Cobra Exhaust Tuning Recommendation.

[one2dmax]

The simple fact is that they don't have any scavenging and no amount of modifications are going to improve that. The other issue is they don't replace the small 1.5" pipes (which all full aftermarket systems use 1.625")

 

[lilredrooster]

The cobras are a slipon exhaust which bolt up to the standard headers, it is what it is.....

Clearly it is not cost effective to change the headers, and, to change the mufflers for a performance increase over the stock exhaust, you would just buy a performance exhaust in the first place....

I think you have to compare the cobras with the stock exhaust, standard headers are the same in both cases.

Remove the stock mufflers, install the cobra mufflers, the set-up appears to run very rich and you lose 10HP. Why? Can it be improved upon?

Could it be that scavenging is 100% the cause?

Could it be that the Cobras are too restrictive?

Can the loss of HP be minimised in any way?

Enjoy the Ride...... Ride Safe..... :thumbs up:

 

[Killjoy]

FWIW thats my vmx in a couple of those vids. While the sound is rowdy, I'm going to be installing the stock muffler. I just cant get it right. The noise isnt worth the lack of power and running rich. I think a rear crossover would greatly improve their performance, and im sure my gutted ones flow plenty, its basically an open pipe. But the lack of scavenging is whats killing it. It is more trouble for me than its worth due to a lack of resources to try and build a crossover for the rears. (Although its literally just drilling a couple holes and welding a pipe between them, but has to be in the perfect location too)

But it does sound wicked!

Im going to save money towards a full system. But if i had an extra stock muffler, i suppose one could gut the cans and still retain the cylinder balance effect given the stock is a crossover system. As cool as i am, lol, i cant beat yamaha factory.

 

[Vinmax]

I believe the lack of scavenging is ultimately the reason for the Cobra's to be killing the power over even just the stock system.

That's just a poorly designed system. Even with the small outlet, and even if Cobra decided to put in a larger diameter outlet........... you simply don't design a system where there's no scavenging. The Cobra engineers (if you want to call them that) clearly should have seen that the stock system used scavenging and that it was mandatory to use scavenging on an aftermarket system to get the exhaust gases out of the pipes to help the engine produce power.

Their design is basically putting a restriction (gases left in the headers with no help of 'suction' to get them out) in the exhaust which is killing power and making the engine work harder to push the exhaust gases out. The perfect formula for restricting power.

Vinnie

 

[lilredrooster]

FWIW thats my vmx in a couple of those vids. While the sound is rowdy, I'm going to be installing the stock muffler. I just cant get it right. The noise isnt worth the lack of power and running rich. I think a rear crossover would greatly improve their performance, and im sure my gutted ones flow plenty, its basically an open pipe. But the lack of scavenging is whats killing it. It is more trouble for me than its worth due to a lack of resources to try and build a crossover for the rears. (Although its literally just drilling a couple holes and welding a pipe between them, but has to be in the perfect location too)

But it does sound wicked!

Im going to save money towards a full system. But if i had an extra stock muffler, i suppose one could gut the cans and still retain the cylinder balance effect given the stock is a crossover system. As cool as i am, lol, i cant beat yamaha factory.

G`day Killjoy,
Firstly, really appreciate you coming forward, I assume your bike is in the bottom two vids, the one with the complete walkaround vid..... Nice looking bike Mate..... :eusa_dance:

Couple of questions spring to mind, if you don`t mind me asking...

How much did you remove out of the muffler? the guy with the other bike/vid looks to have punched a small cap (looked like a bottle top) from the front end, then removed the top circular end cap from the tail end?

Did you make/try any changes to the standard airbox?

Did you make/try any carbie changes/jet changes from the standard set up?

Many Thanks

 

[lilredrooster]

I believe the lack of scavenging is ultimately the reason for the Cobra's to be killing the power over even just the stock system.

That's just a poorly designed system. Even with the small outlet, and even if Cobra decided to put in a larger diameter outlet........... you simply don't design a system where there's no scavenging. The Cobra engineers (if you want to call them that) clearly should have seen that the stock system used scavenging and that it was mandatory to use scavenging on an aftermarket system to get the exhaust gases out of the pipes to help the engine produce power.

Their design is basically putting a restriction (gases left in the headers with no help of 'suction' to get them out) in the exhaust which is killing power and making the engine work harder to push the exhaust gases out. The perfect formula for restricting power.

Vinnie

G`day Vinnie, Thanks again for your thoughts and your interest, very much appreciated. Certainly a puzzle.... :confused2:

To be fair, it looks like most/all the slip-ons seem to create a power loss (compared to the stock system), maybe not as much as the cobras? Hard to tell?....

It also looks like it could be possible to claw a couple of HP back with carb tuning/jet changes which is a positive....

Significantly, there are not many 4/4 pipes/4/4 systems to compare the Cobras against for performance..... Working on it.......

Enjoy the Ride....... Ride Safe..... :thumbs up:

 

[Vinmax]

No problem at all. I enjoy discussing the technical aspect of what's different with the Cobra's.

