Manifold design.

[OldWrench]

I have been following the single carb thread for some time as I’m sure many of you have. There is so much to manifold design that will effect the way an engine runs. Do I fully understand it, no way, but I remember my hot rod days when we played with different manifolds and came up with some good and some not so good results.
I found this little bit of information recently an thought I would throw it out to get your thoughts on it.

For a force-fed application, runner design is less of a factor than for a N/A design. Plenum volume is the key---the rule of thumb is plenum volume >= engine volume when force-fed. A large plenum has a few draw backs though so it is not the magic bullet either. A large plenum breathing through a single butterfly will have a lag between throttle opening and engine response.

Basically, there is no easy recipe for intake design. There are some rules of thumb---long thin runners=low end torque, short fat runners=high RPM power plenum volume=engine volume for superchared applications but there is no perfect solution nor is there an easy formula (helmholtz calculations can get pretty scary when one takes valve timing exhaust pulse velocities, intake pulse velocities exhaust length and desired operating conditions into consideration---even then there are 12937492137 not even accounted for so you are nowhere near optimal).

Also, I would not dream of designing a non-symmetric intake without access to a flow bench. I see you are attempting a side draft design and that means you have to verify the flow through each runner to make sure the runners flow about the same CFM. If they don't the you'll end up with a cylinder that can make more or less power than the others---not a good situation. Too much more or less and you'll be scratching your head wondering why your crankshaft failed or why your block decided to turn itsef into to two cylinder engines.

Read more: https://www.physicsforums.com

 

[joedrum]

after reading some of the crap on that forum ... the average post and threads over there ...I don't even want to say what I think of the forum or the people sheesh ... im glad we don't have many of those types trolling around here sheesh ....

 

[Omega Man]

Just imagine what one could do with one of those 3-D printers!

~O~

 

[joedrum]

First off I'm a dummy in the world view. Never did any special schooling. But what is for real. I'm hard to beat. If one wants to know actually I never graduated from hi school or even been to one. I never made it through 8th grade I tried twice. There was nothing there I wanted to sit for at all. What the pulse is? It's simple no matter what cam or compression or whatever all the big words and numbers mean. But lets say the "oldwing is 1 1/4" runners and you could cap it off. It would have a certain suction. It might increase as it gets longer in checking it. But as soon as it drops off,that's a pulse period. It has nothing to do with anything else but the suction stroke. Compression, how its cammed, or whatever. The valves open in this mode at a certain time and that's the only thing. To further this in motor talk. You want the carb right past this point to be a great set up. And you want rather full runner from there to piston as the atomization takes up room. Did I check any of this on hooch? Hell no the carb only fits the frame in one spot. The carb is also too big. It was obvious to me that I was way past the perfect zone for carb. This is why I choked the outlets on the type 4 manifold down to one inch. After that I open it back up to 1 1/4" to the piston. As I have said before I am not experiencing any bogging whatever.
If "oldwing crankshafts were going to break. Most would have already. I've seen the slides blown completely apart from there piss poor carbs and ignition setups. Truth be known I think these same things cause jumps in timing on belts and a fraction of a second later it breaks from piston hitting the valve. So I'm not worried about the crank and my single setup.

 

[Steve83]

I remember the intake on the Dodge/Chrysler/Plymouth slant-6 engines, uneven runner length and minimal heat, but the engine ran fine. There really is a lot involved in an intake design.

Slant-6 Engine

• Steve83
• Dec 3, 2013
• 1

 

[slabghost]

So the runners with chokes basically work as a compression chamber between the choke and valve.

 

[dan filipi]

Steve83 » Tue Dec 03, 2013 3:58 pm[/url]":1sj72xts]
I remember the intake on the Dodge/Chrysler/Plymouth slant-6 engines, uneven runner length and minimal heat, but the engine ran fine. There really is a lot involved in an intake design.

Slant-6 Engine

• Steve83
• Dec 3, 2013
• 1

I guess those physics guys on that forum know more than Chevy engineers...

 

[Joep]

Thought the exhaust needed to be equal length?

 

[slabghost]

Joep » Tue Dec 03, 2013 11:52 pm[/url]":18mtnyq0]
Thought the exhaust needed to be equal length?

That is correct and the basis for many convoluted header designs.

 

[OldWrench]

I guess those physics guys on that forum know more than Chevy engineers...

That is a real good point Dan. The physics may come into play with high rpm racing engines, I don't know. I just thought it was interesting. I find the work you have done with single carb applications really interesting and applaud your efforts and ingenuity.

 

[joedrum]

all in a attempt to make it better for us oldwingers ... its is worthy deal in the big picture of high cost...we all just want to have options for us all .....

 

[AApple]

Basically, there is no easy recipe for intake design. There are some rules of thumb..... but there is no perfect solution nor is there an easy formula...

