It seems like years ago, but it was only 3 months ago, I promised dyno data for the "before" and "after" of my car's exhaust upgrade. It's shown below and was a bit of a surprise.



The "before" indicates my car before exhaust and chip changes and showed 244 hp. After months of issues with the vendor, we finally got an exhaust that was acceptable on the car and the chip installed. The "after" dyno result was no significant change in hp. The exhaust fitted is a set of nice-looking, well-made, equal length SS headers and a dual outlet muffler. No cat or anything else. The before was stock 964 headers, cat bypass, stock primary muffler and a secondary bypass. As my agreement with the shop was at least 20 hp or I don't pay, the exhaust comes off and gets sent back tomorrow or Monday. The big loser is the shop that has about 3 days of labor into trying to get what was supplied to work. The vendors claims were not supported by the dyno results.

The "before" reflects a car with no engine or transmission mods. I now have a LWF but otherwise a stock engine and transmission.

 

Am I reading correctly, you lost 5 horsepower? On the blue (second) dyno run the AFR stays pretty much at stoichiometric except for when the resonance flap opens, almost as if the WOT switch wasn't activated?

 

For a stock car....GHL

 

It's difficult to beat the stock system with a cat-bypass and primaryor secondary bypass overall, especially for the money.

 

Thanks for sharing, Tom!

 

That's very interesting, Tom. It goes to show that Porsche engineers really squeezed everything out of the engine they could...

Do you know how much the new exhaust saved you in weight?

 

Great info, Tom. I'm glad your deal with the shop didn't leave you with an empty wallet without results!
Brian

 

This is said time and time again and is of course completely false I am not going to mention various tuners around that do get substantially higher results, but I have documented fact that my GHL exhaust gave me around 15-17rwhp and around 20lb/ft of torque more anywhere above 2000rpm upwards...I did no rechip or anything else - it was a str8 bolt on.....

I think it is safe to say that Porsche engineers do very well in getting results with the very many compromises that they have to make. The 964 exhaust can flow enough air for pretty big HP numbers, but it is not the best exhaust for a standard engine.....in terms of power and torque.

 

Christer, did you try a de-cat and cup pipe before your ghl system. If not, how do you know that it would not have yielded similar gains to the ghl system at a much cheaper cost (but maybe not sound as nice !) ?

 

I didn't try it personally, but after 4 years on here with everyone trying different combinations, there has been only mention of a few HP gained, or a few lost but with a couple of lbs of torque gained. I think that if everyone were getting 20+hp and torque from bypassing the cat then we would know about it... Or maybe its the best-kept secret out there?

 

Christer: Specifically which GHL parts do you have? I'm still interested in trying to get more hp. My mechanic and I discussed GHL but he had been unimpressed with the quality of their work in the past. We also talked about B&B but he refused to even consider them due to bad experiences with duability and quality of the manufacture.

Garrett: I didn't check the weights. I figured any weight loss would be a bonus, but I mainly wanted the hp.

Jason: Yes, the "improved" version showed 5 hp loss, which I attribute to variability of the dyno and not necessarily a significant difference. The WOT switch and all other components were checked after the LWF install and idle adjustment. My bottom line was the car appears to be running well and the modifications did not deliver the promised benefit.

I will likely have another dyno done when the stock exhaust is replaced. Since I just got my renewal info from the state and they want a smog check, I'll put the cat back in and do a dyno run. Then with the cat bypass back in, I'll do another dyno run. That should some data to debate.

 

I run SCARGO 1 3/4 x 26" header with a Flowmaster duel inlet & outlet muffler on my RSA.

With the SCARGO headers max torque now comes on 500 rpm lower (4750 vs 5250) and the power band is much broader and usable. These headers make a big difference on track, the car has torque all the time. Up "The toe of the Boot" at The Glen the car rips up in 3rd.

See this post:
https://rennlist.com/forums/964-forum/19565-26-equal-length-headers.html
Do not sweat the numbers look at the torque curves, all dyno give different max numbers.

David

 

Tom, I had a full single-outlet system from GHL.

 

This is interesting and here are my thoughts. Overall, I think there is an environment factor that is different from the first run to the second run. The reason I say this is that the up to about 4500rpm, the AFRs are virtually the same, and the curves are the same, but only a few hp or tq apart. Things like transmission fluid temp, air temp, oil temp, cylinder head temp, all can effect the dyno reading a small amount. I've seen cold transmission fluid make a 10ft/lb of torque at the wheels difference compared to warm transmission fluid.

At about 5k, the AFRs go too lean for full throttle, they are showing 14:1 when in reality you would want closer to 13.0-13.2afr under full throttle. If it were richened up a little, you'd see some additional power, and your engine will last a bit longer.

 

I would agree that the loss in hp is probably a result of the air fuel mixture being to lean. If you add parts that allow the engine to flow more air but do not change the fueling you will not make more HP unless the car was too rich to begin with. A/F mixture at WOT should be in the 12.5-13.0 range 14.0-1 is too lean.

john