GSX1100EX Engine mods/tuning (street use)

[BigPhil]

So, I have an 81EX I bought a few yeras ago. 14 previous owners bit rough round the edges, but it goes. I'm stripping it over the winter and planning on making it a stronger and reliable bike for next year. I'm in Sweden, it's a short season over here :-)

I'm thinking Bandit 600 forks for the front with decent springs and gold valves, probably a bandit swing arm. Not sure about the wheels, the selection is limited over here. It already has Öhlins shocks.

• The engine is an 1170 and the bores look almost new
• Standard cams (looking slightly worn)
• The rockers are worn, will be having them welded and reground by Phil Joy
• Standard carbs
• Pod filters 
• Standard exhaust!
• Clutch has re-enforced and welded backplate and new center basket.

I haven't split the cases yet so I don't know the state of the bottom end. But there were no funny noises and the gearbox was fine.

So, to my point. What are some common sense mods to the engine that will leave me with a stronger and reliable lump for the summer?

• Cams? Which ones? (don't fancy bigger valves, looks very pricey)
• Carbs, which ones?
• Porting, "worth it" for street use?
• Would I need better coils?
• Fancy oil cooler? 
• When do I need fancy head studs?
• Exhaust, obviously. Not many people where I am/ride so noise isn't an issue.

I'm interested in a crisp rorty bike that won't need race bike levels of TLC. I have a KTM 450 for that :-)

Something like this, but a bit "less" so :-) https://goo.gl/hrzSBf

Phil

[Gammaboy]

Well, the spec I've got is ported head with big valves, 1170cc, Cams are a VHR042 on the intake, Cam motion G3s, RS36s, oil cooler (it gets pretty fuckin hot down here in Oz), Dyna Coils (my originals were fucked and breaking down @ about 9,000rpm), a mod to the cases to reduce pumping losses, a mod to the oil pickup to stop pulling air, a welded 2nd gear... It works pretty good.

[BigPhil]

@Gammaboy That sounds like a good way to go. The big valves sound like a kerfuffle and I don't know any tuners over here to do the work necessary though. How were the RS36 es to set up?

[coombehouse]

If Phil joy is doing the rockers why not get him to do the cams at the same time. He can do g3 for sure but for a mild motor he may recommend something else like the yoshi cam profile. Or just spend some money with Roger Upperton for a complete  package. He will do the big valves too if you want them & anything else you want

 

 

Edited December 9, 2015 by coombehouse

[BigPhil]

@coombehouse I might ask him to do the cams. I'd love to go the whole way with valves etc but I'm in Sweden and shipping the head over is a bit expensive :-)

[Gammaboy]

RS Mikunis are a piece of piss to set up.

[coombehouse]

Only problem for some of us (me) is the heavy  spring . In the end I took my RS38's off & went with fuel injection. You're right though RS carbs need very little setting up. 

 

Edited December 10, 2015 by coombehouse

[Mr farty]

RS Mikunis are a piece of piss to set up.

OK Ben any tips for me in setting mine up

[Mr farty]

As far as exhaust systems go Dave at exhaustcraft.co.uk if the go to guy. I'd be looking at external oil lines to the cylinder head from a safety point of view and GSX 750 oil pump gears for increased oil flow. Dyna 3ohm (green) coils with silicine leads and Dyna S ignition are good ideas too.

I'm in Oz like Gammaboy too so have fitted a thirteen row oil cooler to mine for safety's sake. Maybe less neede for it in your part of the world but these big old aircoolers produce a shit load of heat when they've been breathed on so an oil cooler won't do any harm(unless installed in correctly,ie, without the EFE oil filter cover or the little alloy plug if using the original oil filter cover)

Hi flow fuel tap such as a Pingel is a good idea too.

 

Have fun

 

[Gammaboy]

Oh yeah, GXS750 oil pump gears was the other thing. No need for the external lines - they're pointless bling unless you've got a heavy duty stud kit that blocks the oil feed.

My RS's had been fucked with so I could (initially) never get them quite right - then I discovered they'd had a different needle fitted. Ordered correct needle, started at the out of the box setup. I tried a couple of different jet sizes (up and down from stock), picked the one that felt like it ran hardest, Tried adjusted needles up and down to get the mid throttle feeling right, (i think i'm half a notch off the middle), called it done.I think I set the accelerator pump up so it didn't hit till 1/4 throttle to smooth the transition when feeding power back in while cranked over. Really, not difficult. Just make sure you don't do like I did initially and thread your throttle cables down the side of the frame so you can swing the rack of carbs out without having to disconnect throttle cables (I initially weaved through the top of the frame. It was a shit idea).

Or you can take it to someone with a dyno and they'll put a sniffer up it's bum and set it up that way.

I fitted a Pingel - i'm thinking I'll go to a WC 750 or 1100 fuel tap, the pingel doesn't clear what I want to do with a heatsheild. Reality is you can feed plenty of motor with the stock petcock unless you're doing banzai runs at 180mph down the motorway.

 

Edited December 10, 2015 by Gammaboy

[Arttu]

One thing to consider while the engine is open is to get the crank checked and welded. Unless that is done already. 81 cranks aren't welded at factory and I have understood they can twist quite easily when ridden hard.

Like said above you shouldn't need external oil lines unless you are using HD head studs or very agressive cams with stiff springs. And stock head studs should be completely fine with your mods.

 

[Pedda]

Street use you say - I say: get yourself a set of 36mm B12 or GSXR carbs and be happy. Presumed you sort the head, obviously.

Edited December 10, 2015 by Pedda
...makes funny things of say what now!?

