Re: turbocharger supercharger
Posted by shinyribs on Oct 01, 2011; 7:01am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/turbocharger-supercharger-tp3374914p3384502.html
Samir,they do make specific blow-thru carbs for turbos and blow-thru superchargers,usually referred to as centrifugal superchargers.They are basically the same as naturally aspirated carbs,but with a few tweaks.They change the boosters to a less sensitive design and have better throttle shaft seals.The main circuit of the carb are basically unchanged except for the air bleeds.You can make the same changes at home to any carb without any special tools.
All carbs work off of pressure differential ,not necessarily vacuum.You are right.You have to overcome the extra air pressure with fuel pressure,to keep the floats from sinking.That is where the boost referenced fuel pressure regulator comes in to play.You typically try to maintain 6-7 psi of fuel pressure under all boost levels.When the boost hits,lets say 10 psi,the boost ref. fpr will bump fuel pressure up to 17 psi. I know it sounds wrong,like it would just come overflowing out of the bowl vent.But remember,atmospheric pressure at sea level on normal weather conditions is 14.7 psi.So if you are typically running around with almost 15 psi of air pressure in your bowl you would think it would do the same.And it doesn't.That is why you lose power in higher elevations.its not so much that the air is "thinner",it is because atmospheric "air pressure" is lower and you lose mother natures supercharger.Cars,bikes,trucks,gas motors,diesils...engines are engines,it affects them all the same.
Think of it this way.When you are running 17 psi of fuel fressure to a fuel bowl that has 10 psi of air pressure,as far as the carb is concerned,you are still running only 7 psi fuel pressure.Its all in the differential,dont let the pressures themselves fool ya.
The roots blowers(draw-thru/under carb mounted)that you mentioned SEEM like they would be a breeze to tune since it is in the the conventional/underneath position,but they create such a massive amount of vacuum that it is not simply a bolt-on deal either.Plus they create air pulses that are hard to tune around.That is where you get that rump...rump...rump blower motor lope.It is actually the sound of a poorly tuned motor going lean...falling on its face...gasping for breath and then jerking back to life.It is absolute murder on valve train and anything else depending on constant oil supply at idle which is ...everything.Much easier to tune though and much more repeatable as far as driveability.Plus they just look way cooler than anything in the world and make that sweet screaming sound at about 7 grand.Dang,i wanna build another blower motor now!
Samir,google blow-thru carburetors.
The carb enclosure that you are talking about Daddyman is a totally different way of doing the same thing.With an enclosure,the entire carb is under the same amount of boost all over(venturis and bowl vents)so the carb uses engine vacuum to create the pressure differential,operating as "normal",but since the entire enclosure is boosted it wil still force feed the supercharged air into the engine.A carb enclosure is an extremely easier way to do the job,as far as carb tuning is concerned.The tough part,and why so many people avoid it now,is leakage.First of all you have to seal all your linkages and fuel lines entering the enclosure,not too hard to do.The real tough part is the throttle shaft bushings.The shaft that the butterflys are mounted on.Once they start leaking it all goes to pot.A typical street driven car will start leaking at the shaft at about 1000-1500 miles.Not real bad,but enough to cause issues when the boost hits.Then you find yourself trying to o-ring your shafts and i havent known anyone to perfect it yet.UNLESS,you use a Predator carb,then the shaft leakage issue is gone,but those carbs suck to tune in the first place...in a major kind of way.Plus they are really only good for WOT
That is the reason why almosy every successful race car you see with forced induction is EFI.I am old school and hate to admit it,but when it comes to turbos and supers,EFI simply rules the roost.
Make sense?Sure it does.My finger just cramped...ow