Thread: Screwy Riva dyno numbers. . .
08-18-2007, 08:51 PM #1
- Join Date
- Aug 2006
- Gonzales, La
Screwy Riva dyno numbers. . .
Okay, so I been trying to figure out how fast I could go with an XS intercooler and S3 supercharger with the stock ECU and 42 lb injectors. This would be basically a S3 but limited to 8100 rpm. Looked up the dyno numbers and found this (All numbers at 8100 rpm):
Stock: 209 hp @ 7.3 psi
Add 3" intake: 211 @ 7.7 psi
Add Vortec S2 impeller: 215 hp @ 8.4 psi
Add Intercooler: 229 hp @ 8.7 psi
Add S3 impeller/cover: 274 @ 9.9 psi
The S3 improvement over S2 just doesn't make sense to me. With only 1.2 psi additional boost, it's making an extra 45 hp? My turbocharged 388 Z28 doesn't even gain 45 hp for every 1 psi boost! Either they are understating the S2 numbers, or overstating the S3 numbers.
For kicks and giggles, I did a little math. The baseline premise here is that speed is proportional to the square root of power. This holds fairly true for anything drag-limited (car top speed, boat top speed, even gas and liquid flow in pipes).
Stock is 68 mph. Lets say we install a Riva Grate and Wedge, so now it goes 70 even.
Add the air intake, and you only get to 70.3.
Add the S2 impeller, and you only get to 71.
Add the intercooler, and you only get to 73.5 mph.
Add the S3 blower, and you get all the way to 80.3 mph.
All the numbers seem about right except the full Stage 2 package, which runs 2-3 mph faster than the calculated 73.5.
If I reverse the calculations going by what people run and calculate hp, the fastest S2's run around 76.5 mph (RXP'in in MI), while the S3 minus ECU runs about 80 (rxp244). To run these numbers, the power would need to be 250 hp and 273 hp respectively.
By this math, the S3 minus ECU matches up about perfect, while the Stage 2 power would need to be quite a bit higher than Riva's advertised 229 hp. Is it also coincidence that the 2008 RXP will have an upgraded impeller and external intercooler (sounds an awful lot like a Stage 2) and advertises 250 hp, not 230?
The bottom line is that I believe the Riva Stage 2 is underrated in hp, but I'm not sure why.
Last edited by engineermike; 08-18-2007 at 08:53 PM.
08-18-2007, 09:05 PM #2
08-18-2007, 09:07 PM #3
08-18-2007, 09:15 PM #4
OK, Mr. 91.8,......I have a theory,......you went and rode the 08. This we know,.....you completely built a bada** 07 and are now selling it for cheap,......
I have several theories here,......
You became a crackhead and are selling everything you own,......
Nope,..that doesn't sound right,.......
You forgot to pay your vendor bills and have hocked your stuff,.....
Nope,....that doesn't sound right either,.......
You think it will be comparable in price to mod the new 08's as compared to 04-07, maybe the 08's have a new hull design and it will do WELL over 90 mph because you're in the know, and knowing what you do for a "hobby" I bet you'll get to 100 mph easy,....... Just a thought,......
08-18-2007, 09:16 PM #5
- Join Date
- Oct 2005
I don't think the S2 is underated at all. Like Jerry said, you have to take into acount that Riva is doing the dyno test with their ECU on. It's timing is allowing it to produce more HP than the stock ECU. That's why you notice the 45HP difference between the S3 and S2 dyno at 8100 RPM. Yes the RS3 SC is worth a portion of it, but like you said no way it's 45 HP. Mike also remember that boost isn't everything. The RS3 SC is moving a larger volume of air too. You have to consider all the other parts in the full RS3 that are helping too. That 45 HP difference at 8100 RPM is divided up a few ways.
08-18-2007, 09:19 PM #6
- Join Date
- Oct 2005
08-18-2007, 09:25 PM #7
08-18-2007, 09:26 PM #8
08-18-2007, 09:27 PM #9
08-18-2007, 09:42 PM #10
HP is not linear. It is an equation. It's a number calculated.
Now the one thing you are leaving out is the rpms, which effect both calculated hp and of course the real life application.
One HP number is taken at 8100. Another HP at 8500. They will be a tad different, and calculate differently.
You MUST take into effect the torque and rpms of the calculation...and the torque isn't flat or linear either. So questioning it, without having all the details AND doing the equation will leave you scratching your head.
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