GSXR600 TBs

[imago]

Quick question for those who've used GSXR600 TBs for a turbo set up. Do you remove the secondary butterflies?

I'm modifying the spacing for a B12, but it's normally aspirated so I'll be using the secondary butterflies. It seems that converting to injection is mostly done as part of a turbo install though so I'm just curious as to the differences between NA and Turbo use.

[Arttu]

Yes, the secondary blades are usually removed.

It's another question if it would make sense to use them, on normally aspirated or turbocharged engines... Based on manufacturers advertisements it seems their purpose is to improve torque at lower rpms but I think their main purpose is to limit torque at lower gears and low power drive modes. Most likely they are also used to limit noise for noise certification tests. They can be used to tame down throttle response too. It's possible that you could gain some low end torque with them too but I don't know how significant improvement it would be. Most likely not very dramatic.

If you are going to use them you'll need an ECU that can support them. At minimum that would mean electronic throttle support and in addition the control strategies should support this dual throttle arrangement somehow.

As bottomline I wouldn't worry too much about them. Unless you are definitely sure that you want to keep them.

[Gixer1460]

Are you retaining the OEM ECU to drive them? Otherwise can't see the point for including a intake restriction even if open!

Just seen Arttu has given better explanation ✓

[imago]

The main part of their function is to control intake velocity on throttle opening, as you rightly point out the bottom end/low RPM side of things. The ports are sized and shaped for optimum velocity within a rev band, and below that they're too large and free flowing. The secondary butterflies modify that at initial throttle opening and lower rpm. IMHO for a NA road bike they're a big benefit for 'normal' riding. So I can see why they'd have a negative effect for something with a bloody great turbine fitted. 

The more I look into ecu control the more I think that although it's a fair bit of work and head scratching I might as well go the whole hog. It's a main feature/part of the plan for this build, and the hardware side will be reasonably straightforward. The mapping and programming will be 'challenging'. 

I've been thinking about trying to set up ride by wire too, but that may turn out to be a step too far. On the one hand it will give a huge increase on the level of control. On the other it would be an exponential increase in the mapping complexity. Again though, it's in keeping with the 'all in or leave it alone' approach to the electrical and electronic side of this build.

In terms of mapping it may be better to use a race map for a bike with all the bells and whistles, then de-tune everything to nearer normal parameters and use that as the starting point.

[Arttu]

1 hour ago, imago said:

The main part of their function is to control intake velocity on throttle opening, as you rightly point out the bottom end/low RPM side of things. The ports are sized and shaped for optimum velocity within a rev band, and below that they're too large and free flowing. The secondary butterflies modify that at initial throttle opening and lower rpm. IMHO for a NA road bike they're a big benefit for 'normal' riding. So I can see why they'd have a negative effect for something with a bloody great turbine fitted. 

Generally agree with that. But open questions are how much you can affect on port velocity with the throttle blades and how big that "big benefit" really is. NA or turbo doesn't make much difference here, IMO. The same principles apply on both.

Basically the secondary butterflies do the same than using part throttle instead full throttle. Only difference is that you can automate their operation. In some cases I have noticed that engine seems to make more torque at part throttle than full open, typically at certain rpm spots at low revs. By this far I haven't systematically tested how big this difference really is, maybe I should try some day.

So if your goal is to optimize all possible aspects, yes, this is something that you can try. But just a word of caution Over the years I have followed numerous EFI conversion projects and one quite common pitfall seems to be being "overly idealistic". This means trying to make everything theoretically right, inventing problems that don't really exist in real life and spending huge amounts of time and effort to solve these. And all that before even getting the engine started. Quite often these projects don't get ever completed. So try to avoid that

[imago]

Agreed. I think the only thing I'd pick up on is the difference between turbo and NA using the same port profile. Unless the port profile was designed for turbo (higher volume and velocity) then adding a turbo but keeping the secondary butterflies will move the optimum to a different rev range. Removing the secondaries will move it 'back' to an extent. I don't want to do that because it's remaining NA, the ports will be unchanged, as will the valve timing etc. So all I will 'gain' will be efficiency and smoothing out the transition through the range.

