Exhaust-ed

[TADracer]

A matter of preferance.

This is a great thread.

Having run the OEM pipes, Jardine 4-2 spaghetti pipes and now the MAC 4-1 header I can tell you what I have noticed from actuall experience with these specific systems.

The OEM pipes are great for all around tooling or for riding with a passenger or heavy luggage. Great low-end torque and adequate high-end performance. That is exactly what they were designed for, good performance at most all ranges, with and without a load. I must say the engineers had it right with the OEM pipes but sadly, mine fell apart and had to be replaced.

The Jardine 4-2 system was similar in performance. But I noticed that the power band rose about 300 RPM and the low-end torque was dininished alittle bit. The Jardines (and I suspect any other 4-2 system) is a good replacment for the OEM system with little or no change in jetting or tune-up. Plus, they had a nice sound.

The MAC 4-1 system has a very drastic effect on low-end performance over the two 4-2 systems. The power band is raised significantly (about 800-1,000 RPM over stock) and it is really noticeable when the power comes on. In stop and go traffic or on neighborhood streets I notice I stay one gear lower than I used to with the 4-2 systems in an effort to keep the RPMs up closer to that magic level. But riding on the road where you can work above 3,500 RPM alot, there is nothing like the performance of a good header with proper jetting and tune-up.

Since I live on the very edge of the New Orleans area, I rarely ride towards town but instead I head out of town alot. So I ride alittle bit more agressively than a 'commuter' would ride. The 4-1 system suits me best in my riding condition.

[Wildkat]

1 -2 - 4 -3 firing order

Is what it looks like on a set of cams that John has in the parts box... He gave me a quick tutorial on them.
(it's good to have your own Guru )

SO much great info in this thread!
Going to go digest a bunch of it and see what happens.

Thanks all!

[Jerry]

firing order

1-3-4-2 is used on V-4s and opposed engines like the old VW Beetle. However, the Honda sohc in-line 4s of '69 - '78 use 1-2-4-3. I am assuming our in-line 4s also use 1-2-4-3, which Yamaha uses in the R1 engine.

Next time someone is dong a valve adjust, watch and see the order in which cylinders have both valves closed, begining with #1, and report back!

Opposed, V-4s, and some other in-line 4 cylinder engines do use 1-3-4-2, but I think most Japanese bikes out of the '70s and '80s use the 1-2-4-3 sequence.

[Pat Kelly]

My valve cover is off the MNS.
1-2-4-3 is the fireing order

[79XS11F]

I searched through both my factory and after market manuals today looking for the firing order. Never found the info in ether which is odd because I have never in the past owned a manual that did not include the firing order. It's good to know.
Rob

[Ken Talbot]

According to my Cycleserv manual, "No. 1 and No. 4 cylinders fire together. Therefore, when No 1 cylinder is timed, No. 4 cylinder is also timed. No. 2 and No.3 cylinders fire together exactly 180 degrees from No. 1 and No. 4 cylinders. No ignition timing adjustment is required for No. 2 and No. 3 cylinders"

[JWSanders]

Originally posted by Ken Talbot
According to my Cycleserv manual, "No. 1 and No. 4 cylinders fire together. Therefore, when No 1 cylinder is timed, No. 4 cylinder is also timed. No. 2 and No.3 cylinders fire together exactly 180 degrees from No. 1 and No. 4 cylinders. No ignition timing adjustment is required for No. 2 and No. 3 cylinders"

I had thought that too. How else could they run 4 cylinders off of 2 coils with no distributor? If they were in odd order you'd get a spark in one of the pairs off-time. Plus, I remember the outsides then the insides cycled together when I had the head off and rotated the crank by hand. This conversation was confusing me greatly..

It kinda makes the spagetti pipes make sense, too.

