Eric, see my post above. First you can't say that a given tranny robs X amount of horsepower... only the percentage. Second, as reiterated per the link in the previous post, numbers at 20% loss or higher are pure BS. Here's a quote from another article:

The worst scenario case for a rear drive setup is on the order of 12.5% in 4th gear, not the 20 -25% often published. If 25% was being lost in the drivetrain, the oil would boil in the differential housing in short order and aluminum transmission cases would fatigue and break from the temperatures generated. On a 200 hp engine, something on the order of 37,000 watts would have to be dissipated out of the transmission and differential housings. Obviously, this is not the case.

My dyno testing has shown that on a standard DynoJet chassis dyno, the ~18% loss is a good ballpark, and provides relatively realistic numbers. Again, there is no chassis dyno in the world which can ever show you flywheel hp, no matter what they claim. The only way to get true flywheel hp is to pull the engine and put it on an engine dyno. If you do this, it will also show you the actual drivetrain loss, but only for the chassis dyno you used with the same engine & chassis.


About the modified vac signal to the EZL, see my previous "blood from a turnip" post. Dude: It's a stock M103! Just accept it....


:deadhorse:

Eric

You are correct as you can't tune any car on an inertia type dyno like a DynoJet.
On an inertia type you are just accelerating and spinning the rollers to get a power reading.
In essence it's about the same as revving your engine.
Great for a baseline, but no use in tuning through the RPM range for max power !
To tune you need a load against your rear wheels so you can vary and hold RPM ranges to read AFR and if boosted the psi.

Ed

No URL's just empirical data from baseline RWP runs versus manufacturers published BHP. They are the only two numbers that can be used to calculate the drive train loss. Assuming that the manufacturers BHP is accurate then the calculation is simple mathematics.
Whenever I have made my "claim", I have clearly stated that the RWP was from a load dyno.

My response to your "numbers above 20% are pure BS" is based on articles that refer to inertia type dynos.
So then please show me how my calculation of 177HP Mercedes published BHP divided by 136RWP documented by a load dyno = 1.30 or 30% is BS ?
I prefer this calculation over 136/177=.76 or 24% ( still above your BS threshold) as the 136 is a proven number and the 177 although published, not sure to what SAE if any standard the engine dyno was performed under.

Also keep in mind that drive train loss includes the tires and there is a big difference if the dyno is a single or dual roller type...dual rollers like many of the load dynos will show more loss.
Dual rollers make the car more stable but also mean two tire contact patches.

The number you get really means nothing unless you are using the baseline to determine what additional power you get from a mod.
I'm not trying nor do I care to estimate BHP after I make mods as it really doesn't matter. If at this point I've doubled my RWP and Rtorque over baseline then that's all I care about.

The fact that you can't tune using a DynoJet inertia type is the reason that I've only had cars on various load dynos.

To be accurate in tuning or modification comparison you should use the same dyno as the baseline pull.

I've posted my Mustang pulls versus published dat so please favor us with your DynoJet pulls versus published data...

This will be conclusive proof on the differences between load and inertia type dyno....

Dave, you are not entirely correct on this one. It has been thoroughly proven and documented repeatedly through the years that some automatic transmissions rob more power than others. Sometimes it's because of poor design, sometimes it's because it's an outdated design, sometimes it's because of higher reciprocating weight as we see in this example: Many a Mopar nut has gained a 2 tenth reduction in E/T just by swapping out their 727 Torqueflite in favor of a 904 torqueflite which is no surprise because because 904s only rob about 25 hp while 727s rob about 45 hp. These 2 automatics are about as similar as they can be, with the 727 simply being a scaled up version of the 904 that debuted about 2 years after the 904 did (1962 vs. 1960). If you put that same car on a chassis dyno after swapping in the 904 you will find more power getting to the wheels, and again, the car will be about 2 tenths faster in the quarter mile. So obviously, this is a clear cut example where a one size fits all 18% factor does not and will not apply to at least one of those automatics. Another example are the C4 and C6 Ford automatics with the C6 being the 2 year newer (1966) scaled up version of the C4 that takes 20 more hp to drive it. A Ford jockey will gain a MINIMUM of a .2 second reduction in E/T when he/she tosses a C6 in favor of a C4. It goes without saying though that when one swaps out the beefy, heavy automatic for the lighter one, they will also be gaining a trans that won't live as long. It's a trade-off that many racers have gladly accepted through the years though. Why? because many races are won or lost by less than 2 tenths of a second! And for the record, in both cases the heavier autos are only about 25 pounds heavier than the lighter ones are so you can't claim it was just simply a reduction in the overall weight of the car that netted the E/T improvement. In the case of the 904, it is mostly from the 13 pound reduction in reciprocating weight. (I'm sure the reason is the same for the C4, I just don't have the exact reciprocating weight reduction number for you for the Fords.)