My aim really is to do it, which sounds a bit daft but what I mean is it's the exercise/challenge of making it work that I'm interested in much more than I am in gaining power or torque although I expect that there will be some modest improvements in both.

Sound advice on keeping things achievable.  Roughly speaking my goal is ECU controlled sequential spark and injection. The approach will be the physical components gathered and fitted, then a big learning curve with the software and mapping including some dyno time with someone who knows what they're doing with whichever ecu I end up using.

Once I get the bike physically built the electrical and electronic work can happen in its own time. 

[Arttu]

6 hours ago, imago said:

Agreed. I think the only thing I'd pick up on is the difference between turbo and NA using the same port profile. Unless the port profile was designed for turbo (higher volume and velocity) then adding a turbo but keeping the secondary butterflies will move the optimum to a different rev range. Removing the secondaries will move it 'back' to an extent. I don't want to do that because it's remaining NA, the ports will be unchanged, as will the valve timing etc. So all I will 'gain' will be efficiency and smoothing out the transition through the range.

When comparing boosted and NA engines the port volume flow and velocity aren't that much different. Just air denisty is higher on boosted ones. So optimal intake tract sizing isn't much different either. The secondary plates should cause only minimal restriction when they are fully open so for high rev range it doesn't make much difference if you keep them or remove them. At lower revs where you possibly can gain something by limiting opening of the plates a turbo engine isn't making any boost so the gain would be similar for it. And even if it makes boost it would still get the gain.

[imago]

1 hour ago, Arttu said:

When comparing boosted and NA engines the port volume flow and velocity aren't that much different. Just air denisty is higher on boosted ones. So optimal intake tract sizing isn't much different either. The secondary plates should cause only minimal restriction when they are fully open so for high rev range it doesn't make much difference if you keep them or remove them. At lower revs where you possibly can gain something by limiting opening of the plates a turbo engine isn't making any boost so the gain would be similar for it. And even if it makes boost it would still get the gain.

Forgive me, but surely that omits the effect of the intake pulse which is directly affected by inlet shape and length? For NA pulse is purely valve opening and piston movement. With a turbo the pulse is flattened/smoothed to a degree by the boost from the turbo.

The secondary butterflies will make more difference to a NA engine at low rpm where the pulse would have greater effect without their damping effect. The boost from a turbo will already be damping that pulse so partly open butterflies will be causing a greater restriction than needed. 

As you say, once the revs are up or at WOT secondary butterflies make no difference as they're wide open in line with the wide open primaries.

Edited December 8, 2022 by imago

[DAZ]

24 minutes ago, imago said:

 

As you say, once the revs are up or at WOT secondary butterflies make no difference as they're wide open in line with the wide open primaries.

My experience is that on std bikes they are also sometimes used to limit top end power actually closing slightly to "save" the engine very prevalent on 1250 blandit,and on h2sx results in an easy 30+hp gain with a remap to keep them open 

[Arttu]

22 hours ago, imago said:

Forgive me, but surely that omits the effect of the intake pulse which is directly affected by inlet shape and length? For NA pulse is purely valve opening and piston movement. With a turbo the pulse is flattened/smoothed to a degree by the boost from the turbo.

As far as I know boost doesn't flatten the intake pulses and resonances. That should work just like on NA engine. Only resonance frequensies / rpms may change a bit due to higher pressure and temperature. But relatively these are less important on boosted engines since by modest boost increase you can easily get bigger power increase than by matching intake resonances perfectly.

[imago]

It doesn't flatten them exactly, but it does dampen the effect and take off the peaks or extremes. The plenum is under pressure and it maintains that pressure within a range but never drops as low as atmospheric. NA engines have the air box (or trumpets etc) at a theoretical maximum of atmospheric pressure which drops to a negative. The pulses in a turbo don't run through as wide a range as they're (in theory) at a maximum 1 bar + boost pressure dropping to a minimum (in theory) of boost pressure. Pulses in a NA is going to drop from 0.5 bar to -0.5 bar (again theoretically). 

So as I understand it the pulse for a turbo will be most 'damped' at low boost/low rpm/moderate throttle, which is where the secondaries are having most effect in a NA engine.

I'm not really familiar with more than the basic theory of turbo chargers and their effects, and I haven't any practical experience of them on petrol engines. I've only ever worked with them on big diesels.

