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Message started by philthymike on 05/14/20 at 20:01:02

Title: Stock airbox VS open filters?
Post by philthymike on 05/14/20 at 20:01:02

I recently ordered a new OEM filter for Thumpy since the old one was looking raggedy. I remember reading in here somewhere that there's nothing to be gained ditching the airbox and swapping a pod or other open filter. Is that still the conventional wisdom now?

Is the airbox sufficient for the engine's performance range?
Or does ditching it help matters?

I ask because since reading that old posting I noticed many folks in here are running open filters with no airbox.

Title: Re: Stock airbox VS open filters?
Post by verslagen1 on 05/14/20 at 20:32:25

if you have a stock bike, it's designed to be balanced.
if you open up the muffler, you should do the same for the intake.
but it's going to require a rejet.
and if you drop the intake restriction, you'll have to swap the petcock for a raptorcock too.

Title: Re: Stock airbox VS open filters?
Post by Fast 650 on 05/14/20 at 23:12:04

Search for the thread where DragBikeMike posted his airbox and filter tests, along with the mods he tried. The airbox is more than capable of flowing enough for a hotrod in the 40 plus HP range.

Title: Re: Stock airbox VS open filters?
Post by batman on 05/15/20 at 10:15:19

A pod filter and rejet can increase performance , IF it's done properly. Placing the filter directly on the mouth of the carb isn't the way. The hose that runs between the stock carb and air box isn't there for looks, it's there to allow the air flow to straighten before entering the mouth of the carb. (and can be used as a basis for intake tuning)

Title: Re: Stock airbox VS open filters?
Post by philthymike on 05/15/20 at 14:04:29

I'll try to find what DragBikeMike wrote about. Thanks.

Title: Re: Stock airbox VS open filters?
Post by philthymike on 05/15/20 at 14:05:40

66657069656A303C040 wrote:

How much of an increase are you talking about?

Title: Re: Stock airbox VS open filters?
Post by DragBikeMike on 05/15/20 at 14:50:42

Mike, this old post tests several modifications to the airbox. It should give you some ideas for mods to your airbox.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1523302904

This old post tests all the pertinent filter elements. I personally like K&N. Been using them for 50 years or so. Always worked great for me but they are expensive.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1543600189

This more recent post gives some details on setting up your airbox for a cylindrical filter. It will work with just about ant cylindrical filter (K&N, UNI, etc.). It allows retention of all the stock mounting for side covers and igniter box. It's about as good as your gonna get for air flow. Cheap too.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1583103640/0#12

I see you have a little more displacement plus a tad more compression along with a souped up bumpstick. If you have improved your exhaust too, more airflow is in order.

Looks like your project is pretty close to blast off. You certainly have plenty of stopping power. Are you fixin for some high velocity operation? 8-)

Title: Re: Stock airbox VS open filters?
Post by Ed L. on 05/15/20 at 15:31:52

If you want to keep the stock air box but increase the air flow at higher RPM's drill a bunch of 1/2 inch holes in the air box cover. I Swiss cheesed the air box on my '02 which improved the top end air flow along with helping the mid range. It was a noticeable improvement over the entire power band and didn't affect the idle.
One mod I'm thinking of is taking the side cover and hammering it into an air ram pushing air into the air box when at speed. That would take a bit of torch work and would be pretty ugly. My bike is slowly turning into a rat, LOL
Of course pulling the stock air box and all the associated cr@p makes the bike look a lot better and removes a bit of weight.
I'm also running a K+N stock air filter replacement.

Title: Re: Stock airbox VS open filters?
Post by philthymike on 05/15/20 at 16:32:26

4E48473B393E3A0A0 wrote:

Oh heck yeah. That was the reason for the desperate search for stoppers, so I can go faster ;D
I did make a promise to make my bike safer before I made it any faster. Promise fulfilled. Learned some valuable lessons from riding the 110HP Ducati. I've got its stopping power now. I'll never get its hp from Thumpy but I'll see how far I'll get. 40 hp would be cool!

