How to determine flywheel hp from rwhp
Registered User
Joined: Mar 2003
Posts: 194
From: Maysville Ky.
Originally posted by Injuneer
If you do the math right its even worse than that:
390 / 557 = 0.700
Your losses are 30%. Seems unreal with a locking convertor.
-Were both engine and chassis dynos "SAE corrected"?
-Were both dyno's done at approx. the same rpm/sec acceleration rate?
-Was the full air intake and exhaust system (to the extent possible) installed fot the engine dyno test?
-Was the convertor in fact locked up?
-If not locked, have them plot (or give you the data table for) HP vs. engine rpm vs. MPH. With that data, you can estimate the convertor "slip". Mine is about 11% under 800 lb-ft torque. The guys who do all my work tell me that is a reasonably tight convertor - I don't know, because I know NOTHING about automatics. This is the first "racing" automatic I have ever owened.
The Ford 9" is worth an additional 3% loss, according to published (National Dragster) data. So.... 25% for your drivetrain, assuming they didn't lock the convertor, and allowing for the 28" tires.... yes, they WILL make a difference on a chassis pull..... seems not unrealistic. But then the TH350 is supposed to be more efficient than the TH400.....
If you do the math right its even worse than that:
390 / 557 = 0.700
Your losses are 30%. Seems unreal with a locking convertor.
-Were both engine and chassis dynos "SAE corrected"?
-Were both dyno's done at approx. the same rpm/sec acceleration rate?
-Was the full air intake and exhaust system (to the extent possible) installed fot the engine dyno test?
-Was the convertor in fact locked up?
-If not locked, have them plot (or give you the data table for) HP vs. engine rpm vs. MPH. With that data, you can estimate the convertor "slip". Mine is about 11% under 800 lb-ft torque. The guys who do all my work tell me that is a reasonably tight convertor - I don't know, because I know NOTHING about automatics. This is the first "racing" automatic I have ever owened.
The Ford 9" is worth an additional 3% loss, according to published (National Dragster) data. So.... 25% for your drivetrain, assuming they didn't lock the convertor, and allowing for the 28" tires.... yes, they WILL make a difference on a chassis pull..... seems not unrealistic. But then the TH350 is supposed to be more efficient than the TH400.....
Both dynos were SAE corrected.
Engine dyno was done from 3,500 rpm- 7,300rpm
Chassis dyno was done from 3,000rpm -6,400rpm.
Was using full intake with filter from outside source on engine dyno
Was using no intake at all on chassis dyno.
Both dynos done with open headers
Converter was locked up. We did not lock it up in 2nd gear just 3rd.
I do beleive that using the 28" slicks with only 14 pounds of air cost me HP. Should have used street tires with 40 pounds in them.
Was also wondering if my torque converter is to loose. I will be calling Precision Industries tomorrow.
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