Has anybody ever used a Stone Mountain Racing Wastegate? They are loads cheaper than the other wastegates of the same size. I remember reading somewhere that they are using an old hks mold or something but I can't seem to find the post in the search function. Any experiences out there before I pick one up? Thanks guys.

 

If this is the Stone Mountain Racing stuff you find on ebay, avoid it like the plague. Their stuff is really low quality. There are a lot of guys even on the turbo honda boards that notice their "top of the line stainless steel" manifolds cracking and splitting after getting heat cycled a few times. I've heard too many stories also on problems with the wastegate spring sagging under pressure and blowing the seals - either jamming it open or jamming it shut. Stay away from Stone Mountain stuff.

You can get a new Tial 38mm wastegate for like $205 shipped usually. If that's all you need, I'd reccomend Tial, or a turbonetics unit.

 

Yeah, it's the stuff on ebay. I'm not exactly sure what size I'll need, but I figured bigger is always better with wastegates anyways. I've got a 393ci with a T76 with a 1.0a/r ptrim. I was hoping for 600chp so I think I'd need something bigger than a 38mm.

 

I've got a 353cid with the PTK setup and a GT45 with pretty much the same A/R as you have - and I'm using the 38mm Tial. I'd talk to Jose at Forced Inductions on what he thinks - depending on how you're running things it might be all you need.

Edit: And my goal is 650-700rwhp on pump gas...

 

Talk to Jose about it.

 

its the opposite. You need a larger wastegate if you run large amounts of boost. More boost, more cylinder pressure, more exhaust gas

 

It seems to me that you need a bigger wastegate for low boost, because you need to bleed off alot of boost. If the T76 will spin 20psi no problem and he wants to run only 6psi, that wastegate needs to evacuate alot of psi. To me a bigger one would get it done better than a smaller one.

 

Actually its a bit of both. If you take a given engine and you want it to run 6psi, there is alot of gas that you have to bypass to keep the turbo from spinning up to high. However, if you run high boost you then have more air flowing out of the exhaust due to the extra boost so then you need to bleed off the extra flow from that. Kinda like a catch 22.

Alot of it depends on your a/r ratio on your turbine housing. If you've got a .6 it won't take much to spin it up and then you need to bypass the rest, where as with a 1.3 you're going to be able to push alot of air through it without needing to open the wastegate much.

Well, if those ones on ebay are junk I guess I'll see if I can pick up a Racegate from somewhere. Anybody selling one or know where I can get a good price on one???

 

Not sure why you think its a catch 22? Sleeper orignially said you need a larger wastegate the more boost you run. That doesnt sound correct at all. Running low boost on a turbo, doesnt matter what size for example purposes, then the wastegate needs bleedoff alot of boost for you to maintain your low boost setting. Lets say the turbo maxes out at 20psi and you eant to run 6psi, then the wastegate needs to bleed off 14psi in a hurry. Thats why you want a bigger versus smaller wastegate. A small one may work fine, but going bigger doesnt hurt. Going bigger on the waste gate should also be related to size of turbo T60, versus T76 versus T88...etc. Now for high boost, you dont need to run a bigger wastegate because the toughest job for the gate should be at low boost. Going back to the example of 20psi max, no lets say you up the boost from 6psi to 18psi. Now the wastegate only needs to bleed 2psi. Therefor, running "more boost does not require a larger wastegate". If you have the correct size wastegate for the correct size turbo, then the wastegate would have an easier time with high boost versus low boost.

Thats my take on it. Maybe Jose can chime in.

 

The discussion was that you could use a smaller wastegate running higher boost. But look at it in cfm. How much exhaust do you have with 6psi compared to 18psi? Obviously you have more with 18psi and once the turbo is spooled then it doesn't take too much power to keep it going.

Also turbo's don't "max out" at a given boost, they just tend to keep spinning until they destroy themselves.

