Max Boost pressure only in gear 2 and 3?

Guys, today I checked my MK3 after replacing the timing belt, I did also an Wagner intercooler, got it for an affordable price. After that I was surely interested about boost pressure and intake temps. The temp maybe more interesting with more boost after remapping, I didn´t do that as yet, want to fit first a bigger 200 cpsi cat and a big sized exhaust (already in my shop). What I tested was the boost pressure, to my info it should be max. about 1300 / 1350 mbar, some are telling 1400 ( I have 273 hp). I tried it on the Autobahn, in gear 5 +6 it got only about 950 mbar, really flat down, with 3000-4000 rpm. After I tested in gear 3+4, then it got about 1300/1350 mbars, car accelerates so quick that you have to look to the road...I have no feeling that power is low. All pressures are shown on the R-Link. Anyway, if boost is too low in gear 5/6, there would be a lack of topspeed, I couldn´t check this out due to the speed limit here around. Thanks to share your experiences.

 

Hi, with respect, I don´t think so. Usually, in low gears the car accelerates quicker than the increase of boost will be present. If I´m riding in - let say - 5. gear with full throttle with 2000 rpm, there´s plenty of time for the charger to rev up to perform high boost. The chargers boost is depending from gas flow through the engine, not from big rpm. I noticed very well that the boost in 5. gear was climbing up straight to 950 mbars, then stopped climbing immediately, as there´s an limiter function. In the lower gears - in 2. and 3. surely, maybe as well in 4. (have to check out again) the boost climbed up straightaway way more than 1000, up to 1300-1350. In an German forum there were romours about 1400 has to be reached at least on 273 hp cars. To mention is yet that I have fuel 98 ROZ and I tried it in the race mode. Does anybody know whats the official stating from Renault about the boost ? Unfortunately, yesterday is was very hot in Germany ( almost 30°C) so it was difficult to judge the different to the weeks before when it was much colder. My car was resting due to the works i did the last week.

 

Hi, I´m close to Stuttgart. No bothering about your post. What shop did remap it? I´m looking to do it as well, but want first to fit my exhaust mods to get the condition how the engine works after the remap. As yet, I don´t feel any power influence from the bigger intercooler. But I think it´s much more noticeable with the exhaust and remap. Bigger boosts make higher intake temps. The intake temp is now About 10° lower that before, rarly more than 32° when outside is 24°. But I have to admit that I´didn´t have had the opportunitiy to ride hard the car. I think biggest Benefits from the intercooler would be Long Autobahn or Nordschleife Nürburgring. When the engine is long time on full throttle, it will be felt much more.

 

OK, I have some new points. As I´ve told, my car rested for about a week due to the timing belt and other things (not so good to work on Easter…) Of course, the battery was disconnected. After the repair, the first testing ride was really disappointing due to the issues I´ve told. The car was not entirely on top power, surely difficult to judge, it´s just a feeling. But I noticed the poor boost. Yesterday, I made an extended test ride a bit harder and felt after some km that the car is much better on power. Yesterday afternoon I´ve made an acceleration test in 3. gear and saw now that the boost was on 1300 mbar. For me, it´s quite clear that the ECU has to lern a lot depending on the cycling you are riding. Maybe it´s reset after disconnecting the battery and needs 30 or 40 km to lern. Supposedly it didn´t get full boost after the reset. My Feeling was that there´s an 20 hp difference between before and after. Anyway, I don´t think that you feel the difference from the bigger intercooler. With short accelerations ( not steady state on the Autobahn) the lower termp. of 10-15°C maybe a 5-10 hp difference inj peak power. Hard to feel. I think the real Advantage comes with remapping, higher boost pressures and a big exhaust. Then it should be a 15-20 hp benefit just from the intercooler. Hope to get 330 hp with big exhaust 76 mm, together with 200 cpsi cat and remapping. The only downsize of the intercooler ist 5 kg more weight on the front axle...Unfortunatly, around my location there´s no free Autobahn to check top speed. Everywhere limited to 120 km/h. Have to go at least 70 km.

