Basch SC dyno question

[Khuang]

I saw at Daliracing.com, that a Basch SC alone increased hp from 239rwhp to 366rwhp, 53% increase, how can that be?

At 5 psi, it is 5/14.7 = 34%, so that should be the maximum hp increase at 5 psi under ideal condition. The car is definitely not going to be alot more efficient after the blower when nothing else changes.

 

[Yellow Rose]

You are making a fundamental mistake in your math.

It is not 5/14.7=34%. It is (5+14.7)/14.7=134%. You were dividing gauge pressure by absolute pressure. With the correction in the numerator, you are now dividing absolute pressure by absolute pressure.

Before you jump to conclusions, no, increasing manifold pressure by 134% does not imply that HP is increased by that same percentage. There are internal thermodynamic inefficiencies that negate this much boost.

[This message has been edited by AndyVecsey (edited 21 March 2002).]

[This message has been edited by AndyVecsey (edited 21 March 2002).]

 

[Kirthasa]

Andy, I think you completely missed his point. When he says 134%, he's saying a 34% increase in incoming air pressure from stock (100%) setup. This is exactly the same as what you are saying. I don't doubt the BBSC, but I must admit that I've asked myself the same question - With only a 34% increase in incoming air pressure, how does power increase over 50%? I feel that I must be missing something, but I can't quite put my finger on it. Any physics-whiz gearheads know the answer?

Aaron

 

[Khuang]

Andy:

Kirthasa is right, you missed my point + I say ideal condition, we are not under idea condition. The initial 100% of air makes 239 rwhp. Now we are supposed to add approx. 34% more volume of air from the SC, one can't expect 34% increase in power, let along 50%. With compression of air, it also heats it up, the heads has to flow more air, exhaust flow more air. IT should all decrease the efficient to 25% or so. So one should expect 25% increase in HP or so.
One way to get high dyno #s is to dyno at higher elevation since dynojet corrects for elevation. With the large Basch SC, the SC can easily supply the same amount of air at sea level as at 3500 ft but dynojet will add about 10% correction factor. Another possibility is the SC is putting out more than 5 psi.

My main question is how can a 5 psi blower increase rwhp by 50%, I know it is not possible even under idea condition.

Originally posted by AndyVecsey:
You are making a fundamental mistake in your math.

It is not 5/14.7=34%. It is (5+14.7)/14.7=134%. You were dividing gauge pressure by absolute pressure. With the correction in the numerator, you are now dividing absolute pressure by absolute pressure.

Before you jump to conclusions, no, increasing manifold pressure by 134% does not imply that HP is increased by that same percentage. There are internal thermodynamic inefficiencies that negate this much boost.

[This message has been edited by AndyVecsey (edited 21 March 2002).]

[This message has been edited by AndyVecsey (edited 21 March 2002).]

 

[Andrie Hartanto]

Hey Kerry,

Nice to see you back socializing with the NSX community. So, are buying NSX again?

 

[Khuang]

Maybe, getting over the crash and getting the itch. I will sent you pics of my cracked blower, etc.


Hey Kerry,

Nice to see you back socializing with the NSX community. So, are buying NSX again?[/QUOTE]

 

[Russ]

First, before calculating % HP gain, one must first add in parasitic drivetrain losses in order to compare apple to apples. Thus if a stock 3.0L is rated 270 HP and RWHP is 239, that yields 31 HP drivetrain loss. Add that into 366 and that yields 397 HP at the crank. That indicates a 47% increase in actual HP, not 53%. That's closer to the theoretical 34% but still well above it.

Second, the BBSC increases the the RPM at which torque and therefore HP peaks. In stock trim torque begins falling off above 6500 RPM and decreases up to redline. In BBSC trim max torque is reached at 7000 RPM and does not decrease nearly as much as stock above that. Since HP is a factor of torque and RPM, and the BBSC torque curve is significantly different than stock, it's easy to see how peak HP of a BBSC setup can exceed that which would be suggested by a simple boost pressure analysis.



------------------
Russ
'91 black/black

 

[grippgoat]

Russ is right on.

HP = Torque * RPM / 5252
Torque = HP * 5252 / RPM

Because of the supercharger design, peak torque is higher than stock, around 7k rpm, and it's peak is about 37% higher than stock. This is according to the graph at scienceofspeed.com, which I think is the same as the one at dali-racing's site.

Now, stock, the torque at 7750rpm was below 160ft-lbs. But on the BB, it was still around 250 ft-lbs.

Doing some math, you see that:
160 * 7700 / 5252 = 234
250 * 7700 / 5252 = 366

And thus, with a peak torque increase roughly equivalent to the amount of air going in, you end up with a considerably more than 50% increase in horsepower, because of WHERE that torque is made.

