dynos, rwhp, hp, etc...

[wastintime]

Hey everyone,
I've got kind of a dumb question, but kind of a good one too. I recently chipped my car and after one nightmare the third chip is amazing. The car feels great and has tons of power, so I for the heck of it took it to another local shop that I just found out about because they have a chassis dyno. We put the car on the dyno and did a few runs, all of which were with 1hp and 2ftlbs of each other.
I know i was stupid, and should have done a run before chipping the car so I could have a baseline to see how big of a difference it made, but I was excited and felt like screwing around with the car. Anyway, the best run had a RWHP of 250.0 and 232.1 ft lbs as the max torque.

These numbers at first seemed a little dissapointing as they are almost the factory figures, but then I remembered the factory figures are the actual engine powers at the flywheel, not at the rear wheels. I was just wondering if anyone could make a little more sense of them than I can. Assuming a 15% loss is crazy because it puts the car way too close to 300hp and I just haven't done enough to it yet. A tiny bit of intake, a tiny bit of exhaust. If I had headers and a mass flow sensor on it already I could almost go with being really close to 300hp, but it just doesn't seem right to me.

Anyway, just thought I'd throw this out there... anyone that wants to throw in their $.02 go ahead.

Thanks

[Craig 930 RS]

You are right on with the RWHP range of 1990 to 1994 3.6 engines on a Dynojet 248C -

MAF is a 4 or 5 hp waste of money.
Headers........up to you. Emission test? What muffler?

Let the game of variables begin!

[Jack Olsen]

IMO, dynos are useful for A/B comparisons of mods on the same car on the same dyno. Trying to compare different runs from different machines is an exercise in futility. There are far too many variables, in spite of what the dyno operators typically claim.

If you think headers, a chip and a MAF will put a 964 motor at 300 hp, then I've got a nice bridge in Brooklyn you might be interested in...

[Craig 930 RS]

There is no way, zero, that if you added all the 'bolt-on mods' in the world you will ever get close to 300hp at the wheels on that dyno.

[rdane]

250 at the wheels is 295 at the crank with a 15% loss. 993 engines locally are doing 270 at the wheels plus or minus a HP or two. You are pretty much where you should be with a 964 3.6 in a good state of tune.

Easy enough to make 300 at the crank from your dyno @ a 15% loss but it is going to cost you some coin. I suspect your new exhaust is why you are @ 295. If not that is where I would look for HP. Porsche did just that in the 993.

As Jack and Craig mentioned already, no way to make 300 at the rear wheels with bolt ons.

[Cookie Porsche]

Sorry to be the bearer of bad news here - but you loose a lot more that 15% btw flywheel and the road.

Remember, even Porsche (though always conservative) tested their engines without P/S, A/C. Factor in drivetrain loss, and a more realistic number is 30% loss.

250 bhp on the wheels would be closer to a 340 bhp engine, which is unrealistic with your mods. SO - your dyna shop has added what is known as a correctional factor (taking into account ambient temp, altitude, etc).

Good news is that Porsches (normally) loose less bhp through their drive train than most other cars so if one assumes that your dyna was 'spot on' for a average car - THEN you would have a little extra bhp from the standard 250.

NOW - carefull with the chip. Check the mixtures under load as these aftermarket units often run the car VERY lean (mid and high range) to make power. It works for a while and then PSSSfhhhhpop - burnt valves and pistons. Seen it plenty of times.

On a standard street engine like yours with the mods done - say 10, max 15 bhp. Still good though.

Regards, Tom

[rdane]

Originally posted by Cookie Porsche
Factor in drivetrain loss, and a more realistic number is 30% loss.

Curious where you got the 30% number and the data that backs it up.

There is documented info on the various Porsche gear boxes (and other cars/percentages for that matter) and their estimated drive train losses on a chassis dyno.

SAE corrected dyno can be up or down from actual. Important to know the difference in the numbers you were quoted to have a realistic look at your engine.

[Chuck Moreland]

Why not swap the OEM chip back in for another dyno session? Easy swap that will answer your questions.

[dickster]

guys,

i think he is refering to 300 at the flywheel

30% seems way too much to me. what jack said makes sense for comparisons. it is also useful to know what other 911's are making on the same dyno. when i had mine done (USA spec) i was told that they typically see 230hp for euro 911's (3.2's of course).

