Boost Creepin'
 

I've been having boost creep issues since turboing my current car. I wanted to run my setup by you guys and see if anyone had suggestions, because I'm pretty stumped.

Setup:
gtx2860 turbo
tial mvs 38mm wastegate
atp external wastegate turbine housing
cast log manifold
wastegate plumbed into downpipe
exhaust is 3" to a resonator and a turndown before the axle

https://www.miataturbo.net/attachmen...ine=1417390596

http://i272.photobucket.com/albums/j...6FD5C7022D.jpg

I started with a 4psi wastegate spring, the turbo spools, the wastegate opens, then it gradually creeps up the 200kpa overboost protection a little before redline. By that point I'm pushing my stock motor and RX8 injectors to the limit so I dropped overboost to 190kpa.

I've tried changing the source of the wastegate and gone to a bigger vacuum line which did nothing. I then put in a 7psi wastegate spring, which does the same thing, just with boost creeping up a little quicker.

https://www.miataturbo.net/attachmen...ine=1417390509

It almost seems like the wastegate just can't flow enough air. The turbo is really efficient, the exhaust has basically no back pressure; but it still seems crazy to think a MVS can't flow enough air for a 200hp car.

If you guys have suggestions of thing to try or potential issues please let me know.

You can solve it with timing believe it or not. Jared's car:

https://www.miataturbo.net/build-thr...p-build-62826/

Had some pretty bad creep, but after we told the knock sensor to STFU, and messed with the timing and ebc, it all but disappeared.

Talk to a competent tuner, and on a real dyno.

Thanks for the tip, I'll read up on the thread. Timing is still pretty close to the basemap right now. Since I was running low on fuel I didn't want to add timing and end up going lean up top. That'd be awesome if that's the problem. I've got some bigger injectors on the way, once they're here I'll add a few degrees and see how it does.

The boost creep you have looks beneficial to me?

Is the wastegate physically opening fully?

Running 150kpa that creeps to 190kpa by 5800rpms before you run out of injector and have to shift to the next gear really sucks. It's be significantly quicker/faster/more responsive/enjoyable/reliable/safer if I could just run 180kpa all the way to redline like it should be able to.

When I pulled it off to swap the spring I looked it over and compressed it, nothing looked unusual but I don't really know what to look for. Is there something I should check or any way to tell if it's opening all the way?

FWIW, it worked perfect on my old set up. But that was a slightly bigger turbo that ended up having a torn up turbine wheel so I assume it took a lot more to get it to spool.

Remove all springs and lines from the wastegate and it'll essentially be like tying an internal gate open.

I really dislike your wastegate setup. I'd like to see the EWG sit directly on the turbine housing, and have the dump tube incorporate the 90* bend currently being made by the IWG. The 90* pipe means you have a bunch of pressure loss in the pipe leading to the EWG, which inhibits wastegate function.

^ I was initially wondering about that as well. That is a relatively tight bend. I seem to recall from fluid dynamics that every 90 degrees gives roughly the same amount of drag as 10 feet of straight pipe of the same diameter. That's a rough figure but gives you a good idea of the importance.

How exactly is it plumbed & controlled right now?

That thing makes really awful low-end torque.

The wastegate is plumbed directly to the intake manifold (no mbc/ebc for now). I know it's better to run pre throttle body but it should be fine for a wot pull.

I think the low lowend torque is primarily a result of basemap timing + weak wastegate spring. I'm sure it'd look a lot better if I could properly control boost.

I've been meaning to pull the spring out completely and see what happens, I guess that's my next test. Thanks for the advise on the wastegate, I hadn't considered the 90 to be a problem. I'll have to check fitment with the hood and if there's room to mount it directly on the turbine housing it should be pretty easy to have it redone.

Wait, wat?

I might have found part of the problem.

and lower port only?

does this EWG have more than one lower port? if so they need to be blocked.

Yes, it does have 3 lower ports; 2 are blocked and the 3rd sees the boost source. The top ports are left open. I'll double check the blocked lower ports to make sure they're tight, it'd be awesome if that was the problem.

you might have a better job preventing creep by using a pre-intercooler source.

But it seems that something is preventing it from venting enough. Unsure why. Could be the 90° before the EWG like savington mentioned.

What source are you using on the IM. Coming off the brake booster might be a smarter idea. Actually, I'd test that one, by temporaily removing it from the booster jsut to see. But make sure you have plenty of stopping room after a pull to redline :P

Figured I'd update this. I'm still having the problem. I've tried several wastegate sources off the intake manifold that didn't make a difference.

