future objectives

[redyaris]

I will post more info in the future such and fuel consumption log and pics. The next mods I have in mind are thunder street headers to reduce pumping loses and rear wheel well covers. I am confident that the wheel well covers will work, but I am not so sure about the headers. The probem is; will the lower exhaust gas velosity resulting from larger diameter tubs be more than made up for by the more consistant tube diameter throughout the rest of the exhaust system? changes in tube diameter/cross section consums energy... What goes on in the exhaust system can be quit complicated.

[Bicycle Bob]

Aye, neighbour; around here, I hear more about Alberta than the rest of Canada, because that's where the kids got work.

You are probably about to be hosed with opinions about exhaust gas velocity vs temperature, the necessity for backpressure for various functions, etc. It would be nice to have a system tuned for a steady cruise if you have a preferred output level. Those lumps in the power curve charts are from resonances. All else being equal, though, bigger pipes and reduced backpressure help a bit for cruise, and several bits at max HP. However, factory engineers don't seem to put bigger pipes or better manifolds on their super-economy models.

[redyaris]

because pipe flow fluid dynamics are so complex even engineers return to the test bench and find out what really works. I have flow tested the two headers and the thunder street header flows 25% better, weather that turns into redused pumping loses and better fuel economy remains to be seen. I will know in the next month or so.

[Christ]

I will only mention that the flow increases may or may not have occurred at a flow rate similar to that which you will see in normal operating circumstances.

I will also note that vacuum flow is much different than flow under pressure inside a tube.

[redyaris]

When in doubt test the hypothasis...

[Christ]

Originally Posted by redyaris

When in doubt test the hypothasis...

I agree completely, my (hidden) point was that flowbench testing doesn't often account for the actual flow the engine will see under a given duty, rather just giving a concrete response that "X part flows Y more air", without any qualifier, which leads people to believe that it's universally better, which is almost never the case.

Now, if, OTOH, you tested the flow of each specifically at the volume and pressure that would occur under X circumstance, and noted an increase, that would elicit a different response.

Fluid dynamics is one of my favorite subjects, so please don't be offended. I love to discuss it, and learn more about it, and I'd be excited to be shown that (for your specific case) a header outperformed the existing manifold, then explore and understand why it did.

I can think of a few cases where headers have significantly outperformed OE configurations, and I can also mentally recall many that have not, and even a few that have been neutrally resultant.

In all cases, I've tried within my current means to understand the outcome, rather than just accepting it.

[redyaris]

I to have had flow test bench improvements that when presented to the real world amounted to nothing; it was on a Honda GX100 motorcycle engine intake system; used in mini road racing. The engine performance only improved when the exhaust restriction was removed, because that was the limiting factor in the SYSTEM... which is what makes modification to one part of a system so challenging and fun. the frustration and confusion caused by the lack of emagined results leads us down the road to better understanding.

[Christ]

Well, at least you "get it"... I look forward to your results, sir. (You're a "Sir", right?)

[redyaris]

I have installed the new street thunder after market header with new and better exhaust heat shraud which I use to duct heated air to the intake air filter box. There is no fuel consumption data yet but one big change is the intake air temperature. With the old stock set up I only could get 20 deg. C [68F] with the ambiant air temp at -5 deg. C [23F] and now the intake air is at 65 deg. C [149F] with the same ambiant temp.
One of the problems with cold and snowy climate is that winter driving conditions can lead to a 50% rise in fuel consumption! Partly the result of cold air and partly the result of higher rolling resistance due to snow on the road. So I am gratified that I can keep the intake air warmer in cold temperatures.