-Mike

 

[ChopsJazz]

Come on guys, when I signed onto this forum they said there wouldn't be any math.

 

[Hrant]

Originally posted by ChopsJazz:
Come on guys, when I signed onto this forum they said there wouldn't be any math.

Hey Ken, I thought music was all math ......

 

[Number9]

So we've established an argument as to how a lossless 5-lb. boost might give the measured result. But in the real world (where I live, BTW), I would invoke Occam's Razor and conclude that the BBSC 5-lb spec is merely nominal and that the actual boost is higher.

[This message has been edited by Number9 (edited 23 March 2002).]

 

[Russ]

Interestingly, visually interpolating from the HP curves posted on Dali's site shows that, at 6500 RPM, stock HP is roughly 235 and BBSC HP is roughly 320 HP. This yields a 36% increase and, correcting for parasitic losses, a 32% increase.

Certainly it's true that these tests could have been run with boost exceeding 5 lbs. However, it seems unlikely that Mr. Basch, who has a very good reputation for integrity & honesty, would be fudging his dyno results.

"Things should be made as simple as possible, but no simpler." -Albert Einstein



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Russ
'91 black/black

 

[Number9]

Originally posted by Russ:
Certainly it's true that these tests could have been run with boost exceeding 5 lbs. However, it seems unlikely that Mr. Basch, who has a very good reputation for integrity & honesty, would be fudging his dyno results.

No one is impugning Mark's integrity. Certainly not me - that's why I didn't have an SC installed until he was available to do it. But all parts have tolerances and frankly in a preproduction system, I wouldn't be surprised if the system might produce somewhat more peak boost than anticipated. Sure is easier to believe in the present context than 0 internal thermodynamic inefficiency and 0 mechanical losses from having to drive the compressor in the first place. To reiterate, I trust and respect mark too, but all specs imply an error bar around it.

 

[NSXnBRLA]

Well has anyone who has the BBSC installed, had their own dyno test done? Perhaps they could post it here to remove any doubts/questions.

------------------
1992 NSX

 

[burbel]

OK, from page #198 in "Maximum Boost" by Corky Bell, he covers a twin turbo setup for the NSX (kinda neat that his book's test mules is an NSX, but I digress...)

In the book example, Corky is turbo charging a 3.0L NSX, by adding two aerocharger turbos running 5.2 lbs. of boost, with the goal being a 100bhp improvement.

By Corky's calculations, the Aerochargers would give 100bhp at 5.2 lbs. of boost. The formulat that Corky used for the performance gain comes out to [(275 + 100)/(275)] - 1, or .36. This is close to the math that Khuang originally posted, for the gain for the 5 lbs. of boost for the BaschBoost (note: that calculation is based on power changes, not efficiency).

The target cfm for Corky's turbos are 520cfm, split between two turbos. At 260 cfm, the flow map for the aerochargers show an efficiency of 58%. Looking at the specs for the Novi, the cfm is rated at 850.

Therefore, while the aerochargers max out on the NSX with a ballpark 100bhp gain, the Paxton, which I think is operating closer to it's peak efficieny (which I could not find on the Paxton site), since it's well under it's maximum of 850cfm at 5psi), loses less energy, and, therefore, can create more power...

Seem reasonable?

I am an interested party in all of this, since I'm on the list for a BaschBoost myself...

 

[NSXGOD]

Originally posted by burbel:

<snip>
I am an interested party in all of this, since I'm on the list for a BaschBoost myself...

So am I. [both interested and a customer] The Paxton NOVI 1000 SC that is used in the kit takes a maximum of 11HP to run at full speed. I quote the engineers at Paxton.

As for the post questioning the dyno testing above; all runs posted were done at whatever feet over sea level that PHX is - nothing needs to be fudged to make it look good on paper - the system just works - pure ands simple. If you have any doubts as the to accuracy and truth of Mark B's published info you can always choose to buy something else - that is the magic of a free market system.

------------------
need more info? please private me @

[email protected]

Mark Johnson, CEO of Custodial Services @ Dali Racing, a Not For Profit Company.

 

[grippgoat]

Just to clarify, my post was simply to explain how roughly how 35% torque gain could turn into a 50% hp gain simply by explaining the relationship between torque, rpms, and horsepower. The original question was "how can there be 50+% more horsepower when there's only 30% more air?"

As far as the real-world is concerned... That's what the dyno plots are for.

-Mike

[This message has been edited by grippgoat (edited 25 March 2002).]

 

[David]

"There is no such thing as a contradiction. If there appears to be a contradiction, check your premises."

- Ayn Rand

 

[David]

Come on, guys. Think about your assumptions.


Anyone? Anyone? Bueler?

