Hmm. GS intake tubes? Snake oil or miracle elixir?

[basketcase]

So I'm getting my head around the history of this RT I bought and find that it has GS intake tubes in it.

 

Two main questions -

1. What is the supposed benefit?

2. What are the potential (or real) downsides?

 

Personally, I'm not much on tinkering with stock states of tune, as I think the automotive and mechanical engineers who design these things generally strike a good balance between power delivery and performance for the design of the bike.

 

Besides that, 3 mph additional top-end on a bike that will already do 125 mph or better is useless because (1) it will already go fast enough to get you a big ticket anywhere one rides in the US and (2) because it will not outrun the helicopter the LEO is in.

 

So -- what about this modification? The bike runs fine to me but as it is my first RT I really don't have anything else to compare against. If there is a benefit to the mod I probably will never appreciate the difference.

 

And to the second question, is there a downside to the modification? (Intellectual honesty demands counting the cost both ways).

 

For example, on the DR650's (my other bike) some riders will boost the low end by opening the intake and changing the main jet (CV type carb) to get a richer fuel mix. Yes, they get a bit more grunt on the low end but there is a down-side. The richer mix and higher velocity of air create a "wash" effect on the cylinder walls, so that a top-end job shows up sooner over the life of the engine. So we get a bit more grunt today that costs us .... say, $1,200 later for a top-end job.

 

So what -- if any, is the downside to changing the intake tubes on the R1100RT from the factory setup to the GS tubes?

 

If there is not a downside that impacts the reliability or the serviceable life of the engine I'll just leave it as it. If there is a downside I'll probably have it switched back. (The PO did give me a big zip-lock back with all the OWM parts in it.)

 

Thanks in advance,

Rick

 

[EffBee]

Swapping out for the GS intake tubes is THE single largest performance improvement you can do to an 1100RT for under $500.

 

First, the engines on the RT and GS are almost identical. The GS, however, has more low-end and especially mid-range punch. The RT has more on top end. Swapping out the shorter RT tubes for the longer GS tubes, will noticeably punch up the mid-range, especially between 3500 and 5000rpm. Actually, what it does is gets rid of a dip in the torque curve from which the RT suffers at those rpm.

 

When you ride the bike, you will notice that it pulls stronger and smoother, but has lost that mid-range "hit" that takes place as the engine climbs out of that torque dip. The dip is gone. The engine pulls more evenly, and thus feels much stronger in the rpm range you're going to use it in, 99% of the time.

 

There's no downside (although I noticed a 1mpg dip on both bikes, from 44 to 43mpg on average). You're just increasing the intake air velocity at a lower rpm, creating better cylinder scavenging and filling. That same extended length intake tube is also what works to limit intake velocity and volume at maximum rpm, thus the 3mph drop in top speed. Personally (and as you point out), I don't ride my bike at 131mph very often, so 128 (indicated) is just fine. Note that sophisticated intake systems such as those used on uber-high-end Mercedes and Ferraris, use servo-controled variable intake tract lengths, to achieve the desired low-end/mid-range torque, with the desired top-end power. With the RT, it's one or the other. And you'll LOVE the RT with more mid range.

 

I did it to my first 1100RT and it was the very first modification I made when I bought my second (and current) 1100RT. Just buy the tubes for the 1100GS and be sure to replace the skinny o-rings for the throttle-body-to-intake-tube junction (the ones that fit over the throttle body intake bell).

 

This goes back a ways, but way back at the first Tech Daze, around Labor Day, 2000, we actually did roll-on tests on an uphill section of NV93, outside of Boulder City (Las Vegas). The bike with the intake tube swap, rolling on from 3000rpm in third gear, pulled almost two bike lengths on the stock bike, before shifting was required.

 

You'll have to remove the tupperware, loosen the intake tubes and slide them up into the airbox (wipe the outside of tubes clean first, as well as any grunge built up at the tube/airbox junction). Remove the throttle bodies and then remove the tubes. Insert the new tubes (be aware there's a left and a right), put the throttle bodies back on, put the new slim o-rings back on the throttle bodies' intake bells, then slide the intake tubes back over the throttle bodies and clamp everything back in place. The performance change should be immediate. You'll also notice a bit more intake "honk" when grabbing a handful of throttle.

[philbytx]

Just saw Fernando's post....

 

The GS tube mod is said to increase mid-range performance but will increase the intake noise a little.

 

HERE is a BMWST thread on the subject.

 

HERE is an interesting article on the modification.

 

And HERE is a thread on the subject from ADVRIDER.

 

Consider yourself educated LOL!

 

[Bud]

So I'm getting my head around the history of this RT I bought and find that it has GS intake tubes in it.

 

Two main questions -

1. What is the supposed benefit?

2. What are the potential (or real) downsides?

 

Personally, I'm not much on tinkering with stock states of tune, as I think the automotive and mechanical engineers who design these things generally strike a good balance between power delivery and performance for the design of the bike.

