What kind of dyno?

What was the A/F ratio?

 

Are those corrected numbers? (SAE or DIN)

Actually don't know why you should be dissappointed. Using a 15% loss factor, that'd be 275 bhp. Ain't the spec 280? And don't forget that the Porsche numbers are (usually) DIN which will a bit more than SAE.

 

Jim,
That was a Mustang dyno. He did a measurement of loss and it came out at 25 hp loss which equals a corrected max hp of only 270. BTW, any news on a new ride yet or still working on it?

GlenL, Factory is 288 so down 18 - I have chips and exhaust mods as well.

 

You might want to double check against other sources on the loss ratios.

I have seen where folks have done a comparison of Mustang vs Dynojet and has come up with a conversion factor to correct to low Mustang numbers to the equivalent Dynojet for RWHP. Then apply the standard 15% to 18% loss to the corrected dynojet equivalent numbers in order to compare to HP postings here on Rennlist (most of which I have seen are Dynojet).

Unforunately, the only website that comes to mind off the top of my head was for the powerbroker - he shows Mustang charts with Dynojet factors. His site does not show the Mustang to Dynojet back to back runs that generated the adjustment factors however.

I suggest that you check for this information a bit. A "standard" 25% loss ratio leaves a lot of room for error when trying to measure a 5% increase at the crank from a performance modification.

If you research, please let us know what you find.

Thanks!

 

246.2 top rwhp with 25% loss ratio:

246.2/75% = 328 estimated crank HP.

328 versus the 285-288 per publications and owners manual. That doesn't look bad to me.

 

234.3 / 75% = 312 estimated crank HP.

Also not bad at all, unless I do not understand what the Mustang guy was calling the loss ratio.

 

Anyone surprised about the difference of with and without intake tubes and filter?

 

Makes me wonder about the condition of the filter going in. Also, was there cool-down time between those runs? Was there a giant fan blowing into the hood area?

Dynos raise a bunch of issues around repeatability and replication of on-road conditions.

Last year I dyno'd my car with an open-top filter housing and _gained_ 5hp going to the tubes!

 

You can figure on about 15-17% drivetrain loss with a 5-speed (17-20% for autos). You also need to figure in altitude loss, 3-3.5% per 1000' altitude. If your dyno system is compensating for altitude (as some do) you can ignore the altitude compensation.

 

Regarding the loss of power from crank to rwhp, he did a test to start where he runs it up to speed then puts it in neutral til it stops - takes about 5 minutes. From this, his dyno states that the car loses 25hp - not a %.
I too was very surprised at the change from taking the intake off. Yes, he had two pretty big fans that were moving the air quite hard at the car. As for the differences, the car performed better when cool. First run was higher than 2nd and 3rd, then we let the car cool. Then pulled the air box off and got an extra 10-11 hp. I am going to scan and post the charts today.
BTW: Air filter had about 500 miles on it.

 

whall,

Picking this up this week end- http://pg.photos.yahoo.com/ph/akitamike/album?.dir

Did they measure A/F ?

 

Here is a pic of the dyno results. An interesting bump at about 2700 rpm??? Sorry about the quality, this is the best I could get and still upload.

Jim, that link doesn't work for me.

 

coast down only tests rolling friction, without the street friction. 25hp is kind of high. what about that, as well as the fact of the losses are mainly in the gear box in gear, but you can measure that unless you leave the clutch in , but thats only frictional losses then. we did the coast down and its 20hp from 130mph to 100mph and then 10hp on down. (for 240 at the rear wheels for my old part euro 4.7) whats missing there is the gear ratio losses, as that does measure the actually rolling friction as the wheels and tires are connected.

SAE is what you get when they do the correction for altitude . i like to look at actual uncorrected too. the 25% loss is pretty high. more like 15% and 20% if its an automatic. AND, this is variable too! more at 6400rpm than at 4000rpm

also, when you do the test, its very good to do everything the same. I like to start at 3000rpm, and roll on the throttle the same way EVERY time. if you start at a differet rpm or hit the gas differently, things can change. Mixture is good to monitor. when on a Dyno jet, get the tire pressures up to 34psi too, and see if it is getting strapped down the same way. strap down can vary hp too!(on a dyno jet)

MK

 

Mark,
Again the 25hp is the parasitic loss measured by the dyno. This works out to a total of just 10% which is not consistent with the 15% stated in threads here which seems odd. The owner of the dyno just got it and wasn't totally confident in it.
Does anyone have any reason that there might be a spike at 2700 rpm as shown above.
BTW, the measurement was done in 4th gear - does this have any bearing on anything.
Thanks again for any comments.

 

define "parasitic" loss. if its the rear wheel dyno, but no a dynojet, so there is no tire contact, the only loss you can measure in neutral for a coast down is just the friction ofthe wheel bearings and bearings in the transmission for neutral. like i said, i did a very accurate coast down that added the rolling friction of the wheels and tires and it was 20hp at 130mph and 10hp when it got down to 80mph or so. this is extremly accurate, besides the additional clamp down force needed to assure no wheel slippage.

15% loss is the efficiency of the entire drive train and this includes not only the transmission in a particular gear, but the rolling friction losses. the inertial effects are washed out in the fact that the time for the slow down is so long, as it is with the engine hp test, that it is not a large factor. ( run up test is 7-9 seocnds while coast down is much longer)

4th gear is a good gear as you reduce the losses the closer you get to 1:1 (ie 5th) generally, i saw a 8hp loss going in 3rd and i suspect, if you could not get wheel spin, another 8hp for 2nd, and so on.

again, what ever that 25hp was measureing, it was independant of the gear train losses, as you cant measure that with your guys or anyone's dyno. I guess, you could leave it in gear and coast down with the clutch in i guess? then you would have to add in any forces the clutch bearings have on the coast down, but it may make for an interesting test vs neutral coast down.

(may have to try that!)

anyway, your guy may be misleading you by accident as he doesnt have the understanding of the concepts down.

the efficiency loss range is in the 12% to 16%

MK