 

Do you know the exactly difference between 250/265/273? It´s sometimes difficult to find out. To my knowledge, the 265 is 0,2 bars higher in boost than 250. Of course, the mapping will be matched, accordingly more fuel due to the bigger air amount. About 265/273 : Some rumours say that the engine is completly identically al least mechanically and turbocharging. My 273 is Euro 6 and this ECU includes completely a different structure, but nothing concerning power output. Some are saying that at least power of 265 and 273 would be the same in race mode.

Apart from that: I think you are very conservative with your expectations concerning power. With big exhaust 3" from cat to tailpipe, together with the Wagner intercooler and remapping 300 HP should be going for a walk. Some guys are telling that they have 300 hp only with remapping. I think from 330 hp up you need a bigger turbocharger with a bigger manifold, maybe bigger injectors and in consequence stronger rods and forged pistons. Such an engine will be entirely lose it´s properly fine-tuned balance what nobody could do better than the vehicle manufacturer, not at all a tuner on a half-day ride on the rolling road.

There´s a German-speaking swiss Megane RS Forum , strange, hardly no more motion within, but there were lots of guys who talked about their cars and lots of them went on Nürburgring. Most of them claimed about 320-330 hp with the mods we talked about, and lots of more torque ( I`ve heard about 470+ Nm). Surely, it´s a question what power figures they will evaluate on their rolling roads, sometimes they state about 290 hp from a not modified 265 HP-car. That would be suspicious for me. I would be happy if my car has really 273 hp.

Did you test your car on a rolling road before /after you switched to the Wagner?

BTW: About your exhaust, I have a Friedrich 3" complete. But be aware that this uses the pipe with the stock flex piece after the stock cat from the stock exhaust. The entrance of the stock flex pipe is only about 56 mm in diameter. I do my flex pipe by myself and use a 3" flex pipe. Want to say: Don´t use a big 3" exhaust and a 3" cat and don´t forget to open up the flex pipe also to 3". Otherwise, thats the bottleneck what causes a lot of power.....

 

Didn´t know that 275 has wideband Lambda, perfect! Would make matching of a new mapping a bit easier especially in WO throttle.

Rolling road results: You are often rigth, I know RRs which are Offset with 30 hp or more to reality. Some specialists are measuring the intake temp behind the turbo and are correcting this temps to ambient air…...or some other crazy cheatings. But there are as well some good shops with RR which are determining results of stock cars ( Porsche / BMW /Mercedes / Hot Hatches) very close to the claimed OEM figures. In Germany, there´s Sport Auto, a well reputed Magazine, they are located in Stuttgart and they are tesing a lot of Porsche. With every Supertest on Nürburgring, they are checking the engine performance on the same rolling road from Maha, the leading Producer of these RRs, and as well the Porsche engineers will get involved if power figures are strange, too low or too big. Some years ago (I think in 2018 or so) a Porsche Turbo was tested with about 40 hp too much and the Magazine talked to Porsche. They found out that the ECU of the last Porsches compensates the boost via the ECU if it notices that the ambient pressure is apart from usual. The Dyno guys didn´t know that and did correct the temps and air pressure what they shouldn´t have been done due to this self-adjusting function. Then they repeated the rolling road-run and got exactly the power what Porsche claims. What I want to say: Todays rolling roads are really able to determine real figures, but the staff have to know the behaviour of the dyno, especially cooling, fixing issues on the dyno and so on. A friend of mine has also an rolling road, unfortunately 270 km away from me....but he also measures power figures which are very close to claimed ones. I myself was involved in race engine development in the 90s and tested my engines on a real dyno. We often rechecked them on our rolling road afterwards and there was not a big gap between if you know what you do.

 

To my Knowledge, Sport Auto didn´t make a supertest with the Megane 3 RS what´s completely strange. At least, I don´t know one. They tested the Clio 3 RS with the N/A engine and the Clio 4 RS with turbocharged engine even twice, the older version with 200 HP and the newer with 220. Due to the fact that the Megane 3 RS is " godfather of hot hatches" I´m wondering about. I´ve a lot of Sport Auto Magazins, but I have no subscription. I buy them once I find it interesting.

