Dyno question
 

How much does the chosen gear affect the HP rating? I dyno'd my car in fourth, with a 7/31 R+P.

It occurs to me we're comparing dyno numbers, for cars with different final drives, tire sizes, etc. Is there any formula or percentage that can be applied?

It shouldn't matter that much, usually a higher gear is used because tolerances are less noticable in high gears, plus there's a lower chance of tire slippage. The power that they give you when it's dynoed SHOULD be corrected.

I believe that the dyno program is sophisticated enough to recognize that HP/Tq being measured is relevant to quickness of the drum spooling up vs applied resistance than just wheel speed.

I know this to be factual because my drag bike's dyno time. Initially I had a small displacement, high rpm engine on NOS. It had a very low (high numerically) final drive. I later installed a large displacement, long stroke engine. I dynoed this engine first with the original gear set and then changed over to a much higher (numerically lower) final drive to take advantage of the new long stroke engine. The end result HP/ TQ was almost identical. Probably the only difference was the air quality, if I remember correctly.

On a properly operated dyno the final drive , gear ratio and tire height are all part of the input parameters supplied by the dyno operator.

This is one(of many) ways dyno operators can fudge their #s

Most of the dyno#s reported bear only a passing resemblance to the #s the factory gives. As such they are only valid when used in comparison to other #s derived on the same dyno under the same conditions.

"Most of the dyno#s reported bear only a passing resemblance to the #s the factory gives. As such they are only valid when used in comparison to other #s derived on the same dyno under the same conditions."

Great comment! Many on this forum either are not aware of this or ignore it.

When I dyno'd the 3.6 SC last summer the tech said 3rd gear.
2 weeks ago he insisted on 4th gear.

No difference for my car between the gears -- I had him run both 3rd and 4th on the 2 week ago run.

Did he change the inputs into the dyno for the different gears?

I did not see him do this - but it doesn't mean he didn't.

FWIW I have ran specifc 3/4/5 gear runs and they were all basically the same.

Thay said it is easy to skew the numbers if you want too..third gear is the common one to do that with. (but that is only one of the ways to skew the numbers to the plus side.)

"(but that is only one of the ways to skew the numbers to the plus side.)" - rdane -

This thread should be linked to threads that provide dyno results!

Might be worth a discussion.

FWIW I think the Dynojet 243 is a pretty reliable machine if the operator is "honest". Pretty easy to see the dyno results that are skewed if you follow and log the different engine builds.

From my 3.4 results and previous data I though that Ralph's 3.5 would be pretty much where he ended up on the dyno. I've seen other engine's dynos that are easy to pick apart. When someone gets a LOT more HP that anyone else from a similar build you can bet the dyno is bad. If you see an engine that is delivering a lot less HP than it should get a second opinion and then take a very close look at the build. Compression is a good place to start with a 911 engine.
Here are some of the ways to skew dynos...

Heat soaked engines
super cooled engines
running different gear than the norm (4th is the norm)
cheating tire size
clutch spikes

Vision dyno's all their cars in 3rd gear for "safety" reasons, perhaps because it is an above ground dyno, I don't know. If you look at the image I posted in the other thread, you can see the oil temp and the shift lever in the 3rd gear position. Tire size is the same 245/45/16 tire size used for the baseline runs.

The 246 rwhp number was not a one time peak number that couldn't be backed up. I have 3 other runs within 1 hp and all 12 were within 7 hp. So, throwing out every run (and Steve Wong's excellent work) except the initial run, is 239 rwhp accurate or is that still too high for this motor built in its configuration?

Maybe one should consider the 15% drivetrain loss that is thrown around. Most dynojet operators seem to quote this figure regardless of the car type, perhaps 911 driveline losses are actually quite less. If you ASSUME 10% rather then 15%, crank horsepower on my application drops to 273 from 289.

In my instance, the only parameters that changed were the 3+ months to build the motor and break it in. Unfortunately, I don't know anyone that can build a motor in a day and I don't have the deep pockets necessary to build a spare 3.5L motor to immediately swap the 3.2L. I think the 47 rwhp gain the motor achieved is accurate given my mods and the fact that both the before/after runs were on the same dyno run the same way. There was no mixing and matching like some dyno comparisons I have noticed.

