Cobra Exhaust Tuning Recommendation.

Discussion in 'Exhaust' started by lilredrooster, Jul 8, 2018.

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  1. Jul 8, 2018 #1

    lilredrooster

    lilredrooster

    lilredrooster

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    Looks like the Manufacturer recommends that the Cobra Exhausts require re-jetting and tuning......... Does not seem that many get done!!!......


    Yamaha Cobra Exhaust Website link below:

    https://cobrausa.com/yamaha/v_max_85...ashcut/2168SC/

    VMax Cobra Exhaust Fitting Instructions (See Attached)

    Cobra Fitting Instructions Quote "IMPORTANT: It is recommended that you re-jet your bike with a Cobra Jet Kit, available from Cobra part #92-2168."

    Recommended Cobra Jet Kit # 92-2168 Instructions & Parts List (See Attached)

    Cobra Jet Kit # 92-2168 appears to have been developed by Dynojet.


     

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  2. Jul 8, 2018 #2

    lilredrooster

    lilredrooster

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    Recommended Cobra Jet Kit # 92-2168 Instructions & Parts List (See Attached)

    Yamaha VMax 1200 Dynojet Stage 1 Jet Kit Instructions & Parts List (See Attached)


    Interesting that many of the parts listed are shared in both kits......


    Very Interested in any resident carb guru/enthusiasts thoughts/opinions on the suggested PAJ Pilot Air Jet modifications/changes......... [​IMG]
     

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  3. Jul 8, 2018 #3

    Redbone

    Redbone

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    The issue with the Cobra exhausts are that they use the stock headers that are too small to handle the increased flow from the engine that a jet kit provides. If the jet kit does not push more air/ fuel out of the engine is just there to make it run smoother I would guess. :confused2:
     
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  4. Jul 9, 2018 #4

    lilredrooster

    lilredrooster

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    G`day RB, Many Thanks for your reply, very much appreciated...... :thumbs up:

    The stock exhaust with stock front headers are good "generally" for around 113Hp for a stock bike on dyno. (given variations in dynos and bikes).

    Looks like the Cobras with stock headers are around 100Hp. (seems few bikes with cobras have dyno numbers and fewer still install the cobra recommended jet kit).

    The Cobra jet kit info is attached, it suggests quite a power gain, see graph and comments.


    Questions that spring to mind are:

    Are there any Vmax owners out there that have the Cobra exhausts running the Cobra jet kit??

    Are there any Vmax/Cobra exhaust owners (stock-ish normally aspirated engine) out there that have achieved decent performance and how?

    Is there any improvement (no matter how small) to be had, running the Cobra jet kit?

    Anyone got any Dyno numbers with the Cobra exhausts and Cobra Jet kit?

    Always grateful of any/all sensible thoughts and comments....

    Enjoy the Ride..... Ride Safe.....
     

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  5. Jul 10, 2018 #5

    Vinmax

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    Seems with the Cobra, they have you run a 150 DJ main, which is really small for sea level operation (lt's right around a 141 Mikuni jet). So it would make sense that if the Cobra system makes the bike run very rich with regular jetting, and therefore the bike would lose lots of power when running so rich.

    I always thought the biggest problem with the Cobra was the lack of the crossover tube between the pipes at the rear. The Dale Walker slip-ons utilize a crossover design as do many other slip-on style pipes. This keeps the scavenging action in check and doesn't upset the stock jetting too much (when using this style of slip-on with stock head pipes). The Dale's run a type of 'Y' pipe at the rear as they feed into the larger muffler section. I think the Cobra's run separate pipes and then branch them back into possibly a more restrictive muffler section. I'm not too sure why this would cause a rich condition though. Unless if makes the bike pull in less air that has to be compensated for by a smaller main.
    Usually it's the higher flowing exhausts that cause more scavenging effect, that can get away with a smaller main as they pull in air 'harder' and make more fuel come from the main through a stronger suction effect at the carbs. Who knows............ I'm speculating here.

