#1. What would cause my boost to quickly drop to 8psi (and hold at 8psi) from 12psi at exactly 5000rpm? For example, if I do the standard boost test, I'll hit 12psi on the 1st turbo, 8 psi at transition, right back to 12ish but at 5000rpm, like clockwork, it drops instantly to 8psi and stays there til redline. It doesnt matter if I back off the throttle and do a 10/8/10 run, it will still always drop exactly to 8psi at 5000rpm. Shouldnt a boost leak slowly drop psi's instead of an instant drop from 12 to 8??

#2. What would cause lazy wastegate response on the primary turbo? Sometimes (but not always), if I floor it in 2nd/3rd/4th at 2500rpm, around 3000rpm boost will jump to 13psi, then taper down to 12psi before transition.

I'm running a dp/highflow cat and catback but stock everything else. Yes, I know I need a boost controller BAD. Will a boost controller allow me to cure these problems? Arent these pretty high boost numbers for a relatively stock car??

 

Doesn't sound like a boost leak. I suspect that you are being limited by your stock intake. It is "THE" big restriction in flow for you right now. Modify it, and get a boost controller:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/cheap-stock-airbox-mod-121491/

 

What he said. I think stock boost is 10-8-10, so your a bit high, but not retarded. Allthough I have more mods then this, and I only run 13lbs. You know while your at it check the vacuum lines that connect to the back half of the Y-Pipe. I had a similar problem when I switched to the efini Y-pipe, and I found that i mixed up a connection. check to make sure they didnt pop off or crack. Just a thought

 

bump

 

Just a guess, but you may be collapsing a hose or something on the intake side due to the vacuum building up (intake restriction) at 5K RPM.

 

I agree, I think you're at the limits of your stock intake. Check your air cleaner, maybe it's dirty. Do you have a K&N drop in at least?
You are probably getting boost spikes from the high-flow exhaust. You should not be seeing 12psi with no boost control.
Your wastegate isn't lazy, it's that your spiking to 13psi because your unported wastegate cannot evacuate the exhaust fast enough.
I do not think you have any problems with the system other than you just need to upgrade the intake side to catch up to the exhaust side. However, just getting a boost controller isn't going to solve all your issues. If you get an intake and IC pipes, you'll be beyond the "3 mod-rule," which means you will need some kind of fuel control (PFC, EMS, upgraded ECU, etc.). If I were you, I would get the fuel control first, then start upgrading the intake side - just to be on the safe side.

 

BTW, how can you have been around this forum that long and have that many posts, and not know about the infamous "3 mod- rule?"

 

UHHHHHHHHHHH.....

Anyone reading posts about the 3-mod "rule" the last few days? I guess not....

 

Boost spikes are due to the stock WG solenoid not being able to respond fast enough. Boost creep is the wastegate's enability to handle the amount of air (thus requiring more air restriction or porting of the wastegate).

This is why aftermarket boost controllers can control boost spikes but not creep.

As for the 3-Mod rule:
https://www.rx7club.com/3rd-gen-archives-73/stock-ecu-10-psi-myth-308996/

 

lol


I agree the intake is limiting the boost at high RPM, here are two third gear run logs. first one is with a DP, CB, and a MBC. The second is adding a stock airbox mod. You can see the increase in boost at higher RPMs with the intake mod. The first thing you need to do is get your boost under control! With out going into the "three mod rule" myth, I think most will agree that boosting above stock levels with the stock ecu is very risky.

 

I'm gonna guess that one of your blow-off valves is venting when it should be held shut. The charge relief valve has a vacuum-actuated switch that should keep them from venting when under throttle. If the switch isn't locking it shut, it vents at 7 or 8 psi. The air bypass comes off the manifold. Although it's curious that it happens consistently at 5000rpm, maybe there a threshold of pressure or flow that causes things to trip off.

Try disconnecting each one from the airbox (vent to atm.) and do a boost run - if at 5000 you hear a piercing shriek, you know that's what's up. It should only vent the moment you let off throttle.

Dave

 

LOL! It's only infamous on this forum and I think it's a pretty dumb "rule"...

 

Sorry, I meant creep.

The only thing that thread proves is that those guys think that blowing a motor due to excessive mods will never happen to them. It's just like the smokers that say, "My grandpa smoked for 70 years and didn't die from lung cancer, so it is OK for me to smoke."
There is a lot more factors than just A/F ratios. Wouldn't it be better to just take the extra precaution to upgrade the fuel control; it is a lot cheaper than a new motor.

And I still think that RXcetera car is fine. He just needs to upgrade his intake syst.

 

Well, I setup a manual boost controller and now I'm getting a reliable 10-8-10 (more like 10-7-10) pattern so it's becoming easier to see exactly how the car is behaving. What is happening is that at around 5k rpm (basically right after hitting 10psi after transition), boost drops instantly to 7 psi then builds up to 8psi again by 6k rpm before slowly trailing off by redline.

I'm going to try what dgeesaman said and unplug the blow off valves. Any other ideas?

 

Did you check to make sure no hoses, etc., are collapsing? Still sounds like a possibility to me. You may be able to look at the intake hoses after the air cleaner and before the turbo inlets and see folds, wrinkles, etc., if they are actually collapsing. Longer straight hoses should be the first suspects.

 

Yes, there is a lot more than just A/F ratios (like charge temp, etc) when thinking about running "safe". However, those all come into play regardless of whether the ECU is stock or not.

The fact is that the stock ECU can support all bolt-on mods *IF* the boost is kept at the stock 10 PSI. The tricky part is controlling boost with certain combinations of flow mods. There are many dynos proving this including the research that was done on Wade's site.