It's too bad I couldn't put the motor on Andial's engine dyno, I guess that would have ended any talk of me or anyone connected to my motor "fudging" the number, eh? Loren, if you would like to foot the bill for Andial's dyno services, I will gladly remove the motor.

Why don't we all plan a summer trip to a mid-point location and dyno all of our cars on the same day on the same dyno? Maybe that end the scuttlebut once and for all? :)

Ralph

FWIW, my Swami guess was made knowing that your engine was going to run on a Dynojet - seems right on to me
after seeing many 911s run on a 248C over the past 5 yrs.

My four runs 2 weeks ago ranged from 277 when warmed up right after a nice spirited drive with another 3.6 owner, to 266 on the 4th run in a row on the dyno when the engine got hot(ter).

My engine cooling is still not what it should be. Front B&B cooler which is way to close to the pan, & a Carrera cooler with 2 fans (both of them off during the run, doh!)

Will be taken care of soon with the F&R bumpers -

And we'll send Loren in the other direction:p

Absolutely not! I would cordially invite (even insist) Loren to join us and bear witness to all of the dyno runs and even run the tests to the parameters he specifies. I don't want there to be any excuses...

I'll buy him the first round when my motor does exactly what it is supposed to do. There's nothing wrong with questioning results, but he getting personal with his little snippets (they weren't sarcasm as he suggests) is uncalled for.

I've never met Loren but he does provide useful information on this BBS as well. It's just his manner of presenting his objections and his belief that everyone but him is always wrong that I believes rubs people (including myself in this instance) the wrong way.

I think damned if you do and damned if you don't applies to me with this whole dyno nonsense.

Ralph

Ralph I am not sure your read my comments as inteneded. I had expected your engine to come in very strong from the beginning and made that comment several times in the past on other threads. I believe your numbers are accurate. It is what I would have expected from a similar build.

Like I mentioned, on a "honest" dyno my numbers didn't change between 3rd and 4th gear runs. I don't think you would see any difference in numbers on your car. Those that can't swallow the numbers need to get out more. :)

For additional help on the dyno numbers I would also add the race gas edge and headers (many over look that mod ) to that bit of dyno "tuning" to bump numbers. You want a "bad" dyno just run several in a row as Craig found out when his numbers kept dropping. Heat sink with proper ventilation would be the most accurate dyno numbers IMO. But our cars are very suspectable to heat sink and lower numbers.

There are so many variations and ways to skew a dyno but in general most of what we see here on Pelican is just a simple and repeatable dyno run with good numbers.

If you do enough dyno runs most of this becomes pretty clear quickly. When we start using different dyno operators, in different conditions and with different machines things can get confusing fast.

FWIW I think the Dynojet 243 is very accurate and repeatable, if you and the operator do it the same every time.

Forgot to add, while I don't know what the actual 915 gear box loss is I have talked with a number of dyno operators and the tech guy at Dynojet. 15% is not the norm for every tranny but in general the acccepted number for a 915.

Not that it means much Ralph but I think you have good numbers and Steve obviously did a great job tuning on the chip. An "atta boy" to both of you for your efforts and taking the time to post them for everyone's benefit.


This may or may not mean anything to the doubters but a 5% increase in displacement on the 3.4 CIS engine (conservative numbers I am confident in) would give 230hp and 224 ft/lb. for a 3.5 CIS. Add a programable and easier breathing Motronic induction, twin plugs and the headers and Ralph's number are easily believable. My CIS falls in exactly where I would have expected with BBII and Ralph's 3.5. on the graph.

Dane,

My statements were not directed at you, I just used your quote to get started. I too believe your dyno data based on what you have presented in the past and from my experiences at Andial.

I think that you have done an excellent job trying to round up data from different engine configurations, dyno types and locations from around the country and try and present it to people the best way possible. If people can't appreciate that, well...

