I'm thinking about going with a 3" dp and mp and am wondering if this will provide a performance benefit for me or would it be a waste of money - (I'm going to be increasing fuel and boost fairly soon)

Also, I'd like to get rid of the oem pipe between the dp and mp. Isn't there a company that makes a 3" setup that does NOT use this middle oem tube. I have the Bonez dp and mp now and it retains this pipe.

 

I believe the superior S5 wastegae can handle the extra flow from a 3" exhaust without causing boost creep. If this is the case you'd be nuts to go 2½" when a 3" will flow so much more.Um, doesn't the downpipe bolt to the midpipe? What bit are you talking about?

 

I have the Bonez 2'5" dp AND midpipe on the car now. This setup retains the factory pipe aft of the original precats and would normally bolt to the front of the main cat. It is the piece that is bolted between my dp and my mp.

My wastegate is ported, so I guess it's safe to go with 3" -I was concerned about loss of backpressure??

 

A question- isn't the stock downpipe 2 1/2inch? If it is, why do people get the Bonez one, when it's the same size?

Definatly do not worry about loosing backpressure..
You only need the high-speed flow in the manifold.... after that- 3" is the best for flow!

Also- precats? I didn't think TII's had them...

 

There is one precat, right off the turbo. The exhaust has to do nearly a 70* bend to get out of the turbine housing.

3'' all the way! The RB downpipe is cheapest, but no midpipes bolt up. It cost me $75 to have a 3'' mp made for it. Also I hear the Thunder fabrications dp/mp is good, and I've seen from the pics that it is one piece.

 

I know what you are talking about with that pipe inbetween. I have an 87 turbo and the downpipe bolts to that skimpy pipe before the midpipe...I'd like to get rid of it myself also.

Dan

 

I would go for 3" so you don't have to upgrade again soon. I saw that Mazdatrix now has a 3" downpipe that is 2 1/4" for a tiny bit out of the turbo and then 3" all the way down- looked good. I have also considered a Corksport SS 3" downpipe and midpipe, though I like how the 2.5" RB downpipe/presilencer combo I have sounds- so I am a bit worried about losing the presilencer...Ian.

 

Check out www.thuderfabrications.com and the have a really nice 3" turbo to cat-back single pipe, i had one and it was bad ***.

 

Um that was www.thunderfabrications.com

 

here it is http://www.thunderfabrications.com/M...components.htm

 

You would be insane not to buy the Corksport 3" SS. If I was in the market for a downpipe you wouldnt see the cash fly out of my pocket and into theirs. It would be moving too fast.

 

[QUOTE]Originally posted by BLUE TII
[B]I would go for 3" so you don't have to upgrade again soon. I saw that Mazdatrix now has a 3" downpipe that is 2 1/4" for a tiny bit out of the turbo and then 3" all the way down- looked good.

What's the use in that, since an exhaust will only flow as much as the smallest point.

 

Smallest point being the turbo...

 

Yeah, while youre at it pick up a T88.

 

You should learn not to make statements of "fact" on topics you obviously don't know much about. You are completely wrong, but feel free to put a 2.25" exhaust on your turbo...

 

some people on this forum are SO unpleasant at times...

 

That's the one I'm looking at - I guess I'll e-mail them to see if this also uses the oem pipe in between the dp and mp like the Bonez.
May have to get a custom 3" to slap in between them.
Thanks to all for the input...

 

I was planning on getting the Corksport SS DP and MP but always assumed that they bolted together and would then bolt onto a catback.

 

My exhaust starts out at 2.5" and I don't think I am being "choked" at all. I don't think that extra .5" diameter comes into play until more mods are added. Personally, I don't want a bigger exhaust until I upgrade my fuel system anyway.

 

I was referring to the mazdatrix downpipe that is 2.5 inches for 6 inches and then goes to 3 inches. Explain to me how this can flow just as much as a full 3 inch downpipe since it have to go through the 2.5 inch section before it goes out to the 3 inch part. If I'm wrong I'm wrong we are all hear to learn. If I'm wrong explain it like an adult not an

 

Oh yeah, I meant to comment on that too. If you act like a jerk and give someone **** for being wrong, explain why.

 

Well it was late and I really couldn’t be bothered going into it, but since you asked so nicely...
What you’ve just said has nothing to do with the comment I replied to, specifically “what's the use in that, since an exhaust will only flow as much as the smallest point.” This is completely wrong. Restrictions in pipes are cumulative, that is each part (straight pipe, bends, reducers, splitters, mufflers, etc) has a specific amount of restriction, and each of these are added together to get a total. These restrictions are typically measured as pressure drops, with pipes on a per length basis. So if your system is say half 2.5” and half 3”, you’d calculate the pressure drop of the 2.5” section, calculate the pressure drop of the 3” section (which would be much less), and then add them together. Obviously it would be less than if the whole system was 2.5”.
So in the Mazdatrix downpipe you describe, the 2.5” section will be more restrictive that if it were all 3”, but it doesn’t make the whole system flow the same as if the whole system were 2.5”. Your original statement referred to the fact the turbine’s outlet is only 2.25”, but that doesn’t mean that’s how big the exhaust should be. In fac the first section should be the biggest because that is where the gases are hottest. The 3” system on my last car had cone on the flange that went from the turbo’s 2.25” outlet straight to 3”.
You always want to maximise the pressure difference across the turbine wheel, and you do this by minimising exhaust backpressure. This means reducing the restriction in the entire exhaust system.
I hope this explains it for you. Sorry if I came a across as an *******, I just get grumpy when I see statements of “fact” (as opposed to opinions) that are short on fact.

 

Thank you for that explination, I was under the impression that if you had a say a 2.5" section that no matter how big the rest of the system was that is all it would flow. But I understand what you are saying. You did however make a mistake on my original post I never referred to the turbo outlet being only 2.25" I was just talking about the mazdatrix downpipe. If you read again you will see. But again thank you for the explination.