 

Besides that, 3 mph additional top-end on a bike that will already do 125 mph or better is useless because (1) it will already go fast enough to get you a big ticket anywhere one rides in the US and (2) because it will not outrun the helicopter the LEO is in.

 

So -- what about this modification? The bike runs fine to me but as it is my first RT I really don't have anything else to compare against. If there is a benefit to the mod I probably will never appreciate the difference.

 

And to the second question, is there a downside to the modification? (Intellectual honesty demands counting the cost both ways).

 

For example, on the DR650's (my other bike) some riders will boost the low end by opening the intake and changing the main jet (CV type carb) to get a richer fuel mix. Yes, they get a bit more grunt on the low end but there is a down-side. The richer mix and higher velocity of air create a "wash" effect on the cylinder walls, so that a top-end job shows up sooner over the life of the engine. So we get a bit more grunt today that costs us .... say, $1,200 later for a top-end job.

 

So what -- if any, is the downside to changing the intake tubes on the R1100RT from the factory setup to the GS tubes?

 

If there is not a downside that impacts the reliability or the serviceable life of the engine I'll just leave it as it. If there is a downside I'll probably have it switched back. (The PO did give me a big zip-lock back with all the OWM parts in it.)

 

Thanks in advance,

Rick

 

Rick,

 

If you don't take those off immediately and send them to me for safekeeping, your engine will explode, you will lose your hair, your friends will laugh at you and your bartender will call in your tab.

 

For your own good, do this today. I will be happy to reimburse you for postage (medium flat rate box with $200 insurance) and in return you will have peace of mind that those German engineers knew best.

 

Don't listen to those other guys, they don't know what they are talking about.

 

No, no need to thank me. I consider it a public service.

 

[roger 04 rt]

So I'm getting my head around the history of this RT I bought and find that it has GS intake tubes in it.

 

Two main questions -

1. What is the supposed benefit?

2. What are the potential (or real) downsides?

 

Personally, I'm not much on tinkering with stock states of tune, as I think the automotive and mechanical engineers who design these things generally strike a good balance between power delivery and performance for the design of the bike.

 

Besides that, 3 mph additional top-end on a bike that will already do 125 mph or better is useless because (1) it will already go fast enough to get you a big ticket anywhere one rides in the US and (2) because it will not outrun the helicopter the LEO is in.

 

So -- what about this modification? The bike runs fine to me but as it is my first RT I really don't have anything else to compare against. If there is a benefit to the mod I probably will never appreciate the difference.

 

And to the second question, is there a downside to the modification? (Intellectual honesty demands counting the cost both ways).

 

For example, on the DR650's (my other bike) some riders will boost the low end by opening the intake and changing the main jet (CV type carb) to get a richer fuel mix. Yes, they get a bit more grunt on the low end but there is a down-side. The richer mix and higher velocity of air create a "wash" effect on the cylinder walls, so that a top-end job shows up sooner over the life of the engine. So we get a bit more grunt today that costs us .... say, $1,200 later for a top-end job.

 

So what -- if any, is the downside to changing the intake tubes on the R1100RT from the factory setup to the GS tubes?

 

If there is not a downside that impacts the reliability or the serviceable life of the engine I'll just leave it as it. If there is a downside I'll probably have it switched back. (The PO did give me a big zip-lock back with all the OWM parts in it.)

 

Thanks in advance,

Rick

 

If you're running with an O2 sensor and Coding Plug they do nothing to richen the mixture after the Motronic has had time to develop its Mixture Adaptations.

 

The do increase the speed of air moving through the throttle bodies and change the intake resonance, which likely benefits certain RPMs.

 

There is no material downside to changing the tubes but they were designed for a motor with different heads and invalve cams.

 

Don't expect a huge change.

 

Swapping out for the GS intake tubes is THE single largest performance improvement you can do to an 1100RT for under $500.

...

 

I would say THE single largest performance improvement you can make to an R1100RT is to run without a coding plug, or to install an AF-XIED for BMW. I have the prototype, which is plug and play.

 

I'm confident enough about this that I'll pay the two way postage for a trial if the OP would like to try it. You will thank me later.

 

In all seriousness, I'll dig up the link to a guy who did just what I'm suggesting you do. He'd tried everything before finding the AF-XIED. Or you could call Mike Figieski at Beemerboneyard. He made a pile of mods to his R1100RS before finding the AF-XIED, ask him what he thinks.

RB

 

[Selden]

A picture is worth 1000 words:

 

[terryofperry]

Selden

 

What type of run does that represent? Is it 4th gear WOT?

 

Thanks

 

Terry

[mikeR1100R]

I may be wrong but I remember reading or hearing somewhere that the R1100R'S have the GS intake tubes?