Here is some more good reading on the subject of chassis dynos: http://www.hotrod.com/techarticles/general/hrdp_1103_chassis_dyno_testing/index.html

And yes, I know it's only a M103 (not totally stock though) but I also know that my 200 hp 210 tq goal for it is not unreasonable. Remember, you once told me my 14.7 E/T goal for my 400E was not realistic unless I ditched my 2.24 rear gears. We all now know that my goal for that car wasn't so unrealistic after all. And I'm still proudly running those 2.24s. I just feel like since I was able to get my 400E to go a full second faster than it did stock I outta be able to get this 300E to go at least a half second faster than it did stock. I've only got about 2 more tenths to go. That's not unreasonable.

That reminds me. I've heard that a 1 tenth reduction in your 60' time will net you a 2 tenths reduction in 1/4 mile E/T. Is that true? Seems like voodoo math to me.
Regards, Eric

Dave..I know you like URL's so here's a pdf which contains:

computer that does all the calculation....."

http://www.carvtechpc.com/uploads/3/7/7/9/3779419/dyno_vs_dyno.pdf

Here is another article that will help you better understand differences between dyno measuring methods:

http://www.aera.org/ep/downloads/ep10/EP04-2010_34-39.pdf

And this article:

Crankshaft horsepower vs. true rear wheel horsepower. That's a tough one. As each vehicle is different, the best way is to dyno the engine and then dyno the vehicle to see exactly what the loss is. The best estimate I can give you based on experience and research is take crankshaft horsepower, subtract 14.5% ( search SAE ), take that, and subtract around 10% to 15% and you'll get about true horsepower at the rear wheels.

( Using published 177BHP x .845 x .9 = 134.6 HP and my load dyno was 135.9..pretty, pretty close...eh? )


http://www.mazdas247.com/forum/showthread.php?123629978-DynoJet-Horsepower-Vs.-Real-World-Horsepower-Good-Read!

Eric

I wouldn't give up as I'm an old hot rodder.....

All engines that come off the assembly line are not equal...some built within production tolerances and every once in a while one is spot on...
All to gain and nothing to lose...!!!

I've seen 1.15X to 1.5 X on ET from 60 improvement....based on same car, same driver, same track, same day, same conditions....;)

Ed A.

I thought we covered this before? Might have been a different thread. Answer is generally no, although it depends where exactly the 1 tenth gain is coming from in the 60'. If it was traction issues at takeoff (i.e., in the first 10 feet or so) there will be NO additional gain in the top end (still 1 tenth, not magically 2).

Now if there was some serious increase in bottom or midrange power, depending on gearing, etc that made the gain more towards the middle/end of the 60'... yes, it could be more than 1 tenth at the top end. But not much, 2 tenths is probably optimistic. This would be a very unusual situation as the 60' is almost always the bottom half of your rev range, after the 1-2 upshift it will never be back down below ~4k or so (varies with your enigne & tranny, but we're talking 722.3 autos specifically).

BTW, I still don't buy the claims of 20-30% loss via powertrain. And I seriously don't care enough to try and prove otherwise. Believe what you want to believe, whatever makes y'all sleep at night. The awful inertia dynos work perfectly for my cars, must be some weird Bermuda Triangle thing here in Boise.

