Twin 45 Custom Airbox

[porter_bmx 0]

hi all,

i'm looking to make a custom airbox for my carbs as im having trouble with them running lean at high revs due to force feeding air into the trumpets. my rads lowerd and theres nothing behind the grill so the air is pretty much force fed straight into the carbs. i know sean (track-monkey.com) made one but i'm struggling to get dimensions and what pannel filter to use. rather than me going through trail and error with this i was thinking that i could ask you guys for advice and pointers.

thanks

Edited July 25, 2010 by porter_bmx

[EdCherry 34 1 Cars]

Hi!

[porter_bmx 0]

Hi!

 

lol thats me hitting the return key faar to early lol

[welshpug 1,657]

sounds like they need tuning to suit, but then at lower speed's you'd be running rich, that's carbs!

[porter_bmx 0]

was set up just over a week ago. Leads and coil need replacing could this be the problem? Was fine on rollers had 176 wheel horse power at 7500 rpm

[boldy205 75]

why not put a panel infront of the inblets to 'baffle' the incoming air rather than a complicated airbox?

Matt

[porter_bmx 0]

may do that then. Something like a pressed plate around the carbs

[welshpug 1,657]

what kind of filter do you use? typically carbs have a chrome topped K&N that face the front, so the air doesn't hit the trumpets straight on.

[porter_bmx 0]

not running any filters just got 60mm trumpets. Thats why i think there geting too much forced air

[welshpug 1,657]

no filter think of all those bugs and dust your engine is ingesting

[porter_bmx 0]

yea i know not good. I'm drew up some plans and i'll make one up at work. Based it around the dimensions of a seat air filter 163 x 183. This might be a silly question but are filters bhp rated?

[welshpug 1,657]

If you look at http://www.greenfilters.com you'll see loads of filters and most are rated to a certain BHP, or at least I thought they did you can see the bhp level of whichever filter you choose though in most cases.

 

having a flat filter in front of the carbs wont really help against the difference in pressure the carbs will see, they'll see less of course. than without any filtration.

Edited July 25, 2010 by welshpug

[porter_bmx 0]

will have to give it a try the only other thing would be to make a box with a side filter. Or a similar thing to the piper cross stuff hmm idea's idea's lol

[Cameron 16]

Making an airbox is a pointless exercise as I found out when I was trying to design one for mine. There isn't enough room to get a decent entrance to the box from the side that doesn't mean sucking in hot air from the engine bay or masking cylinders.

 

Just save yourself a whole load of hassle and fit some over-trumpet filters like people have suggested, or fit a Pipercross "sausage" filter. Do it ASAP too, you really really don't want to be running without an air filter and I'm really surprised your tuner didn't warn you!

Edited July 26, 2010 by Cameron

[woodsy 0]

I been using a pipercross px600 filter for few years with my carbs, just got the deepest one that will fit.I cut some

of the slam panel aswell to make bit more room.

[porter_bmx 0]

i had some filter socks, but was told they were no good? "fire socks" the guy called them. ill have to get a set, if you guys are running them with no problems then i should be ok. he did say get some k and n filters on them, as the carbs dont get on with forced induction.

[MrG 3]

I run deep (85mm) K&N filters with 40mm trumpets inside and so far so good, however I had an issue where my carbs had no filters fitted & digested some debris and the engine didn't like it one little bit. In fact I needed a new one as it split the liner good and proper. lesson learnt there for me!

[porter_bmx 0]

im going to get some for sure now. just deciding which ones since i have 60mm trumpets

[Sandy 191]

Socks are bad (i'm sick of being told they're ok by some people with limited experience, I've had some dreadful effects from them that dissapear on removal), air boxes usually cost power and dull the noise. A PX500 or JC50 filter will work best in most cases.

Edited July 26, 2010 by Sandy

[MrG 3]

you need a clear depth from the mouth of the trumpet to the inside of the filter, not sure what it is though but I think its a min of 40mm

[porter_bmx 0]

cheers ill have a look at some 100mm filters then. i know they do them in socks but not sure on how good the socks are.

[Cameron 16]

Don't get socks! They can have some nasty effects on the power but also heard plenty of stories of them being sucked into the engine. Please just listen to our advice!

 

I think the minimum distance from trumpet to filter is equal to the trumpet mouth diameter, but that's just something I read on the internet so don't go taking it as fact. It seems pretty sensible to me though. You just need to make sure that there's a good amount of space in front and around them so you get the most of your inlet tuning.

[porter_bmx 0]

ok, i've heard that min distance from trumpet to filter is 19mm but ideal distance is 37 plus. So like you say the more space the better. I'll get a set of either piper x or k and n at a depth of 100mm (gives me the ideal space)

[notamondayfan 44]

Rather than "I've heard....", just go and speak to who ever it was that setup the carbs in the first place.

The trumpet length / distance to filter / engine size / engine characteristics can all be calculated and a half decent tuner should be pretty close. It will save you a whole lot of time and hassle!

[porter_bmx 0]

the tuner is who i got the info off. got two k and n box's at a depth of 100mm will let you guys know how i get on