Talking to someone at that race I heard that multiple 175s were popped. The theory was the long periods of high RPM was the source. Can’t say from experience though, this was just stuff I heard.
Yeah that’s the closest example I could think of, but at that it’s just a peak vs the long sustained torture of a road course.
Daytona would be a good litmus test. Who’s up for that?
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Any details on the nature of the failures?
I don’t know to be honest, I’d have to ask.
@Rdub3 - many of the 175’s at the event were under our tent, Harden Motorsports Group, and the only failure that I remember was Race Liberante after starting one of the heats on a freshly changed piston with essentially zero break-in. You can guess how that went…lol. There may have been other failures outside of our tent, but as I mentioned above, we adapted the jetting to meet the needs of the half of the track that was full throttle minus one or two downshifts.
@KartingIsLife Yeah definitely not the same, but the 2020 configuration was about as close as you can get on a “sprint-style” course. They removed the T2 barriers completely, and also tweaked the bus stop in a way that made it significantly faster than before. Pretty fast and fun layout, in that it also had a 1st gear true hairpin turn!
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I’ll be watching this for the road racing angle.
Unfortunately no local series allows either of these engines yet. I think they are just waiting for the 125s to all die and then be rid of high speed karts altogether. 
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Hi Mikko
Thank you for your comments. I have read some of your earlier posts on your 175 SS.
Can you just give a bit more information on the piston seizes down the main straight when you lifted? What are the lessons on that front?
Also, what’s going on with the pre-detonation and why the need for the Lamda sensor (rather than just the EGT)? From your separate posts, I know you’ve been fiddling with the squish etc. Is that the reason or something else?
Tom
Hi James and Evan
Thank you for those comments. Given I don’t come from a mechanical background, can you give me a bit for information on the “over rev” - it’s not a concept I’m familiar with?
Just on the aero side with our Superkarts, in my Stock Honda class it’s only a front nose on a KZ CIK chassis, nothing on the rear (other than a rain light and some side number plates). They are the class rules. For the classes above (125 Open, 250 National and 250 International), the rules change and allow for a rear wing, plus a longer chassis is allowed with larger side pods, and I think, 6 inch wheels.
As to the top speed with my CR125, I hit just under 180 km/h (111 mph) coming into say corner 1 at Phillip Island and we go flat through it. Even now I find it puckering albeit C2 as a double apex often causes me more grief. On that circuit I’m running a 23T rear sprocket. The better guys than me (which is just about everyone) can do faster given their entry into the main straight is higher.
Our 250 Internationals are doing about 230 km/h (142 mph) through that same corner - miles above my pay grade.
I am aware of the original restrictor in the 175 SSE. Why was it initially required, and the why was it dropped?
As to long/road circuit running in the USA with the 175 SSE, there is some on the east coast with the AKRA/Woodbridge kart club. I believe there are at least two drivers using the 175 SSE (a very small sample) in their mixed stock gearbox class, but it’s mainly KZ and CR125 (not sure the 175 is technically allowed so they start at the rear of the grid - there’s some YouTube posts). I’m told the 175 SSE is just not marketed that extensively on the east coast compared to the west, so the engine has never taken off (but that’s just what I’ve been told and stand to be corrected).
I have had a good chat to one of those drivers, who is based in Maryland. He’s had a very good experience with the engine running the Tillotson. No mention of getting too lean or any bottom end issues. He runs a 20T rear sprocket from memory and that was causing some chain wear issues. I think his top speed was about 115 mph (185 km/h).
Perhaps an interesting discussion point is whether extended WOT on long circuits is that bad for/demanding on an engine given the fuel mix flow. I’ve heard some differing stories on that front. My CR125 has been (relatively) bullet proof. In five seasons on long circuits I’ve never seized a piston and never had problems with the bottom end. The piston/top end is done once a year (say 15 hours) and the bottom end at two years (say 30 hours). The only problem I’ve had to-date is the piston ring pin dislodging post a re-build - that did cause a mess of the barrel and the head (and replacements required)
Tom
Hello Tom
Well mostly seizing the pistons is due to my lack of experience on 2 strokes. I couldnt tell right off the bat is the engine now experiencing a lean or rich condition - why doesnt it pull hard between the corners. Leaning out the low jet made the engine pull between corners but then expansion chamber would start "ringing " coming off throttle or having a mid throttle situation. So I played a lot between high and low screws - trying to get it pull well between corners and not detonate elsewhere. Peter Haake adviced to fit a stiffer 46gr spring and that solved the issue between corners. I didnt need to turn low screw so lean anymore
I used late Alvin Nunley´s advice on egt tuning when started driving this kart and by monitoring the egt temps from the datalog I could see that temps were raising on the main straight in good tens of degrees C` steps when mixture screws were on the ball park. But I didnt develop understanding how to read egt between corners, mid throttling, am I closer to lean or rich. I could hear now and then not all is well from the expansion chamber - the noise would tell me there will be another piston change due soon if I dont ease off
By raising the compression ratio the egt goes down. I also experienced that by adding compression+toluene the egt moves slowly. Its not a rapidly raising curve anymore like with the low compression head. It was hard to see from the data, by just looking egt, in what part of the circuit - is the engine in lean or rich condition.
