Custom exhaust question

[atvpyrofreak]

I recently had a vision for my 78' GS1000 which involves a 4-1 (or 4-2-1) exhaust. So, baring all the other issues concerning intake/filter/jetting.... My question is 2 parts.

1. Where do the performance gains come from in a production aftermarket exhaust? Are the head pipes larger? Is it just the overall design/flow. Does the muffler just flow more freely? Is it a combo of some or all of these?

2. My vision involves cutting my stock head pipes near or before the crossover, fabing them to come into some sort of 4-1 or 4-2-1 collector/midpipe, and then running the midpipe out and using a stock gsxr can (looking at the 01' range 1000cc). Does this sound like a ok idea? I know i have the skill and equipment to make the system work/fit the bike, but does anyone see any mistakes I could make that would cause this to be a poor flowing/performing system? As long as the bends/transitions are smooth, and unrestricted, does this seem like it would work? That Muffler should flow well enough shouldn't it?

Just in case any are wondering, my reasonings for this are... my stock exhaust is shot, i don't have an abundance of cash (college), equal or improved performance, appearance, ground clearance, and just to be different.

Thanks for all you guy's help in advance, the GSR is awesome!

 

[Steve]

There is only so much you can design into an exhaust system. Factors that affect the performance include the diameter of the head pipes, length of the head pipes before the collector, collector size and restriction of the silencer.

-- The diameter of the pipes will affect exhaust flow (back pressure).
-- The length of the pipes will affect the rpm for peak efficiency (most power).
-- The diameter of the collector can affect how narrow or wide the peak power band is.
-- The restriction of the silencer will affect overall exhaust flow, therefore efficiency.

Believe it or not, a sizeable gain is realized simply by the reduction in weight over the stock system. :shock:

I see nothing wrong with what you have in mind. I have had a similar idea, but I am also interested in getting rid of the crossover pipe between cylinders 2&3 that exists on bikes newer than yours. I am not sure it does anything for performance, but it does give the bike that unique Suzuki exhaust note.

Let me know if it works, I'll bring you another bike to work on. 8-[

Oh, and you don't really need "reasons" to do this. We ALL like to try stuff to make it OUR bike.

.

 

[rphillips]

Weight & Flow design, mainly in the collector, makes the pipes work better than stock exaust. Some after mkt. pipes don't improve hp, just make the bike weigh less. What you are trying to do will probably work, but don't expect performance gains, as it could go the other way. For the trouble this looks to me like a NO. Something used & cheep, from here, in the wanted section, or e-bay would be a better option. Good luck

 

[SPARKSS]

" Just in case any are wondering, my reasonings for this are... my stock exhaust is shot, i don't have an abundance of cash (college), equal or improved performance, appearance, ground clearance, and just to be different."

With the above statement, It's more likely that what you'll accomplish will be an exhaust system that works basically. Performance exhaust has specific objectives, usually maximizing HP or TORQUE at a specific RPM or with the tradeoff of broadening that into a power band needed for a purpose. Usually this doesn't translate well to normal, or usual street riding. Fabrication accuracy can impact your results - poorly fit "Y", collector or bent or cut angles (which may look good outside but have sharp, extended or interferring internal edges) will change how the set flows at different points and without the means to flow test or dyno your changes and results, it comes down to living with your results.

I'd never say "don't try 'er" but just be a little realistic when it comes to your objectives.
Maybe document your effort and post some pics and results

 

[Nessism]

I think a custom exhaust would be a good project. As noted by Steve, there are various factors to consider...but in the end I don't think there is much horsepower to be had despite what some people think. A 4 into 1 system has the potentional for a power gain in the high rpm range but at the expense of some midrange. Dyno charts of stock vs. 4 into 1 w/pods typically show about a 5% power gain, but there is often a power dip, or hole it's sometimes called, in the midrange somewhere.

My issue with aftermarket exhausts are the noise and the rust. Rust that forms on the inside of the pipes can be sucked back into the engine with the reverse power pulses - the particles will then cause ring/cylinder wear. Not good. The factory systems rust also but typically further downstream in the system so I think they are less likely to make it into the engine. At any rate, that's my $0.02. Reusing the factory head pipes but fashioning some sort of high quality mufflers would be a good way to go.

