TM R2 vs Vortex VTZ vs Iame S4?

How do the newer Vortex KZs (VTZ, RTZ, RSZ) compare to a TM R2 or even R1 in terms of power, build quality, maintenance, ease of tuning, etc.? The IAME screamer also seems to be rising in popularity a bit, how are these compared to the gold standard TM? Do the Vortex KZs have the same gear box as the rok shifter? Out of the box are the Vortex KZs prepped? For the same price as an out of the box Vortex I could get a prepped TM. Same with the IAME, 6k retail, is it prepped? What you guys even mess with getting a IAME?

Looking to move from Rok to KZ for 2024.

I know nothing except Danny Formal just said he was the only Vortex in the entire SKUSA field in Pro Shifter. (He Won) so… maybe if done correctly the Vortex can be quite good.

Yea, he also won in 2019 on the Leading Edge FK with a Vortex KZ. Seems like they have good pace in them, I’m not sure why people don’t run them more often. I wouldn’t think that, it being an OTK product would stop people that aren’t on OTK chassis to run it so there might be other things? I believe Kremers also ran one at the FIA world championship a couple months ago. I’ve tried to look online but can’t really find much first hand info about running them.

Pretty sure you can buy a retrofit kit to convert your ROK to KZ spec. If you’ve got a good motor and know how to work on them I would start there before buying a brand new engine package.

The way I see it…it all depends on what you can and want to do with your time, knowledge, connections (and money)

Example: if you are racing without the support of a team and have no tuner, then you are better off with a TM.
If you have access to a tuner, then it will probably be either TM or Iame, depending on what the tuner is using.
If you have connections or a tuner that is developing a “boutique” engine, then you can go Vortex. As an end customer, Iame and Vortex will be far more expensive to run than a TM, but they are all very capable platforms


I raced today, 3 Roks and one TM (R2).

I went with a Rok due to the longer service intervals and availability of parts. I’m on a KR chassis, so I’m ambivalent to Vortex being an OTK product.

I have lots of time, good knowledge, and zero connections really. I’m in Socal and run a GFC with FW, I’ve been having Swedetech work on my Rok, mainly honing the cylinder and had them rebuilt the gearbox and go through the crank and such. Though they rebuild it I wouldn’t really say I have a relationship with them to where they’d help me with tuning besides some simple jetting, especially since its a rok and theres not much to do. Though some of “factory” guys rok engines sound very different to a normal one… I really enjoy the tuning and working on my kart/engine just as much as driving, so I think I’ll take over a lot of the maintenance besides honing and other things that require equipment I don’t have. After reading through your post about maintaining a KZ I’ve found that it seems cheaper to run than a Rok. Is an IAME harder to tune? Why would you advise only getting an IAME if I have a tuner? I was looking into Vortex and base retail price they’re already more expensive than a TM, which is a proven engine, especially with a factory prep. PSL has some R2s for sale since supernats just ended, would you advise against getting an engine that was used for one race like supernats? Do they usually run them hard and on the edge, so much so that it’d be a bad purchase second hand?

I’ve thought about this, but I’m kind of leaning towards just buying a new engine package. 1 because TM seems cheaper to run besides a couple things and 2 i just really want a TM again. Also I think that if shifter has a chance of getting back to anywhere close to wear it once was it will be through commitment to the KZ.

Out of the box, a factory-tuned (black edition) TM is a very solid engine you can unbox and race. The R2 is the 4th iteration of (pretty much) the same engine platform. So tuning, jetting etc is common knowledge across tuners and racers around the world. New piston is $67 and new conrod kit $225 just as a reference point.
The Screamer 4 is a slight variation of the 3, it had very small market share but recently made a giant leap forward in terms of performance and adoption in Europe but also in US. However, it’s still a much less common platform, so tuner knowledge makes a difference in this case, knowing what works vs what doesn’t. Again, if you like to tinker and test and try there is nothing magic about it, just less reference points. Piston is $100 and conrod kit is $305 so quite a bit of a jump vs TM. BUT if you get good used engines and support from Swedetech, maybe it makes sense especially as they would be familiar with jetting and setups that the rest of the GFC team uses, since you are on that bandwagon.
As far as buying either engine brand from Supernats, I would have no qualms…they are for sure good engines to begin with, used by pros that know what they are doing. I’d rather have that than an engine of unknown origin, potentially used by somebody who tried to engine brake by downshifting at 17K rpm. Just don’t overpay for it.

Formal’s Vortex, Wick’s IAME Screamer 4, and Denner’s TM KZ-R2 represent the end point of long and expensive development programs and selective assembly and dyno tresting of the resulting parts. They are probably the 3 strongest reed valve 125cc engines ever built. The sale of many similar sngines and chassis depend on their success. Their builders prefer to keep them in the hands of drivers and teams capable of winning the SuperNationals.

