Sapphonica

I've got a ported Renesis with boost controller & high flow cat. No matter what, it just won't hold more than 4 # of boost at high rpms. No, I don't think the cat is buggered, otherwise it wouldn't spool up lightening fast, produce ample boost, and run smooth as butter at low/mid RPMs.

Could this be due to higher flow? That is, on a non-ported Renesis the exhaust restricts and 'backs up' the flow, so pressure goes up. So, on an engine with greater exhaust flow capacity, more inlet flow would be required to make a certain psi?

The only other possibility I can think of is some crazy vacuum and/or boost leak. I get ~16.5-17 " vacuum at idle (~800 rpm). This is a bit low-ish, but not out of spec.

epitrochoid

are you using the greddy t618z?

Sapphonica

I'm using the stock GReddy turbo.

rkostolni

Tighten down your wg rod. Freeing up your exhaust flow will also help.

two rotors

Just as a matter of interest,have you monitored your airflow before and after porting?If your motor is sucking more air now maybe you have outrun the compressor.

rkostolni

The problem is usually high exhaust back pressure forcing open the WG flap. It is resolved through the above two methods.

The effect of a turbo overspinning is generally decreased efficiency-skyrocketing intake temps, hence reduced massflow, and not limited boost pressure. That is until you reach choke, at which point the pressure will not go any higher.

Sapphonica

I tried cranking down the WG actuator as tight as it would go AND I have a high flow cat. Neither helps at high RPMs. Prior to my engine blowing up (it was non-ported), I was able to hold 7 psi to redline without maxing out the duty cycle on the boost controller. This was with stock exhaust, which makes more back pressure.

So, I've tried both of the above methods to no avail.

rkostolni

Not sure what you mean by as tight as it could go. That's probably not the ideal situation either. But, in that case I would suspect clogged cat. Can you pull it off and take a peak?

Ajax

The stock T618Z is too small to flow as much as you're probably capable of handling. It's too small to flow enough for the car w/o being ported. Talk to Scott from mazsport about his greddy turbo upgrade when it's ready.

Just out of curiosity, what kind of porting did you have done? Just clean up work or a half bridge or maybe even a full bridge?

Sapphonica

I'll talk to Scott when I have money again someday!!!

No bridge porting, just clean up & a little widening that has minor impact on port timing. I should have asked Rick to take pics.

guitarjunkie28

think in terms of hp, not psi.

Sapphonica

I think of mass flow rate

guitarjunkie28

which is directly porportional to hp.

you're the one asking questions here.

epitrochoid

cranking the WG down will help, but yea it is the turbo. at least I know a larger one will put out 9psi, and probably 12, all the way to redline

MadDog

I know we don't have the exact maps for the T618Z (whatever the hell Greddy does to a TD06-18g), but don't the maps for similar turbines/compressors indicate that this setup is just about perfect for the ~1.8 pressure ratio that most of us are running - even considering the Renesis flow rates out to redline? If that's the case, how can it be that the turbo is running out of steam?

Ajax

It's running out of it's efficiency range. The turbo is small. It's made to spool up incredibly fast and have instant on boost but in small amounts. It does a great job at that. The problem is, the RX-8 has aux ports which don't open until later causing a massive flow increase (really, they're like 3/4 the size of the primary ports.. maybe 2/3, but they're big!) The turbo really isnt appropriately sized to flow enough air at that point, well, enough air beyond what greddy originally tuned it for.

They sell/market the system to run like 6-7lbs of boost and it does a pretty good job of holding that much boost up to redline. If you augment those ports to flow more, the turbo isn't going to be able to produce enough CFM and you're going to drop PSI.

A slightly larger turbo, or a different compressor wheel would help.

Cranking the wastegate down will probably work to a point but it'll also probably shorten the life of the turbo by forcing it to work outside of it's operating specifications (whatever those are, stupid greddy).

MazdaManiac

iTrader: (3)

As MadDog pointed out, the compressor map for the Mitsu turbo in the kit will produce enough flow for even a ported Renesis at max RPM and 11 PSI plus.