For me fitting a lambda brought certainty to my adjustments. I can see exactly while driving what my afr is and make corrections on the fly.
When I bought this engine - the deal included several used pistons and more or less, they are all sand blasted around the edges. So the previous owner has had a detonation issues, I have had a detonation issues but now, my piston crown looks like new
I suspected that the large (1.3mm) squish clearance was the main cause for detonation so started reducing it until piston kissed the head. What I found its a carb issue or in better words lack of knowledge how to tune the carb in my case. Going to tighter squish doesnt cause more detonation on this engine. Tight squish makes the engine sharper but nothing radical. Iame did a good job making this package. Even by modding it way, way past the regulations or spec, performance doesnt change much
Im my experience the 175ss doesnt detonate if the carb is adjusted right. If the piston crown edges have any sand blasted appearance, theres work to be done with the carb
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I think the deletion of the exhaust spacer came about for two reasons. First, it was possibly to help the engine race better against the KZ. Second, it may have been deemed unnecessary once other reliability issues were sorted out with the motor.
I would define overrev as the engines capability to stretch higher into the RPM range past peak power. The exhaust spacer caused a rapid decline in power past 12,800 or so, and it was able to rev much better with the spacer removed.
Interesting to hear that you’ve had issues with the locator pin on the Honda pistons. I’ve seen that a handful of times with the 175 in colder conditions or when people try to warm up the motor too aggressively.
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Evan, with the removal of the exhaust spacer and the “other reliability issues being sorted” (perhaps you could elaborate) I’m beginning to struggle with the rationale to develop the SSE in lieu of the base SS for SKUSA purposes (where the starter motor had to be dropped because of other internal changes - a significant attribute shift and when available provides a major benefit for large grids, particularly in warmer weather when we’re waiting for other classes to clear the track and don’t want to overheat our engines). Thoughts.
Given that detonation is induced by increasing temp to ignition point, & gas heats when compressed & cools when it expands, how would a larger squish band increase detonation, or conversely, a tighter band not increase the chance of detonation?
Good question, and one I don’t have the answer to. I would speculate that the decision to remove the onboard starter is probably aimed at simplicity, i.e. removing the starter makes for fewer parts that can fail.
I’m not sure how the starting grids work where you are, but for us starter or no starter is inconsequential when looking at grid size or weather. Instead it’s just a matter of having someone there to push you if you’re not capable of starting yourself…pretty much everyone has someone there who can push them off the grid. If I’m in your scenario where engines may overheat, then simply don’t start them as soon.
Well Im no race engine builder by trade but my past drag racing hobby with a turbo motor gave some experiences with the squish stuff. I have also read ton of stuff from the internets so who knows whos right
I would say the best way to find perfect squish to the engine you are racing is to do a lot of testing. On a turbo motor good chance if the engine doesnt tolerate advance is that the squish gap is too large. It should be made tighter. Or way, way larger. I prefer tighter as then you induce more peripheral gas to the combustion process and more gas you successfully burn and in time, the more power you make
Loose squish compresses the peripheral gas, the gas heats up. In the meantime spark plug ignites, pressure rises accross the chamber, meets this heated up gas, pressure compresses the heated up gas more, heated peripheral gas auto ignites, starts moving towards spark ignited front and these two fronts collide, make piston look sand blasted around the edges
Tight squish compresses the peripheral gas, the gas heats up, but it is also squeezed out into the more open volute - to the combustion chamber. There will be no gas left in the squish volute that could get heated up - waiting for additional pressure to autoignite it
Very loose quish or no squish at all. Well the aim in a race engine is to burn all the fuel that is fed and only burning fuel produces horsepower. Squish makes the last stir to the pot - to give as much of chance for air fuel molucules to mix and match. Theres a lot of gasoline hanging around in the combustion chamber that is not mixed with air. Gasoline thats not mixed with air doesnt give power - it doesnt burn in the combustion process. Either at all or too late on the power stroke to have any effective pressure - if it burns, most likely continues burning in exhaust manifold or in expansion chamber. Unburned raw fuel doesnt show up in lambda sensor as its a gas analyzer
There are you tube videos that show inside a running engine, there are literally rivers of gasoline entering the combustion chamber in all sorts of forms, liquid, droplets, some is mixed with air.
The tight squish may cause a problem with the spark plug if the ejection stream hits the spark plug and starts taking the spark out. Or the spark may catch the stream and turn into a long arc. Making a long loop between electrode and ground, several mm long. I have found oem stuff has plenty of potential by just tightening the gap
In my drag engine, 1 degree more advance made the engine from sluggish no responsive slouch into a rocket.
