Recently bought back a modded 400 I sold years ago. It's pretty much all a race mod with the exception of an hpd trail pipe. I always wanted a CPI pipe when I had it. Before but can't find one now. Any real difference between the rcr , hpd, aaen top end pipes? Which would u reccomend

 

All of the pipes that you have listed are designed to be ran with a stock cylinder.There are also slight differences in the design of all of those pipes that require clutching with slightly different stall and shiftout speeds over each other to work properly.If you have a race mod engine then that implies that you have a heavily ported cylinder so why not run a race mod pipe like an Aaen or HPD race pipe to match the flow requirements of the cylinder?

To answer your question there is a difference in the way that some of those pipes deliver power across the RPM range.Here's an old article comparing an Aaen, Hot Seat and stock pipe.You can see the difference in the design of them fairly clearly.



If I tried to run one of the pipes that you listed on my Sport 400 with its race mod engine it would kill the performance of it.Here's a picture of my 400 with it's race mod pipe

 

Is than an hpd race mod pipe on your bike?

 

Yes

 

Thanks for the great response. I definitely want one with expansion chamber up front. Hpd it is.

 

The HPD race pipe is a great pipe IMO as long as you have your cylinder ported for it and are running the right carb, compression ratio, reeds and clutching.If you try to run this pipe on a bolt-on Scrambler with a factory cylinder you will actually lose power from what I've seen on the dyno and at the track.

 

Have Rcr race porting , 39pwk, 14:1,.factory reeds with a spacer

 

To get the most out of the race pipe I would run a 42mm TMX, a V-Force reedcage, a roller secondary and a primary spring with a stall of 110-120 and a shiftout of 290-310 depending on how aggressive Rick got with your porting.

 

He went pretty far but not quite as far as he would go for a full drag bike told him.I wanted to keep a little rideability. I'll have to look at my primary spring and check Hpd chart. Not going to spend the money on another new carb. Maybe reeds ill see how it runs

 

You can still make decent power with the 39mm PWK but your going to be leaving a lot of power on the table by not going with a 42mm TMX.The 38mm and 39mm carbs are good for bolt-on 400's and 400's with a mild trail mod port job but the race mods really respond well to the 42mm TMX.

The stock reed cage is good on a stock quad, but for a race motor it's definately killing your power.Here's a couple of pictures of a stock reedcage with aftermarket reeds compared to a V-Force reedcage.