A little research would eliminate speculation like the above post.
Now, it is "small" on the turbine side - which accounts for the fast spool. It also accounts for the very high exhaust pressure which is what it opening the WG.
An external WG is probably the best option for a high flow application.

OfficerFarva

I agree. An external wastegate would do wonders for this. Thanks to u Mazdamaniac I was able to apply ur fix by plumbing the line into the wastegate and drilling the hole on the outlet pipe. Clearly, a flaw on Greddy's part from the factory w/ this cheap internal wastegate. So, I feel like an external one could work sum magic for this setup.

Sapphonica

Sorry to repeat myself, but I know some of you guys on this forum know a LOT more about this stuff than I do, so thanks for bearing with me & sharing your expertise!

Well, I've got a ported Renesis, and it isn't holding boost up top, even with a high-flow cat, 100% duty cycle on the bleed valve, & the wastegate actuator cranked tight. Prior to porting, it held 7psi to redline with stock exhaust, < 100% duty cycle on the bleed valve, & the wastegate actuator less tight.

It idles fine, spools blindingly fast at low rpms, makes full boost below 3000 rpm, will overboost if I'm not careful in the mid-range, & gets better gas mileage than stock when cruising.

From my limited knowledge, it doesn't sound like a clogged cat. The only other explanation is that the port is letting the engine flow so much that the turbo can't keep up.

Ajax

Well, I was speculating.. so if i'm wrong, I'm wrong.
No big deal here. You do know more about this **** than I do, lol.

I'm still surprised that a wastegate can cause that much trouble.
Just for reference sake, I've looked around for the TD06-18g maps and I cant find them. The closest I found was the TD06-17c.

MazdaManiac

iTrader: (3)

For every PSI of boost you see in the manifold, there is 2 PSI of exhaust flowing at a minimum.
Really, you are seeing more like 22 PSI of exhaust pressure in the exhaust manifold and it just can't make it through the turbine, so it pushes the WG flap aside.
Really, if it didn't do that, you would be overspinning the turbo. However, I'd rather have the WG decide when to open based on a signal from the compressor. That is supposed to be how the relationship works. Exhaust spins the turbine, the compressor makes the proscribed amount of pressure and then tells the WG to do its thing. It is a continuous feedback loop.
This is why having the WG plumbed to the IM instead of the compressor outlet is a bad thing.
Even a tiny Tial WG plumbed into the DP would probably do the trick.

The TD06 part is all that matters. The suffix is related to the turbine A/R.

guitarjunkie28

larger compressor, clip the turbine, problem solved.

my greedy-powered renesis is going into an fb or fc chassis, so i'm blessed with enough room to weld on a t3 flange and run a much bigger hot side.

MazdaManiac

iTrader: (3)

You can probably go to a 15° clip on the exhaust, but I think a bigger A/R is really a better solution.
There is a reason the 7 folks are running exhaust A/Rs close to 1.
My T3/T4 hybrid has a .63 A/R, which is why it flows more yet has a spool-up close to the Greddy turbo (and why it is really the ideal turbo for the application).
You could probably go up to a .80 A/R on the hot side and still have an acceptable spool.
When I go back to this turbo in the fall, I am going to bash the crap out of the floor pan near the turbo to make room for normal engine movement so that I can get rid of my stiffened motor mount (and its somewhat amplified transmission of NVH).
I don't think the passengers will notice 1.5" of reduced floor space for their left foot.

guitarjunkie28

^ i was thinking about using a hammer to get a t3 hot side on that thing in an 8 chassis, but most guys that buy that kind of kit want everything to pretty much be "factory" style.

i'll see what the big hot side does, then maybe, possibly clip it. oh wait--i cna always just get a bigger turbine. nevermind, all is well

MazdaManiac

iTrader: (3)

All installs require a bit of "bending" - even the Greddy needs some additional coolant hose clearance that is acquired via persuasion.
I intend to keep it clean and "stock" - I'm just moving room to the outside from the inside.