Spike
 

i am having a boost control issue that i want to get rid of. I am not sure if this is typical, fixable, or just a characteristic of turbos.

I was previously using a toggle switch to switch between WG pressure (6psi) and MBC pressure (10psi). WOT from low rpm to redline would provide steady boost at the target pressure in both settings. However only with the MBC on i would get a boost spike of 1-3 psi either when i used flat-shift or if WOT was applied at >5000 rpm. This did not happen in the lower boost setting so i thought that the issue was the MBC not responding fast enough.

So today i tried using a WG actuator set at 11 psi and removed the switch and MBC from the system. It held 11psi +/- .25 through redline. However, if i used flat-shift or hit WOT at >5000 rpm i would het the same spike and hit boost cut. So clearly, the MBC is not the main issue.

Does the WG just need to be ported? I cleaned up the rough casting when i installed it but did not port it.

Would a better exhaust system help or hurt this spike issue? (currently stock exhaust)

Is there some other sort of a device that i can use to get rid of this spike?

Should i just deal with it until i can afford the externaly WG setup that i want?

Thanks,
-Jared-

A more breathable exhaust will actually make your spiking worse if the wastegate port is too small.

hmm, so perhaps porting it would be advisable?

lengthen your wastegate rod slightly.

I was having the same problem for a while but I fixed it by changing where the MBC was getting its signal from. It seemed that the turbo created a pressure wave and by the time the MBC sent the signal to open the WG, boost as already too high. I had to move my signal line to the outlet of the turbo instead of the inlet to the intake manifold. Where is your signal taken from?

My signal is on the turbine outlet.

Brain, i have tried two different wg actuators (garret 5psi, and china 7psi) both with and without the MBC. Lengthening the rod is only going to decrease my target boost level w/o the MBC. With the MBC i have seen no real effect with the WG rod lengthened other than increasing initial spool time.

I would try that first. I am trying to get Corky to write up a DIY porting instructions. I can post them as soon as he has them. Chances are, we did not port this turbo.

A free-er flowing exhaust will make the problem worse. Until the problem is resolved, I would not change exhausts.
Stephanie

Yes stephanie, it is not ported. i cleaned the rough casting and ridges with a drimel when i got it but did not enlarge or change the port shape. please do provide the porting instructions once they become available.

From the pics i've seen the size of the hole actually doesnt change, it looks like the flow is just directed more towards the WG.

yes, it does have a bit of a direction change, but it also appears to be of larger diameter.

Any idea what the minimum seat area is for the wastegate door?

any updates on those instructions?

It is on his to-do list. I will keep pestering him...
Stephanie

Subscribing:


I would rather DIY on the wastegate porting since shipping the Turbo to you guys will take 57 days and cost $72.96. Well not that bad but its still a pain from Canada.

the turbine housing should fit in a USPS Medium flat rate box.

home porting with a dremel after about an hour:

http://www.boostedmiata.com/gallery2...2/CIMG1366.JPG

http://www.boostedmiata.com/gallery2...2/CIMG1367.JPG


begi porting:

http://www.boostedmiata.com/gallery2...2/DSC_0006.JPG

http://www.boostedmiata.com/gallery2...2/DSC_0007.JPG


one of these methods worked worlds better than the other, care to guess?

Wastegate porting:Extreme S4 Wastegate Porting

In addition to enlarging the actual orifice, might I suggest adding in a "ramp" from the turbo inlet to the actual wastegate hole.

Then shim the actuator from the bracket so you can lengthen the rod without losing any preload on the swingarm. This should allow more movement to open the wastegate per boost level. That is if my brain is working correctly.

I've never dremeled into manifold cast iron. Is it that tough, since it makes the process look to take 10 hours at that rate when comparing the 2 or were you using a round bastard?

i am thinking that i should try another go at it with my dremel. The last time i did, i only cleaned up the rough casting. i am thinking that i should try an air grinder this time, since the dremel is really weak.

-Are there any things that i should specifically avoid doing while i am grinding away in there?
-What is the best method for cleaning up the shavings?

Can you make the actual size of the hole larger? or are you just opening up the area behind it so it flows better?

If you can get away with actually making it larger (viewed from the flatter side), I would probably just throw mine on the mill and take some out, and then port from the inside a little.

my shanghai boosts to 10psi + with the actuator disconnected and wastgate tied open will be porting very very soon. just to add im not driving it at 10psi!