What I have observed from fellow competitors : a turbomotor without squish usually drops the power early as rpms rise. It wont tolerate advance at all or very little
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In which case it would be interesting to see if SKUSA allows the base 175 SS to run in addition to the SSE. Anyway, one for you guys.
As to grid logistics here, it’s an issue of shared tracks with other Clubs driving anything you can imagine (from the Formulas, to Radicals, Porsche Cup cars down to Hyundais). Anything can happen.
In Victoria, we race through the entire year (including winter), other than a break over our traditional holiday period from mid December to the end of January. Formal races will start in early February and run until at least November.
If we share a track like Phillip Island, we buy our Club’s time from a master promotor. Time (and thus cost) is of the essence. We may run a mixed grid of up to sixty (60) karts. Most are push start. When we get called to grid up it means we need to be ready to go. Many/most will have started. Fine for most circumstances, but almost without fail, the larger the grid, the hotter it will be and at the last minute in the race in front of us someone (or multiples) will have gone off the track. So we’re stuck while they clear and eventually have to switch off so we don’t overheat (even with the CR125 and its internal water pump let alone all the other classes with their external axle run pumps). Suddenly we get the re-start call up and it’s logistically challenging.
If we are to grow the sport locally, the “KZ TaG” concept for that reason alone is attractive (particularly for more novice drivers/limited support teams). Also the opportunity to restart karts mid way in a race would be good as well (we have plenty of off track adventures and spins in a high speed race and grids of this size - catching the clutch is often easier said than done).
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It was/is the reason. Tom Kutscher told me so in an email response when I’d inquired about it.
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Spencer
Post an exchange I had with Billy Musgrave, my understanding is that there were also some physical changes to the SSE crank for “durability” reasons. IAME did not want to go to the trouble of a redesign (tooling etc), so the starter motor had to be dropped. Billy did also mention that they tried very hard to retain the starter motor for the SSE and the reasons were never really that clear (other than for the words around the crank re-design).
I’m really keen to make available a reliable/durable “KZ TaG” engine option locally. Which goes to your earlier point on the TM KZ10ES - another engine alternative being suggested here but not so easy to obtain at present locally (interestingly, the TM Euro web site makes no mention of the ES version of the engine, but the US site does; not sure if the engine is US specific).
What I don’t want to do is push an engine replacement for the CR125, say the 175 SS and/or SSE, and, despite all of its potential/promise, a couple of years down the track find that IAME is looking to drop it from the line up.
One of the concerns I have is the move away from the engine in the Euro IAME race series towards KZ. Moreover, at least in part, there is indication of a similar market weighting in the US. We are a micro market taker in Australia - so for duration reasons the success of the engine in both Europe and the US is very important.
I had really hoped this engine (even if just the SSE) would really take off, thereby giving IAME the confidence to keep promoting it. It all becomes self-fulfilling then with market criticality/scale.
However, I’m just not so sure now, which would be a really great shame. I hope I’m wrong.
The last thing I want to do is push the concept locally only to find it’s heading for lead weight status in a short period of time. I’ll be in the doghouse, and it does nothing for local market growth and confidence. The last thing we need is a short term CR125 replacement story (which was great while it lasted and a number here, quite understandably, don’t want to give up on it).
Not the first time this problem has come up. I just don’t want to be at the pointy end of a marketing calamity.
So I’m really keen to find that my concerns are a non-issue. I have tried to find out how many 175 SS/SSE units IAME is producing at the moment, but have had no luck. Any thoughts on that front would help.
All a first world dilemma of course.
I actually spoke about it with Will Musgrave via phone over a yr ago (super nice guy, btw), & he liked the starter. We both agreed that EFI would’ve been the ticket, but that’s a whole different discussion. They changed to roller bearings on the SSE, & the diaphragm carburetor, among other things.
Italian Motors USA, run by the Valiente family up here in WA, is probably the main TM importer in the US. That’s where I bought KZ10ES from, & they do seem to move them regularly enough. Interestingly, Claudio Valiente was influential in getting the KZ-ES category started, with it originally appearing in the K9 series.
Curious that it isn’t listed on the Euro site, because I’ve seen it discussed on European kart forums, so I know it’s out there. Not sure what to make of that. I would think if the Australian market demand was there, TM would find a way to support it. It’s a nice engine package.
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Okay, may need to come back to that idea. Thank you.
Just for your information, both the x30 shifter and the Rok shifter are based on 2010 KZ engines. Obviously the x30 they added the electric start and detuned the package. I haven’t looked into that one in depth, but probably a different pipe and maybe cylinder. I know the Rok shifter is based off the Vortex RVXX, bottom end is the same. I just bought the RVXX cylinder, head, and pipe so I could upgrade my Rok to a KZ. I’ll still have the Rok bits when I want to run a Rok event.
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