Outside of that - a “color coded” TM KZ-R2 will have a pretty decent level of preparation, and TM has the production volume and experience to build high quality parts. For $5500 you can get yourself an engine that will rarely be found wanting and will probably make it to its annual rebuild without trouble.

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How do small shops like Swedetech end up with these top tier engines? Is it from taking a run of the mill engine and just tuning it and modding it to make it the best or do they buy a ton of them and keep the ones that make the most power out of the box or what?

TM seems to be the better choice for me. When looking into the costs I was surprised to see how affordable they actually are, for some reason people like to push the narrative that they’re just insanely expensive to maintain and need to be fully rebuilt after a few hours. When in actuality the intervals aren’t much different to my Rok shifter AND the parts are much cheaper. I don’t have a good enough relationship with a tuner to learn about the Screamer 4 whereas with the TM I can find tons of info online.

Parametric study: they’ll take cylinders and modify them step by step on port height, transfer angle, transfer radius, etc, between the as-manufactured starting point and the rules limit, running it between each change on a flow bench, then take the most promising configurations, plate the cylinders, build them into engines, and run them on a dyno with several pipes until they find a local optimum configuration.

Then they’ll build several engines the same way, test them, and with any luck get a couple of very strong ones.

looks like it, you’ll be happy with it!

TM have been the market leader for ‘privateers’ for a long time.

Reine Persson (owner/tuner) is a bit of a genius is why.


Also he has to be the largest volume shifter engine tuner in the US.

Swedetech also works on plenty of TM stuff. The TM that Fore won with in Masters was a Swedetech KZ R2. If you’re already working with Swedetech via Formula Works then I would just call Reine and talk through your options with him.

As Charles pointed out, Formal’s engine is essentially hand picked from the OTK factory. I’ve seen others use the Vortex here in the US, and while they have reported strong dyno numbers, the on-track performance hasn’t been quite as strong as it was with the TM (same team, same drivers).

I’ve been extremely happy with the quality of the TM (R1), and would absolutely recommend the engine for anyone looking to step up to KZ.


I’ve always wondered, are engine tuners getting cylinders that are unplated, or do they strip the plating before doing extensive port work, and the subsequently replate them?

What is meant by parametric studies?

A parameter study is a systematic way to vary several model parameters and have the system automatically run one or several analyses for each combination of parameters.

I am no wiser for this alas

Parametric Analysis - Basic Tutorial

  1. Step 1 - Create a base model. …
  2. Step 2 - Run a standard simulation. …
  3. Step 3 - Define optimisation problem on Optimisation Analysis Settings dialog. …
  4. Step 4 - Open Optimisation Calculation Options dialog. …
  5. Step 5 - Start the Parametric analysis. …
  6. Step 6 - Analyse results.

Ah, ok. :thinking:

The one part that is not mentioned above is that a massive factor is the on track, pre-session tune that is been done by tuner and driver. I bet if we were to test the top 10 engines the day after the race, we’d find out they are pretty leveled. Jetting, pipe selection, stiffeners and all those small little tricks, when done at the right time, all combined make a measurable difference at that level. That’s why Franco, Swedetech and all the top dogs are there in person, there is no rocket engine that alone saves the day because it was built with voodoo tech. I know top tuners that do not believe in plating, flow benching or dyno. I just talked to one that won national titles multiple categories, and didn’t do any of those 3 things but is firmly convinced the secret is somewhere else. KZ yes he run different pipes…2 in total so nothing that cannot be replicated (if you know how). And that’s the whole point, the difference is made by people who know what they are doing and tweak things at the right time in the right way. And remember it’s tuner but also the driver who knows what to relay back and how. And even at that level they make bets that some time work, some time don’t so you can’t really infer by what happens in a final.

Go check what Simone posted about Pex at the FIA World finals in the other post, it would have been impossible if the secret was inside the engine and guarded by the big teams. You can go at it from multiple angles and every one has its own recipe and beliefs, but it all comes down on how you dial in and chase conditions for the given session.

I can go on and so apologies for the long rant but that’s the beauty of KZ, infinite opportunities that anyone can have access to, if enough time is invested :slight_smile: I think it’s important for people to understand that spending a fortune on super special engines or this brand or that brand will not automatically translate in super special results. It’s more complicated, you need to know how to manage what you have on hand. So working with a tuner that is open to discuss options and try things with you, or doing and learning by yourself is much more valuable than any extra money you spend on uniquely crafted engines.

That is a totally different mindset and work approach compared to a spec class, so teams that built their success around managing a spec platform had to adapt (most did it and did it very well, few didn’t), but I can assure you it’s not a matter of having access to special equipment.

Now I’ll go back to my basement and stop posting for a week, I promise :man_shrugging: