Do i need one-piece valves for power up to 300 hp ? The car is for everyday use. I already have a turbo from mk3 with standard map. And 70mm custom exhaust (Blue Flame) I plan to open the engine and change internals . Pistons,rods,bearings vales ... I'm also looking for a used low mileage cat. I'm afraid to buy a sport cat because of the noise in the cabin. All suggestions are welcome.
If your going to be forging the engine, then fitting different valves is a good idea, it is also a good idea to replace the valve springs as the standard ones are quite soft, even Supertec valves are two piece (so i have been told) but there a lot stronger, i had a standard valve break luckily on a standard engine.
when that valve burst occurs ? at higher RPM ? My car doesn't like higher revs. I do not know why. I had the opportunity to try rs 250. In an hour of driving I managed to reach the speed limiter 3 times . it rarely happens to me in my megane . Maybe once a year
The Mk2 turbo isn't big enough to supply that much air right at the top end, it could also be that the valves are starting to float, there is quite a lot of difference in the spring tension on the these engines and replacement ones, the original ones are quite easily compressed. Mine let go coming out of the top of Eau Rouge flat in 4th just about to change to 5th 7300rpm ish. The 250 has a bigger turbo and vvt, my 265 pulls all the way to the limiter, i could feel the power drop after 6000rpm on my 225.
Thanks for the advice. Valves and reinforced springs added to the list. It remains for me to decide what to do with the exhaust. I'm more and more attracted to id to return to standard exhaust. I haven't had a chance to try the 225-R26 with an exhaust from another manufacturer. I bought Blue flame a long time ago. The noise in the cabin is quite annoying on long journeys. In other words. There is a very good sound outside. Inside, the sound is pretty dull and boring + there are some vibrations that I never managed to solve. I have to change the factory catalyst. It started to fall apart. I don't know how much the sport cat would amplify the noise in the cabin. A couple of years ago I put a new RS 250 turbo. Nothing happened . I have the impression that even the car is slower on the highway. I expected at least minimal power boost.
No .. Standard map . it's just changed. Turbo and exhaust manifold . Both have cracks in the metal . After that, he had even less power at higher revs.
I know that. I expected at least a little more power . In any case, the car has a lot of kilometers. Probably something would have happened if I had done it before opening the engine. I should have done it two years ago. On a couple of occasions I ordered parts and waited for them to arrive for 2 months. The seller simply does not have them in stock. He's probably ordering them. In the end, he offered me another manufacturer for pistons . I hope to have more luck this time.
You will need to run a good free flow 2.75 inch exhaust or a 3 inch one, the standard exhaust is okay but it won't be much good for over 275-280hp at best. A sports cat will make a difference but going full decat is best, with a good exhaust you shouldn't have any restriction. If you have fitted a RS250 turbo and not mapped it, it's going to run lean, 225 and the R26 have a fuel rail problem that causes number 1 cylinder to break the ring land. there is really a few other bits you need to do if your wanting some decent power from the 250 turbo, the injectors will be at there limit around the 280-290hp mark, the turbo should give you 300 ish+. This is the start of the slippery slope
Changing the ex valves is more a matter of exhaust temperatures than about high revs. If you´re going to put power to 300 hp ( starting from 225), your exhaust gas temps will be (estimated) raise from maybe 800 to 900+ °C with full throttle (due to my experiences in engine development). The valve temp at the tulip is usually about 100° lower than exhaust gas temp, so you can expect 800° instead of 700 on the part itself. This is significantly a much more stressing situation for the valve, but it has to be relativised that problems will be occuring over longer time cycles with full throttle (some 100 hours), applied with the temps just talked about. Over long times, the valve will loose its alloying elements and hot-gas corrosion will be present what can lead to valve cracks ( not required to talk about the consequences...) On high loaded turbo engines, the ex valves should be Nimonic or Inconel, with a big amount of Nickel what makes the valve heat-resistant. On engines with lower output such as 225 hp, I would suggest that the valves are out of X50 what is able to manage max. 760°, but it´s just an estimation. If I would upgrade my 275, I would go for Nimonic valves.
