Huh???!!!!!! I will guarantee it makes way more than 550 rwhp. :thumbsup: 5% efficiency seems just a bit low................ ;) 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.

Well if it is more efficient than 5% than the base engine power number is lower than 550. I know you understand that - IF the blower is 6% efficient than the base motor would make 512 whp. This assumes 12 psi of boost.

550whp is about the max I've seen for the 427Ls motors that are in what I would call the "streetable envelope", and Mark has always setup his cars to have reasonably tractable drivetrains. So I don't think it is "under rating" it to arrive at 550, that is a huge number, somewhere north of 650 on the motor dyno. That's why I'm always very curious about idle speed and vacuum, its the only way I know of to get some idea of how aggressive the engine is.

Not trying to be "one of those guys", I'm just genuinely curious about what went into such an amazing engine.

I think you and I have a different definition of efficiency. If I say a blower is 5% efficient then that means it's 95% inefficient, it costs nearly as much HP to run as it makes.

Since the stock ZR1's dyno in the 540-550 rwhp range (Dynojet) and make 638 flywheel HP, I'm not sure how you'd add 240+ flywheel HP and still dyno at 550 rwhp.

Yes, the blower costs HP to run. If he's making 880 HP he's probably using fuel for 1000 HP+ to cover running the blower.

To answer your question on engine specifics, we'll wait on Mark. I do know that Red Devil idled like a stocker at 600-650 rpm, so the cam doesn't have a lot of overlap.............. ;)

Yeah my mistake - I'm totally using the phrase "blower efficieny" incorrectly. By that I mean you gain 5% power per psi of boost. The max "efficiency" possible is 7% (100 % / 14.7) which is close to what turbos get. Blowers (especially PD style) usually dip down to 5% per psi of boost.

When I say the "base engine makes 550whp" I mean with (theoretically) no boost or blower restriction the base engine makes 550

I was under the impression those dyno results I saw were chassis numbers, but I went back and those are engine dyno numbers. So if I run my little rule of thumb -
5% * 12 psi = 60% more power

875/1.6=550 base engine power at the flywheel. That actually makes more sense to me as a 550 hp Ls 427 is well within a streetable, tractable envelope.

Either way a tour de force, especially as we know the work has been done so it can live under track abuse.

Now I understand. :thumbsup: 550 n/a FHP is probably close, knowing his conservative boost level. Hopefully Mark can share the engine specifics that aren't secret. :unibrow:

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.

Great Read! I haven't heard "adiabatic" in awhile! I really miss Thermo. I remember all of those assumptions we made -- - lots of 100% adiabatic compressors in those old homework problems.

This level of engineering and preparation is what makes Mark's cars special. - - they are true representations of the Scientific Method

Plan
Do
Check
Act


Can't wait for this project to reach the first iteration of "Act".

thanks for the info Dave. I understood most of it......... :lol:

Are you coming out for Optima?

Yup - I'll be there! Always a good time to catch up with people and see some awesome cars.