine CFM.  By this standard, my Webers would probably be rated at 500 CFM, or enough to feed a 350CID motor @5000 RPM. Webers are capable of atomizing the fuel with less pressure differential than most carbs. The next step up from Webs is a system that can atomize the fuel with zero pressure drop: fuel injection.

[Terry in Australia]

Not sure if this alread posted....

I have a Posa 4 into 1 that I probably don't have time to work on...

Woohoo! How much do you want for that thing mate? Is it for a 750? Cheers, Terry. (thanks for the tip off FFJ!)

It's for a cb750... At least that's what I'm told... it matches up to the 750 4 set up.
I bought it for 85.00... LOL.. now it sits on the shelf... I was thinking of trying to put on an SU Carb.... but life happens..yadda yadda...    I'd sell if for what I paid + shipping.

Wrap that sucker up mate, because it's SOLD! Woohoo! I'll PM you with my details, I look forwards to dusting off my NOS POS-A carb and blowing those knockers into the weeds with that awesome new found power! (if it disappoints, I can always install it on my Hyundai, it needs something................... ) Cheers, Terry.

[oldhondarider]

I'll snap some pics of it along with it lined up to a rack off an "F" I have..

[Honda!]

One of the problems that was noticed on the Posa carb/intake systems was the lag in throttle response. This was due to the distance of the carb from head. Another strange phenomenon exhibited by them was that the intake would frost over, freezing the fuel pooled in the intake runner, leaning the mixture out. I read the physics behind why this occurred one time, but can't for the life of me remember it. I do remember that the pooling of fuel in the intake was partly due to the insufficient intake vacuum of the SOHC engine throughout the rpm range. If the engine was run WOT (like in drag racing), the puddling & lag was non-existent. There have been some who have built there own intake manifolds with a rubber liner to combat the frosting/freezing problem with some success. If you can also alleviate the runner length & pooling issues & build a streetable single carb/multi-cylinder system, you would have something that could be used by many different bikes.

One carb per cylinder is still the most efficient system.

Random note:  Volkswagen air-cooled engines suffered from intake icing, as they have one carb for 4 cylinders.  The problem was resolved by welding a pipe that connects to the exhaust to the manifold.  Keeps 'er nice and toasty.  Second random note:  Honda C77s are twins with single carbs, along with Triumph Tigers.  Not the best or most efficient, but it works.  That is all, carry on.

[Terry in Australia]

I'll snap some pics of it along with it lined up to a rack off an "F" I have..

Thanks mate!

[faux fiddy]

I did this  as a similar thread a while back because I have a 34mm flat slide and wanted to attempt to do it on a 350f.

Pulses, yes likely. Pair of carbs instead of 1-4 prolly better. Pair the "right" (inner w/ Outer)  two together to eliminate pulse intake, a bit more complex manifold.

But for me, it was more about just setting up a backyard foundry that I can pour/ port a quart of molten aluminum and then perhaps find out from there that it's not as good, or that carbs available made it worth while..

That being said, there are  250 twins that use  a single carb and manifold forever.

[phil71]

this sounds like a great way to bring all the performance of a 1990 nighthawk 250 to your SOHC4! Do it!