VF500 Exhaust

[GazVF500]

Hi All,

I've got a VF500F2F that I'm busy restoring.

I've looked at the various mods that people have done, and am going to do the CBR6 wheel swap (both ends) and the CBR F4i shock swap, for now.

One thing I need is an exhaust. Being a practical kind of guy, I'd like to make my own exhaust. Before anyone tries to dissuade me I know how much work goes into doing this! I've done it before on a university project.

So, the original Honda exhaust is a 4-into-1-into-2, but what type of exhausts do these bikes like? I was thinking a 4 into 2 into 1, with front and rear cylinder pairs merging together first, and then all merging together to try and maximise the pulse effects. I've got a Micron silencer that will go on it nicely.

Anyone tried this before? What lengths did you use for the various pipes?

Looking forward to hearing what people have done.

Gareth

[YoshiHNS]

Somewhere there is a thread floating around on VF500 exhausts. They were trying to get one of the manufacturers to make a production run of exhausts, but there was an argument of the correct configuration.

[InterFester]

I had done a few sketches of what should fit and merge correctly. It's important to step the diameter up correctly and not go too big anywhere. Headpipe diameter and length before the merge is the most important. I'd use the OE headpipes, or most of them, and go from there. Make them all the same length before they merge.

Rough headpipe estimates for an engine that redlines at 10,500rpm is 20" to 24" long before merge. Depending on how much of the OE headpipe you can use, step up only one pipe size, like 1" to 1 1/8", until they merge.

A proper merge is 30 degrees combined angle. Meaning each pipe is at a 15 degree angle from the centerline. This can be done with a chopsaw using a wooden jig to hold the pipe correctly.

The shape I came up with for a 4-2-1 was an "H". The fronts merge with the rears as they all bend towards the center. Then those two merge and bend towards the rear in the middle of the "H" cross bar so to speak.

What is the ID or OD of the original headpipes?

[GazVF500]

I had done a few sketches of what should fit and merge correctly. It's important to step the diameter up correctly and not go too big anywhere. Headpipe diameter and length before the merge is the most important. I'd use the OE headpipes, or most of them, and go from there. Make them all the same length before they merge.

Rough headpipe estimates for an engine that redlines at 10,500rpm is 20" to 24" long before merge. Depending on how much of the OE headpipe you can use, step up only one pipe size, like 1" to 1 1/8", until they merge.

A proper merge is 30 degrees combined angle. Meaning each pipe is at a 15 degree angle from the centerline. This can be done with a chopsaw using a wooden jig to hold the pipe correctly.

The shape I came up with for a 4-2-1 was an "H". The fronts merge with the rears as they all bend towards the center. Then those two merge and bend towards the rear in the middle of the "H" cross bar so to speak.

What is the ID or OD of the original headpipes?

Right. armed with a tape measure, my camera and the grinder, I've had a bit more of a look at this.

The original pipes are 30mm ID, and the front pipes are ~450mm (17") long. Using the formula for the resonant frequency of a single organ pipe (F = Speed of Sound / (Length + 0.3*Diameter)) gives ~11,000 RPM.

The rear pipes themselves are much shorter, but the extra length is hidden in the collector. Like this:-

So doing a 4-1 with those lengths, using a merge collector is going to be difficult.

So I've decided to try to use the exhaust to help boost the mid-range, by using a 4-2-1. This may sacrifice some top end power but should help general road manners. The RC30 and RC45 are both V4 engines with 360ª cranks, and they both use 4-2-1 systems with front pipes into one side of the "2" and both rear pipes into the other. It doesn't seem to hurt them!

I don't know if the organ-pipe modelling methods work for this type of thing, it definitely does for inlets. But here goes:-

Using the organ pipe-type method for the resonant frequency of a pipe, and using 7700 RPM (128Hz - pipe resonating twice per cycle) and 11000 RPM (183Hz), I've got 460mm and 659mm for the lengths of the primaries and the primaries + the secondaries respectively.

If the length of the tailpipe (which I've assumed includes the straight-through silencer I have) is 659mm + 75mm, as recommended by A. Graham Bell in his book "4-Stroke Performance Tuning" then the resonant frequency of the entire system should be at 3600RPM. I've assumed that primaries and secondaries are both 30mm ID, and the pipe linking to the can is 50mm.

Does anyone agree/disagree?

[CornerCarver]

Color me intrigued.

Keep up this thread and I may have to ship you a factory ehxaust to use as a jig (if needed). (edit - I was typing that as you were posting post mortem pics of your exhaust).

[InterFester]

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.

[GazVF500]

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.

The centre stand pivots behind the collector box. So I'm planning to keep the exhaust 4 into 2s in the space that the collector box originally took, then route the pipes around the centre stand, because I want to keep it.

