This question could sound stupid but is it normal that when I go right away at WOT when I'm changing gears the car is overboosting (sometimes 14-15 PSI) and if push gradually the gaz pedal I get my steady 10-8-10 PSI boost patern ?

Thanks !

 

No, not that high. You could damage your engine at those levels. Exhaust mods will make this worse.

Search this forum for 'boost spike'. You may need a boost controller or similar.

Dave

 

Sounds like a you're having a boost issue

Check the vacuum lines for cracks etc. That could be the route of your problem. And you definatly don't want your car boosting that high without some sort of ECU upgrade.

 

Do not put the pedal to the metal again until you have this issue resolved.......you're risking serious motor damage. Check all the vacuum lines and check valves you can get at, and make sure that your wastegate actuator arm is properly functioning. If the small horseshoe clipped worked it's way off, your wastegate could be stuck partially closed......

 

read here:

http://www.autosportracetech.com/RX-7

 

So a stock FD should never go over 10 PSI at WOT even with intakes, downpipe and catback ?

 

Not without the proper fuel management to even out the Air/Fuel ratio for the higher boost settings.

 

WTF?

How can you call an FD with intake, d/p, and c/b STOCK?

Of course you are going to boost over 10 psi with those mods.....

 

Ok thanks for your help guys, very appreciated, I will have a friend configure my Greddy Profec-B correctly, maybe I have a problem with my wastegate...

 

OK guys, as soon as I read his first post and then checked the sig pics I saw he was running an intake and exhaust system.......then I saw he had no ECU.

Hell, I aint even that dumb

 

I'm sorry that I'm not as bright as you are and that's why I'm asking questions so I won't damage my engine.

I won't push to hard until I get a Pettit Racing or Power FC ECU.

IMO having intakes, downpipe and catback are not big modifications compared to streetported engine, single turbo, fuel pump and those things.

Please keep your bad comments for yourself and try to help other RX-7 owners.

 

He's right. Give the guy a break.

But the modifications you list can cause you to overboost, which is exactly what you are seeing. Keep the boost at 10 psi until you can provide more fuel and you eliminate the fuel cut. Even then, I wouldn't go over 11 or 12 without an intercooler.

 

my comments really weren't meant to bust on him. Just that no one noticed.

 

You guys are correct and giving good advice telling him to check the status of his engine and to make sure his car is equipped to properly run that level of boost, but there is something else that is rarely mentioned.

It sounds like, from what he typed, that he is talking about being at a cruising speed, flooring the throttle, encountering a boost spike and then shifting.

If that is the case, this is a critical problem and the reason for more FD engine failures than lack of fuel or anything else you can sey.

Under low load the engine, in completely stock configuration, can boost spike. People are never told that there is a way one should drive a turbocharged or supercharged vehicle.

Boost and wide throttle openings at low RPM absolutely will kill an engine.

If you are at 50mph in 5th gear and you want to pass someone you don't floor the throttle, you are not driving an automatic. You must downshift first BEFORE moving into boost. The revs must be high enough to have the amount of exhaust velocity to counter the boost being created by the turbo(s).

If you are "boosting" below 3000rpm from throttle tip-in you are simply driving the car incorrectly.

 

What about in first gear? Say you just get it rolling (similar throttle position to cruising in 5th) and then gun it. You're saying the boost will spike? Or

Whataya mean by exhaust velocity being great enough to counter boost being produced by turbos? Turbo rpm is directly related to exhaust flow, which is again directly related to engine speed. How can this balance be off sometimes, and on others?

I'm not trying to critique you here, I just don't understand what you are saying.

 

Exactly the kind of tips I was looking for thank you !

My overboost problem happens at around 5000-6000 RPM when I push it hard WOT but like I said if I accelerate gradually there's no problem (10-8-10 PSI).

 

And it sounds to me like he is encountering spikes after the shift. I think he really meant "when I go WOT AFTER changing gears, the car is overboosting."

 

but i could be wrong....

 

Yes it is AFTER changing gears that I get the boost spike...

 

That statement made absolutely no sense whatsoever.

That's funny because the whole purpose of the twin sequential system is for quick spool-up at low rpm. I get on the throttle all the time below 3000 rpm and enjoy the rush that begins at 2500 rpm or so. I have never noticed a boost spike in my car, even with the record feature on my Defi gauges or now with the PFC commander time plot.

I do agree that I've seen a lot of people blow their engines pulling from a low rpm but IMO, that is due to a poor fuel map rather than boosting at a low rpm.

 

Do you have basically a straight pipe? this can cause overboost somehow... I forgot...
w/ the stock ecu it is best to have some back pressure or the computer will try and change some stuff... again I've forgotten the details but thats the jist of it!

 

What happens is with free flowing exhaust you experience boost creep. The wastegates cannot keep up and vent off the boost quick enough to keep the boost at 10psi when using free flowing components. More boost = more air. The ecu does not compensate for this and it results in a lean condition that causes detonation; which kills motors.

 

I've witnessed many people driving an FD for the first time, and they try and drive it like a normal car. Well, it isn't, and you shouldn't . I cruise from 3k to 4k rpms, and if I'm above 5k, I'm WOT. That's all there is to it. I've let a good bud drive my R1 and he went partial throttle all the way up to 7k. Not a good idea. That's the last time he ever did that. Now, first gear may be the exception to the rule, but my bud was doing this at highway speeds......

 

by the way, he has stock ECU, main cat still on and the wastegate was ported.

i beleive there might be more of a problem with the boost controler

i suggest you try to bypass it Carl, do you still have your boost pills?

 

More specifically, do you have your precontrol pill?

How do you have your Profec B hooked up?