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Finger lickin' good...
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Ok, I've been reading on few different Miata forums, it seems that the way to get the most power out of the Greddy kit for the 1.6 is to run a 3" exhaust. IED uses/used a stepped system (2.5 - 3 after the down pipe near the trans. which I've considered coming from offroad bikes) I have a good friend/ custom auto shop owner that's interested in the project. He said to do some research and find out what was the best performance gain and we'd go from there. I originally planned on doing a custom 2.5" left exit exhaust, but then read about everyone using 3", but on a 1.6l? That's where I got confused. Any 1.6 turbo guru's out there that can help me a little with my problem? Is the 3" turbo back really necessary?
 

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The theory behind this is that you wand all the the exhaust back pressure to be focused on the exhaust turbine. By having oversized exhaust piping you are ensuring that there will not be a restriction, causing pressure to be lost at the turbine blades. Therefore fast spool and highly effiecency(sp?). But I have learned from experience that no exhaust back pressure means less "low-end" torque........the car does not pull as much in the lower rpms but pulls harder in the higher rpms, something you might want in a race car but might not want in a street car. :D

IMO, you should use 2.5 all the way to the back untill you get some nasty bends and then use 3" from there on.

good luck :D
 

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Finger lickin' good...
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Discussion Starter #3
The theory behind this is that you wand all the the exhaust back pressure to be focused on the exhaust turbine. By having oversized exhaust piping you are ensuring that there will not be a restriction, causing pressure to be lost at the turbine blades. Therefore fast spool and highly effiecency(sp?). But I have learned from experience that no exhaust back pressure means less "low-end" torque........the car does not pull as much in the lower rpms but pulls harder in the higher rpms, something you might want in a race car but might not want in a street car. :D

IMO, you should use 2.5 all the way to the back untill you get some nasty bends and then use 3" from there on.

good luck :D
Thanks for a bit of insight. I was planning to have the least amount of bends in the exhaust. I guess I should have mentioned that the car will be driven daily, but also a weekend racer when wanted. I think the best optionwould be to have a stepped system, correct? 2.5" for the bit of backpressure for low-end and then the 3" back starting near the tranny for the top end flow. :-k
 

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if it was mine, I would do 2.5" all the way to the rear diff, and when the exhaust starts to curve up to the muffler/bumper area go with 3". You will not notice much of a difference if any at all, when switching to a .5" larger pipe in straight sections, after 2ft or so from the turbo......diameter really helps the most in bends. If you go this route you also might save yourself .25" ground clearance or more and maybe a few pounds of weight. If you wana do an experiment to feel what i have been talking about....run the car with just minimal piping to get the exhaust out of the engine bay ( like the first bend in you dp, or no dp at all). Then make the full dp and go for a spin, and then make the rest of your full exhaust and drive it one more time. Each time you add length to the exhaust you will notice a good amount of more low end torque. You can tune a set-up to match you wants by repeating this. Might not be the most legal way to to r&d but I bet you end up with a nicely matched exhaust system.
 

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back pressure doesn't effect torque very much with turbo applications. you won't need a 3" exhaust until you begin to approach 300 hp. You just don't have that much exhaust flow before that. The small turbo you are working with on the greddy kit will be more than satisfied with a 2.5" dp and exhaust.
 

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back pressure doesn't effect torque very much with turbo applications.
I agree about the 300 hp, but can you explain this to me? I thought that back pressure directly effected the torque and horsepower curves on ALL internal combustion apps. including forced induction, expecially turbos. :?:
 

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If you're going to do a custom exhaust then go 3" all the way so you don't have to redo it later. I went from 2.5" w/high flow cat exhaust to 3" catless and I felt a big difference especially in higher rpm's and turbo spoolup and lag.
 

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The ideal set-up for any turbo is an open downpipe.

Case in point, my friend's homemade turbo set-up. Bottom number was with the exhaust opened up, top is with full exhaust. HUGE jump. I know of a few Honda guys that aren't even running an exhaust. Just a downpipe from the T3/T4 turbo housing. Sounds BAD-ASS when winding up!



He bought one of those electric gizmos that open the exhaust with a touch of a button. I've driven the car and it is FAST either way. His honda was featured in SCC a few months back in their budget turbo issue. Check out the stealth install....







And it's for sale...

http://hybrids.jp/forum/showthread.php?t=23540
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BOV hidden in the stock airbox.

That's rich!

:twisted:

Now I wish I hadn't chromed and polished all of my stuff.

#-o
 

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back pressure doesn't effect torque very much with turbo applications.
I agree about the 300 hp, but can you explain this to me? I thought that back pressure directly effected the torque and horsepower curves on ALL internal combustion apps. including forced induction, expecially turbos. :?:
your motor still sees backpressure between the head and the turbo, but the turbo out should be a free as you can make it, less bends, larger diameter pipe
 

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You'll see gains between a 2.5" and 3.0". Most likely in spool-up time and a few HP. Although 2.5" is suffficent, if you have the means then going 3.0" will be benefitial, no extra $$, and no extra sound Dbs.
 

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sport compact car did a myth edition and this was one of the questions. In a all motor car you could put to big of a exhaust on a car, but when testing a turbo car the 3" exhaust always put out more hp than the 2.5". On a stock dsm the diff in the 1/2" was around 5 hp.
 

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backpressure on a turbo application slows spool. boost is what creates power in a turbo application, so you don't want to slow the build of boost.

While I agree there will be a difference between 2.5" and 3", with the turbo the size in the greddy kit you will see little power difference.

And in my experience, larger diameter piping creates more sound.
 

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Finger lickin' good...
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Discussion Starter #15
I just opened up a whole can of worms, huh? :shock:

Thanks for the replys and info guys. I'm just gonna go ahead and do a full 3" all the way back to the muffler. I ordered an insert along with the muffler from Apex'i, so if I need a little bit of back pressure, it'll get it there. This way I won't have to go through the muffler setup twice and it'll leave room for improvement, a little more is never enough for me, but I like doing it in steps and learning the power curve :mrgreen:
 

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bigger is better on a turbo car. there was a sport compact car article that said when is a turbo exhuast to big? when it drags the ground.
 

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Here is some info from one site (not a sponsor so they will go nameless but I will be buying from them.

Quote

I have dyno tested all of my exhaust and this is what I have found
works best for these Miatas: (accounting for sound and horsepower)


2.25" = Normally Aspirated Miatas and 6 psi or less Supercharged Miatas (5-8 hp increase) (stock size is 2" and 2.25" will not affect low end torque). Miatas have a relatively low compression engine which is not affected by backpressure. Through the dyno tests the 2.25" works very well in increasing both horsepower and torque.



2.5" = Turbocharged Miatas @ 12 psi and less (19 hp gain over 2.25")

3" = Turbocharged Miatas @ 12 psi and higher ( 3 hp gain over 2.5" but a 400 rpm quicker spool up)

Unquote
 

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You can name non-sponsor companies here. We encourage you to share knowledge to help the community out. Our sponsors are great businesses (that's why we chose them and they chose us) and you should seriously consider the value of doing business with them. But we also understand that CR.net is new and not every business recognizes the value of forum sponsorship or is interested in this particular market.
 

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The link is

http://www.enthuzacar.com/faq.asp

They are going to make form me a cool 3" exhaust like this one http://www.enthuza.com/

And if you can read into what I posted before you know what I am going to do to my car :twisted:

Now if I can only find a good supplier of a 3" in/out cat that will just bolt in
 
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