Jetting Thread

[tomacGTi]

True, but really where was the power made? And of course, everyone's setup is vastly different as well as how Suzuki was feeling that day when they built the motor.

If you gained a peak HP higher in the rev range but it was softer in the middle is it necessarily better? Big reason why R6's are lauded on the street but are loved at the racetrack but 675s and overbores are more popular backroad toys.

I understand that ultimately the highest HP prevails but if it costs driveablity down below versus gains elsewhere is it worth it?

Comes down to what you're tuning for.

[andrewsw]

Thief400: in my opinion, removing an snorkel is vastly different than removing a snorkel *and* drilling more holes. Removing a snorkel potentially "detunes" an airbox resulting in a loss of power at certain revs. You may simply be making up for that by putting more holes in the box thereby allowing good airflow at all times. But you still may be missing that all important "tuning" of the air box.

tomacGTi: nice read. thanks. I like the math... we just did fluid flow in a tube in calc last week.. ;) It makes sense to me. Anybody got accurate dimensions of a B4 snorkel? Mine is long gone... I'll happily do the math and see what I can figure out.

What we really need is a series of controlled studies of different airbox lid configurations, with the bike rejetted to match, and then dyno'ed. But that's a pipe dream I suppose.

I've often wondered about just removing the airbox lid altogether. The whole thing is pretty well protected in there already. Of course then what would you do with the EGR hose...

A

[tomacGTi]

total length: 150mm
internal flare: 38mm
External falre: 55mm
Interior tube diameter: 38mm

[Thief400]

The only reaon the snorkel was in the air box was for noise, Your giving Suzuki to much credit here remember this was the late 80's when this bike was designed. Now a days everything is a tuned working package that can't really be improved upon. But back then there was a lot of power left on the table just waiting for someone to find it

[Herr Tod]

The laws of physics work at all times, even in the 80's

Still I have removed the snorkel, I don't care about mid-range power. What's that anyway on a 400? Top end is the way to go

[Banditmax]

Herr todd have you got holes in your airbox too? Im toying with removing the lid completely but im unsure about the jetting for european temperatures and pressures.

[Thief400]

Well to put this all to rest we did do a dyno pull with just the snorkel removed and it made .5 more HP with NO dip in the mid range as you keep suggesting would happen! We just put duct tape over the 2 extra holes and jetted way down to get the EGTS back up to where we wanted them, I will see if I can find the dyno sheets I think they are still on my old puter that I don't use any more. When I get time to plug it all in again I will go searching for them

[tomacGTi]

Just did a little experiment on my bike using the 97.5 Mikuni jets that everyone runs in their Factory Pro kits. As soon as it came onto the main jet (right around 8k), it fell flat on it's face and would lean surge until it came back below. This was at all throttle openings . Everywhere below that (8k), it rode just like normal.

The Dynojet needles must have a wider tip in comparison to the Factory Pro needles as these require a much bigger jet up top then otherwise. They honestly look very close to the OEM needles with the exception of the taper going up. I don't even think that running a 100 MJ would make a difference and a 105 is just a bit too fat. I'm also using Mikuni jets as I wanted to achieve a baseline as it's difficult to locate Dynojet jets. They're also less expensive and easier to reference.

For those of you wondering why I'm running a modified snorkel, I honestly don't like the sound an open airbox makes. The resonance gives me a headache, even wearing earplugs, so I measured the airbox opening without the factory piece and made my own snorkel.

My setup:

-14.5 float height
-Stock pilots
-Stock airfilter
-3.25 turns
-48mm int. dia snorkel (made it out of 2" PVC)
-Gutted stock collector/headers with Cobra F1S slip on with custom 2" perf'd baffle
-102.5 MJ (stock)
-195* thermostat
-3rd clip with a washer (3.5 clip)
-Stock slide springs (shorter one transitioned rougher onto the main)
 
It's a little lean until it warms up but once it does, it's nice and smooth up and down the range. Got a tiny bit of tailpipe soot and I've been told as it comes off the needle and onto the main it puffs a bit and clears right out.

[andrewsw]

Interesting. I haven't had time to get back to it, and with the bike desperately needing new tires, I haven't ridden hardly at all to test out changes.

@Banditmax: as HerrTodd says, the laws of physics apply all the time, even in Europe!

A

[Banditmax]

Yeah i know it works the same but im a good 1000feet below most of you in the us i think. Was just looking for some baseline figures for jetting.

[Herr Tod]

I'm at about 90 to 275 meters above sea level, which is 300 to 900 feet. I've had holes in the lid for a while, took it off completely too but in the end I just run a stock lid without the snorkel. That little bit of extra top end power just didn't weigh up to the fuel costs. Maybe if I only used the bike to ride for fun, but not on a bike that's used to go anywhere I need to go. I ride about 25000 km's a year on my bikes, mostly on the Bandit. So I was satisfied with the power it makes with the stock lid, all I really care about is good throttle response from idle up to 15000 revs, which was perfect. Just took me a while to get the 1000 to 3000 rpm range to respond well.

[Banditmax]

What jetting are you running with the snorkel removed then?

[Herr Tod]

#100 main jets, 32.5 pilot jets, Factory Pro ti needles 3rd clip, 15 mm float height, Factory Pro throttle valve springs, stock throttle valve and needle jet, air jets stock too. running on 95 octane fuel. I have a replacement K&N air filter, 195* thermostat, GSX-R 400 GK73A CDI, Yoshimura 4-1 headers with a titanium mid pipe and the stock end can. The stock can takes away some top end power but it keeps the police inside which is more important.

Having a broadband A/F meter really helps

[Thief400]

Witch system did you buy?? the A/F one

[VW_NUT]

Hangin_Biposto's jetting

Height above sea level: Around 100 feet
 Outside Air temp: 70-80 deg f
 Bike is: 1991 With Cobra F1S slip-on and mid pipe restrictor removed.  Stock 32mm carbs.
 Jetting:
 Needle: Factory Pro needles on 4rd clip down (I tried 3 like everyone else here has, but it was a tiny bit lean.)  You could feel a slight hitch when you roll into it.
 Main: 97.5
 Pilot: 32.5
 Mixture screw: 3 turns out.  (Could probably go back to 2.5 and have it run ok, but it was a little hesitant on warm up this way.)
 Float height 15mm