Lagavulin

Andy, I'm extremely anxious to know how your car dynos out as my calcs seem like they might need some tweak-age. Here are my concerns regarding the calculations versus ‘real–world’ results.

The 'new power' formula given in Corky's book is as follows:

Power = (original power) x (new pressure ratio) x (density ratio) x (vol efficiency ratio) x (drive power efficiency)

For your car using our calculated 6.2 psi I have:

Power = 316hp x (1.42 PR) x (84% DR) x (1.05 VE Ratio) x (90%)
Power = 356 crank hp

That can’t be right...

And for rwhp, I am not using the ‘standard’ 15% drivetrain loss; I’m using Corky’s method instead:

rwhp = (‘New HP’) - (Original HP x 15%)
rwhp = 356 – (316 x .15) = 308 rwhp.

If anyone wants to flame me on this method, that’s ok as I’ve never personally dyno-ed and engine all by itself, and then dyno-ed that same engine in the car on a chassis dyno as Corky has. Oh well, flame-suit on!

But as you can see, you’re getting killed by the DR as you ‘lose’ 16% of your charge density by not using an intercooler, but we expected that up-front.

Orig CFM = 477
New CFM = (Orig CFM) X PR = 477cfm x 1.42 = 678 CFM
Actual CFM = (New CFM) x DR = 678cfm x .84 = 569 CFM

Net CFM Gain = (Actual CFM) - (Orig CFM) = 92 CFM

With an 85% efficient intercooler, the DR becomes 97% which means you’re only losing 3% of your new-found charge density, which ends up giving you 411 crank hp, or 364 rwhp.

I’m thinking the culprit in the calculations could be in the ‘Volumetric Efficiency Ratio’ which is the ratio between the two ‘air pumps’: your engine, and the supercharger.

SC VE = 92% for a roots and screw-type
Eng VE = 88% for 4-valve, and 80% for 2-valve

VE Ratio = (supercharger VE) / (engine VE)
VE Ratio = .92 / .88 = 1.05
VE Ratio = .92 / .80 = 1.15

As you can see just by looking at the calculation itself, as the engine VE decreases, the actual VE Ratio increases. The author does justify this, but I do not know what to think.

I am missing something somewhere, so I’m hoping your results will help me out. Or someone else can correct me, please!

Lagavulin

GoRideSno

Lagavulin,
I don't know. I do know that I drove around the block a few more times today and the car felt strong. With the 5.25 lower pulley it spun the fairly fresh 265s from a dead stop. It held 4 psi pretty steady durring acceleration and I think I saw 5 psi or more at one point. I never reved past about 5k rpm. The passenger said it felt faster than my neighbors C5 Vette. I probably won't be able to drive it again for 2 weeks.

I hate to mention it but you used the #s for the old M112 I am using the new MP112. It has teflon on the rotors so the exit temps are lower. The graph earlier in this post shows the stats for the MP112.
Cheers,
Andy K

Lagavulin

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> I probably won't be able to drive it again for 2 weeks.</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Whew, I’ll bet that’ll be an excruciating wait!

Were you able to schedule a dyno session yet?

Do you have an air/fuel meter installed, and if so, what was it reading while terrorizing the neighborhood? <img border="0" alt="[hiha]" title="" src="graemlins/roflmao.gif" />

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">I hate to mention it but you used the #s for the old M112 I am using the new MP112. It has teflon on the rotors so the exit temps are lower. The graph earlier in this post shows the stats for the MP112. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Doh! I’m glad you did mention it. So I went sniffin’ around Eaton’s site and could not find an MP112, so I did a Google search on ‘Eaton MP112’, and ‘MP112 Supercharger’ and got back only two pages worth.

This vendor’s site

<a href="http://www.capa.com.au/eaton_mp112_4th.htm" target="_blank">http://www.capa.com.au/eaton_mp112_4th.htm</a>

lists one. I wonder why it’s not listed on Eaton's site?

I looked at the two graphs as you suggested, and the appreciable difference, and a significant one at that, it that the MP112 spins to 14,000 RPM versus 12,000 for the M112.

As for heat generation, both are nearly identical up to 12,000 RPM, as well as power consumed to turn it, and flow.

Going from a max of 12,000 RPM to 14,000 RPM is a nice jump, but there is a price to pay as it requires more power and will up the discharge temp too. In the meantime, since you’re not spinning anything close to that, it’s good to know you have plenty of headroom to play with if you ever decide to install an intercooler.

GoRideSno

Lagavulin,
Here is the link to <a href="http://www.magnusonproducts.com/" target="_blank">Magnuson Products, the sole distributor for Eaton in the US.</a> You will be able to find a little more info there.

I have an ARM1 air fuel ratio meter. I am getting more than enough fuel through all RPMs. My rail pressure is 46psi at 1k rpm idle, vaccum hoses connected.

