Freshdot

Here's how the story goes, it may get a bit confusing so i'll be as descriptive as possible.

I own a Greddy 18G with its factory WG actuator. Before my tune I decided to purchase a 14psi wastegate actuator from ATP turbo and swap the WG's in order to be able to reach my goal of 22psi.

On the day of my tune, I didn't realize that I had installed the ATP actuator with a bit too much slack on the flapper and made only 8psi initially not hitting my desired 22psi until really late in the powerband, say 5500rpm or so where it was useless. Bear in mind this ATP actuator was supposed to be no less than 14psi out of the box. Basically it was leaking boost until enough pressure built.

I should also note at this time that I have an S300 and PWM boost by gear.

Now...the day after my tune, I strap the 18G factory wastegate back on and make 10psi in first gear at a more desirable RPM basically how a greddy 18G would spool, nice and early. 3rd gear I'm now hitting 17psi, which is nice but i'm tuned for 22psi..something the factory greddy actuator just will not reach.

Changing variables:

So yesterday I install the ATP 14psi actuator again, this time properly. Nice and tight over the flapper, not allowing boost to escape early on and building pressure like an 18G should

1st gear - 14psi, great
2nd gear - 16psi, great
3rd gear - wanting to go passed 22psi and car going into boost cut.
didn't even proceed going through the rest of the gears as i'm sure this issue would persist.

I'm trying to make sense of this because my boost by gear is set to only make has high as 18psi in 3rd gear and 22psi in 4th and 5th.

So why this spike? why won't it hold at 18psi in 3rd?? could it possible i got overzealous with the tightening of the actuator rod on the flapper as to eliminate the boost creeping out into the exhaust? so much in fact that now the flapper doesn't want to open enough??

however if this is the case...then why no significant boost cutting spikes in 1st and 2nd?

thanx in advance to anyone that takes the time to read this and lend a hand.

sanman000719

when we set my boost cut it is always 2-3 psi higher than my desired boost

ill emagine the load is differant from the rollers to the track, and this is what causes the fluctuation

Freshdot

i'll give this a shot, and maybe loosen the actuator rod a thread or 2. thanx man

TheShodan

iTrader: (14)

Flapper door. You didn't address the fact that the flapper door and the wastegate port inside the turbine housing have to be ported in order to allow exhaust to vent to eliminate the spike. The door itself doesn't open anymore than about 45*, and the wastegate door is only about 31mm opening. Once you port that open (not too much or you have to change flapper doors), that will eliminate the spike.

This a lot why many weld the door shut and go external wastegate by creating a dumptube off of the downpipe itself. Others replace the flapper door to open 90*, port the opening as they change actuators.

Freshdot

granted and thanx for the input but is there anything i can do to fix my current situation..i'm going to increase the boost cut to 25psi and see if it cuts out..if its hitting 22 and staying at 22 i'm fine with that.

TheShodan

iTrader: (14)

Other than my previous post, that's what needs to be done.

303Turbos

You are correct, sir. The td05h turbos are surge happy after you get bigger than a big 16g because the turbine housings are so small. The internal gate design just doesn't work well on 18 or 20g turbos.

You could port the housing, but that may take your rotor speed down too much between shifts and you may not like it. You could run a bigger turbine housing as well, but the best way to go is with an external gate.

303Turbos

What footprint is the turbine housing? t3 inlet? t2? DSM? Greddy "compatible with nothing" triangle?

TheShodan

iTrader: (14)

The Greddy 18G shares the same Turbine inlet/downpipe flange as the GT28R series turbos with the Internal gate 5 bolt housing. (Not to be confused with the 5 bolt Ford SVO housing style that Garrett,Precision, and Turbonetics use.

303Turbos

Hum, I wonder if it is the same turbine housing that is on the 18g kit for the sylvia? If so, that is the biggest cm housing that I know of, and it runs a t2 flange.

EDIT: yes it is, 9cm housing. you need a 12cm from this turbo 49178-02130 not sure about the footprint, though: may not be t2.

TheShodan

iTrader: (14)

That footprint is a DSM Radius flanged setup. you would use a .86A/R equivalent from the garrett line to fit that cartridge, not a mitsubishi. Mitsubishi parts are the compressor housing and compressor wheel ONLY. once you get to the cartridge and turbine fitment, it turns into Garrett parts.

303Turbos

Ah my bad, may I present my credentials http://www.303turbos.com I deactivated the store because I am not a vendor on this site yet (I have other sites)



Not sure what you mean, the greddy unit is a MHI and so is the pn I provided. The MHI bearing systems are dissimilar to garrett units: MHI have their own bearing housings and bearings.

The gt28 turbos come in t2 or t3 inlet: I'm pretty sure the greddy is a t2, unless you are saying it's a greddy with a MHI flange?

Freshdot

my turbo is a T25/28 flange on the manifold side, and a 5 bolt T25/28 exhaust flange as well. basically I just want to stop this dang thing from spiking so much, i really think i may have tightened the actuator rod a bit too much making it almost impossible for it to swing open and leak exhaust in order to keep the PSI in line...i'll also step my boost cut to 24psi and see just how out of control this thing is getting.

TheShodan

iTrader: (14)

Thank you, as I am aware of that. However, The Greddy 18G unit is a hybrid turbocharger. Meaning that it utilizes Mitsu Compressor wheels, Compressor cover and cartridge. The turbine housing is notMHI, and is compatible with the Garrett housings, as does the T518z, and Silvia versions though believing that the turbine housing is an MHI is a common assumption. I've had that turbo since 1998. hasn't changed yet.

Congrats on your rebuild business. You'll find feedback here..... interesting.

303Turbos

You learn something new every day! The greddy turbos you talk about are pretty rare, I have never even seen one. The only greddy units I have seen are greddy rip offs from taiwan, and they are all MHI parts.
So the turbine housing bolts to the bearing housing-there is no vband? You sir just blew my mind.


The rebuild thing is pretty lame, and I'm looking to get back into performance because it is more fun and because my balancer is just just sitting around. Most turbos should not be rebuilt, so I just sell turbos most of the time instead of rebuilding them.

Freshdot

well I am happy to report that after alittle bit of rod lengthening (pause) that I have solved my boost spiking issues and I am now holding at 22psi in all of my gears after 2nd making considerable power nice and early in the powerband holding all the way to redline! thanx for the help all!

TheShodan

iTrader: (14)

Absolutely. There are many cases in which rebuilding is useless, and too many people buy horribly used turbochargers that "just need a rebuild", not knowing that the company (IHI comes to mind) may not have the parts available, or cannot be rebuilt. Then the owner feels shammed because they basically bought an expensive paper weight.

When it comes to rebuilding, you've learned this already as I have. Our balancer is old, too, it is easier to actually contract out for more precision than to keep the older one.

V-bands are rare on Greddy turbos except for larger TD06 /T4 turbine housings. One could purchase a GT25/V-band adapter, but that's about it.

Congratulations. since you're keeping the gate closed longer before release, you may have been able to stave off any spike. But check that flapper.

wantboost

iTrader: (2)

I don't even want to think of compressor outlet temps at 22psi on an 18g

boostedtk

^ wayy to hott !!!

Freshdot

my IAT's haven't been over 126, and its been 80 degree's everyday here in NYC for the passed 3 days...also this is a weekend car, and never driven in extreme heat no matter what.

thanx shodan! you're always the flippin man in the forced induction section!

Freshdot

also, i do not have an intake or filter on my turbo yet which i know will lower temps a bit.

TheShodan

iTrader: (14)

And save the turbo, also.

Freshdot

oh yea, that too lol