calculate your rear wheel horse power

[grumpyvette]

most guys would love to have a dyno, but most guys don,t have the space funds or skills, so theres an easy way to get a fairly accurate measure of the power the engines producing, to your cars rear wheels, (remember theres about an 18% drive line loss) the most reliable way if your looking for rear wheel hp is just to weigh the car accurately and get your 1/4 mile trap speed

1. Torque (lb.in) = 63,025 x Power (HP) / Speed (RPM)
2. Power (HP) = Torque (lb.in) x Speed (RPM) / 63,025.
3. Torque (N.m) = 9.5488 x Power (kW) / Speed (RPM)
4. Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488.

or go the simple route
5. The equation to calculate horsepower is simple:
Horsepower = Torque x RPM / 5,252.


so as an example
350 ft lbs at 3000 rpm/5252=200 hp
350 ft lbs at 4000 rpm/5252= 266 hp
350 ft lbs at 5000 rpm/5252=333 hp



USE THE LINKED CALCULATORS
http://www.wallaceracing.com/gear-speed.php
http://www.race-cars.net/calculators/et_calculator.html
http://www.wallaceracing.com/calc-rgr.php
http://www.datsuns.com/Tech/whentoshift.htm
http://www.frontrange4x4.com/forums/sho ... nformation
http://www.carcraft.com/techarticles/cc ... to_01.html
http://purplesagetradingpost.com/sumner ... index.html
http://www.tciauto.com/tc/gear-ratios
http://www.5speeds.com/ratios.html
heres some calculators to play with

http://robrobinette.com/et.htm

http://www.wallaceracing.com/et-hp-mph.php

http://www.competitiondiesel.com/Phil/bg/

http://www.stealth316.com/2-calc-hp-et-mph.htm

http://drag-zone.com/calculators.html#1

http://www.leeracingteam.com/et.htm

http://garage.grumpysperformance.co...trans-choice-made-correctly.11697/#post-54816


many guys wonder how much difference there will be between an engines flywheel dyno power figures and those off a rear wheel dyno, the general concensis is that an automatic trans , and common tires and a differential will cost you about 18% loss
a manual transmission is going to absorb a bit less power so figure about 12%-15% loss
heres a quote from a transmission company concerning ONLY the transmission loss

I hear people state numbers on how much power is lost in the driveline so I decided to do a little research.
Since I purchased my trans from SilverSportTransmission (Jack Silver) I decided to start there. They contacted Tremec directly
Reply from Tremec via SST:

There are many variables to consider in looking at the data:

1. There are MASSIVE discrepancies between shops
2. The SAE J607 correction factor that hot-rod shops like to use has a lot of “drift” as air conditions worsen. This is why J1349 or derivative standards are used by OEM’s
3. The customer does not know what the inertia factors are for his axles, driveshaft, wheels/tires, etc. etc. etc.
4. Customer does not know the efficiency percentage of his differential/gears
5. Transmission efficiency is measured at lower RPM, so we do not know what the transmission’s efficiencies are with high input shaft RPM

Having said all of that…….


It is only going to make 420-450-ish HP (J607 correction) on an honest engine dyno if the customer has a typical 383-ish CID small block Chevy with:

• Street car cam (220°-235°@ .050” duration)
• 23° heads (not raised runner)
• 1-5/8” - 1-3/4” headers
• Performer RPM intake or similar
• 750-800 CFM carburetor

Here is what I got back from the testing people at the Tremec – see pasted table & chart below.


Speeds in each gear ranged between 1000 – 2500 RPM input shaft RPM.