Comparing Performance of mixed Evo and Pre-Evo Rotax Max Parts

rotax_max

(Daniel Gauci) #1

Hi,

I currently drive a 2005 Rotax Max FR125 engine, and soon the first ever Rotax Max Challenge will be held in my country. I have recently rebuilt the engine, and in my opinion it runs very well (easily revs up to 13,800rpm), however most of the competing drivers will be running the new EVO engines.

While I have considered purchasing a new EVO engine, I am hesitating to do so since the X30 engine just got a local importer, so I’m hoping that once it will gain some traction I will switch over to it.

Given that my current engine will not be competitive against the EVO package, and most of my current parts (such as the exhaust) will not be legal for the competition, I am starting to consider the EVO upgrade kit. With this upgrade kit, will my engine be as competitive as the new EVO engines, even though I will be running the old block? I have heard a lot of people at the track saying that the EVO has a significant bhp jump over the non EVO engine, however I’m not sure if it is strictly attributed to the updated carburettor, ignition and exhaust (the parts that I will get in the EVO package), or if the engine block itself is more powerful.

Any feedback would be appreciated. Thanks!


2018: The Year in Review
(James McMahon) #2

Welcome @danielgauci. That’s exciting that the RMC is going to be held for the first time… where do you live?

@Eric_Gunderson might be able to give a little insights on how the EVO might run against the “PrEVO”. I’m sure others will have insights too regarding cylinder and other changes, I can recall what the essential parts were to get the EVO level performance. I do remember a rod update that was intended to be a reliability thing.

Here’s some articles from when the EVO first came out that might help:

https://www.kartpulse.com/article/90/questions-answers-about-the-rotax-125-max-evo-engine

https://www.kartpulse.com/article/99/rotax-evo-packages-now-available-in-usa

https://www.kartpulse.com/article/105/rotax-evo-test-in-south-africa


(Daniel Gauci) #3

Thanks for informative reply @KartingIsLife! In my last rebuild I changed the rod to the new EVO one (along with the piston and ring of course), so I should be good to go from that aspect. According to one of the articles you linked, it looks like block itself is just as fast:

The new EVO base motors were finally fitted in each class and proved equal to the top 2014 motors (fitted with all the 2015 bits) used in the test. This would not normally be so because traditionally the new motors from the factory were assembled with small clearances and needed many hours of running before delivering optimum performance. The EVO engines are now built with “racing” clearances so no need to have them blue printed (artificially aged) by an engine tuner. More importantly we can confidently confirm that this demonstrates that a 2014 (or much older) motor can be upgraded to the exact same spec and performance as a new EVO engine.


(Marin Vujcich) #4

We have run the EVO since its inception in New Zealand (including all the iterations). You will not be competitive without an upgrade kit. The older short block will not make any difference. How competitive is your engine against your competitors. I say this, as the barrel is the holy grail to Rotax. If you have a fast PrEVO engine, chances are the barrel will be competitive. If not, you will need to upgrade to the CNC barrel. This has proven to bring engines inline with the most of the best.


(Eric Gunderson) #5

(disclaimer: not a Rotax expert). My understanding of the latest iteration of the EVO package is that the main area where it has a significant power gain is in the cylinder itself. Some of the ‘suitcase’ motors of years past were confiscated, copied, and Rotax focused on refining their production process for cylinders and heads to be as similar to this as possible, therefore (theoretically) leveling the playing field. The side effect of this of course is that at least in the short term, some older Rotax engines will simply not be as powerful.

However, with that said, my thought is that you may want to just go run a race, and see how it goes! There’s a lot more to running well than just horespower, you might surprise yourself with a decent showing!


(Marin Vujcich) #6

Even without the new cylinder the EVO kit was a marked difference. Easily 3-4 tenths around an 800m track. Also the way you drive/ gear them is different. Here in NZ we have a lot of track with very low speed corners and reasonable straights. Most tracks peake at 60-65Mph top speeds. We found that with the EVO, we all ended up revving the crap out of them and gearing for lowest RPM of 6500rpm. This is because there is more to be gained coming of the corner fast than pulling fast at the end of the straight. Most are running Gen 1 ECU as it has no rev limiter and we pull 15k rpm at most tracks. We have one very Euro style track in my area and that is run more “Rotax Conventional” with max rpm around 13800rpm.

The carb and ignition timing in the EVO makes it a far more driveable engine package.


(Daniel Gauci) #7

Thanks for all of your replies! Unfortunately I didn’t run against a lot of pre-EVO engines, since by the time I bought the engine most people had already replaced their engines with an EVO engine. However, given the points you mentioned I think the ideal solution is to get the EVO upgrade kit, and then upgrade the cylinder in the case that there is a significant different in performance with the other engines.

@Marin_Vujcich does this mean that the Gen 1 ECU is superior then, or are there some advantages to the Gen 2 ECU if high RPM is not the priority? Also, how reliable are the engines being revved up to 15k rpm? With my engine I’m afraid of going past 14k since I thought it might rapidly reduce the lifetime of the engine.


(Marin Vujcich) #8

You probably won’t be able to get a gen1 ECU if your supplier hasnt been bringing them in since inception. Rumour is Gen2 ECU was only brought in to stop revving them to 15k rpm, because yes, it does shorten the life of bottom end and I have seen a few piston failures. But as a general rule 20hrs on a piston. 40hrs on a botton end seems to be safe.


