Horsepower For Early 911S

Presently my 1969 911S is stock -- original 2.0 with MFI. Runs very smooth with new butterflies, restored MFI, etc. It's supposed to generate around 170 hp or so. What are some ways to milk out a few more horses WITHOUT a complete tear down, restroke, boreout?

In other words, what mods would you do first? Exhaust, Air filter, other? What mods give the most bang for the buck?

Very curious to hear what you may have tried or seen tried.

There are not too many choices out there that I would consider inexpensive, and probably few people out there have ever bothered to try ...

Without a doubt, a dual outlet 'sport muffler' gives the most bang fot he bucks, and around 12 hp is cited by most sources as a possible gain!

But, next, I have the feeling that 2.2 'S' cylinders and pistons, recalibrated MFI pump, coupled with extrude-honed heads, and maybe a Garretson Enterprises GE-60 profile set of cams (or whatever Web-Cam has in an 'equivalent' grind) ... would be worth something like an additional 10-15%.

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Warren Hall
1973 911S Targa

Thank you, Warren. I really appreciate your input!

A couple of follow up questions.... My mechanic -- into early 911 racing for many years -- says he just guts the original muffler instead of replacing with aftermarket sport exhaust. Sound acceptable? If buying the one from AJ-USA will be better in the long run, I will insist on it.

He also would stay with the stock "S" heat exchangers rather than going to SSI's.

I'm all for saving money for future goodies, but I would like input from the group on this one.

I've run the AJ-USA / AJR sport muffler conversion, and this conversion definitely adds a few ponies, as confirmed by Bruce Anderson's testing, but it is LOUD!!! I now have a single-outlet sport muffler I'm about to install with some SSI heat exchangers. It should be a lot quieter than the factory style dual-outlet one, but still a little more agressive, and looks stock too.



FWIW, the SSI's are CLONES of the factory heater boxes, but are made of high-quality stainless steel and built extremely well. If your stock heater boxes are in great shape, your mechanic is correct that you would be "wasting" your money...but mine are pretty crusty & rusty after 30 years so the SSIs are in the cards for me. It does not make sense to spend $700-800 on factory mild steel heat exchangers when the SSI's are around $900 and vastly superior. Just my $.02. Will post results when the new exhaust is on the car!

Chris C.
70 911E Targa

I have heard from several people, some who have dynoed their cars with homemade sport mufflers that they are the way to go.

You don't really need to gut the muffler. Just drill to holes in the middle for pipes and kncok out one of the interior baffles. I have an article if you want it faxed.

I sincerely appreciate everyone's input. This board is wonderful!

Ever notice that Porsches seem to appreciate a little money being thrown their way? I have gotten the same feeling again and again. If you spend some money and restore one piece, the whole car perks up. If you work over the breaks or get a new headliner, it should not improve the smoothness of the engine -- but it does. Am I alone in this?

Today my car gets its sport muffler. The local racing whiz mechanic is going to make one out of my stock muffler. He's convinced that homemade is better.

Those posts about back pressure convinced me to get him to do it. I am quite curious how it will feel to have a few more horses. I was shocked how much difference the low profile tires (205/55) made in the acceleration -- not to mention crisper handling. I would assume that the sport muffler should be even a better boost.

You might want to make sure your exhaust specialist knows how his mods will affect your engine's performance with the MFI system in place. Exhaust for MFI as opposed to Webers is a different animal. I picked up a Bursch exhaust, specifically designed for MFI. Compared with the standard Bursch for carbs, the MFI model has a couple of extra smaller glass packs before the main muffler, where the standard Bursch glass pack has only the main muffler section.

It has to do with back-pressure and each fuel system's operating characteristics. If your motor was originally MFI, your stock exhaust was designed for it. Modifying your stock exhaust will give it a different tone, but may not change HP; it may even reduce it. Just food for thought.

My Bursch is definitely louder, but I think it helps 'smooth' the engine's operation a little. I can't say definitively that I rec'd a HP increase--

JW

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Wow, what a difference! I love that customized muffler -- racing shop made duel outlet sport muffler. Drove through a whole tank of gas yesterday cruising the hills with the top off!

Nice improvements in sound, lower RPM's pull and quick throttle response. Those of you with early 911s, SERIOUSLY consider making the switch -- I should have done this YEARS ago!

The sound is awesome -- the only way I can describe it is like a cross between an early Ferrari and your typical early Porsche. Acceptably quiet, but a bit more trumpety in most situations. Loud as hell with your foot in it -- THAT is a sound I will never get tired of.

Power.... The power increase is more noticeable at lower RPMs (3000 or so). It is not earthshaking like a 2.7 RS motor upgrade would be, but it is definitely noticeable. The nice thing is that the low RPMs is where the "S"s need extra HP anyway.

Throttle response.... This was something I was not really focussing on until I got the mod done. The quick throttle is a really nice feature. Just makes the drivetrain feel more responsive.

I notice a bit more "chortling" and a few pops on hard deceleration, but it seems smoother than before in mid throttle. On balance, I don't notice any big disadvantage in the way it runs -- i.e., the "backpressure issue."

If you can find a mechanic to make you one, I would 100% recommend it as an "bang for your buck upgrade."

Thanks for the guidance Warren and others!!!

I'm in the process (such a longer one than I had expected) of restoring my early 911S and was also looking @ how to increase power. After reading all the responses, I've decided to add a sport muffler as well. Guess the neighbors will just have to get used to the beautiful and distinctive sound - I know I will!!

'67S,

You asked me about how I did the muffler conversion... I did it the old fashioned way -- I paid an expert to do it (Tom Amon at T&D Porsche in Campbell, CA). This morning, I asked him for you what he did to it and he said "mirrors and rubber bands." He obviously does not want to give up what he thinks is a novel way of approaching the issue -- and I respect that.

FWIW, I will tackle most things where there is a "right answer," like I will be updating my chain tensioners on my own in a month or so. However, the people here on the board convinced me that you could screw up the way a MFI car runs by doing the muffler incorrectly. I am not a Porsche "artist" so I hired one. Easy fix and only $215. Cheaper than buying a sport muffler and installing it myself.

FYI, I did some research and the AJ-USA looked like the most interesting after market sport muffler. Here's the link I found -- http://www.ajusa.com

Good luck with it -- in my opinion, putting on a sport muffler is WELL worth the effort.

I have a 1972 911 2.0s engine and it has the performance products dual outlet SS 3inch exhaust. That thing sounds awesome!!! It sounds like flow masters at idle but once you get on it, it mellows out. I sure have all those darn Hondas and mitsubishi's after me. Too bad they use coffee cans for exhaust!!