[Brian_D]

Originally posted by Ken Talbot
According to my Cycleserv manual, "No. 1 and No. 4 cylinders fire together. Therefore, when No 1 cylinder is timed, No. 4 cylinder is also timed. No. 2 and No.3 cylinders fire together exactly 180 degrees from No. 1 and No. 4 cylinders. No ignition timing adjustment is required for No. 2 and No. 3 cylinders"

This is correct - Yamaha (along with many other manufacturers) use a "waste spark ignition" where the coil-pair cylinders are on opposing strokes. On our bikes, when #1 is on the intake stroke, #4 is on the exhaust stroke (likewise for #2 and #3 cylinders). The coil firing on the exhaust stroke is the "waste spark".

The intake stroke firing order was the implied question answered by Pat.

Originally posted by Pat Kelly
...1-2-4-3 is the fireing order

given a stock setup, it appears that with a 4-2 exhaust system, the 1-4 and 2-3 exhaust header pairing is beneficial, but with this pairing:
a) what is the optimal I.D. of the individual header tubes?
b) what is the optimal length of the header tubes BEFORE the 1-4 or 2-3 pairing?
c) is there any benefit to a cross-over pipe in this type of 4-2 system? and, if so, what is optimal placement for the cross-over AFTER the 1-4 and 2-3 pairing?
d) finally, how much would the above figures change for '78-'79 cams vs '80-'81 cams? '78, '79, '80, '81 timing? stock displacement vs 1196 big bore?

I know, I ask alot of questions and as you can tell, after 3-1/2 years and still under 200 posts, I'm no XSpert, but I'm really interested in learning to design a custom exhaust for the '79F and the '81LH

[Pat Kelly]

I'm at work and have no way of measuring the pipes out in the parking lot. But if I remember correctly, on the spagetti pipes, the header pipes are 1 1/2" od and the od of each collector is 1 7/8".
The crossover tube is a part of the mufflers.

On the 4 into 1 (RC Engineering I was told) the header pipes are 1 1/2" and the collector is 2 1/4". When I customize it to 4 into 1 into 2 I'm using mufflers with a 1 7/8 inlet. This will copy what the engineers use for the Jardines. Going to 2 mufflers instead of 1 is purly for astetic reasons. I don't expect any performance gain.

[Wildkat]

c) is there any benefit to a cross-over pipe in this type of 4-2 system? and, if so, what is optimal placement for the cross-over AFTER the 1-4 and 2-3 pairing?

This is the set up on the Jardine spaghetti pipes with the crossover tube being just in front of the rear tire... I know it aids in scavenging... but I wonder about bringing the crossover closer to the front of the bike? Will be interesting to see what happens with xschops pipes with the two crossover tubes...

Pat... it must have been your post I read about the 4 - 1 - 2 set up... Wouldn't the addition of a 2nd muffler aid in flow and decreasing the back pressure? or is there not enough velocity for it to really make a difference?
In your design... where did you plan on placing the collector?

[Pat Kelly]

(yes, that was my post)
It's a (I was told) RC Engineering 4 into 1 with the collector square in the middle of the bike. As it is now, the pipe that connects to the collector runs thru the centerstand and then curvs to the left to the muffler.
I'm planning on a "Y" instead of the left curve. It may possible end up a "T" but I wasnt the flow to be as smooth as possible.
The flow (velocity) should be the same as the Jardine 4 into 2 as key points in the system will be the same dimensions. The real difference is the collector instead of a cross-over.

Jardine:
header pipes 1 1/2" dia x 4 (6" area, sort of),
muffler inlet(s) 1 7/8" dia x 2 (3 3/4" area)

My set-up:
header pipes 1 1/2" dia x 4 (6" same as above)
collector 2 1/4" diameter (venturi effect I hope)
'Y' pipe
muffler inlet(s) 1 7/8" dia x 2 (3 3/4" same as above)

I am using SuperTrapp mufflers so I can add or subtract discs as needed to get the best flow/least noise compromise.

I still need to get the bike back on the road. Last little details are holding me up. The valve adjusting is giving me problems (this time).
I will prevail..... if allowed to.