I love the pre-intercooler wastegate source idea. I ordered some aluminum bungs just waiting for them to arrive so I can get them welded in, I didn't want to screw up trying to tap the pipe myself.

I bought some ID1000 injectors, so there's no lack of fuel now. I added timing and saw no change. Then switched to E85, added more timing, and the boost curve is basically identical. The turbine housing flange is 44mm and my wastegate is 38mm so it's not as simple as moving the wastegate to avoid that 90 so I'm hoping the pre-intercooler source + adding a EBC will allow me to tune around the crappy wastegate setup.

I ran my 93 E10 datalog vs E85 datalog through virtual dyno to compare.

https://www.miataturbo.net/attachmen...ine=1417981967

I'd have to see your torque curve but your boost curve looks a lot like high hp stock engine/5 speed boost curves should.

I am unaware of your setups particulars though.

Maybe the virtual dyno log isn't doing the boost curve justice. Here's the same pull from megalogviewer.

https://www.miataturbo.net/attachmen...ine=1417990644

Every other turbo miata I've had built boost until the wastegate opened, then held that pressure to redline. I don't feel like this is normal for any car, and certainly not something you'd want on a stock motor car.

Would there be any way to weld the ewg off the manifold and rework the outlet?

It is what you want because you get lower boost at peak torque than you get at the top where the head is choking so you have a safer curve AND will make more power. Stop and consider it for a moment and you will understand.

You can. Definitely rework it I've done a few wastegate on turbo arrangements and wastegate on cast manifold (rb25/45mm Turbosmart hypergate are popular here) so you can make it flow awesome and it will hold perfect boost within the psi.

What annoys me is the common misconception about boost pressures. If you are trying to stay under a torque limit your boost curve should look opposite to your n.a torque curve which gives a flat torque curve.
You keep the torque below your limit and flat rather than with a big midrange spike to the limit and heaps less everywhere below (waiting to spool) and above (head is flowing less and less as revs rise and it chokes but boost pressure remains the same).

Dann

I'm not sure. It's a plain ole BEGI cast manifold, I think I read about people trying to mount a external gate on them but not sure how it turned out. I don't think I want to mess with that. Hopefully moving the wastegate source helps a good bit.

Thanks for explaining that, it makes more sense now. I guess I'm too hung up on boost pressure determining the limits of the motor. Once I get the wastegate source moved to pre-intercooler I'll bump up my overboost protection and see how it handles going to redline.

"hung up on boost pressure determining the limits of the motor."

Can hardly blame you this is how most cars guys talk about it.
Its very misleading however.

If I was creeping to 180kPa, I'd make my lowest boost 180kPa.

Having a torque curve like a centrifugal SCer on a turbo car is weak and lame and something only an Aussie would do purposefully.

you're leaving 3psi off the table between 3500 and Redline. That would probably bring you power up to 240hp/240tq.

Pdexta, your first post suggests at the limits of Yellow top, but your sig says ID1000. Which are you running, and did you indeed run out of fuel with the Yellows, or just "almost"?

When I initially posted I was on rx8 yellow injectors, a couple posts up I swapped to id1000s. Megalogviewer showed 95% duty cycle and the car wanted to go lean at high rpms even when I kept adding fuel so they were definitely at their limit on stock fuel pressure.

Yes it might make 240tq at a single rpm, with boost tapering on you can make it from midrange to redline.

https://www.miataturbo.net/attachmen...ine=1418072074

Dann

Ok have you double checked the vac port on the EWG to make sure that the eye bolt or whatever is fully open? Sometimes you can rotate the vac port on the wastegate to limit air flow and increase boost. You might not be getting a large enough amount of air flow through there.

I hadn't considered that, I'll take a look at it tonight.

I dropped my intercooler pipe off the. bungs to be welded on it. I went ahead and did one before and after the intercooler so I will have 2 options to play with. I should have it back tonight.

Took a small baby step in the right direction I guess. I got my intercooler piping back from the welder and hooked up the wastegate right out of the turbo.

I also checked on ScottyP's recommendation. The banjo bolt on the wastegate was exactly 90 degrees off of a direct flow. I marked the bolt so I could line up the line perfect. Not sure how much difference it made, but any little bit helps.

I datalogged a pull that was considerably better, but still disappointing. You can clearly see boost climbing slower, I'm assuming that's attributable to Brain's recommendation of running a pre-intercooler wastegate source. Having the wastegate open at 7psi, then hitting 14.5psi boost cut before redline sucks, but at least I'm getting closer.

