Boost creep

[86lance]

What are the most common causes for boost creep? Car is an 89 daytona shelby with dual stocker intercoolers 3 inch exhaust dumping after the downpipe and a mbc with a vacuum black from mcmastercarr. I just put in a good quality boost gauge (autometer phantom) Turns out i was only running about 10 psi or so from going off the stock boost gauge. Anyways i went to up the boost a bit today to 12 psi. It spikes to 14 psi or so then settles to 12 where i want it then slowly creeps to cutout. So any ideas?

[Aries_Turbo]

the hole in the exhaust housing that bleeds off exhaust to control boost cant flow enough to prevent the creep. youll have to take off the turbo, port the hole (not too large or the puck cant seal) and put it back together.

or, socket the ecm and burn rob's 89 t2 cal over at D-cal http://autos.groups.yahoo.com/group/D-Cal/ to a chip and install... dont forget the +40's and a 3-bar map. I think thats easier than popping the head off to get the turbo off. :)

Brian

[86lance]

But you see it didnt boost creep before. I shouldnt have a problem running stock boost on a stock turbo. A vacuum leak can cause creep right?

[Aries_Turbo]

before what? the 3" exhaust? when you add a 3" exhaust the pressure differential is greater and requires the stock wastegate port to flow more to achive stable boost.

Brian

[86lance]

Yet some of the guys running mitsus can hold higher boost with a large exhaust and not creep? My garret must be possible. Also i have retained the stock 2.5 downpipe.

[Dave]

Mitsus have problems with creep. I've never had a problem when I used the good 'ol Garrett. It always hit the boost dead on. I ran 20psi on it all day long and it always hit on. Although mine was an '88 with the 2.25" SV and small can.

You could have a funky MBC. Or what I'm thinking, your WG can is weak. Try shimming the WG bracket and see if that eliminates or helps the problem.

In my opinion atleast 1psi spike is what I consider "normal." 2psi and more is excessive.

[86lance]

well if the can is weak i think i would get low boost correct? Im thinking it is my boost control so im going to try a couple more i have lying around. any idea if i can just hook the grainger valve directly between the wastegate and the intake source?

[Dave]

well if the can is weak i think i would get low boost correct? Im thinking it is my boost control so im going to try a couple more i have lying around. any idea if i can just hook the grainger valve directly between the wastegate and the intake source?

If the can is weak that could be why it's not holding the boost. It spikes because it simply can't bleed the boost fast enough through the WG, therefore it spikes, then it falls down to a lower boost point because the spring in the can just can't hold "14psiG" so the puck just flies open.

Try the boost controller and then try the WG. Changing MBC's is a little easier than shimming the can.

And yes you can hook the g-valve directly from the intake, to g-valve, to WG can. The nipple on the turbo is just a better source IMO.

[86lance]

Alright i can do that. But if i shim the can wont it open the wastegate can more?

[86lance]

alright well i went to the more reliable boost controller and the same thing. If not a little bit worse. Its connected as follows. Vacuum line from wastegate to a .025 mig welder tip. with a tee connecting to the spring side of the boost controller. Then the other side of the boost controller to the vacuum block on my intake manifold. Im pretty sure i have it connected correctly. Do I? So what whats left shim the wastegate?

[86lance]

Now if i shim the can with the some washers they have to go between the Wastegate can bracket and the compressor housing correct?

[86lance]

Anyone else?

[BadAssPerformance]

mitsu or garret?

[86lance]

garret

[BadAssPerformance]

The simple setup:

[Intake]----[Grainger]----[wastegate actuator]

If it creeps bad then you may have another issue/leak in the vacuum or exhaust somewhere as previously mentioned

[86lance]

hmm alright im going out to check everything else.....again

[BadAssPerformance]

see how it runs right off the manifold... we can look at it at Grove.

[86lance]

AH HA!!! found my problem jt. The damned vacuum line coming off of the compressor is torn.....and dangling on my transmission! LOL When i had the trans out for the clutch i knew it looked like it should be replaced and i guess so!

[BadAssPerformance]

Cool, glad you found the leak! :thumb:

[86lance]

Yeah its tons better now. Still creep some but its about 1-2 psi. So im getting rid of a few more vacuum lines and shortening some other ones that could use a trim. Any other ideas? the creep is really slowly if that means anything. Also there is NO more leaks right now. Unless the hvac stuf is leaking inside of my dash. Everything else should be good as i used the propane test last night.

[BadAssPerformance]

When it is creeping? rpm? sure it is not just slowly building more boost? if it stops it might be that nad not specifically creep... creep doesnt stop raising...

[86lance]

Ok yeah it never stops raising but it is pretty slow compared to before. I dont have a restrictor after the boost controller should i put the stck yellow restrictor in or a .025 mig welding tip? It starts creeping between 3k and 4k somewhere. Right in the powerband. If i only had it set to 7psi i wouldntcare because i could just let it creep and be fine but at the strip i need it at 14 psi.lol

[86lance]

A restrictor should go after the boost controller correct?

[MiniMopar]

My 88 Shadow with a Mitsu and an IC was a real pain to get the boost to hold steady. What I did was replace the vent restrictor between the actuator and the grainger with a bleed valve. Tuning this valve allowed me to keep better control over the boost and how fast it built-up between shifts (a trade-off). You may be venting too fast for the grainger to keep the can pressurized.

[BadAssPerformance]

You said you had a vacuum tap in the comp housing? Plug it.

[Aries_Turbo]

wait a min... if you have creep, it will rear its ugly head on a long, hard top gear pull. do one of those... if it eventually hits cutout, you have creep. if it stabilizes, you dont have creep.

sounds like you just have some goofy boost control.

Brian

[86lance]

Well it turned out being a bit of both. Goofy boost control as well as not one but two leaks in my intercooler piping. Going to remove the intercoolers in the morning and use some different clamps and some new hoses for it. Otherwise with the old clamps tightened its a TON better

[BadAssPerformance]

Yeah, was thinking you had a leak last night. If there was no leak I was going to suggest switching to a single stock I/C but if you're plugging leaks, thats cool. Glad you're making progress!

[MiniMopar]

Those rubber plumbing couplers are not "corded" at all and they don't handle the heat too well. After a while they start cracking and splitting. The next best thing is truck radiator hose. A truck supply store should sell it by the foot. The stock IC fittings require 2.25" ID hose.

Silicone and T-bolt clamps are the best, but I ran truck raditor hose with doubled-up worm gear clamps for many years on my Shadow without any problems.

[BadAssPerformance]

NAPA use dto sell the 'diesel' turbo hose by the foot too... tough hose right there

[86lance]

Well it isnt the plumbing connectors that are coming undone. Actually those are doing better than the rest of the car,lol The ones that are coming undone are actually truck radiator hosing,lol Because the intercoolers sit so darn low in the nose of my daytona they tend to be brave and scrap when going into driveways or something like that when im not careful to take them at an angle. So the way the two coolers are mounted together with metal allowed them to bend away from eachother causing one of the hoses to seperate from an intercooler. Im going to take the intercooler off of the car tomorrow morning and see if i can get some better hose clamps from the junkyard. I remember seeing some that come on small nissans like sentras that are basically mini t bolt clamps that are strong as hell.

[MiniMopar]

LOL, well there goes that theory. :) I think the plumbing stuff lasted about one summer before one of them exploded on me. I've seen those wire t-bolt clamps on various intakes. Probably better than drier duct clamps for sure. Then again, I've seen T-bolt style drier duct clamps too.

[86lance]

heh. Yeah. The connectors you saw on my intercooler piping seem to be alot stronger from the ones ive used before but eventually will get replaced when funds allow