How tight can i build my exhaust based on engine movements?

[martensson]

Hi all.
I'm a bit worried my plans regarding the exhaust build might backfire...
The car is a 911 -71 with a 3.6 engine from -91.
I'm currently running om 911 engine mounts & gearbox mounts.

The space where i want to fit a muffler is the area between the oil tank & the fender.
I there have a space of 4.7", the smallest area, & want to fit a muffler which is 3.5". That gives me a clearance of 0.6" to nearest item, fender-oiltank.

Is this possible? Stiffer engine mounts recommended, which ones?
I have tried to find vids on youtube showing revving 911's, but none that shows it good enough.

The black pipe is a dummy just to show location.

[Dpmulvan]

Bad idea

[stownsen914]

.6" is a little close, for both physical interference and also heat transfer to the oil tank. If you could get 1" and put some heat containment material on the muffler and some heat shielding on the tank, personally I could get comfortable with the arrangement.

Scott

[Jeff Higgins]

I have to ask - why?

There are plenty of proven solutions for your application. There is plenty of room in the traditional locations for anything from stock to some pretty creative ideas. You are kind of treading "where no man has gone before", and there are plenty of sound reasons why we have not. Are you doing something unusual with the space available in the traditional locations?

[Tyson Schmidt]

You could do a 964 oil tank conversion or the full ‘72 oil tank conversion and then you’d have plenty of room.

[martensson]

Originally Posted by Dpmulvan

Bad idea

thanks for a very informative response. That helped me a lot.

Originally Posted by Tyson Schmidt

You could do a 964 oil tank conversion or the full ‘72 oil tank conversion and then you’d have plenty of room.

This is probably the best idea.
If we could move or rebuild the oil tank to get more space underneath, that would be great....BUT, there is always a BUT. The car is already built & painted so we don't want to start taking it apart again. Relocating the tank is a good point, thanks for that, but not at this time. That leaves building a custom tank as our alternative...might be worth it.... Have had plans to do so a few years back...

Originally Posted by stownsen914

.6" is a little close, for both physical interference and also heat transfer to the oil tank. If you could get 1" and put some heat containment material on the muffler and some heat shielding on the tank, personally I could get comfortable with the arrangement.

Scott

Great input. I already got heat shielding in mind, but yes its a bit tight even without shielding at this point. I can manage to get that little bit extra space

Originally Posted by Jeff Higgins

I have to ask - why?

There are plenty of proven solutions for your application. There is plenty of room in the traditional locations for anything from stock to some pretty creative ideas. You are kind of treading "where no man has gone before", and there are plenty of sound reasons why we have not. Are you doing something unusual with the space available in the traditional locations?

"where no man has gone before"...& that is why i do it
I have read every topic I could find on the exhaust subject & the conclusion is almost always the same. Nobody is 100% satisfied with their exhaust system, for street use. If you don't want to get a bolt-on system & pay loads to do so, & still end up with a compromise, you have to custom make it or custom order it.

Considering the list with demands on our own exhaust, there are no ready solutions, hence my question regarding engine movement. We have to go with what we got except maybe some minor changes...

- Car from -71 incl. oil tank
- 3.6 engine from -91
- 993 headers
- 911 GT3, GT3RS, 935 style exhaust tips
- 2.25" secondary piping. Piping w mufflers to meet decibel requirements in Sweden, for both road & track use.
- daily driver
- will add cut-out valves for those "special occasions"

[RarlyL8]

We have mufflers for this application. The early chassis has less room in the muffler area than do the later impact bumper cars which limits how large the muffler can be. Our sport muffler case size will fit and can be tamed a bit if looking for a less robust sound. Tailpipe options are wide open, anything you can do for the impact bumpers can also be done with the early chassis.

[martensson]

They do not meet my demands, but they look really nice
Are these with catalytic converters? dB-level? Price?

IN my case i can chose to temporarily replace a muffler with a cat, if the authorities demand it. In a case like below I do not have that choice.

Originally Posted by RarlyL8

We have mufflers for this application. The early chassis has less room in the muffler area than do the later impact bumper cars which limits how large the muffler can be. Our sport muffler case size will fit and can be tamed a bit if looking for a less robust sound. Tailpipe options are wide open, anything you can do for the impact bumpers can also be done with the early chassis.