    I'd have to see a set of Cobras to draw any real conclusion there if there is or not some type of crossover pipe designed into the rear muffler section.

    Vinnie
     
  6. Jul 10, 2018 #6

    Conman

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    +1
     
  7. Jul 10, 2018 #7

    lilredrooster

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    G`day Vinnie,
    Many Thanks for the Grrreat reply, very much appreciated :eclipsee_gold_cup:

    Totally agree with your comments, I just wanted to say that I have stumbled across your carbs/tuning posts many times and have always personally found them very, very helpful.... :thumbs up:

    The Cobras have 4 x individual slip on rear pipes which attach to the original Vmax front header (header has original single crossover pipe for front cyl 2 & 4, no cross over for rear cyl 1 & 3). Some owners have messed with the internals, baffles out/modded/gutted etc, but, little/no feedback & no dyno numbers (mostly to improve sound)... Generally all the slip on exhausts struggle to match the original exhausts for HP (All credit to the original engineering). Without any positive feedback or dyno numbers very, hard going to gain any potential benefit without a lot of hacking/welding/dyno time....

    Just Maybe?...the Cobra jet kit might show some gains? Also might explain the lack of power as you suggested? Maybe not?
    Hopefully someone out there has used the Cobra jet kit and will provide some feedback?

    Enjoy the Ride..... Ride Safe..... :hippy biker:
     
  8. Jul 11, 2018 #8

    Fire-medic

    Fire-medic

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    I don't think anyone on here has ever realized a dyno increase from running Cobra 4-into-4's. Matter-of-fact, they usually report dyno numbers in the 90+ RWHP range, not-even hitting 100 RWHP. Cobra 4/4's look good but they cost you power. Stock VMax's usually run in the 106-115 RWHP range. I think the highest motorcycle magazine article I ever saw was a 119 RWHP rating from one.

    The factory actually did a good job of balancing power, tone, and appearance with the stock system. When you install a complete aftermarket system and you re-jet, that's when you get additional power and noise. If you're somewhere you have to pass equipment checks, that probably rules-out such things.

    Cycle World August 1988 10.88 sec, 125 mph

    Cycle World March 1987 117 RWHP stock
    Dynojet Stage 7 and Kerker 4/1 125 RWHP

    Paul Civitello's chain-drive conversion (stock engine) a best e.t. of 10.05/135 MPH

    Dale Walker did a 10.64/128 MPH for Cycle World in 1985 at the bike's debut with the magazine. The value of a highly-skilled rider is shown when in-comparison the magazine editor David Edwards did 11.18 seconds, 122.95 mph in August 1988 (a different story from the first-mentioned run at the top).

    Motorcyclist April 1986 10.74/126.8 at Baylands Raceway CA.

    Speak to Sean Morley about getting a good performance system and jetting which will put you in the ballpark. Don't wast your time/$ on the Dynojet Stage 1 system. The Stage 7 system is better for making power, but you need a complete exhaust to make it work well.
     
  9. Jul 11, 2018 #9

    lilredrooster

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    G`day FM, Many Thanks for your reply, very much appreciated....:thumbs up:

    I think we both agree that the Cobra 4/4 exhausts lose power when compared to a stock exhaust, around 13HP or there-abouts....
    Indeed most slip on exhausts similarly lose power by comparison to stock (All credit to the original engineering).
    VMax owners buy slip on exhausts for a variety of reasons, generally not expecting the highest level of performance.

    It would be good to discover a way to minimise the HP loss over stock, even if only by a small amount.

    One way seems to be by modifying the exhaust. (not very practical or cost effective).

    One way seems to be installing the manufacturers recommended Cobra Jet Kit.......

    Very Interesting fact is that the vast majority of VMax/Cobra owners do "not" seem to:
    (A) Install the Cobra Manufacturers Recommended Jet Kit (earlier attached).
    (B) Enjoy very little time on the Dyno.

    Which poses the question:
    Are the weak dyno HP readings being quoted for VMax/Cobra exhausts combinations that do not have the manufacturers recommended jet kit installed ???

