Lemming

I wouldn't run the supertrapp on the street myself, I don't like the sound! But, it works for the track.

Don't have dynos on my work comp, will post them up tonight. 10 discs worked on my #2 engine but not on my #1, both of which were running the same chip and header. I don't have an explanation for the difference, but you will agree when you see the dyno

Jason Judd

Good job Tim!

I'm afraid that with my modest mod's to my car, I'll be in NASA's GTS2 category...running with the big boys for sure!

If I learned anything from making changes to my car...it's that you really need to consider how it will affect your classification standings in the future.

On the other hand, if you're not going to race...then just have at it!!

Jason

Lemming

Below is a dyno from #1 and #2 engine, both running 10 discs. There is a clear difference but I haven't a clue as to why. Same chip, header and exhaust.

Lemming

Here is #1 and 2 engine running with no discs (#1 has the greater hp)

300guy

Thanks for posting Tim! I really value people like yourself who are willing to share info like this.

Very interesting in the gains with no muffler - this goes against what most people have said about the 968 motor.

mikew968

Remember this is racing, headers, stage 2 chip and no one really cares below 4000 rpm. The one engine seems to have a problem about 6000 rpm. Any idea what that is?

Lemming

I have no idea why that engine has the valley with the addition of discs. Engine #2 does not.

As for "this is racing... below 4000 rpm"; I have yet to see any dynos of a stock 968 run on a dyno with and without restriction. If you look at the beginning post in this thread, you will see that hp and tq are increased pretty much across the board with the open pipe relative to the 16 disc run. Yes, I am running a chip, header, and "test-type" pipe. Feel free to show me data on a stock 968 with and without restriction. I'm a firm believer in data, not dogma

Lemming

Just had a thought, at what RPM does the knock sensor kick in? Could the valley on the resticted engine be related to retarded timing?

RajDatta

I never scanned my dyno runs but will make it a priority to get them scanned and post. They are from my completely stock 968 cabriolet.
I also did a run with airbox mod and picked up an additional 3rwhp.
Dyno post to follow.
Raj

FRporscheman

Tim, that paint job is sweet! Where else can you do that but on a race car! Race car paint jobs gotta be off the wall somehow!

Lemming

Gotta keep the 8-yr-old happy

968workaholic

The knock sensor doesn't kick in at any certain RPM. If there is detonation then it will kick back the timing accordingly to try and stop it. It may be from your knock sensor, or just the differences with the muffler.

luckett

"Most people's" motive is to sell you a muffler...

luckett

Any chance there could have been tire slippage on the dyno rollers?

Do you feel it drop off when driving the car? That's a pretty abrupt drop and regain of about 40hp/tq. My guess is that it would feel like hitting a brick wall at that rpm. If the two engines feel the same, it's probably just an artifact of a bad dyno measurement.

Lemming

When I pulled that engine (#1) at the end of 2006 there were times on the track that I felt a dip at high rpms, but it was erratic to say the least. At that time I was running a dynomax turbo muffler, but everything else was similar. After doing a refurb on that engine this winter, it ran great at the dyno when it was run with little to no back pressure. When we used only 10 discs it sputtered up high and did this on two consecutive runs. We then removed the discs and it ran great (did nothing to the tie downs or anything like that), suggesting to me that it was from the restriction.