Rick Carter

Interesting Hot Rod article drive train losses may be more than you expect.

j.kenzie@sbcglobal.net

My eyes aren't so good, but I don't see the RWHP listed by Carl.
Nice job, BTW, as always,
Dave

Carl Fausett

Here you go, Dave. All of the numbers printed directly on the dyno charts represent rear wheel values:

Carl Fausett

A long time ago someone told me that the right drive train loss for the Porsche G28-series 5-speed was 15%, when the dyno is done in 4th gear, which is 1:1. Pretty standard stuff.

We do a lot of baseline dyno pulls before we supercharge a car to make sure all is at it should be. And I have to say, time and again, you take the RW number and add 15% and you land dead nuts on Porsche's published HP numbers.
So, for us, the 15% drive ttrain loss on the G28 transmission is very many times confirmed for me.

Then later, I found out I was doing the math wrong. I was simply taking rear wheel X 15% and adding it on. That's wrong. Somebody here that knows math a lot better than I do showed me the right way is RW number divided by .85 = Engine.
Thats what I use now.

Carl Fausett

Must say my "thanks" to John Speake of JDS Porsche: thank you for your excellent and quick service. Sent John the LH, EZK, and the MAF sensor from this car after we had put it all together and the GTS map wasn't happy with the GT cams - lumpy idle. John found the hot wire sensor was off calibration and fixed it, and he modified the GTS's low idle to produce the higher idle that is needed for the GT cams.

The parts came back in about 10 days round-trip, went right in, started right up - idles great and runs nice.

Thanks John!

SwayBar

Teamwork!

John Speake

You're welcome Carl. Great result !

ROG100

Hi Carl - about to do the same to my 93 GTS - pull the engine and drill the pistons - Why did you replace the pistons? If it is a trade secret I understand but I do not plan on replacing the pistons and did know you had to.
I am replacing the rods because mine has the weak rods.

OK I see why as you opened the bore slightly - forget I asked - sorry

SwayBar

How do you know you need to drill the pistons; do all GTS' require that this be done?

And/or are you experiencing oil control issues?

Bigfoot928

every GTS engine needs the holes drilled. Period. Most will have a nice clump of carbon on them that needs to be cleaned off as well

ROG100

My GTS has covered over 170k now. Having seen a few GTS heads and pistons during rebuild I wanted to remedy the oil ingestion once and for all. The build up of carbon is alarming to say the least and the resultant effect on timing (up to 9 degrees) is bringing the power down.
Many GTS engines were rebuilt by the factory if oil consumption was below 500 miles per Liter IIRC.

GregBBRD

And the great part: New oversize S4 pistons are now coming with the holes not drilled.

(Of course, all the GTS pistons come without the holes drilled.)

GregBBRD

It would just be nice if we all used the same correction factor, so apples could be compared with apples. I can easily change...although the horsepower numbers get really high, really quick. I just finished a GT engine that I made into a 5.8 liter engine. Every single part (besides the crank, pistons, and rods) was absolutely stone stock. Stock intake, stock exhaust (stock cats), air pump, stock cams. it made 341hp at the rear wheels, which translates into 401 hp at the crank, if using your driveline correction.

Seems overly "optimistic" for a simple displacement change (although it does run like a scalded cat .) Therefore, I "used" an more conservative 1.125% factor, when talking about it, which is what I generally use for a manual. (I use 1.2% for a manual.)

I can do it your way, makes no difference to me.

What do you want to use for an automatic?

ptuomov

What we've found by varying boost etc. is that a reasonable approximation for a 5-speed manual 5.0L 928 S4 might be obtained from the following formula:

Flywheel hp = 10 hp + rear wheel hp / 0.88

It's not the truth but seems to match our data reasonably well as a crude approximation. Wide standard errors, of course. It's obviously not a valid formula for zero or 10000 rwhp.

Randy V

All that for an additional 39 HP?