    Bearing in mind the below Cobra Fitting Instructions Quote
    "IMPORTANT: It is recommended that you re-jet your bike with a Cobra Jet Kit, available from Cobra part #92-2168."
     
  10. Jul 12, 2018 #10

    Fire-medic

    Fire-medic

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    Are the weak dyno HP readings being quoted for VMax/Cobra exhausts combinations that do not have the manufacturers recommended jet kit installed ???


    If you look at the historic record on here, the DJ Stage 1/Cobra jet kit (apparently sharing many parts) gave disappointing results for the users. To make power, if you like the four canister look, consider the UFO Quadzilla. Be warned, like most UFO products they are probably LOUD! I'm not sure if the new owner of what became the North Royalton OH company after Jon Cornell's death is still offering them. https://us1075826762.fm.alibaba.com...Exhaust_System_1985_2007_Vmax_Motorcycle.html

    OK, there it is, the new UFO name, Star Rider Performance. http://starriderperformance.com/1985-2007/exhaust/

    Star Rider Performance

    5271 Wooster Rd W

    Norton, OH 44203-6262

    I know you would like to probably keep what you already have, but, the right tool for the job makes things a lot easier. Sell the Cobra to someone who wants looks over performance and get the proven performer, with a jet kit. Sean Morley has a good one, and an advantage is you can contact him for tuning advice. He might even have a used UFO Quadzilla.
     
  11. Jul 12, 2018 #11

    lilredrooster

    lilredrooster

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    G`day FM, I think you are under the impression that I am looking for a new exhaust?

    Just to be perfectly clear, I am most definitely not looking to purchase a new exhaust, very happy with the Cobras.
    This is why I am asking for people to come forward to share their personal experiences trying to improve the Vmax/Cobra exhaust combination....


    From a previous exhaust related post (01/July/2018) :

    ""G`day All from Australia, attached a pic of my bike for anyone interested....

    Firstly, all the evidence points to losing 10Hp with the VMax & Cobras combo... I get that, so, moving on..... I like the look and the sound and would like to persevere with them regardless.....

    Anybody like to share your past experiences (preferably with Dyno proof) trying to improve the Cobras??

    Certainly there seems to be plenty of Dyno proof that they loose power, BUT, does anyone out there have any positive (sensible) Dyno proof of changes made to improve the Cobras (even by a small amount....) for instance carb tuning etc...

    Many Thanks in advance of any and all contributions.....""
     
  12. Jul 12, 2018 #12

    Fire-medic

    Fire-medic

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    I understood you were looking to minimize the power loss that Cobra 4 into 4's give you over a stock exhaust. Because the design isn't conducive to making power equal-to stock, and because the DJ Stage 1 has not been a successful install for the members on-here who tried it, my suggestion is to consider replacing the pretty but non-performing Cobra with something similar in appearance that can be and has successfully been tuned to equal a stock exhaust, and to make more power, properly-tuned, albeit with an increase in noise.

    In the not-too-distant past, I rode a clean later model equipped w/a Cobra 4-into-4. The power was noticeably lower everywhere, and it even seemed to rev more-slowly. For-sure, the VBoost was not the equal of a stock bike. The VMax was designed for one thing to be done exceedingly-well: to be the fastest accelerating bike on the market. Upon its release, it was, and it took the supersports 1000 and 1100 cc bikes a few years to catch-up. There were many people who didn't want to be forced into the sportbike crouch to go fast. They liked the neutral seating of the VMax, and if you could afford the tickets, the bike was the 'baddest' stock bike for several years, and still gets plenty of attention on bike nights.
     
  13. Jul 12, 2018 #13

    lilredrooster

    lilredrooster

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    We all love the VMax, often for different reasons, I can see and appreciate the beauty of almost all the never ending variations I see and have seen, from stock, mild to wild.....

    I agree in 1984 it was a radical bike and remains a cult bike to this day... That is some of the history...

    If I was to take the attitude of selling everything off my bike for maximum performance my VMax would be unrecognisable.... In fact before long you would sell it and buy a Gen 2 for a short while before buying something bigger/better etc, etc.... Personally I think that is missing the point, like my Vmax how it is..... Did I mention budget....


