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Nigel, can you explain a bit more how to calculate these values, also if i am using the .86 housing? I would really like to know how much power I can expect with 1.3 bar or so, and when will this come (on std engine internals)...

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Understanding compressor maps

Refer to my post at the top of the page, simple calculation to get a understanding of airflow / efficiency, or for anyone who doesn't want to read it, i will paste it here

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Simple way:

the pressure ratio you have to always add 1bar on, this is for atmospheric pressure, so if you want to run 1.5bar of boost, you need to look at 2.5bar on the compressor map.

The lbs/min is your airflow. From various scouring of the t'internet it seems 1lb/min = 10bhp, so if you know what your BHP aim is, you know can work out your airflow.

So in whittlers case he is doing 320bhp/10=32lbs/min

There is a more complicated way of working your airflow out which is...

(L x rpm x VE x Pr)/5660

L = Litres
rpm = Max rpm you want to run
VE = Volumetric efficency (90% for std engine, 95% for headwork and 100 or 105% for race engine)
Pr = Pressure (boost)

So for my engine it would be something like this

(2 x 8000 x 95 x 2.2) / 5660 = 590.81CFM

to convert this into lbs/min multiply it by 0.7

590.81 x 0.7 = 413 (add a decimal place in)

so my airflow @ 8000rpm with 1.2bar boost is 41.3lbs/min, so you go and look at the compressor map and plot the boost against the airflow, then you know whow efficent it is at max rpm

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How much is this costing you from turbo dynamics if i may ask as im guessing about £1200+?

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No, you can't ask - my wife occasionally looks over my shoulder when I'm browsing the forum

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I've spoken with Craig again at TD - he feels that Stichl has probably bought an off-the-shelf GT2871R with a 0.86 AR turbine housing - hence the lag.

Here's the exact spec of my turbo:

0.64AR turbine housing
76 trim turbine wheel (same as GT28RS)

48trim compressor wheel , with 49.19mm inducer and 71mm exducer, in a 60AR housing

1 bar actuator

Basically, the GT28RS turbine side, in 0.64 AR form is known to be good for the Coupe, and as long as the engine can flow the exhaust gasses, is plenty enough to drive a bigger compressor.

The 71mm compressor side of the 2871 will simply flow more air, without costing lag fom the turbine side.

I'm not 100% sure I understand all the above, but Craig is certain that I'll have no more lag than a 0.64 GT28RS, but will have better power than a 0.86 GT28RS

Best of both worlds?

Lets see......

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