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A Tale of Two Airboxes!

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A Tale of Two Airboxes!

Postby nsaints » Sun Jul 11, 2021 12:21 pm

Recently taken two small block kitted scooters to see Al @ Diablo, and got some dyno results around airboxes which I thought would make an interesting post

First up my TV. RT195, standard crank, 25 PHBL, GP modified airbox with the internal baffle removed, BGM mk 4 exhaust

Image

Dyno result below where Al took an as delivered base line (blue line) and 2nd run with the air filter hose removed, carb run open mouth, (red line)
I was surprised how restricted a standard GP air box was with the baffle removed!

Image

Air box was then modified with a 12 mm drill, per the below
this then de-ristricted the airbox allowing more air, and releasing more performance. see graph below comparing to a GT kit

Image

two weeks back I took my SX - Chris Sturgess fettled GT kit, 25 PHBL, scootopia clubman. I didn't want to pepper holes in a SX airbox so fitted a big bore airbox (from scooter resto')
I thought this would still need additional holes in the sides, but it didn't

Here's a graph comparing both RT and GT kits
Red line = GT186 (chris sturgess modified), 25mm PHBL, Scootopia Exhaust, big bore airbox
Blue Line - RT195, 25mm PHBL, BGM Mk4, Heavily modified GP airbox

Image

I'll let you draw your own conclusions ;)

edit:
in summary:
1, if you want to run an airbox for standard looks, whilst running a kit, don't expect much performance gain when just removing the internal baffle. you need to drill holes in the side of the airbox as well
2, the big bore air box performed better than expected, without the need for additional holes being drilled in the side
Last edited by nsaints on Sun Jan 23, 2022 7:09 am, edited 3 times in total.
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Re: A Tale of Two Airboxes!

Postby Psychedelicropcircle » Sun Jul 11, 2021 6:11 pm

I’ve yet to meet a dyno gadgie who doesn’t say the words it’s called open mouth carb for a reason!

My small block GT knocked out 16.5 hp on JG’s dyno the other week. 60/110, 28mm delly(open mouth)mb clubman.
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Re: A Tale of Two Airboxes!

Postby Warkton Tornado No.1 » Mon Jul 12, 2021 11:36 am

viewtopic.php?f=6&t=14062

I reckon your experience confirms what I said on that Post.

IMHO the OEM air boxes will never allow full performance to be achieved. It's a lot like struggling with an old vacuum cleaner when everybody else has a Dyson.....(not that I'd buy one of his revolutionary products since the multi-millionaire up-sticks to exploit cheap labour abroad)

However. Stepping down from my soapbox :roll: Because I believe that air filtration need not be restrictive, I have a 'project' in hand to utilise the envelope of space provided beneath panels with toolbox, tank & battery in place to create a plenum/airbox capable of delivering an adequate filtered air supply fed via the standard frame air scoop hole. The base motor for tests will be circa 25+ BHP with efficient carburation up to 34 mm. It needs to be serviceable & suit standard OEM size, larger &/or downdraft carburation.

Who knows? If it works, I might even try it with a PH carburettor before I finally throw it off a cliff :lol: as so many of you appear to have them....
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Re: A Tale of Two Airboxes!

Postby vegansydney » Tue Jul 13, 2021 11:11 pm

Fascinating! I knew they were restrictive, but had no idea that drilling holes would result in 3HP extra! I'm not a fan of warm, dirty air from the under the panels so on my RT195 (58x116, 65mm TS185 piston, TM24) I use a late S1/early TV S2 wide neck airbox and here is the airbox I've recently made for my current GT186 (also Mikuni TM24) project. The top was salvaged from a rusted out S3 airbox and drilled out with a hole saw to accept a piece of Ø50mm OD pipe.

Image

PS: That early TV is beautiful. Very nice work. Early TV S3 are the pinnacle of Innocenti design IMHO.
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Re: A Tale of Two Airboxes!

Postby nsaints » Sat Jul 17, 2021 10:55 am

Nice work on the airbox

I agree with what you're saying about warm air being inducted into the engine, and better to use cooler air. I may fit a larger neck airbox to the TV as a result of what I now know.

Regarding how hot it get's under the panels, when I bought the TV (incidentally it's a US import) it was a hot day in London. I caught the train down to Paddington, with a plan to ride it back to Oxfordshire. Being prepared I took a small 1 litre petrol can of fuel just incase. Met the owner and the TV at the prearranged place, exchanged monies and paperwork and I was the new owner. Some tools I bought along as well as the fuel all fitted inside the standard toolbox. And off I went - must have been a 30 degree day.
Nice ride out of central London, down the west way, dropped onto the A40 and back through high wycombe, oxford and home.
When I got back and opened the toolbox door I realised how close I was to a complete disaster. The heat from the day and the engine had expanded the fuel in the canister so much it was like a balloon! I almost couldn't get the canister out the toolbox through the opening it was so large. I shudder to think of the consequences if it had burst on the way home. :o

Moral of the story, never ever carry spare fuel in a standard lambretta toolbox...
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Re: A Tale of Two Airboxes!

Postby Storkfoot » Sat Jul 17, 2021 11:50 am

nsaints wrote:Nice work on the airbox

I agree with what you're saying about warm air being inducted into the engine, and better to use cooler air. I may fit a larger neck airbox to the TV as a result of what I now know.