    Back to the Cobra exhausts, couple of points:

    I am not referring to the D/Jet stage 1 or the D/Jet stage 7 (either one is a can of worms in their own right), you mention the D/Jet stage 1 in your post....
    I am referring specifically to the Cobra Exhaust Manufacturers Recommended Jet Kit # 92-2168 developed by D/Jet solely for the VMax 1200/Cobra Exhaust combination.

    Interesting about your test ride on the Vmax with Cobras? Was it tuned for the Cobras in any way? Did it have a Jet Kit fitted? Do you have any dyno figures?

    Personally I find it very difficult to measure small HP increments by feel?

    Interesting conversation, many thanks for contributing

    Enjoy the Ride..... Ride Safe
     
  14. Jul 14, 2018 #14

    lilredrooster

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    G`day Vinnie,

    FYI, I think you will find that the Cobra Jet Kit is using the DJ 155 as the main jet = 145 Mikuni (I think you also use the 145 Mikuni mains in your own bike as i recall)
    They are using the DJ 150 (140 Mikuni) as the PAJ2 (Standard 170 Mikuni)
    They are using the DJ 080 (075 Mikuni) as the PAJ1 (Standard 090 Mikuni)
    I think you had gone to the 095 Mikuni with PAJ1 & retained the Standard 170 Mikuni PAJ2.

    Very interested in your thoughts/opinions/comments on the Cobra Jet Kit choices of PAJ1 & PAJ2 sizing?? Particularly compared to your own PAJ jet selections, with you both sharing the same size main jets......
     
  15. Jul 18, 2018 #15

    Vinmax

    Vinmax

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    Hi,
    Yep, I was using the 145 main (Mikuni brand) at my 5280' altitude (and higher of course when I ride up the canyons of Colorado).
    I've gone as low as 142.5 for mains also, but with no noticeable difference compared to the 145's.

    As for the PAJ 2's, I currently run 180 Mikunis. The bike runs much crisper in the midrange with that setup. Seems you want to keep the PAJ 2's large to keep the mid from running too rich. That setup makes for a really crisp midrange.

    I think with the Cobra's, you have less 'suction' and scavenging effect in the exhaust system due to no crossover tubing or collector pipe built in. What does this cause? Well, I'm thinking it may cause a less efficient condition because you don't have the suction to pull out the exhaust from the cylinders once the exhaust valves open.

    Does this make the bike richer or leaner? I'm not too sure. I think it may simply make the bike produce less power. I don't think a lot of the efficiency loss of that exhaust system can be cured by going richer or leaner.

    My thoughts are this;
    I think going leaner with the Cobra's or any exhaust, will produce more power. Reason being, the stock setup is set a bit rich for safety. The factory puts the same jetting for 49 states regardless of altitude. So, I think they run rich and even when actually at sea level, the density altitude is always quite a bit higher. That would mean when you're actually sitting on a bike right by the ocean's side, the density altitude may show that it's the equivalent of being 1000' in the air.

    So, Cobra's probably like a bit of 'lean' tuning. This means smaller mains, and larger PAJ 2's for the midrange. BUT, the stock exhaust system benefits with this also.

    Here's the scenario I'm thinking:
    1) stock system not tuned compared to Cobra's not tuned (loss of quite a bit of power due to less efficiency, due to less scavenging effect from Cobra's).
    2) stock system not tuned compared to Cobra's 'tuned' for better running (you'd experience less of a power difference comparing the 2 systems. Maybe Cobra would only see a 5-6hp difference in loss compared to the normal 10hp difference).
    3) stock system 'tuned' compared to Cobra's 'tuned' (you're going to see that both systems tuned will make more power compared to un-tuned setups, but the Cobra's will still never come close to stock and you'd be back to the 10hp difference *loss with the Cobra's).

    For all running, I'd try and go leaner on the PAJ 2 and get it as crisp as possible in the midrange. Too lean of course and you cross over the crispness peak and you may experience jerky throttle in the midrange when cruising.

