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Discussion Starter · #1 ·
Calling all gearheads for comments to this theory.
I have a borla cat back exhaust with a volant cold air injection system, and was trying to figure out the actual HP with a set of headers. So I did a search for dynamometer tests that were posted on this forum. I found three 1) stock, 2) borla cat back plus volant, and 3) headers, borla and a cold air system. All tests were done on the same type of dynamometer, but in different locations. The results are as follows:

1) stock 258.2 RWHP 279.1 RWT
2) borla and volant 280.9 RWHP 300.98 RWT
3) headers, borla and cold air 314.38 RWHP 356.23 RWT
The increase in #3 over stock is 56 RWHP and 87 RW Torque. If we adjust these by just 17% for driveline losses, which is on the low side, we get 65.5 HP increase and, 101.8 foot lbs. of torque increase. Now take these increases and add it to the stock advertised numbers we get 405.5 HP and 491.8 torque!!
Currently accepting any and all comments. It sounds high but the theory seems logical. :rolleyes:
 

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I'd like to add to the question.
If you consider the PCM, what would be the estimated increase in HP/TQ in the 3 above cases with the code being cracked?
 

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I don't know, but for what it's worth there's a dyno post on the 425HP SRT-8 bone stock putting 367HP and 353TQ to the wheels.

Either the SRT-8's are underrated, or the drivetrain losses aren't that bad.
 

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Discussion Starter · #4 · (Edited)
vvv90 said:
I don't know, but for what it's worth there's a dyno post on the 425HP SRT-8 bone stock putting 367HP and 353TQ to the wheels.

Either the SRT-8's are underrated, or the drivetrain losses aren't that bad.
That would make driveline losses at 16% for the HP. I figured 17% in my calculations.
Wow the SRT-8 had 353 RWTQ while the modified 300C had 356.23 RWTQ.
 

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Holy crap the drivetrain loss in a 300C is 25%? Or are they overrated at 340?

In any event, you can't really count your gains like that. If a mod adds 20 rwhp, it doesn't necessarily add 25 hp at the crank. How does a CAI result in increased parasitic loss?

The actual parasitic loss has both a fixed and percentage component. Simply put, the more HP you add, the lower the parasitic loss as a percentage. Not much of an explanation, but it's all voodoo anyway. There are so many variables you can't really compare unless you're fooling with the car while it's on the dyno. THe car, the dyno, the weather, etc. all can have a significant effect on the measured RWHP.

The 300C that dynoed 258 at the rear wheels was either put together the Tuesday following a 3-day weekend or was dynoed hot on a day with miserable weather on a stingy dyno.
 

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Discussion Starter · #6 ·
Dutch said:
Holy crap the drivetrain loss in a 300C is 25%? Or are they overrated at 340?

In any event, you can't really count your gains like that. If a mod adds 20 rwhp, it doesn't necessarily add 25 hp at the crank. How does a CAI result in increased parasitic loss?

The actual parasitic loss has both a fixed and percentage component. Simply put, the more HP you add, the lower the parasitic loss as a percentage. Not much of an explanation, but it's all voodoo anyway. There are so many variables you can't really compare unless you're fooling with the car while it's on the dyno. THe car, the dyno, the weather, etc. all can have a significant effect on the measured RWHP.

The 300C that dynoed 258 at the rear wheels was either put together the Tuesday following a 3-day weekend or was dynoed hot on a day with miserable weather on a stingy dyno.

Thanks Dutch, that's a good point that I missed, if for example 25 HP is lost to turn the driveline it would always remain the same no mater what the total engine HP. I thought something was out with the logic but I couldn't pin it down. The first numbers on the stock engine being low also distorts everything.
The one very interesting thing is that the 5.7L hemi with headers, borla, and cold air injection had a higher RWTQ then the stock SRT-8.
 

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Drivetrain friction losses at full throttle are always a percentage of the power output, no matter how much or how little power is made.

Usually an automatic driveline loses between 22 and 25%, a manual transmission driveline about 18%. FWD is worse than RWD due to more changes in direction and friction in the CV joints etc.

When talking about a known figure of powertrain loss, you are talking "coast-down" losses. These can remain the same no matter how much power. The difference is under power the friction increases as power increases, so you can use a steady percent. Coast down does not take the engine into consideration usually. Coast down numbers are taken in neutral.

I used to own a Dynojet chassis dyno, thus my nickname (actually got it before the dyno shop days as one of my heros was Dyno Don Nicholson from the 60's super stock days. My first name is Don and I can power shift like ole' "Dyno" does, or almost). :)
 

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FOAMAVEN said:
That would make driveline losses at 16% for the HP. I figured 17% in my calculations.
Wow the SRT-8 had 353 RWTQ while the modified 300C had 356.23 RWTQ.
Keep in mind the SRT-8 only has 30 more ft lbs of torque over the 5.7 to begin with.

HP and Torque are a trade off. Typically speaking the more HP you have on the top end the less torque you will have and vice versa.

Let's also keep in mind the 6.1 revs a lot higher. I've been beating this point to death, and it makes a big difference in performance numbers and not just "HP" numbers.

The 5.7 obviously has a proven butt load of performance improvement it can take, and that's awesome! I can't wait for people to start modifying their 6.1's with the same type of components.
 
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