supercharger

[bob58o]

Ok then...

Doesnt change the bottom line being that a 24mm is the largest reasonable carb for a standard N/A set up. Depending on the intake manifold length used a 22mm could in some cases possibly perform better.

(not that it has been a specific goal, but it doesn't exceed port size by a relevant amount)

Is this not a supercharger question?

 

[A Manco Dingo]

I think I’m planning on using a 30mm on supercharged 212.

100% VE with forced induction?

in the following formula we will use the constant, K, as being proportional to VE.

0.65 for crappy VE
0.78 for average VE
0.90 for race engine (ported, gasket matched,…)

I’ll use 0.925 for forced induction, but maybe 1.00 works too. Maybe depends on quality of blower.

D = K x Square Root(C x n)

where:
D=carb diameter, in millimeters
K= constant between 0.65 and 0.90
(Higher than 0.90 for forced induction)
C=cylinder displacement, in cubic centimeters
n= RPM at peak power/1,000

K= 0.925
C = 212cc
N = 5000 / 1000 = 5 (rpm = 5000)

D= 0.925 * SqRt(212 * 5)
D= 0.925 * SqRt (1060)
D= 0.925 * 32.6

D= 30mm

I could probably create a better formula that uses intake valve size as an input so that for NA engines, the carb diameter isn’t ever bigger than the intake valve.

In general for NA engines, maybe….
If looking for top end…

24mm carb for 25mm intake valve
26mm carb for 27mm intake valve
28mm carb for 28.5mm intake valve

smaller carbs if looking for snappy throttle response and stop/go driving

i am using this go kart for drag racing so i mainly want a more wide open throttle than a snappy while acceleration is a big part in drag racing if i accelerate real fast but then i don´t have enough speed and if i have a supercharger/ smog pump the fuel has to pass trough a supercharger and a long pipe i might as well use a bigger intake i don´t really know when i read the reviews on the carb pwk 30mm carb link it is the same one you where going to use

 

[Rat]

i am using this go kart for drag racing so i mainly want a more wide open throttle than a snappy while acceleration is a big part in drag racing if i accelerate real fast but then i don´t have enough speed and if i have a supercharger/ smog pump the fuel has to pass trough a supercharger and a long pipe i might as well use a bigger intake i don´t really know when i read the reviews on the carb pwk 30mm carb link it is the same one you where going to use

Ok so for a longer intake set up a smaller carb will keep some semblance of velocity, except with the charging set up boosting the intake velocity smaller becomes problematic by flooding.

I still say a 28mm is the best size to start with for the set up.
There is one problem, get enough pressure moving through the intake tract and slide carbs tend to get stuck open.

I'm not sure if it's the column of flow putting lift forces under the slide, or if it's just the "wind speed" plastering the slide to the inner body... but I do know it's no joke.

 

[A Manco Dingo]

also i am making a ram style intake

 

[Denny]

A ram style intake is of no value to a supercharged engine. A carb scoop is only of value above 150mph.

 

[Thepartsguy]

I still say a 28mm is the best size to start with for the set up.
There is one problem, get enough pressure moving through the intake tract and slide carbs tend to get stuck open.

I'm not sure if it's the column of flow putting lift forces under the slide, or if it's just the "wind speed" plastering the slide to the inner body... but I do know it's no joke.

 

[Rat]

also i am making a ram style intake

View attachment 147492

NOPE!

Even on an N/A You get more gain from a short velocity stack pointed out of the wind than you will any form of attempted ramming.

 

[Rat]

View attachment 147493

Which is why I went with a 24mm Koso PWK copy [Keihin does not make amthe PWK smaller than 28mm] which has a Flat (actually its a D) slide

You did not indicate an exact carb type or branding. Mikuni VM (round), Mikuni TM (flat/D) Keihin PWK (flat/D) Keihin PE (round)

 

[A Manco Dingo]

NOPE!

Even on an N/A You get more gain from a short velocity stack pointed out of the wind than you will any form of attempted ramming.

is a short better than a long velocity stack

 

[bob58o]

i am using this go kart for drag racing so i mainly want a more wide open throttle than a snappy while acceleration is a big part in drag racing if i accelerate real fast but then i don´t have enough speed and if i have a supercharger/ smog pump the fuel has to pass trough a supercharger and a long pipe i might as well use a bigger intake i don´t really know when i read the reviews on the carb pwk 30mm carb link it is the same one you where going to use

That’s the style of carb I use. I normally cap off the “power jet” which pulls fuel from the bowl and dumps it into the air horn side of the carb. It’s simpler to tune just a main jet vs a combination of main jet and power jet. And AFAIK you need to make your own power jets if you want to play around with tuning it.

 

[A Manco Dingo]

That’s the style of carb I use. I normally cap off the “power jet” which pulls fuel from the bowl and dumps it into the air horn side of the carb. It’s simpler to tune just a main jet vs a combination of main jet and power jet. And AFAIK you need to make your own power jets if you want to play around with tuning it.

Thanks this helps out alot!

 

[A Manco Dingo]

That’s the style of carb I use. I normally cap off the “power jet” which pulls fuel from the bowl and dumps it into the air horn side of the carb. It’s simpler to tune just a main jet vs a combination of main jet and power jet. And AFAIK you need to make your own power jets if you want to play around with tuning it.

For a velocity stack on a carborator could i do a self adjusting velocity stack like on the mazda 787b

 

[ezcome-ezgo]

 

[A Manco Dingo]

View attachment 147511

"I need the biggest one you have"

 

[Rat]

That’s the style of carb I use. I normally cap off the “power jet” which pulls fuel from the bowl and dumps it into the air horn side of the carb.

