Topic: to all the pod and pipe people, past present and especially future.

[phil71]

Last week, a customer brought me a pretty solid 1980 GS 550 Suzuki. It didn't run awesome to begin with, but he had a brand new kirker 4-1 and K&N Dual-flange pods. I really should have gotten it running great in stock trim first, but I was going thru the carbs anyway..  Also, by-the-hour labor rates meant that I'd be saving him money trying to get it all done in one shot.
   Sure enough, the carbs were #$%*ty.. .and the nifty little kit he bought had new jets and tuning hints for that bike and these mods. Pretty slick.
   The bike did run okay, but not great.. so I went up on the needles.. that helped. Still, not perfect. then up ANOTHER jet size.. which made for 110s. now, 110s are huge for a little 550...
  STILL, not running great. WTF? Well, it turned out that to really get it right, using about 10" of goriila tape wrapped around the pods did the trick... and the bike ran fantastic. BUT, I seriously doubt it was any faster than stock. That the customer THOUGHT it was faster, was only due to the fact that he had never ridden it running correctly, or on all 4 cylinders for that matter.
   The carbs came on and off 6 times in all, and the customer was very happy when he rode away, but this got me thinking, and I wanted to share some thoughts with all the younger guys who don't understand why these 'performance mods' are impossible to tune, and don't provide the gains they think they're entitled to.

  An engine is an air pump. On a VERY SIMPLE LEVEL, it's reasonable to assume that if you provide it access to more air, and the ability to get more air out faster, it ought to make more power.
  The problem comes from not thinking about what's really going on during all these strokes.
  Even though there's the possibility for more flow.. the cam still keeps the valve open the same distance (lift), for the same amount of time (duration). THe lobe center is still the same, so the useful horsepower and torque curves are still in exactly the same RPM range.
  Just because you can get more volume of air and fuel in and out, the compression ratio is still the same as it was, and can only ever squish but so much air and fuel together to make the 'charge' that gets lit off.
     All you'll really do with these performance mods is make it tougher for the engine to create the right balance of pressure differential from the outside atmosphere to the vacuum the engine is trying to create.
At best, with no modifications to the cam or pistons, you will really only use a little more gas to make the same power it already did, and cost yourself a lot of time or money to make it run like it did before you did any of this bull$#it.
     
    Wanting it to look and sound cooler are 100% valid reasons for doing this work. OWN THAT, say it out loud... "I THINK IT LOOKS COOL". Don't delude yourself into thinking there's going to be any appreciable difference in performance.. In fact, expect it to run worse until you do the work to make it behave more like a stock bike. (I think that might be one of the definitions of irony.)
   We all know (or know of) people who put pods and pipes on their old beater and didn't have to do anything at all.. and it just ran.
        To that I say.. "that's not the whole story". Every brand and style of filter and exhaust is different, every combination is different.. and some folks get lucky.. some folks also bought a bike that is a frankenstein to begin with. Maybe it was upjetted 20 years ago.. but no one knew about it.. or, some yahoo put a set of carbs from a 750 on a 550...
  You will only ever know someone who lucked out in this way. You will never actually be that lucky. Except for 'Lucky" here on the boards.

   

[Deltarider]

Excellent post. BTW, just the other day I pointed out to a lady stranded at a traffic light how to adjust her clutch cable. One of them old GS 550 Suzuki's. Incredible bikes, reliable and bulletproof. I told her to keep it forever.

[754]

 That is one point of view, I think they would have stopped making them already if they were useless.. I will say this though, if idle qualityand performance up to 3500 rpm is most important to you.. maybe stick to stock..

[Deltarider]

That is one point of view

Well, it's a bit more than that, don't you think. Your's more like a point of view.

I think they would have stopped making them already if they were useless..

O, but they're far from useless. They're very handy to get money out of pockets of 'Cool' and the gang.

[Duke McDukiedook]

BUT THEIR KOOL MAN!!! DON'T HARSH MAH BUZZ, BUZZKILL!!! 

[phil71]

I never said they were useless. And if people did work to the engine internals those parts would be integral to better performance. But in stock form, not so much. That's not a point of view. It's physics.

[Eydugstr]

Sometimes it's not always cosmetic.  I really wish someone would come up with a 4 into 1 exhaust for the older Kawasaki Concours, mainly because it would make rear tire changes easier (You have to remove the exhaust cans to make clearance for the rear axle).

But yeah for the most part, I'd stick with the stock airboxes, if one's available.

