T4 .81 Turbine & .70 compressor

[LT_Z]

I have seen t66 with like .58 work on KA but will this turbo work on KA ? I was thinking it might have some lag but wasnt sure, and if it did what kind of HP would it probly flow ? Its Turbonetics.

[WDRacing]

The .81 AR is too big, it'll be a lag monster. I had the exact same turbo on my Skyline, it came on boost at 5000 rpm. A .63 AR would be much better.

WD

[MikeMurphy]

Since this question seems to be already answered,

I understand a larger AR on the turbine side will allow exhaust to flow by easier thus creating less manifold pressure. Now, what about using an usually small AR but having lets say the tial 40mm wastegate? Maybe something bigger?

When I go turbo my largest concern will be to get the least amount of manifold pressure possible, but I want some reasonable boost at reasonable RPMs. What about using a very aggressive wastegate along with an effective manifold for such a setup? Anyone familiar with this?

[MikeMurphy]

WD? Nistech? Structure? Nismo_Freak? others who I have missed?

penny for your thoughts

[C-Kwik]

The wastegate size is not of much significance to manifold pressure as long as it is not too small to bypass enough air for the given set-up. The wastegate will hold shut until the desired boost is acheived. And to reach the desired boost, a corresponding amount of exhaust manifold pressure will need to be reached. And this pressure will be dependent on how much velocity and flow is going through the turbine nozzle. A smaller nozzle(A/R) will allow a higher velocity to be reached sooner so it will spool the tubro sooner.

To simplify a little, think of it this way. The wastegate does not do anything until desired boost is reached. Regardless of the size and type, they all will open at just about the same boost(if they are set to the same peak boost). So any lag is dictated strictly by the turbo andit's response to the engine's airflow...all other things equal.

[MikeMurphy]

what if the turbine was unusually small?

[C-Kwik]

No difference. Like I said, the wastegate does absolutely nothing until you reach the desired boost level. A smaller turbine will actually necessitate higher manifold pressures to reach the same boost level as a larger turbine. A wastegate remains closed and starts to open just before peak boost. It only bypasses enough air to keep the boost at that level. If the wastegate is too small, it will not be able to bypass enough air and may cause the turbo to overboost(boost creep). But it will have no effect on how the A/R of the turbo does anything for flow or spool.

[WDRacing]

But a larger wastegate will allow for more flow once the desired boost is reached helping to eliminate that top end backpressure. ATleast that makes sense in my head...

WD

[MikeMurphy]

But a larger wastegate will allow for more flow once the desired boost is reached helping to eliminate that top end backpressure. ATleast that makes sense in my head...

WD

exactly what I was thinking, but just wanted a second opion

[WDRacing]

Great minds think alike, what can I say...

[:: orion ::]

Guys - Not really.

As long as the WG is large enough to vent the exhaust gas that's not needed to produce boost, it make no difference whether it's 35mm or 65mm.

Now, if you have a problem with boost creep, then there's an indication that the WG is too small.

But if boost stays level, you will see no benefit from a larger WG IMO...

Think about it - A TiAL 35mm may have to open 70% to vent the needed exhaust gas...and a 40mm may open 50% to make the same boost...you're still venting the same amount of exhaust.

Later - Brian