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Dyno Fan and Traction Issues

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I am testing an f1x pro charged z06 on my dyno-mite twin roller dyno and traction has become a big issue over about 750-800ftlbs the car will spin even with the weight of three people in the back. I also am having trouble doing steady state testing since above about 2500rpm the coolant temps will rise too far. I recently purchased a 19000cfm axial flow 48 inch fan and it is still not enough to cool the car. On the road it does not overheat in the same circumstances. What are you guys doing out there to get big hp cars to stick on a twin roller dyno and what kind of fan is needed for steady state testing?

Try Red line water wetter coolant for the overheat issue!!

is it really that good? The car doesn't overheat on the road when it has airflow through the front, only on the dyno from what i assume is a lack of airflow. Does anyone have insight on the type of fan for steady state tuning, preferably an affordable option if it exits?

I use a couple of carpet-blower type fans, similar this one:

http://www.globalindustrial.com/p/janitorial-maintenance/floor-care/floor-dryers/3-4-hp-3-speed-floor-dryer-blower

Sometimes I make a cardboard duct to force all the air to into a radiator. I have one of the big axial fans like yours but that is only useful for keeping the general area free of exhaust fumes, so that the engine only gets fresh air.

David sad it right, an axial fan is really not the right fan to get air flow through the coolers. The problem of axial fans is, the have nearly zero flow in the center and on the outside maybe 80-100km/h air speed. So you cooling your coeffe beside the car very goood, but nearly nothing is blown through the coolers, since the center of the fan sits just in front of the cooler.

What you guys really want is an proper radial fan (these one which look like a big turbo). Radial fans supply a high speed laminar flow with enough pressure to press the air trough all coolers.

I use such a unit and have a luxury problem with it; I have to pay attention that cars don't get too cold! 175km/h air speed does a great job :-D

I've used those carpet blower fans and they are good but very limited to the amount of flow, as a result I've had to bring one of my fans that I'd bought for the dyno cell I've planned:

http://www.solerpalau.es/tcbt-4-800-h-400v50hz-v5.html

Whilst the centrifugal fans (carpet blowers) that I have can put out 40MPH each the amount of airflow is nothing in comparison to this which on full speed can put out 50MPH but I have over cooling issues so it tends to get run at about 30mph.

*edit: Eventually found the flow data on the fan I use, it flows approx 17,657CFM at full flow, which compared to the carpet blowers 2455CFM you can see why I don't need to run it at full power.

as it's been said, there is a dead spot dead centre of an axial fan and the fastest airflow is at the outer edges, which is why fan placement is most important, you can't have them sitting blowing directly on the radiators like you can with the centrifugal ones. Mine is mounted at an angle to get the lowest flow going under the car and the top aiming for the front. This is only a temp measure till my cell gets built but seems to work well, as I said, it doesn't need ran at full speed, probably most of my tuning is done running it between 40-60%.

interesting, thanks for advice guys its much appreciated. Any one know of a good place to get a centrifugal fan for a reasonable price? Doesn't seem to be many available online and those that are super expensive and don't seem ideal for a dyno set up.

Traction:

I bet you are pulling the car backwards with your straps, instead of downwards.

You need to arrange the straps in such a fashion to pull down only and let the wheel climb up the front roller slightly under power, leaving the rear roller. This way the tyre bites into the knurling and thus grip is improved. Properly done, no additional weight, especially not humans, is / are required in the trunk of the car.

A third or fourth strap to limit forward travel of the vehicle is also recommended.

interesting idea dynodom. I have noticed that many twin roller set ups have a bracket that allows the strap to pull down and hold the car. In fact my straps are only holding the car back and not down. Im just unsure how to accomplish that. My dyno is also in a pit which may make that more challenging. I noticed the idea you are saying in this video https://www.youtube.com/watch?v=nROqhD4QKa8 a while ago, looks a little dangerous though honestly. What is your experience with it?

That is EXACTLY how it is done. In this vid, it climbs a bit too far for my liking.

Even though it is 3AM now here, I will go to my garage and take some pictures of the arrangements for ya. It can still be done in-pit.

This technique was invented by Dynodynamics (the machine in the video is also DD), Mainline and maybe others have now copied it.

