Quote:
Originally Posted by camcojb
Now I understand.  550 n/a FHP is probably close, knowing his conservative boost level. Hopefully Mark can share the engine specifics that aren't secret.  |
After beating mercilessly on Red Devil for a couple years without issue, Mark was almost set to have Brian Thomson (
http://www.thomsonautomotive.com) just build another copy of that engine - after all, why mess with a proven package? However, we were always talking about how he could use more HP, while giving up some TQ. As well, the thermal requirements for Red Devil were getting a little difficult to say the least.
The goal of engine for Mayhem was to address all of these 'short comings' - and I think the results show at least a couple of those have been meet very well (won't know the whole cooling factor until installed and run in car).
As far as calculating power per % boost - it gets a little more complicated. Positive displacement superchargers like the TVS Eaton series are quite efficient from an adiabatic standpoint. But like any compressor, they have an efficiency map that shows where you are operating based on total airflow and pressure ratio. Adiabatic efficiency determines how much you will heat the air for those given parameters (airflow & pressure ratio). This factors into a couple parameters you are most interested in: Density ratio and temperature.
While everyone running a boosted motor likes to talk pressure ratio (PSIG), what you really care about is density ratio. That determines the amount of oxygen you are moving through the engine (and therefore power). The more efficient the compressor, the less heat added for same amount of pressure (which results in higher density ratio).
As well, less heat means less heat to remove with intercooler. If you had 100% adiabatic efficient compressor, you'd need no intercooler as outlet air would be same temp as inlet air (and density ratio would be same as pressure ratio).
Added to this, with an engine driven compressor, there are mechanical power losses associated with powering the compressor. Again, these are plotted out on an efficiency table, but one that relates pressure ratio and compressor RPM to power required. (Turbo's have losses too (backpressure - just not directly mechanical - there is no free lunch....)
So what does this all mean when we designed Mark's new engine? Well, we knew the goals (more HP, less TQ, less heat). And we had all the data from Red Devil. So we targeted efficiency improvements to reach these goals.
Adiabatic efficiency was plotted for desired airflow (@ density ratio) to increase power and calculate intercooler demands. Blower losses were plotted to calculate mechanical efficiency. Airflow of engine was altered with revised cylinder heads and cam shaft design based on modeling.
Original target for Mayhem engine was a conservative 850 HP / 800 TQ while reducing cooling demands. Result was we overachieved our goals from the power side - and data from engine dyno shows we are on right track from cooling side.
Red Devil made 780 HP / 830 TQ @ 15 PSIG in final calibration form.
Mayhem is making 875 HP / 815 TQ @ 11 PSIG (and we're not done yet!)
My old thermodynamics instructor would be proud! Actually still using that knowledge....
Bottom line, with all the parameters involved, it is never as simple as using a fixed percentage increase per measure of boost. Many, many pages of notes and calculations for all this - just scratching the surface.
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
Short clips: Goodguys Pleasanton autocross and pit videos
I remember when they were first starting the dynoing of the ZR1's their first dyno pulls were making close to 700 rwhp. They definitely backed it down for the production cars.
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