Twin silincers on a R

[XRMANU]

I just bought an Arrow header set for a 650R and 2 carbon silencers from a V6 or V8 5l Aussi race car. In the first (double)part ,the headers are 30mm innerdiameter like most aftermarket headers,the second part (2 in 1) is 44mm inner.The 30mm pieces are lose from the second part and hold together with springs. Can I dish the second (2 to 1) part and go straight to one silencer? A 2 to 2 system.What would be the effect? Or is it better to use a 2 in 1 in 2 system?The set-up is for a street SM bike but I want to keep some low end power and torque. What diameter of tube should I use going to the silincer? Keep the 30mm or going up to 35 orso? The innertubes (stingers) in the cans are 50mm, i think I will modify them an put a 35 or 40mm tube in there to have some backpressure and keep the non productive noise low.

Any thoughts about this??

I have to modify the subframe to make room for a left silencer,so the stock airbox will be removed.

Can I use a clamp-on filter only or is it better to put it in a selfmade alu airbox (against turbulences or for "still" air... )behind the Showa spring?

Is an air box a must? Stiil ..I want still some torque and low-end.

The bike will be dressed in CRF250 (twin can) plastic ?

[smicer]

i'm so dumbstruck with the theories above....but wat the hack....i want to see when it is done pls.........?

[Billahjack]

My opinion is...

Use primary tubes for the header at the same size as the stock ones right before they taper down. I haven't measured the primary tubes but I'm guessing that they are closer to 30mm. This is the size at the first inch or so of the header where it mates to the cylinder head.

2-1-2 header system. You want the exhaust pulse to unify into one pipe to get the best scavenging before splitting off into two cans.

I like your direction with modifying the stingers for smaller inner tubes regarding backpressure.

Airbox - If you make a new airbox, you need to make sure you have at least 1 liter of volume (~1.5 x Displacement minimum) in your new airbox, preferably >2 liters. The airbox works with the motor pulses as it draws in air. If you go too small, then it messes up an effect called resonant ram tuning where the pulses actually push air into the motor before the valve closes.

[XRMANU]

Thx Billahjack for the info. ?

I'll keep it all in mind. ?

And what about a clamp on filter without an airbox ? It's for street use only. What effect can I expect?

[Billahjack]

The clamp-on filters lose the airbox and your resonant ram tuning usually gives you a narrow spike higher up in the rev band with such a short intake tract. If you don't have a cam and exhaust to match the power spike, then the resonation effect is void because your bike cant push the exhaust out efficiently at the intake resonation range.

There are some LeMans cars from the 50's through 70's that have V-8's with 4 long intake runners and 4 short intake runners to give power hits at two different rev ranges. Dual plane American V-8 intake manifolds use the same concept.

Some passenger cars, a couple street bikes, and many race cars now have variable intake tract length to maximize ram tuning over RPM ranges. Think of it like a trombone....short tube - high pitch, long tube - low pitch, and multiple resonations for a fixed tube length. It is possible to get a rev hit centered at 4000 RPM and another centered at 8000 RPM (doubling frequency).

For your bike, I would probably get an HRC cam (good mid to high) or a Hotcams Stage 2 (good mid, better high). I have only played with the Hotcams Stage 1 and HRC so far. Try it with the clamp on filter and custom exhaust. If it seems to bog and hit, then go back to an airbox setup.

[nate992v]

The Honda Baja racers in the mid-nineties had a dual Bassani pipe set up. Find someone that has those, and you should be on the right track.

[XRMANU]

The Honda Baja racers in the mid-nineties had a dual Bassani pipe set up. Find someone that has those, and you should be on the right track.

Yeah, thx ... but I'm in Belgium (Europe),so...

[XRMANU]

BillahJack, this bike is a hobby project and the engine is in perfect condition.When finished ,I gone sell it.So I will not dump a lot of extra cash in a healthy motor. The Hotcam or HRC cam would pull the powerband even more in the higher zones. I will try the twin can set-up with the Arrow headers ,prob. with the stock airbox modified (with a custom made filter)to let the left exhaust tube pass.

In the past,I had some problems with the Stage 2 Hotcams in my own bike. Mods: HRC piston,Stage 2 Hotcams,1mm OS intake valves ,5 angle job and slightly ported head. My bike died on idle after a few seconds,tried many different jetting.I putted the OEM cam back in and the problem was (almost ,for 80/90%)over..

Thx for the input.