Boost problem "take 3"!!!

feelio · October 03, 2005, 11:54:16 AM

Hey again,

Cut a long story short, mainly standard 93\' twin turbo with cat back exhaust, after market dump valve and "Redom" ECU. (Thats all I know of anyway!!)
When I got the car, both turbo\'s were boosting to 0.8 bar. I lost 0.2 bar on the second turbo (ie now boosting to 0.6 with 0.8 still on the primary turbo) Took it to Gary Gooding at G A Racing developments (good guy!!) but he said its running as a standard car should do and that I had already done most the things he would check. That being, vacuum hose job, tested most the Solenoids, followed testing procedures for turbos, all passed like vacuum tank, pressure tank. Followed testing procedure for actuators (top one and bottom one, forget the names, but not the ones with boost pills)
He tested the Solenoids with a PFC?? said they were working properly, put a diagnostics on the car, again, no problems. He suggested I might have got the boost pills in the wrong way round, So I got home and swopped them round, now I get 0.7 bar on both turbos.
If anyone has any clues what the problem might be, I could do with some advice!!!

nikp · October 03, 2005, 11:58:23 AM

0.7 bar on both turbos is pretty much correct boosting pattern for stock setup.

nikp · October 03, 2005, 12:02:57 PM

Running much more boost than that with a stock setup (I know you mention an ECU - not heard anything about them before!) is bad! Real bad! It\'s the road to re-buildsville!

andrewrx7 · October 03, 2005, 12:31:57 PM

There is the 10-8-10psi pattern that people say "should" happen. There have been alot of posts over the years where people get 10-8-8 (or near), which seems to be nearer reality. What you\'re saying is you have upto 0.8b then 0.6b after the transition (equiv to 11.7psi then 8.8psi). Sounds like you\'ve got a pretty good response actually - maybe even a little too high on the first turbo? Maybe not perfect, but then so many people seem to spend forever trying to get "perfect" but never achieving it!

For reference, I took this image off a forum, by a guy who used to own a 99/00 spec FD (since sold it on). Look at his boost pattern: just under 0.8 then around 0.6b (as you\'ve got). His rwhp was 209, which if you assume the magic 18% tranny loss - gives 255fwhp - bang on the money.

nikp · October 03, 2005, 12:41:47 PM

As I understand it, 209 rwhp is a tad low for a 99/00 FD.Should be pulling more like 225ish. but i suppose that\'s besides the point of this thread! :p

andrewrx7 · October 03, 2005, 12:52:56 PM

Quote from: nikpAs I understand it, 209 rwhp is a tad low for a 99/00 FD.Should be pulling more like 225ish. but i suppose that\'s besides the point of this thread! :p

Ooops...point taken! :rolleyes: (Unless it was an auto (255fwhp)), it should read 265 - which is around 217rwhp. Of course all numbers are taken with a slight of pinch of salt - it comes back to this tranny loss number - no-one ever seems to settle on what is best (18% loss from the fly, or around 50hp whatever the hp, for a std tranny setup).

As yo say, besides the point anyway - just trying to suggest that his boost figures may not be as bad as he thinks they are - they are probably very good!

nikp · October 03, 2005, 12:59:36 PM

Quotejust trying to suggest that his boost figures may not be as bad as he thinks they are - they are probably very good!

Agreed. The figures look fine to me. I think the boost he is getting is spot on.

Steve Burnett · October 03, 2005, 01:10:32 PM

I have the same sort of problem and have sorted it by fitting an Apexi PFC. Pip mapped it and had to put in some very strange figures.
I think my problems are either the wastegate or the turbo manifold cracked.

feelio · October 03, 2005, 02:02:51 PM

Thanks guys,
I know what your saying, and I am more than happy with the cars performance. Its just the fact that I\'m sure I used to get 0.8 bar on both turbos, I\'m just never fully happy when I know that something is not quite right!
Just to confirm.......not that I\'m 100%.......the Redom chip inside a standard ECU just gives you a richer mixture to prevent from running lean which enables minor modifications. Thats the way I understood it anyway (Looked it up on the net!!).
I need to get an air filter and replace the hoses to the blow of valves, and see of that makes a difference. anyone know where to get an aftermarket panel filter??

feelio · October 03, 2005, 02:06:51 PM

Quote from: Steve BurnettI think my problems are either the wastegate or the turbo manifold cracked.

Do you have to take the turbos off to check those??

nikp · October 03, 2005, 02:12:37 PM

Quotethe Redom chip inside a standard ECU just gives you a richer mixture to prevent from running lean which enables minor modifications

That may explain why you were running higher boost. Not sure. If you run higher boost, you need to run a richer mixture to counter balance it safely. I guess the problem is there though, is that it sounds like that chip is not mapable, so you cannot be sure as to hoiw much extra boost you can run. Whereas if it was all mapped properly, then it would all be setup exactly as you would require, for all your modifications.

feelio · October 03, 2005, 03:21:00 PM

Are you saying that the boost is controlled by the ECU? I didn\'t think it was. But then I am still learning!!

You have a fair point about the ECU not being programable. But why would it reduce boost?? I haven\'t changed anything on the car, except spark plugs and oil!!! Although there is evidence of there being a decat pipe being on the car (the air pump was disconnected from the cat when I got it) so they might have replaced the cat to sell it.

nikp · October 03, 2005, 03:27:36 PM

Yes, the ECU controls the boost. To maintain 10psi of boost on the first turbo, it directs some exhaust towards the second turbo to \'pre-spool\' it. (I think that\'s the turbo pre-control solenoid - but may be wrong there) Once both turbos are in operation, it controls boost using the waste gate and wastegate solenoid. However, there are also \'pills\' used in one of the vacuum lines to control boost too, but can\'t remember, and don\'t have the time to find out where and how!

Steve Burnett · October 03, 2005, 05:09:07 PM

Quote from: feelioDo you have to take the turbos off to check those??

Yep, and that means a good few hours labour for something it might not actually be.

Martiny · October 03, 2005, 05:40:48 PM

Nik is correct. The 1 st Turbo vents pressure through the pre-control. Think of the pre-control as the "wastegate" for the Primary Turbo. The waste pressure is fed to the Secondary Turbo between about 3k to 4.5K to pre spool the 2nd Turbo.

After 4.5 K, the wastegate controls the Secondary boost, well, both of them I suppose. THere are pills in the lines for the Pre-spool Actuator and for the Wastegate Actuator.

The ECU DOES control boost by very quickly switching the Waste gate solenoid on and off. However it can only really do this at a preset speed ( so it cannot adjust itself if it sees too little or too much boost) so we say that the Mazda ECu does not ACTIVELY control Boost.

http://www.autosportracetech.com/RX-7/rx7stuff.htm

A very useful site to start understanding how our cars (are supposed to! ) work.