Another Header Performance Thread

[Nessism]

Ok, so a lot of you guys busted my chops when I posted this thread about header performance awhile back… http://www.thegsresources.com/_forum...d.php?t=135059

That thread referenced series of dyno test showing that a GS1100 with a header and airbox mods showed a modest HP increase over stock at best (2.1 hp), and a power loss at worst. The complaint many of you guys had with that test was that the intake side tuning was not optimized to go along with the header.

Found another old magazine performance test today, in the January 1983 Cycle World, titled In Search of the Free Lunch. This test took a GS1100 and ran a series of dyno pulls after progressively adding a Kerker KR header, removing the stock airbox lid, removing the stock airbox and installing K&N pod filters, and lastly adding VM33 carbs. All dyno tests included CO checking and rejetting so the carb mixture could be verified and optimized.

The bike used for this test was obviously tired but it does show representative gains by adding the equipment noted. They ran another GS1100 at the end of the test and it made 12 hp more than the test mule in the stock configuration so the baseline was verified as low.

I’ll scan this article for you guys tomorrow so you can read it for yourselves, but one of the most interesting things to me is that the results obtained by removing the airbox lid are only 1 hp short of pods. The author also said that the required carb rejetting was only minor with the airbox lid off but with the pods, extensive rejetting (not just changing the mains) was required before the bike would pull properly on the dyno.

Bottom line is that the header and pods was good for 4.9 hp or 6.8%, but the VM33’s are the big winner.

[posplayr]

Ed,
Thanks for that graph. I just recently read the same article somewhere and even have a copy I think??? . Post if you don't mind.

Anyway I think one of the ways to look at these types of studies and perhaps what is overlooked is that these relationships are not additive. What that means is that a pod of a lid on an air box does not add 1 hp regardless of what the other combination of changes is. The improvement works in concert with others.

To be even more specific, if we look at the motor simplistically as a big air pump (as it has seen variously described), then we realize that in making changes we are pulling impediments out an the overall flow capacity which makes performance increase to the next highest flow restriction.

As a simple example, I would figure that the VM33 improvement of 10 hp was only seen with the pods and that full amount would not have been realized with the lid off the air-box. This is basically because when the air box lid was removed, the air pump flow simply increased to the next limit of the stock carburetors. The change to a Pod may have been minimal because the stock carbs were the overall limit, but then when the VM33's were added the extra flow rate of the pods could be realized because the air box flow restriction were now removed.

So if you start thinking in terms of weakest link or lowest flow capacity in the air pump flow chain, the incremental improvements to changes might start to make more sense. This certainly would explain much of the disagreement in observations in incremental performance changes (as this data suggests)and others experience with certain combinations providing great improvements on the track.

The above maybe a bit of a simplification, but we do know that there is no reason to think that each modification creates a fixed incremental improvement by itself. Comments welcome.

Jim

[Nessism]

I'd like to see a test with the stock exhaust and the airbox lid removed. The header by itself didn't add much power but when the airbox lid was removed the bike picked up several HP.

[49er]

I'd like to see a test with the stock exhaust and the airbox lid removed. The exhaust by itself didn't add much but when the airbox lid was removed the bike picked up several HP.

I'd like to see a torque graph comparison on all these combinations.

Everyone's hell bent on more HP, often at the expense of a decent range of strong torque.

When airbox lids are removed, there must be a reduction in lower end torque. If that's not the case, then Suzuki seriously got their intake system design wrong. From feedback and personal experience, this is not the case.

I modified my 850's airbox by fitting a reed valve assy into the bottom of it centrally and just below the filter. I installed a set of stiff reeds that would not open until the vacuum level was relatively high. The reeds are solely there to supply extra air flow at higher rpms. I reasoned that this was the best solution to avoid a loss of bottom end torque, but still gain airflow up top.

After much testing, I have blanked off 50% of the reed intake area to optimise the engines performance and air demands. This would change if I were to fit larger carbs, but so would the bottom end torque!!

