GS intake runners fitted to my 1100S: WOW !!! Pics added.

[Steve1200S]

I thought the point of the mod for the old 1100/1150 RT and RS models was that the inlet pipes from the GS are larger (bigger inside diameter), so alows the engine to breath better....

From the photos, the old S inlets (aka runners) are much larger than the GS replacements.

Unless i have it the wrong way round, and the advantage is a smaller inlet to boost torque....

[Dai wiskers]

I thought the point of the mod for the old 1100/1150 RT and RS models was that the inlet pipes from the GS are larger (bigger inside diameter), so alows the engine to breath better....

From the photos, the old S inlets (aka runners) are much larger than the GS replacements.

Unless i have it the wrong way round, and the advantage is a smaller inlet to boost torque....

The GS inlet pipes are the smaller[thinner] ones Steve

I'm not quite sure how or why it works, but i think having a smaller inlet to the throttle bodies would be working with the restrictive exhaust better, a motor can breath through a small opening but if you restrict the exhaust no matter what you do to the inlet side of things it will never run spot on

A few years ago my then wife [now gone thank f###] bought a Honda RS 250 with a race cam fitted[no rev counter drive and different valve timing] now this bike ran well it had the standard carb fitted but after a motorway run when you stopped at the end of the slip road it would cut out but restart after a few kicks i played around with the jetting this only made matters worse, after a few months of this i drilled four 6mm holes in the end of each silencer problem solved the exhaust was strangling it

I think the BMW cat is pretty restrictive so i do feel the smaller intake rubbers would work well for a boost in torque on a more or less standard bike but i also feel this would cost a couple of horses at the very top end but be honest how many of us are often there
Then again the rocket sprockets i rave about shave a bit from the very top end as well

Nearly forgot Blwyddwyn Newydd Dda All

See i know a few words Dai

[HerrFlick]

I thought the point of the mod for the old 1100/1150 RT and RS models was that the inlet pipes from the GS are larger (bigger inside diameter), so alows the engine to breath better....

From the photos, the old S inlets (aka runners) are much larger than the GS replacements.

Unless i have it the wrong way round, and the advantage is a smaller inlet to boost torque....

Hi Steve.

The GS runners are 2mm smaller diameter (and much longer) for the specific reason of giving the GS more midrange torque in keeping with its intended application.


There are two effects at work:

- higher air colum velocity, giving better cylinder filling
- and with the longer runner, a greater mass of moving air.

This concept has been known for as long as engines have been built.

For the life of me I can't understand how the stock 'S' runner shape is meant to work. For a start it's not only a cone, but one with 'extra' convergence - a no-no as far as air flow is concerned.

I've never seen another engine with anything resembling this sort of intake. Would like to BM's thoughts.


Have a look at the link in my original post.


Cheers

John C.

[Dai wiskers]

All done for looks cost and emission [spelin] control

I took my wife's car for it's first mot Hyundi i10 the emission part of the test involved holding it at 2500-3000 revs for 30 seconds the dam thing runs so week at those revs it took 8 attempts to get it done it was dam near impossible to hold it there
My diesel fiesta surges like hell at 2000-2500 pound to a penny that's where emission test is done on diesels
I know i should know this doing a bit in a local garage but we tend to fix more than service
All the best Dai

[HerrFlick]

Booked in for a dyno run next Tuesday.

Can't stand the suspense.

Cheers

John C.

[Neil178]

You going to do runs with both the S and the GS pipes?
Will be watching with interest.
I have a feeling that the final 1000 rpm will have the S pipes well ahead.
Fancy trying the pipes from your GT? Nice colour as well. I run a GTS for my sins!
Don't forget your ear plugs ...............

[oyster]

Now i can see what you have done i don't think there is enough room in my airbox to get the longer tubes in, but there are a few unmodded bikes out there that may benifit from this mod.
Cheers all Dai

Anyone with the SJ or Val Singleton dump truck air filter will not be able to enjoy this cheap mod. However, I too read that this mod is an easy bolt on power gain for mid range for those with stock air filters.

[el-nicko]

Have I got this right; if you want to fit these 'pipes' you have to junk the standard air filter and rely on that flimsy bit of sponge instead?

[nab 301]

Have I got this right; if you want to fit these 'pipes' you have to junk the standard air filter and rely on that flimsy bit of sponge instead?

Nope, it's just a pre filter to stop road dirt terminally clogging the main filter.

[HerrFlick]

Have I got this right; if you want to fit these 'pipes' you have to junk the standard air filter and rely on that flimsy bit of sponge instead?

Nope, it's just a pre filter to stop road dirt terminally clogging the main filter.

Thanks NAB. That's correct. I ride a lot in foresty-type areas and so pick up lots of small pieces of leaf litter. It makes it's way down between the filter pleats and can restrict airflow without the paper element being clogged. That's what the pic of dirt on the floor is all about.

The stock filter stays in place. Whew!

[el-nicko]

Have I got this right; if you want to fit these 'pipes' you have to junk the standard air filter and rely on that flimsy bit of sponge instead?

Nope, it's just a pre filter to stop road dirt terminally clogging the main filter.

Thanks NAB. That's correct. I ride a lot in foresty-type areas and so pick up lots of small pieces of leaf litter. It makes it's way down between the filter pleats and can restrict airflow without the paper element being clogged. That's what the pic of dirt on the floor is all about.

The stock filter stays in place. Whew!

Oh, right. That's a good idea. I'll try that. In my neck of the woods, it's straw that's the problem. Come hay-making time, getting stuck in narrow lanes behind a trailer is just asking for a clogged filter.