 

[focus frenzy]

revers power pulses?? it's a four stroke and doesn't have radical race cams, at least not stock.

the one main problem I see is the stock pipes are dual wall and it can be difficult to re-arrange them without special jigs and equipment.

scour wrecking yards and ebay for a crusty aftermarket system. they can be found cheep and with plenty cheep elbow grease can be brought back to look good again.

 

[80GS1000]

If you're going this route, try building a 4-2-1. It has better midrange than a 4-1, and better ground clearance too. Pretty much all sportbikes since the 90s have had a 4-2-1 for these reasons. The 89-92 GSXR 1100 exhausts and the oil/aircooled Bandit 1200 exhausts will fit a GS1000 with some modification.

You have to cut the manifolds off the GS1000 and then GSXR 1100 header and then weld the GS1000 manifolds onto the GSXR header.

Here's some pics:

http://www.thegsresources.com/_forum/showpost.php?p=567870&postcount=180

 

[Nessism]

revers power pulses?? it's a four stroke and doesn't have radical race cams, at least not stock.

Ever hear of exhaust tuning? The size of the pipes effect the back pressure and the reverse pressure wave that stuffs fuel lost during the overlap period back into the cylinder.

In my last job working for a major Asian OE auto company, we had a huge problem where the catalytic convert would break up and get sucked back onto the cylinders, due to exhaust reversion. The small bits of ceramic material would then tear the crap out of the cylinder walls leading to oil consumption...which would then lead to running out of oil...which would then lead to a rod coming through the side of the block...which would then result in a fire. True story.

It's my concern that rust inside the pipes can get sucked backwards into the cylinders. Based on what I've seen before it seems plausible to me. Stainless is the way to go in my opinion but stainless systems for old GS bikes are hard to come by.

 

[atvpyrofreak]

Thanks for your help guys, and keep it coming if you have it. I guess I am not really expecting any performance gains, but would just hate to cut up my stock system, and then be stuck with some set up that i couldn't get tuned in to run properly. I guess i wont know until i try! Ill defiantly take some pictures and share with you guys if I do under take this project.

The only issue i now see is... are you saying the stock headpipes are 2 layer of pipe? From the head to the crossover pipe? If so, are these pipes fairly tight within on another, or is there some "slop" between them? This is something I didn't know and could defiantly be a problem if i need to re-do some angles here and there.

To all those who this seams like lots of unnecessary work to and think i should just find a cheep aftermarket system.... I have lots of time and time is free (in a sense), My pops has a 2000$ mig welder, and access to a tig. I have a pipe bender (however its not good enough in my opinion to form a complete new system). I also have in my opinion, a fair amount of fabrication skills. Besides... I really like to build custom parts, take pride in my work, and dont mind learning a few things when things dont go as planed. Yes, aftermarket would be easier... but every joe out there has a MAC or a KERKER, or a V&H, or other brands I'm forgetting... but be it good or bad, NO one will have my set up.

 

[Steve]

In my last job working for a major Asian OE auto company, ...

Dare we ask which company?


.

 

[Nessism]

Hey Steve,
I worked 21 years for Nissan, in their engineering department. The QR25 is the one that used to eat it's own cat, but the larger VQ35 would do it too given the right (or wrong) situation. The point is that the exhaust pressure pulses are very strong and particulate matter on the inside of the exhaust pipes WILL move backward into the cylinders. I'm frankly not sure how much real world risk there is but it's enough to put me off - say no to rusty exhaust systems.

 

[focus frenzy]

Quote:
Originally Posted by Nessism
In my last job working for a major Asian OE auto company, ...

Dare we ask which company?


.

yea so we can avoid them! LOL

 

[Steveb64]

Hey Steve,
I worked 21 years for Nissan, in their engineering department. The QR25 is the one that used to eat it's own cat, but the larger VQ35 would do it too given the right (or wrong) situation. The point is that the exhaust pressure pulses are very strong and particulate matter on the inside of the exhaust pipes WILL move backward into the cylinders. I'm frankly not sure how much real world risk there is but it's enough to put me off - say no to rusty exhaust systems.

Hmmm - and I've been running various exhausts from original, to original modified and patched, to shop made tuned 4 -1, to home made tuned 4 - 1 over the last 23 years.
I never had any problems with the engine inhaling junk from the exhaust - but I melted down a piston at 240 kph (150 mph) one day - due (I think - actually pretty sure) to a manufacturing defect in one header causing the related cylinder to run lean and start detonating. The joys of home made. Trouble was, the cams I was running were so radical, I HAD to make my own exhaust, just to get it to tune properly.

