Right now I enjoy the occaisional autocross or road track. My car N/A is plenty of power for this, mainly because it's almost too much car as is for my driving skills. However, I'm an idiot and just like to build stuff so I started a 76mm turbo build.

So for drag racing and street use i'd like to run probably 12-15 psi havent decided yet. Now if I wanted to go autox, could I just swap the spring down to almost 0-2psi, provided I have it tuned correctly for each setup? Are the wastegates this flexible?

 

You could run an extremely light spring to get it down to a couple psi. This is of coarse if the gate is big enough (flows well enough) to relieve that much exhaust to keep it from spinning the turbine wheel. Also gate placement will be key here too.

 

If your doing the front mount setup like most guys are doing, you can run twin wastegates. One on each runner before the merge for the turbo. Itll make for rock solid boost control. The problem i see with some guys wastegate setups on here is that there wastegate is mounted at a 90* at the merge. Problem with this is you can have exhaust flow past the wastegate causing boost creep issues. Its ideal to have the wastegate runner at an angle with the flow of exhaust to the turbo. That way when it opens, it has a clear easy passage through the wastegate.

 

^ That's a very good point. I was going with a single 44mm just like you talked about, i'm assuming I could just use two 38mm or maybe smaller.

 

This may sound like a stupid idea, but what if I just took the wastegate off? I know you can't run the gate without a spring because you can ruin them, but if you remove the wastegate provided the port was big enough no boost would build.

Would this damage the turbo at all? I know it would vent to atmosphere, but my car doesnt have cats anyways. I'd probably only be doing this when I was road racing the car.

 

i think the smallest spring is 3 psi

if you remove the wg you;ll probably effectively run no boost at least until redline. However, itll stink pretty bad and its a lot of unnecessary heat dont you think ?

 

Yeah just run the smallest spring. No way how you slice it you'll still have way more power than you'de ever need at an autox event. I am running a pretty much stock motor and we run our autox at a military base air strip and you go up the runway one way go across the cross over road and then come back on another runway, so its no where near as tight as some of the mall parking lot courses I've seen and I still cant go WOT for more than maybe a full second at a time before your back on the brakes heading into the next corner.

I doubt that with that power level you'll ever really be able to effectivly see WOT without blowing the tires off

 

If you run a light spring in the wastegate and then run a regulated air line to the top side of the diaphragm you can adjust the boost with a turn of the ****. If you set it up this way the lowest boost you will see will be spring pressure (3 psi, if you choose that spring), but if you clamp the regulated line down you can go so far to never letting the wastegate open. I've set up a lot of compund turbo diesel setups this way and it works great. The proper placement and sizing of the gate(s) will apply, of course.

 

The car will need to make SOME boost to get it back to NA power level ( see sig) As the big turbine wheel in the way kills power, if there is nothing being pushed in the engine

IMO, you need to run twin 44s, and the lightest spring possible. If you need to, cut the spring to maintain a consistent 4-6 psi, which will still be manageable.

 

Remember, the wastegate is just a regulated hole in the exhaust. removing it, it will still make boost depending on the size of the hole.

Also, remember backpressure has a lot to do with the minimum a gate will open. 3 psi may still open at 6, because the P/Rs are not high enough.

 

The wastegate opens by boost pressure. Not Exhaust backpressure. You disconnect the vacuum line on the wastegate and it will stay shut. At least my tial 44mm was like this.

 

Exhaust back pressure has a LOT on how a wastegate opens

Think about it

 

Im running twin 38s on my pt88 setup which I think should be MORE than enough to control boost down to a few PSI.

 

How much backpressure does it take? Cause it's alot of backpressure in a turbo manifold. There not meant to leak or open like that.

 

Personally i wouldn't gamble on not controlling the wastegate. It's your motor though.

 

High back pressure and the gate opens sooner. Lower back pressure and the gate opens at a higher boost, because its not helping open it.

Its really elementary.

 

Sorry guys but I'm wrong. So much pressure will open the gate. One thing you gotta make sure of is you have a really good wastegate placement. Otherwise no matter what spring you have, you could get bad boost creep.

 

Hmm, really not sure what I want to do.

Louis, say I had twin wastegates positioned well. If i took them off completely and the openings were large enough to create no boost. Would I be risking damaging the engine/turbo in anyway. My head is saying no, but i'm kinda new to the turbo crowd.

 

No you wouldnt but the tune would be off and it would be like having a horrible exhaust leak and probably sound ridiculous. Run both gates and get small springs to run 3-4psi and you should be fine

 

ummm, you could always run just off the wastegate springs and unhook your intake piping if you really wanted no boost. but your turbos wouldnt know the difference