InterFester

Since it's a 4-2-1 or a tri-y the individual head pipe length can and should be shorter. They all don't merge and jump up to collector size like a 4-1, the pairs step up and then merge. Different program to figure all this out.

Looks great GazV! Now hurry up and start the engine so we can hear it. JK, worth the wait. Duc888, those cans look right at home on yer 1KR. Sometimes mixing old and new really works.

Body work looks to be a combination of years. Kinda dirty, dash looks well weathered. I'd be interested but for less $. What are you looking to spend? What do you hope to do with the bike or how do you want it to be, daily rider, show piece?

I guess I missed the most recent updates, 'bout time you got busy welding. So it's been a few months, how does it look? Surely you have pictures by now. I recently purchased a really nice '84 VF500F so I can start moddin'. I really should leave it alone but I know I won't. I can justify mods if they are easily reversible right? The more I think about it, the more important fit and sound are to me. I still plan to pair 1/2 and 3/4 for fit and easy plumbing sake. They aren't 360 degrees apart but they aren't super close either, at least 270 degrees. Besides, if they all merge into one then they are all gonna share all the pulses. I'm looking forward to working with smaller diameter tubing, lot's tighter designs can be done the smaller it is. 2"OD gets to be tough.

That looks at least 250% better. I haven't welded SS with my Mig yet so I won't criticize your welds. Looks strong.

Are you going to use Steel or Stainless? There is a vendor in Oregon that sells mandrel bent 304 stainless pipe pretty cheaply but the shipping to the UK would surely offset the savings. Actually there is a vendor on eBay who sells muffler core tubing in SS cheaper than I can find anywhere else, he might have bends too. http://cgi.ebay.com/3-inch-90-degree-Mandrel-Bend-3-T304-Stainless-Tube-/220579025669?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item335b88d305 Can you weld SS? I can weld steel and have a MIG but not SS yet.

...except that doesn't work on a V4. The 90° phase angle between the front and rear cylinders make that fly right out the window. If you look at only the front two cylinders (or rear two) separately then equal length is ok, but as soon as you join them you are hosed. The phases will never lay over top of each other at all rpms. Lots of theory involved with that, but there are ways to determine "sweet spot" rpm range for a 4-1, but normally it's easier to just take your best stab at it and see what the dyno says - then iterate. Keep us up to date on your progress! I wondered about that and asked the guy who came up with the headpipe specs for my TL if an uneven firing order should be compensated for with different length primaries but didn't really get a clear answer. He worked for Graves MotorSports at the time and used an exhaust design program. Ironically the lengths he came up with are very similar to the OE exhaust system but with larger OD piping. He also said specs for the collector after the merge involve many other parameters and the options are many but weren't nearly as critical as the headpipe length and OD. Fitment and sound are as important to me as squeezing out every last bit of HP. The design I have for my TL is not for peak HP but for best all around and lagest area under torque curve with little peakiness, a street pipe. This is what I'd shoot for with the VF500 as well. The OE system on the VF500 is technically a 4-1-2 just with a large merge "box" volume. I'd think a properly sized 4-2-1 that steps up correctly to keep velocity high would improve on it across the range.

Visualizing a picture and getting things straight in my head isn't as easy as it used to be. So.... #1---90*---#4---------270*---------#3---90*---#2---------270*---------#1 Pairing the fronts together and rears together would give you 360* between pulses. Pairing the left side together and the right side together would give you 270* or 450* between pulses depending on how you wanna look at it. This is also how my TL fires, only half as much since it's a twin. I wonder if the different pairings sound much different. A parallel twin with 360* crank, what the front or rear bank by itself is basically, does not sound awe inspiring. A single pin 90* V-twin, or L-twin, does sound pretty sweet. Times two in an uneven phase and who knows. Too bad I can't find a YouTube video of a 4-2 Yosh system. I've heard they were loud that's it.

Ok, I found a nice top pic of some cases. The cylinders are spaced the same between each other but the rear bank is offset to the left. It's rear headpipes must be spaced more narrow just for fitment reasons in the frame. So Left rear is #1, Left front #2, Right rear #3 and Right front #4. http://cgi.ebay.com/ebaymotors/Honda-VF500F-86-upper-crank-case-/330407253641?cmd=ViewItem&pt=Motorcycles_Parts_Accessories&hash=item4cedce9689

I didn't know that about the VF and VFR having different firing orders and different cranks. I don't really know too much about either model at this point, I'm in the market for a VF500F and thought I'd visit the experts before buying one. I had an '84 way back in 1987 and really loved it. I recently moved to hilly and curvy Eastern Tennessee and just realized how unnecessary alot of horsepower is here not to mention likely fatal for a Florida native. The above exhaust system is more like a 4-2 since it has such long secondary pipes that slowly merge into 1 just before the muffler. More like they merge so as to have only one muffler than to take advantage of the tuning benefits of a 4-2-1. I've seen some I-4 pipes do this too, for what reason I'm not really sure.

The merge in the picture is the beginnings of a 2-1 system for my Suzuki TL1000S. Instead of starting with two straight pieces of pipe, welding them at a combined angle of 30 degrees and then trying to connect to that merge I just used two bends and welded them together about an inch from where the bend stops and the straight leg begins. I coulda/shoulda shortened that to about half an inch of straight and saved me some space but it'll still work. It's a proper merge as described by the folks at Burns Stainless, http://www.burnsstainless.com/crossoversmain.aspx I just wish their beautiful work wasn't so expensive.

It looks to me like the front bank of cylinders is set wider on the VF500F and the rear is narrow so left front would be #1, left rear #2, right rear #3 and right front #4. Other VF motors, like in a Sabre on another thread, look to be opposite, wider set in the rear. Where did you get the info on the firing order and cylinder arrangement numbering system? I've seen a Yosh 4-2 system on this site that merged left front to left rear and right front to right rear. I'll have to thing about this for a bit as to how many degrees of rotation takes place between each cylinder firing. All rods mount to a single pin crank and the "V" is 90 degrees so it fires like a V-twin two stroke since the front pair of pistons move together as do the rear pair. Another primary length rule that Ducati uses is if they can't be equal then the longer pipe must be 1.5 times as long or 2.0 times as long as the shorter. The longer pipe should not be 1.25 times or 1.75 times.

Are the OE headpipes 30mm ID ? That seems large to me for 125cc per cylinder. Keeping the headpipe the same as OE or just one size larger and then increasing the size out of where they merge to just under 2X the area into the final merge and then ~2X that area for the tailpipe. The tail pipe can be stepped up to make it easier to find a common muffler ID. Something like 1" headpipes merging into 1.5" merging into 2" for the tail pipe.

Keeping the lengths equal helps across the rev range. Is there room in front of the collector box under the engine or does it hang down? There looks to be plenty of room just in the area of the collector box to merge both left side headpipes together and both right side headpipes together and then merge both of those pairs together. My idea is to have both of the front headpipes turn towards the center using a 75 degree pipe. The rear headpipes would do the same but since they are spaced closer together there would have to be more bend in the pipe. Now both left and right are merged and facing each other. They would merge the same way in the center bent to face rearward. There should be plenty of room under the right rear headpipe for the collector to follow the same path out as the OE muffler does. It could even be split back into two mufflers. A merge like this: My drawring of the system expanded slightly:

I've been a wonderin' what it looked like inside the collector box on the VF500F. Makes sense that they would extend the length of the rear headpipes so they are equal or closer to that of the front. It does come down to what will ultimately fit so even the best design usually has to have compromises. Where does the centerstand pivot in relation to the collector box, in front of it? A 4-2-1 would be better fit and more streetable power.