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Thread: Exhaust system....I need your ideas?

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Posts: 21-30 of 61
2010-08-05 02:10:59
It's not a like a 2 liter bottle at all WTF. It's like a bottle with a hole cut on the other end to let air in maybe at best.

I'm not against a good argument with sound physics and shit, but this is beyond the pail.
2010-08-05 02:33:37
I'm beginning to think that there is no convincing Ben, or changing his mind...
2010-08-05 03:06:43
I change my mind all the time. All it takes is a good argument, and/or strong evidence. Show me dyno sheets of cars losing power by going to a larger exhaust and maybe you'll convince me. Good luck finding them though. =/
2010-08-05 03:35:08
Fluid and Gas flow differently. Period.

That is hilarious.
2010-08-05 15:31:01
Right I am not saying it is the same principals at work. Picturing things happening helps some people to understand. Since Ben doesn't seem to be able to picture hot exhaust flowing through pipe. Granted it is not like we see exhaust flowing at around at hundreds of feet per second on a daily basis, it is a little hard to come up with a better visualization.

These are pretty basic theories for building exhausts, just type "how big is too big for turbo exhaust" into Google just try to avoid the forums there seems to be quite a bit of mis-information around.

CobbTuning.com - Exhaust Design

Turbo Exhaust Theory

Viprdude I am pretty sure the word fluids describes liquids, gases, and plasmas your statement kind of contridicts itself. Car exhaust does have fluid properties.
2010-08-05 15:36:51
I vote for a simple 2.5" exhaust with cat/resonator/muffler. Then put an electric cutout in.

I currently have a full 3" turbo back system. I am not particularly fond of it for daily driving. When I have the cash, I am going to move to a smaller system, with an electric cutout. If I can do a boost actuated cutout, that might be in the cards as well, so I never have to deal with opening it myself.

The side exit exhaust looks pretty trick on your car. My suggestion is make that the cutout if possible.
2010-08-05 15:43:26
Originally Posted by Viprdude
Fluid and Gas flow differently. Period.

That is hilarious.

Gas is a fluid. You meant to say liquid and gas flow differently.
And you're wrong. They don't. They are both fluids, and fluids flow just about the same.

I agree that the cutout method is probably the best option for this guy.
2010-08-05 16:03:59
Originally Posted by jere
CobbTuning.com - Exhaust Design
I just read their bit on turbo exhaust sizing and they dance around the topic so much it's like they are trying to avoid saying bigger is better. But they do eventually say it, and if you read between the lines then you can see that bigger is better (after the turbo). No need to keep velocity high.

I read their bit on N/A cat-back sizing and I completely disagree with their recommendations. They also provide no proof that keeping velocity high is a good thing. I've seen countless dyno sheets showing the opposite, and like I said the fluid dynamic calculations also show higher mass flow with a larger pipe even with the resulting slower velocity.

Originally Posted by jere
Turbo Exhaust Theory
I read the N/A exhaust advice here too and he says the same thing everyone else says. For header design velocity is important (duh) but he doesn't give advice for what to do after the last merge collector. If I had to guess, he'd probably recommend smaller pipe, but that's because he's falling into the same trap everyone else does. Header design does not hold true anymore after the last collector, and the largest exhaust is best always.

The advice for turbocharged cars however is accurate and echos what I've said in this thread, and what Cobb Tuning said. After the turbo you want the largest exhaust possible.

If we can agree on one thing I believe it can be that the following statement in this thread related to a turbo car is completely false:
Originally Posted by LukaMcCloud
You want flow while keeping velocity up. With too large an exhaust you lose all your velocity thus losing power.

We can debate N/A exhaust sizing in one of the many threads already devoted to that topic in the other forum sections if anyone would like to bump one.

Sorry Bull GTi for the off topic debate. =(
2010-08-05 17:26:13
It's all in good fun, my man.
2010-08-05 17:37:35
Cheers guys, I have decided to go with the 4" system.

I have taken a look at the car, and I think 4" is do-able.

Thanks to no longer having air conditioning I can modify the alternator so that it runs on the outer ribs of the crank pulley.

That should give me another 8-10mm past the alternator.

Couple that with a sharp 4" bend, like so... and it should clear the alternator housing.

Getting it past the sump and gear linkage is easy, and I have talked to Cobra Sport, who have stated that they will make a custom silencer for the centre section.

I can get 4" stainless piping locally, as my work has a contract with a stainless supplier, so that isn't an issue.

Now onto the main problem...the rear axle.

I have studied various photos of the underside of the chasis / floorplan and remember how tight it was when I used to have a 3" system from front to back. In order to get a 4" pipe over the axle I may have to modify or remove the axle stabiliser. Now, the Nissan Micra (K11) uses a similar setup, so I may be able to fabricate something which isn't as bulky, so it may not be that bad to do.

I better get my ass in gear if I want to get it done before the next race day in October!

I'll keep you all posted!


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