GS450 2 into 1 Exhaust Lengths?

[lake_harley]

koolaid kid....you're not interrupting. Old hot rodder here too. If my fuzzy memory serves correctly a longer primary will retain low/mid RPM power, and for top end power the primaries get shorter....or is it the other way around. Oh well I have a 50/50 shot at making power somewhere along the RPM range.

Somewhere, I have a book that had a formula to use as a starting point for tube diameter and length based on engine displacement and the desired RPM range the exhaust was to be most effective. Where that book is is anybody's guess. I've searched some on the internet for similar info but didn't locate anything I found helpful. Maybe my searching skills are weak.

Working out pipe routing can get interesting to achieve equal length. On the Honda system I got the lengths within about 1/2" of being equal and called it good at that. Also, here's a picture of the merge collector I built. The primaries could be fitted to the angled outlets on the head individually and then the collector slipped into place.

I just saw the barely visible 23 1/2" notation in sharpie on the lower pipe in the picture. I'm guessing that was my primary length, at least on that tube.

Lynn

[koolaid_kid]

You are correct on the primary length, but you won't have to worry about that since you have to wrap around the engine and under/past the rider. Have you decided whether you are going low or high? I really like Pete's scrambler-style pipe, but most go for the low style. Most go down and to the right, Pete went high and to the left. Just thinking out loud.
If you look at examples of 4 cylinder headers, they do fancy stuff with the routing of each pipe to make them as equal of length as possible and meet in the collector at relatively the same place.
Took me a minute to see that you joined between the peg and the frame. Does the peg get a bit toasty?

[SVSooke]

I'm going to throw another consideration into the mix.Engine configuration and exhaust timing because of it.I'm not sure how the 175 you worked on is set up put the later 400 Honda's was a 360 degree design with the pistons going up at the same time.Meant that the exhaust pulses are (IRRC)360 degrees apart.The GS450 is a 180 degree engine with the pistons "rocking".The exhaust pulses in this configuration are 180 and 540(?) degrees apart.The 360 engine will lends it's self to a 2>1 much better than the 180 does.Might just want to look at doing a 2>2 instead.Not saying a 2>1 will not work OK but a 2>2 might be better for power.
Edit:I might have the math wrong,early here and my math is not good at best.Hope you get what I mean inspite of that.

[pete]

I'm not going to even pretend to know what I'm talking about with exhaust tuning

My headers aren't even as the measurements show, but that was never going to happen with the scrambler style...

Because it's a high pipe going under my ankle/shin, I had it ceramic coated rather than chromed and that definitely makes a huge difference to the outside temperature it runs at.

If you are going to go high, you're definitely going to have to go left instead of right if you still want to be able to check your oil level. Going high also means no issue with side stand or centre stand clearance.

My initial cardboard mock up was on the right and it was all good until I saw the dipstick... no way was it coming out with the exhaust on that side.

The only potential issue with it on the left was getting to the choke lever on the carb's, but I already had made an adaptor and used a later GSXR left control to get a 'bar mounted choke lever so that was no issue. In the end I think it would've been fine anyway, but I hate the lever on the carbs.

Interestingly enough, with the new pipes and K&N's, the seat of my pants says definitely more get up and go, and it gets going probably 500RPM's lower than with the stock setup. Used to have to be 5 - 5.5K RPM for her to really get going, now more like 4.5 - 5K.

[lake_harley]

Thanks again for the replies and thoughts. My plan would be a low exhaust system, only since that's my preference.

I was aware of the 180* firing rather than 360*, but I'm not sure how that might affect exhaust design. Thinking maybe one cylinder might get scavenged more than the other by the un-even firing I guess? Good question. More research might be in order.

2 into 2 would be a piece of cake....hardly worth doing anything other than stock. We can't have that....can we?

On the 175 there was barely enough room to thread the two primaries through the gap between the peg/frame/engine. I hoped, if anything, it wasn't too close to the engine from a heat standpoint, but I never noticed any heat issue on the peg, even on a 560+ mile weekend ride.

Thanks, as always.

Lynn

[SVSooke]

I think Pete's experience proves it can work OK with a 2>1 but in theory the exhaust pulses are to far apart or to close together for the perfect scavenging to work.In theory the 4>2 on most GS's aren't ideal either, the way they "should" be is like this:

With 1&4 and 2&3 paired up.Funny that most bikes run just fine with1&2 and 3&4 paired up

[Mekanix]

With 1&4 and 2&3 paired up.Funny that most bikes run just fine with1&2 and 3&4 paired up

Isn't All twins 1&2 or 3&4, I wonder what the theory is to that ?

Also interesting: All gs500's are 2 into 1, And all aftermarket gs450 exhaust's are 2 into 1.

Mac

MAC

[pete]

Interesting... now I'm wondering if my uneven headers are actually a good thing?

[koolaid_kid]

You might be losing 2-3% of your power. Since you might see a 5% increase with headers, that means you may only be gaining 2-3% (once you tune the carbs, of course).
Trust me, on a 450, you won't notice the difference. All aftermarket systems are 2 into 1, if for nothing else than the weight savings.

[lake_harley]

A thought occurred to me about headers and exhaust pulse timing. I have a background in circle-track racing, stock cars and modifieds. A small block Chevy has an uneven firing order if headers are matched up 4 into 1 based on the left and right sides of the engine. There are headers that pair up the even-firing-order cylinders, where each of the collectors has a mix of right and left bank cylinders, to evenly space the exhaust pulses. Cars with these 180 degree headers can easily be picked out of a pack of cars on a straight, just by the distinctive sound. In years at the races, I have yet to see that a car with 180 degree headers ever did any better or worse than any others. Lots of factors in play on a dirt oval track, no doubt, but I don't think I ever saw one of the 180 degree header cars win, but then the % of those cars was always very low. I think too, that dyno results would have made them more popular if the HP results were there, or if there seemed to be more advantage on the track.

I'm not saying I'm right, but the direction I'll probably go is to not worry about theory and build the 2 into 1. My bike will probably never see a dyno anyway. I do appreciate the topic coming up though. It's always good to think a bit.

Lynn