914World.com [Powered by Invision Power Board]

Posted by: Thack Nov 20 2007, 04:38 PM

When I had my 911, a race mechanic told me that most aftermarket mufflers lost power over the stock unit. Is this true with the 914? Any dyno evidence out there?

Posted by: Rand Nov 20 2007, 04:43 PM

Depends on the muffler. Even some of the cheapo turbo mufflers are very free-flowing and cause no power loss. Then there are other variables too... Engine build, tuning.... Different combos net different results.

Posted by: Thack Nov 20 2007, 04:52 PM

I kind of want the stock sound level. Performance is the least on my list of needs. I like reliable, docile streetability.

Posted by: Gint Nov 20 2007, 05:16 PM

Stock muffler on a FI motor is very quiet. Too quiet IMO.

Stock muffler with carbs sounds pretty good and not nearly so quiet, but not loud either.

As for the performance difference I can't say.

Posted by: Cap'n Krusty Nov 20 2007, 05:42 PM

The only 911s to suffer serious power losses with some aftermarket mufflers were the MFI cars. Too little backpressure, allowing the some of the fuel charge to pass right through the combustion chamber. The Cap'n

Posted by: Blood red 914-6gt Nov 20 2007, 06:53 PM

Most of the dyno charts I've seen show that most aftermarket exhausts increase hp over the stock. For the 911's and 914s that is.

I don't think any performance exhaust would decrease hp. If that was the case, why would race cars run straight pipes?

Posted by: Brando Nov 20 2007, 07:02 PM

Race cars and our cars stock are 2 different worlds. Race cars run straight pipes because they run at WOT most of the time. Tons of fuel (burnt and unburnt) running straight through. Wild cam profiles, lots of overlap. You run a straight pipe so that expanding gasses going out the muffler draw that next charge of air and fuel into the cylinder. Chances are, on a race car you're running carbs or PEFI - so all the variables are tunable.

Different worlds...

Posted by: Blood red 914-6gt Nov 20 2007, 07:14 PM

But the guy said he was a race mechanic. Now if your just talking about a stock 914 I agree that you need to change certain things to make it all work properly, but in all you should get more hp out of your car with an aftermarket exhaust. No?

Posted by: Bleyseng Nov 20 2007, 07:16 PM

Grassroots Motorsports did a dyno comparison on a warmed up 2056 djet 914.

Stock 914-good hp
Bursch-good with +2hp at high rpms
Monza- lost hp

so its either stock or bursch.....

Posted by: Thack Nov 20 2007, 07:21 PM

Performance parts are sold because people buy them thinking they increase power or told that they increase power. The mechanic who told me about exhausts loosing power tunes engines in 911s and GT3s that go to Le Mans and 24/Daytona. I saw his dyno and his shop was full of race cars.
I myself have tested 2-stroke bikes on a dyno where aftermarket silencers decreased HP, yes decreased HP. I was shocked because the manf. was huge in the motocross business.
Unless you tune the whole system, sometimes aftermarket parts are a let down. I just wanted to know if it applied to 914s because I haven't seen any charts or info on exhaust parts, stock or otherwise.

Posted by: Blood red 914-6gt Nov 20 2007, 07:21 PM

It would be nice if Dave, Triad, would do a dyno on one of their cars to see what it would do in comparison to a stock exhaust. On my six you can feel a big difference, but I don't know the numbers.

Posted by: Blood red 914-6gt Nov 20 2007, 07:24 PM

QUOTE(Thack @ Nov 20 2007, 05:21 PM)

Performance parts are sold because people buy them thinking they increase power or told that they increase power. The mechanic who told me about exhausts loosing power tunes engines in 911s and GT3s that go to Le Mans and 24/Daytona. I saw his dyno and his shop was full of race cars.
I myself have tested 2-stroke bikes on a dyno where aftermarket silencers decreased HP, yes decreased HP. I was shocked because the manf. was huge in the motocross business.
Unless you tune the whole system, sometimes aftermarket parts are a let down. I just wanted to know if it applied to 914s because I haven't seen any charts or info on exhaust parts, stock or otherwise.

Well, I guess your guy would be right in that reguard, but in every case you need to tune the whole car. However, if you do tune the car correctly a stock exhaust is not better than the Triads I have run, but I do tune the car for them.

Oh, and the 911's that are in the ALMS do NOT run stock exhausts.

Posted by: Thack Nov 20 2007, 07:29 PM

The mechanic was Sam at AutoTechnik in Houston. A lot of people add mufflers to their stock cars and he tunes street cars too. I have an aftermarket muffler on mine and I don't want to have to tune my engine to damn near race specs. I want a nice stockish output. Street cars spend so much time at low to mid throttle and it seems some of these aftermarket mufflers flow too much for low rpm. That's just seat of the pants testing. I appreciate your inputs. This forum is great.

Posted by: Blood red 914-6gt Nov 20 2007, 07:37 PM

What you have should be fine without any tuning unless you have a really extreme exhaust on there. The PO may have just change yours out due to the OE rusting out.

Posted by: rhodyguy Nov 21 2007, 09:23 AM

bear in mind that most aftermarket exhaust systems are far cheaper than the oem units. i think most people want a racier sound, and are looking to save some money. if they feel they are getting a bit more power that's just a bonus.

k

Posted by: championgt1 Nov 21 2007, 08:44 PM

QUOTE(rhodyguy @ Nov 21 2007, 07:23 AM)