[Jerry Rxman Griffin aka MuthaF'er]

Better airflow is only "better" if it was restricted to begin with. More air means more gas means bigger bang means more HP, as long as the air to fuel ratio is optimal. As Phil says it will only do so much with what you start with. Give it a reason to consume more air then give it more air. Also keep in mind the turbulence our air filter boxes help to eliminate.

Cool is cool 

[Deltarider]

Also keep in mind the turbulence our air filter boxes help to eliminate.

Right and exactly that is often overlooked.

Cool is cool 

Right again and drool is drool and sometimes money is burning in people's pockets. Cool people, cool.

[lucky]

QUOTE:

" so I went up on the needles" I have no idea what that means.

Does that mean you moved the needle up?
Does that mean you moved the clip up one notch?  Very confusing.
 Can you just tell us which of the five notches the clip is on?
If the clip is the middle notch that is VERY clear.

Moved up on the main jets to #110's from what size? unclear.

[TwoTired]

....
  An engine is an air pump. On a VERY SIMPLE LEVEL, it's reasonable to assume that if you provide it access to more air, and the ability to get more air out faster, it ought to make more power.
  The problem comes from not thinking about what's really going on during all these strokes.
  Even though there's the possibility for more flow.. the cam still keeps the valve open the same distance (lift), for the same amount of time (duration). THe lobe center is still the same, so the useful horsepower and torque curves are still in exactly the same RPM range.
  Just because you can get more volume of air and fuel in and out, the compression ratio is still the same as it was, and can only ever squish but so much air and fuel together to make the 'charge' that gets lit off.
     All you'll really do with these performance mods is make it tougher for the engine to create the right balance of pressure differential from the outside atmosphere to the vacuum the engine is trying to create.
At best, with no modifications to the cam or pistons, you will really only use a little more gas to make the same power it already did, and cost yourself a lot of time or money to make it run like it did before you did any of this bull$#it.
     
    Wanting it to look and sound cooler are 100% valid reasons for doing this work. OWN THAT, say it out loud... "I THINK IT LOOKS COOL". Don't delude yourself into thinking there's going to be any appreciable difference in performance.. In fact, expect it to run worse until you do the work to make it behave more like a stock bike. (I think that might be one of the definitions of irony.)
   We all know (or know of) people who put pods and pipes on their old beater and didn't have to do anything at all.. and it just ran.
        To that I say.. "that's not the whole story". Every brand and style of filter and exhaust is different, every combination is different.. and some folks get lucky.. some folks also bought a bike that is a frankenstein to begin with. Maybe it was upjetted 20 years ago.. but no one knew about it.. or, some yahoo put a set of carbs from a 750 on a 550...
  You will only ever know someone who lucked out in this way. You will never actually be that lucky. Except for 'Lucky" here on the boards.

Nail hit squarely on the head.  Well formed and reasoned post.  I've been trying to relay this same message for years.
I did a "What is wrong with the stock air box" post, and I did an "Understanding duct physics" post to get more people to understand what it was they were doing with the physic when they did a "style" change.  For the most part, since it didn't coincide with their preconceived assumptions, it just went over their heads and it was generally agreed that shooting the messenger was the most appropriate reaction from the fad followers.

I will add that the inlet duct physics are the primary determination for jet sizes on a stock bike.  Shorten the duct and more atmospheric pressure reaches the jet orifice exit, naturally reducing fuel flow.  Novices delude themselves that increasing jet size has given them more power and with a louder bike it simply must be faster.  Which is just wishful thinking, rather than objective thinking.

I will concede that at or above red line rpms where intake velocities are very high, a longer intake runner has more drag, and the filter membrane itself begins to take on a aspects of a solid wall, which reduce available oxygen that would otherwise be available for combustion.
You might be able to eek out 1-3% more HP with intake and exhaust mods made to the stock engine at red line.

Further, the inlet and exhaust changes sometimes become mandatory for an engine with a cam change, displacement increase, or head work, that has the natural ramification of NEEDING more oxygen/gasses to traverse inlet and exhaust system to make them most effective.

PODS and pipes are cart-before-the-horse actions, which in most instances, diminish the package that came from the factory in one way or the other.  ...unless, of course, you are lucky.   

Cheers,

[phil71]

Lucky, I think you're missing the point. The needles went up , the clip went DOWN.. so what though? I'm not asking for advice for how to get it running right.

[Deltarider]

Both Phil's and TT's posts here are excellent and make I don't know how many other posts redundant.

[lucky]

Lucky, I think you're missing the point. The needles went up , the clip went DOWN.. so what though? I'm not asking for advice for how to get it running right.