[Mr farty]

. No need for the external lines - they're pointless bling

Nothing wrong with bling

 

[Jonboy]

Get it breathing properly have no experience of modern B12 carbs etc so cant comment, but a decent large bore exhaust with an absorption type baffle (not for noise but for a little bit of back pressure) will help massively and also velocity stacks on whatever carbs you choose.......

[Gixer1460]

Why does this MYTH of 'needing a bit of back pressure in an exhaust' persist? It may make the engine a bit more tolerant on the jetting selection, but only because its not working efficiently. I've never known anyone who goes seeking max power say lets throw a silencer on if they didn't have to under regulations! Hey we've got a 10,000hp Top Fueler, lets add an Acropovic and see how she goes? Its FANTASY - back pressure is bad - period! Turbo's create massive backpressure in an exhaust hence lower outputs off boost - its just that the boost over comes the restriction but its still a trade off!

[berty]

Why does this MYTH of 'needing a bit of back pressure in an exhaust' persist? It may make the engine a bit more tolerant on the jetting selection, but only because its not working efficiently. I've never known anyone who goes seeking max power say lets throw a silencer on if they didn't have to under regulations! Hey we've got a 10,000hp Top Fueler, lets add an Acropovic and see how she goes? Its FANTASY - back pressure is bad - period! Turbo's create massive backpressure in an exhaust hence lower outputs off boost - its just that the boost over comes the restriction but its still a trade off!

not sure i would agree with that - least not with a N/A engine . Which from what I have read , is what we are talking about .

from my experience . Ever tried running your N/a bike/car/lawnmower without an exhaust ? Runs like a sack of sh1t . Just my opinion of course . 

[Jonboy]

So, setting up an engine for primarily street use. I would say, to quote Gixer1460 

 'It may make the engine a bit more tolerant on the jetting selection, but only because its not working efficiently'.

Most street engines are a compromise, and as such not working to peak efficiency( i would love to have the resource to enable me to build a blueprinted tight tolerance engine). So perhaps a bit of back pressure would help with everyday street use builds if only to act as an 'efficiency compromiser'. 

[coombehouse]

The reason the vehicle would run badly without an exhaust is because it has been designed to run with one. The intake & exhaust on production vehicles are designed as a system. Change one & you will upset the other. If you had a clean slate & were clever then back pressure is not desirable or necessary provided you were able to build the system as a whole (like motogp, no baffles, no noise probs). Alas this is beyond most of us so we make the best of what we can make or buy. I would use an absorption baffle for noise reasons & then try to adjust the intake accordingly. TBH it isn't worth arguing about really but it passes the time I guess.

 

 

[BigPhil]

So, I'm thinking this:

• 1170 (as now)
• G3 cams or "Yoshi cam profile" (regrind) And welded and reground rockers. £400
• Case breather £60
• RS36 carbs £765 (What the bike cost, pretty much...)
• APE Camchain tenstioner £50
• Jaygui pipe (or Racefit legend if I win the lottery...) £850 / £1350
• Pingel, maybe. Won't be doing that many "Banzai runs at 180" :-)  £110
• Will (try to) get the crank checked and welded 
• GSX750 oil gears, they're very pricey. Worth it for this level of engine? £250!!!
• Dyna 3 ohm (green) coils with silicone leads and Dyna S ignition, possibly. £275

This gets expensive quickly, but hey, the wife wants a horse. For THAT kind of money I could buy and run a Moto GP bike.  :-)

/Phil

 

Edited December 12, 2015 by BigPhil
added ape camchain tensioner

[Pedda]

GSX 750 engines are cheap. For the oil pump gear you better get yourself a complete engine for a 50 quid note. You'll have some spare engine covers in addition. Or just bin the rest.

[coombehouse]

If you can't find a gsx750 engine you can always buy aftermarket hi volume oil pump gears. They are not cheap but a lot less than £250.

Ref your list I would suggest these & a crank  check & weld should be at the top. 

You could save a few ££ by just using a gas tap from Screwfix instead of a pingle. No reserve though.

 

 

 

Edited December 12, 2015 by coombehouse

[BigPhil]

If you can't find a gsx750 engine you can always buy aftermarket hi volume oil pump gears. They are not cheap but a lot less than £250.

Ref your list I would suggest these & a crank  check & weld should be at the top. 

You could save a few ££ by just using a gas tap from Screwfix instead of a pingle. No reserve though.

 

 

 

No chance of a cheap 750 engine where I am. 

I just split the cases and the crank is already welded. The gearbox looks good, to the naked eye anyway.

I'm at that stage where I have two cases and a billion bits (labelled) in various boxes and I'm thinking "Ah crap, am I ever going to get this together again?" :-)

I did all this 28 years ago when the clutch basket went on the way back from Le Mans. The bits took out the crank bearings and a few gears. So I know i'm up to it!

[Mr farty]

I know that these old air cooled motors can get very expensive when upping the performance on them. I probably spent as much if not more money on safeguarding my engine, whether it was deemed "necessary" or not, as much as making it produce more power so that I have confidence that my engine will hold together regardless. This approach was based on many disappointments, ie, breakdowns of my old ET motor which I acknowledge was largely due to my own ineptitiude and ignorance in set up and maintenance ,etc.

I also had my engine assembled by a trusted and respected engine guy here in Melbourne. An expensive approach maybe but I see it as insurance because boy do these old aircooled motors put a big shit eating grin on yer dial when you twist the loud handle. Each to their own I suppose on how far you want to go and how you choose to go about it. Good luck with your project.

[BigPhil]

@Mr farty The journey is half the fun. 

[Mr farty]

Indeed it is. My journey took took me four and a half years to finish.