[Jeff Higgins]

So, it sounds like you are trying to meet legal requirements in Sweden while having an easily reconfigurable exhaust that can be opened up a bit for "special occasions", correct? And part of the legal requirement is to run a cat, but you want to be able to easily remove it? And replace a cat with a muffler? Most guys when removing a cat simply put a straight pipe in its place. I guess I'm trying to picture what you are after - I cannot think of a situation that would require a cat, but no muffler. Can you explain further?

[martensson]

Originally Posted by Jeff Higgins

So, it sounds like you are trying to meet legal requirements in Sweden while having an easily reconfigurable exhaust that can be opened up a bit for "special occasions", correct? And part of the legal requirement is to run a cat, but you want to be able to easily remove it? And replace a cat with a muffler? Most guys when removing a cat simply put a straight pipe in its place. I guess I'm trying to picture what you are after - I cannot think of a situation that would require a cat, but no muffler. Can you explain further?

Yes i know, it's a total mess trying to achieve my own demands & our technical inspection....& street/track noise regulations

I have earlier registered an Audi & managed to lower noise by some minor tweaks to it. I passed tech inspection, but at a track meet i didn't even get to go driving due to noise regulations, it's that tough.
People cut the mufflers of their daily drivers & stuck them to the track car just to be able to drive... That is not the way i want to go with the 911.
Therefor, i rather have more, than less, from start. It's easier to remove one muffler than add one afterwords...
This gives me the possibility to swap between muffler & cat at the yearly tech. inspection & a straight pipe or muffler on street/track
Being able to throw the cat away, & free up the exhaust, is a big bonus in terms of power.

That is why I "go where no one has gone before" & insist on building an all purpose exhaust.

I already got some ides from earlier inputs here regarding tightness & assembly. Feel free to keep'em coming though.

SO the only question now is still engine movement, anyone

[Arlo911]

You could try some Cabrio/Clubsport engine and gearbox mounts, they are a bit stiffer than standard, and would lessen engine movement a bit. Also pretty cheap mod. As it is a street/track car I wouldn't use solid mounts.

[RarlyL8]

You can run a 993 cat for smog testing. If it is too loud run a pair of flat mufflers in each fender horizontal to the ground. It's temporary so doesn't have to be perfect.

[Jeff Higgins]

Originally Posted by martensson

Yes i know, it's a total mess trying to achieve my own demands & our technical inspection....& street/track noise regulations

I have earlier registered an Audi & managed to lower noise by some minor tweaks to it. I passed tech inspection, but at a track meet i didn't even get to go driving due to noise regulations, it's that tough.
People cut the mufflers of their daily drivers & stuck them to the track car just to be able to drive... That is not the way i want to go with the 911.
Therefor, i rather have more, than less, from start. It's easier to remove one muffler than add one afterwords...
This gives me the possibility to swap between muffler & cat at the yearly tech. inspection & a straight pipe or muffler on street/track
Being able to throw the cat away, & free up the exhaust, is a big bonus in terms of power.

That is why I "go where no one has gone before" & insist on building an all purpose exhaust.

I already got some ides from earlier inputs here regarding tightness & assembly. Feel free to keep'em coming though.

Wow, tough situation. I can see why you need to get a bit creative.

Originally Posted by martensson

SO the only question now is still engine movement, anyone

I'm not sure there is an easy way to check this. The kind of "cave-man" way would be to simply jack underneath the engine in various spots and measure deflection. That would give you the maximum upwards deflection allowed by the mounts. Then move to the jacking sockets on the tub and jack it up, which would allow you to measure the maximum downward "hang" allowed by the mounts.

These figures may not be indicative of a running condition, though. And it won't give you side to side, which it sounds like you really need. Or the "twist", or reaction under torque, unless you can infer that from your maximum up and down deflections.

This is a tough one. I'm not sure anyone has ever thought to try to measure this. You might be the first...

[stownsen914]

I really think that if you can get 1", you'd be fine. I've done a lot of fabrication including exhaust over the years on a highly bastardized 914/6.