I did a complete delete, blocking may work but it's just not good enough for me. Much the same as when I delete a governor theres no going back because I knock the gear off the crank end as well, FULL DELETE.

It’s simpler to tune just a main jet vs a combination of main jet and power jet.

It's only simpler because a powerjet serve no purpose to a 4cycle engine other than to flood it.

Powerjets are very specific to 2cycle race engines; when youre riding the powerband of the expansion pipe hard at WOT and are in the 12k + zone you need to dump a lot more fuel than the main and pilot can accomplish at such a high rpm. Without a powerjet those engines would either A.) Never get above 9k maybe 10, or B.) Run lean and torch a hole right through the piston crown in short order.

And AFAIK you need to make your own power jets if you want to play around with tuning it.

That's not accurate even a little, the different range nozzles that drop down just aren't easy to find.

 

[Thepartsguy]

I did a complete delete, blocking may work but it's just not good enough for me. Much the same as when I delete a governor theres no going back because I knock the gear off the crank end as well, FULL DELETE.

It's only simpler because a powerjet serve no purpose to a 4cycle engine other than to flood it.

Powerjets are very specific to 2cycle race engines; when youre riding the powerband of the expansion pipe hard at WOT and are in the 12k + zone you need to dump a lot more fuel than the main and pilot can accomplish at such a high rpm. Without a powerjet those engines would either A.) Never get above 9k maybe 10, or B.) Run lean and torch a hole right through the piston crown in short order.

That's not accurate even a little, the different range nozzles that drop down just aren't easy to find.

Yupp I settled on a TM24 due to it not having the powerjet like the pwk‘s.. I need to plum a boost gauge line and get a few simple clamps and I’m ready to test fire this contraption.

 

[65ShelbyClone]

Hey will a 30mm be to big for a 212

A carb configured as a draw-through needs to flow enough to not restrict the boosted engine's max power.

Speaking to a different post, forced induction doesn't change an engine's volumetric efficiency. You're also not likely to know what your engine's exact VE is because it's not easy to measure. OHV utility engines are likely in the 70% range based on HP/L. Flatheads are worse. Don't get too stuck on it.

Regarding velocity stacks, longer is technically better, but there comes a point where longer is not measurably better. A simple radiused inlet is quite a bit better than nothing at all.

There is one problem, get enough pressure moving through the intake tract and slide carbs tend to get stuck open.

I'm not sure if it's the column of flow putting lift forces under the slide, or if it's just the "wind speed" plastering the slide to the inner body... but I do know it's no joke.

A draw-through isn't going to be exposed to pressure though.

 

[Rat]

the flywheel can’t take much of anything past stock 3,600rpms because the magnet on the flywheel is held on with a screw and glue... (China)

Not true. Yes they are epoxied on and pinned in place with a metal plate and a single screw, which is specifically to compress the air bubbles out of the freshly blobbed on epoxy.
Better quality flywheels will actually have a plastic cap sandwiched in there that keeps the excess squished out epoxy contained leading to a more solid bond.

That said you need to stop with bad info because the majority of all stock flywheels are perfectly solid up to 5k. This does not mean that there has never been a bad or abused flywheel that blew up between 3800 and 4800... there have been plenty.
The odds of getting a factory cast iron flywheel that frags under 6k are about the same as buying a dud ignition coil... extremely rare, but shıt happens. The factory original cast iro 3 magnet flywheel on my 208 gets spun at 5k-6k frequently.
Just today I flogged the throttle and accelerated from 5-35 up a steep grade whith the tach reading above 5600 and that's not even letting the engine go until it stops accelerating.
I readjusted my TC and got the rpm pull down they are known for to be less agressive even with the 5.4:1 FD and 23.9 tire diameter.

If you intend to run boost seriously your gonna need at least a flywheel.

This is true, and a cast aluminum PVL is QC'd to 17k... more than any other engines we play with are going to turn, built, boosted, or both.

 

[Rat]

A draw-through isn't going to be exposed to pressure though.

How do you figure that?!?!

If there's no pressure there would be no boost and more importantly if there's no pressure then no fuel would ever leave the carb bowl.

Negative pressure is still pressure all the same, so I have no clue what 'tard sauce you been drinking but for the sake of functional brain cells put it down and walk that fuq away!

With a draw through its quite the opposite, the carb would actually be exposed to even MORE negative pressure since the the open port/descending piston would also have the negative pressure boosted by what ever amount is generated by the charger at x-RPM.

I'm Old school beyond my years, not No school like you and a couple others make yourselves seem.
I have probably forgotten more than most of these gen Z twats will ever learn

 

[65ShelbyClone]

How do you figure that?!?!

If there's no pressure there would be no boost and more importantly if there's no pressure then no fuel would ever leave the carb bowl.

Negative pressure is still pressure all the same, so I have no clue what 'tard sauce you been drinking but for the sake of functional brain cells put it down and walk that fuq away!

I did nothing to pick a fight, and I'm not going to abandon context in order to spar with you on technicalities. In this context, pressure is widely understood to mean boost. Boost is what's likely cause slide carbs to stick...blow-through carbs. A draw-through carb isn't exposed to it. I think you knew that and have just been drinking or something.

With a draw through its quite the opposite, the carb would actually be exposed to even MORE negative pressure since the the open port/descending piston would also have the negative pressure boosted by what ever amount is generated by the charger at x-RPM.

How is the carb going to be exposed to more more than a differential pressure equaling atmospheric? Explain how that works so we can all better understand.