overboost / popping under heavy throttle

LITLV6

WESTSIDE LOWRIDERS
Need a little help or assistance possibly. I have an 86 GN with Turbo tweak chip, siemens injectors, stock turbo, adjustable waste gate, stock IC, built trans, and rear end.

so the problem i'm having is under full throttle i'm having the car pop back and causing 25psi of boost, should be only around 20lb. I have noticed that it seems as if maybe when it pops that its kicking the vacuum hose off of the Turbo? not sure if this hose set just went bad or if its something else? i checked the 2 other vacuum check valves on the driver side of the intake and the one going to the vacuum canister. i know that little hose set from the wastegate controller with the Y on it can be pretty problematic but i DO NOT know what it is that goes wrong with them? and is it worth buying the original style or just replacing it with a new Y and new hoses and having to route them so they dont get melted? any help would be appreciated!
 

750H.P.V6

Brutal 6 Racing
You need to get the boost under control or you'll be risking severe damage in short order. Even 20psi on pump gas without alky injection is too much in my opinion. Max allowable boost will depend on the available octane of the gas you get locally.

To keep you out of harms way while you trouble shoot this problem you should plumb the wastegate actuator directly to the compressor. This will lower your overall boost and you'll will be relying only on the spring tension of the wastegate actuator . When configured this way you should see approximately 12 psi boost.

If the boost is considerably higher then someone has swapped the actuator for a higher PSI version. The reason this is relevant is that this sets you base boost, the wastegate duty cycle commanded by the ECM increases boost above that. if the programmed wastegate duty cycle isn't correct for your actuator you'll have more boost than you need / want.

If you choose to use the stock turbo Y fitting configuration you can reuse the fitting itself and replace the hoses with 7/32" vacuum line hose. All vacuum hose isn't the same, get the thick wall hose if you can.

I hope this helps.

Neal
 

LITLV6

WESTSIDE LOWRIDERS
You need to get the boost under control or you'll be risking severe damage in short order. Even 20psi on pump gas without alky injection is too much in my opinion. Max allowable boost will depend on the available octane of the gas you get locally.

To keep you out of harms way while you trouble shoot this problem you should plumb the wastegate actuator directly to the compressor. This will lower your overall boost and you'll will be relying only on the spring tension of the wastegate actuator . When configured this way you should see approximately 12 psi boost.

If the boost is considerably higher then someone has swapped the actuator for a higher PSI version. The reason this is relevant is that this sets you base boost, the wastegate duty cycle commanded by the ECM increases boost above that. if the programmed wastegate duty cycle isn't correct for your actuator you'll have more boost than you need / want.

If you choose to use the stock turbo Y fitting configuration you can reuse the fitting itself and replace the hoses with 7/32" vacuum line hose. All vacuum hose isn't the same, get the thick wall hose if you can.

I hope this helps.

Neal
Neal, First and foremost THANK YOU for taking the time to help! I want to give you a little more info to go on about the setup. I run a chip from Eric at TT and it is setup for 100 octane which i run in the car. i actually wasnt getting any reading on the caspers knock gauge while any of this is going on so i'm not as worried about removing my head gaskets unwillingly just yet LOL.... but you have already taught me something.... i wasnt aware that you could be a higher psi wastegate actuator? Im wondering if this might be why i have always gotten 21 to 22psi instead of 19 to 20 like eric suggested that it should be from the chip he sent me!

so if i'm understanding you correctly i should be able to plum the vacuum line directly from the wastegate actuator directly to the compressor wheel and the then the wastegate can be set to a baseline? If so i will DEFINITELY do that! it has an adjustable arm on the wastegate as well so maybe i could back that down to 12psi so the computer controls it correctly?

so i have 2 questions that have popped into my head while reading this that may REALLY help me know a ton more about this setup.... .
1. is that little Y metered in some way or just restrictive in nature do to the I.D.?
2. should one side of the wastegate actuator not have anything on it at all? like just an open vacuum line port? one of mine has nothing on it and the other is attached to the Y setup?

knowing these couple things could help me tremendously! i was thinking maybe i was having an issue with a vacuum leak or maybe i just need to replace those 7/32 hoses on the Y setup?

I am also contemplating changing the factory down pipe since my exhaust needs redone and was considering a stock location replacement IC... If i really go that far am i crazy not to replace the Turbo as well or not? Ive owned the car since 2007 and i know some of what was done prior but i believe the valvetrain is original to the car. 92k miles original parts, built trans and rear end.

Again thank you for any insight or help you can provide!
 

750H.P.V6

Brutal 6 Racing
Just to be clear so there is no confusion, the actuator is on the turbo and the spring tension is adjustable, the wastegate solenoid is on the valve cover and is controlled by the ECM. The solenoid is a calibrated leak venting a portion of the boost signal to atmosphere thereby reducing the signal to the actuator itself resulting in higher boost.

