I installed my first boost gauge this past weekend. After a few days of driving I've noticed a few things...

First, when I am just cruising down the road in 5th gear using very light throttle my gauge shows 20 vacuum. If i give it a little bit of gas the gauge shows about 10 vacuum. This is my first turbo car, but it seems like it would be 0 psi using 0 throttle, and then increase in boost as my rpms increase. Or, should it show a constant vacuum until I hear the turbo(s) spool?

When I do hear the turbo(s) spooling in lower gears the gauge only shows about 6-7 psi and there doesn't seem to be decrease in boost at 4500 rpms. Does the changeover only happen if I am making over 7 psi?


The car was stock (and seemed faster, or I'm just used to it now) 3 weeks ago. I've since changed the spark plugs + plug wires and replaced the stock precat with a HKS DP.

If the DP was not on tight enough would a leak there fall under the intake?

If this is a job for a mityvac where would I find the pressure numbers that I will be looking for?

 

The vacuum readings are normal.

You probably have an issue with a broken solenoid or misrouted vacuum hose. Best thing is to take the car to a rotary specialist to sort out the boost problem.

 

A few other key notes... These turbos work a bit differently than other stock set-ups because of the seq. system... You can use a mityvac to check for leaks but the system is very complicated and unless you are prepared to have your car down for at least a weak and are very confident in your abilities around cars I would take it to a professional. You can grow to love and hate the RX7 just around its seq. turbo set-up... Here are a few key points to know about the turbos.

1. As you have probably already read a perfect boost pattern is 10-8-10( Before 4500RPM the first turbo should spool very quick almost immediately )
2. Transition from primary to secondary happens around 4500RPM
3. After the transition at 4500RPM while cruising the turbos stay locked together untill you drop back below 3500RPM I believe it is. Which means building boost will take a little longer and you will not feel a transition.

A few situations to go over..

So if you are never seeing 10lbs of boost at full throttle then there is a leak somewhere(Vacuum Lines, IC Piping, Solenoid, Vacuum chamber). If you are only seeing 10lbs before the transition then there is a leak somewhere in the secondary system( Probably a line of vacuum chamber or solenoid) Hope this helps at all... These cars can be very hard to self diagnose unless you know exactly what it is suppose to be doing and can expalin exactly what it is doing.


Chris

 

The transition point is higher under low throttle. Right in the service manual it is listed as 5500 rpm.

 

Thank you very much guys.

 

I finished up my y-pipe and radiator install last night and I have fixed my boost issue!

12psi when i punch it compared to 5 psi before... Wow, what a friggin difference 7 psi makes!

 

Unless you have an aftermarket ECU your engine may not be long for this world.

 

Now you have too much of a good thing. Stock ECUs aren't really able to run 12psi safely.

David

 

lol, well crap... what do you think the chances are that my defi boost gauge is just off by 2 psi? Also, if its not off I'm guessing that I need one of those hallman manual boost controllers hooked up to the primary turbo, or do i need one for each turbo? Your thoughts on the DIY home depot manual boost controller and it's effectiveness/reliability compared to the hallman? Kinda broke right now after getting a radiator, y-pipe, AST, and the various hoses and gaskets from Ray...

All good advice welcomed!

 

It is a Defi, not an Autometer so the chances are not high. A rebuild is going to cost $3-$5k so I don't think you should be playing the slots in any case.

 

If you get a boost controller you should be able to keep it at 10psi, which is the most you want to run on a stock ECU.

You already went quality with the Defi gauge, keep up the quality with a good electronic boost controller. On the low end, you can go with a Profec B, which is easy to install and tune. They also show up used here and on Ebay frequently, you can probably find one for a good price. Or just get a new one .

When you start opening the intake/exhaust, the factory boost control can't keep up and you get boost creep. A good boost controller will fix that and also serve you well into the future.

Dale

 

If your'e on a budget I suggest JoeP inline boost controllers. High quality pieces and just $40/ea. You could probably do just fine with only one installed on the wastegate but I'm running one on both the wastegate and precontrol. I got them from boostcontroller.com.

Some folks make their own boost controllers, but for $40 the JoeP unit is really nice and not expensive at all.

 

Okay, so electronic and/or manual boost control. I plan on getting a PowerFC in a few months so would it be worth it to get an electronic boost controller now, or go manual?

 

Get a good boost controller. The PFC just allows control of the stock boost control system and you still run into the limitations of it. Just do it right and get a real boost controller - solid boost control is critical to making good power and SAFE power.

Dale

 

Will do, thanks for sharing the wisdom once again Dale. Its truly appreciated.

 

In my humble opinion, if you plan on keep the car relatively stock-ish and not chasing high horsepower numbers, a manual boost controller is perfectly fine.

If you plan on going after more ponies, and/or want the flexibility, spring for a quality electronic boost controller.

I'm a big fan of Greddy boost controllers (Profec B or E-01 if you can swing it), and Turbosmart EBoost2 and the new EBoost Street series of controllers are also very nice.

 

Screw the electronic gadgetry. Get a Hallman cockpit mounted manual boost controller. Rock solid, never fails. Simple = win, particularly in an FD.

http://www.hallmanboostcontroller.com/