If the lengths of the four branches varies slightly it'll help spread the power around a bit at the expense of a small amount of top-end, so I think that's OK.

[InterFester]

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:

[InterFester]

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.

[GazVF500]

That collector looks just the job! Did you make it with 2 bends with the mating section cut out and then seam welded?

I've had a look at the engine in the bare frame, had a rough estimate with the tape measure and the issue with your sketch is that the cylinders collect in the wrong order.

The cylinders are numbered from left to right in the order that the con rods connect to the crank. So no1 is back left, number 4 is front right. (EDIT - All lefts and rights are as you sit on the bike). The firing order is 1-4-3-2, so for the 4-2 bits to work properly we have to link cylinders that fire 360° from each other. So that's 1 and 3, 4 and 2.

This means that the front two and the rear two have to join together first.

My idea is to run the front primaries together down the left hand side of the oil pan and then join them roughly where the OE front pipe finishes. The secondary pipe will then turn to the right side of the bike.

The rear pair would initially turn to the left, to maximise the length of pipe tucked behind the engine (as there's no longer the convoluted pipes in the collector box). They'd come down together and then merge, before turning to the right side of the bike to meet the secondary from the front cylinders.

These would then collect and go to the silencer.

Oh and if all the cylinders have the same length pipe attached to them then they all make the peak power at the same time. If the lengths are staggered slightly (+/- 25mm) then each cylinder makes peak power at a slightly different RPM, so making the power curve broader but reducing peak power slightly. As you've said before, making the thing fit is the driver behind this as much as anything!

My idea would look something like this:-

[InterFester]

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.

[InterFester]

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.

[GazVF500]

The info regarding the firing order and cylinder nomenclature came from my Clymer manual. Not infallible, I know, but it's the only info I have.

The firing intervals are:- (assuming the Clymer is correct)

1 - 0°

4 - 90°

3 - 360°

4 - 450°

I believe that this is the same as the RC30 (also a 360 degree crank), which on Honda's own 4-2-1 system links both fronts and both rears, as shown on CMSNL.com's parts diagram.

The early V4s have a different firing order to the VFRs, as I'm sure you know, as the VFRs have 180 degree cranks.

[InterFester]

The info regarding the firing order and cylinder nomenclature came from my Clymer manual. Not infallible, I know, but it's the only info I have.

The firing intervals are:- (assuming the Clymer is correct)

1 - 0°

4 - 90°

3 - 360°

4 - 450°

I believe that this is the same as the RC30 (also a 360 degree crank), which on Honda's own 4-2-1 system links both fronts and both rears, as shown on CMSNL.com's parts diagram.

The early V4s have a different firing order to the VFRs, as I'm sure you know, as the VFRs have 180 degree cranks.

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.

[InterFester]

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

[GazVF500]

Yes, you're absolutely right about the cylinder numbering. At least we agree! Phew, was doubting myself then!

[InterFester]

Yes, you're absolutely right about the cylinder numbering. At least we agree! Phew, was doubting myself then!

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.

[JamieDaugherty]

Keeping the lengths equal helps across the rev range.

...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!

[InterFester]

Keeping the lengths equal helps across the rev range.

...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.

[JamieDaugherty]

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.

Agreed!

[GazVF500]

Keeping the lengths equal helps across the rev range.

...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.

Yes, you've hit the nail on the head there. You never get an exhaust to work over the entire range of engine speeds. So the tuned lengths of all the parts in the 4-2-1 must be calculated to boost output in strategic places. I've chosen numbers on mine that, when multiplied, do not match other areas of the system. For example I would not have a tailpipe tuned to exactly 5000RPM and then have the primaries tuned to 10000RPM, as the two may well cancel them out. That's why, in the original post, I mentioned 3600, 7700 and 11000, as these numbers don't cross over

I think I plan to make my first system a test one, and have adjustable slip joints as far as possible, so that it can easily be tweaked and then fixed where it works best.

[InterFester]

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.

[GazVF500]

I can't yet, but plan on learning. You can weld SS with MIG, apparently you need a shielding gas with low (<3% CO2 content).

It's a practical skill that I'd love to learn, and hope to in the course of this project. Lots of practicing before I touch any tube, methinks!

[InvisibleCities]

GazVF500, I'm very interested in how you are making out with your 4-2-1 exhaust system. Any updates on this project? Thx!

[GazVF500]

GazVF500, I'm very interested in how you are making out with your 4-2-1 exhaust system. Any updates on this project? Thx!

Interesting you mention that. I have now got a box of stainless bends waiting to be chopped up, I'm just trying to work out exactly the best way to calculate the lengths required.

I've seen a very common equation for the lengths required, but with no derivation or evidence to back them up.

Once I've done this I will update this post!