difference in horsepower R1100RL/R1100RT

[Matthew Miller]

why does the RT make more horsepower than the RL series. Can I modify my RL so it is the same as the RT in Horsepower. The RT makes 90HP and the RL makes 80HP. I know that there are lots of ways to increase horsepower but I want to know the difference between these 2 models of the same motor.

[mneblett]

Back then, the RT/RS were tuned for power, the GS (and I believe the R) were tuned for torque. A popular modification in the day was to install the GS's intake tubes in place of the RT's to increase the RT's bottom-end torque. IIRC, the valve timing was also different.

 

Tuning a R to RT/RS standards may result in a couple more HP, but it also would make the R less desirable to ride, at least to me, due to the decrease in torque in the low-/mid-range, where 99% of riders ride 99% of the time.

[Matthew Miller]

thanks for the information I will keep mine as it is.

[SinNH]

I installed the GS tubes on my RT just for giggles, ugh, awful intake honk with WFO, maybe just a touch of more mid-range grunt, but my bike, with the TPS set up with 0=0 and the TB's correctly balanced, lost at least 10 mph on top end, at least.

Also tryed the different mapping with a wire jumper, the stock set up was best for me.

[Matthew Miller]

from the sounds of things BMW obviously got everything just right the first time. It seems most modifications when tested on a dyno have had little or no noticeable improvement. I am really glad I bought a perfect Motorcycle.

[AndyS]

Congratulation Matthew, But the bikes are NOT perfect.

We love them and live with them, but there are issues. Be ready for them and don't be disappointing.

Issues may include HES lead deterioration, Final Drive bearings, Surging, Gearbox issues, Neutral Switches. etc.

[Jim Moore]

why does the RT make more horsepower than the RL series. Can I modify my RL so it is the same as the RT in Horsepower. The RT makes 90HP and the RL makes 80HP. I know that there are lots of ways to increase horsepower but I want to know the difference between these 2 models of the same motor.

 

I don't know where you're getting your info, but there's no way the RT makes 10 more horsepower than the R. You just can't do that much with a little valve timing and intake tubes.

 

That being said, your R has the same intake tubes as the GS. They are designed for more midrange grunt at the expense of top end power. The RS and RT share different tubes, designed for top end power over midrange. We're not talking big differences here, a few ft-lbs, a couple horsepower.

 

If you find yourself using the top 20% of the rpm range on a consistent basis (like me) you may want to consider swapping your GS/R tubes for a set of RT/RS tubes. You will feel a difference, but not a "Holy crap!" difference. They're easy enough to swap in and out if you like to experiment. I'll bet you could find a set of RT tubes practically for free on this site. Lots of folks have them sitting in the garage.

[Stan Walker]

I don't know where you're getting your info

 

80 HP for R & GS. 90 HP for RS & RT. Thant's according to my 1977 BMW catalog.

 

So you need to let BMW know they were wrong.....

 

Stan

[Jim Moore]

I don't know where you're getting your info

 

80 HP for R & GS. 90 HP for RS & RT. Thant's according to my 1977 BMW catalog.

 

So you need to let BMW know they were wrong.....

 

Stan

 

Where would I even start?

[bmwnomad]

The R & GS have:

- Longer and narrower intake tubes.

- Different cam profiles.

- Lower compression (10.3 instead of 10.7).

- Different exhaust headers (not equal length).

 

These differences from the RT & RS will easily drop them 10 hp.

[Jim Moore]

Raise your hands if you've ridden all those bikes (My hand is up. I've ridden them all extensively). Now, keep them up if you felt a 12.5% horsepower increase in the RT and RS. (My hand is back down. Sorry, no way.)

[bmwnomad]

It helps to understand that horsepower numbers are given as "peak" HP, which typically occurs shortly before redline.

 

I've ridden and dyno'd all those bikes. Both hands up, but then again I dyno various bikes nearly every day.

 

The R and GS have more low end torque and quicker drive due to their different final drive gearing but you can easily feel them start to fall flat at 5.5-6k rpms, where as the RT and RS keep pulling.

