Cobra Exhaust Tuning Recommendation.

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

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  1. Sep 3, 2018 #101

    lilredrooster

    lilredrooster

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    I believe this thread is and will continue to be very helpful for anyone interested in the VMax and the Cobra 4/4 exhausts combination....

    It is a credit to everybody who has contributed to this thread, that it has for the most part kept on topic, this forum is an incredble resource with many gifted and knowledgable members.

    There is a lot of interesting information on this thread that hopefully will help and assist those people interested in the Cobras to draw their own conclusions about them....

    Although we all have the VMax at heart, we are all unique individuals with different needs, goals, age groups, responsibilities, skill-sets, mind-sets, budgets, time restrictions, backgrounds, experience, etc, etc.....

    Consquently the Cobras are going to find some admirers amoungst the group for any variety of reasons.....

    Without doubt they cannot be considered a performance exhaust and for the most part people are not buying them for their performance attributes, or lack of....
    In saying that this is also true, of most, if not all slip on exhausts....

    Generally those seeking a performance increase would, should and do, go for a full system with bigger headers, jet kit, etc, etc....

    There is also undoubtably a slice of the VMax community that find the Cobras appealing for a variety of reasons....


    Enjoy the Ride..... Ride Safe..... :bike1:
     
  2. Sep 21, 2018 #102

    lilredrooster

    lilredrooster

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    Follow Up on my previous modifications and above Quote:

    I have now drilled the Cobra Exhaust internal baffle plate solid disc out to my final size of 21mm and road tested the bike, as previously stated it is a little bit more noisy but not a major difference by any means.
    Had to reset the mixture air/fuel screws to lean it out further, overall very happy with the results, bike runs much smoother now at low revs around town and in traffic, cleaned up all signs of the rich running at the exhaust tips and the spark plugs, plugs have cleaned up 10 fold....

    This is a summary of the total related changes I have considered and chosen to make to my bike:
    Standard Air-box with Y-piece lid fully fitted, standard profile K&N Air Filter.
    Mikuni 147.5 Carb Main Jets fitted. (Standard Mikuni 152.5 Main Jets).
    Retained original standard Carb Mikuni PAJ1 & PAJ2 pilot air jets.
    Mixture Air/fuel pilot screws 2.25 turns out. (Originally 3.5 turns out).
    Cobra Exhaust Internal Baffle Plate Central Solid Disc drilled out to 21mm Dia.
    Other than the drilled holes in the baffles the Cobra Exhausts are otherwise standard and the front headers are standard Yamaha exhaust pipes.

    I do not intend to make any further changes to the Cobra Exhausts.

    Personally, I do not think there is anything to gain by removing any further material from the Cobra baffles or baffle plates.

    Personally, I do not think there is much if anything to be gained by modifying the exhaust collectors entering the Cobra Exhausts.

    I have taken the bike to my local drag-strip to get some idea of the 1/4 mile terminal speeds, first impressions to me are that the bike is approx 7.5 BHP down on power compared to a standard Gen1 Vmax with standard exhausts.


    Enjoy the Ride..... Ride Safe..... :bike1:
     
  3. Sep 21, 2018 #103

    lilredrooster

    lilredrooster

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    Re: Power Q!!!!!!!!!!!!
    Quote:
    Originally Posted by Kurtmax [​IMG]
    well then i will probley sell the cobras and get the stock mufflers back on there till i can afford a full system, any body got some stockers they want to get rid of???

    Before you put the stock mufflers back on. Drill the center of the baffle out with a 1 inch drill bit mounted on an extension. Work up to the 1 inch drill using a smaller drill as a pilot hole. If you look with a flash light down into the baffle you will see that it is blocked so the exhaust flows around it and out of the little perferations in the baffle. Drilling through this blockage will allow some exhaust to flow straight through. Derestricting exhaust flow this way will allow the motor to rpm higher, you do not have to rejet for this modification, so don't. It just let's the engine exhale better and allows it get more intake charge. The sound will be a nice deep muscular tone also. You will notice a seat of the pants difference in performance, not tons of horsepower! Your Max will run cooler and be torquier. That's it!! I can send pics of the finished product if necessary.


    This post Ref: 08/29/2007. Thread Title: Power Q. Posted by "TurboMark"

    Interesting and Relevant Post for anyone considering modifying the Cobra Exhausts.
    FWIW, This above post describes the Cobra exhaust modification I chose to make on my own bike.


    Enjoy the Ride...... Ride Safe...... :peace out bike:
     
  4. Sep 21, 2018 #104

    Redbone

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    Have to acknowledge your dedication to the Cobra exhaust and trying to find a solution to your liking.:clapping:
     
  5. Sep 21, 2018 #105

    lilredrooster

    lilredrooster

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    G`day Redbone, Many Thanks for your kind words, very much appreciated Mate..... Cheers..... :cheers:


    Have attached a couple of photos of my bike for anyone that maybe interested.....


