Powridah

What is boost creep exactly. im getting a new block from RX7 Specialties in Calgary and I plan on 680' secondarys. But the boost will creep like crazy on a S4 with a fcd i hear. well if it creeps what will that do ?

jmseven

back off....

Boost creep will happen with a down pipe. In order to fix it, you will have to the wastegate port.

Do a search. I thought I had saved the link for it....sorry.

jmseven

Actually...I had found it.

http://fc3s-pro.com/TECH/MODS/TURBO/wg.htm

dra_gon_lee

boost creep, is when the wastegate can no longer control the flow of air, and lets a few psi of boost go by... say with my tb mod, 5inch greddy intake, and full 3" exhaust turbo back, im getting 12psi....

watch out when you put a full 3"exhaust and do the tb mod no turning back, unless you want to put a restrictor in the exhaust, or intake, or port the wastegate... i wish someone would've told me this when i was upgrading my car....

but you want a fcd with anything over the stock boost levels, because without it the fuel gets cut on the rear rotor over 7-8 psi and can kill the engine...

scathcart

If you ahve a boost controller setting the boost at say 8 psi, but the wastegate cannot flow enough exhaust to slow down the turbo, you get boost creep. The boost will ramp up like crazy all of a sudden. It is a problem for those without fuel mods.
dra-gon-lee: The addition of an FCD to a stock psi will kill a motor much faster than fuel cut. Fuel cut doesn't snap apex seals, detonation does. With an FCD, you are much more likely to overboost and add more air than the duel system can provide gasoline for, leading to detonation, which can snap a apex seal the first time it happens and kill the motor.
Detonate once, your motor dies. Hit fuel cut many many times, nothing happens except you lose power.
I can name a few motors that have been killed by FCD's, but everyone who experiences fuel cut more worries about the HUGE cut in power when they floor it.

Kyle, how about I just give you a hand and we port your wastegate?
Sean Cathcart

scathcart

In fact, dra_gon_lee, at 12 psi, you are way past your limits. Port your wastegate and watch your right foot. You are by far superceeding the limits of the stock fuel system, and at 10 psi you are way overburdening the stock TMIC. I'm surprised you have a motor left. What's your timing look like? Retarded?

2DoritosOnAStick

You are slightly wrong. Generally fuel cut will give you slightly more of a saftey margin against detonation (comparitively), because the period of time you spend under fuel cut is usually less. Fuel cut is by no means "safe", the engine is still under high load, the rear rotor is simply not getting fuel. High load + no fuel = extreme chances of knock and engine failure.

The problem with a generally lean condition, is you are in that lean condition everytime you are under boost and the fuel system can not flow enough. Usually people detonate under long pulls, and you are especially at risk when in higher gears, under high load. This is where the EGTs skyrocket. Also, creep is proportional to load, so you may run 8psi in 1st gear, and 16psi in 5th @ 4500rpms. FCDs by themselves DO NOT increase the risk of detonation. Fuel cut is more like a reminder that "your stock fuel system ain't going to cut it". With an upgraded fuel system, you can run very conservative a/f ratios. The ECU determines fuel delivery from 02, and MAF readings.

My car detonated numerous times before it blew. I always detonated in 4th gear (if I had run out the previous gears), or 5th gear (if I had started in 4th). The potential damage of detonation is proportional to airflow. Running a stock turbo, you have a significantly less chance of blowing a seal (when detonating) than if you were running say a T-series Garrett. I could count at least 10 times I detonated. 2 of them were very severe. You can tell I really cared about THAT engine .

The moral, and my advice. Port your wastegate, run an upgraded fuel system that you have some degree of control over. Run and EGT guage. And run water/alcohol injection for added saftey. On 93/94 pump gas you can run the stock turbo to 18 psi (especially on 8.5:1 rotors) with good engine life if: Temps after the IC are kept low, you run water injection, and you tune a conservative 11.2:1 a/f ratio. Power from 310-330 bhp can be had on pump gas.

(Some info on stock turbo power levels given from RICE RACING, thank you Peter )

-Brian

dra_gon_lee

i know i know im past the limits on the stock fuel system, i have 680cc or 720cc's secondaries, the guy didn't know that sold me the car. im running rich, but i think thats because the o2 sensor wire was all hacked up, and i replaced it with non-shielded wire. I'm getting the ignition looked at hopefully today or tomorrow, by some local 2nd gen guy, and im putting a restrictor in my intake too to lower boost to around 8-9 psi.... thanks for the concern though, also doing some mods to the cooling system, and won't boost over 10 till i get my fmic hooked up...