4 stroke turbos?

superchargers are much more expensive/difficult to setup AND they aren't very efficient. If nothing else, you would have to have a drive system coming off the crank, which would be very fragile, make the bike engine wider. Not what you want on a dirt bike

There is no lag whatsoever with the smaller turbo's. Literally, cruising at 30mph, I have 3psi showing. I get 3psi just by blipping the throttle in neutral. You can't compare it to any car you've ever driven.

what he described is a draw-thru system. IMO, they are always crap. Horrible drivability. Needs to be blow thru. Only problem with blow-thru is you have to have a fuel pump, so you have to have a charging system and battery.
The system he is mentioning was not a draw though. It wasn't even a supercharger. It was really nothing more than an oversized computer chassis fan that mounted in a modified filter cage in the air box and ran off the ignition power. The fan had no shrouding, and no attempt to pressure balance the float bowl was made, in spite of the fact that it was, or would have been, had it actually created any pressure, a blow through system.

Ideally, a turbo should always have the throttle plates on the atmosphere side of the compressor, but ideally, EFI would be used in place of a carb, eliminating the behavioral problems carbs bring into the equation whichever side of the windmill they are mounted on.

The system he is mentioning was not a draw though. It wasn't even a supercharger. It was really nothing more than an oversized computer chassis fan that mounted in a modified filter cage in the air box and ran off the ignition power. The fan had no shrouding, and no attempt to pressure balance the float bowl was made, in spite of the fact that it was, or would have been, had it actually created any pressure, a blow through system.

ah, never mind then. Its more likely to restrict the system than create added power no matter where the fan is...

Ideally, a turbo should always have the throttle plates on the atmosphere side of the compressor, but ideally, EFI would be used in place of a carb, eliminating the behavioral problems carbs bring into the equation whichever side of the windmill they are mounted on.

and why is it better to have the TB on the turbo inlet? I see nothing but disadvantages for putting it there.

there is no "behavioral problems" with carb'd blow thru. *none*

and why is it better to have the TB on the turbo inlet? I see nothing but disadvantages for putting it there.
The Throttle plates are exposed to more normal pressure influences, and will create normal manifold vacuum between the plates and the compressor stage for systems that depend on that. It is how virtually all of the factory installed turbos are done, carbed or EFI.
there is no "behavioral problems" with carb'd blow thru. *none*[/QUOTe]Using a blow though layout, in which the carb is mounted between the compressor and the engine, requires that every area of the carburetor that is exposed to atmospheric pressure is a normally aspirated installation be pressurized to match the pressure being delivered to the intake. Why this is true is obvious. Carbs depend on there being lower pressure in the carb throat (venturi) than in the float bowl so that the higher pressure in the bowl will raise the fuel through the jets, and into the intake air stream. If the float bowl remains at atmospheric pressure, all fuel flowing through the jets would cease as soon as any positive pressure was created by the turbo/supercharger.

The usual way this is handles in cars is to enclose the entire carb in a sealed air box of its own, creating a balance with the compressor pressure to all parts of the carb. Not even the bowl overflow line can be allowed outside, and any fuel lines or linkages that enter the box must be sealed.

Then too, fuel must be pumped to the carb at pressures exceeding the expected boost. This can create problems when expected boost pressures will exceed 5-7 PSI, because of the very high fuel pressures, relative to ambient float bowl air pressure, when running below boost. Flooding can be a problem unless a boost sensitive fuel pressure regulator is used.

Neither of these problems are present with draw through systems. What is encountered is difficulty with droplet suspension because of the length of the intake tract, particularly when cold.

And, of course with EFI those problems don't exist, either.

The Throttle plates are exposed to more normal pressure influences, and will create normal manifold vacuum between the plates and the compressor stage for systems that depend on that. It is how virtually all of the factory installed turbos are done, carbed or EFI.

Name some of those vehicles that use systems that have the TB before the turbo in the last 20 years. I can't think of any. All of them are TB blow-thru

Using a blow though layout, in which the carb is mounted between the compressor and the engine, requires that every area of the carburetor that is exposed to atmospheric pressure is a normally aspirated installation be pressurized to match the pressure being delivered to the intake. Why this is true is obvious. Carbs depend on there being lower pressure in the carb throat (venturi) than in the float bowl so that the higher pressure in the bowl will raise the fuel through the jets, and into the intake air stream. If the float bowl remains at atmospheric pressure, all fuel flowing through the jets would cease as soon as any positive pressure was created by the turbo/supercharger.

The usual way this is handles in cars is to enclose the entire carb in a sealed air box of its own, creating a balance with the compressor pressure to all parts of the carb. Not even the bowl overflow line can be allowed outside, and any fuel lines or linkages that enter the box must be sealed.

Then too, fuel must be pumped to the carb at pressures exceeding the expected boost. This can create problems when expected boost pressures will exceed 5-7 PSI, because of the very high fuel pressures, relative to ambient float bowl air pressure, when running below boost. Flooding can be a problem unless a boost sensitive fuel pressure regulator is used.

Neither of these problems are present with draw through systems. What is encountered is difficulty with droplet suspension because of the length of the intake tract, particularly when cold.

And, of course with EFI those problems don't exist, either.

You didn't lists drivability issues with blow-thru. You did list some drivability issues with draw-thru

Seems you are agreeing with me.

as for the method you list for designing a blow-thru setup, its quite primitive and not how its done except by people that don't know what they are doing. If you are unfamiliar with proper methods to build and tune blow-thru, no doubt you will have problems. That goes without saying on any mechanical system ever built

I don't want to point out the painfully obvious thing here, but you're talking to someone that BUILDS them. its not just a theoretical discussion, on this side of the table.

I pretty much agree both of you .

But I think one of you is talking about carbs and the other about injection.

I pretty much agree both of you .

But I think one of you is talking about carbs and the other about injection.

makes no difference. A draw-thru EFI system will not have the fuel atomization issues that a draw-thru carb setup has, but you'll still need a carbon-seal the turbo to prevent sucking in oil, you will greatly increase the intake volume with no real benefit, and you pretty much negate (or greatly hamper) the option of intercooling/heat-transfer incorporation.

All of which is thrown way for what advantages? Errr....you don't have to use a BOV. That'll save you $20 in parts.

Draw thru is way old school. It was used heavily before they figured out how to build blow-thru. No one uses it anymore, and for good reason.

Have you guys seen Uncle Bob's turbo charged Suzuki DRZ400? That thing wheelies in every gear. Though it is a supermoto, not an MX.

There's a huge thread over on Supermotojunkie, and a couple of videos on Youtube

my 450 wheelies in every gear:busted: ........

my 450 wheelies in every gear:busted: ........

fish is exaggerating, the turbo'd drz, with stock gearing, will wheelie easily in the first 3 gears. Its only making 34ish ft/lb's of torque. There's plenty of modified DRZ's making a lot more than that.

for a dead stock engine though, its not bad. Maybe some day I'll go to big bore :prof:

My stock 450 will wheelie in every gear, I couldnt imagine what it would be like with a turbo.

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