The taboo question...

[XPC66]

No you did it wrong. The 15 psi 26 lb intercepts are correct, but you need to work the flow at 8 psi independently. Once you have the two points you can draw a line between them and that is your engine lug line for that compressor.

 

[350kmileford]

Oh thanks, let me change that.

Edit: @ 8psi, it recalculated at ~20.5 pounds/minute

Would be acceptable, but not ideal:

 

[Bort62]

Right, so the question now is how confident are you in your VE assumptions?

VE's better than your assumptions will push you to the right while VE's worse will push you left.

 

[350kmileford]

Not sure, haven't built the engine yet :roll:

Is there any way to predict based on different engine setups? 70% does appear to be on the low side, I reckon it would be even higher than that. I think I have another alternative though, let me find it.

Here we go. Go here: http://fc3spro.com/TECH/TURBO/compmap.html
Scroll down to T04E "60"

Here's the map to save some work. I had to map over the site's existing map. Look at the diagonal green line to look at the range I came up with. This is with a range of 20-26 pounds/minute:

Still some room to grow.



I went through the calculator and inputed 85% VE, on 8 and 12 psi of boost. It gave me 25 and 29 pounds/minute. Here are those factors graphed:

Looks even better.

My next big question is: there can be 2 T04E "60" turbochargers, but each can have a different a/r. How can I know which a/r that graph is showing?

 

[wallaka]

The A/R usually refers to the turbine side, not the compressor side. So the same trim compressor wheel can have a different exhaust A/R and so will spool differently.

 

[XPC66]

The A/R has a marked effect on the turbine side, but not a lot of effect on the compressor side.

So just referring to the turbine end:

The smaller the A/R the faster the spool, but a corresponding reduction in shaft torque. So if your A/R is too small the turbine will struggle to drive the compressor at the desirable flow&pressure, especially as you rise through the engine rpm.

So while A/R affects the pressure differential, the trim affects the operating range. Maintaining the same trim, but increasing the turbine diameter will increase the imparted shaft torque, but it will move the operating range up the rpms and introduce more lag. If you increase the trim value by increasing the minor (inducer) you will also make it more laggy, but effectively shift the compressor map to the right (biased to the surge region). If you decrease the minor you will effectively shift the map to left (biased to the choke region) and with it the pressure will build faster and at a higher pressure for the same compressor mass flow rate.

You select the A/R based on what exhaust manifold pressure you want in relation to the boost pressure. Compressor trim tends to hover around 72% of the turbine trim for reliable street use..

 

[350kmileford]

That is helpful, thank you. So it appears to me that the T04E "60" would be a good start, even though it is an older Garret T style.

 

[XPC66]

I'd be going the Garrett GT series or the IHI RHF series.

 

[350kmileford]

I was looking around and could not find a to4e 60 trim in the GT series. It seems that the naming scheme is diffrent for the GT series? I imagine they have it, I just couldn't find it.

 

[wallaka]

Something like a GT35R should be close. Modern compressor design and ball bearings go a very long way.

 

[350kmileford]

I looked into that GT35R. Not bad. I did look through quite a few of the GT series turbos, and I now have a general understanding of the GT naming system.