Trouble building boost
Thread Starter
Joined: Sep 2007
Posts: 4,188
Likes: 292
From: woodbine, md
Trouble building boost Having trouble getting boost, 5.3, VS 78/75, gen 3 44 mm wastegate. According to the site, both springs should get me 10 lbs, but only see 3-5. Using a 4 port mac, using the MAP sensor as dome for now. I have a small air filter on it, wouldn't think its a problem with low boost, but will rem it next test. I ordered a sensor to run dome pressure, so will switch to that. In the meantime, I would like to find the problem. If I pull both lines off the WG, or leave one from the turbo to the bottom port, shouldn't that give me the 10 lbs, eliminate all the other stuff. Been lucky on the other cars and haven't had to trouble shoot, so trying to find a good starting point. Pretty sure it's not a boost leak, ck'ed over all the conns (FMIC). Car runs great, actually pretty peppy for what it is now, just needs more boost, lol.
TECH Addict
Joined: Dec 2004
Posts: 2,178
Likes: 627
From: Florida
depends on lots of things. if you have excessive backpressure, that pushes on the valve to open it which reduces the wastegate spring rating.
i dont really put a lot of weight in the rating of wastegate springs. i generally just pick one thats on the low end then use solenoids to go up from there. my current setup should have had 10psi springs but it made about 6.8 on gate only.
be aware that 4 port works well but does have a fairly narrow range that it controls boost. i was seeing 1-2 psi changes with like 1% duty cycle changes in certain ranges, and almost no psi changes across 10+ % changes in other areas.
a good starting point might be to use open loop boost control and just throw 20 or 40 or whatever % at it and see what happens.
i dont really put a lot of weight in the rating of wastegate springs. i generally just pick one thats on the low end then use solenoids to go up from there. my current setup should have had 10psi springs but it made about 6.8 on gate only.
be aware that 4 port works well but does have a fairly narrow range that it controls boost. i was seeing 1-2 psi changes with like 1% duty cycle changes in certain ranges, and almost no psi changes across 10+ % changes in other areas.
a good starting point might be to use open loop boost control and just throw 20 or 40 or whatever % at it and see what happens.
In a perfect world, one line to the bottom (none to the top) with 10lb springs should net around 10lbs. Run a straight line to the lower port with nothing else and verify the boost level. I always put shop air on it with a regulator and see if its actually cracking at 10psi. Be sure its working on the bench correctly first. Then trouble shoot why its not on the car. Its likely the BC putting additional air to the dome. How do you have the 4 port plumbed?
Thread Starter
Joined: Sep 2007
Posts: 4,188
Likes: 292
From: woodbine, md
I have A going to the top port, B to the bottom, vent is opposite of A, comp. to port opposite of B. If the Mac valve isn't working, boost would go thru B, and try and open the WG, so I need to verify its working. Still it would have to fight spring pressure. I tested the blowoff valve, it took about 15" to open, its adjustable, pretty sure it is staying shut under boost, although I could pull the line and test. I wouldn't think back pressure is a problem yet, 3" to the rear bumper, one straight thru muffler. Turbo has the .96 AR, 3" out, same setup I had on my Hornet. They keep building houses out here, so the good spots to test are shrinking, lol.
