Moi!
Mulla on erikoinen LET kone.
Alakerta on vuosimallia "vanha" eli ennen -93 tehty. Männissä lukee C20LET.
Kansi taas on cosworth uudempi kuin 93 koska cosworth ei tehnyt kansia tähän vuonna 91-93.
Jakohihnarullat on taas vanhaa ennen 93 mallia.
Kansiremppaa teen parhaillaan ja 12venttiiliä solmussa.
Tätä on selvästi rakenneltu joskus ja mietityttää noi nokat, tietääkö kukaan GM koodia XE nokille ja vakio LET nokille?
Mun nokissa oli koodi GM GC 4949 tai jotain sinneppäin, pitää tarkistaa uudestaan kun käyn tossa tallilla.
Haluisin vaan tarkistaa ettei siellä jo ole XE nokkia.
Haluisin laittaa XE imunokan koska siinä on korkeempi nosto, ja ainaki ton max-boost sivun mukaan jos vielä laittais hampaan myöhäsempään niin toimis paljon paremmin. Onko kukaan tehnyt tällasta moodia? Pakonokka sais olla vakio LET.
http://www.max-boost.co.uk/max-boost/cy ... C20LET.htm
(stock LET)
IN: 7/64, i.e. duration 251
EX: 50/20 i.e. duration 250, overlap 27 degrees
(XE inlet retarded by a tooth)
IN: -3/78, i.e. duration 255
EX: 50/20 i.e. duration 250, overlap 17 degrees
The XE inlet cam has a bit more duration, and more importantly 1mm more lift (9.5mm instead of 8.5mm).
Setting 2 (or even better XE inlet retarded by 5 - 8 degrees) has the following cumulative advantages:
There is better filling of the cylinders as the intake cycle now lasts a bit longer and lift is 1mm higher (more area under the curve)
There is less overlap, reducing reversion at high revs. This addresses a serious limitation of the stock KKK16 exhaust setup The graph below is from the racing version of the LET and it, too, was plagued by reversion from 4500rpm upwards. Typically this feels like the engine runs out of breath - with this mod it feels more free-revving.
The intake valves are kept open for longer during the compression stroke, 14 degrees in the extreme setting 2. This reduces the dynamic compression ratio, something quite useful for engines running high boost while keeping the stock CR. It's a good way of slightly decompressing the engine without affecting the squish band. The compression test figures (dry) were stock: 12.0, 12.0, 11.8, 11.9. With inlet cam setting2:10.4, 10.9, 10.2, 10.8. So from an average of 11.9bar it came down to 10.6 This is like fitting lower-compression pistons!
A by-product of less overlap is smoother idling. It purrs like a pussycat and the servo is happy too.
Mitä ootte mieltä tosta?
Ja tosiaan pakonokka sais olla vakio LET koska tuolla sanotaan näin:
What the best tuners also know (and keep to themselves of course) is that symmetrical cams don't work well with turbos (The XE cams are symmetrical, they rhyme 18-62/62-18). Of course when you start advancing/retarding them, they stop being symmetrical.
In my experience with turbos:
-They want a bit less lift on the exhaust side (compared to the inlet) and a bit less duration too. These valves can get red hot, and appreciate spending quality time in contact with the cylinder head, it's their main way to cool off.
-Early opening of the exhaust valve eats up part of the power stroke (not good)
-Late closing leads to more overlap (not good either, especially if the exhaust-side A/R ratio is below 0.6).
-Right on the stock marks, the XE exh cam opens about 12 degrees earlier. That's eating into the power stroke by almost one tooth - ouch. We need the exhaust gases to spin the turbine, but if that's at the expense of using our hard-earned power stroke, maybe it's not worth it.
JA JOS JOLLAIN LÖYTYY XE/LET VENTTIILEJÄ NIIN SOITTAKAA 0440150170 TUUN HAKEMAAN POIS! (tänään heti nyt)
Muokkaus:
Imunokka on koodi 0950 ja pakonokka 0949
muokkaus2:
Googlen mielestä noi ois XE nokat mut ei se ollu ihan varma..
muokkaus3:
Nytku mulla siis on oletettavasti XE nokat niin toi pakopuoli ei oo hyvä juttu, aukee liian aikasin ja se vie tehoja, eikä sitä voi siirtää hampaalla, menee liian myöhäseen??
To avoid this early opening, and bring it closer to the stock LET exhaust timing, we need to retard the cam by those 12 degrees. Naturally, this will result in a 12 degree increase of overlap, so it's swings and roundabouts.
A compromise would be to retard it by half a tooth, that's around 7 degrees. But that would affect the ignition timing, and that's unacceptable (except if you run aftermarket ignition timing)
Voinhan mä ajaa tollasella overlapilla mutta pitäis tarkistaa ettei pakopaineet ole ahtopaineita suurempia? Ja miten pakopaineet sit mitataan kotitallissa..
Eli imunokka hammas laitetaan hammas myöhään, ja pakonokka kans hammas myöhempään?
Ja eihän toi 12 overlappia oo paljon?? ja saattaa olla ihan positiivinen vaikutus toi overlappi
Voisko joku viisas kertoa miten nää asiat oikeesti on? Ajeletteko XE nokilla jako 1hammas väärässä molemmissa nokka-akseleissa?
Oon lukenu kaikkia aken hommia mutta selvää ei oikeen ota noista...
Niillä nokilla kun pääsee hyvin lähelle sitä ja pakopaineet pysyy jopa alle ahtojen jos ahdin ei ahdista
