175SSE vs Modena vs TM KZ10c for “open” racing

2 Stroke Kart Engine Forums
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No problem - Im happy to post results - have learnt a ton about go karts and karting through this forum so I´ll try to give something back.

Thank you for sharing your views and tuning experiences - I believe you are right - the motor needs quite a bit of development/ tests, in many areas, to get any worthwhile gains. For sure just one mod aint going to make 10 hp everywhere. For me this is a tool to study and hopefully learn more about motors

I havent had any problems with bosch wideband sensors before, but was surprised it works also on a 2 stroke without fouling. My tuner is used to afr so Im used to staring it vs lambda

Installed this AIM kit to the mychrom5. The threaded insert has quite low profile - might not have enough material if one wants to shape and contour the insert to match tight radius pipe. I used a taller one - ordered from ebay. Mounted the sensor high so it doesnt gather water, oil etc. Installation was quick, just plug on and choose from the display sensor list what you want to see while driving, lambda or afr. I didnt see afr values in the lap time memory but maybe its doable

We aimed at the dyno to keep afr around 13. We tried to lean out the 10-12.5k rpm area but the motor just didnt want that - it bogged / jolted on the rollers and just made a mess from the run

Went to the track yesterday and tested the kart with the lambda - it was nice to see for once where the afr is. With having little experience with 2 strokes it just made the carb adjusting easy. With egt gauge I could get the temps keep on rising the whole main straight but had no idea where I was at - specially at half throttle - was this a lean or rich condition. Now I know

Ran the day with 0.8 squish high comp. It punches harder than 1.3squish stock head but as there was no top end hp improvement - didnt gain more top end speed - hit the limiter about the same place.

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Did you try seeing if it would pull a taller gear

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I was expecting that maybe it would now hit limiter sooner - took couple extra spare sprockets in case it would need a taller gearing. But after few laps just kept driving - the gearing seemed perfect for good lap time. My local track is quite slow and short. Max speed on the main straight is something like 102-107km/h

I havent had success with tall gearing on this track. Maybe its my driving or kart adjustments but shorter I have made the gearing - the faster I have gone

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Nice lambda sensor! Bosch :ok_hand:

Let’s see, were was I?
Since we are talking about improving engines, I’ll talk a little bit about my DD2 testing adventure, maybe I should say “my frustrating DD2 testing adventure”
So, after doing a bunch of test on a Dyno with a DD2 engine and getting nowhere, I bought the 140cc Kit, tried everything you could possibly try, played around with the squish, played around with the Dellorto carburetor, played around with a modified cylinder head, played around with a modified carbon reed valve (reed valve with double set of reeds, more flow through the inlet system for better throttle response and more punch out of corners, complete with inlet manifold to fit Dellorto 34mm carb), played around with bla, bla, bla, bla, a total of 4 full days of testing on Dyno, constantly comparing the stock 125cc with the “super” 140cc Kit.
Results: Waste of time, waste of money, couldn’t get one single extra hp from the 140 kit, the only difference between a 125cc and a 140cc is that you reach full hp a bit earlier, about 200-300 Rpm earlier. Pathetic if you ask me.

Talked to Italkit, makers of the 140 kit, after I sent them the results of course, they pretty much came to the same conclusion when they tested the 140 kit in their factory.
I asked them “why are some karting dealers claiming that the 140 kit will add about 5 extra hp?” They replied “We don’t know, we never said the 140 kit will add an extra 5hp”
Talked to an old friend who was a professional karting mechanic, he actually won the World Rotax Championship few years ago, as a mechanic, not as a driver, and then he worked for Rotax for a number of years, he said “you would probably need to design a new exhaust pipe to get anything extra”
So, it’s very, very…very difficult trying to get extra power from a two stroke engine without changing a lotttttt of things.

Anyway, it would be very interesting to find out what EGT you get when you have a perfect lambda reading, since you have both sensors. I’ve been wondering about this for a long time…

By the way, you need to go to a track with longer straightaways, I did 140 km/h today with the Super Shifter, about 87 miles/h for our American buddies, you want to experience that speed on a kart, trust me! :racing_car::dash::dash::dash::dash::dash::dash::dash::dash:

PS, I couldn’t agree more, this is right now the best karting forum there is, I wish a forum like this one would have existed when I started out, it would have saved me so much frustration (and money :moneybag:) whatever little I’ve learned about karting, it’s been through trial and error, congrats to the founder :clap::clap::clap:

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I didn’t realize the draft was worth 33 MPH or so with a 125. 120 MPH in draft around a park with nearby trees - that’s what gets your heart beating. :slight_smile:

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It depends on the two stroke in question. Karting engines are reasonably optimized already compared to say a typical marine engine without an expansion chamber exhaust.