[posplayr]

I'd like to see a torque graph comparison on all these combinations.

When airbox lids are removed, there must be a reduction in lower end torque. If that's not the case, then Suzuki seriously got their intake system design wrong. From feedback and personal experience, this is not the case.

!

Is this a similar effect to having loss of torque from an open header at low RPM? My understating is that the loss of back pressure causes the gasses to flow through to fast at low RPM and there is a drop in torque and Hp.

[49er]

Is this a similar effect to having loss of torque from an open header at low RPM? My understating is that the loss of back pressure causes the gasses to flow through to fast at low RPM and there is a drop in torque and Hp.

Slightly different but air flow is still the key.

With a header, it's all about optimising the burn off rate. If the system is too free, the minimal back pressure doesn't allow enough time for the fuel to fully burn off in the cylinders reducing the potential energy/torque available during lower rpms. This is more evident in engines with cams of greater valve overlap than stock. It can take quite high revs before a big improvement in torque is noticed.

With naturally aspirated engine intakes, you're relying on vacuum demand to drawn in the charge. The faster you can draw it in, the more torque you will make. If you have low resistance to airflow into the carbs, through running pods or an open airbox, you slow down the gas flow into the engine at low engine speeds. The intertia of the gas is overcome as the rpms rise until the engine reaches the low end of it's efficiency. This is when you suddenly notice good things happening. Trouble is, you've often reached over 5000 rpm before you get to this advantage.

Engines tuned like this are not user friendly for road use.

[posplayr]

Slightly different but air flow is still the key.

Engines tuned like this are not user friendly for road use.

Thanks for that explaination

[rapidray]

I only have 1 thing to add. A 1400cc GS motor loses torque NO WHERE!!! If torque is what you want, build a BIG motor & stop screwing around with these less than 1100cc MOPED motors!!! LOL!!! Ray.

[rudy]

Hey Ray. If by some chance you find yourself with a surplus of 1400cc engines, please, send one my way. I'd LOVE to try that torque out! And I thought my stock 1000 had decent torque. BOY, was I mistaken!

[sharpy]

Hey looks like me memory is still ok! LOL .....

General chat back in the 80's was carbs are worth about 8hp over stock CV's. Have 29mm smoothies on mine only because my 33mm smoothies had a "mate" borrowed them for his drug habit when he was staying at my place... They say 29s are better for the street but would have loved 33s as i rode my bike with the 33s when is was new as my boss owned it back then and did 2nd gear roll-on wheelies.

http://www.thegsresources.com/_forum/showthread.php?t=137669

[sharpy]

I only have 1 thing to add. A 1400cc GS motor loses torque NO WHERE!!! If torque is what you want, build a BIG motor & stop screwing around with these less than 1100cc MOPED motors!!! LOL!!! Ray.

We are building a 1300cc road race engine at the moment but the boss wont let me take pics. JE pistons, Falicon crank, straight cut gears, ported by boss all going in a Crosby F1 Replica frame brand new from Harris. Ray have you heard of a Dave McClurg? Used to run Australias fastest top fuel bike back in the 80's using a Honda 16 valve engine

[TheCafeKid]

I still like the OTHER graph better...the one that showed the 1100 with the SuperTrapp and the lid off and kit making 98 HP or whatever it was...

[Speedo]

VERY interesting posts, guys. Now, from my car hotrodding days (vw and ford) and having read several very interesting hotrod books -most notably by David Vizard, I have a few things to say:

1. Looking at your gs1100 numbers, I now must seriously question the dyno numbers I paid for/given to me w my current setup which were 90hp peak at rear wheels (columbus, OH, mid 90's, I forget the shop).

2. Indeed, torque is more important than peak HP. The big thing the dyno #s almost never tell you is part throttle feel. My setup before my current setup was a MAC header with baffle totally removed (talk about "wake the neighbors") and carbs jetted dead on. Bike was loud as hell at all speeds, cantankerous as hell at all but full throttle, but absolutely ran like a "rapedape" when wide open.