    Very Happy with the Cobras and My Version of the VMax...... :angry flame devil:


    Enjoy the Ride.... Ride Safe.... :bike1:
     

    Attached Files:

    Last edited: Oct 13, 2018
  6. Nov 17, 2018 #106

    lilredrooster

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    Just wanted to add some further detailed information/comments to my above original/previous quote:

    Above I have listed all the modifications I have recently made to my Vmax with Cobra exhausts and also listed my findings of an estimated loss of approx 7.5 BHP based on my drag strip runs terminal speeds compared with expected/listed/published comparable standard Gen1 Vmax with standard exhausts.

    I can now honestly say that my bike sounds and runs the best that it has ever done in the 8 years that I have owned it, it has a mean lopey tick over at idle and sounds quite V8ish which I often recieve compliments upon, particularly the evening I took it to the drag strip...

    I had a total of five runs at the drag strip, my only reasons being to check the terminal speeds to compare them with a standard vmax with standard exhausts and to compare my bike with like for like estimated BHP of both examples from the terminal speeds.

    Although on the night I found my Vmax to have an approx 7.5 Bhp loss. I believe given more practice, better track conditions, better weather conditions, upgraded clutch springs and a decent rev counter (not the standard tank mounted console version which is awkward to read in motion) I would almost certainly have improved my terminal speeds and reduced the 7.5 Bhp loss result I got on the night.

    Anyways, I only use my Vmax for road use and am very, very pleased with it, it does everything and more that I ask of it, I have no plans to go back to the drag strip and no plans to put it on a dyno in the future.

    I have been running an upgraded Barnett clutch conversion with the Barnett fibre plates, standard Yamaha steels and standard Barnett clutch springs for around five years with no issues on the street, for sure on my best two runs I could hear either clutch slip or wheel spin at 2/3 track which would hurt the terminal speed a little, I have now ordered/received new upgraded Barnett heavy duty clutch springs, it is riding season now so do not intend to install until next related maintenance, don`t think I will need them for road use.....
    Note: (It may not have been clutch slip, it could have been bad track conditions causing wheelspin at 2/3 track that I experienced, not 100% sure).

    In Summary:
    Although during my one night at the Drag Strip I found my personal Vmax to have had an estimated loss of approx 7.5 Bhp in an approx comparison with a standard Vmax with standard exhausts.
    I am very confident that this loss could be significantly reduced under more favourable conditions. (See Above).

    Take from it what you will......

    Enjoy the Ride.....
     
    Last edited: Nov 17, 2018
  7. Nov 18, 2018 #107

    one2dmax

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    More favorable conditions on the header would have been even better. I've said it before and will say it again. If you want to lose power with no way practical to regain it then install yourself a set of Cobra's.
     
  8. Nov 20, 2018 #108

    lilredrooster

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    There is no guarantee that installing a larger header with the Cobra slip ons will increase BHP, as far as I know nobody has done this and there is nothing to support that any gain with this set up has been achieved with a bog standard Vmax engine.

    The Cobra exhausts are a slip on, intended to fit the original Yamaha front headers, any Vmax owner primarily concerned with a performance gain generally would not consider a slip on exhaust of any kind/brand, as generally, they do not show a performance increase over the standard Vmax exhaust.

    Vmax owners replace their exhausts for a variety of reasons, the main drivers for exhaust selection are visual improvement, audible improvement, less weight, cost and performance are also factors.

    The Cobras are a very popular, low cost, Slash Cut, Hot Rod Style alternative in keeping with the original VMax Hot Rod design, you either like the look or you do not.....

    For the majority of Vmax owners cost is a major consideration, around $500 you can get a new set of Cobras and call it done.... Yes it is well documented that you will almost certainly lose a few BHP.....
    If performance is your main goal, it would not be smart, sensible or cost effective to buy new larger dia front headers and new rear slip ons of any brand/style and build your own high performance exhaust system.....
    If performance is your main goal, you would buy an off the shelf high performance full exhaust and would then need to add various tuning goodies to get the performance gain from it, a decent full exhaust system is going to set you back around $1500 to $2000 dollars with the extra tuning goodies on top of that figure.... It is debateable if you will actually see or feel any performance gain, particularly on the street and to measure a gain will cost you lots more $$$$ of dyno time too.....

    Rarely do Vmax owners install new exhausts that they do not like the appearance of.

    Rarely do Vmax owners install new exhausts to achieve a performance loss.