<a href="http://www.turboneticsinc.com/liquid.html" target="_blank">Turbonetics/Spearco</a> makes several intercooler cores that will fit underneath the blower down in the V.

Dyno time is atleast 2 weeks out.

<img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />
Andy K

Tony

Thanks for posting those links guys.

Lagavulin..what effects/adantages would be seen by lowering the CR on the S4 motor to 8-9:1?? Does CR play a role in your calculations?

Is the MP112 capable of pumping enough air to take advantage of that lower CR? Whats the max boost it could provide?.

Keep up all the good converstion!

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

GoRideSno

Tony,
If one SC was not big enough you could always put two on there. Lets see...... starting w/ 400 HP from stroker crank, throw in some steel sleeves and some oh so special pistons 8:1 CR, a whole extra fuel system from a donor shark, pump her up to 20 PSI and the SC HP calculator says........
856 HP dream on!

Andy K

Lagavulin

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Lagavulin..what effects/adantages would be seen by lowering the CR on the S4 motor to 8-9:1?? Does CR play a role in your calculations? </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">The primary affect of lowering the compression ratio is the ability to safely run more boost without detonation. To get an idea of how much, re-read my post within the thread we’re in right now regarding John's 22 psi Audi on page 3.

You don’t want the cr too low as you’ll loose low-end torque and the engine ‘crispness’ a higher compression ratio provides. If I were to build a blown street engine, at this very point in time I would go for either 9:1 or 9.5:1 cr.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Does CR play a role in your calculations?</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Yes and no.

No:

No in that it’s not used in the horsepower calculations, yet. Both Corky and Graham Bell state the each point of compression ratio is worth 4-5% horsepower. However, at this point I’m not confident (..although I've been thinking about how to do it correctly, if that were possible) to suggest a horsepower number if you said:

I have an engine whose stock hp is x, stock cr is y. I plan on lowering the cr to z and run xx amount of boost; what will my ballpark hp numbers be?

The horsepower calculations ‘work’ because all else being equal, we are ‘merely’ cramming more air/fuel into the same stock engine in a given amount of time. No other variables were changed such as the compression ratio. And by the way, that is why bigger engines produce more power than smaller engines because since they are bigger, they are able to burn more air/fuel in a given amount of time over the smaller engine. Now with a blower, we have the smaller engine acting like a bigger engine.

Yes:

Yes, since the first thing to check for is the heat generated by the combination of compression ratio and desired boost. That should be first and foremost on anyone’s mind as the health and longevity of the engine depends upon that temp to be below the engine's detonation thresh hold, a certain combustion chamber temp that Corky suggests as 1,075 absolute as a good starting point.

However, a fellow 928er and I have had ‘heated’ debates regarding this number, 1,075, with respect to the 928 S4 engine. He rightfully argues that the S4’s engine number will be higher by virtue of it’s aluminum construction and it’s head design; he suggests that the 928 head design is worth a full point of compression which is HUGE with respect to these calculations. So in other words, the S4 can safely sustain higher than ‘normal’ combustion chamber temps without going into detonation. I would ask him, 'but what is that 'magical' number for the S4?'

If you’ll re-read my initial post within this thread, ..I’ll quote it instead:

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Now that 1075 is ‘an arbitrary’ figure from Corky, and the actual number will vary for an engine type. But the question is, how much variation for an S4 and it’s favorable aluminum heads and pent-roof combustion chamber?

Well, the light bulb finally flickered when I recalled that Mark at FAST ran his centrifugal blower non-intercooled at 5 psi with apparently no problems (..a 32 valve ’85?). The combination of 10:1 compression ratio at 5 psi of non-intercooled boost produces a seemingly ‘S4 safe’ combustion chamber temp of 1,167, 92 degrees over the 1,075 'max'. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Ok, so it looks like we have found a 'magical' S4 safe 'max' combustion chamber temp of 1,167; actually it's a minimum as the car ran safely at that number. Now 'Z' comes along with some apparent real-world-proof (..versus merely calculated) which suggests that an S4 with a non-intercooled centrifugal at 8 psi is safe :

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Tim Murphy's S4 was running 8psi of boost for a year or more, with no intercooler. Even with some leaner than optimum air/fuel ratios before he got that straightened out, there were no problems with the stock 10:1 pistons. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">That combination of 10:1 cr and 8 psi gives us a theoretical combustion chamber temp of 1,229, which is 154 degrees over the arbitrary 1,075, another HUGE number. It does sound incredulous, but if in fact that is indeed true, the S4 is a robust design just waiting for a blower to be carefully/thoughtfully installed and tuned.

To give you an idea of how huge that is, using an 85% intercooler efficiency, we can theoretically run over 100 psi of boost before the chamber temp hits 1,229. Keep in mind we’re only looking at combustion chamber temps and not the stress induced on the system by such large amounts of boost.

