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Re: Cobra Exhaust Tuning Recommendation.
  #101  
Old 09-03-2018, 10:41 PM
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lilredrooster lilredrooster is offline
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Location: Perth Australia
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My VMax: 1998 Black
Default Re: Cobra Exhaust Tuning Recommendation.

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.....
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Re: Cobra Exhaust Tuning Recommendation.
  #102  
Old 09-21-2018, 09:59 AM
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lilredrooster lilredrooster is offline
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Default Re: Cobra Exhaust Tuning Recommendation.

Quote:
Originally Posted by lilredrooster View Post
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.....
Quote:
Originally Posted by lilredrooster View Post



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.....
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Re: Cobra Exhaust Tuning Recommendation.
  #103  
Old 09-21-2018, 10:20 AM
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lilredrooster lilredrooster is offline
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Default Re: Cobra Exhaust Tuning Recommendation.

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.


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Re: Cobra Exhaust Tuning Recommendation.
  #104  
Old 09-21-2018, 10:50 AM
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Default Re: Cobra Exhaust Tuning Recommendation.

Have to acknowledge your dedication to the Cobra exhaust and trying to find a solution to your liking.
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Re: Cobra Exhaust Tuning Recommendation.
  #105  
Old 09-21-2018, 02:21 PM
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lilredrooster lilredrooster is offline
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Default Re: Cobra Exhaust Tuning Recommendation.

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


Enjoy the Ride.... Ride Safe....
Attached Images
File Type: jpg 2018-09-22 09.02.01.jpg (87.2 KB, 5 views)
File Type: jpg 2018-09-22 09.02.28.jpg (88.0 KB, 5 views)
File Type: jpg 2018-09-22 09.15.05.jpg (98.5 KB, 5 views)
File Type: jpg 2018-09-22 09.01.29.jpg (86.1 KB, 4 views)

Last edited by lilredrooster; 10-13-2018 at 12:17 AM.. Reason: Updated VMax Photos
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