Boost Creep? ... or?
 

Ok all... Went down to Dyno4mance yesterday and got my car tuned on my newly installed FMII kit. Made 222rwhp on their DynoDynamics with a conservative tune. Really happy except for one issue.

On wastegate only, the boost would creep up to 16psi close to redline, then we would have to let out of it.

We put the MBC on and got it leveled out a bit, but it still creeps to higher than what I'm comfortable with on my stock shortblock. I want a steady 14 psi, no more.

Just a few questions...

I plan on taking the turbine off and porting the wastegate, but what else can I do to fix this?

Is this a textbook definition of boost creep?

Should I source the signal for the MBC/Wastegate post I/C and pre TB like I have read in other posts or is this more for boost drop-off?

Sounds like boost creep to me
Isn't 222WHP pretty low for a 2560 on a 1.8 at 14 psi? Just curious

This is usually what they make on a dynodynamics with an excellent tune.


Are you on 3" exhaust? Sometimes smaller exhaust helps with overboost. You can try porting the turbine housing around the wastegate, but don't expect a miracle.

you can also lengthen the wastegate rod (and take all pre-load out), or get the WG signal "pre" intercooler where pressure is higher.


external wastegate > *

I was really happy with those numbers on that dyno, car pulls like a train... Yeah hustler, straight 3" with a small round magnaflow...

The dyno4mance guys are really cool.

Andrew still owes me a pull on him. They're just so damn far away.

you can try some of those ricer "silencer" thingies then the tip at the rear and I bet the overboost goes away.

Yeah, they were awesome. Unfortunately Andrew is packing up shop. Dyno is going to Knoxville... :( Ewww. No silencer ricer tips, i'll try porting the wastegate first.

Porting won't work. Restricting flow will. External gate, well...that's where miatas are going.

Does your wastegate have a threaded rod? If so, that's the old design, and it doesn't have enough throw to open the flapper enough, which causes the boost creep you're experiencing. I just went through the same scenario.

Call up FM, and if you're the original owner of the kit, they'll send you the updated wg and bracket for free. If not, it'll cost you about ~90 shipped.

C

I forgot about that.

$90? Find it on ebay.

Yeah, for a generic one. If the one from FM with their bracket fixes my boost creep, I'll forget about the $90 right quick.

C

No, its a solid rod. New kit, new design. I'll call them today and see what they say.

I'd like to hear what they said. Mine is on the way, and I hope it resolves my problem. Bell was offering free wastegate & housing porting at one time, even if you didn't buy your turbo from them. Not sure if that offer still stands.

http://forum.miata.net/vb/showpost.p...5&postcount=45

C

that offer still stand and it's your best best in curing boost creep.

FWIW, I get creep to 15psi with 10psi can and a BEGi ported housing.

External is da bomb. Thought about S6. Then thought about a junkyard LS1. Mmmmm. Junkyard LS1.

Interesting, I'm running 13psi with a old design FM bellmouth elbow and a Hallman MBC and I get no such creep :dunno:

What's your WG can open at? Mine's 10psi rated but has always been 12psi functional. No external boost controller.

This didn't start until I put in the new engine management, and I should note I only took 2 pulls on it. It was pretty stable with the Xede piggy. So something's probably funky with timing. I dunno.
Some simple tuning and adjustment to the wg actuator arm might cure my problems.

I know this is a knock on against my BEGi vs FM downpipe argument on the other forum. I'll stand by my previous statements that the BEGi DP is built for performance and the FM DP is built for mass fabrication.
I'd wager my exhaust flows better than yours, and I'd further wager that my non VVT car will spool up better than yours.

You know not.
Actually, my post was directed at the entire thread and how i'm not seeing such issues on a "less-than-optimal" setup and none of these tips/tricks/upgrades that other people have. Don't get any ideas that every post is always directed at you :rolleyes:

What does spool matter when the driver doesn't/can't use it?

Do you have a 1/4" ID vac line going to the wastegate? I had a 1/8" and it made my tial gate overboost too.

Ben, I would wager that your exhaust does not flow any better than mine... I've seen yours in person. This is my exhaust plus a 3" downpipe.
https://www.miataturbo.net/gallery/f...3/2/web004.jpg

Hustler, my vac line going to my wastegate is 1/8" or maybe even smaller... FM told me to check the opening psi on the actuator and to make sure the wastegate is opening all of the way... Duh... Then they said if that doesn't fix it to port the wastegate.