Quote:
Originally Posted by semtex
Well, the thing about advertised gains, I've noticed, is that it's always the gain if that's the only mod and everything else is stock. In other words, it wouldn't surprise me if one really could get a gain of 20hp from just the headers -- if that's the only thing they did.
As I'm sure you're well aware, once you start doing multiple mods, diminishing gains comes into play. I did the headers after I had already done the CBE and HFCs and intake. If you look at my dyno from the intake, for example, I got a nice gain out of that, even though I did them after the CBE and HFCs (+14.7 whp). But I think by the time I got to the headers, everything in my intake/exhaust was already pretty well opened up, hence any additional gain from the headers was minimal.
Here's a link to my journal thread, btw. You can use it as a jumping off point to all my other dyno charts along the way if you want. Semtex's Monterey Blue 370Z |
Not so sure I agree on this one. Really was sponsored at one time by a dyno shop (actually two of them) and seen quite a few cars have headers added, then dynoed right after and not what I've found from my personal past experience. It's always the weak link you're trying to fix and the system works as a team to optimize the entire system. For example adding headers to a Z06 is not cost effective as the factory put on damn good exhaust manifolds on the car and quite a few of the LS3 guys are doing Z06 exhaust manifolds instead of headers. Obviously my feeling is headers on the 370Z is also very cost ineffective. Especially if you do like me and booger up both 02 sensors.
If the exhaust manifold was the major weak link, it will show regardless of what other mods are present. CFM is..... CFM. Frankly was surprised as to how good the stock manifold was mfg as they look more or less like headers and were port matched better than the Stillen headers.. Wimpy tubing and not equal length, besides that....headers.
Obviously the stock cats are a major weak link and personally got a 12 hp gain just from doing cats.
Quote:
Originally Posted by kannibul
The other thing about gains, is that it applies to the peak output.
It never makes claims based off an average increase...the only thing some of them do is post dyno charts, but even those can be a finaggled.
For example, a turbo can boost top-end HP by a TON under WOT conditions, at a given RPM or above. Looks great on paper - makes 700WHP. However, the torque curve is jacked, and from 3K and below, it makes less HP...
All I know is that the more air (and fuel at the correct ratio and dispertion) I get through an engine, the more power it will make.
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Bingo on the average power output within the intended rpm range, Bingo on being a huge air pump and Bingo on manipulated dyno results.
Read Chapter 1 (Basic Engine Theory) in John Lingenfelters book as he emphasizes application plus what he calls "The Golden Power Rule": Always emphasize power within the rpm range where the engine spends a majority of time.
The guy who ports my heads (Trevor Johnson) at one time worked for the Nickens Bro pro stock team and just talking with him at his shop has really further enlightened me quite a bit. He does exactly the same porting heads on the flow bench as he never pays much attention to peak flow.....it's average flow within the lift range of the cam. He'll back cut valves which hurts peak flow but helps lower lift flow to get a better average.
Truthfully whenever I do a mod typically post peak hp gain at peak hp, but privately have a spreadsheet that computes average hp gain and average hp gain within a simulated 1/4th mile run. This is the one I really look at, not the dyno sheets. The dyno sheets are just input for the spreadsheet.
In my Corvette On I-635 from a second gear punch ending up racing a turbo car that made over 100 hp more peak power. Immediately started pulling him but saw him start to pull me and catch up. This didn't last long as soon as he shifted out of his peak power, the car lost momentum and I kept walking. Still average power that wins races.
No question people whom sell performance items pick an area of the curve which supports the most gain, quotes that figure and are not afraid of finding "Optimal Conditions". One unintentional aspect I see people do is they take a hot car, dyno it and post the output. Then they put the mod on letting the car cool, redo and it shows a gain. My car shows over a 10 hp difference between hot and optimal temperatures and the only mod was letting it set for a while.