Monday, April 18, 2005

HPT Dyno spreadsheet

This is an ugly one for now. It's very much an 'engineering sample' so tread with caution.

As about a week ago I was playing with MAP pressures, I had all this data in a spreadsheet, and it got me thinking: what if I had multiple columns and could somehow see the correlations between MAP, MAF, timing, etc on the actual acceleration. The problem is of course that I don't have any acceleration data. So I went after that first, thinking "if GTech can do it, why can't I?"

So I started with the assumption that samples are taken at 10Hz and then I go off the speed data gathered through speed sensors. Two problems:
1. I actually looked at the high-resolution timing and saw that the intervals weren't exactly 100ms
2. Speed data is given to us only with 0 decimal places

So you put the two together, and the precision of this system is bunk. often times you got two pieces of data that both show 73mph, while in reality is more like 73.1 and 73.9, but if you ask for delta of speed, you'll get a big fat zero. That's no good.

Back to drawing board, take 2:
1. Take the timing from the high-resolution timing ticker and use it to get 'composite' time in milliseconds, kinda like unix-style time. The problem with this is that Excel knows about hours, minutes and seconds, but apparently has no clue about milliseconds. Thus, we're doing this old school: parse the string for 4 parts, and calculate it all back together to make it into the composite millisecond time (who cares what it is, as I use it only for intervals anyway). Ugly, but fairly straightforward, too bad it takes a lot of screen real estate.
2. Velocity--to get this sucker in precise manner is a bit tricker. I decided to go off RPM, as I hope they got precise numbers as far as fireing a spark goes :)
So you take your RPM, tire size, gear, final gear and you get velocity. Great, but now you line them up with the velocities from the sensors and suddenly it doesn't agree. what's different? gears are pretty un-variable (is that even a word?), so probably the tire diameter is off, as it reacts to pressure, temperature, and of course it's rubber squished with 3500lbs of mass so it has good potential of changing. So of course I go by the go adage of "life gives you lemons make lemon vodka out of it" and use the discrepancy to find the more realistic tire size.

How do you do that, you might ask. Well children, you take your calculated velocity and you subtract that from the speed indicated by the speed sensors, and make a separate column for it. then you sum up this column. The idea is that to keep the sum zero, as an indicator that the variances were equal on both sides. Then you use Goal Seek from Excel, and you tell it to make that variance sum to be zero, by playing with the tire size. You'd be amazed how well this works!

Ok, so now that we have rpms, gears, and good tire size, time to get velocity with some precision, finally!
The next step is instantanious acceleration, as a function of dV/dt. Of course there must be some conversions, as your speed is in miles an hour, but your time is in milliseconds. Having an Eurotrash background, I of course pick the SI units for the middle ground, and end up with acceleration in m/s/s, which actually ends up with quite descriptive and easy to remember numbers.

As you look at most 'official' dynometer outputs, you will see 'smoothing' with a value attached to it. I always wondered why that was, until I actually threw some real data at my spreadsheet and saw how jerky the acceleration graph was! So in a general theme of copycating everything in sight (GTech, dynos) I decided to have smoothing of my own. All I did for that is to use bigger intervals, not the ~100ms that it normally gives you, but 'hop' over few cells of data, so you have speed variance over let's say ~500ms divided by ~500ms itself. So it's kinda a moving average I guess. I did it for 4 different smoothing levels, using 1,3,5,7 cells at the same time. Using the 5 cell spread is the most useful I think, seems to almost have the consistency of 7 cell spread, but without eating up too much data.

The best part about this spreadsheet is this:
you get to see how long (in miliseconds!) it takes you to go through a given interval of speeds! This is exactly what all car geeks always wanted: effective not theoretical, and 'area under a curve' not peak numbers! This is about as real as it gets, folks.

There are a few pitfalls/unautomated things:
1. I would like to pick an automatic range of speeds I'm interested in and get stats on that range specifically. (like time, for now I just look up speeds manually, copy the related values for time and do subtraction on them).
2. Automatically changing gear ratios for the calculations, probably based of acceleration dropping off.
3. Automatic recognition of what gear/tire/trans you're using based on rpm/speeds reported.
4. More statistics (so far I do min/max/avg/sum and calculate Injector Duty Cycle on the fly)

Well, it's allmost midnight, I'll put up pictures and such later, for now , this is just the link to the spreadsheet with some example data in it.

EXCEL (209k)

Saturday, April 16, 2005

injector duty graphs

just a quicky:
when i was logging my car on the road, all i saw was 'injector pulse width' wondering what duty cycle i'm at. after talking to HumpinSS again (thanks man!), he got me an equation:
duty(in %)=pulse*rpm/1200
so i made up a quick graph for it:

it's also useful to look at it a different way:

so according to this, when i got to 21.5ms pulse @ 6100rpm, i was at about 109% duty cycle. not good. looks like i might put in the new injectors this weekend, so hopefully i will not have this problem anymore.
we'll see.

Thursday, April 14, 2005

out of injectors?

I think i'm starting to get close to the limits of my injectors, which is cool, cause with proper AFR (and i'm pretty damn sure it's good) i am finally making some decent power!

