Roller Barrel throttles investigation / fabrication

[Davidv]

Hi, I have been giving some thought to making some Roller Barrel throttle bodies. 

So firstly if you havent seen them, the idea is that they are a rotating tube (barrel) with a hole in it.



Rather than a butterfly valve which always has something in the flow path, even at full throttle.

There are only a few cars that run these, or have run these - For a few good reasons. 
But the BTCC Vauxhall 2 litre engine ran these with a cool looking set. And made somewhere in the order of 320hp NA:



https://racecarsdirect.com/Advert/Details/82002/swindon-rollerbarrel-throttle-body-kit-vauxha

One of the Caterhams runs roller barrel throttles from factory, with a set made by Titan/Cosworth.

Apart from that, and a few references to them previously being used in F1 cars at some point, there seems to be very little information about them.

So the benefits: 

1. Gimmick factor
2. Low restriction 
3. Can keep the entire intake length, the same profile as the port easily. Rather than needing to go to a round shape to suit a throttle plate
4. Very compact 
5. Very easy to fabricate compared to butterflies 
6. Apparently generates very little vacuum at part throttle 

The downsides: 
1. They have a tendency to jam
2. Not very resilient to fuel sludge residue or small particles coming into the barrel / housing clearance. 
3. Apparently the opening rate is very very very non linear. Like, quarter throttle feels like full throttle. 
4. Apparently generates very little vacuum at part throttle (Yes this is a benefit and a downside)
5. If the roller is very close to the head you can have poor quality of airflow/airspeed and so poor air/fuel mixing. 
6. The inner part of the barrel pulls some amount of vaccum, and you can have fuel pooling issues inside the barrel with extended periods of part throttle.

So here's why I'm going to make some anyway even though they are pretty much unreliable garbage: 
1. Gimmick factor
2. They are very light
3. Learn how to make something new 
4. I can use e-throttle to overcome the traditional disadvantage of a non linear opening rate
5. Gimmick factor
6. Possibly slightly higher horsepower potential
7. Gimmick factor

So the first thing was to draw up a model. Pretty blatantly copying the Vauxhal and Cosworth design here.
Two cylinders per barrel.
But with dimensions to suit the ports of my engine. 
No point in reinventing the wheel. (Well, lets ignore the fact that roller barrels are shitty so I'm essentially reinventing a triangle shaped wheel)



Then made some molds for the trumpets, for making some molds for the trumpets, to make the trumpets. Without the return edge on the bellmouths for starters while I try figure out how to make molds and use carbon fiber and so on.

Gotta love 3D printing.







Then after about 500 iterations and failures, making one that turned out alright. Not quite there but learning something from each iteration. Nearly good enough! 



I might add some draft angle / taper to the length of it and mmaaaayyybbeeee think about the allowance of a secondary fuel rail at some point. Seeing how I've got enough injector drivers and so on for staged injection with the Xtreme.
I've 3D printed a test pair of the throttles, that I've test fitted to a dummy engine. But need to pull my car's actual intake off at some point and test for clearance to see how long the trumpets can be. 
I'm anticipating that they will need a curve in them for bonnet clearance, for the length I'd want. But that's not an issue.

From here I need to finalise a few bits such as, decide what sort of bearings to use to support the rollers. 
Decide how to fit return springs to the roller assemblies. 
Decide how to balance the two halves together. 
Decide how to actuate the throttle, either cable pull for starters or e-throttle. 
The outer housings themselves though, and the flange to the engine are as good as finalized though. 
So just need to find a few chunks of alloy and start machining!
Or possibly get the housings cast instead. 

I am anticipating that MAP readings will be next to useless. So it will likely be Alpha N based tune, or depending on how the airbox and intake arrangement works out. Possibly MAF based so long as the pipe isnt too big. Thinking that 4" pipe might be about the limit before you dont get much resolution from a MAF. But could perhaps use an Alpha N / MAF cross over. Will see how it goes.
First thing is to start/finish making them haha.

Dont hold your breath for updates this is going to take me a few months of mucking around to get sorted from here.
But a brain dump of what I've been doing so far will help keep me motivated! And some peer pressure haha.

[Adamw]

For an all out NA race engine I think barrel throttles are a good option.  As you say the main benefit is the fact that you make the throttle profile any shape you need to keep the air flow as laminar as possible.  The picture from Mikko Kataja's 4AGE set below demonstrates this nicely.   With some of the 16V engines I have played with looking for more flow, once you go beyond about 51mm round butterflies you just have too much taper for it to work well.  Interestingly though about 10years ago I had a friend that used to design the throttle bodies for one of the Aussie V8 supercar teams, his designs used retangular butterflies (V8 retangular ports) with a vertical throttle shaft (aligned with the valve guide).  He claimed that with the shape of the butterfly and shaft (I assume they were tapered) they could reduce the disturbance that the valve guide and stem hanging into the port causes and made better flow than the barrel design (dont see that idea working on a 4valve engine tho...).

I have been planing a set of roller throttles to try on my brothers BTTC car one day (slide throttles at present) so will be interested to see how you go.

Mikko Kataja 4AGE throttles:

[Davidv]

3 hours ago, Adamw said:

I have been planing a set of roller throttles to try on my brothers BTTC car one day (slide throttles at present) so will be interested to see how you go.

Mikko Kataja 4AGE throttles:

Oh my - Your brother has a BTCC car? Details please! 

And yes that 4AGE / starlet is the business! 

Also, with regard to linearity of throttle actuation. 

I ran this through the flow bench calculator thingy at different throttle opening angles, to measure the restriction in 5 degree iterations. 
Doesnt look nearly as bad as I thought, but this is hoofing an absolutely tremendous amount of air through a runner in steady state. 



But I'm thinking part of the reason people talk about drivability issues at part throttle could be on account of the roller barrel being so close to the head, and negatively impacting air/fuel mixing & airspeed. 

It's also possible that when the airflow demand is much smaller it will reach peak required amount of airflow at a very low throttle angle. 

Something else that I've noticed about the Titan rollers, they actually have a trimmed out part on the front face of the roller, so the inside of the barrel doesnt fill with partial vacuum. 
At idle conditions there's a 6mm gap between the front roller edge and the housing, while the back is shut. 

That probably solves the fuel pooling issues and weird issues that arise from having two "cut off points" in the flow path at low throttle angles.

[Adamw]

17 minutes ago, Davidv said:

That probably solves the fuel pooling issues and weird issues that arise from having two "cut off points" in the flow path at low throttle angles.

The more common way to do it is as per your swindon picture, your primary injector would be after the throttle so there can be no "pooling", the secondary outboard injector would only activate at WOT.  

 

22 minutes ago, Davidv said:

Oh my - Your brother has a BTCC car? Details please! 

http://www.supertouringregister.com/register/vehicle/96/

[Davidv]

Thats awesome! 

Is the head reversed on that? Am I right in thinking its a gen 3 3SGE based engine. 

Pity it's not a beams or you could use my same roller setup. 

And re: fuel pooling, a friend said that when he tried it (with inboard injectors only) you'd just get fuel vapour/mist partially sucked into that inner part of the barrel because it holds a partial vacuum. Then it's got nowhere to go because of the barrel angle. 

So then when you go WOT it all dumps into the intake. 

Not sure how much of an issue it really is though.