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Spiky Dyno Graph

Practical Dyno Tuning

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Hey guys,

I am fairly new to dyno tuning and have been dyno tuning my 1960 VW beetle. I have encountered an issue with the power/torque curves becoming "spiky". Engine is a turbocharged 2827cc air-cooled running E85. Compression is a very low 6.8:1 and in this run the car is running 16psi boost. The red trace in the picture is the blue trace run +2 degrees timing. The engine definitely seems to love the timing and power levels are well above the previous run, however it becomes spiky around peak torque. I am suspecting that it is wheel spin but I would like to know if anyone has encountered this phenomenon before. Is this a classic symptom of wheel spin or would you suspect something else? Cheers

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It could be - any reason you're using that gear - it is rather low for that weight and power level?

Try using 4th/top and see if it is still an issue - but before that I'd check the wheel balance and wheel/tyres for roundness as they may be 'bouncing' on the rollers.

Oh, sounds like a really fun build - if I had (relatively) unlimited funds something like that has been on the back burner for years, but for hillclimbs, rather than sprints.

I assume you're familiar with "The Dung Beetle"?

Thanks Gord,

I chose this gear as i have a much taller diff than standard and I thought 4th might have too much speed as its geared to do about 230kph @ 7000rpm. However after seeing the low speed and high torque of 3rd (and only revving to about 5700rpm on the dyno), 4th definitely seems to be the better option. This is my streetcar and it has been a very fun build! I am familiar with the Dung Beetle but the latest I hear is they have ditched the air-cooled engine for something from a Subaru

There's a range of possible causes. It's not generally something I'd relate to wheel spin as usually (but not always) once the car breaks traction the wheel spin becomes worse and we see a significant drop in power/torque. I see similar spiky dyno plots with engines that have a slight misfire so that would be one possible scenario. I'd also suggest running in a higher gear and see if that helps out your cause.

Great thanks Andre! I'll have a thorough check over before the next run. The car is running LS1 coil packs so I'm hoping that they're adequate for the boost levels

Is there any smoothing applied to the curve? Remember that a lot of the dyno sheets you see on the internet are smoothed.

Hi Arghx7,

I'm not too sure about smoothing. I'll have to look into that. It's strange that the spikyness only appeared with an extra 2 degrees of timing even though the engine seems to like more. All of our low boost runs (8psi) were very smooth as well once the car got enough timing.