I know cobra's have a bad name but really?

[Slamfire]

A friend and I had our max's dynoed today.

His is all stock 2002
stock jets,
stock air filter, stock exhaust
amsoil engine oil


Mine is a 1997
stock jets,stock air filter , cobra pipe
15w40 rotella

he posted 117 hp/ 113 ft torque

me ... 100hp and 71.75 ft torque

Is it possible that the cobras are hurting my performance that much? I know mine seems torun alittle richer than his?

 

[Biker Dash]

The readings seem on the lower scale for what Cobras will give you. If you adjust your jetting, you might get a few more ponies at the wheel. Not much though.

The big reason for the loss in power is because it is a 4-4 system, which causes you to lose the scavenging effect up top that the stock design, as well as most other aftermarket designs, give. My bike drops off above 8500 RPM due to that fact, running rich. Considering that I rarely, crank my bike up that high, I find it an acceptable sacrifice for the combined benefits of looking how I want and being considerably lighter than the stock exhaust.

While it may be possible to modify the exhaust to get that power back mostly, the money, time and effort required make it HUGELY impractical. Especially when there are other aftermarket designs out there with a similar look that will support a significant increase in power over stock.

Myself, I like my Cobras, only right now wishing for a little quieter sound with a little more back pressure which might give me a slight boost in low end.

 

[caseyjones955]

I just learned a lot about tuning a piped Vmax, but I have so much more to learn. Mine was to rich with a DJ stage one jet kit, K&N drop in and the Kerker pipe. I had a 4k stumble I thought was lean mixture but turns out it was way to rich. After letting down from DJ170 to DJ160 (different than MK jet numbering) and moving the metering rods to the leanest position I picked up 20 seat of the pants HP and no stumble. I'm at 3500'. The guidance I got in this forum has been priceless and probably saved me tons of time and headache.

Let me just throw this out there, A quick compression test to make sure your not fighting something other than fuel management. Valve lash within spec? I'll step back to make room for the guys that REALLY know their stuff, I just wanted to keep you busy until they get here :worthy:

 

[one2dmax]

That is about right for cobra power. I think we recorded 96 on the last one that was in here.

The torque you have listed for your buddies bike I suspect wasn't read correctly by the graph (look to see if there was an ignition spike). He should be more in the low 80's for torque.

 

[Damon]

A friend and I had our max's dynoed today.

His is all stock 2002
stock jets,
stock air filter, stock exhaust
amsoil engine oil


Mine is a 1997
stock jets,stock air filter , cobra pipe
15w40 rotella

he posted 117 hp/ 113 ft torque

me ... 100hp and 71.75 ft torque

Is it possible that the cobras are hurting my performance that much? I know mine seems torun alittle richer than his?

Not really a fair comparison being that they are two different bikes. Run a dyno test on the bike with stock set-up then switch to the Cobra's? I have seen Cobra's dyno around 112 RWHP

 

[Slamfire]

That is about right for cobra power. I think we recorded 96 on the last one that was in here.

The torque you have listed for your buddies bike I suspect wasn't read correctly by the graph (look to see if there was an ignition spike). He should be more in the low 80's for torque.

He just called me. Said it showed 82 torque the second and third runs. Your right on

 

[Biker Dash]

I have seen Cobra's dyno around 112 RWHP

From a 1300cc Max with an aftermarket ignition, perhaps?

 

[Fire-medic]

I think a 108-112 RWHP on a Dynojet 250 is about what a stock bike will make. Mine did. "They hurt performance, Cobras do," said Yoda.

I've seen Vmaxes in the mags test up to 119 RWHP but who knows if the bike was prepped to do better than usual? After all it's being tested by a big bike mag, and the manufacturer wants to get a good report.

 

[CaptainKyle]

Maybe you should use amsoil. LMAO ! that is what the sales rep would tell you.:rofl_200:

 

[Dorney]

I have Cobra's on my bike & I have 8 3/8" holes drilled in them. I think Cobra's in stock form are to restrictive .