Yesterday i was scanning some second gear runs, and for example:
6100rpm, 73mph (top of 2nd with my 3.73s and 315/35-11 rears)
i was getting 19.7ms injector pulse, that means i'm right under 100% duty cycle according to

And it makes sense too, i was logging torque delievered, and i converted that to hp, and the injector duty follows the shape of HP curve, which it is what it supposed to be. either my car kicks all ass, or the lookup table is overly pessimistic, because there are people with H/C making 440rwhp on 26.4 lb/hr injectors that I have.

I played around with BSFC calculator ( and i'm either making 460 crank hp (with 0.50 BSFC and 95% duty cycle) or my BSFC is different. i did an experiment and it said that i'd be making about 420 crank hp at 0.55 BSFC and 95% duty cycle.

Where i SHOULD be at is about 390hp (0.50BSFC and 80% duty cycle) hmm...i better get to the track soon...

Wednesday, April 13, 2005

more on MAP pressure drops and Intake tract

Yesterday night I went out with a friend of mine who is pretty much responsible for me getting into cars at all. As the matter of fact, my '99 Formula used to be his. This time around, he's got a '01 formula M6 with zero options, making it a very light (read: quick!) car. He has very basic mods, Lid, Fram air filter, and SLP Loudmouth. So I decided to see how healthy his car was (it was _very_ healthy, if 'comparative driving' is a measurement is worth anything ;) ).

Turned out his VE is a bit out of whack, as well as his MAF. With his crazy driving, we gathered enough data that in an hour we had both of them inline, along with a slightly better PE settings. We left timing alone for this time, as it was getting late and I had to get home.

But in the process of scoring lots of data, I managed to get his MAPvsRPM data, as per earlier post about intake restrictions.

So now i got 3 sets of data (my z06 cammed car, OtE's stock cam, and Camaroguy's TR224) they both have FRAM filters and stock MAF, while I got K&N and Granatelli MAF. I graphed out 2 scenarios for each car. One is a graph of MAPvsRPM for all data with 90%+ of throttle, and the other graph is 'top 400' samples of biggest MAP values.

OtE's stock cammed car peaked at 99kPa in 2800-4400rpm
The same car would also get 95-96kPa above 5500rpm.

Camaroguy's TR224-112 cam'ed car would do 97-98kPa in 2700-4400rpm
The same car would get only 90-95kPa above 5500rpm

My car (z06 cam+LS6 intake) peaked at 98-99kPa from 2000-4400rpm , (second graph)
This setup would get 94-97kPa above 5500rpm, (second graph)

The 3 cars push different amount of air (from the tiny 01cam through my z06 to 224/.563) they all have different MAF's, lids, filters, and mufflers.
My car seems to have the smallest drop in MAP at higher rpm (smallest bottleneck, I guess bigger MAF and smooth bellows do help a bit) or just the FRAM filters aren't as good as K&N.

There's enough variables here that I can't really make any conclusive comparisons, and there are few unexplained things (why does car with the smallest cam suck the most air?)

Tonight, I will hopefully have a chance to get another set of data for stock 01cam+Mac headers+LoudMouth, so I will probably put up more graphs.

any comments? anyone wants to send me more data?

Saturday, April 09, 2005

Intake restrictions measurements

So the other day I came across an interesting post on about MAP not holding steady as the rpms increase. Apparently that's an indicator that you have a bottleneck/restriction in the intake system. After talking to some people, it seems to be a rather reliable source of information about how well your intake is flowing.
So I dove into some logs of mine, to see how mine fairs, and heres few figures:

96-97kPa at 4500rpm-6100rpm and 80%+ throttle
98-99kPa at 2700-4300rpm and 75%+ throttle

So while it is not a huge drop, of course it would be better to not have any at all, especially that I'm mostly interested in the higher-rpm operation. I'm not sure what I can improve, as I have just about all the intake-side mods: SLP lid, Granatelli MAF, LS6 intake, K&N filter (probably dirty after winter, might be the culprit). Another thing to do would be to start porting and polishing everything in the path of air, namely MAF and Throttle Body.

A sidenote: why won't someone test all the various lids with this method? it's a quick bolton, and all you need to do is few 'in gear' runs from 2-6krpm and see how MAP behaves throughout the rev-range.

So I wanted to compare my 'drop' to someone else's 'drop' to see if mine's bad or just minor.
The past few days I've been helping this kid with a typical 'got new cam, I get mad knock now' story, so I looked at his logs how his car compares. This is a 2002 Camaro with SLP lid, Fram Filter, FTRA

He has a bigger intake restriction:
1800-3200rpm can get 98kPa in MAP, while
4600-6200rpm gets 92-96 (with 92 on the high rpm side and 96 on the lower).

I will post pictures demonstrating the dropoff later. If anyone has any good logs/screenshots of really bad (or not at all) dropoffs, please send it to me, I'd love to see more extreme cases and see the effects of them.

Friday, April 08, 2005

Improvments on AutoMAF spreadsheet, ver 2.5

Car's still in the shop for some upgrades, so I haven't been doing much with it lately. I have however been sitting on a new version of my AutoMAF spreadsheet for a while now, I don't know why I didn't release it yet.

It's kinda cool, it basically keeps 'running totals' for number and sums of all samples, so you can keep on adding more and more data as you log throughout the year. The point is to gather the most data, so the results are truly representative of how your setup behaves in different conditions. Of course if you change airflow, then you gotta zero history out, and start from scratch.
is the link as always.

Let me know if it works for you.