71 chevy

iTrader: (18)

Say you have three different turbos

80mm,88mm and 94mm, but the turbine side is exactly the same. Would spool be effectively the same between the three turbos?

HydroStream6

iTrader: (16)

No they will be different. Larger comp wheels are heavier and harder to turn. Larger comp wheels bring larger comp housings which in then take longer to pressurize as well.

71 chevy

iTrader: (18)

that sounds reasonable. how big of an effect would the compressor have, vs the turbine side.

HydroStream6

iTrader: (16)

From my experience, the cold side does have less of an effect than the hot side. On my current vehicle, I've run 3 different turbos. A T60 and a T70 which were both P trims on the turbine, and a TC76 which is an F1 on the turbine side. There seemed to be less of a difference between the T60 and the T70 than the T70 and the TC76.

Keep in mind I have no boost/dyno graphs to back this up, this is just my experience on my vehicle. Your mileage may very.

What is your specific application? Or are you just wondering in general?

71 chevy

iTrader: (18)

im faced with a choice between t70s or t60s on a 5.3

same hotside so i was wondering if spool would be same but it sounds like the 60s will spool faster

topend

no difference in spool. The turbine is what effects spool.

MR2liter

iTrader: (11)

rotary1307cc

iTrader: (5)

X2

the size ratio between the compressor and turbine plays a big role in spooling, surging, ect

killernoodle

The time it takes a charge pipe to pressurize is miniscule, so that isn't a factor. Spool is determined by how long it takes to accelerate the wheels up to speed. The larger the wheels, the more air they can potentially flow, but the slower they can spin up to speed. A smaller turbine wheel could cause a faster spool because of reduced mass and more exhaust velocity, but excessive backpressure is a bad thing. A smaller impellor makes for a faster spool because of reduced mass, but it won't be able to flow as much air.

Its a fairly simple really.

71 chevy

iTrader: (18)

also, just thinking out loud here - apart from the weight of the compressor side itself, doesnt the compressor impart a load on the turbo by trying to move all that air, so wouldnt it stand to reason that a compressor that moves more air with its bigger blades would also put more of a load on the exhaust side, resulting in slower boost?

again, just thinking out loud

HydroStream6

iTrader: (16)

Exactly.

topend

bigger compressors are capable of putting more load on the turbine because they could flow more than a smaller compressor. Spin the bigger compressor to flow like a smaller compressor, will require the nearly same amount of load on the same turbine.

why does the PT88 t4 spools faster than a GT47-88mm t6????? both turbos use 88mm compressors??

71 chevy

iTrader: (18)

would that have to do with the inducer/exducer relationship?

interesting reading on this. dont know if this is science or bullshiz but its interesting

http://hondaswap.com/general-tech-ma...ulator-174676/

HydroStream6

iTrader: (16)

We are really splitting hairs at this point. I think we all agree that turbine side effects spool more than the compressor side, but the compressor side still will have an effect.

Think of it this way as well. For every rotation of the turbine wheel, it still has to turn whatever is on the other side.

CarsandWomen

iTrader: (19)

your comparing two very different turbos, designed for different engines. the exact same turbo will spool different on 2 350 cid motors if one 350 is short stroke big bore vs. one with small bore long stroke

the t4 pt-88 spools different than the gt47-88, and the only thing thats different is the shapes of the wheels and housings *to my knowledge.

71 chevy

iTrader: (18)

as an update, the compressor side definitely had an effect on the spool.

twin t70s on a 4.8 , 3400 rpms to positive territory
twin t60s on a 4.8 ,3050 rpms to positive territory.

NOTHING else was changed

So.jerZ-28

iTrader: (20)

go twin 70's with a 68 a/r if 347 and 81 a/r with 400+ is what I would do.

Boo"SS"t

iTrader: (2)

I'm just curious. Could you be more specific on what were these results from? like what tranny, turbine wheel and turbine housing a/r?

71 chevy

iTrader: (18)

th400 trans, 60mm vs 70mm wheel, and both .68 ar

bmech211

Also keep in mind that as engine load, VE, and boost increase so does the thermodynamic load on the turbine wheel by way of higher gas pressure and temperature. This in itself is enough to overcome most "boost related" rotational loads granted you're not stalling the compressor (surging).