Cheap HP

[thevojtiseks]

I'm interested on ideas to gain a few extra HP without investing a small fortune (Ideally proven on a dyno or such). I have a 1971 911 S, 2.2, with approx 180hp. It's stock except for a K&N air filter and some nice plug leads. I drive it mostly at DE events....Seems it's already fairly well tuned from the factory but can I get more ??

Thanks for your ideas !

[silverc4s]

No easy mods to that engine, alas. Sport muffler and a good solid state ignition maybe.

Try making the car lighter, the suspension more raceworthy, and the brakes better.

Take a high speed driving course.

[kenikh]

HP is directly proportional to $$$. The cheapest way to increase net HP is to gut your car of every unneeded interior component. You may not like driving the car, but that extra speed will be free.

[Tyson Schmidt]

The factory sport muffler, with the two tips coming straight out the back below the license plate panel, is good for 15HP.

That's the cheapest you're going to get. Sounds pretty nice too. Not too obnoxiously loud, but a real sweet sound. I've seen the dyno proof, and Bruce Anderson has stated the same thing in his 911 Performance Handbook, with dyno sheets to prove it.

[afterburn 549]

Throw out the spare and jack.Get rid of the stock batt and put in a PC 680. This will raise eyebrows -throw the stock muffler out and all related crap put in a generic "turbo" muffler (cut to fit) add a tail pipe(s).....Now your movin

[Tyson Schmidt]

Originally posted by afterburn 549
Throw out the spare and jack.Get rid of the stock batt and put in a PC 680. This will raise eyebrows -throw the stock muffler out and all related crap put in a generic "turbo" muffler (cut to fit) add a tail pipe(s).....Now your movin

Good addvice, except about the muffler. MFI is very particular about what muffler you use. There are only a handful of mufflers that work well with MFI. Many cause flat spots in the mid-range.

The factory early sport muffler is the shiznit on an MFI car.

[safe]

One thing I have been wondering about.
Are there any mufflers for the post -74 exhaust that will gain a few HP?

[silverc4s]

Originally posted by safe
One thing I have been wondering about.
Are there any mufflers for the post -74 exhaust that will gain a few HP?

Magnus,
You can backdate the heat exchangers or go to SSI's, then add a 2 in 2 out Sport Muffler. That will gain you some HP, and AFAIK will work fine with CIS systems and retain your heating.

[safe]

Originally posted by silverc4s
Magnus,
You can backdate the heat exchangers or go to SSI's, then add a 2 in 2 out Sport Muffler. That will gain you some HP, and AFAIK will work fine with CIS systems and retain your heating.

Yes, I know. I was just thinking it was possible to tinker with the existing system.
For example removing the pre-muffler (on pre cat cars), such as my euro -77 or getting more "free flowing" muffler.

[jluetjen]

Originally posted by thevojtiseks
I'm interested on ideas to gain a few extra HP without investing a small fortune (Ideally proven on a dyno or such). I have a 1971 911 S, 2.2, with approx 180hp. It's stock except for a K&N air filter and some nice plug leads. I drive it mostly at DE events....Seems it's already fairly well tuned from the factory but can I get more ??

Thanks for your ideas !

What's to improve? You've already got one of the highest HP/liter motors this side of a Honda S2000. And it took another 30 years of technology to achieve the S2000.

There are very few if any mufflers that will "improve upon" the HP vs. noise compromise of the factory muffler. If the muffler does end up changing the engine's performance by much, you'll find that the 3D space cam (aka: injection map) will no longer be synchronized with the engine's performance and you'll wind up with issues like the flat spot mentioned above. Changing the air filter won't improve the performance. You can prove this to yourself just by removing the filter all together and taking a quick spin down the road (avoiding dusty areas BTW). You'll most likely discover that you can't even notice the difference.

You're best bet to improve the car's performance will be to remove weight, and give the driver more experience (by driving it!).

[kenikh]

I lay awake nights imagining variable valve timing on a 911. 'T' cam torque down low and 906 HP on top. A two liter 911 would give an S2000 a serious run for the money in that case.

[jluetjen]

Originally posted by safe
Yes, I know. I was just thinking it was possible to tinker with the existing system.
For example removing the pre-muffler (on pre cat cars), such as my euro -77 or getting more "free flowing" muffler.

To be honest doing stuff like that is just playing around the fringes. The big issue with the environmentally friendly exhaust is that the primaries are too short to provide any exhaust tuning effect. Swapping on a set of early style heat exchangers (or SSI's) will resolve that issue.

[thevojtiseks]

Thanks for all your responses, I'm already off down the lightening track so good advice here. Refererring to the chart in Andersons Book (pg 141) for the 2.4 S Stock v Sport muffler does anybody have a similar chart showing benifits/otherwise for a 2.2 ??? I must admit I'm slightly sceptical about this data - max power at 5500rpm on a 2.4 S ? - seems about 1000 rpm shy ?

[wirihana]

does the early factory sport type muffler increase power for early carburetted cars as well?

or is any gain specific to the MFI induction?

thanks in advance

nathan

[silverc4s]

Originally posted by wirihana
does the early factory sport type muffler increase power for early carburetted cars as well?

or is any gain specific to the MFI induction?

thanks in advance

nathan

I think you can expect a similar 10 to 15 hp increase with Webers, carb jetting will change with the freeer flowing muffler.

[rswannabe]

Originally posted by thevojtiseks
Thanks for all your responses, I'm already off down the lightening track so good advice here. Refererring to the chart in Andersons Book (pg 141) for the 2.4 S Stock v Sport muffler does anybody have a similar chart showing benifits/otherwise for a 2.2 ??? I must admit I'm slightly sceptical about this data - max power at 5500rpm on a 2.4 S ? - seems about 1000 rpm shy ?

I just saw this thread and can add a little to the discussion. I did back to back dyno testing of a sport muffler and stock muffler on my 2.2S. Sport muffler is definitely better, but nowhere near 10-15 HP worth. See the thread below for the full write up and graphs.

http://www.early911sregistry.org/forum/showthread.php?t=4752&page=3&highlight=k%26n

Brooke

[silverc4s]

I agree with rswannabe.

My experience is that the 10 to 15 hp increase is optimistic at best on an early engine that already has free flowing heat exchangers. The data may have become somewhat muddled over the years as mid year cars were backdated and a sport muffler was attached...