[cris nitro]

No, the RS does not have the GS intake tubes. I installed them on my brothers 1995 RS and could definately feel the added torgue. Plus it sounds cooler. Love the added "honk"!

[basketcase]

Thanks to all for the feedback.

 

The bike already has the GS tubes installed and based on what I'm reading in response to the question I can safely leave them.

 

I just need some warm weather so I can ride. Our high here today (38* Fahrenheit) has been passed already today and we about the same in the daytime and single digits at night over the next few days. So it may be next week before I get to take another ride on the thing.

 

 

 

[Joe Frickin' Friday]

The bike already has the GS tubes installed and based on what I'm reading in response to the question I can safely leave them.

 

Definitely safe. My 1999 R1100RT had about 40,000 miles on it when I switched to GS intake tubes; I sold the bike 7 years later with 135,000 miles on it. in all that time, the engine was the healthiest part of the bike; oil consumption was always modest, and I never had any other weird symptoms.

 

You'd have to switch back to the stock RT tubes in order to realize what a difference their making. This is probably not worth the trouble, because you'd very likely turn around after a short test ride and put the GS tubes back in.

[Selden]

The graph is from Rob Lentini's article, and he doesn't provide dyno information. Also, he died a couple of years later...

 

PS: I tried Lentini's suggestion of replacing the cat code plug with a GS unit, and found it to be a miserable failure, as the bike was nearly unrideable when cold, and would stumble badly off-idle — bad news when exiting from a driveway or parking space.

[SinNH]

As said they do increase the mid range pull a bit, the much louder intake "bellow" didn't bother me too much, but what was the deciding point to replace the stock tubes was the substantial loss of top end on my stock RT.

[basketcase]

As said they do increase the mid range pull a bit, the much louder intake "bellow" didn't bother me too much, but what was the deciding point to replace the stock tubes was the substantial loss of top end on my stock RT.

 

My RT does have the intake bellow or "honk" as some others have called it. On my first ride after getting it home I noticed it and thought that either the air filter was missing, or that perhaps the previous owner installed a K&N filter. (Several bikes ago I owned a Gold Wing with a K&N that bellowed the same way under hard acceleration).

 

I received a fairly good set of service records and went back and looked and the air filter was replaced at 40K. Likewise the valves were adjusted at the same service, so other than a precautionary fluids change I think I'm good for a few thousand miles.

 

Mainly I need some good riding weather. This arctic blast that is coming south this afternoon is bringing overnight lows in the single digits to Alabama -- not exactly the kind of weather that inspires me to get out and ride!

 

[flat_twin]

My last oilhead, 2001 R11RS, had the GS intake tubes. For a short time I had this RS and a 99RT to compare side by side. I liked the honk and the extra grunt in the mid range compared to the stock tubes

[Happy Wanderer]

I must be de-sensitized. I put GS intake tubes on my '00 RT and frankly, other than a bit more honk when you really twist the throttle I did not notice these great performance increases at all.

 

I removed them recently after installing an LC-1 from Innovate (AF-XIED's datalogging daddy) and did not notice any performance drop at all.

 

Don't really get what the fuss is about and consider my experiment with them a failure really. When I look at the chart that was posted there's not much evidence of a big increase at all. Maybe I'm missing it.

[Selden]

...When I look at the chart that was posted there's not much evidence of a big increase at all. Maybe I'm missing it.

In real world riding, torque is where the action is, and there is a big hole in the RS torque curve 4000-4500 rpm, which is exactly where I spend most of my time. 83 Nm vs 92 Nm is a full 10% increase. I've never noticed the honk (possibly due to ear plugs), but I noticed the torque difference in traffic immediately after making the switch. The only disadvantage to the GS tubes is that they make removing the throttle bodies and/or air box more difficult.

[Jim Moore]

Here's one thing to keep in mind. I removed my GS tubes because they caused pinging at very high temperatures (like 100+). If your bike starts pinging next Summer you might want to swap tubes and see if that helps.

[drtnsnw]

How do you tell the difference in the 2? Would like to know if mine has them.

 

Chris

[AndyS]

The RT items are about 5" long. The GS ones are nearer 8" long.

 

My own experience with these items were. On the 1100 the mid range punch was READILY noticeable.

 

On my single spark 1150 I did some test rides trying them back to back several times and I found an improvement mid range and also my fuel consumption improved. I think it was due to the bike generally not needing to be used so hard in lower gears.

 

On my 1150 twin spark I have noticed no difference whatsoever. However, I still use the GS items as I had them laying around.

Personally I have not noticed the intake noise change (despite listening for it). I do not ride with ear plugs and my hearing is good.

So my suggestion is go for it, you have nothing to loose unless you are the type of rider that wrings the bike's neck all the time. You may well notice the missing top end and increase in fuel usage. You also may well have the wrong bike for your needs!