Inline 4 Exhaust question

[Hammered]

As some of you know, Ive been working on a GS750 for some time. Its a custom build and with that Im doing things not quite like Mr. Suzuki did. Id like to build a custom exhaust. It would be 4 short headers tubes feeding into a single chamber header that then becomes an exhaust pipe on either side of the engine. Think 1940s Indian exhaust but with two exhaust pipes.

The fabrication is simple enough. My question is, Do you think that with mufflers, Ill have enough back pressure? Or will single anti-chamber that the 4 headers feed will create too much pressure?

 

[Agemax]

there is no real answer unfortunataley. different exhausts produce different power characteristics. its a case of trial and error really.

you got to compromise between the look you are after and the performance. low end torque would sound better for a bike of that style rather than flat out power

 

[Hammered]

there is no real answer unfortunataley. different exhausts produce different power characteristics. its a case of trial and error really.

you got to compromise between the look you are after and the performance. low end torque would sound better for a bike of that style rather than flat out power

Yeah. I was just wondering about creating too much Back pressure. I dont mind the loss of some performance since Ill be re-gearing for better top end/fuel mileage. And Im pretty sure the 750 should still have far enough Ummph to push my butt down the road with little effort. I wont be pulling uo beside you anytime soon and challenging a race but Im hoping it will look great while cruising. Ok off tot he auto store for some straight exhaust tubing.

 

[Agemax]

depend on how you want it to sound a well, loud when screaming or nice and quiet all round. quieter means more baffling, which means more back pressure, less back pressure and less baffling means a more breathable engine

 

[atb1998]

So from the sounds of it you are going from the engine to one collector, back to 2 exhaust pipes? If so , you need to make sure your header pipes going into the collector are the same length, you 2 pipes coming out of the collector are the same length. i wouldn't make the collector any larger than 2" or it will really be flowing air and back pressure will be hard to maintain. Kind of like a large diameter race header. You also need to be careful how close you put the collector to the engine as the different cylinders will cause pulse and pressure on each other and the cylinders won't properly scavenge

 

[Hammered]

So from the sounds of it you are going from the engine to one collector, back to 2 exhaust pipes? If so , you need to make sure your header pipes going into the collector are the same length, you 2 pipes coming out of the collector are the same length. i wouldn't make the collector any larger than 2" or it will really be flowing air and back pressure will be hard to maintain. Kind of like a large diameter race header. You also need to be careful how close you put the collector to the engine as the different cylinders will cause pulse and pressure on each other and the cylinders won't properly scavenge

Ill be running all tubes the same length. I hadnt thought about it altering the scavenging effect. Ill have to come up with a baffle in the header to help that. I think most of that issue will be resolved with the heads and exhaust being thermal barrier coated.

 

[Agemax]

Ill be running all tubes the same length. I hadnt thought about it altering the scavenging effect. Ill have to come up with a baffle in the header to help that. I think most of that issue will be resolved with the heads and exhaust being thermal barrier coated.

header length wont make too much difference if you are not looking for outright performance as long as they arent radically different.
please dont tell me you are going to "wap" the headers!!!!

 

[Hammered]

header length wont make too much difference if you are not looking for outright performance as long as they arent radically different.
please dont tell me you are going to "wap" the headers!!!!

No Im spraying them with Techline's Thermal barrier coating. Im not sure what color yet, all performs the same function.

 

[Agemax]

No Im spraying them with Techline's Thermal barrier coating. Im not sure what color yet, all performs the same function.

good man, pics when completed please! what colour you thinking of?

 

[Hammered]

good man, pics when completed please! what colour you thinking of?

Techline has a Silver and a black. Im waiting on them to return on my question about mixing colors. If I can get a metallic black, I think that would really work with the black.red scheme Im working with.

 

[reddirtrider]

No Im spraying them with Techline's Thermal barrier coating. Im not sure what color yet, all performs the same function.

I used their black ceramic coating on the Yoshi header I modified for the GS750ES. They recommend using an air brush in their literature - DON'T. I used a HVLP gun and laid on just enough to cover. You don't need to put on multiple coats or put it down thick.

