Cobra Exhaust Tuning Recommendation.

[lilredrooster]

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:

 

[lilredrooster]

Out on the bike this morning, first impressions, little more noisy but hardly noticeable (Was not exactly quiet in the first place...), seems to rev easier/faster but early days and only a fairly short ride....

Next step if happy with the new mods is to drill/enlarge the holes in the solid discs from 16mm to 21mm (final size)....


My thoughts/comments on direction and mods:

As discussed, very little hard data available featuring the Cobra Exhausts.....
As discussed, very hard to find hard data on VMax 4 into 4 Exhausts (Other than Cobras)......

Only really two main options with exhaust modifications, merged collectors entry or de-restricting the internals....

No evidence of anyone successfully modifying the collectors, no proof this will work, mostly merged collectors are featured/popular on 4 into 2 pipes, not 4 into 4 at all.... Often balance pipes are used for smooth running/mid range, not exactly high performance..... Expensive in time and money to modify and no history or high likelihood of success.....

On close internal inspection of the Cobras, very likely that they are highly restrictive due to bad design and cheap manufacturing practices.... History of similar modifications with very little data, cheap and easy and quick to modify.....

Interesting relevant data on 4 into 4 exhausts:

Ref: http://www.vmaxforum.net/showthread.php?t=44187

Above link shows standard engine, standard front headers, no merged collectors, no balance pipe, 4 into 4 exhausts, 1/4 mile ticket and runs at 11.5 and 117 mph, exactly the same times and speeds quoted of a standard VMax in the Haynes manual..... This suggests that this bike does not drop 13 BHP like the Cobras........


One other VMaxxer in the UK is running 4 into 4, moto-gp replica mufflers, no baffles, standard front headers, virtually standard engine, ignition upgrade, carbs upgrade pulling around 120 BHP.....

The above two examples suggest that the issue lies with the Cobra exhausts not with the merged collectors or the balance pipe......

Neither of the above two examples have the same or similar highly restrictive internal baffle system (tortuous path) of the Cobras.....

​

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:

 

[lilredrooster]

Re: Power Q!!!!!!!!!!!!
Quote:
Originally Posted by Kurtmax
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...... eace out bike:

 

[Redbone]

Have to acknowledge your dedication to the Cobra exhaust and trying to find a solution to your liking.:clapping:

 

[lilredrooster]

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:

 

[lilredrooster]

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:

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.....

 

[one2dmax]

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.

 

[lilredrooster]

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.

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.....

 

[sdt354]

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.

 

[one2dmax]

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 **** 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).

 

[[email protected]]

What happened to all the emoji's?
That one with dead horse getting hit with a stick would fit this situation perfectly.

 

[Fire-medic]

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.

 

[lilredrooster]

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 **** 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).

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:

Bracket.

I AGAIN beat my record: 11.52 @ 188 Km/h, and won 3rd place in my category. Somehow they let a GSX-R 1000 in my class and he ran a 10.99 against me. :confused2:

I just got home and it's very late. More pictures and details later.

Ref: Vmaxforum Quote 2:

Answers:

Yes, I left the Cobras on the Hungarian V-Max and brought the custom pipes back to the US with me. I bought another set of Cobras here, so I have the same options as I did in Hungary. Cobras for everyday use, and the louder custom set for weekends or when I feel rowdy. :biglaugh:

I did not FEEL any major power gain or loss by using either system. I have stock down pipes (standard front headers).

A couple months ago, I had my V-Max dyno'd with the custom pipes on - 109.9 HP at the wheel. No dyno in Hungary - only 11.52 1/4 mile time. Neither bike here or in Hungary had any engine mods. Only the exhaust pipes.

Attached is my OKC V-Max I currently ride and love.

 

[lilredrooster]

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.....

 

[lilredrooster]

Bongo said: ↑
Ok I've heard enough bashing on the Cobra exhaust system. I bought a 1995 orande Vmax last year with 13,000 and some change on it from the original owner. It rates a 8 out of 10 on the scale. It came off the floor with the Cobras on it he doesnt know if the they jetted it it or what. He liked it bought it rode it home. 22 years later i buy the bike from him. He buys a 2017 gen 2 max. Ok my best freind has a 1985 killer red max kept in immaculant condition. He put super traps on it and had it dyno tuned. He got a 123 hp out of it I've seen the paper work. Its freaking fast!!
We have road together for 3,000 plus miles now. Yes he can beat me not like you guys exaggerate. From a rolling start to 100-120 hes no more than 2-3 bike lenght a head of me and sometimes i stay with him pretty good. Just depends on who gets the best jump on each other. So enough of the over the top BS on Cobras. Lol.