(Christopher Ramnauth) #9

Sorry for resurrecting this post, but Marin you seem to be quite knowledgeable on these rotax motors. You mentioned the barrel is the holy Grail of rotax and that the newer barrels are made to more be more even across the board, but do the latest cylinders match the kind of performance that would have been seen on say one of those rear “special” older engines? I ask this because I have a 09 barrel on mine and was wondering if there’d be performance to gain if say I purchase one of the brand new 2018 cylinders.


(Marin Vujcich) #10

The new cylinders just brought the bottom performing engines up to near the “special” engines. But there are still a few freak barrels that will outperform the new ones. How does your one compare to others?


(Christopher Ramnauth) #11

Its nothing special, I would say average at best. The top runners do seem to have some more umph than mine and their engines were said to have been ex PSL karting engines.


(Marin Vujcich) #12

The new barrel will definitely help, I have been told the top guys is worth 1/10 on a 40 second a lap track (that was back to back on their good top barrels). Wish I was that consistent…*sigh. I inadvertently sold a very fast engine with my old kart, when I got my new engine the data traces showed the old barrel was better. Things you learn…think I lost some respect when some people knew I had sold it.LOL
You will get more benefit from driving off the corner well. Good drivers make it look like they have fast engines.
They appear to be the good everywhere in the rev range. If you can stick on someone’s tail and then they pull away at the very end of the straight, I would look changing if I was you.


(Christopher Ramnauth) #13

What exactly are you looking at on the data traces to assess one barrel vs the other?

What I’ve found happening with my engine is that I have geared it 4-5 teeth shorter than everyone else to try to gain an advantage on the competition but they all seem to be pretty close if not even with me out of the slow corners and then up top on the straight they’re pulling away a lot.


(Marin Vujcich) #14

4-5 teeth is a massive difference. That may not be wrong though. we have a track here that you can run anywhere from a 78t-83t and do the same times, just depends where on the track you want the advantage. general rule, you want to gear 6500rpm as the lowest rpm.
If they are keeping up with you off the corner, I would look at how you are coming off the corner kart wise. Remember the torque curve drops off significantly at 12500rpm and picks up again a little over 14000rpm (the better barrels). so if you are spending longer in this band you will loose ground on the straights.
In the data trace you are looking at the slope of the speed trace. The slops is the acceleration. If it is steeper you are accelerating faster.


(Christopher Ramnauth) #15

Our track is small and has some tight slow hairpins. The competition are on 12x85/86 and I have tried 11x80 and 11x83 and still slower by almost 0.5 of a second.

With the 11x80 my data says my average min rpm is 5100 and my average rpm per lap is around 9800. With the 11x83 my average min rpm is 5300 and my average lap rpm is 10200. I was also quicker on the 11x80 vs the 83, its all very strange. In particular down the mains straight when I hit 12500rpm the longer gearing shows significant gain in speed vs the shorter.


(Marin Vujcich) #16

Be interesting to see what the competition is running down too in rpm. If they are running the same min corner speed they would be down to around 5000rpm. The torque characteristic of the engine is poor in this range. We have tight tracks here in NZ and we rev the nuts off them on these tracks. We find the punch from 6500rpm offsets the drop off after 12500rpm. Some of us still have first gen ECU’s and will punch 15000rpm+ As long as we can punch through the dead zone from 12000-13000rpm the torque rise is significant after 13000rpm.


(Christopher Ramnauth) #17

Remember these engines we are talking about here in Trinidad are the pre-evo engines…not the evo. What gearing are you using on those tight tracks where you rev the nuts off them and get 6500rpm as ur min rpm?

I am getting to compare data from another driver soon so will let you know what I find.


(Christopher Ramnauth) #18

Have a look see what you think Marin

https://drive.google.com/drive/folders/1Au_1pwGLh4bLJwCOe3i4F3P5BV_miC_v


(Robert Chalmers) #19

Hey sorry to jump in on this discussion but I noticed you say the band over 13,000 picks up again on a good engine mine has always done this since then I’ve had a rebuild and carb strip now I don’t get it, would this be due to carb settings or what?

I’m like the lad on here I’m thinking about a evo upgrade on my KR barrel.


(Marin Vujcich) #20

Hi Chris. TJ might shed more light on this. Your low speed acceleration looks good. I saw your mychron hitting 13000rpm on the longest straight. This is typically right at the end of the “dead band” from timing being retarded and torque drops off. In my opinion you need to gear so you are just under the 12500rpm, but this will hurt you slow speed exits. Or put a couple of more teeth on and punch through it and aim for 14000rpm Max. It doesn’t look like much grip on track either, so the kart maybe sitting to flat through the fast stuff slowing you also. If there is not much grip you could try really hustling it through the hair pin, a bit of slide may help you.

Robert, The non evo is very jet/needle sensitive. If it does not rev and does not pop in the exhaust, go leaner until it pops in the exhaust and then go back one jet. Make sure you note the weather conditions for future reference. Don’t stress about going really lean with a rotax as they let you know with a pop in the exhaust and wont cause any damage.