I really don't care what crank HP is. The dyno is a tuning tool, when a change shows a repeatable +10hp at the wheels, the change was worthwhile. It seriously doesn't matter to me if that means going from 200 to 210 or 300 to 310 on the sheet, it's still +10 gain either way. You'll never be able to compare numbers from different dynos. The whole "my dyno is better than yours!" thing is silly to me, as long as the dyno is able to provide enough load for the engine/chassis being tested... some very high power or high torque vehicles need enough load for a proper reading; some dynos can't even give accurate numbers when NOS is used. But other than that limitation, it's back to "so what".

The area under the curve is far more important than the numbers, even the shape of the curve. You can run the numbers through whatever calculator you want, it won't change the power output!

Dave ...

You're not saying anything different then what I've posted...
Nobody is concerned with BHP or crank HP..I've stated this ad infinitum.

You're comment that "you don't care enough to try to prove otherwise" is only because you know you can't and are just trying to save face..
You are an extremely knowledgable individual who has amassed a great amount of data on the 124's..Kudos to you..
But nobody is correct 100% of the time...We all can learn something every day.

You can't deny empirical data and the differences between dynos...
The inertia dyno never did and never will provide any load or resistance on the rollers as it's basic design and operating principle precludes that.

Tell me then how do you tune a car on an inertia dyno??????
Or perhaps you've never set up your parameters when on a dyno.

Big difference between using a dyno as a comparitive measurement device versus being able to tune real time on a device that allows RPM to be varied and held at certain points to make adjustments for max power.
Much easier doing it on a dyno then to make adjustments and test drive then return to the dyno for results.
So much easier to dial in your power and tweak for max power while on a dyno...
Not sure when you were first exposed to "dyno tuning" but I go back to the late sixties-early seventies when I ran a SS/AA ( eventually SS/CA ) car out of Jenkins shop in Malvern Pa...a lot was learned from Nicholson and Stahl about dyno tuninng.
In fact Jere Stahl built my headers while the car was on the dyno..tuning the variable collector lengths for different torque output..Lengths were charted and we could adjust at the track based on traction conditions.
Couldn't do this real time on a DynoJet !!!

I've posted several charts from my load dyno pulls...
Please post your baseline then any chart after any mod...
Without a baseline pull then all else is pure conjecture on how much power a mod has added or subtracted. :)

Ed A.

P.S.

Link to my drag racing creds...was a second tier factory driver...orange car is mine:

http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=5881191&page=0&fpart=1&vc=1

http://sports.groups.yahoo.com/group/StockSSDragRacing/message/91194

No, I seriously don't care. But I get really tired of people leaving misinformation on forums for millions of other people to read and then spread as gospel. "I read it on a Mercedes forum on the interwebs, it must be true!" If I don't at least make a weak attempt to offer an alternative viewpoint, it's the same as agreeing with you, which I don't (at least not entirely - you do have some good points and accurate info).



Thanks.



When I'm wrong, I'm happy to admit it. Ask Eric about me being wrong about the 4.2L thing in almost every conceivable way. In my defense, I was basing my initial claims on factory data which turned out to be incorrect. I later bought a 4.2L and did my own testing, then Eric went further than I did and came up with impressive results. But I was still wrong initially, and learned a lot along the way.



I think your definition of "tune" is different than the vast majority of other people's. Do baseline, make change, do another run, compare graphs, observe difference.



What you are discussing here is waaaaay over the heads of >90% of people who want to put their car on a dyno. In many areas, you're lucky if there is one or two dynos available AT ALL. Many people can't pick and choose what dyno type to put their car on. Where I live, I know of 2, maybe 3 total and I'm nearly positive all are inertia types (couple DynoJets, one Mustang, IIRC). That doesn't mean they are all useless junk providing useless data to suckers who pay money to put their cars on them, as your post strongly implies. This is where I very much disagree with you. Sure, your preferred dyno may be better (in some ways - no design will ever be perfect), but if you don't have access to one of them thar fancy thingys, what's the point?



Very cool, but you are talking about pro race teams with access to what was likely the most advanced tuning equipement in the country, at seriously high cost. We are talking about Joe Blow forking over $75 for three pulls on his street car. C'mon, man, consider the audience here! :)



I can't dispute this, but I'd be very curious to hear what the response would be from the DynoJet tech department. Maybe I'll forward them a link. Of course I expect the forum responses to anything DynoJet says to be "bah, they are biased towards their product, therefore anything they say is lies, and damn lies". Or something to that effect.