For the 140cc Rotax cylinder you would need a larger expansion chamber I’m sure, then tune the length and even steps in the expansion chamber to match.

That said, peak HP doesn’t tell the full story. It’s really the area under the curve that does the work.

I don’t have any numbers for the 175 in road racing (AKA long circuit in Europe) in the US. But to give an idea on VMax a group of KZs running nose to tale bump drafting each other… 119MPH is possible. That’s what I recorded on my Maxter MxO in 2013. I think the gear was something like 19:20 or 19:21. That was three of us on the same team trying to see how fast we could (Safely) go at Gateway Motorsport Park.

But we’re also not meant to bump draft anymore :hushed:

I’ve enjoyed reading this topic so far.

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I was thinking from the perspective of the new setup on your engine. It may pull the taller gear and improve laptime. But since it wasn’t hitting peak RPM any sooner, perhaps not.

The other thing with karts is engine braking. Naturally more engine compression kills some entry speed, leading to folks building (Open 125) engines that were killer on the dyno, but not great on the track.

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“Larger expansion chamber” is probably the answer, there is a YouTube channel, I believe it’s called “2 Stroke Stuffing - building the most powerful two stroke engine” I believe the guy is up in Norway and he’s been building that two stroke engine for, I don’t even know how long, he’s still working on it. I look forward to the day of testing.

119mph wow! That’s about 191km/h, that would erase any lingering thoughts from my mind, now you’re moving into superkart territory, not too many road racing competitions here in Europe, obviously Le Mans and few others but not that many, as you know it’s all sprint racing here, or mainly.
Gear 19-21, that’s wayyyy up there!! I’m using around 18-25 at Campillos International Karting Circuit (South of Spain) It’s enough for me without a seatbelt.
Gateway Motorsport Park, never been on an oval circuit, but would love to! Love to watch the Indy series, way more competition between drivers, as opposed to F1, which is an engineering competition mainly, during the last few years it has become a parade, let’s hope the upcoming changes for the next season will make it more of a drivers competition :crossed_fingers:

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As an aside, I have to wonder if shorter, more technical circuits would enable more passing. HP output is exclusively an engineering exercise.

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We ran the road course\roval at Gateway

UK still has some road racing going on. Outside of that I’m not sure there us much else. I remeber the KZ\ICC championships being at Carole with fondess.

Here’s Grattan Raceway and some bump draft action that’s not meant to happen:

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Wow! Awesome to watch, thanks for sharing! Watched the whole thing, minute 16:25 was really cool, you were kissing the guy in front :clap:
Endless straightaways, you guys have an EGT or Lambda to keep an eye on what’s going? And what tyres are you using? Seemed like the grip was fine?

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That’s not me driving, just a track I’ve run.

The tires are open brand and compound. However the races being 25mins long, people select something in CIK medium range. Soft typically doesn’t last the race. In fact sometimes the medium will start to blister at a place like Grattan where it tends to be a hot weekend and the tires get a lot of punishment.

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My max egt was around 590 - 618´C with 13 afr, 0.8 squish high comp. I adjusted the high a little during the day. Btw Peter - your 1h 45min high was spot on for 13 afr :ok_hand:

The low with 46gr spring starts to be too lean at mid throttle at 1h 10min or so. The engine will seize at 0h 45 min low - when you come off throttle

Take note that my egt doesnt compare to your motor as I have higher compression + squish = my pressure diffrerential is bigger after the combustion event = exhaust gases are cooler because higher pressure drop. Same as when detonation happens - the egt plummets because high pressure drop after the said event

You really did a lot of work/test to your dd2 :+1: I guess you should have spent some more - change the exhaust and fit even bigger carb - now I have to spend and check what happens :laughing: Thank you for writing up what you did to your motor - very valuable information about tuning these kart engines

I guess supershifter needs 38-40mm carb to make more at top end. Have looked around what 125 & 250 motocross motors use and questimated on that. I guess if motor wouldnt rev to over 13k it wouldnt need such a big carb. 500cr kx etc use about the same size carbs as smaller bikes but they produce the max power at quite low revs 6-8 k

Heres Dellorto chart about venturi sizes
dellorto

Dam you guys have some fast tracks :sunglasses: :+1: Over here the closest track is near Oulu - some 200-250 km away. Its on my list to visit, havent seen the place but should be pretty fast.

