philchil

My dyno #s were at the wheels? Something is sticking in my head about the tranny looses 15 percent, so the dyne guy thought my cup piprpe and chip must have incread my numbers.

As you probably know, my rsa was rated at 247 hp fm the factory...is that # fm the wheels or adjusted?

philchil

Here's a link to a utube video done by performanceautosports.com showing my RSA being dyno'd...

its the first video if the link doesn't work...don't know how to imbed the utube video into this post...enjoy!

NC TRACKRAT

"But once you've got everything apart anyway, it's only a couple of minutes per cylinder."
Sure, if you've got the compressor and the leakdown tester...but, if someone's paying for a PPI and they got good, even compression, my point is why go to the extra expense? At, say 170-175 psi/ cyl, you're not going to see bad leakdown numbers.

ca993twin

Auto factories (and some builders) use engine dynos, which are far more accurate and predictable than chassis dynos. The numbers provided are AT THE FLYWHEEL, not at the wheels.

philchil

Thx Steve...

The dyno shop stated the numbers are to the ground (rear wheels). Is it just semantics...play on words?

Can you explain so I can understand the difference?

Also, do you know how the factory measures HP ratings?

Any insight would be appreciated and will certainly help the p-car new guys...

Thx!

Phil

ca993twin

Phil,

Please don't confuse me with an actual expert in this area. But that never stops me.

Your chassis dyno run recorded 243 HP... that is to the wheels, or "to the ground". Chassis dynos have lots of variables, and it very difficult to compare one against another. They are very useful for recording differences after modifications... on the SAME dyno. The number can vary by 10% or more from one dyno to the next. All dynos (engine or chassis) factor in a correction factor for some SAE standard temperature and humidity. Chassis dynos do NOT try and factor drive-train losses to determine engine HP, but your guess of a 15% loss is probably realistic.

So, assuming your chassis dyno is fairly accurate, and 15% is a good guess for drive-train loss, your 243 "to the wheels" would translate to approx 279 HP at the flywheel. This represents a nice gain over the 247 HP claimed by the factory.

race911

Really? I've got a Spec Miata right now in the backyard with good compression and almost 30% leakdown in a hole.

Back to the original point though. You're paying for a PPI. If *I* were doing it, I'd tell the customer it's an extra 1/2 hour labor (to be GENEROUS) to also do the leakdown. And I'd guess any shop will have the compressor and leakage tester.

It's not a nice gain, it's a gain-for-the-ages. I've always been amazed how a 964 with the stock headers and a little software tune (and still with the flapper door restricting the intake) can make as much power as the revisions done with the 993 in intake and exhaust. (I won't claim to know how the software differed.)

When all the RSAs rolled out into competition in the early '90s, seemingly EVERYONE said they were getting 300HP with a little of this/little of that. Odd how my club racer that still had the cat on it, in stock class, never lacked for trap speed when I got around to running my own 7-8 years later. (Granted, we didn't have data, but I took exhaustive notes on RPM v. point on track for all my customer cars and mine.)

ja78911sc

Is it possible to have a valve issue and still have good compression?

If it is a ring issue, would the compression #'s be low on that cylinder?

NC TRACKRAT

"Is it possible to have a valve issue and still have good compression?"
Inquiring minds really want to know how that can be!

race911

Haven't taken the engine apart. Tested on separate occasions, with different equipment. Happy to report back when I get to it; but given the GT3RS money that went to rescue the vending business, I don't think there's much in the piggy bank for cars/track/racing until I sell later this year.

philchil

Thx Steve, aka ca993 twin...Phil