Rx7 backpressure question

[GotNismo?]

Ok, i have a question about relieving TOO much backpressure on rx7. Specifically turbo'd. on a stock turbo 2 motor, would 3 1/8 inch exhaust be to big. this is a turbo back system offerd by corksport more or less its a straigt pipe system. but is that too big? shouldnt relieveing too much back pressure have a negative affect on the poiwer output? or is this exhaust designed for a 400+ hp range? thanks for any general exhaust flow info you can throw at me.

[theflatlander]

not for turbo,generally less backpressure=faster spool. And a 3in exhaust can support well above 400hp.

[su_maverick]

the faster the exhaust travels out, the faster the turbo can spool up so the less backpressure the better.

[GotNismo?]

so the 3 and 1/8 inch exhaust wont hinder anythign?

[su_maverick]

Originally Posted by GotNismo?

so the 3 and 1/8 inch exhaust wont hinder anythign?

just your hearing

[GotNismo?]

lol thanks

[dreamdrivedrift]

unless if it causes a vacuum, no it shouldnt

[su_maverick]

how is it going to create that?

[theflatlander]

Originally Posted by dreamdrivedrift

unless if it causes a vacuum, no it shouldnt

and the award for idiotic thought of the day goes to.......^^^^

[su_maverick]

I constantly have the problem of my exhaust sucking things in... stupid turbo spooling the wrong way

[dreamdrivedrift]

exactly it wouldn't, meaning that it should be fine

[su_maverick]

not trying to be a complete jerk man but until you have some working knowledge of the car, dont post... all you do is either confuse people or make yourself look like a fool.
I suggest www.howstuffworks.com , its a great way to learn about pretty much anything.

[GotNismo?]

was that toward me or the other dude?

[Infini IV]

You WILL have boost creep... unless you have the wastegate passage ported out (over 35mm) and have a larger flapper door welded on (I'm assuming you have an S4 TII). If you have an S5 TII, you should be fine just porting the wastegate passages out to the edges of the flapper door (but don't port the passages larger than the diameter of the flapper doors). Your stock wastegate spring in the S4 turbo wastegate actuator is a 5pound spring I believe. If you are boosting more than that, then you are getting boost creep.

Your stock fuel system and intercooler will only safely support less than 12 pounds boost on the stock turbo.

[su_maverick]

Originally Posted by GotNismo?

was that toward me or the other dude?

no, not you dude... dreamdrivedrift

[epicz]

i dunno if it possible for a car but goped pipes acctualy creat a vaccum to suck out air.tha bigger=more accel tha smaller=more top end.just some input.my freind has a stock SR20det and he has 4in pipe i alwayz tell him thats too big but he says he has plans for his engine(hes a broke F*u*c*k)

[GotNismo?]

im new to turbo systems in general, but is the s4 wastegate internal or external. and if i bought a 38 mm wastegate would that reduce or stop the boost creep? and how bad is boost creep for my engine?

[Infini IV]

Almost all factory turbocharged car's turbos have an internal wastegate system as it is sufficient for most factory cars. Hence, why I said to port the wastegate passage and get a larger diameter flapper door welded on.

An external wastegate works with an external wastegate setup, but if you have the time and money to waste, then you can get an external wastegate, then take off the stock internal wastegate actuator and divide the turbine outlet from the wastegate passage and route the wastegate passage to your external 'gate. This is a waste of time, money, and effort though when you can just port out your factory wastegate passage to around 35mm and have a larger flapper door welded on.

Any time your boost gets above whatever your wastegate spring is rated at is bad, unless you have a boost controller that raises boost to a set limit (remember, boost controllers CAN'T LOWER boost). However, if you have enough fuel, and a slow-enough-burning fuel, and your timing is way-retarded... then you can overboost a little. Just remember, anything over 12 pounds of boost on the stock turbo is getting out of it's efficiency. What this means is that however much MORE amount of air it is pushing out is offset by the fact that the air it pushes out is getting "super-heated".

[GotNismo?]

who could do that kind of work, i can weld the flapper door on myself. but the porting, and i have no experience with turbos like i said so i wouldnt know what i was doing. Any old turbo/speed shop?

[Infini IV]

Well for the flapper door... find something that is a little larger than ~35mm in diameter (most Honda valves will work... just cut off the stem on the valves, and weld the valve to the flapper-door arm.

Then with porting the wastegate passage, do you know anyone with a die-grinder? If not, just get a Dremel and spend some time on it. Just make sure to keep the diameter of the passage smaller than the diameter of your flapper door, otherwise your boost will leak and you will have shitty spool-up and not be able to build more boost if you turn up the boost via a boost controller.

All in all, it's a very easy thing to do to protect yourself from blowing your engine, or hitting boost cut (at 8psi)... shouldn't take more than an hour or two with the right tools.

[GotNismo?]

k imma try that... any other problems i may run into with the large diamiter exhaust? and another question i have.... how hard is it to mount a fmic myself?

[theflatlander]

I thought u were going with a larger turbo? T04? And about the FMIC are u talking about a kit? You have to pull the front bumper to fit, might have to make some brackets and you prob. wanna cut the front opening for more flow. Plus most kits come with instructions so it won't be too much of a problem. And as for porting the wastegate on the turbo i'd go as big as possible on it, i've seen up to 40mm. Here's a good write-up on it http://www.rx7club.com/showthread.php?t=352816

[GotNismo?]

yea im doin the to4, but not for a while. im just tryin to cover all my bases before i start so i know what im getting myself into.

[Trots*88TII-AE*]

If you want more info on wastegate porting, or anything on FC mods, SERIOUSLY check this site out. Its pimp. http://www.fc3spro.com/TECH/MODS/TURBO/wgp.htm

this is another section of the site that deals with safety/performance. more great info. http://www.fc3spro.com/TECH/FM2W/fm2w.html

[hatebbobbarker]

im all about the 4 inch sewerpipe exhaust on rx7s