Drilling the airbox....is rejetting necessary?

[sparks]

Hi Lee. The problem is that, at $60 a time, I couldn't afford to Dyno test the bike after each modification! I believe that improvements, however small, are worth doing because they all add up... "small drops fill the barrel" as they say!

If I had an XS1100 which I didn't want to maintain as completely original, I would fit the K&N air filter, remove the airbox snorkel, fit Iridium plugs, Dyna coils, remove the resistors from standard HT caps, replace the OEM HT leads with carbon-fibre silicone ones, fit a Dynojet stage 2 jet kit (which is meant to run with a non-OEM exhaust and OEM airbox with freeflow filter), replace the OEM exhaust system, if still on the bike, and possibly advance the ignition timing by up to 4 degrees depending on where it's at as standard (I don't know because I never tried it on the XS1100). Doing that lot is guaranteed to increase the BHP of the bike. Any one of those mods on its own would maybe not have such a great effect and would be therefore "hardly worth doing", as some people have pointed out (I agree) but, once you add them all up, you start gaining something worth having.

I really wish I'd had the bike Dyno tested before the mods!

People here in the UK that have achieved that measured 125bhp are gaining virtually 20% over the original setup. More, really, in that the BHP is measured at different points. And that's without any changes to valve timing or cam profiles or anything mechanical. Also, the bikes continue to run smoothly and tick over etc. Once you start messing with cams and putting high-lift ones in, it's a trade-off in terms of tickover smoothness etc.

According to the tester, the peak power is at the usual point... approx 5,000rpm. There's just more power at that point, rather than moving it. Without doubt, the bike is a LOT faster than pre-mods. It was noticeable immediately. The bike is as fast as I'm ever going to need it to go, so that's it now! No more mods until the pipes rot off (I'll have rotted off before then, methinks)

I was fortunate. Our shop had a chasis dyno. We could sort of measure as we went. Naturally a problem with a lot of mods that add power.. Downstream components often cant handle it.. Stock bottom ends often cant endure a lot of "bolt on power" for any length of time as well.. I dont know much about the xs11. I had read the advertisements of the time and (wrongly) assumed that since they were touted as the fastest, they were, indeed "dialed in"..

I'm glad that I'm happy with the power I have ad hand with this puppy as it is.. Would probably kill myself with any more power.

I didnt mean to sound critical.. I was just curious.. Sounds like you have done your homework..

Regards
Lee

[James England]

I didnt mean to sound critical..

Hey! People being critical here can save people from making big mistakes. And that's how we learn. I've had one or two barmy ideas which have been shot down in flames, thank heavens, otherwise I'd probably have done them. That's what's great about this forum.... it's the best there is.

[cywelchjr]

Hey! People being critical here can save people from making big mistakes. And that's how we learn. I've had one or two barmy ideas which have been shot down in flames, thank heavens, otherwise I'd probably have done them. That's what's great about this forum.... it's the best there is.

There is a user on here who doesn't come on really much anymore who went through all the stuff finding out what could be gotten out of these engines and unlike newer bikes where there is quite a bit to be gotten for a pretty small investment, it takes a significant investment of money to break 100HP with these bikes, and the closer you get the more it takes per HP. Most of the stuff you talk about doing only moves some of the HP from one area of the RPM range to another, and you LOSE a lot in the other parts of the range. They really did pretty much get just about all they could out of them without something like turbo or supercharging or similar types of mods.

[James England]

it takes a significant investment of money to break 100HP with these bikes, and the closer you get the more it takes per HP.

Yes 'the law of diminishing returns' is what they call it. I'm surprised re not being able to add anything much to the XS1100 though. They weren't manufactured in a high state of tune, were they?

[cywelchjr]

Yes 'the law of diminishing returns' is what they call it. I'm surprised re not being able to add anything much to the XS1100 though. They weren't manufactured in a high state of tune, were they?

What Dan Hodges found is that they were. A little bit can be gotten, but because of what they were going for, they were tuned to the max that the overall engine tech (heads etc) are capable of. Most of the stuff that you do to modern bikes to increase HP actually causes these engines to lose power, and they actually perform best with the stock exhaust and with the stock airbox.

