Tally TransAm

iTrader: (17)

On a rear mount setup (done correctly: coated manifolds, exhaust wrap, small turbo, etc) with with wastegate referenced at the intake manifold, is it normal to see slightly less boost than the spring pressure?

just finished a rear mount 05 gto (dont worry pics soon, came out great), the wastegate is SUPPOSED to have a 7psi spring in it and im seeing 5 psi at the motor and obviously down about 50 hp from where I want to be.

first check I will do is the wategate spring, then boost leak test. I was thinking being referenced at the manifold would see spring pressure but, im seeing about 2 psi less

Thanks

Nitroused383

iTrader: (10)

Most wastegates spring pressure are rated for a 1:1 back pressure ratio. If you have a little more back pressure they will open sooner and vice versa the opposite. Check for all the obvious things like you suggested first.

Tally TransAm

iTrader: (17)

i pulled the spring out of the wastegate (turbosmart ultra-gate 38mm) and it has a large purple and green spring which according to turbosmart is the 7psi spring.

didnt have the correct cap to boost leak test it so i will do that monday.

Do wastegate springs fatigue? I know this wastegate has been sitting (new in box) for 3+ years

nodrok

I wouldnt worry to much. It is more common with rear mount to see less boost. You can check your gate by simply depressing the valve with your finger and block of the to vent of the wastegate and see if it holds the valve open. Im sure its fine. Wastegate placement can also effect when your gate is opening. You may just want to run a boost controller or up to a 10 or 12 psi spring.

Tally TransAm

iTrader: (17)

yeah i did some thinking on it tonight and it makes sense itll just take a stiffer spring to make the desire boost. gonna see if he wants a different spring or just run a mbc

b4ckid02

iTrader: (8)

I have an sts kit with a 67mm Garret. When I was having my car tuned I had a wastegate spring in it for 7.2 psi according to the tial wastegate spring chart and the car made 5 psi at the intake. I put a spring in it rated for 10.1 psi and I made 8 psi at the intake. So I had about 2 psi drop

JoshuaGrooms83

iTrader: (2)

im starting to see a pattern here lol im experiencing this but on a huge level.
im still thinking i have an exhaust leak that needs to be pinned down with a smoke test but i have a T76 .96 AR On3 turbo, 44mm wastegate 10lbs spring, 31x12 intercooler, remount and i at best only have seen 5psi on the boost gauge. with a manual boost control (nxs boost controller) was the only way ive gotten 5psi. before i couldnt even get over 0psi.
is it just an inherent thing that rear mounts need to have larger spings to operate higher boost pressures? i havnt done a no reference test yet but im close to considering it

GMouldy

You'll gradually lose boost pressure with the longer charge pipes. When I had an STS kit I had 5psi full boost. When I added an intercooler I lost a few psi. Rear mounts take some work to get all the kinks out. Good luck

JoshuaGrooms83

iTrader: (2)

i was reading over zombies thread.... again lol., and it looks like he was running 14.7lbs spring and was only getting 10psi on his earily builds before he went further into it like he had. not sure if that had any bearing on whats going on here, but thought id mention it.

Nitroused383

iTrader: (10)

I could be wrong but I thought it was always recommended to run your wastegate reference to the intake manifold on a rear mount setup to avoid these pressure loss issues? Whats the point of referencing the compressor housing if it's making 10lbs at the housing and only 3 at the intake?

JoshuaGrooms83

iTrader: (2)

im seeing the same pressures between both. im still trying to figure out what the hell is going on with my exhaust though

Tally TransAm

iTrader: (17)

you got a leak somewhere


for what its worth on the year and a half old thread bump, we put an eboost street in and dialed it in. nice piece, but way to much **** to do with one button on the controller

rotary1307cc

iTrader: (5)

No one listens to this guy???


He is exactly right and you are still looking for a problem

Put a pressure gauge tapped into the turbine scroll and then compare that too boost. You will see why the waste gate is opening

JoshuaGrooms83

iTrader: (2)

im not the OP but im having simular issues.

im going to the exhaust shop to have any leaks welded up. found some this after noon after i did some spray and bubbles checking. idnt get any bubbles, but i got water coming out the exhaust tips... go figure.
im suspecting the cats. had leaks there before and i don tthink it got fixed.

however, you are right though. got some damn leaks to patch. also tightened some botls on the intake manifold and headers bolts.

JoshuaGrooms83

iTrader: (2)

i found this explantaion on another fbody forum that made sence to me:

Compressor outlet:
best control over wastegate in regards to response and ability to consistently control boost to a given value. The bad side is that torque -curve rise will suffer slightly as this source will create the earliest possible wastegate cracking point. This early cracking point will offer some relief thermally because the entire system will virtually never see more boost than the basic setting of the wastegate. This can be important in avoiding a quick heat soakin of the intercooler.

Intake Plenum:
will lightly imporve boost response since the turbo is free to take all the boost it can until the pressure reaches the signal source and is transmitted to the wastegate. The fact that the turbo is free to make a brief spike of boost will cause the intercooler to be hit by a greater slug of temperature. Greater temperature is always to be considered a negative. For a blow through carb system where the wastegate and fuel pressure regulator must see the same signal simultaneously, the plenum signal source is best.

Intake manifold;
only when turbo response is of the highest importance and the short blast of extra heat can be tolerated or ignored.