Something interesting to check though,,,,, with some slip-on setups you should take a look at the collector pipe that feeds the end muffler. Check out Dale Walkers and the DAM exhaust slip-ons (even the Supertrapp's). In all those systems, you'll notice a definite collector assembly that feeds the muffler canister.
That's what's missing on the Cobra's.

Dale Walker has put in time to not only get the collector right, but also worked with the jetting and the size of the muffler to un-restrict the exhaust and still use the stock headers.
I'm not saying his slip system is as good as a full on exhaust, but the gains he made over stock is through proven un-restricting the exhaust and working with a good collector to keep the scavenging effect.
I think the Cobra's look great. I think they sound great. But as far as 'engineering,' I think they just messed up big time. Too restrictive of a muffler output and no collector/cross-over tubing.
Basically, they built them for looks and thought nothing about putting a bike on a dyno to actually check out the running performance of them. This is something Dale Walker did with his system.

I think the Walker/Holeshot exhaust and the DAM system wanted good looks in their slip systems for the Vmax, but also wanted to back it up with improved power through proper design.




Vinnie

 

[one2dmax]

I wish I had done a dyno after we swapped out the Cobra's but the power difference in riding was extreme. Here's the Cobra dyno sheet and our changes to get the fueling correct (which took a number of pulls). Never did crack the 100 rwhp dyno number (which at the same event we had plenty of stock motored bikes getting 120's and a few higher mileage bikes even into the 130's).

Do what you want. We've already been there and it's just not worth the cost and effort to try and improve these.

 

[lilredrooster]

Many Thanks Sean and Vinnie, :thumbs up:

Interesting take from Dale Walker too...... :hmmm:

First Video, says his mint, stone-stock VMax Best Pull was 99HP at his new location in Nevada, Best Stock Vmax`s he had seen were around 104-108HP at his old location in California... (the differences being due to elevations at/above sea level at each location)...

The good Dyno runs with his slip-ons were 110HP in conjunction with his stage 1 Jet Kit installed and tuned (Not Stock!)....

https://www.youtube.com/watch?v=EeOF5D-_epo

https://www.youtube.com/watch?v=69Y8W3mniwU

https://www.youtube.com/watch?v=X_vD9LZERJE

https://www.youtube.com/watch?v=b4WSS7sofJE

 

[Fire-medic]

The slip-ons should give you the same HP as the stock exhaust. You keep the crossover, you are only replacing the heavy chrome or black megaphone trumpets with less-restrictive, louder canisters. The stock system is relatively-quiet. The slip-ons are always louder from what I've seen.

My stock engine & exhaust on the one time I dynoed, did 109 RWHP.

There are threads on here about people who tried repeatedly to make the DJ Stage 1 setup work, but they always seemed to have problems somewhere, and out of frustration, went back to stock jetting, to regain smooth operation. The DJ Stage 7 seems to work with the full exhaust replacement, I've installed a Stage 7, no engine mods, full UFO Dragstar 4/1, I kept the VBoost, and it seems to butt dyno higher than when I ran it on the dyno, stock engine & stock exhaust.

 

[lilredrooster]

G`day FM,

Many Thanks as always for your thoughts and comments and for taking the time to contribute, very much appreciated, always good to share experiences and dyno numbers..... :eusa_dance:

Enjoy the Ride...... Ride Safe.... Cheers.... :icon_jook:

 

[lilredrooster]

Thought this article (See Btm Page) was good reading, generally looks like the VMax suffers a fair difference between crank HP (145HP claimed, Full Power) and actual RWHP (90/95HP?!).

Couple of Quotes/Readings from the same article (See Full Article Link and Motorcycle Dyno Database at Bottom of Page):


"All because some guy thought that a 1985 over bored 1400cc prerelease version V Max made 145 crank hp according to the marketing dept. and he couldn't have his "new" inertia dyno read 90 hp on a stock dealership V-Max. Well, he was correct at 90-95 effective hp, but he made it read 120 to sell more of his dynos. And that's where the chassis dyno hp mess started. Read more about inflated hp numbers"


And..... (See Data Base on same article)

Yamaha V Max, till 08 all stock ~90 True HP
Yamaha V Max, till 08 with Holeshot exhaust ~97-99 True HP
Yamaha V Max, till 08 with Cobra exhaust ~93-95 True HP
Yamaha xvz1300 Royal Star all stock John Baron's bike ~60 True HP
Yamaha xvz1300 Royal Star w aftermarket exhaust and our big air kit John Baron's bike ~63 True HP



Article Link with dyno readings database as follows:

http://www.factorypro.com/dyno/true1.html


Enjoy.....

 

[one2dmax]

Pretty old article. FP dyno's read differently so you can't compare number to number with a DJ dyno.

You can go research all you want. We've dyno'd probably more vmax's then maybe 1-2 other guys on the planet with many different combinations and mileage variations. From stock to big bore engines, chain drive, and more.