They also say you need to cure at 750 degrees. I put it in the oven at 500 and it worked fine. The smell wasn't too bad either. Just give the wife $50 and send her shopping for a few hours and she'll never know.

 

[Speedo]

Hammered,
I'm going to quote the army drill sergeant from "Officer and a Gentleman" :

"I can't believe what I'm seeing here"

First: answer yourself this question: why? If you want an Indian, get an Indian (ps see the movie World's Fastest Indian - awesome).

2nd: In my early days, I tried to turn a 72 Datsun 510 wagon into a sports car (porsche was my dream), then later, a VW GTI into a sports car (again, porsche was the goal). Finally (and fortunately) a friend of mind finally posited to me this gem: "If you want a Porsche, why don't you just buy a Porsche and be done with it?".

Wisest advice I ever got.

Look, without going into all sordid details, I have a whole sh*tload of experience to back this up, besides the 510, there was teh 72 351W Merc Montego (think Gran Torino), the '84 VW GTI, the '78 Porsche 911 that I wanted to be a "turbo" (wtf was I thinking? I spent a sh$$itload of $$ on that thing and it ran no better - and that would be still great - than the day I bought it)), then 78 F150 truck for which I bought and built a 351C4v (um yeah that would be a Pantera / BOSS 351 Mustang motor) for a ridiculous amount of $$ only to blow it up a year later as it was not the right fit as far as motor to ride.

So if you choose not to listen to me, it wouldn't be because I haven't paid my dues / sunk enough $$ into hotrod projects over the years.

Anyway, I now still own and love my old GS750 which still runs "like a r*ped ape" on good days, just like 20 years ago. And I've ridden tons of bikes that are all awesome, but I'll still take "Suzi". [I have to admit that that the Ducatis are so tempting that Suz will prob eventually get a "friend"]. Also, I finally bought a "stock" (old - 12 yrs old) porsche 911 a few years back and you know what? All those old guys were RIGHT! Bone stock and the thing is WAY more awesome than anything I threw $$ at over the years.

Ok, now specifically about exhaust / headers. You are reading this post from a geek...er...guy who has not only thrown a buttload of $$ at stuff but actually read like all the hot rod books (most David Vizard and Smokey Yunick, etc, etc. etc.). Exhaust flow is a science and the people who know what the hell they are doing (Yosh, Kerker, V&H, etc) flow and dyno test the crap out of thier stuff b4 offering for sale. You think you can just cut / bend and get a couple of email "amens" from other people just as non-knowlegable ("ignorant" sounds too mean and that is not how I want to sound here) and you have a good/optimized exhaust? If you don't really care about power & throttle response, then go for whatever look you want but don't kid yourself -or let anyone else via "sounds good in theory" emails - into thinking whatever you're doing is adding HP.

 

[Speedo]

ps As far as header / exhaust coating. Do not do yourself. Don't D*ck around and send it off to JetHot (or EQ). They have all the powder coat paint booths and ovens and will do it right. My Gs750 JetHot coated Yosh headers have lasted 20 years and counting. No rust. No problems. My Ford 460 truck headers got Jet Coating (silver as opposed to black on Suzi) 5 yrs ago as well....look perfect and brand new. Just an opinion from someone who has spent a buttload of money on various hotrod stuff (and a ton of my own time too) over the yrs and knows what's what and what's worth it....

 

[Hammered]

Thanks andrew but I dont want an Indian, Im just looking whats called a log ram Exhaust like the ones 1940 Indians used. My question was about how testy the GS was about backpressure. Ive been doing this style of stuff for a long time, so Im sure the fabrication wont cause me any issues. As far as spraying the coating, Ive done that sorta thing for a long time as well. Its a simple matter and really its the point of my building a Suzuki. Ive never done one so Im doing all of it to be able to say IBM ( I Built Mine) Just one of those things I consider as much worth as the ride when Im done.

 

[Speedo]

Ok hammered. Looks are looks and are cool, and basic theory that if u give the motor any kind of decent 'drain' (i.e. exhaust), it will work pretty well.

Just sayin' that don't expect anyone on this site to give you good advice on "how sensitive" gs's are to backpressure, etc? C'mon man. Do YOU have sophisticated flow/back-pressure testing eq in ur garage? Neither do we (at least most of us as far as I know/have read).

