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Jerry
Jerry Reader
2/28/13 1:38 p.m.

So, I had some work done on the MR2, and my garage guy said we should dyno it and see how much help the various bits have added.

The last dyno run after a manual fuel pressure regulator to get A/F ratio into a good number gave me 110HP at the wheels. He said that's pretty good, and the figure about 85% of the engine HP at the wheels, so engine output should be about 129HP.

Question: Is this correct? About 85% at the wheels equals engine output?

Swank Force One
Swank Force One MegaDork
2/28/13 1:39 p.m.
Jerry wrote: So, I had some work done on the MR2, and my garage guy said we should dyno it and see how much help the various bits have added. The last dyno run after a manual fuel pressure regulator to get A/F ratio into a good number gave me 110HP at the wheels. He said that's pretty good, and the figure about 85% of the engine HP at the wheels, so engine output should be about 129HP. Question: Is this correct? About 85% at the wheels equals engine output?

It's a rule of thumb that's different for every car.

But.... why does it matter? Wheel horsepower is what matters.

Enyar
Enyar Reader
2/28/13 1:40 p.m.

Depending on drivetrains I would say 15% is about right.

SCARRMRCC
SCARRMRCC Reader
2/28/13 1:44 p.m.
Swank Force One wrote: But.... why does it matter? Wheel horsepower is what matters.

My butt dyno agrees.

the only people that care about anything other than Wheel horsepower.. drive automatics.

Keith Tanner
Keith Tanner MegaDork
2/28/13 1:45 p.m.

That's a fudge factor that is primarily used to inflate the ego of the tuner or the owner. Ignore it. At the wheels is what was measured, at the wheels is what you use.

The Brits, I believe, swear by flywheel hp. However, they also do a coast-down to measure the inertial losses directly.

An MR2 would have a lower amount of drivetrain loss than an FR car because the power doesn't have to turn 90 degrees.

Jerry
Jerry Reader
2/28/13 2:09 p.m.

In reply to SCARRMRCC:

"the only people that care about anything other than Wheel horsepower.. drive automatics".

Gotcha. Quick question, when you see HP ratings as a new car, is that also at the wheels or engine?

dean1484
dean1484 UberDork
2/28/13 2:10 p.m.

If it matters i use to get 115 to 118the at the wheels of our IT prepared mr2. All it had was a decked head that had some minor porting. The rest of it was stock.

Swank Force One
Swank Force One MegaDork
2/28/13 2:13 p.m.
Jerry wrote: In reply to SCARRMRCC: "the only people that care about anything other than Wheel horsepower.. drive automatics". Gotcha. Quick question, when you see HP ratings as a new car, is that also at the wheels or engine?

Engine.

In 99.9% of the cases.

oldeskewltoy
oldeskewltoy Dork
2/28/13 4:43 p.m.

post it......... (the dyno sheet)

here is my first dyno for my FR Corolla(figured about 18% loss - so 135 @ the crank?)

10.3 to 1 CR, Web 294 cams, ported seats to bowls (no other port work), 4/2/1 header, stock engine management

oldeskewltoy
oldeskewltoy Dork
2/28/13 4:50 p.m.

Oh... concerning the percent rule... have a VERY good read - http://www.modified.com/tech/modp-1005-drivetrain-power-loss/

yamaha
yamaha SuperDork
2/28/13 5:33 p.m.

In reply to oldeskewltoy: Eww, dyno dynamics.

oldeskewltoy
oldeskewltoy Dork
2/28/13 5:44 p.m.
yamaha wrote: In reply to oldeskewltoy: Eww, dyno dynamics.

It has more to do with operator then dyno...

here are 3 different dyno readings from my current 4AGE..

145hp - http://i79.photobucket.com/albums/j143/oldeskewltoy/ae71/dyno2610surreptitioussmaller.jpg

141hp - http://i79.photobucket.com/albums/j143/oldeskewltoy/ae71/2012dynosheetfromPSIadjusted.jpg

140hp - http://i79.photobucket.com/albums/j143/oldeskewltoy/ae71/Surreptitious1stdyno.jpg

different times... different places... slightly different tunes....

so I don't buy one dyno over another BS.... besides...it really isn't the numbers, as much as the shape of the plots - whp AND torque.........

..... THAT is why I wanted to see the OP's dyno... he's told me the numbers... I want to see the plot

Keith Tanner
Keith Tanner MegaDork
2/28/13 5:53 p.m.

I've got three different dyno runs of the same car that show a 9 hp variance.Same car, same operator, same dyno, same day - runs are back to back even. Guess what happens when your intercooler is too small?

Jerry
Jerry Reader
2/28/13 6:19 p.m.

In reply to oldeskewltoy:

You asked, here you go.

First sheet is from last month, all we did was add a header, no cat, and fairly open muffler. Otherwise stock 4AGE in a 1987 craigslist MR2. First run as is, second and third plot of the three was when he plugged a vacuum line to the crank case and went from 100 to 104HP.

This sheet is the recent one. He added a mechanical fuel pressure regulator to get the A/F ratio in good specs and I think he was going to advance the timing a bit (I wasn't there for this set so not sure.) Up to 111HP.

I've seen listings for a stock 1987 MR2 at 112HP brand new. I was curious if that was engine-only, or at the wheels, and how that compared to above.

yamaha
yamaha SuperDork
2/28/13 6:38 p.m.

In reply to oldeskewltoy:

That can be true, but as someone who has evidently been wronged by a dynodynamics operators twice by your reasoning(2 different locations).....so hopefully you can understand my distrust of them. They read LOW.