Fantastic Post Bongo..... Good to see some accurate, honest, unbiased, sensible, current, real world, comments coming from a Cobra exhaust owner sharing their actual personal experiences.....

Many Thanks for sharing....


See Below Quote Ref Link Below:

https://www.vmaxforum.net/threads/cobra-exhaust-hp-loss-explained-please.5579/page-4

Fantastic Post Bongo..... Good to see some accurate, honest, unbiased, sensible, current, real world, comments coming from a Cobra exhaust owner sharing their actual personal experiences.....

Many Thanks for sharing....

 

[lilredrooster]

I know of two guys from way back that were both VMax Racers, VMax Tuners, VMax Builders, VMax Fabricators/Mechanics, both had VMax Speed Shops and both had their sole, individual, dedicated Dynos.

One owned and tuned his personal bike over many years and recorded the data & history from his Dyno, as follows: Stock motor, stock carbs & exhausts, set up: Max = 108 RWHP. Added Kerker 4/1 Full Exhaust, Jet Kit inc KN Filters, set up: Max = 121.4 RWHP. (Plus 13.4HP). Added 4 x Flat Slide Carbs, set up: Max = 128.5 RWHP (Plus 7.1 RWHP).

The other quoted the very best stone stock Vmax bikes he had ever seen on his dyno was 104-108 RWHP (Avg 106RWHP). He also owned an immaculate stone stock VMax that pulled 99 RWHP, same Dyno.

The above suggests that both guys Dynos were similar in their BHP measurements, it also suggests that around 107/108 RWHP is right up there for an all stock VMax and that 99 RWHP is good/average.....

Typical/Realistic Gen1 VMax Qtr Mile Times/Speed is 11.5 Secs at 116 MPH. (Terminal Speed = Power).

A common Internet performance calculator converts the above Terminal Speed at 102.5 RWHP, this also seems to broadly correspond in line with the Dyno numbers from the two separate Speed shops above.

My VMax (Original Stock Motor) is now around 22 years old, I am very pleased with my Cobras and have no plans to change them, my experience so far tells me with my personal bike it is between 2 BHP and 7.5 BHP (5 BHP AVG Loss) below a very good/top notch performing all stock VMax.

The data I am using with my VMax is based on less than a handful of runs at night at the Dragstrip, in very average conditions with some clutch slip. I am very confident of closing that gap now that upgraded clutch springs have been installed.


To date, my stock engined Gen1 Vmax with Cobras has the same performance as an average stone stock Gen1 VMax and is around 6 BHP down on some of the most powerful stone stock Gen1 VMaxes out there.

 

[lilredrooster]

Three x Stock Engine VMax`s each with Cobra 4/4 Exhausts versus other similar VMax`s without Cobra 4/4 Exhausts Comparisons. Ref: Continued from Post # 116 above:


VMax with Cobra 4/4 Pipes, Combinations & Comparisons Summary Notes:

Previous Post # 116. My personal experiences to date show a power loss of approx 5 BHP, my bike had slight top end clutch slip at 2/3 track during this one evening of testing.

Previous Post # 115. VMax owner experienced a loss of approx 2 x bike lengths compared to a modified VMax during multiple rolling speed testing to terminal speeds of 100 to 120 Mph, Power Loss = Negligible.

Previous Post # 114. VMax owner, Same VMax, Same Dyno, Exhaust Swap from Kerker 4/1 to Cobras 4/4 resulted in a power loss of 4 BHP. Link to Data in this post #114 including snapshots of Dyno Sheets.

Three different owners, three different VMax`s, all with Cobras 4/4 exhausts, three documented sets of experiences with Data, showing power losses around 4 to 5 BHP.



Significantly “Below” "Many" "Alarmist" Cobra 4/4 Exhaust "Haters/Bashers" claims of "Un-measured" "Un-documented" "Un-confirmed" "Un-substantiated" "Ill-Perceived" "Fictitious" power losses in the region of 15% to 30% (15.5 BHP to 31 BHP)..........


To be Continued.......

 

[one2dmax]

I've got a Kerker if you want to try and get a feel for the real world experience.

 

[lilredrooster]

G`Day Sean, No Thanks Mate.....
If I was seeking a real world experience I would just buy a Gen 2 or Hayabusa or something.....
Very, very Happy with my old Gen1 and the Cobras 4/4..... Speed is just a number on a dial, just one very small part of the experience....
FWIW, personally I find the 4/1`s, Kerkers and the Gen2`s, Butt, Fugly...... Takes all sorts, gladly.......
My old Girl is plenty fast enough for my needs, very happy with everything about her..... I much prefer the old world experience..... The next real world experience will be electric bikes!! No Thanks!!
All the Best.... No Worries.....

 

[lilredrooster]