There is is, plain and simple. Volume manufacturers have to design/engineer parts/systems to work in a wide variety of geographic locations, different driving conditions, and drivers. Most ANY mass produced part is a compromise between function, manufacturing costs, and....profit. The stock Honda induction system is fine when new, and even when old, for most riders. But...there ain't nothing wrong with trying to improve it at all. It's in our nature to want to make things work better...hunter/gatherers....and tinkerers.... :mrgreen:
I think it's great youse guys are tackling this single carb deal....we're ALL learning from the fruits of your labor, time, and $$$.
Don't anyone EVER say say "It can't be done" or "It'll never work" around here....someone will step up and prove ya wrong! :clapping:
I love this place! :clapping: :thanks: :moped:

 

[Steve83]

+1!!!

 

[Joep]

AApple » Wed Dec 04, 2013 12:58 pm[/url]":1kmvtxyv]
Don't anyone EVER say say "It can't be done" or "It'll never work" :rtfm: around here....someone will step up and prove ya wrong! :clapping:
I love this place! :clapping: :thanks: :moped:

Just get out of the way if those doing it.... :smilie_happy: :smilie_happy: :clapping: :smilie_happy: :smilie_happy:

 

[ianstaley]

My bike is not a racing bike and I personally don't have a number cruncher to do all the math for me or even a design team designated to get me 2000 HP from my 1 Litre engine. As far as I am aware the highest HP engine made was the 1.5 Litre Coventry Climax V8 of the early 60's that produced about 500 flywheel HP per litre, however it was a racing engine. The situation as I see it is I need to make my OLD bike run, the current carbs are foobarbed, I could spend a lot of time cleaning them refurbishing them and getting them to work, total cost ? or I can look for an alternative that is not only a reasonable price but would have a better than good chance of working well.

The solutions that have been put forward here in various threads has led me to my choice. I have a 32 DFT duel choke Webber Carb, that not only has lots of spare parts available but choke sizes, air mixture needles and about NNN needle sizes that I can change to suit my needs. If I am wrong please shoot me down but as I see it my plenum has to provide a mixture of air and fuel, in the old system the plenum is before the carb so in theory if I require x amount of air before the carb then I can only make use of the total volume per second of the plenum. My reasoning is thus, the plenum is before the fuel feed. therefore the amount of air used is in any one cylinder at any time cannot exceed the total volume of the plenum plus or minus a few cc's due to piston suck through the valves I can say this because the faster you go the more air you need to burn to keep the engine running effectively, note here effectively not efficiently as no 2, 4 or whatever stroke combustion engine can be efficient.

Now by changing the carb set up, the plenum is now after the fuel delivery but that fuel delivery is dependant on the volume of air passing the fuel jet. this is no longer defined by the plenum but the butterfly on the primary and secondary cokes. All the plenum does in the new situation is to deliver the mixture to each piston as required. In my opinion this is a much better and controllable arrangement, as the plenum does not dictate the volume of air it becomes nothing more than a delivery system. I do believe that the internal diameter of the inlet manifold tube will have an effect on the velocity and hence density of the air/fuel mixture reaching the cylinder. At this point my brain is beginning to hurt and at this point I refer back to those that have experimented and there real world results.

In theory everyone in world can be a multi billionaire but in reality how many are there.
Personally, I am with the suck it and see crowed. in theory, theory is a great tool but rarely does theory and reality match.

 

[joedrum]

sheesh a lot said there but I really like the last statement ... real world testing ... you are absolutely right there ... in your case im sure England has it own real world conditions as oppose to mine ....the biggest reality is the travel length of charge for motor .....your motor is 600ccs short on draw for the carb being a 1000 so your results are going to be different .... but I can tell you ...if it was me I would choke the type 4 plenum to 1 inch in the oulets and go from there ...but there are others who say you don't have to ...that wasn't the case for me ...its seems in theory that you would for sure need to on a 1000 motor .....

but the best thing you can do is just set it up the best you can ..and give it a shot ...and let the real world testing start at your house is the best guidance I can give Ian ...one thing for sure you have some great parts to work with this I know for sure

 

[ianstaley]

/Oh yeah dude I fully agree with you there, when the time comes I will collecting all the info I can on this, I may even pay out and have the tubes bent especially for this carb set up. so I would be looking at using the original mounting rubbers on the tubes and plenum end.

 

[slabghost]

No one has tried installing the type 4 plenum sideways. 4 90s on the runners might be better than bending and the carb turned 180 might allow use of the choke. Just a thought.

 

[ianstaley]

That isn't such a bad idea either, at least you should be able to make the runners near equal length. Worth a look anyway.

 

[Dusterdude]

Hmmm,thats a thought


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