AIM Engine Analysis - getting it right....

[BeerBudgetRacing]

I have a 94VD FC Pinto for which I have no specific knowledge of hours on the engine.
I also have no Dyno sheets, etc. I had contacted the original builder and they did not have dyno sheets.

So, what I'm trying to do is determine the power band of my engine. With my different data samples there are slight variances up and down...

To make it as accurate as possible:
1. Does anyone know the Cx and front surface area's for a mid-year VD FC like mine?

2. Can I assume HOW the car is driven during the sessions will have an effect on resulting power estimates?

3. What about the curve? Should the curve (peak torq/power) always be in the same RPM range?

4. How accurate can this analysis be?

Thanks.
Paul

[David Ferguson]

Good luck. I've never been able to make that feature work successfully.

The best way to determine your engine power band is with the result of the dyno test - either an engine dyno (usually provided by the engine builder), or a chassis dyno.

[Steve Demeter]

Be careful with a chassis dyno. I have seen ace cars torn up on them if the operator is not experienced in testing cars like ours. Seat of the pants always worked for me. Or maybe that is why I am so slow

Seriously though one way to determine best shift points assuming that is what you are after is to come onto a fairly long straight at a repeatable speed, and vary the shift points and see which one gets you to the end the quickest.

Note that top speed and getting there quickest are not always congruent with each other.

[BeerBudgetRacing]

Good luck. I've never been able to make that feature work successfully.

The best way to determine your engine power band is with the result of the dyno test - either an engine dyno (usually provided by the engine builder), or a chassis dyno.

My next question was going to be: What's the loss of an LD200?...

My primary goal is to learn to operate within the power band better by first identifying it...

I know there are tons of factors - including gearing......

If you run the analysis on a known engine you've dyno'd, ignoring the numbers, does the curve match? Close?

[Raceworks]

1. Does anyone know the Cx and front surface area's for a mid-year VD FC like mine?

I haven't even been able to find those numbers for my new Spectrum.

2. Can I assume HOW the car is driven during the sessions will have an effect on resulting power estimates?

Yes. If you're not full throttle or don't shift consistently at the same point it'll have an effect. This is why dynos are more accurate.

3. What about the curve? Should the curve (peak torq/power) always be in the same RPM range?

Yes.

4. How accurate can this analysis be?

It depends on what you mean by "accurate." As an absolute measure of torque / horsepower even if you plug in completely accurate numbers you're going to still be limited by whatever assumptions are built into the software. So my answer is "not very accurate at all."

If you just want to see at what RPM the horsepower starts to drop off just plug in the numbers you know & make educated guesses for the ones you don't, and you might get a rough idea of where that is. Or just ask someone what the typical numbers are for an FC Pinto prepped to whatever level yours is. In limited-prep or spec classes like FF, FC, FM, & FE all the engines of a given type (Pinto, Kent, Fit, etc.) are going to have pretty much the same torque / HP curves within 100 RPM unless someone is cheating or something is seriously awry.

[RussMcB]

I hope this question still pertains to the topic...

Be careful with a chassis dyno. I have seen ace cars torn up on them if the operator is not experienced in testing cars like ours.

Can you elaborate, please? What happened to them? What did the operator do wrong?

I've taken several formula cars to the chassis dyno and it's pretty much always been productive (for my low tech goals). It's pretty straightforward - Tie the car down, blow air on the rads and make a few runs.

I'll probably take my next car, too, so I'm interested to hear what I might want to avoid.

Thanks.

[Jnovak]

I have a 94VD FC Pinto for which I have no specific knowledge of hours on the engine.
I also have no Dyno sheets, etc. I had contacted the original builder and they did not have dyno sheets.

So, what I'm trying to do is determine the power band of my engine. With my different data samples there are slight variances up and down...

To make it as accurate as possible:
1. Does anyone know the Cx and front surface area's for a mid-year VD FC like mine?

