Hello Peeps!

Earlier this spring I was asked by a WRX driver about the purpose of an exhaust port that is open below the engine of my 84' brat. I explained that it must help somehow in pushing out the engine exhaust. Then the kid went Einstein on me and started asking technical questions about "scavenging" and warning me about getting fresh air to the valves. I laughed him off at the time, but the little spoob got me to thinking. 84' technology for a standard Soob... the exhaust port must be there to help keep the velocity up so the car doesn't stall out right? So I tiptoed thru the archives for months pulling up a number of various topic headings and created more questions than answers. I'm at a loss....So I'm looking for a little knowledge! Here's my questions now...

Regarding this 80's design of an open port and the issue of back pressure, is there a sacrifice of the lower end or mid range power vs stalling out? If I replace the stock exhaust with a newer replacement, will it run like crap if I use a larger diameter exhaust? (2" instead of 1 3/4") Any directions or answers are much appreciated.

 

That is just a shroud around the manifold that is used to supply heated air to the air filter box when its cold. There should be a dryer vent looking pipe that runs from that shroud to the round port underneath the air box

That's just a heated baffle.

If you look at the exhaust, that "port" is only in the shroud.  Tube from that "port" up to the air filter box was meant to supply warm air to engine for warm up operation, but it's basically useless.  

All of the actual exhaust exits at the back.

You could disregard it and make an entire new y-pipe and it won't make a damn nit difference.

2 hours ago, FerGloyale said:

 That's just a heated baffle

no your just a heated baffle...................................................................

 

sorry i couldent resist i thought it was funny any way

 

..  ohh and a few more ....

 

Tell the WRX driver his UEL headers cost him HP, and see him Einstein out of that..

Tell him he will gain a few extra horsies if he did same to his WRX, But has to be in titanium ( guffaw,guffaw,guffaw)

When the flap in the snout if the air filter housing snorkel us working as intended, it has a flap that forces the snout entry closed upstairs, so it has to pull exhaust heated air via a flexible convoluted foil tube that should be between your mystery powerful grade and underside of air filter housing snorkel

Should be a not fully sealed join at exhaust header to allow fresh air entry. Not sure if the flap fully closed off upper engine bay air or gradual blend, but suspect it as on or off affair

To answer your question on pipe size increase

If you are handy enough and can build your own and like the exhaust note of an EJ turbo you could do what people call unequal length or UEL.

Funny though, if you measure the original pipes length, they are not equal to start with !!

The uel follows the path of turbo pipes by left bank bend turning towards front, skip across below oil filter and pump before either T in below RHS port or a pipe from each side doing a two into one further back

I have heard an EA81 with slightly bigger engine pipe in turbo path, straight through where rear diff was and out

An EJ WRX owner declared " that is no pushrod engine under the bonnet"

He was wrong and it sounded like an early EJ20 turbo

Willyfisterbottom of the gen1 forum owns the ute with this system

Yep, go too big in pipe diameter off heads you will lose low end torque measurable in seat if your pants

 

Edited August 23, 20196 yr by Steptoe

42 minutes ago, dfoyl said:

Tell the WRX driver his UEL headers cost him HP, and see him Einstein out of that..

Ummm... but the EA81 exhaust had exactly the same thing minus a turbo and a “better” engine. 

If you replace the exhaust and make the prerunners or the exhaust manifold/extractors too large you’ll effect the peak power output in the rev range. Too large and you lose the scavenging effect low down in the rev range. Too small and you choke it in the top end. 

But we’re talking about an EA81... pretty hard to muck it up. An exhaust builder mate of mine says the Subaru Y pipe is too large right from the head for the size of engine. Same for the EJ22... 

Cheers 

Bennie

Low budget suggestions years ago was to try a Y pipe from an EA82 on EA81

I did

I don't know if the pipe is any larger diameter, though this claimed. Factory carby EA82 Y pipe is double skinned