[Jim Moore]

I'm intrigued, but I'm still having a hard time believing it. Do you have dyno graphs for an R and an RT saved on the computer somewhere? I'd love to see them. I'm always happy to learn something.

[tallman]

Jim,

Pretty sure those are the published BMW specs in many sources.

The weight difference between roadster and RT would help.

 

This is a pretty neat resource and pg 37 has the 80 HP spec.

 

Covers all models up thru @2007 I think and at the end has total production numbers.

Fun to peruse.

[Stan Walker]

R1100R = 235 kg

R1100RS = 239 kg

R1100GS = 243 kg

R1100RT = 282 kg

 

From 1997 BMW Catalog

 

Stan

[Jim Moore]

Sorry guys, I'm still having a hard time believing it. First, I am skeptical that you can get an additional 10 hp out of an engine with a few simple tweaks. Second, if it were possible, there's no way BMW would leave 10 hp at the factory. If nothing else, horsepower is a valuable marketing tool.

 

I have no confidence in the 80/90 numbers from BMW. If someone has some dyno results that show those bikes on similar days I'd love to see them. (Note: I don't mean that sarcastically. I'd actually love to see them.)

 

 

[SinNH]

Matthew, now see what you have started.

 

 

 

[roger 04 rt]

I don't have a hard time believing that there would be a HP difference between various R1150 engines. After all, horsepower is torque times RPM. So if you move the peak torque to a lower point in the RPM range and as a result torque at higher RPMs drops off, you lose horsepower, pure and simple.

 

On a GS or GSA, since those bikes were marketed with off-road credentials, it makes some sense that BMW would shift the torque band lower. They also delivered those bike with different intake tubes, cams, heads and exhausts. In particular, the longer, narrower intake tubes seem likely to restrict the amount of air entering the engine at high RPMs.

 

All in all a shifted torque band and lower top HP seem likely to me. And as a side note I wouldn't put any faith in the results of an Inertial Dyno test. There are just too many ways to mis-interpret that data. All an inertial dyno tests is how fast a wheel--with about half the resistance of riding on the road--can be accelerated, for a few seconds.

 

 

[tallman]

Jim,

HP back then wasn't a big factor,IMO, wrt BMW marketing, esp considering Euro attitudes/restricions, tiered licenses.

When the went after conquest buyers/came out w/the wedge/redesigned the boxers etc

HP became more of a marketing feature.

Go back and look at the early "new" K bike ads wrt speed and horsepower for their class.

Back in the day it was still reliability, technology (like para/tele/ABS).

 

Again, considering tiered license issues in the world market, it isn't surprising BMW produced bikes to address that.

[Matthew Miller]

I've always know even perfect bikes have their own querks and maintenance issues. that is what makes them perfect for the people who ride them.

[Trullion]

The R & GS have:

- Longer and narrower intake tubes.

- Different cam profiles.

- Lower compression (10.3 instead of 10.7).

- Different exhaust headers (not equal length).

 

These differences from the RT & RS will easily drop them 10 hp.

 

All that information can be verified from Haynes and the book by Ian Fallon that talks about the development of the oilheads (amongst others). The very early RS bikes had bigger valves too. If the RS/RT had the same engine as the GS/R models nobody would have bothered with the intake mod (i.e. putting the GS/R intake tubes on the RS/RT to gain midrange at the expense of the top end). I have done this on my RS. Whilst it does produce a bit more midrange power it is at the expense of the top end rush (in relative terms; it's no R1)I used to get and it also produces a more raucous intake noise. There is a graph floating around on the web of the dyno results demonstrating the torque and bhp figures of the "before" and "after" settings. It is to be found on the RS Owners Forum and was commissioned by a writer for Ride magazine. Next time I have some servicng to do I may well put the originals back on; just personal preference. IMHO to get the same performance as a GS/R the cams would need to be changed too, as well as the FD ratio. (The RS, whilst having the same engine as the RT has a higher ratio FD). Whilst to me there is no doubt that the GS/R and RS/RT do indeed have higher maximum bhp outputs (and the 1100S is higher still at, from memory, 98bhp) these are only claimed figures. Then again, BMW used to be conservative on their claims - not so now, it seems if the actual figures on the F800 forum are anyhting to go by.....