Another interesting thing to note is how big a role intercooling plays by reducing combustion chamber temps to achieve a 'safe' 100+ psi versus only 8 psi non-intercooled.

John..

8:1, 14 psig...

Z

I do have problems with putting a huge amount of faith in that 1,075 temperature as far as detonation goes. First of all, it's given as a "one size fits all" kind of a number. Different engines, with different design and construction characteristics, can cause variations from what actually happens in the combustion chamber, and from what the theory of that number suggests. Unless you actually measure it, you really have no idea what that temperature in the combustion chamber really is either. The assumption is made that the air is heated by the compressing of the supercharger, and takes into account a rough estimate of additional heating due to whatever the supercharger's efficiency is. That temperature air is then compressed by the piston in the cylinder, and that's the calculated temperature that's being assumed to be in the cylinder. The temperature that you come up with that way is wrong. Depending on the under hood temperature, construction, length, and routing, of the intake tract, manifold, and heads, the air will be either heated or cooled to some extent after the supercharger compresses it, and before it gets into the cylinder. There will also be cooler fuel sprayed into the flowing stream of air at some point along the line. The fuel will cool the air because of it's lower temperature, and also due to the phase change as the fuel goes from a liquid to an atomized state. The amount of fuel sprayed will have an effect on the amount of cooling that occurs. That's at least one of the reasons why a boosted engine typically makes peak power with a mixture that's richer than the ideal mixture of a normally aspirated engine. Once in the combustion chamber, this mixture will either gain or loose heat from the pistons, cylinders, valves, and surface of the combustion chamber in the heads. The surface area, shape, and material that those things are constructed of will all have some influence as far as that goes. The ambient air temperature is yet another factor that gets thrown in there, and changes things too. In the laboratory theory, if you compressed a volume of air by the amounts stated, in a perfectly thermally insulated enclosure of some sort, the temperature of that air would probably be very close to the calculated 1,075 that's mentioned. That may also even be very close to the temperature at which an air/fuel mixture of that temperature ignites at. There's absoultely no way that the temperature that's really occuring, in a real world, actually operating engine, is able to be known unless you measure it though. Tim Murphy's car and the F.A.S.T. car are both clear examples that the 1,075 theoretical temperature that's calculated to occur, and be when detonation occurs, doesn't reflect what really happens in a hard and fast way.

BC

This tempature number - Does this tell us that because of the 928's efficient head design, that we could run some nice turbos through an intercooler if we could figure out the plumbing? People always talk about the inherent differences between the boost that occurs with a turbo system, and that of a Centrifugal system (and a bit differently, but also engine speed-connected - a Positive displacement such as GoRide's MP)

At 4k, under no load, an engine of most any size, when mated to the correct sized Turbo, CSC (Centrifugal), and PDSC (Positive Displacement) will be (This is a invitation to discuss):

Turbo: No real boost, as there is no load

CSC: Boost, but not as much as a loaded 4k, as it is engine speed dependance

PBSC: NOrmal Boost, no matter if you are accellerating from 100-120 through 4k, or sitting in your garage at 4k.

Am I right? And to continue this threa din it original form on this 3rd and fourth page, the coolest air with normal intercooling will be the Centrifugal, and the warmest will be the turbo.

GoRideSno

Brendan,
With my slight experience I will have to say no to garage V/S 100-120 being the same boots with the PDSC.

Andy K

GoRideSno

Here is a <a href="http://www.caranddriver.com/article.asp?section_id=4&article_id=1910" target="_blank">link</a> to a Car and Driver.com article about the Lingfelter Eaton MP112 roots supercharged Corvette Z06.

530 HP (125 hp gain)
5.5 psi
NO mention of intercooling
3.7 sec 0-60
11.7 1/4 mi
197 mph estimated top speed

"The $185,000 Porsche 911 GT2 trails it to 60 mph by 0.1 second and to 100 by 0.6 second and does the quarter-mile in 12.0 seconds at 121 mph."

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

Andy K

Tony

On the topic of ROOTS, whats the latest on the "Huntley Project"

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

Jim V

Brendan, I don't think any of them would make boost no-load even a 4K RPM; even a N/A engine takes a pretty thin throttle opening to maintain no-load engine speeds and whichever -charger you use can't compress air it can't suck in. ( I know theres some analogy about sucking something through a straw-but it escapes me).

I think the turbo idea has alot of potential, I've been kicking around the TT idea for a couple years and it always comes down to plumbing and intercooler placement. I've looked at everything from cutting some holes in the inner fenders and mounting them behind the lights to cutting a hole in the hood and mounting them atop the engine with a fan to move the air. Latest thoughts are to replace the radiator and condenser with something that has a smaller profile or laying them down Vette-style so the coolers can be placed up front. Of course I want to retain my A/C, and having been turbo-spoiled before 5-7 psi ain't gonna cut it.