Re: sound regs, we have a similar situation at some tracks here in the US. I live near Lime Rock and drive there regularly, so have contended with 88 db measure trackside (nominally 50 feet distance). This is pretty stringent, and some cars with stock exhaust do not pass. With my racecar, I have a custom muffler and have a turn-down with a provision for extra baffling if needed. Laguna Seca has a similar sound limit at most track days. Do you know how they measure at your track? You may get good advice if you ask around

[martensson]

Originally Posted by Arlo911

You could try some Cabrio/Clubsport engine and gearbox mounts, they are a bit stiffer than standard, and would lessen engine movement a bit. Also pretty cheap mod. As it is a street/track car I wouldn't use solid mounts.

I am already on it Thanks for the info, appreciated. I'm having difficulties finding specifically cabrio bushings. I found clubsport & Powerflex. Just have to figure out what might be the best option.

[martensson]

Originally Posted by stownsen914

I really think that if you can get 1", you'd be fine. I've done a lot of fabrication including exhaust over the years on a highly bastardized 914/6.

Re: sound regs, we have a similar situation at some tracks here in the US. I live near Lime Rock and drive there regularly, so have contended with 88 db measure trackside (nominally 50 feet distance). This is pretty stringent, and some cars with stock exhaust do not pass. With my racecar, I have a custom muffler and have a turn-down with a provision for extra baffling if needed. Laguna Seca has a similar sound limit at most track days. Do you know how they measure at your track? You may get good advice if you ask around

Seems you have some experience on the matter in deed. Thanks for sharing. Appreciated I have a few alternatives I'm going to look in to. I'm confident i will find the extra space

At some events they measure dB behind the rear of the car, on our tech inspection as well. If you exceed 95 dB your out.
On other tracks they measure when you pass the straight/finish line & a dB-meter is positioned 33 feet away. 95 dB is max. So, very often people have to cruise by on top gear not to get banned.

Originally Posted by Jeff Higgins

Wow, tough situation. I can see why you need to get a bit creative.

I'm not sure there is an easy way to check this. The kind of "cave-man" way would be to simply jack underneath the engine in various spots and measure deflection. That would give you the maximum upwards deflection allowed by the mounts. Then move to the jacking sockets on the tub and jack it up, which would allow you to measure the maximum downward "hang" allowed by the mounts.

These figures may not be indicative of a running condition, though. And it won't give you side to side, which it sounds like you really need. Or the "twist", or reaction under torque, unless you can infer that from your maximum up and down deflections.

This is a tough one. I'm not sure anyone has ever thought to try to measure this. You might be the first...

I have to reluctantly admit i forgot about this type of "cave-man" way to check. It's just as great as it is obvious. Definitely the way to go to get a hint on how much it may "twist". This, together with Arlo911's & stownsen914's input on the matter, will absolutely help solving my problems.
Thank you for taking the time to help out

The...project...bastard, clone...or whatever you might want to call it

[Jeff Higgins]

Looks like an interesting, challenging project, martensson. Best of luck with it - I'm sure you will work out a solution.

[stownsen914]

Martensson - sounds like your sound restrictions may be comparable to our Lime Rock and Laguna Seca restrictions. If you search the Pelican site, you'll find some tidbits about people's challenges making sound at those tracks, and possibly about some specific mufflers that have passed sound (or not).

[Mixed76]

Lots more room in 993 quarters

Sent from my Nokia 7.1 using Tapatalk

[martensson]

Originally Posted by stownsen914

Martensson - sounds like your sound restrictions may be comparable to our Lime Rock and Laguna Seca restrictions. If you search the Pelican site, you'll find some tidbits about people's challenges making sound at those tracks, and possibly about some specific mufflers that have passed sound (or not).

Sure sounds like it. I know how people had to do at an event called Gatebil, a world wide gathering in Norway. People had extra mufflers attached to their rear spoilers & luggage trunks, just to meet sound regulations....

Originally Posted by Jeff Higgins

Looks like an interesting, challenging project, martensson. Best of luck with it - I'm sure you will work out a solution.

Thank you
It sure is....there have been a lot of challenges & headache during the build... but hey, i have managed so far to solve problems others have not. Sometimes however, it's easy to get stuck inside the "box", so a push from others is needed.


Thank you all for the help & if you have anything more, just keep it coming