Rx7 backpressure question

[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

[f8ldzz]

Ok, i have a question about relieving TOO much backpressure on rx7. Specifically turbo'd.

No such thing.
Owners have gone 4" exhaust and ran into major boost creep problems with the stock wastegate.