I'm almost ready to buy a slip on for my 400. I talked to the guy who is our top local racer that also owns his own shop. He recommended a White Bros E-Series slip on, K&N air filter and carb adjustment. I thought he would say rejet but he said it isn't necessary with that pipe. So here are my questions.

1. Is there a more powerful slip on that I can run?

2. If I get a more powerful slip on but put a silencer and spark arrestor on it will I be right back to the hp numbers of the White Bros E-Series anyways?

The E series is an excellent tunable pipe/silencer, but I sure wouldn't take you friend's advice to the bank re re-jetting unless your elev. is quite high above sea level. Any pipe that flows a significant amount of air flow over OEM will almost certainly require fatter main jetting, especially if you plan to run additional discs for more top end.
You didn't say where in the band you wish to make more power and various pipes are designed to produce their best performance in a specific area of the band. After deciding that question, you might contact prospective manufacturers to obtain that info.
Of course the tunable models solve that problem by using the number of discs appropriate to the rider's choice. The E series and the Super Trapp(don't discount this one..the original tunable silencer) each come with a certain number of discs, some of which can be removed for more low end, or added to for more top end. When I had my Warrior, I ran 20 discs in the 4"OSD Super Trapp for maximum top end. This, along with a vented lid & Pro Design filter, required considerably fatter main jetting, even at 3200' elev.

I'm looking for more power low to mid. I ride mostly aggressive trail riding with some jumping and play racing. I occaisionaly get to got an mx track and screw around. I wasn't talking about moding my air box so I assumed he didn't suggest a rejet because the K&N air filter would be the main increase in air flow. Again I'm all theory and no practice when it comes to any real wrenching. I was wondering if other pipes would put out more but every one I know with a race shop pipe has no spark arrestor or silencer and I can't do that. That is why I was wondering if any of the other pipes made by Trinity, Curtis Sparks, etc put out more with the spark arrestor and silencer.

I would mod my air box but I've heard horror stories about mud and dirt getting in there and causing all kinds of mayhem. I live in the north east so I submit my quad to year round riding in all sorts of weather and conditions. I want 3.5 to 5 hp without sacrificing a lot of realiability.

I also heard that you can do something called an ignition advance that would increase hp and throttle response throughout the powerband. Does anyone know anything about it? Is it bad for the engine? It's fairly cheap to do.

Again, most any slip in pipe/silencers (with certain notable exceptions) will flow more air and consequently require more fuel to compensate, thus avoiding a lean-running engine, If you go with a tunable slipon,they normally come with a number of discs to provide power in the low/mid range by flowing just a moderate amount of air. The SuperTrapp will allow one to reduce that number of discs somewhat, down to the minimum reconmmended for even more low end, thus reducing both decibals and air flow.
I would never drill or otherwise vent the air box itself, but I did, and still do on the Raptor, modify the lid to allow better airflow. Improved airflow together with appropriate re-jetting= power= increased decibals.
I have not used a timing key so can't comment on that.

Do not use a slip on they is no gain. A full exhaust will give only 1 to 1.5 horse gain. That is all systems. The best bang for the buck is to put a 11 to 1 in your cost should be around $120.00 for parts. Leave your stock exhaust on and out run everone that has a pipe, jet kit and K&N on there bike. It will just make them mad wondering why there bike is so slow. You spent around $120.00 they spent around $600.00. It does work I sell alot of these kits.

Duncan claims they can get 5hp out of a slip on, air box mod, and jets. The numbers I read that where getting 1 to 1.5 hp out of all full pipe where with no rejet or air box mods. So basically they increased the exhaust flow without increasing fuel and air to take advantage of it.

That 5 horsepower gain is in the mid-range, not on the top end. So, yes it does give you a boost in power...and in my opinion, the mid-range is the most important place for your power gains unless all you do is ride with a full open throttle down gravel roads. For trail riding, jumping, hill climbing, dune riding, etc... A pipe makes a big difference. But, don't forget the jetting and higher airflow (filter and airbox mods).

<< Do not use a slip on they is no gain. >>


HUH? What planet are you on???
A slip on is one of the easiest mods you can do for a power increase. I've run a WB e serias and currently run a Pro Circuit T4. BOTH pipes give you huge power gains over the stock pipe. I'm not bashing anyone, but anyone who says a pipe doesn't do anything has lost their mind. Come to where I ride and i'll let ya take a ride. You'll be surprised.

I am really happy with Duncan pipes. Thet advertise correctly it will make your machine faster. It will hang with a stock raptor.