    For those Vmax owners that own/like/appreciate the Cobra exhausts they should expect a slight performance loss compared to the standard engine, standard exhaust set up, are there practical ways to improve this lack of performance, Yes, there are and i am sure more practical ways will follow.....
     
    Last edited: Nov 20, 2018
  9. Nov 20, 2018 #109

    sdt354

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    I installed a Mark's 4-2 system, $700 at the time, I hadn't done anything to my carbs yet. The difference was air under the front tire in first gear. Lots changed after that.
     
  10. Nov 20, 2018 #110

    one2dmax

    one2dmax

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    Where in the hell are you spending up to $2000 for a full system and "the extra tuning goodies"? I sell the Voodoo's new for $650 for a full system (4-1 or 4-2 all stainless) up to our Morleys Marks system for $1250. Add $325 and some shipping and you're over your $1500 threshold but as I showed you can be well cheaper then that. You don't need a jet kit to get a very nice performance improvement (the bulk of the improvement is in the header).

    I did not mention anywhere that you would replace the front stock pipes with larger stock type pipes and try to make the Cobras work. They will never work due to the loss in scavenging.

    You don't generally buy a Vmax so you can figure out how to look cooler but be slower. One of those specifics in the equation doesn't match what the average guy buying one has goals to do. Maybe one in 20 don't care about the power output and are only in it for sound. The Cobra's don't even have that. They sound like shit with an uneven tone output. What they do have and I have liked about them for 30+ years is that they look cool! It sucks you have to remove the centerstand to ride safely (I tried it a long time ago without doing that and almost wrecked the bike when the stand grabbed in a corner).
     
  11. Nov 21, 2018 #111

    mabdcmb@yahoo.com

    mabdcmb@yahoo.com

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    What happened to all the emoji's?
    That one with dead horse getting hit with a stick would fit this situation perfectly.
     
  12. Nov 21, 2018 #112

    Fire-medic

    Fire-medic

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    I'd say it's like an unfaithful "girlfriend" who steps-out on you, doesn't try to hide it, but for some godforsaken reason, the schmuck welcomes her back, time-and-again. It's an obsession, a fixation. In-spite of all evidence to the contrary, the one-sided "love-affair" continues, the cuckold oblivious to the opinions of others.
     
    mabdcmb@yahoo.com likes this.
  13. Nov 21, 2018 #113

    lilredrooster

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    There is no guarantee that modifying the collectors and/or introducing scavenging with the Cobra slip ons will increase BHP, as far as I know nobody has done this and there is nothing to support that any gain can be made by introducing scavenging with a bog standard Vmax engine, stock headers and Cobras.

    There is a member on this forum running a true 4 into 4 exhaust system with no scavenging, 4 x slip-ons like the Cobras, original front Vmax headers, standard motor running times equal to and better than published stock Vmax times.
    This proves that a stock engine Vmax can run equal/better times with 4 slip ons (As the Cobras) without modifying the original headers and with zero scavenging.......
    This also proves that a stock engine Vmax can produce equal/better horsepower with 4 slip ons (As the Cobras) without modifying the original headers and with zero scavenging.......
    This strongly suggests that the stock headers and the lack of scavenging are not the issue.....


    Ref: Vmaxforum Quote 1:


    Ref: Vmaxforum Quote 2:

     
    Last edited: Nov 21, 2018
  14. Nov 21, 2018 #114

    lilredrooster

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    VMaxforum Post showing Kerker Exhaust versus Cobra Exhaust Bhp Comparison.
    Same VMax, Stock VMax Motor, Same Dyno

    last year bought a 00 vmax with 10k with a 4-2-1 Kerker exhaust. i put on Delkevic front header, and rear stock header and put on cobra slip on. I just like the look of dual exhausts(4 pipes). Hear is the results of dyno before and after, i am guessing it's been rejetted with the Kerker exhaust. i did not rejet with cobra ex. Had problem with left rear slip on, only go on 1/8 in. Cobra said i doing something wrong.lol. After reading what i can do to increase hp on a stock motor does not look like i can do much, KN filters,carb syn?



    Quote Ref and Link Below:
    http://www.vmaxforum.net/showthread.php?t=22440&highlight=cobras

    See Attached Dyno Readings:

    Same Dyno. Same VMax. Stock VMax Engine.

    Kerker 4 into 1 Full Exhaust = 112.92 BHP. (Switched to Cobra 4/4 Slip Ons) Cobra 4 into 4 Slip Ons = 109.11 BHP.

    Note: Dyno Sheets attached to original Vmaxforum thread listed in Red above.[/QUOTE]


    In Summary:
    We are looking here at a difference of 3.8 Bhp and 3.4% Bhp loss between a full Kerker 4 into 1 presumably with larger headers and scavenging, against the Cobras.....
     
    Last edited: Nov 21, 2018

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