Apart from that, Renault themselves made a record ride on the Nürburgring in 2014 with the Megane 3 RS Trophy-R ( the 2014 Special Version with 100 kg less weight and some goodies) They broke the time record of FWD cars that time with 7:54 ( you´ll find it on YouTube). Maybe that was the reason of Sport Auto to restrain from a test because some rumours are doubting about this lap time. Maybe they wouldn´t expose themselves with a slower lap time. If the YouTube is not cheating, Renault has rent the Nürburgring for this event, on the lap there was no single other car to see. I think Sport Auto wouldn´t rent it and they wouldn´t have perfect conditions to make a comparable time. The Journalist who normally makes the supertest laps is Christian Gebhardt and he is really a brilliant driver. He drove the Clio 4 with 220 hp - as far as I remember - 8:20 around the ring. I think that Sport Auto was a bit pissed about the Megane record lap time and therefore they didn´t perform a test. Just an assumption. Some time ( maybe one year) later Honda made a new record with the Civic R with 7:48 or so. They used semi Slicks ( Renault didn´t) and argued that that would compensate the bigger weight of 30 kg due to the rollcage they had fitted. To my opinion, semis are more worth than 30 kg of weight of the Nürburgring. Some strange behaviours around these compagnies. Now Renault is again the leader with the new Megane 4 RS, I think they drove 7:40.

About the power, just do a top speed run on a flat road, maybe both directions. The speedometers are nowadays really exact, maybe 2 km/h advancing. If your car is running 255, power should be ok. On the german Forum, there stated some guys that their cars only would make 235 or so and they found some issues with boost or something. No Megane 265 will make 260 km/h on the flat, for that you would need estimated 15 hp more than for 255. Remember that your 265 is rated to 254 km/h, my 273 is rated to 255 km/h. It´s just 1 km/h with 8 hp ! Supposedly in reality both engines are the same or nearly the same, you don´t need 8 HP for 1 km/h, I think it would be 2-3 km/h or so. But your car will never run 260 - unless you don´t notice that the road slopes a bit. Or you have tailwind. And if the car struggles to achieve 250, there´s some power missing. If a car would have 290 hp like some guys are claiming, it would easily run 265 - 267 on the flat.

 

You´re right, Sport Auto should heve tested the Megane 3 long before this Nürburgring-Event. Probably I drop them an Email and ask them.

RS 275 makes power at exactly the same rpm (5500) as 265 ( and 250). And Top Speed will be reached in 6th gear at rather this rpm ( whats exactly the Right matching) If you make the 6th longer, the driving restistance ( air drag) will increase and engine performance isn´t big enough to approach top speed. Basically, if gear is too long, it takes an Extended long time to hit top speed and the smallest hill will drop your speed immediately. So I find the gear perfect matched. Gear changing is an different topic......

 

I`ve calculated the speed by myself, basic wheel circumference 235/35-19 is 203 cm. So I´ve got 5500 rpm = 239 km/h, 6000 rpm = 260 km/h and for top speed 255 km/h you need (with this tires) 5870 rpm. You are right, the box is a tiny bit shorter than optimal, but that causes to reach top speed relativly sure - theoretically…...Supposedly you calculated with circ. 1,99 m, so you get only 234 at 5500. I calculated the circumf. by using the standard tire dimensions with rim dia + 2 x sidewall ( 35% of 235 mm)…..so I got 2,03. Maybe there are more specific statements from the tire manufacturer. Don´t forget that the tire will increase it´s diameter at this speeds by centrifugal force.

 

There seems to be something wrong. If you car performs really 300 hp, it will easily override 260 km/h, should make estimated 270. I don´t think you car has 300 hp, though with your mods it should do ( if you have an 200 cpsi cat). Maybe there´s something wrong at the mapping, less fuelling on longer time high speeds and power drops. It´s dangerous if someone tampers on the ECU who has not adequate knowledge. It´s seems strange to me that your car had initially 275 hp from a basis 250 hp engine. Maybe there´s something running out of order between dyno test and real driving conditions. Did you replace the cat to an 200 cpsi within the downpipe or did you keep the stock cat ? You have to keep in mind that your Turbo engine needs more fuelling on top power than a N/A engine, due to the high piston/cat/ exhaust temps to make the parts survive. You need a Lambda ratio at full throttle of about 0,7. If you go leaner, there´s danger of piston / ex valve / head gasket / turbocharger burning.

 

Thats what I have




I don´t know if these figures are correct. I found the ratios in an german forum. But they seem to be plausibel.