[WMarshy]

What Dan Hodges found is that they were. A little bit can be gotten, but because of what they were going for, they were tuned to the max that the overall engine tech (heads etc) are capable of. Most of the stuff that you do to modern bikes to increase HP actually causes these engines to lose power, and they actually perform best with the stock exhaust and with the stock airbox.

The key word is diminishing return as stated above. The only way to make significant gains is going to be cams, port and flow bench, and more cc's. I think all of that could be complemented with a set of modernized carbs (like off a ZRX) and a free flowing exhaust. All of the above is going to cost slightly more than what the average xs11 sells for in the US... But I think its worth it.

There are some tricks though. From what I have read from Dan Hodges, if your going for low burdet HP without machining then you can build HP by using 80-81 pistons, 78-79 heads and mix the cams. IIRC, use the 78 intake cam and 80-81 exhaust cam (or vice versa..?). He also said something about advancing a cam one tooth too...

[cywelchjr]

The key word is diminishing return as stated above. The only way to make significant gains is going to be cams, port and flow bench, and more cc's. I think all of that could be complemented with a set of modernized carbs (like off a ZRX). All of the above is going to cost slightly more than what the average xs11 sells for in the US... But I think its worth it.

There are some tricks though. From what I have read from Dan Hodges, if your going for low burdet HP without machining then you can build HP by using 80-81 pistons, 78-79 heads and mix the cams. IIRC, use the 78 intake cam and 80-81 exhaust cam (or vice versa..?). He also said something about advancing a cam one tooth too...

Yes, but Dan Hodges spent that kind of money to just barely break 100 HP, as I'm seeing it it's not worth it, your talking what? Something like less then 1/4 second in the 1/4 mile? The amount of extra HP given the fact that you have to spend double or MORE than you spent on the bike in the first place to get it just ain't worth it as any modern sport bike and even any warmed up Harley is going to spank you even after spending all that money and time, and you STILL won't have the cornering or the stopping power to go with even that modest power gain. Face it, the modern Goldwings can take us these days on anything but the 1/4 mile. I think we can take them there, but get into the twisties and their going to leave us in the dust with better handling and better brakes.

[WMarshy]

Yes, but Dan Hodges spent that kind of money to just barely break 100 HP, as I'm seeing it it's not worth it, your talking what? Something like less then 1/4 second in the 1/4 mile? The amount of extra HP given the fact that you have to spend double or MORE than you spent on the bike in the first place to get it just ain't worth it as any modern sport bike and even any warmed up Harley is going to spank you even after spending all that money and time, and you STILL won't have the cornering or the stopping power to go with even that modest power gain. Face it, the modern Goldwings can take us these days on anything but the 1/4 mile. I think we can take them there, but get into the twisties and their going to leave us in the dust with better handling and better brakes.

Some people justify different things for different reasons. I'm sure there are poeple who have spent that same amount of money on just cosmetics... why not put it towards HP..?

You can get hot cams for ~$500 and one of those cheap 1196 kits for $180... add machining cost and your at ~$900... It would be interesting to see how much power you could get from the 80-81 head and the cheap BB kit using what Dan learned about mixing the stock cams.

[crazy steve]

Dan got more than 100Hp, but what he found was that beyond that number the cost per HP ratio went up sharply while the street manners of the bike went down. One of the strengths of the XS has always been it's incredible torque curve; good power off idle, with it building as the revs go up. From a 30 mph high-gear roll-on, there's still few bikes that can keep up with a well-tuned stock XS... At least up to 100 mph or so...

To get bigger numbers, you'll lose that. The cylinder head design simply isn't good enough to compete with modern designs. You can't install truely high-lift cams (at least without compromising reliability), so your choice is having to increase duration, killing the low end power.

The Japanese manufacturers (bike and car) during that era had the unfortunate tendancy of building really excellent motor designs, but failing to allow for any future development in the design. Basic structural design decisions like cam lobe diameter, cylinder spacing, and crankcase volumes to name just few made it hard or impossible for the aftermarket to upgrade most of these. That's why you saw so many 'clean sheet design' motors from them, and why there was so little 'hard parts' support. To this day they're still guilty of this to a degree. A prime example would be the NASCAR motors; the Toyota 355" motors used are very near their displacement limit as-raced, due to the design. But the Ford, GM and Mopar motors are all capable of displacements beyond 400", there's more 'future' built in.