I was interested in what you did. Sincerely. I am not going to give you advice.
You seem experienced enough to find you own solution.

I just like to know the facts.
Sounds like you made all of the right choices to me.

BTW did the duct tape stay on the filters?

The CB750 Honda Airbox on the 1978 only has an opening about 3.7 sq inches !!
The openings on the 4 carb intakes totals 1067 sq inches.
The airbox and filter are like a giant choke.

[MRieck]

Last week, a customer brought me a pretty solid 1980 GS 550 Suzuki. It didn't run awesome to begin with, but he had a brand new kirker 4-1 and K&N Dual-flange pods. I really should have gotten it running great in stock trim first, but I was going thru the carbs anyway..  Also, by-the-hour labor rates meant that I'd be saving him money trying to get it all done in one shot.
   Sure enough, the carbs were #$%*ty.. .and the nifty little kit he bought had new jets and tuning hints for that bike and these mods. Pretty slick.
   The bike did run okay, but not great.. so I went up on the needles.. that helped. Still, not perfect. then up ANOTHER jet size.. which made for 110s. now, 110s are huge for a little 550...
  STILL, not running great. WTF? Well, it turned out that to really get it right, using about 10" of goriila tape wrapped around the pods did the trick... and the bike ran fantastic. BUT, I seriously doubt it was any faster than stock. That the customer THOUGHT it was faster, was only due to the fact that he had never ridden it running correctly, or on all 4 cylinders for that matter.
   The carbs came on and off 6 times in all, and the customer was very happy when he rode away, but this got me thinking, and I wanted to share some thoughts with all the younger guys who don't understand why these 'performance mods' are impossible to tune, and don't provide the gains they think they're entitled to.

  An engine is an air pump. On a VERY SIMPLE LEVEL, it's reasonable to assume that if you provide it access to more air, and the ability to get more air out faster, it ought to make more power.
  The problem comes from not thinking about what's really going on during all these strokes.
  Even though there's the possibility for more flow.. the cam still keeps the valve open the same distance (lift), for the same amount of time (duration). THe lobe center is still the same, so the useful horsepower and torque curves are still in exactly the same RPM range.
  Just because you can get more volume of air and fuel in and out, the compression ratio is still the same as it was, and can only ever squish but so much air and fuel together to make the 'charge' that gets lit off.
     All you'll really do with these performance mods is make it tougher for the engine to create the right balance of pressure differential from the outside atmosphere to the vacuum the engine is trying to create.
At best, with no modifications to the cam or pistons, you will really only use a little more gas to make the same power it already did, and cost yourself a lot of time or money to make it run like it did before you did any of this bull$#it.
     
    Wanting it to look and sound cooler are 100% valid reasons for doing this work. OWN THAT, say it out loud... "I THINK IT LOOKS COOL". Don't delude yourself into thinking there's going to be any appreciable difference in performance.. In fact, expect it to run worse until you do the work to make it behave more like a stock bike. (I think that might be one of the definitions of irony.)
   We all know (or know of) people who put pods and pipes on their old beater and didn't have to do anything at all.. and it just ran.
        To that I say.. "that's not the whole story". Every brand and style of filter and exhaust is different, every combination is different.. and some folks get lucky.. some folks also bought a bike that is a frankenstein to begin with. Maybe it was upjetted 20 years ago.. but no one knew about it.. or, some yahoo put a set of carbs from a 750 on a 550...
  You will only ever know someone who lucked out in this way. You will never actually be that lucky. Except for 'Lucky" here on the boards.

 

Funny....i worked on a GS550 with a Kerker and the same filters several years ago. There were vacuum leaks at the boots , float needles shot etc etc. Worn out parts replaced, valves adjusted etc. I ended up have to go 2 up on the pilot jets and something like 4 sizes up on the main jet. Needles were shimmed as well. One thing I have found is the stock needle shape has barely any taper...same with GS1100, 1150's etc. They can take large jets. I remember seeing 190's or something close in an 1150. A dynojet kit is really necessary with those filters and the OEM GS needle shape....... at least that is what I've found.
  Dynojet claims 10% to 15% increase with the Stage 3 kit/individual filters. They also say there will be no increase on some engines and driveability will be compromised. I'll add fuel mileage can go down the toilet. Stage 1 kits are claimed to give up to 5% increase on most engines. That would include the OEM style K&N filter.
  Dynojet does provide dynocharts showing before and after which as close as you'll get to an individual filter vs airbox/OEM filter comparison today. Of course their kits are made for CV carbs too. And 2 cam engines in general with a stock, higher state of tune than an old CB750.
 As was mentioned earlier, increasing displacement 30%, 40%, 50% with a cam that has about .100 more lift and a highly modified cylinder head changes the game completely. You are looking at a different set of carbs at that point.

