dyno runs difference

**madmaxptt** · 29-03-2022, 17:19

I see that in dyno runs there is always a difference between 1st, 2nd and 3rd dyno runs in power figures!
why is this happening?
Which one is more reliable? 1st run or the next?
I saw recently one Graham’s great video with manifold and Camshaft tests and he says that there was a difference between 1st and second run in power, what is your opinion?

**katana** · 29-03-2022, 20:54

Its inevitable as parts heat up and general water / oil temps come up to operating / stabilised levels. But only to a certain point as excess temp. will lose power. Step tuning involves holding an engine at rpm levels to allow a degree of stabilisation before moving to the next rpm level - easy on a computer controlled load dyno - damn scary on a turbo'd high horsepower chassis rolling road, load brake type dyno. If you want comparative figures - average out a series of runs - if you want bragging rights figures, just pick the highest!

**Graham** · 29-03-2022, 22:13

basically as above, no two dyno runs are ever exactly the same. as you heat up the block head, oil etc power goes up, although i starts dropping off again as coolant temp goes up. i find once the engine is properly upto temp after 3 pulls it stabilizes, i can then do about 3-5 further back to back runs which are all very similar and its those ones i usually average,

most testing i do in accel mode where the engine is allowed to accelerate at a constant rate. i have done step test on the dyno, in accel mode the dyno read power every 100 rpm. in step mode the engine will stabilize the rpm in steps of 250 or 500 rpm, but i dont like doing it because it has to find an exact rpm to take a power reading which means the engine is held under full load for a long time.

**Dyno** · 24-05-2022, 19:50

Originally Posted by Graham

basically as above, no two dyno runs are ever exactly the same. as you heat up the block head, oil etc power goes up, although i starts dropping off again as coolant temp goes up. i find once the engine is properly upto temp after 3 pulls it stabilizes, i can then do about 3-5 further back to back runs which are all very similar and its those ones i usually average,

most testing i do in accel mode where the engine is allowed to accelerate at a constant rate. i have done step test on the dyno, in accel mode the dyno read power every 100 rpm. in step mode the engine will stabilize the rpm in steps of 250 or 500 rpm, but i dont like doing it because it has to find an exact rpm to take a power reading which means the engine is held under full load for a long time.

Fully agree. It takes a few run's before you got "stable" run's and they are repeatable within a very small range. It is for this reason very important you first got stable run's before you change anything. Otherwise you may think you gained power with this modification but in reality, it was stil stabilizing the engine. I also prefer to take the "power adder" back out and see the power does drop again. To be sure you where not fooled by engine warm up, combustions chamber cleaning himself after a few to rich pulls etc..

Slow acceleration run are what I feel best and how slow, slow enough to give a correct power graph but fast enough so the engine is not worn out before it is tuned !!!. Don't think any of us has the budget to replace test engines on a regular base as they can in big car/engine company's.