Every motor is going to be a little different, and I FIRMLY believe that without Steve Wong spending 6 hours with me the week before tuning on the road and final tweaking on the dyno the numbers would have been much lower and probably satisfied other people who are skeptical.

I also wish to reiterate that my numbers were achieved with the motor not being smog legal (i.e. headers instead of the heat exchangers/cat installed) and I believe this also makes a SIGNIFICANT difference in the final outcome. If my original threads are perused again, one can note that my original intention was to run the standard exhaust with cat, then the Dansk pre-muffler/1 in Dansk muffler and finally the headers/dual-in Dansk muffler just to see how restrictive the exhausts are. Again, time constraints prevented that from happening.

I still think it would be fun to hold a Pelican dyno day, don't you?:)

I'm game for a dyno any time. Just give me a reason to drive south, Ralph :)

I think it is worth noting in my 3.4 overlay that the motronic is where the HP gains zoom away from my CIS 3.4 The torque bump on the 3.5 is obvious by the bigger displacement (.144 liter). I think the comparisons clearly show exactly what a well built 3.5 should show.

As Jack mentoned in the other thread his 964 3.6 has never really been tuned for best performance. Neither are the first 3.6's known for huge power.

I made the same "mistake" when comparing my 3.4 to BBII's 3.6 early on. (which is why my car is on a serious weight loss diet) Most of the 3.6's now being transplanted are the '95 and later engines with another 30 to 40 HP.

There are lots of options for engines in our cars and almost any of them will put a smile on your face...with or without dyno results :)

No, no, no! I'm looking for an excuse to go North and visit family at the same time! Besides, I would rather use your better gas. You guys may have to do some detuning to run on our crappy 91.:)

With respect to driveline losses, generally speaking it stands to reason that FWD cars and mid/rear engined, rear drive cars would have a lower percentage of loss then a front-engined, rear drive configuration. I don't know how much more efficient (if at all) the G50 (or the 901 or 930 or G64) is over a 915, but maybe Bill Verburg can chime in again? He seems to know all this type of data. Note that in my sig I quote my rwhp, since I really don't know for sure what actual crank hp is. I should have just bitten the bullet and put the motor on Andial's dyno...

Our intention wasn't to say that a street 3.5L is better then a 3.6L, just that another option that can make comparable power and torque to a mildly tuned 964 motor transplant without having to rev to high engine speeds, high CR, or use race gas to get there. Using Jack's car is great for shock value, as he and his car are deservedly well respected. SteveW is right, he spending some time with Jack's car (and he would enjoy that!) would undoubtedly push his numbers back over mine. As Craig and others have shown, the tuned 3.6L's leave our (didn't you just sell your 3.4L?) motors for dead.

Tod Simpson, I really apologize for kind of taking over and dominating your thread, I hope that you had your original inquiry answered to your satisfaction.

Ralph

"SteveW is right, he spending some time with Jack's car (and he would enjoy that!) would undoubtedly push his numbers back over mine."

I don't think so! Comments like that minimze one's credibility in other threads.

Here's the real problem. All the B.S. about what performance chips can really contribute.
Many performance chip suppliers have been "playing" with the 3.2s & 3.6s for the
last 10-15 years with all the same results, minimal to negligible increases. Now
we have a newer "player" who has "discovered" a major breakthrough. Please!
Those suppliers have been using dynos to tweak the chips and not "playing"
with a laptop racing up & down the streets (a real joke). Come on guys, get real!

I have no problem with the gains from a 3.5 mod, but to state that the MAJOR
results come from the SPECIAL chip tweaking is total B.S. Andial doesn't even
claim that a performance chip provides that much other than minor tweaking to the
final overall mod. They don't even include the chip mod as part of the 3.7 mod.

The chip (512 EPROM - 256 selectable) in the 3.6 we're all talking about is basically the GIAC chip
(in 1/2 the 512, stock in the other 1/2). It doesn't really provide much as can be seen from
the dyno results & it's probably the best there is. It ain't going to get much better with more tweaking.

Bottomline: Don't minimize the real contributors to the performance gain, i.e. the mechanical mods.
Chip mods???????????????????