LCGB Forums

The ability to post messages is restricted to LCGB members. Any questions contact us at lcgbadmin@googlemail.com

Largest carb BGM airbox

Need help with a tuning kit, how do you tune your scooter, which kit should I choose, and all general tuning and modifcations questions are for in here.

Largest carb BGM airbox

Postby ste s one » Tue Aug 31, 2021 1:34 pm

I am thinking of running an RT225 with a 28 mm phbh carb and clubman exhaust through a BGM airbox .
What's the biggest carb /highest level of tune anyone has successfully run through one of these airboxes ?
I'm conscious that if it's too restrictive or limits the size of carb too much , I might as well stay standard and save the money .
What real world experience have people got of these ?

Thanks
Steve
ste s one
 
Posts: 29
Joined: Fri May 30, 2014 7:20 pm

Re: Largest carb BGM airbox

Postby nsaints » Tue Aug 31, 2021 2:55 pm

No direct experience of the BGM airbox, however see my thread 'tale of two airboxes'. I suspect the scooter restorations large bore air box to be similar/the same as the BGM air box
I mean how much difference could there be

Anyhow using the scooter resto' version I was surprised how much more volume the uprated box could supply, whilst using a 25mm PHBL
I also thought I read somewhere (BGM literature) the upper limit is a 26mm carb, before hitting a ceiling in terms of air flow
you may need to trawl the internet to confirm if I have dreamt this rather than fact.
User avatar
nsaints
 
Posts: 162
Joined: Fri May 30, 2014 8:08 pm
Location: Oxford

Re: Largest carb BGM airbox

Postby superhooper » Tue Aug 31, 2021 8:52 pm

I ran a TS1 with 30phbh through one lost a couple of HP but worked fine

Super
superhooper
 
Posts: 204
Joined: Mon Jul 21, 2014 8:23 am

Re: Largest carb BGM airbox

Postby Warkton Tornado No.1 » Wed Sep 01, 2021 6:36 am

superhooper wrote:I ran a TS1 with 30phbh through one lost a couple of HP but worked fine

Super


"A couple of HP" is quite significant when you consider it as possibly 10%, but not surprising. However, if you are running the carb via a LH side manifold to enable OEM filter format that may also restrict power.

Whatever the vacant air box improvements of getting the air in, the volume/filter format will also be an additional restriction.

Factor in further an OEM or enlarged bellows, feeding in turn a PH carb (IMO not very 'restriction' friendly) that will require more air simply because of its bigger bore, then it can be understood that modifying the air box mouth is not the total solution.

The full capability of any carburettor to deliver sufficient filtered air to make good power is totally dependent upon what is 'upstream'


* A deristricted NSR125 will make about 33 BHP with the OEM Dell'Orto 30 mm PH, but the airbox is a BIG box, mostly empty of filtration. It is a 'chamber' rather than a box closely enclosing a filter element.
Warkton Tornado No.1
 
Posts: 2112
Joined: Sun Jan 11, 2015 1:27 pm

Re: Largest carb BGM airbox

Postby ste s one » Wed Sep 01, 2021 8:53 am

Thanks for the replies , all food for thought .
I am about to restore my TV200 that I've ran for 30 years , the last 20 of which with stage 4 top end , AF clubman and 30 mm phbh with breathe sweet filter .
Wanting to put it back looking standard but can't bring myself to lose all the extra poke . Might get some bits together and book a bit of dyno time to see just how much I stand to lose before stripping the bike for restoration
ste s one
 
Posts: 29
Joined: Fri May 30, 2014 7:20 pm

Re: Largest carb BGM airbox

Postby Warkton Tornado No.1 » Wed Sep 01, 2021 12:02 pm

ste s one wrote:Thanks for the replies , all food for thought .
I am about to restore my TV200 that I've ran for 30 years , the last 20 of which with stage 4 top end , AF clubman and 30 mm phbh with breathe sweet filter .
Wanting to put it back looking standard but can't bring myself to lose all the extra poke . Might get some bits together and book a bit of dyno time to see just how much I stand to lose before stripping the bike for restoration


One of my first Lambrettas was a TV200 which I own to this day, albeit in pieces. Like you, I have a plan in my head concerning the rebuild, but how far should anybody go with compromises?

Tyres are a no-brainer, but the rest of the build can resemble very precisely what we aspired to own "back in the day" Also, I recall that nobody wanted panels other than SX200 & would have them on their TV's. Yup! That's what I have planned :oops:

As controversial as ever :!: there's no point (excuse the pun) in going electronic for "reliability" but 12 volt was accessible.

Exhausts can be precise replicas.

The top end may as well comprise an overbored/overstocked piston ported set up so my choice will be between a Webster tuned barrel & H2 piston or a Rapido barrel with TS piston.

Then we get to carburation/air filtration.......

I have my doubts that an OEM air box will ever work well but do believe an alternative can work in the same space envelope & be fed just fresh air via the frame hole/scoop.

I will be attempting to run such a system when time allows.

Much depends on what the machine is intended for. If it's a street racer, then not much looks better than a VHB & polished bell mouth & now I know how to convert them to two stroke carbs. I have several in stock, including both hands. The alternative of a more civilised bike with well-engineered filtration is also appealing & as the carburettor will be mostly hidden, my choice is PWK on a downdraft manifold.
Warkton Tornado No.1
 
Posts: 2112
Joined: Sun Jan 11, 2015 1:27 pm


Return to Tuning & Kits

Who is online

Users browsing this forum: No registered users and 5 guests