Draw thru or push thru

[scotteslic]

What is the advantages and disadvantages  of each 

Thanks in advanced, 

Newbie Scott 

[peter1127]

I would say blow trough is the better solution, draw trough has some advantages but for the street it has too many disadvantages, driveability being the main one.

draw trough con

• hot turbo under the tank: vapor lock
• exhaust close to your leg
• Longer exhaust pipes so more lag
• One large carb 
• Hard to add an intercooler
• Turbo seals  needs to be able to deal with the fuel
• Turbo needs to be able to deal with vacuum
• Fuel can be unevently divided between cylinders: 1&4 tend to be leaner, or difference between 1-2 & 3-4. Sometimes a divider is added to counter that (Iguess you could add 4 injectors in the plenum and have the carb replaced by a large throttle body)
• If the engine backfires you back is literary on fire  because mixture is in the whole intake area (compressor housing, and plenum)
• Very violent on/off performance especially on large turbo big power bikes
• Difficult to add a muffler

draw trough pro

• easier to set up the one carb, because there is no pressurisation of the carb and its very easily accessible
• No FPU needed
• No pressurized carb needed
• Gravity drain of the oil is easy
• Front wheel clearance is not a problem
• Very violent on/off performance especially on large turbo big power bikes 
• looks really oldskool and cool and imo the only good reason to do it 

Blow trough con

• Setting up the carbs can be difficult (could be mitigated by adding injection but that also has its challenges)
• Carb sealing can be a challenge, fuel pressure is critically important to stay in that sweetspot between leaking and fuel starvation and so is float and needle/seat condition.  (Again could be mitigated by adding injection but that also has its challenges)
• Front wheel clearance especially on larger turbo's. I bought header and turbo at proboost and that fits nicely. Still need to experience emergency braking front wheel clearance........
• oil return need most of the time a pump. Can be electrical or mechanically. You could try gravity drain but if turbo sits low it can smoke like a mf

Blow trough pro

• Off boost behaviour is much nicer, depending on CR it can be close to stock so suitable for the road
• Intercooler is possible
• No special seals for fuel and/or vacuum are needed
• Easy to add a full exhaust
• No issue with AFR being different per cylinder (unless fuel injection, then that could happen with poor plenum design)
• Even without intercooler intake air is  cooler so more detonation resistant = more boost = more power

[Gixer1460]

Draw through comments all fairly valid IF using a carb solution! Most, if not almost all go away, if you use an injected solution. Plus Draw Through is Oldskool Cool! 

[imago]

5 hours ago, peter1127 said:

• Very violent on/off performance especially on large turbo big power bikes 
• looks really oldskool and cool and imo the only good reason to do it 

Agree with all of the post, especially those two points as they are exactly the reason I went for a draw through. 

6 hours ago, scotteslic said:

What is the advantages and disadvantages  of each 

Thanks in advanced, 

Newbie Scott 

The first/main question is, what do you want to use it for most often?

[scotteslic]

7 minutes ago, imago said:

Agree with all of the post, especially those two points as they are exactly the reason I went for a draw through. 

The first/main question is, what do you want to use it for most often?

Street bike not too radical

[scotteslic]

This is a GS1100, I was thinking EFI

[Arttu]

EFI with injectors placed on the intake ports should solve most of the fueling issues with draw through setup. But you will still need a carbon sealed turbo...

Regarding original question, I think blow-through is technically better in almost every way. So only reason to select draw-through is that you specifically want it, for example because of style and look.

[scotteslic]

Would you put a O² sensor in each exhaust tube with allow through

[Duckndive]

9 hours ago, Arttu said:

EFI with injectors placed on the intake ports should solve most of the fueling issues with draw through setup. But you will still need a carbon sealed turbo...

Regarding original question, I think blow-through is technically better in almost every way. So only reason to select draw-through is that you specifically want it, for example because of style and look.

There's a couple of really sweet runners using a single throttle body and injector on Faceache  

the videos may be on youtube   

not sure if he's on OSS but Ade Rix did a real sweet one 

[Gixer1460]

2 hours ago, scotteslic said:

Would you put a O² sensor in each exhaust tube with allow through

Waste of time and due to proximity to cyl. head or upstream of turbo (depending on style chosen) would likely fail in short order! A single sensor after turbo is usual placement but be warned if running a shortie dump pipe the sensor can be confused with atmospheric oxygen due to sensor being close to exhaust exit! Try not to fit before turbo as pressure and elevated temps not good for them!

[Arttu]

11 hours ago, Duckndive said:

There's a couple of really sweet runners using a single throttle body and injector on Faceache  

the videos may be on youtube   

not sure if he's on OSS but Ade Rix did a real sweet one 

Sure it's doable that way too. But if you inject fuel before the turbo your fuel distribution between the cylinders is at mercy of the intake manifold design.

[Arttu]

12 hours ago, scotteslic said:

Would you put a O² sensor in each exhaust tube with allow through

Usually not. It would be relatively complicated and expensive. Also there are some issues with placing the sensors before the turbo like @Gixer1460mentioned. Although it's doable if you really need to. Normal solution is to have a single O2 sensor after the turbo. And if you want to monitor individual cylinders exhaust temp sensors are quite good for that.

[Duckndive]

5 hours ago, Arttu said:

But if you inject fuel before the turbo your fuel distribution between the cylinders is at mercy of the intake manifold design.

Some Do Some Don't

The Wizzer Blows the Engine Suck's  i never had any issues using this 

[scotteslic]

Instead of individualizing everything,  use one O² sensor, 4 injectors tied together in the intake runners and one throttle body in a blow thru set up

Sorry for all the questions 

[Arttu]

9 hours ago, Duckndive said:

Some Do Some Don't

The Wizzer Blows the Engine Suck's  i never had any issues using this 

That's exactly what I meant. It can work right away if you have a good proven setup, if you are lucky or if you happen to know exactly what you are doing. But it can be be much more difficult as well...

Edited April 13 by Arttu