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Discussion Starter · #1 · (Edited)
So since i got the Weber carb I've had the tuning bug. First I installed a wideband O2 sensor to get the carb dialed in. Then I thought about having it dynoed, but dyno time is expensive. Enter the LMA-3 from Innovate Motorsports:
http://www.innovatemotorsports.com/products/lma3.php

With this and a laptop I can log MAP, RPM, sideforce, acceleration force, speed, and AFR. So I get it all hooked up and take it for a spin. I recorded this from a 2nd gear pull:




This is a graph of HP, torque, speed , RPM, and AFR. The wierd part here is that the HP seems really low. I know this is wheel HP and that there is some loss in the drivetrain but I would think no more than maybe 15%. The engine is a freshly rebuilt A18 bored out to 2.0L, with a mildly worked head, stage 1 cam and Weber 38/38 carb. The only thing I can figure is that the exhaust is totally killing it, but that would be a little surprising since it has some sort of aftermarket exhaust.
Comments?

Oh, and I'm assuming a vehicle weight of 2200lbs. Too light maybe?

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engine power

Hmm those things aren't great does it add in drag efficency as well otherwise if not that would explain the lack of power reading, and whp power would have more than 15% loss at the drivetrain i think it's more like 20-25%. Best way really is to do your tuning on drag strip that way you can tell roughly howmuch power your putting down by the times your running and the weight of the car, and yes having the weight down incorrectly will alter figures at 2200lb's might be bit too light best bet is get the car weighed. I have a similar tool at home but doesn't do AFR but does everything else, seems pretty accurate as well as i've compared it with dyno runs and when the drag efficiency and weight is correct it's not far off in fact it was about the same.
 

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That looks a bit hard to read haha, but it looks like you only went to 50 mph? I think you're going to have to go quite a bit faster to get the horsepower up. Try topping out 3rd or 4th gear.
 

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Discussion Starter · #4 ·
The equations do take into account aerodynamic drag but not drivetrain or tire rolling resistance. I tried calculating just the aerodynamic drag part but I came up with a ridiculously low number, like 1 lbf, which doesn't make any sense at all. I'm using the frontal area and drag coefficient from a 3g Prelude so that should be pretty close. One of these days I would like to do a coast down test to get an idea of actual tire, drivetrain, and aero-drag losses, but I haven't found a long enough stretch of flat road yet where I won't hold up traffic.

As far as the 15% goes, I don't see how a (manual) FWD car is going to have any more loss than that. Even 15HP of loss would be a tremendous amount of heat to dissipate, which is of course where nearly all of the lost energy goes. For a RWD slushbox, yeah I could see 15% or more. For a FWD manual, no.

2200lbs may be a little light. I was basing that on the fact that I lost enough weight in the front to have to do the pinch fork mod just to get back down to stock ride height. I did try bumping up the weight a little but it didn't make more than maybe 3HP difference.

So about 1/4 mile times. Do you have a formula for calculating HP based on 1/4 mile times and weight? I could work out the physics but if you have a faster rule of thumb calc it would save me some work.

The graph is a little funky I think because the speed signal has some noise in it. I need to see if I can filter it to smooth things out.

Oh, and top speed shouldn't matter. At WOT the engine will put out max torque (for the RPMs at that instant) and will accelerate faster or slower based on the load present. The engine doesn't have any idea how fast the car is traveling. I want to try some 3rd gear pulls but have to watch for law enforcement representatives.

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Discussion Starter · #7 ·
Understood. And I'm not saying that 2nd is any better either. It's just easier to do on short stretches of road without having to worry about officer friendly. I've noticed on all those car shows (like they are THE authority, hehe) that they usually use 3rd. I'm guessing that partly it's to get a longer run. In second gear you get up to redline pretty quickly, especially with higher HP engines. In my case it took 6 seconds to go from 2000 to 6000. :(
 

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We use 4th gear when dyno testing.

