how boost works
 

Hi gang,

I had my RX into the dyno shop recently, and the tech mentioned that the boost was coming rather late.

Would someone who knows, please explain how boost is controlled when using an LTX ECU, and maybe what to look at?

Setup:

Street Port
RB Turbo-Back exhaust
RC Engineering Injectors 550/750
MSD Blaster SS Coils
Walbro FP
Aeromotive FPR
Microtech LTX12

Thanks!

- k -

The ECU has no control over boost unless you are using the boost controller built into it, which I seriously hope you aren't because it's aweful.

Boost coming in late can be due to many factors:
-restrictive manifold/exhaust/intake
-wastegate not closing
-boost leaks!
-turbo too big
-AFRs too rich/lean

Thanks Aaron. I don't think the LTX is controlling the boost; the ECU was installed by a mechanic years before I got the car, but in working on it I don't see how it would. What do I need to check to know? (sometimes, this car makes me feel really stupid.)

your points in reverse order:
I would think the AFRs are correct, since I just had a reputable dyno shop in the area tune it.
The turbo is stock, so that should be okay, right?

Boost leaks were fixed before the dyno trip - the short hose from the turbo outlet to the BAC had vulcanized and broken - the rest of the system is tight.

I ported the waste gate per this write-up FC3S Pro v2.0:* How-To - Zenki wastegate porting
while I had things apart a few months ago and confirmed operation when I re-installed the turbo.

The exhaust is a Racing Beat Turbo Back system (RX7 1986-1992: Exhaust - Complete Systems: REV TII Exhaust System - 87-91 TURBO II -), so I should be okay there.

Atkins Rotary did an overhaul with street port and polish around the time the ECU was installed.

So, it appears that I need to check the intake to the turbo. It is all stock, but perhaps it's inadequate to support the upgrades.

I'll have a closer examination when the weather clears up next week.

Is it just the waste-gate that controls the boost?

- k -