"Dyno Horsepower discussion"

Per my post in the Apex supercharged post from srxspec. Lets hear the experts comment on the many variables that need to be taken into consideration while understanding dyno readings...BBY

Nice try Matt, no takers yet.

Ahh, not so much

I couldn't even fathom trying to type that much. Perhaps Supertuner could elaborate. More than you could imagine though. I know one thing for sure, I get sick of the sales pitchin B.S. numbers out there that many consider gospel.

(BANKS)

http://www.bankspower.com/tech_truthintesting.cfm

"Testing using proper scientific testing methods. That means testing under controlled and monitored conditions, elimination of outside variables, and sustainable results"

"It all comes down to the testing method and the ethics of those doing the testing"

(SnowTech)

http://www.land-and-sea.com/articles/snowtech_dynomite_vs_sledyno.htm

"Both dynos are very capable pieces of equipment, but the data from both can be skewed and misinterpreted, it is very easy to obtain false information, and it is very easy to make either say pretty much whatever you want."

(DYNOTECH)

http://www.dynotechresearch.com/index.htm

"Bender is finalizing their Garrett turbo system on their own SuperFlow dyno, and will pay me to verify numbers for public consumption"

DynoTech
8 Apollo Drive
Batavia NY 14020
585-993-2777

(Xtreme-Performance)

http://www.xtreme-performance.com/custompage.asp?pg=dyno_results

4738 WCR 12
Dacono, CO 80514
303-654-0867

(BIKEMAN)

http://www.bikemanperformance.com/dyno.php

We finally have our SF902 dyno up and running! If anyone is interested in getting an appointment or wants more information, please contact us.

1791 82nd
New Richmond WI 54017
715-247-6060

http://www.superflow.com/sf902/default.htm

http://www.superflow.com/acrobat/sf902.pdf

The SF-902 can measure:
engine speed, torque, acceleration, fuel flows, air flows, liquid flows, air temperatures, exhaust gas temperatures, liquid temperatures, oil pressure, manifold pressure, barometric pressure, humidity, analog voltages.

The SF-902 can calculate:
power, corrected power, air-fuel ratio, brake specific air consumption, volumetric efficiency, mechanical efficiency, and more.

You ensure that the engine does what it’s intended to do. Quantifying the results of your modifications.

(Westech Perfomance)

BSFC is a frequently misunderstood term that rates an engine’s efficiency in terms of fuel usage. More specifically, it is the measured fuel flow in pounds per hour divided by the horsepower. On the engine dyno, this calculation applies to observed power numbers, not corrected power. If you look at a dyno sheet and try to compare corrected power numbers to brake numbers it won't compute. Many people believe BSFC indicates a rich/lean condition, but that is incorrect. The brake specific rule of thumb says that a typical engine will burn one half pound of fuel per horsepower per hour, or .5 BSFC. This is based on the efficiency of a relatively good combustion chamber and reasonably well-matched intake and exhaust components capable of maintaining good dynamic energy across the engine. Most rough fuel requirement calculations are based on a .5 brake number, but this is only an estimated number indicating relatively good efficiency. It means that an engine of average efficiency generally burns about .5 pounds of fuel per horsepower per hour. The best (lowest) brake number always occurs at peak torque where the engine is most efficient.

(M.Performance)

What can you expect to see on your run… Here are some examples…

.73 - .68 - Factory type safe all around…

.67 - .62 - Well tuned all around setup…

.61 - .55 - Snocross - Drag Race…

.54 - .49 - Lean & Mean (short burst drag race)…

(Lowell Horning)

Does a Turbo lose power with altitude? Yes!

Atmospheric Pressure = 14.5 psi, Boost = 10 psi, Total Pressure = 24.5

Atmospheric Pressure @ 9000 feet = 10.5 psi + Boost of 10 psi = Total 20.5 psi

Approximate Pressure Loss = (24.5 - 20.5) = 4.5 (4.5/24.5) = 18.36 % @ 9,000 feet

Turbo considerations: As altitude is increased the turbo fan must increase rpm to maintain a constant boost pressure. With large displacement engines (read 800cc) the turbo fan may have to spin faster than is efficient. The result is slower acceleration. The cure is a larger turbo or lower elevation. Mountain sleds will challenge the best tuners ability to compensate for temperature, altitude, and changing snow conditions! The power loss due to altitude is much less with the Turbo.

Just as important -- BMEP

Brake Mean Effective Pressure

BMEP-PSI = Average Cylinder Pressure in PSI

Two Stroke -- BMEP = HP x 6500 / L x RPM

Four Stroke -- BMEP = HP x 13000 / L x RPM

L = Displacement in Litres (80 cc = .08 Litres) (700 cc = .7 Litres)

Note: 3% Loss of HP & Air Density -- each 1000 ft. of Elevation Above Sea Level

Examples: 1000 T- Cat 166 hp @ 8400 rpm
(166 hp x 6500 = 1079000) / (1 x 8400) = 128.45 BMEP
(190 hp x 6500 = 1235000) / (1 x 8400) = 147.02 BMEP

Ported T Cat ~ Exhaust TA (time area) = 155.6 BMEP @ 8400 rpm
155.6 / (6500 / 8400) = 0.7738 ~ 155.6/.7738 = 201.08 hp

700 Yamaha Mtn. Max 140 hp @ 8200 rpm
(140 x 6500 = 910000) / (.7 x 8200 = 5740) = 158.53 BMEP
142 hp @ 8000 rpm (923000) / (5600) = 164.82 BMEP
150 hp @ 9000 rpm (975000 / (6300) = 154.76 BMEP

982 SRX Union Bay 211 hp @ 8900 rpm
(211 x 6500 = 1371500) / (.982 x 8900 = 8739.8 ) = 156.93 BMEP

Good way to compare engine volumetric efficiency. Engine compression in psi plus pipe working at 110% may? come close to BMEP. If your BMEP is not higher than your compression psi -- you have a problem.

Snowmobile Guidelines:

Less than 160 BMEP = 92 octane Pump Gas

Race Sleds 160 -190 BMEP = 94 octane - C16 Race Gas

i plan on posting afew things matt, but like mike said, there is so much to it you can't imagine. i want to try to make it easy to follow, but it will not be acouple minute write-up. i'll probably get something on over the weekend. jeff

lots of great info hammer, unfortunately most people will not understand it, thats where time will be needed to try and walk someone through it. jeff

Hammer, welcome to this site. As always you have a bunch of info to share, all good too. I've found a lot of good stuff on your Snowest posts.

Keith

Thanks...

I have the all the same questions buzzing around in my head everyone else has so I'm constantly reading up on the topics associated with our sport… I'll take Math, Physics, and Principals of Operation over opinion any day… Just the facts please… I’ve done a bunch of different motorsports but I get the most enjoyment from snowmobiling… Gotta love it !!!

Hammer

I appreciate your post. Excellent info...BBY

KnappAttack said:

I couldn't even fathom trying to type that much. Perhaps Supertuner could elaborate. More than you could imagine though. I know one thing for sure, I get sick of the sales pitchin B.S. numbers out there that many consider gospel.

Click to expand...

Sure I will elaborate but where do I send the bill for 7 - 8 hours of typing?