A question was asked on inlet design last week, so I thought I\'d give a first installment to guage interest in some articles of a more technical bent. As such it doesn\'t give all the answers but will hopefully give some pointers, and if nothing else cause some questions to be asked. There may be some obvious things I have missed, so please come back with the \'hang on\'type questions.
For this discussion I will go through a first iteration of what I am planning to do with the T2 block sitting all lonely in the garage that is intended for my series 2 that is festering in the garden. I don\'t want an out and out drag car, but I do want to be able to experiment with things. I also don\'t have very much budget to work with.
Anyway my requirement is to have 300FWHP between 6500 and 8500RPM The lower limit will depend slightly on my final gearbox choice (but that\'s for another discussion). Whilst this in itself may seem an odd requirement, I want a car where I know that, after each shift I will be back at the same power I was before. It may not give me bragging rights, but I have the purple peril for that.
So 300HP at 6500 = 242ftlb torque
300HP at 8500 = 185 ftlb torque.
Now based on data I have for a number of engines less the losses a turbo manifold will give a peak torque of around 140ftlb with a 10% fall off at +/- 2000RPM. So If I set peak torque to 6500, I will still have 125ftlb at 8500.
Therefore I will need a 1.72 times torque multiplier at 6500 and 1.48 times at 8500. In an adiabatic system this would equate to 7PSI boost at 8500 and 10.5PSI at 6500. No free lunch so it will be a bit higher (iteration required at this point), but lets say 8.5 and 12PSI for now.
At this point I pull the compressor map for a T04 60-1 and the method in my madness will become apparant. 300HP requires somewhere around 35lb/min airflow if you take the rotary rule of thumb (rrt). As I want the same HP across a range, the mass air flow will be the same, just the boost will be different. On the map I am interested, between 6500 and 8500 I am always in the highest efficiency operating point of the compressor at just over 76%. This means that there will be less heat put in the incoming air, so I can use WI as the intercooler and save the cost and pressure losses of a FMIC. I can also get away with a T2 turbo with a hybrid compressor fitted.
Next installment I\'ll have some numbers on the inlet and plenum considerations to meet this requirement and the amount of water I\'ll need to add to keep everything happy.
Hope this is of interest.
Bill
yes this is of interest ... can you show the compressor map too, so we can see where you get your numbers from for the later bit.
Thanks,
Mike
will follow this with interest:)
two things tho\',
what is the rotary rule of thumb?
bit confused as to which turbo you will actually be using, was the reference to the T04 60-1 just as an example? or are you going to be fitting the compressor from it into the T2 turbo?
cheers
Barry
Mike. //www.google.com enter \'60-1 compressor map\' returns
http://64.225.76.178/catalog/compmaps/fig9.html
Barry: Normal rule of thumb is that 10lb/min=100HP. rotaries are around 10% less thermodynamically efficient than a piston, so require about 10% more air. Empirical evidence suggests that 11.5lb/min per 100HP is as good a number as any for a rotary, at least for a first pass.
As for the turbo, yes I am consdering a T2 turbo with a T04 compressor on it. Not ideal, but the ideal setup for me involves a very expensive custom manifold onto a GT35/40, which I can\'t afford, so I\'m going to make the best of the OEM setup for now.