 

[Hammered]

Ok hammered. Looks are looks and are cool, and basic theory that if u give the motor any kind of decent 'drain' (i.e. exhaust), it will work pretty well.

Just sayin' that don't expect anyone on this site to give you good advice on "how sensitive" gs's are to backpressure, etc? C'mon man. Do YOU have sophisticated flow/back-pressure testing eq in ur garage? Neither do we (at least most of us as far as I know/have read).

Actually, yes. The main reason I came here to ask the tech question was because some of the guy and gals here know more about these bikes than the mechanics back in the day. And i understand flow restriction on both ends. knowing if the GS is overly sensitive to different levels of back pressure would tell me to build a smaller or larger header chamber and how many and to what degree all the different angles in the exhaust should roughly be. No, I cant, with the gear in my shop, test the intake to the exhaust CFMs. But I cant build my cold air intake roughly the same volume that my exhaust main header tubing will be. I mean I wasnt asking for a flowchart on the stock numbers these bikes ran 30 years ago, but knowing what others who have owned them experienced helps.


And while on the subject. Anyone ever read about of try running a cold air intake on one of these? Im doing it (A) to hide the intake system a little and fill in some of the open/empty space and (B) cause I havent seen anything on someone else doing it. I did say I was building a custom.

 

[Steve]

Ok hammered. ... Do YOU have sophisticated flow/back-pressure testing eq in ur garage? Neither do we (at least most of us as far as I know/have read).

You would be surprised to see what he has in his garage.

I've been there, I've seen it.

.

 

[Hammered]

You would be surprised to see what he has in his garage.

I've been there, I've seen it.

.

You still in Florence or did you finally get to go home?

 

[Speedo]

wow - talk about being summarily humbled. Genuflection 2 u.

btw, have you seen "World's Fastest Indian"? Seriously. Have you? See it, you'll get all teary eyed and thank me.

anyhoo, see my other posts that may (or not - if not, sorry) be of interest to u...

http://www.thegsresources.com/_forum/showthread.php?t=149740

May I very very humbley ask this question(?): having seen ur basic concept (looks great and really cool btw) which is a leather-british-Brooks saddle-bicycle seat type of thing with an upright riding position, what is the point of obsessing on exhaust flow characteristics etc? Your ride is an aerodynamic brick/dinosaur?

I mean, if I built the coolest looking but Barn-Door-ish hotrod (and there are a LOT of 'em out there), even if I have CFM flow bench (for intakes and the like), and whatever the thehelll they use to flow test exhaust pipes, my "brick" ride (much like a bike) would not be able to take advantage beyond apx maybe 50-60mph.

I guess I'm just asking since I've wasted...err, I mean "invested" SO much $$ in various hotrod projects over the past 25 years.

Ok, fine, assuming you are a hotrodAtheist and won't listen to reason (I never did...well, now i do...):
- so you want "real" flow numbers in CFM off of an official "flow bench" as far as head (combustion chamber), intake, exhaust, etc. Well, may I suggest contacting Vance and Hines or Yoshimura? Their records speak for themselves. These guys know (or used to know).

We average pukes in this forum (again, if I'm off, surprise me y'all...) just want our rides to work, work good/right, and work good/right for the long haul (i.e. not break every other week like drag-racer stuff). Ok and maybe have the rest of us be impressed with your work/ride. Getting something old to look good AND work good is hard. VERY hard and very time consuming. The bikers/rodders who spend all the time and energy to do this deserve a lot of credit.

Rant over.

 

[GregT]

For what you want - a cruiser type power - the system you suggest will work reasonably well IMO.
The CV carbs are quite sensitive to pipe changes yes, but there's a lot of info here which may help.
Your twin tail pipes & mufflers will act as a pressure bleed resistor which can be tuned - washers with different size holes would be easy.
There will not be any exhaust scavenge/crossover problems unless you're planning on running an ungodly long duration set of cams - a six is the only setup which has problems with a collector this close to the ports.
Be careful with your cold air setup - try not to pressurise the airbox as this will cause more problems than the exhaust.

Greg T

And I met Burt Munro a couple of times - he wouldn't have gone on line to ask, he'd have just tried it !