Threoly header and exhaust pipe size

[mobile2]

Hi guys
Sorry for my language

I have samy 92 with G13BA engine and carb system and I plan to swap later to 1.6 8v engine.
I have Doug Thorley headers and want to get high-end horsepower more than low-end torque especially for G16A engine
So, my question: what is best exhaust pipe size if I have modified Yukon muffler?

Most recommendation I found is between 1.75in and 2.25in.
But how?
Doug Thorley comes with 2.5in collector. if exhaust pipe size smaller than collector size, will make "Reducer" in opposite direction. I'm right

please correct me if I'm wrong

More info, my samy is for off-roading in desert only.

Thanks in advance

[gi_zuk]

Fyi, the 1600 8-valve is not a good high end engine. The 16-valve has a lot more up top.

IMHO 2" is the ideal exhaust size for these engines.

[jr4x]

I had 2 inch off the stock manifold and though it was great.

[osok]

i have the thorley and am running 2 and a quarter but am also running a 16v.
They are such small motors, there really isn't that much exhaust flow.
2.25 is good

[AFTERMARKET4X4]

Honestly, you can't go wrong with the Doug Thourley header using either 2" or 2 1/4" exhaust, but whenever I build exhaust systems for customers that want the maximum midrange to high end power I run the 2 1/4" exhaust with the Dynomax Super-Turbo muffler and a high-flow CAT converter or hollow or none for off-road only vehicles.


Good luck with your decision.


Sean

[mobile2]

OK
I already have modified Yukon muffler intalled with 2.75in pipe

do I have to change pipe size (Yukon muffler=2.75in or 3in)?

what will be the power curve with 2.75 pipe size vs 2.0?

[AFTERMARKET4X4]

Originally Posted by mobile2

OK
I already have modified Yukon muffler intalled with 2.75in pipe

do I have to change pipe size (Yukon muffler=2.75in or 3in)?

what will be the power curve with 2.75 pipe size vs 2.0?

The 2.75 is too large and you will not have enough back pressure and will lose power and torque all through the RPM band.


OH, and here's your official WELCOME TO THE PIRATE BBS



Sean

[mobile2]

Thanks Sean and all guys

if I have later any good update, I will update this thread

[Dr_D]

Originally Posted by AFTERMARKET4X4

The 2.75 is too large and you will not have enough back pressure and will lose power and torque all through the RPM band.


OH, and here's your official WELCOME TO THE PIRATE BBS



Sean

I messed up as well and went 2.75 and I had my engine light coming on and found the issue code to be egr related. Not enough back pressure to open egr. Went to 2.0 and it runs great now.

JMO

[mobile2]

Originally Posted by Dr_D

I messed up as well and went 2.75 and I had my engine light coming on and found the issue code to be egr related. Not enough back pressure to open egr. Went to 2.0 and it runs great now.

JMO

EGR isn't an issue because my Zuk for off-road only

I wonder why they make "Threoly header" collector 2.5", while nobody interesting to put exhaust pipe more than 2.25"?

[Dr_D]

That was my question too, but I also have the high flow cat installed as well. Thorley header I am using is for Calif legal smog. They make other headers that are not smog legal.