Where to adjust? MBC or wastegate?

[tharussian45]

i have a quick question for anyone out there that knows turbo's well.... i have an 18g on a 99 gst and i have the boost set at 20lbs on the boost controller, but i was wondering if i should bypass that whole thing and just adjust the wastegate flapper..... it spikes up to 20lbs then drops off, so i maybe adjusting the flapper will get rid of that spike... anyone have any input?
thanks -alex

 

[freshlane]

Are you trying to boost at 20psi? The post is kind of confusing. I say use a MBC because that is what they are made for.

 

[95blackGsTurbo]

If you have an adjustable wastegate you can do that. The best thing to do would be dump all that and go with external wastegate but you shouldn't be losing boost. You are probably spiking to 20 and what you are resting at is your real boost you are set at.

 

[tharussian45]

ok, that makes sense. its an internal wastegate that was preset from the factory, so i threw a MBC on there. compliments to home depot. so if i adjust the internal wastegate flapper and turn the screw a couple of turns... that would be better then having the MBC on there..???

 

[95blackGsTurbo]

You can adjust it a little bit but not much. MBC will still be the best thing if you wanna go much over the set pressure. You may end up damaging something but adjusting too far.

 

[1stGenRocks]

it depends on where you are adjusting the wastegate.

lots of internal gates have a adjustable rod to set the preload on the flapper. this is good to make it spike a bit but hold higher boost, or lossen it a bit and it will spool slower but not spike. but you dont want to set the boost with this because your basicly just letting the flapper be partway open all the time.

some cars like srt-4's usually use a differnt type of adjustable gate. im not sure exactly how it works but you actually set the spring pressure controlling what psi the gate opens at.

or you can swap out springs if your wastegate comes apart like most tial/hks/ etc

 

[MrBoxx]

What vacuum line are you tapping for the pressure signal to your MBC?

Is the 18g ported at all?

 

[tharussian45]

18g is not ported. the vacuum line goes from the wastegate to the MBC to the IC pipe right before the TB.

So i was thinking..... and maybe i can adjust the wastegate to be set at like 17 or 18 lbs without spiking, and then use the MBC to set it to 20lbs. would that be a possibility? or should i just bypass the whole thing and adjust the wastegate arm in a bit more so that it can hold more boost?

 

[spaceball]

18g is not ported. the vacuum line goes from the wastegate to the MBC to the IC pipe right before the TB.

So i was thinking..... and maybe i can adjust the wastegate to be set at like 17 or 18 lbs without spiking, and then use the MBC to set it to 20lbs. would that be a possibility? or should i just bypass the whole thing and adjust the wastegate arm in a bit more so that it can hold more boost?

do you have your gauge tapped in at the same source as your wg?

 

[tharussian45]

no. its tapped in on the throttle body vaccuum lines with a T. it's over by the fuel stuff which is on the Cam gear side of the motor...