I assume the only way to actually fix it is to correct the wastegate setup like Savington suggested.


https://www.miataturbo.net/attachmen...ine=1418349118

except it would be like this:

https://www.miataturbo.net/attachmen...1&d=1418350711

i'd rather have the red plot all day long and night and year and century.

Enjoy your broken motor.

What if you run EBC and ramp up the boost to see if you can level off the boost all the way to redline. I really think all this is due to the 90 deg bend at this point it seems it may as well be internally gated. At the WG vent I think it would be ok to have bends but ideally I would think you would want that wg right on the port. (drunk thoughts)

Because all 95% of us here with this sort of torque output all have broken motors...

what I'm really suggesting is this:

https://www.miataturbo.net/attachmen...1&d=1418386217

if you want torque like you're suggesting why are you building turbo setups and not rotrex setups? the reason you install a turbo is torque and area-under-curve, not your pansy ass setup.


I had creep issues back on an old setup:

https://www.miataturbo.net/attachmen...ine=1418386724

http://i46.photobucket.com/albums/f1...s_solenoid.jpg

wanna guess which one of those configurations was better than the other?

it's also funny that my torque output, when holding boost flat, looks closer to what you drew...


having more torque at 7000RPM is much more dangerous than more at 4000RPM. I'd argue that the cylinder pressures at 4K in my examples are still less than that at redline. And that my friend is what bends rods.

Run it like this


https://www.miataturbo.net/attachmen...1&d=1418390640

Brain.

I have found that in order to hold torque dead flat from peak to redline you need boost to increase past 4500rpm. I have found this tuning stock motors with ms2 rpm vs tps boost control.

Holding flat boost will result in a drop in torque.

There for in order to hover at a specific torque (240 for example) boost needs to steadily increase past 4500rpm by a few psi, I tend to see 16 or 17psi at redline on typical 2560 setups. Some might describe this as creep. Call it what you will.

i don't wanna hold torque flat, i want to hold boost flat.

Enjoy your reduced performance.

Thread sidestep - Dan can you post an ebc table of what you are saying and how you work it?

The top row looks like.

95
95
70
12
15
20
25
30
35
40

I'll post one when I have my laptop.

I literally do pulls with 95%DC until it makes boost. Start at 5% from there and add boost until each rpm hits the torque limit.
I pay zero attention whatsoever to the boost or HP until it's done

:bowrofl: That fact that you've somehow convinced yourself that's having less torque is quicker/better performance and that having more boost at redline is safer makes it even better.

seriously, why aren't you toying with Rotrex superchargers?

Do you genuinely not understand or am.I being trolled?

No troll. I 100% completely understand how ridiculous you are. Otherwise I'd accuse you of trolling.

It's almost like you two are intentionally not actually reading what the two of you are posting.

That is not creep. That is a controlled ramp-up of boost to compensate for tapering airflow. Creep is something you can't control.

I know what you're saying though, I sometimes do the same

probably.

:dealwithit:

Reduced performance... what?

He'll get more out of it by having that boost on sooner vs taper up and having more power under the curve.

Power under the curve is the best thing about being able to tune a car. If you only want some peaky top end... BLEH.

Says the Honda boy.

Goddamnit.

He's saying hit your boost necessary to make your torque target, then taper up from there to keep the torque target from onset all the way to redline.

This gives you no less power anywhere, AND gives you more power up top.

with the assumption that torque output alone, not cylinder pressure, bends rods.

I would agree that, in an ideal situation, I'd rather make 15psi at 3K, then increase boost to redline to keep the TQ from dropping--which really isn't that dramatic on our motors in the first place if you can size the turbo correctly.

Then you guys are in agreement. Don't make me knock your heads together. :giggle:

DO IT!

Ideal situation, like everyone with megasquirt and a mac valve?

Oh ho ho... ima get you.

SAV has the right idea in my view. Your set up is little different than the integral gate.

The right angle mounting of the gate places the valve/flow relationship square on the same geometry as the integral.

The gate should never be "like this." Again, no different than the integral, save a bigger valve. A bigger valve ain't the problem.

Turn the vent from the exhaust housing 90 degrees, leaning it directly outboard. Literally, bore a hole straight out from the inlet flange through the scroll as it begins to turn downward. Patch the present hole.

This puts the wastegate on a path with the centerline straight out from the manifold exit.

While doing that, check the valve seat on the gate, also.

corky