The Cobra's LOSE about 10% HP over stock
Every single brand of slip-on we've ever tested basically makes the same power as stock.
Every full system we've tested measure so close to each other (given similar mileage bikes) as to say there is no single system that makes more power over the other. All of them give an approx 7-10% power increase over stock.

Most stock bikes (on a DJ dyno) make 110-112 rwhp. Some less and a few make more.
Most bikes with full system make high teens and start getting into the 120's.
The higher the mileage the more power they make. 50-60k mileage bikes can make into the 130s

 

[lilredrooster]

Interesting Observations...

It is an old article, it is also an old bike and thought it was still interesting, still current, still relevant....

It looks like you and Dale Walker both use the same D/J Dynos...

For a stock/standard VMax you quote around 111RWHP, Dale quotes around 104RWHP. (Less at his new location, around 100RWHP).

You quote the stock pipes around equal to slip-ons

Your attached dyno snapshot of VMax with Cobras with tuning = 96RWHP

Dale W attached snapshot shows 2 x runs overlaid both with same Stock VMax Bike, Stock Exhausts at 99RWHP v Dale W Holeshot Slip-Ons at 110RWHP.


From the Article, as follows:

Yamaha V Max, till 08 all stock ~90 True HP
Yamaha V Max, till 08 with Holeshot exhaust ~97-99 True HP
Yamaha V Max, till 08 with Cobra exhaust ~93-95 True HP

 

[one2dmax]

Where's his A/F curves to see if it's apples to apples. I've tested his old slip-ons and many others. My testing doesn't agree. You'll also see testing from Dynojet comparing their jet kits and showing monster improvements. We were able to replicate that once with a poorly tuned and jetting bike and then the swap to the stage seven had the massive jump which was mostly attributed to the better a/f that was achieved in the after test.

 

[one2dmax]

Also note, I am not trying to sell any slip-ons or jet kits. I just put out the facts from working with this specific motorcycle for the last 30 years. Not a range of motorcycles with some playing every now and then one one.

 

[lilredrooster]

G`day Sean,

Thank-you as always for your input, absolutely no disrespect intended to either your good self or to Dale W, the purpose of this thread is simply intended to look at the Cobra exhausts and their performance....

After many threads and many posts and much searching, to date there is only one decent screen-shot of the Cobras worth posting, you supplied it, very glad you did, very glad to have it available, it is very helpful in the discussion, as are your thoughts/comments/experience.....

The only other decent dyno screen-shot that I have available to date, is the Dale W one, this is also very helpful, it shows two dyno runs using the "same standard stock Vmax bike" also on the "same Dyno"....

The two dyno runs are of the stock exhausts (very handy) "versus" the Dale W latest slip-ons, also very helpful because:
Cobras are also slip-ons, the standard stock front headers are used in both cases just like the Cobras, significantly, although they are both slip ons the Cobras appear to lose 10HP (Compared to the Stock Exhaust) while the Dale W versions appear to gain 11HP (Compared to the Stock Exhaust)....

As with most things viewed on the internet, good, bad and ugly, each individual has to form their own opinions.....

An informed opinion can only be gained by reviewing the data, unfortunately the data available with the Cobra exhausts is very scarce, non-existant and/or not being shared...

Plenty of here-say, plenty of chatter, plenty of opinions, plenty of finger pointing, but, very little cast iron data available to date.....

 

[jdeitz1979]

This is an interesting thread. There are a lot of vmax exhaust systems on the market, some a lot better then others. Thanks for guys like Sean with the vmax dedication and resources to provide the data and knowledge we all seek. Hopefully this thread will help others looking into the exhaust options for their vmax.



I had never run cobra exhaust but now I know that it robs power from the bike. I currently run a full voodoo set up, but started with a modified stock, then went to kerker slip ons, finally the voodoo. I don’t think I’ve lost power, but I haven’t done a dyno either. Either way, it sounds mean and pulls like crazy, and makes me grin lol


Sent from my iPhone using Tapatalk

 

[lilredrooster]

G`day JD79, Many Thanks for your contribution and thanks for adding to the conversation.... :thumbs up:

Agree with your comments, many exhausts out there and many VMaxxers owning them for many different reasons, looks, budget, weight, sound, performance, etc, etc...

It would be a very boring world if we all liked the same thing.....

Glad to see you are happily enjoying your Voodoo and your journey to get there.... Good Stuff.....

Enjoy the Ride.... Ride Safe.... :hippy biker:

 

[Killjoy]

The Cobra's LOSE about 10% HP over stock

I can tell you in my case this is absolutely true and I can FEEL the power different.

From the stock cobra muffler i took a giant pry bar, and punched a hole in the center tube, then i took a hole saw and cut the end caps off. But it is horrendously loud. But to me i feel stupid knowing i have all this sound but no extra power. =/

Ran it with and without the "Y" on the airbox, runs like shit without it. Never bothered with the jetting because im gonna dump these pipes and get a full system hopefully soon...

Good luck on your quest. They certainly look badass!