Performance Issue

[reprice]

Purchased a set of Marks 4-2 12" with 2.75" openings. Happy with the pipes and happy with the service but can't seem to find any more power and was hoping someone might have an answer. Stage 1 Dynojet done when the pipes were instaled otherwise stock - except K&N and Y tube removed. The good news is the Dyno showed 107.5HP before the kit, so my engine was strong but the bad news is we can opnly manage a best reading of 109.5HP and only in a narroow 4-5K rev band range. Bottom end has suffered and peak is exactly the same. The service ctr has done plenty of machines including 13 or more V Maxes with various pipes - Hindle, Holeshot, etc. so he knows what he's doing but we are at a lost as to where the extra 10 HP that I should get is hiding? He thinks that 2" openings would create a little more back-pressure which would be a good thing for low to mid end drivability. They look great but are overly loud so I think I will have Mark tone them down a wee bit.

 

[Thevmaxrider]

The Stage 1 kit is the problem. Rip that POS out of the bike, put it back to stock, and tune from there. OR your other option, the best HP gain, is to talk to Sean Morley and order up one of his jet kits and fine tune it. An exhaust system will only get you 5-7hp at the rear wheel. The Stage 1 kit will rob you of most of that if not all of it.

 

[grimmie]

+1 on the Morley carb kit. Nice guy to deal with too!

 

[overzat]

yep seans jet kit made my bike a beast

 

[naughtyG]

And your bottom end suffered because you're missing the Y..

 

[06VMAXIMUS]

Put the Y back on and junk the stage 1 kit. Shim stock needles back 1mm (.040) and set mixture screws at 3 to 3&1/2 turns out per Marks recommendations. My stock bike with these settings pulled 113.9 hp. I am running a whisker rich, but better rich than lean! Seans kit will probably squeeze even more out of it.

 

[maleko89]

2.75 outlets are big and are also causing your loudness. Have mark make you 2 inch end caps. I have 2.25 inch endcaps and my bike is as loud as my old open-ended Supertrapps. Increasing outlet size reduces back pressure I believe.

 

[modnrod]

Gday guys, quick question, Sean may be able to answer best I spose.
CV carbs like restrictions, to a degree, airbox's that have no restrictions are a pain to try and tune, and sometimes even the slides don't have enough vacuum to open fully, hence the power loss wyhen removing the "Y" (sounds good but!).:biglaugh:
Sean's airbox upgrade though is a flat panel filter. I know it works, all you blokes and numerous dyno results are proof obviously, but has Sean's kit got some sort of "magical trickery" involved with the airbox under the filter that I can't see?
Yes, I AM going to buy one of Sean's kits when I've finished building my exhaust system, that's no problem, and it will stay on there until I've also finished building my custom inlet system (and probably remain if my custom inlet doesn't work!), but doesn't that do worse than removing the "Y" piece?:ummm:

 

[Thevmaxrider]

Gday guys, quick question, Sean may be able to answer best I spose.
CV carbs like restrictions, to a degree, airbox's that have no restrictions are a pain to try and tune, and sometimes even the slides don't have enough vacuum to open fully, hence the power loss wyhen removing the "Y" (sounds good but!).:biglaugh:
Sean's airbox upgrade though is a flat panel filter. I know it works, all you blokes and numerous dyno results are proof obviously, but has Sean's kit got some sort of "magical trickery" involved with the airbox under the filter that I can't see?
Yes, I AM going to buy one of Sean's kits when I've finished building my exhaust system, that's no problem, and it will stay on there until I've also finished building my custom inlet system (and probably remain if my custom inlet doesn't work!), but doesn't that do worse than removing the "Y" piece?:ummm:

No magical trickery, his kit has air correctors that you install in the inlet to the air circuit that provides the vacuum to the slides. The correctors have a smaller orifice size hence the vacuum is maintained and the slides work correctly.

 

[modnrod]

AAAHHHH!
Thanks man! Thought I was losing it for a second there......:biglaugh:

 

[rubiconroy]

2.75 outlets are big and are also causing your loudness. Have mark make you 2 inch end caps. I have 2.25 inch endcaps and my bike is as loud as my old open-ended Supertrapps. Increasing outlet size reduces back pressure I believe.

I have some 2 inch end caps for the marks pipes that you can try. If you like them, you can buy them, or just ship them back to me!

Jeff

 

[vmax626]

Right on Jim,
Plus the many jet sizes that come with the kit for the altitude where one lives for proper fuel and air flow through the carbs makes magic things happen to your bike.
Seans jet kit is a MUST HAVE for an aftermarket exhaust system.:worthy:
<<Dave>>unk:

 

[reprice]

Thanks for all the help. Maleko nailed it - I had ordered 2.75" openings and the engine definitely likes a bit a back pressure. I got new baffles at 2" from Mark and made an extra 6 HP over the only 1HP I had with the larger openings. Looks and sounds and feels great. Morley's kit will be another project as I'm happy right now how it turned out.

 

[SpecOps13]

I was going to get 2-1/2" Outlets but everyone here convinced me 2" was the way to go. After feeling the seat of the pants gains in the midrange, I totally agree... And, It's still loud..... I'm working on finding or making turn downs, the blast from the exhaust is very disruptive to the riders directly behind me...:biglaugh:

 

[mavgrab302]

Reprice I have pretty much the same setup almost exactly what you said you had. I am to going to get a different jet kit eventually but for now the stage 1 kit works. It took forever to work out the bugs but heres what I got.. marks 4-2, 170 main, 3rd slot dj needle, 150 pj, drilled slides, and no Y, K&N, and about 5-6 turns out on mixture screws. I know thats too far but any lower and idling is erratic, and the plugs look good so, whatever..lol
. I run rich idling no choke at all, but still spins the tire in 1st and 2nd. I can't imagine the bike being any quicker, that would be ignorant quick, but I'm going to do it eventually.