2. Can I assume HOW the car is driven during the sessions will have an effect on resulting power estimates?

3. What about the curve? Should the curve (peak torq/power) always be in the same RPM range?

4. How accurate can this analysis be?

Thanks.
Paul

That feature is not particularly accurate. However you can easily define the peak power and the peak Torque rpms. it is actually quite easy. find a long straight away and put the car in 3rd gear so that it is at a relatively low rpm at least 1000 rpm below what you think peak torque is, say 3500 rpm. Then on a nice flat straightaway accelerate at full throttle up to as many RPM as is safe. Do this about 3 times. look at the acceleration data for that section of your data. You will be able to clearly pick out the peak power RPM and the peak torque RPM. what it will not do is tell you what the maximum power and torque numbers are. there are plenty of calculations that you can make to estimate the power and torque numbers but you need to know a lot more info about the car to do it even reasonably well.

[Steve Demeter]

Basically overrevved to a great degree and cooked motor. Also, gotta watch temps closely since you are running a hot engine standing still. The good guys have BIG fans to blow air over the rads.

Also, with a racing clutch unless the operator is familiar with them it can be hard to get the rollers moving without slipping the clutch a lot and that dramatically shortens the disc life. Watched one guy with smoke pouring out of the bell housing from overheated clutch trying to get rollers moving.

Just saying make sure you have an operator that knows the kind of car you are having them dyno.

[Gary_T]

When we did a chassis dyno - it was me in the seat, no chance of the dyno guy fitting, or getting it going...

[Daryl DeArman]

However you can easily define the peak power and the peak Torque rpms. it is actually quite easy. find a long straight away and put the car in 3rd gear so that it is at a relatively low rpm at least 1000 rpm below what you think peak torque is, say 3500 rpm. Then on a nice flat straightaway accelerate at full throttle up to as many RPM as is safe. Do this about 3 times. look at the acceleration data for that section of your data. You will be able to clearly pick out the peak power RPM and the peak torque RPM. what it will not do is tell you what the maximum power and torque numbers are. there are plenty of calculations that you can make to estimate the power and torque numbers but you need to know a lot more info about the car to do it even reasonably well.

Curious how well this method translates. Obviously, the data will tell you the acceleration rate between any two given rpm points. However, the variable is aero drag and how do you account for that? Or do you? At whatever given gear ratio the aero drag at 7K is 4x of that at 3.5K, wouldn't a much slower speed delta be better, say 30mph to 60mph in 1st gear instead of 50mph to 100mph in 3rd? Still 4x the drag, but 4x a much smaller number....does that make sense?

[Jnovak]

Curious how well this method translates. Obviously, the data will tell you the acceleration rate between any two given rpm points. However, the variable is aero drag and how do you account for that? Or do you? At whatever given gear ratio the aero drag at 7K is 4x of that at 3.5K, wouldn't a much slower speed delta be better, say 30mph to 60mph in 1st gear instead of 50mph to 100mph in 3rd? Still 4x the drag, but 4x a much smaller number....does that make sense?

Certainly if you want to calculate hp you need a lot of data one of which is aero drag. However if you just want define the peak hp rpm and the peak torque rpm the method I described will work very well. Remember the aero drag is essentially the same for this one vehicle and Yes, if you are in a lower gear the aero effects are significantly less. However the acceleration rates are much higher and you go through the peaks very quickly making it a bit more difficult to pick out the changes in the acceleration rates that define the peaks. That said it is not an exact science. We use it for defining final drive ratios and for getting a decent range for shift points when you do not have dyno data. Dyno is much better of course an
you can do math channels that can do a good job of defining the peaks.

[BeerBudgetRacing]

For me getting the most accurate curve is the objective here. Whether I dyno the car or engine doesn't really matter. That can come later - for tuning.

Because of all the varying factors involved, the on track analysis is probably the best.

With the curve I can learn to drive the car in the correct RPM range. I'm still learning. Coming off most track time in a vette with a v8, wide power band, and wide ratio gearing, I need to learn to tighten things up.

So, from the data I've got, and if the curve is right, the power should be best 5000-6500 rpm. The data also indicates I've spent way too much time below 5000rpm - like 4000 ish (which indicates I'm mentally still driving the vette.. )

So, in theory, if I work harder to keep it in the 5000-6500 range, I should see more performance.

If I repeat the analysis after my next event, the curve MAY move a little bit, but wash-rinse-repeat, I should get closer every time.

That's the theory at least...