When I changed to Yosh "race" header with "street" baffle (current setup) I had to rejet. It wasn't as fast but much more civilized at part throttle, lower rpm range, and much easy to ride/more fun. After I changed from 630 to 530 chain along with One Less sprocket tooth (or was that 1 more? I always forget for more acceleration/less top speed), the bike felt about the same at wide open throttle as before. Albeit with lower top speed.

3. I think the peakHP/peakTorque relationship is a bit more complex than 49er and PosPlayr are saying here. Yes, yes, exhaust backpressure is a factor. But also important factors, besides valve overlap, potentially so is valve lift (both intake and exhaust), as well as intake manifold design as far as air speed & restrictions, as well as carb tuning (idle / part throttle / full throttle), not to mention spark, combustion chamber shape/flame front pattern & speed, compression ratio, as well as gas quality and ignition timing.

You can dog the dyno, but it's the only real empirical none "seat of the pants"/not subject to psychological self-brain-washing-into-believing-"bygodyes,I now have more Power" delusion.

4. Unless you have a GS1100 or GS1150 and are the dragracer type, and which dragracers still use to this day (just like Dodge 426 Hemi's), if you want "more" power and a "more civilized" bike WITH the more power, the easiest way to do that is to buy a newer bike (sorry). Any 600 sold in last 5 years will kick the crap out of my hotrodded old late70's/early 80's 750 both in power and weight (and power to weight) and handling etc.

5. Last but not least, if you DO hotrod an older GS, hang in, endure the pains, then you will ultimately have a GREAT running bike that is virtually mechanically bulletproof, cool looking, great sounding, you can ride with anyone to anywhere, AND be able to "run with the kids" (i.e. today's 600's and 750's) - at least in a straight line against kids who don't quite have your "old guy" skills. Not to mention riding NOT= racing. So what if your bike isn't as fast? Is a '65 mustang not cool regardless?

[posplayr]

I found the following extract from the write up "in Search of a Free Lunch". I guess this section calls into question some of the results. Look at the mains that they say that were expertly selected using $100K of dyno and nox equipment with a ground of experienced Motorcycle tuners. All this is with a stock GS1100EZ (82) with pods/4:1 pipes.

My stock ED with pods, pipes, 0.340 webcams and 1150 carbs had 137 DJ jets (equiv to 127Mikuni) and now with 1166 kit and 20% increased head flow I'm only running 147.5 mikunis getting 32-35 mpg.

I hate to think about running 165's

[jimb12]

Well, I don't know about only 2hp LOL. I'll relate my memories of my friends tired '80 GS1100E. He bought it old/stock and it only ran 111mph in the 1/4 mile. Guys we've known who had these things new back in the early 80's told us they ran 120+ back then. Anyway, state of the motor accounted for. Putting on a VHR megaphone pipe (street model) and a Dynojet Stage 3 with VHR filters made quite a difference, now 118mph. Sure the weight savings could explain a couple mph, but not all 7! Then on the better carburetor idea, running a set of 34 RS flatslides bumped it up 4mph more. And when you're carrying over 700 pounds bike and rider, it takes some hp to gain each mph. I'll run the numbers when I can find the formula, I have it written down somewhere.

OK found the formula. I'm going to start with a bike and rider weight of 750 lbs (estimate) for the stock bike. Using that with the 111mph comes out to 80.05 horsepower. Now with the pipe/stage 3 I'm going to guess 30 lbs lighter, I don't recall exactly how much it was worth but I do recall mine with a pipe was like 508 pounds bike only. Using the new weight of 720 lbs and 118 mph trap speed gives 92.33 horsepower. Finally with the flatslides, same 720 lbs and new trap speed of 122mph gives 102.04 horsepower. Conclusion, looks like the pipe/jetting was worth 12 horsepower, and the carbs gave over 9 more than that.