Regarding how hot it get's under the panels, when I bought the TV (incidentally it's a US import) it was a hot day in London. I caught the train down to Paddington, with a plan to ride it back to Oxfordshire. Being prepared I took a small 1 litre petrol can of fuel just incase. Met the owner and the TV at the prearranged place, exchanged monies and paperwork and I was the new owner. Some tools I bought along as well as the fuel all fitted inside the standard toolbox. And off I went - must have been a 30 degree day.
Nice ride out of central London, down the west way, dropped onto the A40 and back through high wycombe, oxford and home.
When I got back and opened the toolbox door I realised how close I was to a complete disaster. The heat from the day and the engine had expanded the fuel in the canister so much it was like a balloon! I almost couldn't get the canister out the toolbox through the opening it was so large. I shudder to think of the consequences if it had burst on the way home. :o

Moral of the story, never ever carry spare fuel in a standard lambretta toolbox...


I don’t think I have ever carried petrol in the toolbox but, to be honest, I probably would have before seeing this. Thanks for sharing it.

As for those egg butties you buy at a Service Station for later on down the road :o
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Re: A Tale of Two Airboxes!

Postby Warkton Tornado No.1 » Sat Jul 17, 2021 3:24 pm

Think about what happens to the rally goer's used chuddies stuffed in the toolbox! They'd be crawling out, especially if they'd been 'Mars-barred' like Warkton Tornado No.2's undercrackers.
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Re: A Tale of Two Airboxes!

Postby Adam_Winstone » Fri Jul 30, 2021 5:51 pm

Nice detail and interesting thread. As WT1 touches on, a decent filter and appropriate flow path (hose) need not be restrictive.
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Re: A Tale of Two Airboxes!

Postby nsaints » Sun Aug 01, 2021 6:13 pm

Any photos of the airbox from Scooter Restorations , dimensions etc?


Sure thing Bruce ;)

Looks all standard, but the difference is under the air scoop and hidden. The air intake is a whopping 49mm internal diameter on the big box versus 37mm for a standard SX!
I've posted a couple of images so you get the idea

Image

Image
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Re: A Tale of Two Airboxes!

Postby dickie » Tue Aug 31, 2021 8:06 pm

nsaints wrote:Recently taken two small block kitted scooters to see Al @ Diablo, and got some dyno results around airboxes which I thought would make an interesting post

First up my TV. RT195, standard crank, 25 PHBL, GP modified airbox with the internal baffle removed, BGM mk 4 exhaust

Image

Dyno result below where Al took an as delivered base line (blue line) and 2nd run with the air filter hose removed, carb run open mouth, (red line)
I was surprised how restricted a standard SX air box was with the baffle removed!

Image

Air box was then modified with a 12 mm drill, per the below
this then de-ristricted the airbox allowing more air, and releasing more performance. see graph below comparing to a GT kit

Image

two weeks back I took my SX - Chris Sturgess fettled GT kit, 25 PHBL, scootopia clubman. I didn't want to pepper holes in a SX airbox so fitted a big bore airbox (from scooter resto')
I thought this would still need additional holes in the sides, but it didn't

Here's a graph comparing both RT and GT kits
Red line = GT186 (chris sturgess modified), 25mm PHBL, Scootopia Exhaust, big bore airbox
Blue Line - RT195, 25mm PHBL, BGM Mk4, Heavily modified GP airbox

Image

I'll let you draw your own conclusions ;)

edit:
in summary:
1, if you want to run an airbox for standard looks, whilst running a kit, don't expect much performance gain when just removing the internal baffle. you need to drill holes in the side of the airbox as well
2, the big bore air box performed better than expected, without the need for additional holes being drilled in the side

Did you have the air scoop in place for any of these tests? If you did, was it also opened up?
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Re: A Tale of Two Airboxes!

Postby nsaints » Tue Aug 31, 2021 8:10 pm

Yes the air scoop was opened up or the baffle removed on my SX
My TV has a GP style scoop so no baffle to remove
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Re: A Tale of Two Airboxes!

Postby duncan1958 » Thu Sep 02, 2021 2:52 pm

What rubber elbow do you use,I have bought the bigger type to fit on my 28mm PHBH for my RT 195 kitted engine.
Removing the internal baffle and the bridge in the air scoop.
BGM air filter
The rubber elbow has a tendency to collapse or pull in when opening up the throttle.
Not road tested yet as not completely finished the scooter.
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Re: A Tale of Two Airboxes!

Postby hullygully » Thu Sep 02, 2021 3:24 pm

I've got an armadillo one on my bored out 26mm Delly
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Re: A Tale of Two Airboxes!

Postby dickie » Thu Sep 02, 2021 8:38 pm

duncan1958 wrote:What rubber elbow do you use,I have bought the bigger type to fit on my 28mm PHBH for my RT 195 kitted engine.
Removing the internal baffle and the bridge in the air scoop.
BGM air filter
The rubber elbow has a tendency to collapse or pull in when opening up the throttle.
Not road tested yet as not completely finished the scooter.


Darrell Taylor uses a cut up silicon sealant tube inside the hose to keep it stiffer.
Gentlemen of a certain age need a little help sometimes.
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Re: A Tale of Two Airboxes!

Postby hullygully » Fri Sep 03, 2021 9:19 am

:lol:
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Re: A Tale of Two Airboxes!

Postby duncan1958 » Mon Sep 06, 2021 12:20 pm

:D
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Re: A Tale of Two Airboxes!

Postby Warkton Tornado No.1 » Mon Sep 06, 2021 1:30 pm

dickie wrote:
duncan1958 wrote:What rubber elbow do you use,I have bought the bigger type to fit on my 28mm PHBH for my RT 195 kitted engine.
Removing the internal baffle and the bridge in the air scoop.
BGM air filter
The rubber elbow has a tendency to collapse or pull in when opening up the throttle.
Not road tested yet as not completely finished the scooter.


Darrell Taylor uses a cut up silicon sealant tube inside the hose to keep it stiffer.
Gentlemen of a certain age need a little help sometimes.


"Gentlemen of a certain age" can also recall wondering if, when they eventually 'emerged', their pride & joy would resemble a poor man's version of Zebedee
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