A Tale of Two Airboxes!

[nsaints]

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



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!



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



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



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

[Psychedelicropcircle]

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.

[Warkton Tornado No.1]

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 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 as so many of you appear to have them....

[vegansydney]

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.



PS: That early TV is beautiful. Very nice work. Early TV S3 are the pinnacle of Innocenti design IMHO.

[nsaints]

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.

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

[Storkfoot]

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.

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

[Warkton Tornado No.1]

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.

[Adam_Winstone]

Nice detail and interesting thread. As WT1 touches on, a decent filter and appropriate flow path (hose) need not be restrictive.

[nsaints]

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

[dickie]

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



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!



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



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



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?

[nsaints]

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

[duncan1958]

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.

[hullygully]

I've got an armadillo one on my bored out 26mm Delly

[dickie]

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.

[hullygully]

[duncan1958]

[Warkton Tornado No.1]

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