Turbo Exhaust Systems

[MacDrizzle]

Ok folks, I have a question that may seem stupid. In school I studied power adder theory, I have never put it to use on my own, besides helping local Turbo Freaks. I am almost certain that it is counterproductive to use a 3" downpipe coupled to a reduced 2.5" exhaust system. Sources not mentioned say that due to the use of an open air waste gate all the exhaust is expelled through said waste gate bypassing the downpipe. This sounds sketchy to me so I would like to get feedback from other Turbo Freaks.

If it were my car I would never attempt this, but....

Mac

[MacDrizzle]

Hep me hep me please!

[dmotoguy]

the exhaust is much hotter while in the downpipe, therefore has a larger volume..

I dont quite get the question, is it a case of not being able to do a 3" or no funds?

easy answer: is it better to have a bigger exhaust on a turbo car.. always.

any pressure you have after the turbo is going to cause even greater pressure(4-5x) upstream.. this may or may not be a huge deal depending on the efficiency of your current setup... if you are maxing out a small turbo it will make a big difference... if you are running a nicely sized turbo, you should be ok with that setup... but 3" exhaust would still help..

[turbo2cam]

what exactly are you asking? if its ok to run an external wastegate? i read your first post 4 times and didnt see a question.

[MacDrizzle]

Cheap ass customer, no names, wants to use his existing 2.5 exhaust with a 3" downpipe. Everything I know is telling me its wrong, I know it will work just not to full efficiency, I don't know it may cause really high EGTS. I will probably talk him out of doing this.

I'm sorry it wasn't really a question I just wanted to see what some others think.

[e2blade]

lol just say its me
basicly i wanna just use the 3" jack gave me coupled with my exsisting 2.5 inch from the midsection out

hes woundering if most of the my exhaust dumps out my wastegate dump.

[MacDrizzle]

we are not doing it that way, period. I'll let you make payments. I don't wanna redo it again when you want 3"

[carfreak]

Why don't you just run a 2.5" down pipe? Your car will be perfectly fine with a 2.5" down pipe.

[NoDestiny]

Going from a 2.5" to a 3" for my setup is generally a 10ft/lb torque gain and spools faster. But it ran just fine on the 2.5"... and my turbo AND engine is way bigger than yours. Just go 2.5" and call it a day.

[MacDrizzle]

he has a 3" stainless d-pipe fo DSM, and he wants to use it. Cheaper for him maybe but not if you replace the whole system, Charles I will however build you a 2.5 down pipe, then you don't have to change the whole exhaust, this seems more logical in my opinion and cheaper

[dmotoguy]

then use the damn 3" downpipe... weld a reducer on the exhaust and put a 3" exhaust on when/if you ever want to... not a big deal... his motor wont splode over it

[MacDrizzle]

mickey mouse does it that way

[turbo2cam]

3" on your tiny tiny tiny turbo and tiny tiny tiny motor is overkill anyway you look at it. i am going to say you will see ZERO difference between a 2.5" dp and a 3" dp on your setup.

on a large turbo setup, yes bigger is better. same goes for a small turbo setup...but 2.5" is pretty damn big for that turbo. the entire turbo isnt much bigger than a 2.5" pipe haha

IMO i would just do a 2.5" setup and call it a day

and if you want to keep the 3" do exactly what dmotoguy said.

[BRINGTHERUCKUS]

^ for realz, problem solved fellas just do a dp and have it all 2.5

[UnderDog]

having a 3" DP will probably kill a little TINY bit of low end but really wont make much of a decrease or increase over 2.5" charles, i say do 2.5" . . . but i don't know what i'm talking about ;)

[dmotoguy]

having a 3" DP will probably kill a little TINY bit of low end but really wont make much of a decrease or increase over 2.5" charles, i say do 2.5" . . . but i don't know what i'm talking about ;)

how would a 3" downpipe effect low end power on a turbo car? lol there is a turbo causing restriction up the ass right in front of it..

[daveyg]

Not gonna matter with as little as the 8v head flows. You could port that thing until you hit the water jackets, put in custom machined valves, and still not need a 3"

[dmotoguy]

Not gonna matter with as little as the 8v head flows. You could port that thing until you hit the water jackets, put in custom machined valves, and still not need a 3"

NONE OF THAT MATTERS. We are talking about a turbocharged engine... all that matters is the pressure differential across the turbo... think it through a little harder.

[e2blade]

dont worry, he thinks like isuzone people. arrogant and ignorant
but its for the 16g, id say its a medium small, not a tiny turbo.

i want 3". i am the customer, but i aints got the money. maybe later

[turbo2cam]

NONE OF THAT MATTERS. We are talking about a turbocharged engine... all that matters is the pressure differential across the turbo... think it through a little harder.

i agree....but not in this case. when the 8v head flows sooooo shitty (and the ports are as big as a quarter...i kid you not, ive seen this head at bobs shop) then the shaft speeds will NEVER get high enough to create a pressure differential great enough that a 2.5 inch dp will become the restriction. the turbo will outflow the head 10fold. no joke. the engine will never produce enough cfm to get the turbo spinning enough to even get anywhere near its efficiency, let alone become the restriction. i think thats the point everyone is trying to make here.

[dmotoguy]

i've never seen the head in question. sounds like a gangster setup.

[bcool]

On n/a cars back pressure matters but on a turbo car you want as much freedom before and after the turbo.

[northendtrooper]

In honesty, you are fine with the 2.5" downpipe on a 16g. If you were to go bigger then I would say go 3". But stay 2.5" exhaust and be happy with it.

[turbo2cam]

i've never seen the head in question. sounds like a gangster setup.

its the smallest 4cyl head i have ever seen, no joke. it looks like a toy. and i just re-read my post...i was pretty shitty drunk, i dont even remember posting it lol

[e2blade]

i think the 1.3 is the smallest ive seen

[northendtrooper]

This is small.
V8 Engine - Video (http://www.metacafe.com/watch/208526/v8_engine/)

[UnderDog]

i agree....but not in this case. when the 8v head flows sooooo shitty (and the ports are as big as a quarter...i kid you not, ive seen this head at bobs shop) then the shaft speeds will NEVER get high enough to create a pressure differential great enough that a 2.5 inch dp will become the restriction. the turbo will outflow the head 10fold. no joke. the engine will never produce enough cfm to get the turbo spinning enough to even get anywhere near its efficiency, let alone become the restriction. i think thats the point everyone is trying to make here.

exact-a-mundo

[daveyg]

This is small.
V8 Engine - Video (http://www.metacafe.com/watch/208526/v8_engine/)

That is so win! I want one! I wonder if the blower really works... Probably does cuz if u gonna go through so much trouble to build it, why make it fake? That is my new Solidworks class final project. I'm gonna make one.