nutz'00 Z28

iTrader: (16)

I just finished up my car and put it on the dyno yesterday. But I am having trouble with the wastegate holding the boost down. First off the car is a 98 camaro 370" PT88 truck manifold kit, l92 heads with carb intake, th400, 9" etc...I am running it off the wastegate(12psi) only, right now no boost controller. While doing the dyno pull it reaches 12lb about 4200rpm and holds it there until it reaches 5000rpm. Then boost starts coming on hard from there on out by 5600 its at 18 pounds and I have to let out of it. Any recommendations on what the problem is? Wastegate is a Tial 44mm with 12pound spring. I will post a couple pics of the location of the wastegate.

nutz'00 Z28

iTrader: (16)

The exhuast is about 5ft long all 4" stainless with mandrel bends and no muffler.

alwaysinboost

Where is your boost source to the WG referenced from?

nutz'00 Z28

iTrader: (16)

from the manifold. It seems to hold fine for about 800rpm then once the motor really start to spin it just seems to overpower and the boost goes up like a rocket.

alwaysinboost

do you have a port on the compressor housing you can use instead of the manifold?

alwaysinboost

it sounds like you're getting boost creep, which usually means the you're moving too much exhaust for the WG to evacuate. Is the path in & out of the WG smooth with no obstructions?

cablebandit

iTrader: (37)

i have a tial knockoff 44mm wg. I have my boost signal coming from the compressor housing...drilled/tapped a hole for a screw in barbed fitting. my turbo is around the same size as yours and i can get boost to go as low as 6psi.
One time i had a prob like yours was inside the wg. my knockoff has 4 setscrews that screw in against the valvestem that holds it in place with the diaphragm. One came all the way out and boost would bleed threw and go to 22psi....the other 3 were loose. Only help i can offer

nutz'00 Z28

iTrader: (16)

Yea its smooth no obstructions the pipe coming from the wastegate is 1 3/4" stainless its about 40" long with 1 90* bend in it.

My compressor housing has a place for a barb fitting in it, I will try running from there to the wastegate. I even tried taking the spring completely out. It wouldn't build any boost until about 5500rpm but then by about 6200 it was at 15lbs and climbing like a rocket.

EGash

iTrader: (17)

In your last post you stated that even with the spring out the boost would come on slow, then rocket past 15psi as the rpms climb. This is a good indicator that there is some restriction in the WG plumbing.

I see a long WG discharge tube, this could be the problem. Does it re-route into the exhaust at some point?

I suggest removing the WG discharge tube that runs down the passenger side for one run and see if you can maintain a lower boost level.

nutz'00 Z28

iTrader: (16)

I will try this tomorrow, whats the chances of the wastegate being to small?
I tried the compressor housing for reference and no change.

chasgiv3

iTrader: (1)

It's very possible that the wastegate is too small. I've seen this before on other setups. This is why folks buy the large racing wastegates or something similar to arrest the problems.

EGash

iTrader: (17)

Thats a possibility. I've seen some big turbo Supras get way with one Tial 44, but many run a larger HKS GT gate, and some use two Tial 44's.

alwaysinboost

If you tried the compressor housing for a boost source and it didn't help then I think your problem might be the result of two things, both related to the WG placement.

I that first pic above where you have the WG attached just below the turbine inlet, it looks as though the exhaust is going to have to make a sharp 90* turn and then travel up even further to reach the WG. That right there makes me suspect that you aren't able to vent enough exhaust to maintain the static pressure your WG is set to.

Does anyone else have a setup like this or is yours a one off? If so have they had simular issues?

Then in the second pic you have an extreamly long dump tube venting the exhaust gasses after they pass thru the WG. now, thats not nessicarly a bad thing, but if it doesn't VTA or smoothly merge into the exhaust path that could cause the kind of problems you are seeing.

I still have 2 other things you could try but I need to hear your answer to the above questions before I tell you about them.

nutz'00 Z28

iTrader: (16)

I made the kit myself, but I have seen people coming straight out of the merged section with the wastegate tubing. The tube goes back past the manifold then down about 18" and dumps onto the ground. Has anyone ever measured the travel of the valve inside the wastegate, Mine only travels about 1/2" still leaving alot of room for another 1/2" of valve travel before the valve bottoms out on the seat. Here is a example pic.

cablebandit

iTrader: (37)

havent checked mine for travel...i will next time i swap springs but that might be awhile.

nutz'00 Z28

iTrader: (16)

I disassembled my wastegate and did some clearanceing so that the valve would open all the way to the seat. Re-installed everything but I left the dump tube off and took it for a ride. First gear was fine it held 15psi pretty steady up to about 6500rpm then I shifted into second it went to 18psi and held there until I let out of it. So I guess the wastegate is to small. Has anyone ever ran 2 wastegate's on a single turbo car? It would be cheaper and easier for me to do this.

chasgiv3

iTrader: (1)

I've seen it in a blower design but never in a single Turbo design. A larger wastgate would cost about $425.00. Then sell your wastgate for say $100.00 that'd be about $325.00. What other costs are there? Unfortunately the larger wastegate will need to find a place to live since the physical size is larger. Also changing the tubing.

Phil99vette

iTrader: (11)

I think you need to move the wastegate, I'm no expert but IMO that is not a good spot for controlling boost.

nutz'00 Z28

iTrader: (16)

blower design? Cheapest large wastegate I could find was around $550ish.

alwaysinboost

thats weird, I didn't know blower used a WG to control boost, lol.