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Its amazing that you can loose so much pace when you fall out of the draft and then just cruise right up when you pick it up again. Not like F1 with the dirty air issue.

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Yeah you’re basically sunk without a draft. It can be worth seconds a lap.

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No “dirty air”… just a big hole

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I had the Low at 1:10 with the silly 42gr, once I went for the 46gr & now 48gr I have the Low at 1:30 (high 1:45) EGT, depending on the day, is around 660-685ºC

Yesterday I spoke to an old friend who bought the S.Shifter about 3 years ago, more or less, his engine came with Dellorto carb, he normally has EGT 725ºC which seems like a lot but he’s had no problems up to now, You didn’t have any problems with such a high EGT either, so :man_shrugging: (Btw, he swears he’s doing 151km/h at his local track :thinking: I’ve asked him to send me a photo of his Alfano 6 showing that speed, I have reservations about the crazy speed, and he’s using gears 17-24 (I’m using 18-25 and I’m not near that top speed.)

I have just order the Dellorto carb, curiosity killed the cat, I want to see if there’s a difference with the Tillotson, EGT, Top Speed, Lap times and so on, we will see (I will keep the one that performs the best :muscle:)

You know you can take the S.Shifter to 17000 rpm, more or less, without limiter… :crossed_fingers:

PS, I could have spent more money on the DD2 experiment or I could’ve purchased the S.Shifter, I went for the S.Shifter, I’m glad I did :muscle: -I still have the DD2- two different ways of driving.

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You did the right choice by deciding to use the money on supershifter :+1: More gears = more fun :tada:

The dellorto should give more top end power as it has bigger throat - 36mm vs 34mm tillotson if Im not mistaken.

I have searched for suitable ~40mm carb. Have read motocross forums about different makes, models, what people have been using and how they have been performing. Some carb models might have difficulties tolerating lateral g forces - my buddy build a shifter kart from early 90s yamaha yz 125cc - the carb cut delivering fuel on the corners - only tolerated gas on straights.

Wrote to Lectron do they have suitable carb. Its quite popular on motocross, dragracing and so on. Havent seen one - only images. Dont know anybody here using one. Sure looks cool

What - To 17k ? That would sound awesome :muscle: :sunglasses: :checkered_flag: How can I pass the limiter ?

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Now you really hit the nail on the head!
I know about carburetors cutting off due to lateral g-force, generally by tilting the carb you solve the problem, generally.
Here is a good question, can that happen with a Tillotson carb? The reason I’m asking is because at my local track, with the S.Shifter, there are two corners where while on 2nd and 3rd gear the engine almost dies, I have to shift extremely fast from 2nd to 3rd and on to 4th (I can’t stretch those gears, it dies) once I’m on 4th I’m good, but those two corners are extremely challenging and they’ve been driving me CRAZY, the rest of the corners are great, plenty of power on 2nd to 3rd and on to 4th, and I can stretch all those gears very well, no problem whatsoever - funny enough, the two corners where the engine tends to die (unless I shift extremely fast) I’m turning left very sharply, that’s the main reason why I’m buying the Dellorto carb… I thought the lateral g-force cutting off problem was mainly with float type carburetors (i.e. Dellorto) and as I said, by tilting it, you can generally solve the problem - unfortunately I can’t tilt the Tillotson carb :rage:

Since you mentioned it, maybe my friend is reaching 150km/h thanks to the 36 Dellorto while I’m finding it very difficult getting to 140km/h (and my local track has a much, much longer straightaway than his local track - providing my friend is being honest) As soon as I receive the Dellorto I’ll test it and we’ll see about those two left corner cutting off and the top speed, got to try, if it all works out, I’ll be over the Moon :full_moon_with_face: I can’t wait!

Thanks for the comments, you’ve got me thinking now :thinking: (the next question would be, just like you, how about a 38mm or a 40mm Carb? The Quest never ends…:rofl::+1:

Sorry, I’m so wrapped up with this questions/issues that I almost forgot about the 17000 Rpm, let me find what I read and I’ll post it, but I would guess you’ll need to get rid of the limiter.

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