hey guys

what do you think about 4" turboback or 3" downpipe + 4" catback ? (both catless)
would there be any benefit for cammed and HX35 powered 2.3 engine or it would be overkill and just the waste of money ?

Have you considered a side exit exhaust? You would probably see a lot more gains from that kind of set up as opposed to a 4 inch turbo back

no, I'm not a great fan of side exit exhausts, besides it's a daily driver and the visual side of the car is also important for me

Going to almost need to raise your car with a 4" turbo back exhaust.. Why do you want or think you need a 4" exhaust?

Edit- also fill in your info about your car, senseless to have to guess exactly what you have on vague info like a cam'd 2.3 engine with a hx35..

Overkill. IMO

I say over kill. Most don't even need a 3" exhaust, but we all know we like them anyway. Mine is a full 3" from the turbo back, but I really don't need it.

Edit- also fill in your info about your car, senseless to have to guess exactly what you have on vague info like a cam'd 2.3 engine with a hx35..

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nothing to write, it's a 2.3 stroked evo4. the project yet, but the most patrs are already bought including S2 cams, springs, retainers, 14cm 7 blade holset, twin tials etc. so thinking about exhaust now, which way to go and begin the build

Overkill. Agreed. If you do 4" you pretty much have to dump it out bumper exit or another fairly close place(hood exit ftw!! ha)

stunt2 said:

no, I'm not a great fan of side exit exhausts, besides it's a daily driver and the visual side of the car is also important for me

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The visual aspect of things, is side exit = sex

Go 4"

^ 4" for a hx35...? Any reason as to why a 3" won't suffice?

I can post you some pics of a nice looking 4" system. Unfortunately I don't have any pics of this car on the ground, don't know how clearance was to the ground. I know the guy used the car this way and took it to the strip and so-forth.

Anyway, my vote would be 3" downpipe with 3.5" the rest of the way back. Join the 3" section to the 3.5" section with a 7 degree or 3 degree transition - like the ones available from SPDexhaust. I could post a pic of that too.
Think about this - what is the exducer diameter of the turbine wheel on the turbo you are using? And what is the diameter (ID) of the actual turbine outlet? If the turbine outlet is 3" ID it doesn't really help anything to all of a sudden jump it up to a 4" pipe. Ramping it up with a transition would be fine if you have room for it.

Here's pics of the 4":

Instead of guessing, get yourself some data. Monitor pressure, after the turbo, and see if there is any pressure in the exhaust when the turbo is flowing its peak airflow. You cannot go too big with exhaust after the turbo.

I wouldn't. It's going to be hard to fit, difficult to work around, heavier, and more-expensive than a 3" system and the chances are high that you're never going to notice the difference in the two.

Just build a clean 3" system with the fewest bends possible. Even the factory exhaust for a Dodge truck that uses a HX35 is 3", and it has a diesel engine with 3 times the displacement and a 17:1 compression ratio.

If you don't want exhaust sticking out of the front bumper, you can come out with it right in front of the back tire. That way you won't have to find a way around rear axle, and it will be couple feet shorter. Put a black tip on the pipe and it will be virtually unnoticeable. Point the tip slightly down and it will re-direct exhaust away from the car.

None of this Is terribly technical or anything like that, but heres a few basic ideas that may help:

The cross sectional area of the pipe is what were concerned about. Here are a few common cross sections.

2.5" = 4.908in^2
3" = 7.068in^2
3.5" = 9.621in^2
4" = 12.56in^2

Now, 3" is pretty common in our world so we will reference it. Its not terribly uncommon to find a 600 hp car that has 3" exhaust. While I agree with most people that it is somewhat restrictive at that point, its still not uncommon. So using some basic math....

600hp/7.068in^2= 84.889hp per square inch of cross section.

So you could POTENTIALLY make 816 hp on 3.5" and 1066 hp on 4". These are just general numbers but they're fairly realistic also. So unless you plan to have the first 600+ hp hx35, just do 3" and save some money and time. If you plan to upgrade in the future do a 3.5".
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No one says exhaust tubing must be round.

Too much thinking "inside the box" going on in this thread.

Hal

I wonder what the cost and availability of oval tube is like.

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It doesn't seem too bad, actually.

Breezio69 said:

The visual aspect of things, is side exit = sex

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Exactly. Problem is, for some of us at least, we want out AC! I might have to dump mine about 4ft back and angle it towards the ground. If it were a car i drive in the city that wouldnt work. Id be breathing fumes. I dont think theres a way to keep the alt in stock location and do a bumper exit, just not enough room there.

Exit behind front wheel would be ok but clearance would still be tough, wouldnt be able to lower the car much(im fine with that though)
Threadjack completed

The only people Ive seen running a full 4" exhaust are Tim Zimmer and LilEvo. So unless you're making 700+ wheel hp a 4" exhaust is going to be overkill.

Hope you guys can see this thread LILEVO Dyno - 770awhp If you cant, its Tanin talking about how he lowered the boost and took a couple degrees of timing out and went from a 3" to a 4" exhaust and gained 65 wheel hp.

My builder ran a 4" but he had a t04z88hta

crash89 said:

The only people Ive seen running a full 4" exhaust are Tim Zimmer and LilEvo. So unless you're making 700+ wheel hp a 4" exhaust is going to be overkill.

Hope you guys can see this thread LILEVO Dyno - 770awhp If you cant, its Tanin talking about how he lowered the boost and took a couple degrees of timing out and went from a 3" to a 4" exhaust and gained 65 wheel hp.

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I run 4" as well. This agrees with my findings on a couple of setups of my own as well as what a Garrett engineer has also shared on the subject.

AK Maniak said:

^ 4" for a hx35...? Any reason as to why a 3" won't suffice?

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No reason 3" won't work. But if he has the means to make himself a custom exhaust, and he intends to run the full length of the car in a performance application it would be measurably beneficial to transition smoothly out to 4" via concentric reducer:


As early as is convenient after the turbine, then use the least amount of bends.

Any post turbine back pressure is multiplied by the expansion ratio across the wheel. This is additive to the drive pressure required to make the shaft torque needed for the compressor to make whatever boost (PR) you are aiming for.

The lower your back pressure, the more power you can make per psi boost and the faster your turbo will spool.. giving your more power over a wider rev-range with faster response. As well as a wider safety margin in your tune on a given fuel.

It's a small investment that yields great dividends. Not just a theory

This is a topic like "big FMIC on small turbo" or "big T4 twinscroll can improve spool and top end vs. Open T3" ... not necessarily intuitive on their faces. Definitely ideas that get rejected around here out of hand often.

Imo it all depends on what your goals and plans are with the car. If your going to be upgrading to a bigger turbo. 4 inch all the way back with no muffler would be hella sick!

3-Inch Vs. 3.5-inch Exhaust Test - Tech - Modified Magazine

Here's a dyno modified mag did several years ago on how much whp could be gained from a switch to 3.5" piping from 3". The application is obviously different(3.0 I6), but on pump they saw a 100whp difference, marginally better spool. On race they were getting timing pulled(edited from "getting knock")and finished up with 'only' 70whp more.

On pump they saw 100whp gain and on race gas they got knock??? Lol have you ever ran race gas? Race gas doesnt knock like pump, you might have your numbers backward.