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Discussion Starter · #1 ·
Hi all,

I have a few airfilter questions

OK, reading through bunches of posts, do I correctly understand that
there were two versions of the K&N airfilter that fit my 1st gen SV?

And if so, are they the same except for round vs oval inlet.

If so, is it desirable to upsize the small round hole to a larger oval?

How is this likely to change jetting requirements?

I'm trying to get as close as I can seat of the pants and with a few roll on measurements
before heading to the dyno next week. Right now I have a round holed K&N, 142.5 mains, and a full Vance&Hines.

All input welcome and appreciated.

Thanks
Roger
 

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Yeah, there were two of them. But I don't think you can even find the first ones anymore. After K&N figured out the problem, they corrected it and stopped making the old ones. I haven't seen a first series air hole in a long time. I'm sure there are still some on a shelf somewhere, but I haven't seen them.

The first ones were more restricting than stockers. The new ones are about equal to a desnorked stocker. So yes, it would be desirable to go with the newer one.

It won't likely change your jetting, because if you have a first series K&N, you are probably running WAYYYY rich. Swapping it with a new one, should help that. If you still have your stocker, desnork it and see how that runs.
 

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Discussion Starter · #5 ·
First, thanks for the replies gang.

Mine, which I got new on Ebay, might have been an old one. The hold is a simple round one,
maybe 1.5" in diameter. Does that sound like an old style?
 

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Discussion Starter · #8 ·
Thanks guys.

Cut her wider. That was exactly my plan, but I thought it best to doublecheck the board's wisdom before proceeding,
what with the process being largly irreversible..

So, is this a bigger is better thing? I.e the more the better?
 

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Discussion Starter · #11 ·
Ok,

I've oval'd her out and spaced the tank up a bit.
I can't say what I'll ultimately need, but I bet TWF's
advice of 150-155 will prove correct. My 142.5s
are now WAY lean. No need to read a plug. Just
whack open the throttle (worse before motor fully
warm of course) and she stumbles pretty good now.

Going to have to figure this one out manually, as my
dyno time has been cancelled due to the shop moving
earlier than they planned. Dyno already torn down, but
still open to sell me some jets. Crap, winter testing
sucks. Not enough light to do any high speed work
evenings/during-the week.

Guess I'll buy everything from 147.5-157.5 and start reading
plugs. Done it plenty times on boxers and 2V ducs.
I sure miss the easy plug access on those motors.

One question. My local shop, which has tuned quite a few SVs,
(they also run a race team) seems pretty convinced I should stagger
the front cylinder one size richer, from their experience. Not due to temp,
as on some rear cylinders on old aircooled Vtwins, or middle cylinders on 4s, but just due to breathing better than the rear, given the heads and carb layouts.

Any thoughts on that?
If positiive, then I can punt and start out either 155F/152.5R, or 152.5F/150R.
Suggestion or similar experience welcome.
 

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I have my jets staggered one size bigger on the front. It works fine.

You will be in the 150ish range.
A desnorkled stock filter flows better than a desorkled old K&N, I tried both.

I finally wound up with a BMW race filter... by far the highest flow.
 

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Discussion Starter · #13 ·
Thanks Donnie,

I now have at least one of everything from 137.5 up to 165.
Some combo should work. Shop thought I'd likely end up
around 157.5/155.0, maybe even 160,which is a tick more than
folks here suggest, so I'll experiment and find out.

It's actually pretty fun where there's not too much time pressure.
Trackday this weekend is starting to look iffy though. Rainy here
til then, so I might not be able to get a safe level of testing done.
Curse the lack of dyno availability!!!
 

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Discussion Starter · #15 ·
Thanks.

Haven't mentioned my config in this thread, I believe.

I have done the cam swaps (intake and exhaust) and have a full Vance and Hines system, which is pretty darn open.
Mine most likely varies from yours in terms of my now-oval'd K&N probably being more restrictive than your . Tank has
been shimmed up a bit too. Seems like this will put me at least to the mid 150s. Think I'll try 157.5 front 155 rear first.

Going to weld a bung for an O2 sensor on there tonight too. Then I can use my lambda datalogger and try to get a handle on m ixture. Never done that on an SV before so it should be interesting.
 

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Discussion Starter · #16 ·
OK, still working on this, but thought I'd share my preliminary results, in case it could prove of use to someone someday, or in case anyone else should like tinkering with dorky data acquisition as much as I do.

Only had time to get the lambda bung welded and the data acq system wired and zip tied in place in the rear seat cavity last night. No time to do the jetting.
Did a short run last night around midnight. Too cold and dark and late for more.

Results, still with the obviously too-lean 142.5 jets:

Idle showed around 12.2 AFR (a tick richer than required, but about what I'd expect with a slightly excessive 17.5 idle jet and 3.0 turns out on mixture.

Light to mid throttle showed around 12.5 AFR over a broad rpm range (low to upper mid) A tad low/rich, for really light throttle or cruise, but not horrible
Easily in the ballpark to allow me to leave it alone until I get the mains sorted.

At higher throttle openings, the AFR rose very quickly and pretty linearly with rpm up to a peak of around 16.5. That's the sort of very lean amount you'd normally see in an econo tuned engine at moderate cruise (steady state throttle) WAY to lean for large throttle openings and loads. Of course, I already knew that given the stumbling and not pulling well at high rpms and loads every since I raised the tank and hogged out athe airfilter opening. I've now just quantified it a bit.

Just so I can learn this motor and requirements better, I'll probably just bump up 2 or 3 sizes (from 142.5 both, to 147.5 rear and 150.0 front) just to see what the graphs show. I know this will probably not be enough given all the advice I've had so far, but I figure it's a good learning experience.

Then I'll bump them that much again, to match the advice I've been kindly given, and to collect a 3rd set of curves. Right now, I just have AFR(lambda) vs rpm.
May have to build a little harness to run the TPS into an A/D port so I can track vs throttle opening too (assuming I can come up with a good voltage vs degrees relationship)
 

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Discussion Starter · #18 ·
Hi, and thanks.

I suspect it's a bit much too. But since my plugs look pretty clean after even prolonged idle,
and mostly because it came that way and I don't want to juggle too many variables at once, I'm leaving it there for now. (also, the AFR at idle corresponds to CO in the 5-6 range, which is high too) But I bet you're right, and that I end up at 2-1/2 to 2-3/4.
Thanks again
Roger
 
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So. My first noob question.

I had a full Yohi exhaust and jet kit installed/done a little while back. So would I have to get another jet kit done when I get the drop in K&N, and is there a better intake system out there than just a drop in element.?
 
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