I agree with you 110%. Maybe 120%. It would be 130% if I had a load-based dyno available where I live. Here's some of my useless inertia dyno data. The performance gain was not mythical just because I'm hampered by the wrong dyno type, I went to the dragstrip and verified the performance gain. We can bench race dyno numbers all you want but at the end of the day, it's what the car does on the pavement that matters.

Before: 17.5 @ 80mph, ~2.75 60'
After: 15.8 @ 86mph, ~2.25 60'


http://www.peachparts.com/shopforum/...chmentid=90237

:vbac47679

I've already wasted half my morning on this topic, but here's a link with some interesting info:
http://wotid.com/dyno/content/view/19/38/

Quote:

"Typically a steady state dyno will give results of up to about 20% less than inertia types. Here is an example of how different results occur. You have a bike that shows a maximum of 100HP on an inertia dyno and xxHP on a steady state dyno. Now we lighten the crankshaft and flywheel, fit a lighter rear wheel, fit a lightweight chain and some alloy sprockets. We run the bike on the steady state dyno and it still shows a maximum of xxHP. We run the bike on the inertia dyno and find it is now producing 105HP. These modifications didn't actually make the engine produce more horsepower just as the brake dyno shows. So why does the inertia dyno now say it is producing more horsepower? This is because the inertia dyno gives a true representation of what the "road" sees. Of course the engine isn't producing more horsepower, but there is more horsepower available to accelerate the bike because less power is needed to accelerate the crankshaft, chain and sprockets and finally the wheel. Because less power is need to accelerate these things more is available to accelerate the bike, and it will accelerate faster on the road. The inertia dynamometer calculates horsepower from how fast its drum is accelerated, therefore in this example the bike engine was able to accelerate the drum more quickly after the modifications so more horse power is available at the rear wheel to accelerate the bike on the road. In my opinion steady state dynos are good for tuning tractors that are going to run at 1500-rpm day in day out. To tune an engine for the type of riding I do, or bush riding or racetrack riding I think an inertial dyno is more than sufficient. How often do you care how much power you're making at a steady throttle? When I'm out having fun, the engine is rarely at a constant speed, it is either constantly accelerating or decelerating."

The author is 100% correct here, and while your example of tuning headers using steady-state loads is excellent, that is not how most people (i.e., Fruit forum members) are using dynos on their street cars.

I have seen a power increase on the inertia dyno by swapping on lightweight wheels, this change should show zero power gain on a load dyno as described above... but the performance appears on the dragstrip time slip. Which is correct? Both. Which do you want to see? Depends on your goal. But neither is "wrong". The inertia dyno data can be more useful to someone who wants to see if a change will affect real-world performance, while load testing can provide more useful data for specific tuning (if you have that capability on your engine - which we basically don't for MB engine management, unless you've converted to aftermarket standalone).

:thumbup1:

my $0.02, the dyno is just a tuning tool and trying to estimate flywheel hp from wheel hp is useless if you don't know the exact losses (for that you'll also have to have an engine dyno,otherwise it's just guessing). However I agree with Ed that a load dyno is better for tuning. Using a load dyno you can keep the engine at a given rpm/load and dial the tune more accurately while compensating for things like heat build up i.e. your keeping the engine for a longer time in the desired load/rpm instead of just passing through like on an inertia type dyno .

P.S. when measuring performance gains, in my opinion the most important thing is to use the same dyno .

So it would appear that we need the inertia dyno so we can see the gains we get by doing things like installing trannys with lighter reciprocating weight and we need load dynos for tuning purposes and so that boosted cars can properly build boost as they do in the real world.

As I told Dave a long time ago, I still prefer the dragstrip! It's cheaper too!
Regards, Eric

Eric

You are so correct...any mods can only be truly proven by a timed event.
Interesting that some Mustang load dynos have a drag strip option complete with Christmas tree......
Extremely accurate as is a G-Tech pro or any simililar device with a 3 axis accelerometer ;)

Ed A.