turbotoaster

Assuming the port, manifold and boost were the same, how could these 2 turbo specs effect the power and boost threshold

Compressor
70.3mm inducer, 94mm exd with a 56 trim and 0.60A/R
turbine
82mm wheel dia with a 84 trim and a 1.01A/R



Compressor
76.5mm inducer, 103.5mm exd with a 58 trim and 0.72A/R
Turbine
67mm exd, 74mm ind with a 82 trim and a 1.00 A/R


Now from what i can see the first turbo has a smaller front end but a larger rear end.

Now i know rotarys are effected heavily by the turbine housing so would dropping the wheel size on the back and increasing the comp wheel cause it to surge and then not produce the big numbers at the top end due to small wheel, or because the rear end are both about 1A/R it wouldnt make a difference.

Can any of your turbo guys give me an idea on how this effects rotarys, i can an idea for piston engines but thought id ask to gain some better knowledge.

the reason i ask is compare the gt4294 to the gt4202, the only difference i can see is a small increase in comp wheel size, i know the gt4202 will produce more power but does the bigger comp wheel increase the boost threshold over a gt4294?

Thanks in advance

Lee

Howard Coleman

iTrader: (6)

since you have no replies and i have a few minutes i thought i would try to be of some help.

you are asking for a comparo of the gt4294 and 4202.

i look at turbos by taking the area of the major and minor and solving for the average area...

gt4294

compressor area in sq inches... 8.384
turbine area............................... 7.527

turbine is 89.7% of compressor

72 pounds per minute max at 14.7 psi boost
85 pounds per minute at 24 psi

max rotary power at 85 pounds is 85 X 14.471 = 1230 CFM/1.92 = 640 rotary rear wheel hp

gt4202

compressor area 9.726

turbine area 7.527

turbine is 77.3% of compressor area

74 pounds per minute at 14.7 psi
95 at 35 psi

max rotary rwhp is 95 X 14.471 = 1375 CFM/1.92 = 716 max rotary rwhp

the above is not the "be all and end all" but should work in most circumstances. it is worth pointing out that anything north of 600 rwhp and you need to build the motor a bit differently, rotor clearancing etc...

of course you will need to run racegas or water and or meth in boost.

HTH,

howard

turbotoaster

thanks howard, i was wondering if anyone would help and your normally the best at this type of stuff.

Now i understand about the larger compressor will flow more, hence the extra max bhp, what i was more asking was how if keeping the same turbine area, would the larger comp area cause a later spool.

the example of the top of my first post mentions to turbos which are both rated for the same power but do it in 2 different ways, one big comp and small turbine and the other more equal.

The main question is, if we were to put them both on a rotary, what would most likely happen, would the small turbine spool earlier but run out of puff, even with the big comp wheel.