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Old 04-08-2008, 10:11 PM   #21
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Just remember, you should never hook your WG signal line to the manifold after the throttle body. Heavy vacuum when the throttle is closed will pull the diaphragm the wrong way over time thus damaging it.
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Old 04-08-2008, 10:35 PM   #22
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Ooook... very strange, I didn't touch the car at all and got in it today to go drive around, got on the gas in second gear and saw 7 psi... but the car doesn't really feel faster than it was....??? Did several pulls, no pinging, deffinately 7 psi and tapers to 6 psi near redline... I DIDN'T DO ANYTHING TO THE CAR... It's like it woke up today and decided to work... but even more odd, it doesn't feel any faster than it did when the gauge was reading 4.5 psi.
GAGH!
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Old 04-08-2008, 10:38 PM   #23
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What port is your boost guage hooked up too? Was it colder outside. If your AFRs are overly rich that couple extra PSI won't feel that much better due to the overly rich mixture.
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Old 04-08-2008, 10:56 PM   #24
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The vac line for the gauge Tees off of the vac line coming out of the top of the IM right after the TB. That ok?
Yes it was colder, and the car was not as warmed up as I normally wait for it to be before gunning it.
Don't know about A/F - the wideband is in the kitchen right now...
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Old 04-09-2008, 12:32 AM   #25
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I was poking around your car while you were sitting on the grid waiting for your runs.

Definitely get rid of the stock weaksauce DP and go 2.5 inches all the way back like BenR and Gay-dar suggested. That will have the most impact on your spool. Not much to add about the GReddy wastegate. That shiznit needs to go.
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Old 04-09-2008, 12:58 AM   #26
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about helper springs: how strong does the spring need to be to help hold the wastegate closed during spool? I picked up a small spring from home depot and it doesn't seem to be helping.
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Old 04-09-2008, 02:32 AM   #27
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It needs to be a pretty beefy spring. Judge it by the tension that the wastegate can has, you'll want it to be heavier. When I used one on my Greddy I made it adjustable so I could tweak it. Got a very consistent 9psi on it with out a boost controller.

You could also shorten the actuator rod or shim the can to create more tension, but then you risk boost creep because you've limited the amount of travel of the wastegate.

You positive you don't have an exhaust leak BEFORE the turbo? When I had one I unplugged the signal from the wastegate can and couldn't boost more than about 6-7psi. The exhaust leak was really inconsistant too, one day I could do 9-10 psi, other days I could barely make 6psi. Once I investigated it was clear.
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Old 04-09-2008, 02:44 AM   #28
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Regarding the helper spring, check this thread from awhile back:

https://www.miataturbo.net/forum/sho...=helper+spring

The Home Depot part number and specs for the spring I used on my GReddy set-up:

SP-9608: 11mm x 6.4 cm x 1.2mm, 11.5 lbs

Some of the coils had to be stretched out a bit or boost would easily hit 15 psi. It worked fine, but over time metal fatigue on the spring just caused the boost to drop again. I'll tell yah, frustrations with the GReddy wastegate was one of the reasons I finally just gave up on the system. I'd suggest just looking into a wastegate replacement now rather than messing around with helper springs and all that.
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Old 04-09-2008, 02:53 AM   #29
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I've got a brand new wastegate actuator that can be modified (Joe Perez has a thread on it) to work with the Greddy.

It's this one:
http://www.flyinmiata.com/index.php?...umber=02-70576

$40 + shipping
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Old 04-09-2008, 03:03 AM   #30
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Old 04-09-2008, 03:59 AM   #31
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Dang, thanks everyone for so much great info in one place here.

FHS - I saw the spring you mentioned at Home Depot but thought it looked too stiff, bought a softer spring, tried it and it does nothing lol. I'll be going back tomorrow to get the same one you used.
A helper spring is by no means an end solution for the situation, but I'll try it and see how it goes.

Quote:
Originally Posted by jayc72 View Post
You could also shorten the actuator rod or shim the can to create more tension, but then you risk boost creep because you've limited the amount of travel of the wastegate.
This peaks my interest a whole lot - as it is, my actuator is shimmed (washers) farther away from the wastegate - same effect as if I shortened the rod. I kind of thought in my head that would effect how the wastegate opened/how much... could you elaborate a bit? I don't actually know what the definition of boost creep is. As of now, with the spacers, it jumps to 8 psi then drops back down to a steady 7 psi and tapers to 6 psi at redline...

As for exhaust leak pre-turbo, that could only be happening at the head to manifold point or between the turbo and manifold... these two locations are held together by a lot of large bolts that are torqued quite a bit... how could it be leaking?
Could a post-turbo leak effect things? I didn't have the proper size bolts/nuts for the connection from greddy DP to stock lower half DP so I used what I had which were still grade 8 but smaller diameter than should be used there. So, I suspect the two halves of the downpipe aren't mated together very well...


-Ryan
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Old 04-09-2008, 04:17 AM   #32
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Boost creep is when you overboost due to the wastegate not allowing enough gases to bypass the turbine. It's either caused by not enough wastegate travel or poor flow through the wastegate opening. Common things done to cure boost creep include fixing the wastegate travel, porting the wastegate opening, and getting a smaller exhaust.

You won't have to worry about boost creep with the Greddy unless you mess with how much the wastegate opens.

An EXHAUST leak after the turbo won't affect spool.

God I'm a freakin turbo encyclopedia.

Last edited by Bryce; 04-09-2008 at 04:30 AM. Reason: Exhaust
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Old 04-09-2008, 04:27 AM   #33
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Quote:
Originally Posted by Bryce View Post
A leak after the turbo won't affect spool.
But it will directly effect manifold pressure and thus what the engine gets and the boost gauge reads.
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Old 04-09-2008, 04:29 AM   #34
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Exhaust leak.

He's talking about between the turbo and downpipe, I didn't clarify.

Yeah an intake leak after the turbo would be bad.

Adding that to my post.
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Old 04-09-2008, 04:35 AM   #35
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Oh gotcha.
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Old 04-09-2008, 02:46 PM   #36
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Gotcha. I'm going to go home and remove the spacers between the bracket and compressor and then see what happens now that the car is miraculously doing 7ish psi instead of 4. If I lose too much boost, I'll try to mount a helper spring...

So a helper spring is basically a more ghetto version of a manual boost controller? Or do some use a mbc with the helper spring? Do they cure different issues?

I also need to get correct size bolts and sort out my downpipe connection... I would reallllly love to get a new DP but with the 700 I'm saving up for megasquirt, another 100+ for injectors, the 200 I just spent on alignment and mounting new race tires, 300 I'm spending in a week to get Shaikh's Fatcat adjustable spring perches, and assorted little stuff I'm kinda maxed out (not credit - I don't use credit) maybe I could find a local place to fab something like urgaynknowit did...

-Ryan
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Old 05-15-2008, 01:16 AM   #37
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Quote:
Originally Posted by cjernigan View Post
Just remember, you should never hook your WG signal line to the manifold after the throttle body. Heavy vacuum when the throttle is closed will pull the diaphragm the wrong way over time thus damaging it.
Zombie threaaaad. I was just wondering... how about with an MBC? A ball and spring MBC works like a check valve, doesn't it? That should keep the diaphragm away from most of the vacuum, I figure.
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