Velocity stacks

[Reinhoud]

Just curious..

 

I know what velocity stacks should do on carburetors, but do velocity stacks anything in a plenum of a turbo charged engine?

 

 

[Arttu]

Yes they do. Basically the same than on N/A engine. In practice they aren't that critical on boosted engine since the effect is relatively small compared to boost. But if you want to build an efficient engine they are definitely one of the things to keep in mind.

[Reinhoud]

14 hours ago, Arttu said:

Yes they do. Basically the same than on N/A engine. In practice they aren't that critical on boosted engine since the effect is relatively small compared to boost. But if you want to build an efficient engine they are definitely one of the things to keep in mind.

Thanks!

I saw it somewhere, and that got me curious..

 

Do you have an idea about dimensions? Or how/ where I can find it?

 

Bike is in parts at the moment, so I can f around with it.

[Blower1]

It can be difficult to find stacks with right dimensions for your plenum.

Dimensions depends on many factors, but stacks should not be too close to the plenum end wall, about 15 mm minimum gap.

Stack "bell lip" should be as round as possible. If you google perfect velocity stack you will find many pictures.

 

There are my solution about velocity stacks in plenum: 

 

[Reinhoud]

Thanks.

I already thought they shouldn't be to close to back wall, no clue how much.

For the rest I'm clueless.

 

But it should be noticeble?

[Slabby11]

The Kawa turbo 750 plenum used standard type rubber connectors with velocity stacks in the plenum - mid 80's tech but might be worth a look to see how they did it.

[Joseph]

Something like this worth using ?

[Reinhoud]

5 hours ago, Joseph said:

Something like this worth using ?

I need steel, and they need to be short.

 

I already have an idea and ordered a cutter to make a radius..

[Joseph]

Yeah. I need alloy, and they can be shortened 

I'm Just wondering if the profile of the ones i have are rounded out enough

[Gixer1460]

Tests on NA ram pipes show that any radius more than 90 - 100 degrees perpendicular to airflow produces little increases. As regards pipe opening to internal plenum face - a minimum of 10mm is recommended - more is better and closer to the outlet wall is maybe best position. If you want steel ram pipes you could use Weber DCOE pipes 17mm is their shortest I think, and dia's of 40, 45, 48 & 50.

[Reinhoud]

2 hours ago, Gixer1460 said:

Tests on NA ram pipes show that any radius more than 90 - 100 degrees perpendicular to airflow produces little increases. As regards pipe opening to internal plenum face - a minimum of 10mm is recommended - more is better and closer to the outlet wall is maybe best position. If you want steel ram pipes you could use Weber DCOE pipes 17mm is their shortest I think, and dia's of 40, 45, 48 & 50.

I'm going to make some myself, the tubes on the plenum to the carbs are a bit smaller. Now I can make it with the exact dimensions as the carburetors.

I ordered something to cut a radius with.

[Reinhoud]

I've got my bike on the road again, haven't really given it to it.

Made a plenum what is roughly 160cc bigger, and made velocity stacks in it.

The bike reacts way more enthusiastic on the throttle.

 

May post photo's later

[Reinhoud]

Right is the stack I made.

Left next to it is what I had, bit smaller than the carburettor.

[Reinhoud]

How it looks from the inside.

Edited October 27, 2023 by Reinhoud

[Reinhoud]

Finished

 

[Maggotbreath]

Looks great!

[clivegto]

Lot of Mr Dunlops early plenums used the standard B12 airbox rubbers which seemed like a good idea to me. 

[Joseph]

So good to see how far his product quality has leaped 

[Gixer1460]

1 hour ago, clivegto said:

Lot of Mr Dunlops early plenums used the standard B12 airbox rubbers which seemed like a good idea to me. 

Unsealed? Looks like it - maybe not so wise with blown application . . . doesn't much matter when NA.

[clivegto]

59 minutes ago, Gixer1460 said:

Unsealed? Looks like it - maybe not so wise with blown application . . . doesn't much matter when NA.

Works though the pressure seals them 

[Duckndive]

48 minutes ago, clivegto said:

Works though the pressure seals them 

Loppie did one using a sealed stock airbox as well just for fun as someone said it would not work 

[Reinhoud]

Update;

 

Got the bike going again after the accident, had to butcher another frame..

The plenum (160cc bigger) I have made defenitly a difference! Better throttle response off boost, on boost I can't really tell because I also put another turbo on it.

But I needed bigger jets.

It's a bit stronger in the lower revs, and a better throttle response, so it wasn't a waste of time