crazyracer

It would be interesting to see (dyno chart) how much HP the cat bypass and ecspecially the (very expensive) SFR cat back/ cat bypass muffler develops. I had all of them, stock, fabspeed, SFR (even the full 3 inch), new lindsey etc. (too much money) and I went back to a simple Bursch bypass/stock muffler from there. Reason? I have different performance meters, G-tech (the old simple one) and another high tech one from the UK (don't know the name right now), the result is - what did I opt for?

toddk911

I agree crazy. I owuld love to see dynos of each set up. I tell people in here I paid 8$ dollars for a piece of stright pipe that was put in to replace my cat and I get the whole, "well that is not as good as the $400+ cat backs and $250+ test pipes." Until someone can show me a dyno of major differences in these to justify paying 10x more, I will stick with my $8 test pipe and $5.75 straight IC pipe

alpenweissisnice

I have little doubt that the difference between the 8 buck welded-in piece of pipe is going to be any less effective than the SFR test pipe. It's a matter of personal choice. Maybe from the stainless won't rust, and it may dissipate heat better. But from a performance perspective, I can't imagine that there is that much difference.

Moreover, you can't even see it.

Now, pardon me while my testosterone leaks out: It's like a hot chick in gorgeous underwear under her street clothes. It may not make her any more beautiful, but it sure is fun to know its under there.

:Back to middle-aged politically correct guy mode:

TonyG

I can guarantee that a piece of straight pipe to eliminate the cat is NOTHING like true test pipe.

You see.... the problem isn't the cat (yes the cat is a restriction... but it's ony 1/2 of the problem). It's the pipe before the cat. Its' flattened out, and often starts to collapse, reducing flow.

I had a $8 piece of pipe to, when I first started out playing with these cars. I couldn't get past 300RWHP.

I purchased a real test pipe, and I picked up (this is from memory) about 25+RWHP and 30TQ to the wheels.

Here's a cut away section of the pipe before the cat (a 2.5" pipe is layed next to the cut away for comparision purposes)...




And trust me... this cut away is of a "good" pipe. You should see some of the others I've seen... much much worse.


Search the archives.... this is old news :-)

alpenweissisnice

Thanks for the post TonyG...It's been my experience you get what you pay for. I have no doubt that the cat removal alone would increase flow, but I'm glad I went the full boat 3" route...Great pics; you always here about the "double wall" but I've never seen it so graphically demonstrated...B

TonyG

alpenweissisnice

Hey.. no problem.

The thing is that people don't understand what the real issues are. On the "outside", one can't understand why a test pipe would be needed if you can simply delete the cat with a $8.00 piece of pipe.

It's not until you finally figure out what it is, and it took me a long time to figure it out, do you truely understand the reason why people say, "Yeah but... it's not the same as a real test pipe".

Now it should be crystal clear.

I'm looking for the pics I have of other test pipes where the center section is substantially more collapsed than the picture above.

toddk911

Love to see those dyno's Tony

toddk911

So only a longer piece of straight pipe is needed to cut back far enough to get the double wal section out. $16 ???

TonyG

The entire pipe up to the cat is double walled, so you'd need a lot more pipe, and the ability to bend it ala mandrel bending...

I've already posted the dynos for that car... on many previous threads. The last one was about turbo selection by bdellis and I recommended a K27/6... you might have to go back a few pages..

2+2

Todd, the problem is that the double wall goes right up to the curved portion as well so you would have to replace the tube from the turbo back to the end of the cat...putting in the curve....which is essentially a test pipe....

alpenweissisnice

OK, OK...We can go round and round about the test pipe vs. welded in straight pipe cat replacement, cost vs. benefit, etc, etc. All I can tell you after installing my test pipe is:

Holy S**T.

It's like it was the missing performance piece. I had the chips and the catback and the high-end DV and the K&N...but THIS is what seems to let all that stuff work so much better. together. I could not BELIEVE the difference in the car. MUCH quicker on the boost and revs up much more freely. I am a believer.

Now, it could be that I'd get the same results with a cat replacement. All I know is that I can HIGHLY recommend the SFR test pipe.

RAPID944

Here is my 951 S dyno - 233RWHP 238RWTQ. Stock car with full 3' exhaust, no cat, free flow mufler (loud ). Not bad eh.
D Y N O

toddk911

So with a stock 951 and just free flow exhaust, (stock boost???), your making about as much hp/tq as those with chips and 15 psi???

RAPID944

Yep. Car is full stock, 75 000 miles, ex- PORSCHE factory car. Stock gauge shows 1,9-2 bar boost. Exhaust is custom-made.

'86 944 turbo

Fredis have you ever dyno the 928 before. Would love to compare the results from your 951.