I hear you when saying that dyno time can be expensive, but tuning the engine is extremely helpful especially if you'd done modifications to the car. Give it some thought for the future.
 

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Discussion Starter · #9 ·
I definitely want to try a dyno at some point just to verify that my own numbers are at least close to correct. Maybe when (If!) I get my header back I'll do a before and after run. I haven't gone back to search yet but has anyone posted dyno sheets for any A series engines?

Any particular reason for 4th gear?

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Where does this get it's speed reading from? Do you have to tap the VSS?

I'm very curious to see actual dyno vs a datalogger dyno result. Very cool stuff! That company has a pretty cool lineup of data loggers too.

My car didn't have enough power to do a 4th gear dyno pull, so we did 3rd. The shop said it shouldn't really matter, you just want to get as close to 1:1 gearing as possible to get the most accurate results.
 

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these are good for comparison numbers when doing you own setup only.
using between cars means nothing.
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it has an accelerameter for speed vs time
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they dyno in 3rd or 4th gear so the ratio is closer to 1:1 (oh, nm. 2nd beat me to it)
 

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Discussion Starter · #12 ·
I'm glad you asked about the speed signal. Reminds me that I took a picture. I tapped off the pulsed signal to the speedometer. The blue wire here:




Ahh, yes. 4th gear is usually 1:1 so it has the least frictional loss. That makes sense.

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Off topic, but:

On the dash picture above, what does the attachment "box" that's labled NST... do? I have mine apart and am trying to install a new display. (I only need to keep the fuel gauge and temp guage, everything else can go.)


I definitely want to try a dyno at some point just to verify that my own numbers are at least close to correct.
Don't get hung up on that. There are different types of dynos out there and they will show different results. There's at least one type (believe two) that the car's front tires have contact with the dyno rollers. Then there's the type which goes directly to the hub (more accurate). From what I understand, this type is much more accurate but does not show as high of a dyno result. Different days can also produce slightly different results. My suggestion was really intended for you to use the dyno session to tune the car (timing, fuel pressure if you have an aftermarket fuel pressure regulator on the car, and a few other basic things).
 

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Yeah, I guess that people debate a lot about which dyno is "right". The debate tends to be DynoJet vs Mustang dynos. DynoJet's always give higher numbers, and some people like them because they're more "accurate" to real horsepower.

Then some people like Mustang dynos because they feel the lower results are usually more realistic WHP.

I think that there are rules for SAE correction, which calculate in the dyno, the temperature, humidity, etc.

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Cygnus: When I ran the dyno, I ran 3rd in my Accord because 3rd is closer to 1:1 (acually ~0.82). 4th is an overdrive gear at like ~1.28 and 5th is like double-overdrive with something like ~1.45.

I only mention this, because I've seen you on 3geez, I wasn't sure if you had an Accord or Prelude. The transmission ratios are different, so take your results and choose gears accordingly.
 

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Discussion Starter · #15 ·
Dash cluster:
Well I know it reads the toothed wheel from the speedo cable and sends a 0/5V pulse stream to the speedo. The blue wire is the pulsed signal and it works out to close to 16000 pulses per mile, or in terms of frequency, 4.444Hz for every mile/hour. 60MPH would be 266.667Hz. Other than that, I'm not sure. The board has other stuff on it that I didn't really look into. There is a larger chip on there that didn't have a familiar looking number on it so I have no idea what it does. But it doesn't look like it would have anything to do with temp or fuel.

Dynos:
Yeah, understood about the dyno specs. That's why I went with my own logging setup so that I can tweek as much as I want for basically a one time fixed cost. The only reason I want to do a dyno run is just to get a sanity check on my own results. So far I've been using the AFR gauge to tune the carb and I've been able to get pretty close to where I think things should be, as far as AFR goes. But as far as maximizing power output, no idea.

Gears:
I read 3geez a lot because of the wealth of technical info. But I drive a Prelude. I know the Prelude gears are shorter and I thought 4th was 1:1 but maybe not. Can't say I ever really payed much attention to that.

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