 

[Slamfire]

I have Cobra's on my bike & I have 8 3/8" holes drilled in them. I think Cobra's in stock form are to restrictive .

Did you notice and change in power after you drilled them ? Change the sound much?

 

[Biker Dash]

I have Cobra's on my bike & I have 8 3/8" holes drilled in them. I think Cobra's in stock form are to restrictive .

If restrictive, as in flow coming out, each exit is larger than the exits on the stock exhaust. If anything, the four Cobra mufflers should flow more, if the restriction of flow was in the mufflers.

The flow restriction is in the headers, which is why you will never see a horespower increase by using slip-on mufflers.

The power loss is from losing the scavenging effect the stock exhaust has.

 

[one2dmax]

You can drill them to the end of the world and will NOT make any substantial gains in HP. Might get 1 or 2 but even then that is debateable. They have plenty of flow capacity. It's the configuration that is the problem.

 

[Rollie]

Did you notice and change in power after you drilled them ? Change the sound much?

I have them on the Speedstar. I drilled 'em and changed the sound to a little lower deeper bass , but no noticeable power increase.

 

[Dorney]

Did you notice and change in power after you drilled them ? Change the sound much?

I heard to many say that Cobra's cut power so I drilled 8 1/4" holes before I put them on. It was easier to get the holes in with them off then I went from there. I also cut the cross over tube out of the front pipes. As far as sound goes I think it sounds real good not to loud for me just right. At this point it runs better then the stock exhaust but then I'm not into the # game but I feel it runs real well.

 

[Lotsokids]

I also cut the cross over tube out of the front pipes.

That brings up a question. Does eliminating the crossover tube negatively affect power even more than adding Cobras alone?

I've thought about doing this also. Probably only affects sound. But I have seen hot-rod articles about adding a crossover tube in dual exhaust to gain some power.

 

[Fire-medic]

As I recall, the proximity of the crossover tube to the cyl head positively affects flow in the higher RPM range the closer to the cyl head. Moving the crossover tube further back bolsters torque more than helping high-RPM flow.

Bassani Exhaust Systems had a very popular X-pipe for the inline fours in the '70's. Who can forget their picture of their bike with about a 60* in-the-air front wheel, prominently revealing to the admiring viewer their X-pipe design?

A popular accessory for the Fox-chassis Mustang V-8's was an X-pipe exhaust. I think it eliminated the cats, so, "for closed-course use only."

In the 1970's and '80's, when I owned full-size vans, 'lake pipes' (rocker panel area visible exhausts) were a very popular accessory. I used to take my van to the muffler shop as soon as I got it, and have them add them. To make it easier to replace them when they rotted-out (tetra-ethyl lead, while great for controlling engine 'knock,' and a great octane # booster, rotted exhausts in several years, besides the health risks), I had the muffler shop add two bolt flanges to the intakes of the side exhausts, so they would be easy to swap out when the time came. I also had them add as-close as-possible to the stock cast iron exhaust headers, a 'balance tube' which was nothing more than a crossover pipe joining the two exhausts. I made sure that the transmission would clear the balance tube, if work needed to be done, without having to remove the exhaust. The mods seemed to make a bit of difference, though I never went to the trouble to dyno the engine, a 351 Windsor in my favorite Ford van, though I also had Dodges. Never a Chevy/GMC, though I did have GMC pickups. My favorite rocker panel exhaust for sound was the 'Thrush."

 

[Biker Dash]

I notice that there is a X-over for the front but not the back... Makes me wonder if maybe designing a X-over for the back might help a bit? Would make for an interesting experiment, I think.

 

[Dorney]

The cross over in the rear as I see it was in the stock muffler. Also all after market exhaust that I 've seen does not have a cross over. So why I had the exhaust off over the winter I thought I try it. Also I had the Cobra's on before I took the cross over out & it runs better now then it did then.

 

[Lotsokids]

Also I had the Cobra's on before I took the cross over out & it runs better now then it did then.

Interesting. Do you have info or photos on how you removed / blocked the crossover?