locote004004

Hi here is my situation at the moment.
I gota a 88 series 4 rx7 with a rebuilt series 5 block with series 5 intakes top and bottom and a series 4 turbo.
I gota Fuel Cut Defender. and Blow Of Vaule. Also a hks air filter.

The car boosts fine no problem at all.
Problem is jus after 5-6 rpms it boost all the way to 12 pound and keeps going to like 13 maybe 14. Car doesnt fuckout no fuel cuts nothing. Just boosting beutifully.

Why does it boost go higher at high revs?
Do i need a series 5 turbo coz i have series 5 engine?

The block is std with std ports.
not Emission crap and no air con or air pump.
2 and half exhaust that splits into 2 at the middle.

Any info would be much apprciated.

Thanks

kep0ne

by no emissions im assuming you have no cats.

a straight through exhaust (no cats) will raise your boost significantly...this is why you're seeing upwards of 11psi. this problem is multiplied tenfold with the S4 turbo; the wastegate can't handle the exhaust flow.

so you have some choices.

1) port the S4 wastegate
2) buy S5 turbo and port the wastegate
3) get a new turbo
4) put your cats back on

you should also look into upgrading your fuel pump.

rotary>piston

yeah, just make sure you have the fuel to support it.

HeffBoost

Yeah, be wery wery careful. 14psi on a stock fuel system is asking for trouble.

Port that wastegate orifice as much as possible. Or, keep your foot out of it until you locate an S5 turbo. Port that while it's out. You'll be glad you did later.

Cheers

chris_stampe

If you port the s4 wg you may still see slight creep especially if you get better exhaust, but you will be able to control it. My advice is to go take off the turbo (2 hours) buy a mbc for like 10 and a grinder bit for like 10 and port your s4 wg. Then you can set your boost to like 9 and maybe it will creep to 11 in third. Your car will be much more responsive and will feel so much faster.

locote004004

Ok i am thinking of taking the turbo off and porting the wastegate. But 1 question what is a MBC ?
I have no idea

HeffBoost

Manual Boost Controller.

Like http://www.boostvalve.com

NZConvertible

One big problem with these turbos is the tiny wastegate that can't handle increased flows from intake and exhaust mods, leading to boost creep. Every time you do this you risk engine-killing detonation, particularly if you're still using the stock intercooler and if you don't have a heat shield and cold air feed for that air filter.
Porting the wastegate can help control boost. Read this page for more info and pics. Preferably you should replace the wastegate flap with a bigger one so you can port it even further. A downpipe like the ones discussed in this thread is also a very good idea.
S5 turbos have a much bigger double wastegate (plus a better manifold), so you should try to get one if you can.
Do you know if the fuel pump's been upgraded? This should be your next mod, as the stock one can't handle over ~10psi boost. Neither can the turbo for that matter. Running over 10psi will result in high intake temps because you're past the compressor's peak efficiency, and will reduce the life of the turbo bearings due to overspeeding.
Hope that helps.