[IROC]

Can I sort of hijack this discussion and ask another somewhat relevant question?

What affect does tire diameter have on chassis dyno results?

For instance, I would like to dyno my car, but I have relatively large 275/40-17s on the rear (25.66 inches in diameter, nominally). Would I be better off swapping on a pair of 225/50-16s or something for the test? I mean, obviously, the larger diameter affects the amount of torque that is applied at the road surface, but I'm not sure how relevant that really is on a chassis dyno.

Thanks,

Mike

[Cookie Porsche]

Hrm... Firstly Jack's right - no two dynas should be compared directly, unless they are by the same manufacturer (hard and software) and / or that they are equally calibrated. Furthermore a 'correct' correction factor should be applied.

One can change the bhp reading to whatever one would like, so why not get an extra 100 bhp from a chip? or 200?

Rdane (pavement inspector?) - We have dyna'ed many Porsches, build engines and modified them from mild to wild. We use a loaded inertia dyna. A standard 250bhp C2 loaded with P/S, A/C, sticky tires, etc will not reflect more than around 175-190 bhp on the wheels. And yes - I've used various dynas over the past years.

Lastly - and not to offend - but gains of 40bhp+ from the mods discussed in this thread are misleading, to extract 40 bhp (at 15% loss) would require a lot more work.

30% may be a bit pessimistic as Porsche engines often produce more than their claimed flywheel bhp - but that's another story.

IROC - your tire rolling diameter, or gear rations, etc. will affect power readings - but only if they are chaged. The load dyna measures the bhp required to run the dyna, thus it will give you an accurate bhp reading - your rpm range may be affected but the bhp is spot on. If you later change tire size, the rpm range may be affected. The wheel weight (rotating mass) will also affect readings slightly.

Regards, Tom
911 with 4000bhp (new chip, corrected dyna!) JUST KIDDING

[ValveFloat]

Here is another way to look at the % loss thing.
Most of the numbers that get thrown around for drivetrain loss are based on the numbers people see on chassis dynos vs. factory specs for crank hp. It is pretty much agreed upon that some inertia dynos read higher than some pure load dynos, so different dyno operators tend to quote different loss numbers.
The point is that the only way to really measure, and quantify drivetrain power loss is to dyno an engine on an engine dyno, by either a "hold and measure", or by a controlled sweep, and then dyno the same engine in the car on a chassis dyno under the same atmospheric conditions using the same rate of acceleration. Stating drivetrain loss without doing that is pure speculation, and I don't understand why people always do it. Just sharing the wheel hp and what brand and model dyno you ran on gives people an idea of where you are at. IMHO of course.

[kucharskimb]

oh, boy! this reminds me when you guys jumped my ***** in this post...

2.2 E stroker HP output

this isn't another case of DIN v SAE, is it?...

matt

[Craig 930 RS]

Whoa hang on here. Let's stick to the original post!

[rdane]

"A standard 250bhp C2 loaded with P/S, A/C, sticky tires, etc will not reflect more than around 175-190 bhp on the wheels."

I have whitnessed a few dynos myself and collected the data off a few more. Most of them from Dynojet machines for all the obvious reasons.

Factory bhp DIN numbers from a C2 are 250 or 247 SAE. Porsches numbers are typically very conservative.

Here are a few examples from my data base in SAE corrected and at the rear wheels.

1991 Porsche 964 C2 (Stock)
216 rwhp
207.6 Torque

964 3.6 B&B headers, NBD Racing chip
243 rwhp
216 torque

Most 3.0 liter SCs with just a set of SSIs on will pull over 175 SAE corrected rwhp. (Factory crank # is 173) Never seen a healthy and stock 964 drop under 215 at the wheels.

The original poster said , "I just haven't done enough to it yet. A tiny bit of intake, a tiny bit of exhaust."

None of us know yet what "a bit of intake or a tiny bit of exhast" means. But BBII has BB headers and a chip...and no intake work and is 243 at the wheels. From Jack's dyno graph there is more in his engine with a little fuel delivery tuning.

