Low HP Reading, or bad dyno? - Suzuki GSX-R Motorcycle Forums Gixxer.com
 
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post #1 of 6 (permalink) Old 07-18-2019, 10:22 PM Thread Starter
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Low HP Reading, or bad dyno?

I recently added a midpipe and a PC5 to my 2018 750 and I obviously went to get it dyno tuned soon after. The business I went to has been in service a very long time and they are fairly well reputable for previous dynos. After everything was said and done, I only had to pay 159 dollars which was great. The owner of the shop (who did the dyno) talked to me for a short bit and explained how he went through the whole rev range, but focused more towards the lower end where I would be spending most of my time. He sounded confident and honestly the bike feels much smoother and I definitely notice a far more consistent power band. The bike was running lean with the temp map I had on the PC5 so it is definitely an improvement regardless. That being said, the dyno chart I was given did not include any torque numbers, and the max horsepower number given was a measly 117.06. Right before I left he said something to the tune of, "in case you are looking for bragging rights, the horsepower number is low because it was almost 130 degrees in there while I was doing it". I am not sure if this meant that he just didn't fully open it up, or didn't run another test, or the air quality was too poor? Being that I ride on the road casually, I haven't really gotten to feel a true power difference, but I am confused as to why the HP numbers were so low. From the little bit of riding I have done so far, I have felt a little less "pow" when jumping on highways, but I think that is largely due to the fact that the powerband is more consistent and therefore the big surge in power that I got around the 6-7k mark previously is just not there as much anymore. Has anyone else had/heard of a lowball HP number? I am not going to get another dyno anytime soon as the bike runs great for every day riding, I am just curious as to what happened.

P.S. I tried so many times to rotate the chart...and failed
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Last edited by FastAndStupid; 07-18-2019 at 10:27 PM.
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post #2 of 6 (permalink) Old 07-18-2019, 10:32 PM
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Re: Low HP Reading, or bad dyno?

Comparing numbers from different dynos is not an effective practice.

You should have asked him what other 750's have turned on his dyno in similar conditions. When he said it was 130 degrees in the dyno room that for one thing indicates to me that he doesn't have a very well setup dyno room as it should have some better ventilation, but the point of him saying that is because an engine is going to make less power. Cold/dense air makes more power.....hot/less dense air is going to make less. 130 degree air is VERY hot for the engine to be ingesting.

He also should have been able to apply some correction factors to the dyno results to normalize them. To be honest, depending on the dyno a 750 is doing to make in the neighborhood of about 120hp give or take. A mid pipe is not really going to make much of a huge difference to that. Couple that with the far less than favorable conditions it was tuned under and I'd say 117hp sounds reasonable. Again, also depends on the type of dyno. If he was using a Factory Pro Eddy Current dyno for instance, those read noticeably lower than a typical Dynojet dyno.


The curve looks nice and smooth but you should have asked for a printout that showed torque and A/F ratio through the range, unless he didn't have the proper hookups connected.
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post #3 of 6 (permalink) Old 07-18-2019, 10:54 PM
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Re: Low HP Reading, or bad dyno?

Other reason for low peak hp is that the STP maps are restricted. ECU flash would take care of that.
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post #4 of 6 (permalink) Old 07-19-2019, 08:23 AM Thread Starter
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Re: Low HP Reading, or bad dyno?

Thanks for the info! That is the way I was thinking from the research I'd done pre-dyno, but this is my first experience with a fuel injected bike despite nine years of riding, so I didn't think to ask if they had a graph with more variables shown. Live and learn I guess! We are in the middle of a massive heat wave here, so I don't think it is entirely his fault, but I do think he did a good job for my current needs. I am currently paying my way through a master's program so the track day luxury is going to have to wait for a while anyway. I did a 100 mile run the day after the tune and despite it feeling "weird" with the more linear curve, the engine was running far smoother and even sounded better. Realistically all I wanted was a proper A/F ratio to not damage the engine, and I am pretty confident that I got that with this tune. In the future I may do an ECU flash, but as someone who could only afford a midpipe and not a full system, I should probably stop spending more money haha
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post #5 of 6 (permalink) Old 08-15-2019, 09:56 AM
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130 is very hot air for the bike to take in with colder denser air you will have more power. I would want to compare to other similar bikes tested in that same environment. You may want to try flashing ECU.
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post #6 of 6 (permalink) Old 08-15-2019, 10:34 AM
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Why would you be doing the dyno with the air temp at 130. You don't ride your bike at those temps, do you? Also if the ventilation is that bad the oxygen level in the air could be low from being previously combusted by the engine or other reasons. Wouldn't this mess up the air/fuel ratio to begin with? You are tuning the bike to the dyno room conditions and then riding the bike in completely different conditions. Doesn't make much sense to me but I don’t know, these are just my thoughts. Someone with a dyno here may know better.

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