So in the near future I will be eyeballing intake and port mods.
Thank alot for taking the time to post all those links. I'll study up!
And try hard not to break or strip anymore bolts!

Title: Re: Stock airbox VS open filters?
Post by batman on 05/15/20 at 21:06:39

Philthymike, I run a stock motor from the bs40 carb to the exhaust header, the only custom part being a Stock H-D muffler and a tuned air intake . Speed when stock was 85mph=5678rpm it is now94=6279rpm having done several mods to the carb ,but still running 52.5/150 jets and E87 fuel @51.5 mpg. I don't think I need or want to get much more out of it . I don't run my bike at 94mph but it does 70 with a reserve for passing if needed. and I'm not paying higher fuel prices at the pump. Tuning your intake is the best bang for your buck , It is not gear dependent ,but rpm dependent which means you reap the boost even in lower gears and the rpm depends only on the length of the intake you choose.

Title: Re: Stock airbox VS open filters?
Post by Dave on 05/16/20 at 03:37:38

I ran my bike with a 95mm Wiseco, ported head, dyna muffler and a performance cam. I ran the bike for a year in that configuration withe the stock airbox and stock carb......it ran great!

While I was breaking the piston/cylinder in and didn't use a lot of throttle or high rpm.......I got mileage up into the 60's - later on it was in the middle 50's for normal rides.

The stock airbox is a good design for the stock engine - and even for a mildly modified engine. It is quiet, keeps water out of the engine, and also functions to dispose of the engine breather air. When you remove it and install a pod filter you now have a way that water can get into the engine when it rains or you wash the bike.

I would recommend that you keep the stock airbox if you can as it works well - it should not be one of the first performance mods you do....it should be one of the last.

Title: Re: Stock airbox VS open filters?
Post by ohiomoto on 05/16/20 at 05:35:53

The simplest answer is that 99% of the time the stock airbox only be removed for looks or space. And don't take that comment the wrong way. I have the stock box on my bike, but I have another build waiting in the wings and I will probably remove the box purely for looks. :)

Title: Re: Stock airbox VS open filters?
Post by batman on 05/16/20 at 17:34:11

I also run the stock( but slightly modified) air box even with my tuned intake for it's obvious advantages, I can run the stock breather hose and drain, and no water enters the carb because I use Oldfeller's air filter installed in the rear of box where it is protected from rain or washing the bike by being centered between the frame and above the rear fender. the bike looks completely stock

Title: Re: Stock airbox VS open filters?
Post by philthymike on 05/16/20 at 17:40:40

37342138343B616D550 wrote:

Hey Batman are the details of your tuned intake in this forum?

Title: Re: Stock airbox VS open filters?
Post by batman on 05/16/20 at 20:38:25

Philthymike , sorry it's not and I'm not sure it would work in exactly the same way for anyone else . I have changed fenders , seat and shocks on the bike, full HD rear fender that is bolted to the lower 2 stock bolts but leans backward to lessen the height between the tire and fender caused by 11.5 progressive shocks and allow an HD seat to sit flat to the upper frame rails and conform perfectly to the curve of the 16" fender. That allows the top of the air box gap to be greater and room for the filter to work in that area.
The length of my intake from the intake valve to the 2" pvc pipe extension I used in the stock hose was about 15" but this should be your choice as the length determines the areas where the boost in EV occurs.

Title: Re: Stock airbox VS open filters?
Post by Dave on 05/17/20 at 16:50:50

If I were going to use my bike as a commuter or touring bike and I knew I would be riding in the rain on a regular basis........I would keep the stock air box as it won't let rain in while riding, or while parked.

Title: Re: Stock airbox VS open filters?
Post by philthymike on 05/20/20 at 20:38:28

I'm keeping the airbox. I get caught in the rain alot now that Philly gets more rain than Seattle.
I also ride on very dusty roads, occasionally unpaved. I don't feel that my engine performance suffers for anything. Once the oversized main jet gets going it's all pull. The inside of my header pipe looks fine.
Just going to pop the new OEM filter in and worry about frying bigger fish for now.