Need to see some Vortech supercharged dyno sheets!

[DocWyte]

Trying to get an idea of how much boost I need to run to make certain horsepower levels. I'm looking at my NASA Time Trial rules and have to fit into certain power to weight targets depending on which class I want to run in.

NASA uses an average horsepower at the wheels measurement, taken from a Dynojet. For my car it's the peak HP, and then the next 5 highest values at 250rpm increments. For TT4, I can't have an average of more than 290rwhp. Next class up is no more than an average of 355rwhp. My car has all the bolt ons, including Schrick 264/256 cams.

Can anyone give me an idea of how much boost I should run to hit those horsepower targets, as well as what pulley sizes I need? I have the RMS 6" crank pulley, so really I just need to know what blower pulley sizes I should be running.

Posting up some dynos showing how much power you've made with what mods/boost levels would be very helpful for me to ballpark where my average will end up as well.

TIA!

[RRSperry]

Ok, Doc. You make max power at max rpm, so you’ll be looking at 1250 rpm less right? It’s really linier so at about 6500 you want 290. Figure about 8-9 psi should be in the ballpark.

im sure butters or others may have better info. Are you using a RMS design or something else? I’ve got a vf, with the stock crank, and a 3.33” pulley, I made 320 at 6750. At 9 psi... s50.

[DocWyte]

OK, thanks. Looks like I'll need a pretty big pulley, at least a 3.4 something....

[RRSperry]

Depends on what setup you have. The VF used the stock 5.5” crank, and RMS/Dinan uses a 6” crank, So the Sc pulley sizes are related.

[pbonsalb]

(crank pulley diameter divided by blower pulley diameter) times blower step up ratio times redline rpm equals blower speed

Use that formula to compare. Blower step up ratio is 3.45 for V1 and 3.6 for V2 and V3.

(5.5/3.33) x 3.6 x 7000 = 41,621

(6.00/3.4) x 3.6 x 7000 = 44,470

Blower trim will also play a role in boost and power but it is harder to relate to blower rpm. Trims include S, SC, Si, SCi, T, and Ti. The C is for clipped and they flow a little less. The i is for improved and they flow a little more.

Redline is used because that is peak boost. Unfortunately there is no way to calculate boost at blower rpm because blower response is not a straight line. Due to the centrifugal nature, peak boost occurs only at peak rpm and the boost at half peak rpm is the square root of peak boost. This is theoretical and actual results vary, but based on the math, Richard’s system that makes 9 psi at 7000 should make 3 psi at 3500. I have read of people doing worse at low rpm but not better. An exception might be a planetary gear drive centrifugal blower like the Rotrex, but it would not do significantly better.

[RRSperry]

Or a roots type blower...

[DocWyte]

Made the decision to sell the supercharger kit, sold it last Saturday. I'll either run a restrictor plate and be able to stay in the new TT5 class, or I'll just run it as is in TT4. I may pick up the RHD ITB's, I think with those I'd make close to my HP target for TT4, just need to decide if I want to spend $1800 on them plus more for a matching tune.

[Bimmerman535i]

Made the decision to sell the supercharger kit, sold it last Saturday. I'll either run a restrictor plate and be able to stay in the new TT5 class, or I'll just run it as is in TT4. I may pick up the RHD ITB's, I think with those I'd make close to my HP target for TT4, just need to decide if I want to spend $1800 on them plus more for a matching tune.

talk to fsmtnbiker on the ITBs before you spend money. He had a set of Euro ITBs on his pretty built NA S52 and could give you some good insight. I'm 95% sure that engine made nowhere near 290rwhp avg, fwiw. Peak, yes.