 

I agree about being able to use a smaller wastegate at higher boost. I understand the cfm aspect, and I agree about more exhaust with more boost. What you are saying is opposite what I am saying as it pertains to the function of the wastegate. At higher boost, the wastegate bleeds off less psi then at lower boosts. Like you said the more boost the more cfm, so when the is car running at a low boost setting, it has to have a waste gate discharge lots of boost to maintain the low boost setting, which is lots of cfm it needs to discharge. So to me the low boost setting the car will run at would be most challenging for the wastegate, not high boost.

 

I guess I don't have enough real world experience to contradict everything that was said. The way I envision a graph of boost vs wastegate valve opening is shaped like a u(flattened out a bit). To get zero boost you end up with it open and at the opposit end you get it wide open again because of boostcreep that we all know about. And somewhere in the middle is a "sweet spot" that it was designed to flow. The key is to make the sweet spot where your maximum boost is at, hence a properly sized wastegate.


This may be the case and could be a generalization, but the turbo, piping, and placement of the wastegate play a large enough factor that each case needs to be looked at to determine proper sizing of a wastegate.

 

In this post you explain your thinking for the "catch 22" you mentioned earlier. I see what your saying now. All I was really stating is that the wastegate has to bleed of more cfm/boost when the wastegate is set at a low psi setting. Thats my understanding of how a wastegate works. It bleeds off boost to try and maintain a certain level based on the springs in the gate. I dont think we were arguing opposites here, I think were are both thinking the same thing, just the words arent quite matching up

Also, boost creap is when a wastegate is too small for the application correct? thats why I said bigger is better.

 

Boost Creep is where your wastegate is too small - so small that it cannot flow enough air to keep the turbo from spinning FASTER, and thusly more boost and more boost and more boost till the car blows, you are correct in that.

Issue here is you need a decent wastegate, relative to the turbo (specifically the turbine housing, more or less). On lower RPM/Boost it doesnt need to be very large. The issue you run into with low boost is low boost at HIGHER rpm. Then you have to keep a lot of flow out or you'll spin the turbo faster. Keeping that amount under control is an issue, as you can imagine...

Other then too small for low boost and too small for high boost and creeping, there still is the issue of it being too large. Usually this isnt a problem, but it can be.

If the spring in the wastegate is too weak, when the pressure in the exhaust manifold increases to a certain point, it might just push the wastegate open (as the valve is larger, more force against it now), which may even lower the amount of boost you're running, no matter what you try to do. I've seen this one with guys using turbos that are too small for the amount of boost they want to run and are often internally gated (from what I've seen) or guys that have a tiny turbo and a HUGE wastegate. I've also seen it from guys that dump the wastegate to atmosphere, but usually it's not an issue for them as when you do that, you do it right or you're a fool...

The next issue you have is that wastegate opening. Now normally you want to vent pressure, and that is true, but if the wastegate were too large, for example, you'd end up slamming open and closed very rapidly and fluttering the wastegate - which is bad for your turbo (not too bad though) but it is bad for the wastegate and will eventually wear out the seals.

Also, the last thing to remember is the frame size of the turbo. As much as the A/R is important, you can have an A/R on a large frame or a small frame. Difference will be how much psi is between the turbine housing and the exhaust valves...

Too big is just as much an issue as too small. The wastegate size will be determined by engine, valvetrain, heads, exhaust manifold/header design and style, turbo, and exhaust (yes, exhaust also matters!)

But Jose knows more about this stuff then I do...

 

Not to be a dick but you obviously have no experience with the topic. I can run my turbos up to 50 psi if I wanted to. Smaller wastegates will give you problems up high not down low. With out writing a book here is a small example. The more power you make the more wastegate you need. When im running 1200hp out of my motor im creating more exhaust gas then I would if i turn it down to make 700hp. Thus, if the wastegate is all the way open open at 1200(25psi) and I want to turn it up to 30psi and im now potentially making 1300 at this level, my wastegate was all the way open at 1200 I have no more wastegate left for the extra exhaust gas, thus boost creep. MN_vette call precision or limit and they will tell you the same thing I did