Jerry
Jerry Reader
2/28/13 6:47 p.m.

(And here's a video link to the first pull. I love this sound! Youtube symphony!)

oldeskewltoy
oldeskewltoy Dork
2/28/13 6:52 p.m.

Jerry...

For now... disregard the horsepower... look at your torque numbers.

Factory USA 4AGE engine was rated 112-115hp (depending on configuration) and 98-100#/ft (flywheel numbers)

Look at your 110hp plot and its torque, now look at my 112hp and its torque.

similar... except your hp peak appears to be @ 6590rpm** just about stock, and I'm at 7100. As I said I'm running a mild cam, so my old engine pulled a bit longer - hold a gear longer.

Do me a favor... get a cranking compression reading.

** - Edit correction... it appears you make peak hp ABOVE the factory camshafts capability.... somewhere between 6800 and 7000. Next time you have those cam covers off you might check to see if those are aftermarket cams..... I'll guess a 256 type of some kind

sorry for all that gibberish...

I made a few ASSUMPTIONS looking @ his plots (1 of which was the color dot was the peak reading)

Let me try to recover... instead of reading your dyno sheets on GRM, I copied and pasted them into my browser.. and my olde eyes were a bit better informed.

your 110 plot, and my 112 plot look very similar. nearly the same peak hp point - both well above stock 6600, nearly the same peak rpm point for the torque reading as well. THAT is why I assume(and still do) that you may have a mild street cam in there already.

Keith Tanner
Keith Tanner MegaDork
2/28/13 8:29 p.m.
yamaha wrote: In reply to oldeskewltoy: That can be true, but as someone who has evidently been wronged by a dynodynamics operators twice by your reasoning(2 different locations).....so hopefully you can understand my distrust of them. They read LOW.

Every dyno reads low when it's your car on it. If it's someone else's car, they read high.

Swank Force One
Swank Force One MegaDork
2/28/13 9:12 p.m.
Keith Tanner wrote:
yamaha wrote: In reply to oldeskewltoy: That can be true, but as someone who has evidently been wronged by a dynodynamics operators twice by your reasoning(2 different locations).....so hopefully you can understand my distrust of them. They read LOW.

Every dyno reads low when it's your car on it. If it's someone else's car, they read high.

Funny piece of wisdom for sure but I'm pretty sure mine read extremely high. I

Jerry
Jerry Reader
3/1/13 6:59 a.m.

In reply to oldeskewltoy:

"Next time you have those cam covers off you might check to see if those are aftermarket cams...."

Bought it on craigslist Dec 2011 from someone that had gone to FL that summer to buy it himself. Supposedly bought for daughter that ended up with different vehicle, he resold it to me. So, except for Carfax listings showing it in FL since birth, I have no history. However, it did appear that it had had some engine work by appearance and I assumed just maintenance.

Hmm... now I wonder if something else is lurking inside there...

MadScientistMatt
MadScientistMatt SuperDork
3/1/13 7:13 a.m.
yamaha wrote: In reply to oldeskewltoy: That can be true, but as someone who has evidently been wronged by a dynodynamics operators twice by your reasoning(2 different locations).....so hopefully you can understand my distrust of them. They read LOW.

Or you can say Dynojets read high. If you're making comparisons on the same dyno, it's more important that the dyno is consistent from pull to pull.

Paul_VR6
Paul_VR6 HalfDork
3/2/13 9:17 a.m.

Load dynos are for tuning. Inertial dynos are for posting numbers on the internet.

I tuned a rather well sorted IT Corrado SLC and we made a whopping 147whp on a Dyno Dynamics. Made well over my expected 170whp on a Dynojet 248c.

I would only make small comparisons within a session (holding all other variables as steady as possible) and big changes on the same exact dyno. Changing any more then this, who knows unless you have track results to guide you. Fwiw sometimes its easier to tune a car on a 1/4 or 1/8mi drag strip then anywhere else.

erohslc
erohslc HalfDork
3/2/13 11:58 a.m.

Consider this, HP is never measured, it is always calculated based on torque and RPM.

Another thing, when using ft-lb, HP, etc. as units of measure, simply because of the way they are defined,
it works out that the raw numbers for torque and HP are always the same at 5252 RPM.

So when you look at a dyno sheet, and the two numbers are different at 5252 RPM, then something is off.

Could be torque meaurement, could be RPM measurement, could be the way it's calculated.

Carter

Keith Tanner
Keith Tanner MegaDork
3/2/13 10:52 p.m.

The 5252 cross only happens with ft-lb and HP. Not "etc" Use different units and they'll cross at different points - or not at all.

As long as you have RPM and torque, HP is a pretty simple calculation.

The most common reason to see the lines not cross at 5252 is if the torque and power lines are using different scales. Happens more than you'd think for some reason.

yamaha
yamaha SuperDork
3/3/13 12:31 a.m.
MadScientistMatt wrote:
yamaha wrote: In reply to oldeskewltoy: That can be true, but as someone who has evidently been wronged by a dynodynamics operators twice by your reasoning(2 different locations).....so hopefully you can understand my distrust of them. They read LOW.

Or you can say Dynojets read high. If you're making comparisons on the same dyno, it's more important that the dyno is consistent from pull to pull.

Two different dyno dynamics.....first time the car made 152whp, second time 191whp, and its only time on a dynojet, 223hp.......car in question, +3psi ion redline.

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