'86 Oil Pump Conversion for the '84/'85 VF500F

I am in no way an exhaust expert, just going by everything that I've read and heard. I believe it has to do with the firing order of the V4 engines that make this cylinder pairing preferable. Take a look at the photos of HRC Interceptors that had 4-2s and you'll see this same setup.

 

Great intel, thanks 80s!

What exhaust system do you have on your race bike and are the mufflers in slightly different positions?

 

The reason you can pair the front two (or the rear two) cylinders together is because they fire at even intervals. In fact, they fire exactly 360 degrees of crank rotation apart. That means at any speed they would remain perfectly phased regardless of primary tube length (assuming equal physical tube lengths). The downside is that 360 degrees of separation is a lot so the scavaging effect is minimal. The result is a mediocre performing system but one that is easy to design.

 

Thanks for the post.

On this note if going 4 into 2 is it better to run the headers a from 1/2 and 3/4 like this system from Vance and Hines?

 

Yes, absolutely.

Edit: Wait, reading this again maybe I misunderstood you. The V&H system is not the preferred way to go. You want to tie the front two (2/4) together and the rear two (1/3) together. I think the MAC systems were designed in that manner. The V&H design is basically a 4-1 split in half. You get all of the downsides without any of the positives.

 

5x5. This is based on the 1-4-3-2 firing order?

 

I have no idea who made it. I've never seen another one exactly like it. I traded a stock system (with RASHED mufflers) straight across (it is loud, but sounds awesome). It also came with additional set of "street" baffles that can be wrapped in glass and slid into the bigger silencers. Yes, they are staggered. The right muffler is farther back to give some length to the rear cylinder headers.
I agree with everything Jamie says. It seems like everything is a compromise, but these sure did seem to work good. Modified 86 air box with 85 carbs... no complaints. Always wanted to try an 85 and 86 air box back to back to see if if I could feel any difference.
Mike.

 

Thanks Mike.

So it looks like either a 4-2 (w/ a 1|3,2|4 pairing & staggered mufflers) or a 4-1 system is the way to go here.

Delving into this a bit more - which is better or are their caveats to both?

 

its now an exhaust for the oil pump conversion thread..continue on gentleman....I am reading this thread, although I have no use for the conversion( I have an 86 oil pump already installed) I am interested in the exhaust talk..I an thinking about changing my stock exhaust out but, not sure which way I want to go with it. Any of these possibilities leave me with my beloved center stand?

 

My bad Tink. I think I may have caused this slight detour based on my question as to whether the stock '84/'85 exhaust will clear the larger '86 oil pan. The caveat to a few of the aftermarket systems is oil pan clearance as well. My plan is to install the '86 oil pan and pump and run the stock '86 (?) exhaust for now. Eventually I would like to fabricate or purchase an original 4-2 (1|3,2|4, staggered muffler) or 4-1 system that will work with the '86 pan.

 

Sort of. The idea is that the pistons in each bank go up and down simultaneously. Since they are 360 degrees of crankshaft rotation apart you get an even pulse of exhaust flowing out if you tie the two pipes together. It's a bump.....bump.....bump.....bump..... etc. The problem is the spacing between each pulse is long enough that scavenging isn't as effective as it could be. Since the pulses are even it allows you to make equal length primary tubes and all is good.

A 4-1 offers a better scavenging effect. The reason is because the pulse ahead is close enough that it can "pull" the next one along. With a V4 engine the 90 degree cylinder phasing makes for an uneven firing order (think: New R1 crossplane). This means you have to design a system with different length primary tubes such that you are lining up the exhaust pulses in an even order. Think of it as a zipper, you want the tooth of one line to lay right down in the gap of the other. In this case the zipper has four lines.

Fair enough, so why won't it work with a V4? It's the fact that the uneven order forced you to make different primary lengths to even out the "stagger", if you will. Different tube lengths have different losses, and the actual losses change as the engine speed changes. That means if you nail it perfect at a certain rpm it will for sure be off at another. That's how you tune the exhaust on a V4. You have to pick an rpm where you want it to work best. If you make that happen the effectiveness of the system will taper off as you deviate from that rpm. Low rpms don't cause a lot of flow so it's not normally a problem area. Where you see this rear it's ugly head is in the midrange.

Now you know why V4's always have a big power dip in the midrange!

 

Derailing the exhaust system detour ;-) here are a few threads with more info:

Dyno charts (stock 4-1-2 exhaust) from Cycle

http://vfrworld.com/forums/1st-2nd-generation-1983-1989/33339-vf500f-top-end-modifcations-tech-questions.html

http://vfrworld.com/forums/1st-2nd-generation-1983-1989/32860-86-vf500f-cycle-april-86-a.html

Info on aftermarket exhaust systems

http://vfrworld.com/forums/1st-2nd-generation-1983-1989/30249-vf500f-aftermarket-exhaust-systems-back-day.html