The stock Y fitting has a metered orifice in one leg which you will see when you replace the hoses. The three connection points for the hoses will be the fitting on the compressor housing, the wastegate actuator and the other branch goes to the solenoid on the valve cover. Double check the hoses haven't come loose or have deteriorated.

To answer your question about the wastegate actuator itself, if you connect the vacuum line directly to the compressor you should get approx. 12 psi boost. If it is a couple psi more possibly the length of the rod has been shortened by a previous owner. If it is over 16 psi is would indicate it isn't a stock replacement actuator.

Neal
 

TIMINATOR

Active Member
"The valvesprings are original to the car."
Stock springs are too soft for 17 lbs IMHO. And yours are 35 YEARS OLD! The popping is likely from them.
Change the springs and retainers to heavier than stock (120# or more, is a good place to start, and I would be surprised if yours are more than 70 something now!) and get that boost under control before you destroy the bearings or head gaskets!
Then you can worry about the other things. Like plug wires and coil pack output.
AFTER you get control of the boost!
TIMINATOR
P.S. read my other posts about boost and exhaust back pressure under the valves, and how it affects EFFECTIVE spring pressure.
 

LITLV6

WESTSIDE LOWRIDERS
Just to be clear so there is no confusion, the actuator is on the turbo and the spring tension is adjustable, the wastegate solenoid is on the valve cover and is controlled by the ECM. The solenoid is a calibrated leak venting a portion of the boost signal to atmosphere thereby reducing the signal to the actuator itself resulting in higher boost.

The stock Y fitting has a metered orifice in one leg which you will see when you replace the hoses. The three connection points for the hoses will be the fitting on the compressor housing, the wastegate actuator and the other branch goes to the solenoid on the valve cover. Double check the hoses haven't come loose or have deteriorated.

To answer your question about the wastegate actuator itself, if you connect the vacuum line directly to the compressor you should get approx. 12 psi boost. If it is a couple psi more possibly the length of the rod has been shortened by a previous owner. If it is over 16 psi is would indicate it isn't a stock replacement actuator.

Neal
yea i understand that part.... .i was typing it back wrong saying actuator instead of solenoid..... i was tired as hell when i was typing that back lol... thank you for the tips! i will try to solve this thing tomorrow hopefully
 

LITLV6

WESTSIDE LOWRIDERS
"The valvesprings are original to the car."
Stock springs are too soft for 17 lbs IMHO. And yours are 35 YEARS OLD! The popping is likely from them.
Change the springs and retainers to heavier than stock (120# or more, is a good place to start, and I would be surprised if yours are more than 70 something now!) and get that boost under control before you destroy the bearings or head gaskets!
Then you can worry about the other things. Like plug wires and coil pack output.
AFTER you get control of the boost!
TIMINATOR
P.S. read my other posts about boost and exhaust back pressure under the valves, and how it affects EFFECTIVE spring pressure.
This is really good info to me. I havent ever dove into what all i should change on the engine to make it all work better. so few people understand these beasts. I have a suspicion that the coil pack could be part of my issue since that has happened to me once before years ago but i was more worried about vacuum leaks and stuff. at what point am i going too far? the valve springs will help a bunch i'm guessing but then what is the next weak point i need to address? i was thinking of doing a 3" DP and do all new exhaust since it needs it. the car has run through dual flowmaster 40 series since i bought it in 2007. i've always felt that they probably have too much back pressure so im trying to decide on mufflers and/or doing a switched cutouts... it would be cool to hear the buzzin half dozen without much exhaust lol
 

TIMINATOR

Active Member
You are on the right track. The 3" dp is a good place to start, as are the blowmasters.
Keep posting as you improve the car, and dont be afraid to ask about what you dont know before you waste time and money. Nobody knows everything. The guys that know about what you ask about, will help you, and the rest of us will all learn from them.
A dual 3" exhaust with low restriction, but quiet mufflers, will most likely run the same performance closed or with the cut out open for most folks. Unless you just want to hear it, spend that cash making it faster. JMHO

TIMINATOR
 

LITLV6

WESTSIDE LOWRIDERS
You are on the right track. The 3" dp is a good place to start, as are the blowmasters.
Keep posting as you improve the car, and dont be afraid to ask about what you dont know before you waste time and money. Nobody knows everything. The guys that know about what you ask about, will help you, and the rest of us will all learn from them.
A dual 3" exhaust with low restriction, but quiet mufflers, will most likely run the same performance closed or with the cut out open for most folks. Unless you just want to hear it, spend that cash making it faster. JMHO

TIMINATOR
any recommendations on who makes a good 3" DP stainless?
 

TIMINATOR

Active Member
any recommendations on who makes a good 3" DP stainless?
I deal with Jason at RJC. I bought my big SLIC, 3" dp, 62/62 turbo, and Scan Master G from him, among other things. His wife can take your order and give you some good info, but if you need a lot of tech, he may have to call you back. Dont be distressed, he will always call you back, just mebbie not immeduatly.
TIMINATOR
 
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