[phil71]

Lucky, I wrapped half of the filters with gorilla tape, used a razor blade on the edges. The tape is like a half moon from the inside, so it does not show. THe tape will stay on a very long time. I would have kept going up in jets, but to be totally honest.. 110s were already bigger than my gut tells me an engine that size ought to have. Believe it or not, I use restriction a lot for tuning, it saves time. Just trying some tape, removing, adding makes getting jetting in the ballpark a lot easier.
In this one case, I felt it better to slow the air down than to continue opening up the main jet. Idle mixtures were sufficient to compensate, but the tape restrictions actually help in that dept too....

[TwoTired]

The CB750 Honda Airbox on the 1978 only has an opening about 3.7 sq inches !!
The openings on the 4 carb intakes totals 1067 sq inches.
The airbox and filter are like a giant choke.

MATH CHECK!  I expect you will go back and correct all the erroneous posts stating 1067 sq in carb intake area?

The carb venturis are 28mm in diameter.  (widely published)
Area = πR²

28mm = 1.10 inches
r = d/2
r= .55
.55x.55=0.303 * 3.14 =0.953 sq inches
4 carbs total venturi area =  3.815 sq inches.
This, of course, only applies when the carb slides are wide open.  Further, velocity matters a great deal in the volume of air passing through any duct, as well as the pressure drop that occurs during the transition.

Still to calculate is the area of the intake runner, and the area of the open intake valve, which is only open 1/4 of the time.

Care to calculate the exhaust pipe exit area?  I need someone to post an accurate exhaust pipe outlet diameter for the 77-78 CB750K model.

Cheers,

[phil71]

He blinded me with science!

[Rookster]

You might be able to eek out 1-3% more HP with intake and exhaust mods made to the stock engine at red line.

Really?  Dunstall published numbers that were much higher than 1-3% at many different rpms with only an exhaust system change and 115 main jets (everything else stock):




How do you account for these increases?

Scott

[phil71]

1-3% of 60hp? This proves your point? so ... $500 later you gain 1.2 HP. finding a small downhill grade is a lot cheaper for the same fun.

Stock airbox.. smart.

[Rookster]

1-3% of 60hp? This proves your point? so ... $500 later you gain 1.2 HP.

Math Check: Lets use 67bhp as the published number for a stock CB750.  10% of 67 is 6.7bhp.  1% of 67 is .67bhp.  The highest number Dunstall published was 11.78bhp increase at 6500 rpm.  So 11.78/67x100=17.58% increase.  Now let's assume that the tests were done on a 60bhp CB750: 11.78/60x100=19.63% increase.

The argument isn't cost v. bhp its what can be gotten from a stock CB750 with intake or exhaust changes.  So I will ask again, if any change from stock could only yield 1-3% bhp increase why did Dunstall get over a 15% increase at 6500 rpm?

Scott

[phil71]

only the first 3 years made that much hp.. but, it's interesting how it only says the increase, not the rear wheel HP. Also, you're looking at an ADVERTISEMENT for an exhaust system.  That is how i mostly account for those figures.

[Rookster]

you're looking at an ADVERTISEMENT for an exhaust system.  That is how i mostly account for those figures.

Are there not laws against false advertising in the U.S.?  Why would Dunstall publish actual numbers that could be checked and verified by anyone who was interested if they were lying? 

I'm not arguing that your argument is wrong, I'm merely pointing out that companies have claimed with actual data much higher increases in bhp over stock with only intake and exhaust changes.  Lets say the CB750 tested only had 50bhp stock: 11.78/50x100=23.5% increase over stock bhp at 6500 rpm.  Dunstall had a business relationship with Honda.  Maybe they were encouraged not to print the actual stock bhp numbers of the CB750 by Honda.  There are valid counterpoints to the argument you made with actuall data.  Where is your data that a stock CB750 cannot be improved in bhp with changes in intake or exhaust only?

Scott

[Jerry Rxman Griffin aka MuthaF'er]

"stock Honda system" doesn't sound like stock Honda motorcycle. Sounds like they are comparing their exhaust to a stock Honda exhaust system perhaps on a high performance bike. Advertising! 

[Duke McDukiedook]

Advertisers and corporations never lie, their numbers are 10000% true no matter what you say to dispute them.

There is laws on the books against it.