    Vinnie
     
  16. Jul 19, 2018 #16

    lilredrooster

    lilredrooster

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    G`day Vinnie, Thats a Grrrrrreat Post..... :eusa_dance:

    Totally agree with your thoughts and Many Thanks for the reply...

    Looks like after all these years, it is still difficult to surpass the original factory engineering, ie, stock exhausts, stock airbox, stock carbs, etc...

    Going to have to start playing and see how things develop, now the bike is off the road for the winter... (I am at 500ft above sea level so going to try the 147.5 Mikuni main jets)...

    Really appreciate your help and advice.. :eclipsee_gold_cup:


    Enjoy the Ride.... Ride Safe.... :thumbs up:
     
  17. Jul 21, 2018 #17

    lilredrooster

    lilredrooster

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    Thinking that there might be a couple of HP to be clawed back after fitting the Cobras, in the carb tuning alone, generally leaning it out as previously discussed, maybe around 2 HP as a guess..... Not a massive amount, but maybe around 20% of the average power loss which at least would be going in the right direction....

    Still not come across any/many owners that have even tried the Cobra Jet Kit? So no data readily available there?
    All the indications are to me that the Cobra Jet Kit is unlikely to work, although the main jets supplied seem right, the rest of the kit seems to be going in the wrong direction, stage1/7 needles are likely to go richer, the PAJ1 down to 075 likely to go richer and the PAJ2 down to 140 also likely to go richer....
    The only advantage I can see with the DJ needles would be the variable clip positions?

    Makes sense to stick with the standard airbox and standard needles...
    Not sure how tunable the standard needles are?
    Can shimming washers be safely/reliably inserted both above and below the needle clip, so the needles can be both raised and lowered??


    Enjoy the Ride..... Ride Safe.... Cheers :icon_jook:
     
  18. Jul 21, 2018 #18

    lilredrooster

    lilredrooster

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    Other options would be to modify the Cobra Exhausts in some way to enhance the performance???

    Installation of a crossover pipe or pipes??

    Modification of the Cobra slip-ons internally??

    Cutting/Pipework/Welding/Gutting/ etc, etc??

    Anybody attempted to install a crossover/scavenge/balance pipe or pipes??

    Could the Cobras be too restrictive internally??

    See You-Tube Links Below:

    https://www.youtube.com/watch?v=g9wworPvNAY

    https://www.youtube.com/watch?v=IczWA3vUOd8

    https://www.youtube.com/watch?v=fHPT3e7yCbY

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

    Having Trouble with the Links, then go to You Tube and enter the following searchs:

    YAMAHA VMAX 1200 (VMX-12) with Cobra Slash Cut 4-to-4 DIY modified slip-ons.

    Yamaha VMAX 1200 - Cobra Slash Cut Slip-ons Modification

    Walk around exhaust sound of my 1985 vmax 1200 #0245 cobra pipes

    1985 Vmax vid #2. Punched out the cobra pipes.


    Obviously noise is also a consideration.....


    Enjoy the Ride..... Ride Safe.... :git:
     
  19. Jul 21, 2018 #19

    sdt354

    sdt354

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    Can shimming washers be safely/reliably inserted both above and below the needle clip, so the needles can be both raised and lowered??

    Yes, many have shimmed the stock needles. For me, with Marks 4-2 pipes and the air box installed, I used .028 thick shims made from #10 stainless washers to raise the needles. Plug reads as a guide. Lowering? I'm not sure how that could work.



    Code:
    
    
     
  20. Jul 21, 2018 #20

    lilredrooster

    lilredrooster

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    G`day Steve, Many Thanks for your reply, very helpful and very much appreciated Mate.... :thumbs up:

    Not too sure how the lowering could be done either....

    I do know there are many very ingenious Vmax owners out there, good chance someone has had a go at it...

    Still hopeful that some such ingenious Vmax guru has had some success improving the HP output from the Cobra Exhausts....... :whistlin:

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

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