Got some exhaust questions

Ok while looking around on google to find pics of our old Interceptors rolling on CBR wheels with a CBR rear shock i found this pic on vfrdiscussion.



Now from the looks of it it is two pipes coming off of the down tubes of the front two cyls with the down tubes from the rear two cyls feeding directly into them with a 2 into 1 collector at the end. So would this be considered a 4-2-1 header set up? If so how effective would they be on our old bikes?

 

Looking at the pic, and seeing it's Fred Merkel's bike, I'm a bit confused, as all the Fred Merkel race bikes and replicas I've seen have twin exhausts (one either side). I wonder what year that picture is from?

This is a left side view of a Fred Merkel replica, which is virtually identical to one I've seen ridden by Fred in a race video...
http://vintagesuperbike.com/graphics/photos/1984HondaVF750R/060U9712_lg.jpg

Here's a different bike, but I think with the same type of exhaust as in your posted picture...
http://www.theriderfiles.com/wp-content/uploads/2009/12/Chandler-SB-87.jpg

 

That's Fast Freddie, as in Freddie Spencer, not Fred Merkel.

 

That's a picture of Spencer during his sweep of Daytona in March 1985!

Another pic: http://www.vfr-japon.com.ar/Imagenes/1985_Spencer_Interceptor.jpg

 

Here's what you're looking for:

Fred Merkel Replica pics: VSB ~ 1984 Honda VF750R

Freddie Spencer's actual exhaust: http://vintagesuperbike.com/graphics/photos/currentProjects/1985Daytona/031_lg.jpg

 

Oops... my mistake.... I didn't pay too much attention to reading the italic writing. Flying Fred had the same italic font on his bikes.

 

I like that bolt screw plug in the middle of the left side case that makes it easy to turn the engine over for valve adjustments without removing the entire case cover.

I also see another little plug so you can look in and see the marks line up.

What you really want to know about that exhaust is what the outside diameters of that tubing is at different points along its path. Then you got something.
They went to a lot of trouble to keep them equal lengths.

 

In general, a 4-2-1 exhaust will broaden and flatten the torque curve, as opposed to a 4-1 which will tend to produce more peak power in a narrower range. As Donald pointed out, tubing diameter and length of the various sections are the elements that will determine the RPM of the effects. What can get really screwy is the length of the intake tract(s), and camshaft profiles that are being used in conjunction with the exhaust system; it really is an entire "system". And there is always the intake and exhaust ports to consider, as well as tuning the A/F ratio to match.

All that being said, a 4-2-1 is a better system on paper if you desire to have more usable power over a broader RPM range. The hard part is determining the lengths and diameters, finding the room to fit it and the expense of fabricating the whole mess. They were used on some NASCAR racers in the late 60's and early 70's (if my memory is working properly), but I have no idea if they are being used anywhere today.

It's also entirely possible that the above information is now obsolete... :smile:

 

Def some good info in here now! Thanks for the info guys. I know some guys have adapted mufflers from newer bikes to these bikes as well. Mostly from machines that have factory dual exhausts. The kerkers on my bike now are from a newer VFR750 that i bought from a member on here a couple years ago. They work alright but are in rough condition. I might take them to a couple machine shops around here and see if they can repair the damage to each can. I know Kerker did still sell repacking kits for them at one stage.

 

a good exaust guy shoul be able to fab a 4-2-1 or a4-1exhaust for your application but will probably need your bike and whichever aftermarket slipon you choose.

 

Just a thought that was asked about on here before but never answered. Would it be possible to cut and modify the original collector box to have one output? Is the collector box baffled inside at all? Truthfully I can't see why it couldn't work but would like to hear everyones imput on that idea.

 

yes you can I actually cut alarger hole around the right side outlet welded in a larger piece of pipe and fitted the can from an R6 to the collector box on an 83 that I had it worked out pretty well oh yeah i almast forgot ; you have to weld a cover on the left side (dont want an exhaust leak) hope this helpsyou out.

 

Awesome! i figured the collector could be reworked into a 4 into 1 collector. What size of pipe would i require for the new single outlet? Chances are i will have my buddy cut the left corner off and replace it with flat steel to form the collector into a wedge shape. Partly to get rid of some weight from the collector box and partly to gain some clearance on the underside of it.

 

the diameter of the pipe will depend on what can or slipon you plan to use so dont change it until you have a replacement pipe. also remember you are going from a dual to a single so you may want to look for an aftermarket performance muffler so you dont choke up your engine.

 

I was def planning on going with an aftermarket can such as a D&D or Two Brothers. Also plan on mounting it higher then stock. Near the top of the tire as shown in this pic.


Might mount it a few inches higher then that even. havent decided fully on that point just yet.