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Actual poof that the airbox mod/rejetting increases horsepower/torque?

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I just got my 2011 DR650SE a little over a month ago and want to give it a boost in power

(at least enough to easily do wheelies, possibly in 2nd).

I've read a lot about air box mods and re-jetting but I am skeptical about these

modifications (I don't want to take away from the economy on my bike unless it

makes a huge difference). I'm finding it really difficult to find evidence that it

actually generates a significant amount more horse power/torque. I was

wondering if anyone has any dyno runs before and after said mods above.

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Go to http://www.thumpertalk.com/forum/showthread.php?t=467615&page=40&highlight=dr+650+needle+comparison and watch the dyno sheets in post #395.

Just from experience I (and anybody else who tried) can confirm that the poor DR 650 starves for air at all throttle-positions above 1/2. Desnorkeling is reversible and already makes up for a noticeable effect (better roll-on-torque), even better when jetting is appropriate. The fully opened airbox-top is where the music plays (roll-on-wheelies in 1st gear with stock gearing, better acceleration, better throttle response). mx_rob had the best results with DJ-needle and airbox top cut out. And he fiddled a lot if you take the time to go through the needle comparison thread by yourself...

2nd gear wheelies without clutch and with BST-carb? Never. Not even with a flatslide @ stock gearing ...

Edited by el capitan

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Without a doubt removing the snorkel and jetting to accommodate the increased airflow is the most cost effective way to increase the DRs performance.

Reaching way back to when my DR650 was new to me (still nearly bone stock):

Well I finally de-snorkeled the DR650. Been holding off doing any significant performance mods because I haven't had time to get my dyno set up after moving into the new shop. Anyhow here is the before and after runs just pulling the snorkel. Gained 2.5 hp and significant torque through the whole range. :busted: Bike still has stock exhaust, complete airbox (except snorkel), 137.5 main jet (one size leaner than stock), .040" shim under needle clip.

dr_dyno.jpg

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Do you think a 350 would benefit from this mod?

Opening up the DR350 airbox is a well known low cost performance mod.

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Without a doubt removing the snorkel and jetting to accommodate the increased airflow is the most cost effective way to increase the DRs performance.

Is 2.5 HP a significant amount for this bike? I have removed the snorkel before... about the only differences I noticed was that the bike was a little louder and I think it popped a little on decceleration. My question would be whether or not the vacuum created by that snorkel is necessary for the carb. On my old atc 70 I remember if I didn't have a super restrictive air box it wouldn't run right. It didn't make a whole lot of sense to me but if I put my hand over the intake side of the carb a lot of gas would build up inside the carb. So I figured maybe a certain amount of vacuum or suction is needed to get gas through ports inside the carb. Could it be possible that it is the same on this bike?:busted:

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Is 2.5 HP a significant amount for this bike? I have removed the snorkel before... about the only differences I noticed was that the bike was a little louder and I think it popped a little on decceleration. My question would be whether or not the vacuum created by that snorkel is necessary for the carb. On my old atc 70 I remember if I didn't have a super restrictive air box it wouldn't run right. It didn't make a whole lot of sense to me but if I put my hand over the intake side of the carb a lot of gas would build up inside the carb. So I figured maybe a certain amount of vacuum or suction is needed to get gas through ports inside the carb. Could it be possible that it is the same on this bike?:busted:

Yes! The increase is almost 10% more power on a totally stock DR650. Look at the HP and torque graphs. The gain is over the entire range.

To take advantage of the better airflow you must modify the jetting setup. Your old ATC70 wouldn't run right without the stock airbox because the jetting was wrong for running without it. If you had jetted the 70 correctly it would have had a significant power increase as well.

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I see, so I've heard putting a hole in the side cover is not a good idea but if I were to put a cover over that hole, like a scoop could I make a big enough hole in that side cover? Then just put a prefilter in the scoop.

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I see, so I've heard putting a hole in the side cover is not a good idea but if I were to put a cover over that hole, like a scoop could I make a big enough hole in that side cover? Then just put a prefilter in the scoop.

Well, you can do whatever you want but if you modify the airbox you have to jet the carburetor accordingly or it won't run properly.

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Well, you can do whatever you want but if you modify the airbox you have to jet the carburetor accordingly or it won't run properly.

Well better yet roughly how big of a hole would you recommend?

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Well better yet roughly how big of a hole would you recommend?

Now you are talking about something completely different than just removing the snorkel. The recommended thing is to cut the entire top of the airbox out. You can't just shim the needle to make this setup work. You would have to install a jet kit to make the carburetor work with the additional airflow.

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Opening up the DR350 airbox is a well known low cost performance mod.

Sweet, thanks!

Is there a thread on this, or, what size of jet do I need to do this mod? I have the DR350 Dirt only model, and someone already cut 3 1" holes ontop of the airbox.

I have a supertrap exaust without a baffle, if that make a difference.

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Sweet, thanks!

Is there a thread on this, or, what size of jet do I need to do this mod? I have the DR350 Dirt only model, and someone already cut 3 1" holes ontop of the airbox.

I have a supertrap exaust without a baffle, if that make a difference.

I don't know, I haven't spent much time tuning DR350s.

There's a big DR350 thread over at ADV rider

--> http://www.advrider.com/forums/showthread.php?t=230695

I'm sure you can get all your questions answered there.

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Kloque,

I did the 3x3 (cut a 3 inch by 3 inch hole in the top of the airbox) on my DRZ and we found that at this altitude we didn't need to change the jetting from the stock jetting. You may find that this is true for your 350 too.

:busted:

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Now you are talking about something completely different than just removing the snorkel. The recommended thing is to cut the entire top of the airbox out. You can't just shim the needle to make this setup work. You would have to install a jet kit to make the carburetor work with the additional airflow.

Is that much of an opening necessary? I mean would a 2.5" diameter hole In the side of the box work just as good?

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Is that much of an opening necessary? I mean would a 2.5" diameter hole In the side of the box work just as good?

Yes. The configuration of the needle in the jet kit requires a very large opening. If you want a smaller opening you would be on your own as far as figuring out a jetting setup that would work properly.

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Yes. The configuration of the needle in the jet kit requires a very large opening. If you want a smaller opening you would be on your own as far as figuring out a jetting setup that would work properly.

Have you experimented with smaller openings?

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Kloque,

I did the 3x3 (cut a 3 inch by 3 inch hole in the top of the airbox) on my DRZ and we found that at this altitude we didn't need to change the jetting from the stock jetting. You may find that this is true for your 350 too.

:busted:

Thanks, I think I'll go ahead and cut it then see what happens. But I guess I need to fix my valves first. :busted:

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Have you experimented with smaller openings?

Nope. I've never seen any point in doing that. There is no known needle with the correct profile for a smaller opening. And why take a very restricted airbox and un-restrict it only half way? If you want to make more power you have to let as much air into the motor as possible.

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