[HerrFlick]

You going to do runs with both the S and the GS pipes?
Will be watching with interest.
I have a feeling that the final 1000 rpm will have the S pipes well ahead.
Fancy trying the pipes from your GT? Nice colour as well. I run a GTS for my sins!
Don't forget your ear plugs ...............

Hi Neil.

Unfortunately not this time (dyno heavily booked).

I'll be looking at the shape of the torque curve vs that of the stock 'S'. It should look the same or better than the one shown in the link in my first post.

Seat-of-the-pants (and tacho) says that the engine is pulling very willingly to 8,000. Exh note has sharpened as well.

I've been puzzling over the why's and wherefore's so looked at the differences between the S, RT, and GS engines. See below:

Valve timing is identical on the S and RT, and the S has higher compression, BUT the S also has 2mm smaller dia valves than the RT and the GS !?!?, but has the higher lift of the lot.

This to me points to the designer wanting high inlet velocity (good cylinder charging), yet he shoots himself in the foot with the shape of the sort intake choob.

Looking at the RS and S fitted with the GS choobs:

I think the S will perform better (a) because it has the higher C/R, and (b) the smaller dia ports will enhance the velocity increase gained from the GS runners.

We'll know on Tuesday. Can't wait.

Lovely cool morning here (25C) so I'm off up the mountains.


Cheers.




BMW R1100S:

Horsepower 98 bhp @ 7500 rpm
Torque 70 lb.-ft. @ 5750 rpm

Compression ratio 11.3:1
Valves 2 x 34 mm intake / 2 x 29 mm exhaust

Intake opens 5 degrees after TDC
Intake closes 33 degrees after BDC
Exhaust opens 27 degrees before BDC
Exhaust closes 5 degrees before TDC

BMW R1100RT:

Horsepower 90 bhp @ 7250 rpm
Torque 69 lb.-ft. @ 5500 rpm

Compression ratio 10.7:1
Valves 2 x 36 mm intake / 2 x 31 mm exhaust

Intake opens 5 degrees after TDC
Intake closes 33 degrees after BDC
Exhaust opens 27 degrees before BDC
Exhaust closes 5 degrees before TDC

BMW R1100GS:

Horsepower 80 Bhp @ 6750 rpm
Torque 72 lb.-ft. @ 5250 rpm

Compression ratio 10.3:1
Valves 2 x 36 mm intake / 2 x 31 mm exhaust

intake opens 10 degrees after TDC
intake closes 36 degrees after BDC
exhaust opens 35 degrees before BDC
exhaust closes 3 degrees before TDC

[HerrFlick]

Have I got this right; if you want to fit these 'pipes' you have to junk the standard air filter and rely on that flimsy bit of sponge instead?

Nope, it's just a pre filter to stop road dirt terminally clogging the main filter.

Thanks NAB. That's correct. I ride a lot in foresty-type areas and so pick up lots of small pieces of leaf litter. It makes it's way down between the filter pleats and can restrict airflow without the paper element being clogged. That's what the pic of dirt on the floor is all about.

The stock filter stays in place. Whew!

Oh, right. That's a good idea. I'll try that. In my neck of the woods, it's straw that's the problem. Come hay-making time, getting stuck in narrow lanes behind a trailer is just asking for a clogged filter.

It's even worse with my 928 Porsche, where I use the same pre-filter idea: the air intakes are about 300mm off the ground at the nose and when wfo the thing sucks 200L of air/sec, so when driving in the same areas all sorts of stuff gets sucked in (apart from the usual leaves, twigs, and small stones) eg grasshoppers, v.small birds, butterflies, plus slow wallabies and the occasional dingo harr hahaha .... not.


Cheers

John C.

[HerrFlick]

Sorry to keep banging on about this BUT:

I've now used 3 tanks of fuel since the GS choobs install, and I've achieved 300-310km per tank, with 1 litre remaining.

bGSc (before GS choobs) I was lucky to make 240km with a litre remaining.

This situation had me scratching about looking for a way to add more fuel capacity, since 240km (150 miles) fell awkwardly and irritatingy short of the range I preferred for the riding I do here. Some US blokes have replaced the ABS servo units with a small aux. fuel tank. Ok - they also hated their 'whizzy' brakes.


Further, when cantering along at 110-120kmh (65-70mph) I've gone to shift into 6th gear... ooops ... I'm already in 6th.

This tells me the engine is running more efficiently than bGSc.

Next Tuesday will tell.

Cheers

John C.

[HerrFlick]

Fancy trying the pipes from your GT? Nice colour as well. I run a GTS for my sins!
Don't forget your ear plugs ...............

Hi Neil... yeah right!

I'm also about to do a cam upgrade on the GT, but in the light of what I've observed with the 1100 I've begun to question the purpose of the variable resonance intake manifold (as sexy as it is) vs well dimensioned intake runners.

In my recent hunting I've discovered a Canadian cam designer, Colt Cams, with a Tri-Flow cam for 4-valve heads. Yeah right - snake oil at 2 miles. Not so. Works on the idea of opening one inlet valve ahead of the other in order to to get a momentary large intake air rush to set up bags of swirl.

With the 32V 928's it's so effective the ignition advance can be taken from 19-20deg to 30+ deg, proving what many engine builders have suspected for some time: that the 32V head dimensions are more suited to 6-litre engines.

Their drop-in GT-upgrade cams are so effective that the RWHP gain is from 280 to 360. }:-O

But at Can$2,200 a set... Arrgh. I could give the 1100S a set of WP double adjustable coilovers for that.

Decisions decisions.

While on the topic of 928's and a GTS, a UK couple emigrated here several years ago, along with their pristine GTS all-options Manual.

Since the 928 community anywhere is small, and the GT/GTS community is even smaller, perhaps you may know of them:

Mark and Julie Goodwin. ex Reading.


Cheers

John C.