Rear exhaust housing (ar) sizes

[Shibby]

Ok I'm a bit of a newby to turbos and was wondering if we had 3 prepped RB25's and bolted the same HKS 3040 turbo to each motor but had say a .6, .8 and a 1.0 rear on each turbo

what would the difference be on each power wise ie low down, mid range and top end which ar would give you the best average power?

what would the gains/losses be?

would this govern how much boost each turbo is capable of being efficient at?

If each turbo is say rated at 550hp how is this possible with 3 different rears or does this not effect the over all power?

[Steve]

Smaller turbine housing - boost will come in earlier, but the downside is they wont have the top end of a larger housing - due to the additional back pressure. Also, with a smaller housing, it is more difficult to control how the boost hits, its either on or off - the net result of this is you would have to turn your boost down to drive on the street safely, and prevent unplanned lane changing.

The boost pressure where a turbo is efficient is dictated by the compressor.

Buggered if I know how a turbo can be rated at 550hp with 3 different rears, unless they rate at the smallest sized housing - which means the larger ones have the potential to make more.

Real world example, I had a 0.61 housing on 3037, boost came in so hard, at around 3000rpm, that the back end would step out at light throttle even in 4th gear and doing around 100kph. Not so bad if you want it to, but not so good in traffic. I am not sure about top end, but the turbo did make 256rwkw at 1 bar with an quick tune.

same turbo with 0.87, 1.2 bar (17.4lbs) at just under 4000rpm. The car pulls pretty hard from around 3500-3700, so around 500 or so rpm more lag (after changing to a higher flowing exhaust). I have 22lbs set all day, and can control the boost with the accellerator pedal. turbo now makes around 285 at 17lbs and 321 at 22lbs (around 1.6bar).

I much prefer the 0.87 housing. Much more lag though would be a bit too much IMHO. If you want my recommendation for a 3040, I would say go the 0.87. Merli had a 3040 with 0.87 turbine AR on his R33, it would be worth asking him what he thinks too.

Steve

[LBR33]

would i gain any peformance/power from having the exhaust housing bored out on the factroy turbo

[Guest INASNT]

would i gain any peformance/power from having the exhaust housing bored out on the factroy turbo

for the cost of taking it out getting the work done and then putting in back on, u might as well throw it in the bin while its off and get a decent turbo

BTW i got a 0.82 rear housing on my 3040 and its easy to drive in traffic and then when u go past 4000rpm its really fun to drive.