As I said earlier the 993s are getting 270 +/- a few hp at the wheels on Dynojets. (Porsche claimed 272/285 at the crank depending on year of manufacture) 250 is not unreasonable out of a 964 engine. The majority of professionals are still using Porsche's recommended 15% drive train loss for the G50 and 915s.

Not seen an engine dyno locally yet come any where close to a factory numbers or a chassis dyno. Example?

"46mm PMO, carbed 3.2 short stroke. with dual plugs.
281 H.P./ 244 ft./lbs. torque at the flywheel on an engine dyno.

Changed muffler and put her on the DynoJet.
222.1 HP and 201.5 ft/lbs. torque measured at the rear wheels"

A 27% hp and 21.5% torque loss by these figures and close to what Cookie is quoting at 30%.

A muffler can make a signifigant change as well. This was a change from a street 2/2 to another street 2/2) Not perfect but you can get an idea.

I might suspect that Porsche actually does know the real numbers and publishes them. But I also suspect as most do that Porsche numbers are minimums. Not uncommon to see Porsche's DIN crank numbers very close to what is measured at the the rear wheels.

I'd be really pissed if an engine builder did an $15K engine for me and told me the engine dyno was 280 and was then measured 220 at the wheels Good reason to argue the 30% loss if the engines are not measuring up to Porsche's numbers or suggested gear box loss.

All said a dyno is a good comparison if the chassis dyno machines used are the same make and model and the testing conditions are the same. Lots of ways to fudge a few hp. in operation. The original question as I read it, "is 250 at the wheels possible from a 964 engine with few mods".

My take...and using Jack's BBII as an example is, yes.

Helmut Bott would be surprised to learn I have built a 319 HP n/a CIS engine I'll stick to the 15% drive train loss.

[Randy Blaylock]

I set up my engine on an engine dyno and followed it up with a chassis dyno run and the difference was 13%. That's using a gear ratio that is as near 1:1 as possible.

[rdane]

I stand corrected Randy..thank you.

[Randy Blaylock]

Just my experience, "your results may vary"......

[Jack Olsen]

Originally posted by rdane
The original question as I read it, "is 250 at the wheels possible from a 964 engine with few mods".

My take...and using Jack's BBII as an example is, yes.

But that's only if you take my dyno results as absolute. I don't. I'd only claim they're meaningful comparing my before and after test (same day, same dyno, not even disconnecting the car) with the NBD chip.

Wastintime put his car on an unknown dyno, and didn't get any baseline number to compare his chip against. That done, he declared his chip a winner -- of what? In my humble opinion (and he even acknowledges it in his post), his time on the dyno lived up to his screen name.

As I've said before, every dyno operator in existence has a lot to gain by working their machine to produce the most optimistic numbers imagineable. If I were a tuner, I'd feel the pressure of the same 'dyno inflation' as any of my competitors.

It's like when they try to get Ivy League schools to hand out as many D's as B's to students who are paying 40K a year for their education. It's just not going to happen.

[project935]

I'm hoping to get my ultra-low mile '90 964 C4 in a few months.

I also (think) I have access to an AWD controlled environment chassis dyno at work - I knew I just joined this company for a reason

Here's my long-term dyno plan - all are with/without AC drive belt;
1. Baseline - totally stock '90 3.6L
2. Single-in/dual out B&B muffler w/cat
3. #2 w/Fabspeed airbox
4. #2 w/cone air filter & adapter

5. OE airbox w/993 headers & US cat, no mufflers
6. #5 w/Fabspeed airbox or cone filter (depending on #3/4 results)

7. OE airbox w/993 euro exhaust (no cat? and mufflers)
8. #7 w/Fabspeed airbox or cone air filter & adapter (depending on #3/4 results)

I have these parts already. If I find another interesting bolt-on I might add it to the matrix (like a 964 cat bypass for the 964 headers). Whatever looks the best and sounds street-tolerable I'll get chipped (Wong probably) and dyno again. I'll be measuring HP/torque and A/F for sure - maybe emissions as well.

I also have a l/w flywheel to replace the dual-mass. Unless the clutch is shot in my ultra-low mile 964 (not likely), that won't get replaced for quite a while.

That's my pie-in-the-sky plan anyway ... will probably take awhile to accomplish, but I think I can use the resource.

Any comments or suggestions?