 

[SpeedDemon]

Hi all,

It seems like everyone here is focusing on this concept of "A 34% increase in psi doesn't support 50% more power.."

I'm no engineer or math wiz, but, it sounds like your basic assumption could be flawed.
It seems like everyone is assuming base pressure is 14.7psi, but are forgetting that.. Engines run under vacuum!

At WOT when a naturally aspirated engine is making max power, wouldn't it be closer to 10-11psi when the vacuum is taken into account? And wouldn't therefore 5psi of boost (over 14.7) be about an 8.7 to 9.7 rise in PSI, giving you the 60-65% increase in power you're looking for (and allowing some inefficiency, to result in a true 50% power increase?)

Marc
97 NSX-T Twin Turbo

 

[true]

Originally posted by SpeedDemon:


At WOT when a naturally aspirated engine is making max power, wouldn't it be closer to 10-11psi when the vacuum is taken into account? And wouldn't therefore 5psi of boost (over 14.7) be about an 8.7 to 9.7 rise in PSI, giving you the 60-65% increase in power you're looking for (and allowing some inefficiency, to result in a true 50% power increase?)

Marc
97 NSX-T Twin Turbo

Hi Marc, your theory is incorrect...if you have a vacuum/boost gauge on an naturally aspirated motor you will see it rise to 0 vacuum (1 atmosphere(14.7)) at WOT. A N/A motor under full load will be 0 vacuum....anything greater then that is boost...so 5 psi = 5psi. One interesting thing to note is the ability for N/A motors to create boost. Some of the top N/A honda dragsters can produce a few lb's of boost because of how well they are tuned. A properly (optimal) designed exhaust manifold can work like a vacuum and suck the burnt mixture right out of the combustion chamber...also sucking air in on the intake stroke. (if cam duration and overlap are correct)

------------------
jack of all trades, master of some.

 

[David]

I believe it gets close to a fulll atmosphere, but still operate at a bit of a vaccum. Only really radical motors are going to be at a full atmosphere at WOT, especially going up through the rpms. I think that accounts for a large part of the boost issue. Also, you really need to measure CFM, as that is what = hp. While psi is a reasonable surrogate, it is not a perfect one. If you set 5 psi above atmoshperic in the intake as producing an actual pressure delta of 6-7 psi, the numbers work out pretty well.

 

[true]

Originally posted by David:
I believe it gets close to a fulll atmosphere, but still operate at a bit of a vaccum.

I don't have lab grade test equiptment but its _basically_ 0. Especially as far as a standard vacuum gauge..you might be right though..a SLIGHT amount of vacuum.

I think that accounts for a large part of the boost issue. Also, you really need to measure CFM, as that is what = hp. While psi is a reasonable surrogate, it is not a perfect one. If you set 5 psi above atmoshperic in the intake as producing an actual pressure delta of 6-7 psi, the numbers work out pretty well.

Im kinda confused at why measuring cfm would be ideal. Vacuum is negative(-), boost is(+) while cfm is neither..it could be either. Are you saying cfm is a more accurate measurement since it's units are different....airflow volume vs. airflow pressure? Thanks.


------------------
jack of all trades, master of some.

 

[grippgoat]

Hrm. A balloon inflated to 5psi above atmosphere has "boost" of 5psi... But the air is just sitting there, so it's at 0 cfm, and certainly isn't going to make any power. So you could have 100psi of boost in your intake tract, but if it still doesn't flow into the engine well, you won't see the horsepower benefits.

Pressure and volume are closely tied when it comes to gasses, though, so if your compressor was putting through a constant amount of air, but it wasn't making it through the intake tract as quickly, wouldn't it cause higher pressure in the intake tract? And conversely, if your intake tract allowed smoother flow, it would stay farther ahead of your compressor, showing a lower pressure with the same amount of air coming out of the compressor?

Or are my layman's physics getting me in trouble again?

-Mike

 

[sjs]

Originally posted by grippgoat:
... Or are my layman's physics getting me in trouble again?

-Mike

I don’t think you are all that far off. Summing up and elaborating on some of the prior posts, I suspect the delta gain is somewhat greater than the simple boost value for the obvious reasons. (sometimes the apparent is actually correct) Although vacuum at WOT is too close to zero to account for much by itself, that’s not to say that air supply is 100% efficient. The fact that it must be pulled in past air filter and through the intake track, not to mention past the valves means there is significant resistance. That’s why even on a super efficient engine like the NSX there is probably a little breathing capacity to be gained with port/polish , bigger valves, further intake runner tuning, etc. (not to say the results would be across the rev range or even where you want it.)

Enter the great equalizer, boost. Although the same mods may also help a boosted car, as a percent of total HP (I’m guessing) they will be less because the air if forced in under pressure and you can pretty much cram as much in there as you want.