 

[Steveb64]

Thanks for your help guys, and keep it coming if you have it. I guess I am not really expecting any performance gains, but would just hate to cut up my stock system, and then be stuck with some set up that i couldn't get tuned in to run properly. I guess i wont know until i try! Ill defiantly take some pictures and share with you guys if I do under take this project.

The only issue i now see is... are you saying the stock headpipes are 2 layer of pipe? From the head to the crossover pipe? If so, are these pipes fairly tight within on another, or is there some "slop" between them? This is something I didn't know and could defiantly be a problem if i need to re-do some angles here and there.

To all those who this seams like lots of unnecessary work to and think i should just find a cheep aftermarket system.... I have lots of time and time is free (in a sense), My pops has a 2000$ mig welder, and access to a tig. I have a pipe bender (however its not good enough in my opinion to form a complete new system). I also have in my opinion, a fair amount of fabrication skills. Besides... I really like to build custom parts, take pride in my work, and dont mind learning a few things when things dont go as planed. Yes, aftermarket would be easier... but every joe out there has a MAC or a KERKER, or a V&H, or other brands I'm forgetting... but be it good or bad, NO one will have my set up.

If you want some reference material, I can recommend the book "4 Stroke Tuning in Theory and Practice" by A. Graham Bell. It's a few years old now (but so's your bike), but gives some great explanations as to why some things should be done in a certain way, and how to do them (like formulae for working out header diameter and length, and tailpipe length, and whether to have a 4-1, or a 4-2-1).

Also be aware - any bends need to be smooth. NO wrinkles in the pipe, or your pipes won't work real well. ...and if you get something wrong, it'll likely cost you more than a cheap, used, exhaust system.... Multi cylinder engines are very susceptible to uneven flow rates between cylinders. They don't like it - and they'll spit the dummy at you, then sit crying oil everywhere. Good luck.

 

[atvpyrofreak]

Thanks for the input steve. Ill defiantly be picking up that book. I may not know what I'm getting myself into! I wish i could find a system I liked, and this wouldnt be a problem. My stock system is kinda rotten, and I dont like the (in my opinion) bulky look of it. AND I dont really care for the look of the aftermarket 4-1's with the huge collector hanging down there. Plus Im not one to push the bike over 100mph (at least that often:-D) I want to keep the power on the bottom end, which is why i was thinking 4-2-1. I'm starting to think i might try using a Bandit header/mid, and gsxr or other aftermarket muffler. Keep the info/opinions coming and thanks to all of you who have already helped.

 

[rphillips]

Years ago, I purchased a V&H 4 into 1 for my GS 1100 E. It came with either 2 or 3 restrictors, that fit in the collector. The smallest restrictor would give more bottom end power, & less top end power. With no restrictor, it would have more top end power, & much less bottom end. Also retarding the cams a few degrees will give more bottom end, but you will give up a little on the top.

 

[rickt]

Rusty exhaust making me nervous

Rusty exhaust making me nervous

When I removed the exhaust system from the '78 GS750 that I was given (and I currently restoring), I noticed a significant pile of rust that fell out of each pipe and muffler. THe pipes and mufflers are in decent condition as the bike had a mere 2000 miles on it when it was parked in 1981. I was thinking of pulling some coarse steel wool through the pipes and trying to use them, but these posts about rust dust being pulled into the cylinders has made me a little nervous. Should I dump the old exhaust and pull out the checkbook to buy an entirely new exhaust system?

Please give me some advice.

rickt

My issue with aftermarket exhausts are the noise and the rust. Rust that forms on the inside of the pipes can be sucked back into the engine with the reverse power pulses - the particles will then cause ring/cylinder wear. Not good. The factory systems rust also but typically further downstream in the system so I think they are less likely to make it into the engine. At any rate, that's my $0.02. Reusing the factory head pipes but fashioning some sort of high quality mufflers would be a good way to go.[/quote]

 

[Guest]

20+ years ago, Cycle put a Kawasaki on the dyno, with about ten different exhaust systems. They tested the OEM system, and after market systems that were mostly made by major companies like Jardine and Kerker. They found that not only was the stock system the quietest, it also had the best compromise of power over the RPM range. I don't remember what they did to readjust the carbs with each exhaust system.

So it seems to me, that unless you have a specific performance goal in mind, trying to duplicate the stock system as closely as possible would make sense.