Here you go. The brackets I made myself. They can slide sidewards to any position and turn about 20 degrees, needed when they more outwards. The strapangle will align them automatically. The front pin of the brackets are located slightly towards the front roller thus, by strapping down the axle is in fact pulled forwards a little bit. The rear pin needs to be located in a fashion so that the strap which goes to the back is juust clearing the rear roller, 5-10 mm is enough.

I hope you find this useful.

Attached Files

Our Mainline has a channel between the rollers with a special moveable bracket with a set of 3 rollers that you pass the strap through. There's one each side and it aligns the strap so that you can pull directly down rather than back. If you do this properly the strap will actually tend to tighten as the car moves up onto the front roller under power.

Proper strapping technique seems to be the most common failure point for traction issues but of course aspects such as wheel alignment, ramp rate and tyre type play a part too.

Your the man dynodom, those detailed pictures are incredibly helpful! BTW beautiful e46 m3 in the background, whats done to it? We have a dinan supercharged imola one here in the states, awesome cars!

Andre I have spent a decent amount of time on the alignment. I have also played with the ramp rate but only till 600rpm/sec which i thought may still be too slow, so I did an inertia only pull which didn't help and gave numbers nearly 50-75 higher then with load. I have also considered that slicks would help a lot and I am going to put them on the car at some point so I will try that as well. It seems to your point that strapping has the largest effect, I tried all of the stuff listed above as well as putting 3 adult men in the back. Adding weight got me another 750rpm before spin but still only got the car to 4300rpm. On a side note I also noticed that when running in inertia only the afr was very different which i figured would happen given that there is no load but I was surprised by how different they were. That and the rather large change in power made me realize how inaccurate inertia only dynos are, are those type of results typical when going from a loaded test to pure inertia?Also what type of fan do you use for steady state? I remember you mentioning in a webinar that you would be building a dyno cell and covering the details, will that be happening soon? Thanks again for all the advice everybody.

Hey Dynodom,

Is that Extra 330 an RC model?

>>Your the man dynodom, those detailed pictures are incredibly helpful!

I agree those pics are excellent, thanks DD.

I should have checked those pics before commenting Dynodom - That's essentially what the Mainline uses except with rollers.

Yes, we will be documenting our dyno cell design and construction. Please don't ask when though :( The sooner the better but we're both a little snowed under right now.

As far as ramp rate goes, I try and replicate the sort of ramp rate the engine will see in 4th gear out on the road. If you can replicate this with the dyno then your results should be an accurate representation of what the car will do in the real world.

No worries andre, I'm from new england in the northeast of the US and most years we get absolutely slammed with snow throughout the winter months. Regardless of when, I look forward to that content! Good to know, I'm not sure how other dyno setups are but in my dynomax software I can only pick pre set ramp rates such as 400, 500, 600, 1000, and 2000. Are these sort of rates usually optimal for most cars?

@Blackrex

Yes, EXTRA 330 L twin seater, 3.1 meter full composite, me hovering it 1 inch off the deck, walking it down the runway, no photoshop. 160 cc twin cylinder engine, 16hp, prop 32 inch.

https://youtu.be/Z_k9mu3Q_1I this explains what the dyno dynamics/ mainline brackets do

My new fan , 1hp Americraft Man Cooler refurbished with new motor and paint to match my 2wd600l Mainline dyno=)

Attached Files
  • 13880384-10157167559380517-4251231986445510353-n.jpg
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Hey Tommy

Nice job! I have similar style fan and if I may be forward I suggest you to build sort of a shroud on the outlet side of it...its shape changing from round to oval or rectangular over a length of 50-80 cm. This way the airflow will be streamlined and much more effective in the center area.

Hey! Already thinking of it! something similar to attached pic. Thanks

Attached Files

Exactly this !! Great find.

>>No worries andre, I'm from new england in the northeast of the US and most years we get absolutely slammed with snow throughout the >>winter months.

AtomicVette, I'm going to go for a leap of faith here but I am willing to bet, and I don't gamble, Andre meant snowed under with work not with fluffy white stuff from an Antarctic blast (although there have been a few of those recently with at least 1 causing snow fall in Queensland Australia).

Michael is right, despite a few recent snow storms (including some light flurries as I write), I was meaning snowed under in the work sense :)

Tommy that looks great! I love the attention to detail on that fan refurbishment!