I had a chance to compare the Torque Inserts (TI) sold widely by Mike’s XS, Heyden and others to the Exhaust Port Optimizers (EPOs) from MMM (650Central). My bike has the 700cc Hoos/Shell1 kit and 1.75” headers with TPOs, Torque Peak Optimizers from MMM, already installed. (The TPOs did a great job eliminating the severe inversion around 5K with the large diameter headers and I reported in that earlier: https://www.xs650.com/threads/torque-peak-optimizer-tpos-performance-dyno-charts.66469/)
First here is a visual comparison of EPOs and TIs.
The EPOs is a work of art. Beautifully shaped for laminar flow and machined precisely to fit snuggly into the exhaust port.
The TIs are from https://yamahaxs650.com/ and I assume they are the same design as those available from other vendors. The TIs are longer, with an internal cone surface (see the cross section view below) to guide exhaust out and fit loosely into the exhaust ports vs a velocity-stack like surface of the EPOs. The exit opening of both is similar in diameter: 1.056” for TI and 1.035” for EPOs. On exit, the TI’s have a lip that seems to be angled a bit strangely, to almost funnel gases back in, while EPOs are opposite of that.
EPOs in the exhaust port
Below is the comparison of air fuel ratio for the EPO and TI setups. The plot shows the reversion issue at 2500 rpm which, I suspect, is due to a reflection from the end of the header pipe where TPOs open up into the mufflers. I did the pre-tuning with the on-board AFR meter before dyno. With the EPOs I was able to lower the needle and reduce the width of the rich interval. With TIs, there was not much change with moving the needle. So, in my experience, EPOs are better at limiting the reversion/reflection than the TIs.
For the horsepower and torque, the output is essentially the same, except for at near the red line. The difference could be due to the slightly smaller outlet diameter and the length of the narrow section of the EPOs, but the bike ‘feels’ more responsive with EPOs than TIs.
The EPO runs were taken ~ 9 months apart, the TI numbers were repeated during two separate pulls on the same day/same session.
It is important to note that results will be different for a different engine/exhaust/intake configuration particularly as displacement/cam timing and exhaust are changed. More overlap and less exhaust scavenging (for example, not having the TPOs installed already) will favor the EPO design even more.
My next project will be playing with the length of the TPOs to move the dip at 2500rpm around to see if I can move it out of the operating range of the motor.
First here is a visual comparison of EPOs and TIs.
The EPOs is a work of art. Beautifully shaped for laminar flow and machined precisely to fit snuggly into the exhaust port.
The TIs are from https://yamahaxs650.com/ and I assume they are the same design as those available from other vendors. The TIs are longer, with an internal cone surface (see the cross section view below) to guide exhaust out and fit loosely into the exhaust ports vs a velocity-stack like surface of the EPOs. The exit opening of both is similar in diameter: 1.056” for TI and 1.035” for EPOs. On exit, the TI’s have a lip that seems to be angled a bit strangely, to almost funnel gases back in, while EPOs are opposite of that.
EPOs in the exhaust port
Below is the comparison of air fuel ratio for the EPO and TI setups. The plot shows the reversion issue at 2500 rpm which, I suspect, is due to a reflection from the end of the header pipe where TPOs open up into the mufflers. I did the pre-tuning with the on-board AFR meter before dyno. With the EPOs I was able to lower the needle and reduce the width of the rich interval. With TIs, there was not much change with moving the needle. So, in my experience, EPOs are better at limiting the reversion/reflection than the TIs.
For the horsepower and torque, the output is essentially the same, except for at near the red line. The difference could be due to the slightly smaller outlet diameter and the length of the narrow section of the EPOs, but the bike ‘feels’ more responsive with EPOs than TIs.
The EPO runs were taken ~ 9 months apart, the TI numbers were repeated during two separate pulls on the same day/same session.
It is important to note that results will be different for a different engine/exhaust/intake configuration particularly as displacement/cam timing and exhaust are changed. More overlap and less exhaust scavenging (for example, not having the TPOs installed already) will favor the EPO design even more.
My next project will be playing with the length of the TPOs to move the dip at 2500rpm around to see if I can move it out of the operating range of the motor.
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