There's a lot of interesting stuff to read through though, including your write ups. The problem with that is it makes it very tempting to get stuck in. 

This is worth a read, a bit wordy and nerdy, but some very good theory/background info. https://www.researchgate.net/publication/290019008_Development_of_an_Engine_Variable_Geometry_Intake_System_for_a_Formula_SAE_Application

[Gixer1460]

Quick correction - a NA airbox never goes below atmospheric pressure. Sub-atmospheric (vacuum) is only present engine side of throttle blades / slides.

My understanding of inlet pulse tuning is that the pulse only extends as far as a change of cross section or an edge ie. ram pipe opening, where it reverses and hopefully gets back to the inlet valve as it is closing. I'm sure that the same pulses occur in turbo installs and are equally limited to the section / edge change, the pulses being not so much measured at 'normal' speed but ultra / hyper sonic and as such the optimum tuning only occurs at a very narrow rpm range unless you get beneficial harmonics as well.

[imago]

Pulse tuning is a very complicated process, and very expensive to change even in development. All the stuff I mentioned is purely about their existence and what/where they occur and change because the tuning side of it is proper head melting level of maths and physics. 

In a standard production NA intake the pulse extends all the way to the filter. That's where I mention the theoretical maximums and minimums with the aim to drop below atmospheric pressure. The filter acts as a damper but there is a big pressure drop between the intake side and the engine side of the filter. From that point on the ideal is to maintain low pressure but the intake pulse comes into effect to balls that up.

With a turbo providing positive pressure before the business end of the intake and after any filter which may be fitted there is less reliance on the pressure being as low as possible to get a charge of air in because it provides push where a NA relies on draw created in the cyls. That push behind the draw overcomes the low end of the draw/depression and also takes the peaks out of the wave.

All of the above (and earlier posts) should be considered as the theoretical end of things. As soon as you add in real world stuff it all changes quite wildly with knock on effects building up all over the place. I guess that's why you can have a poorly set up turbo with an inappropriate carb on a worn engine and you'll still see some 'improvement'.

[Arttu]

22 hours ago, imago said:

It doesn't flatten them exactly, but it does dampen the effect and take off the peaks or extremes. The plenum is under pressure and it maintains that pressure within a range but never drops as low as atmospheric. NA engines have the air box (or trumpets etc) at a theoretical maximum of atmospheric pressure which drops to a negative. The pulses in a turbo don't run through as wide a range as they're (in theory) at a maximum 1 bar + boost pressure dropping to a minimum (in theory) of boost pressure. Pulses in a NA is going to drop from 0.5 bar to -0.5 bar (again theoretically). 

So as I understand it the pulse for a turbo will be most 'damped' at low boost/low rpm/moderate throttle, which is where the secondaries are having most effect in a NA engine.

I'm not really familiar with more than the basic theory of turbo chargers and their effects, and I haven't any practical experience of them on petrol engines. I've only ever worked with them on big diesels.

There's a lot of interesting stuff to read through though, including your write ups. The problem with that is it makes it very tempting to get stuck in. 

This is worth a read, a bit wordy and nerdy, but some very good theory/background info. https://www.researchgate.net/publication/290019008_Development_of_an_Engine_Variable_Geometry_Intake_System_for_a_Formula_SAE_Application

I'll try to find time to take some intake pressure plots from an engine simulator software...

Yes, there are plenty of interesting stuff in those research papers. But usually you have to read them quite carefully to get a proper idea what has been studied actually. Sometimes they have quite narrow and theoretical scope so their relevance to real life might be limited.

[imago]

3 minutes ago, Arttu said:

I'll try to find time to take some intake pressure plots from an engine simulator software...

Yes, there are plenty of interesting stuff in those research papers. But usually you have to read them quite carefully to get a proper idea what has been studied actually. Sometimes they have quite narrow and theoretical scope so their relevance to real life might be limited.

That'd be good if you could. Real world info is always more useful than theory, especially when you're talking about things which are made/modified to work rather than part of a development program.

As I said earlier, I have no practical experience with turbos on SI engines. So don't take any of what I've said as an argument or contradiction, just trying to get things straight between theory and practice for myself.