cumminsdriver635

Well... I modded my 12cm by making my own adjustable wastegate, porting the mouth out just a little, and drilling the divider. Put it on a few days ago figuring spoolup would be much quicker, and that I would really like it. Well; I can tell much difference at all in spoolup, and my egt's have went up a little, and I cant help but feel like I lost a noticeable amount of power.... When I first put the 12cm back on, I had my wastegate(homemade turbo master pretty much) adjusted to about 30 psi. I bumped it up to about 38psi, and still down on power a little with higher EGT's, and not really much better spoolup. I figured it would spool quite a bit faster with about the same EGT's, and definatley no less power.... Not so. I am putting the 16cm back on tomorrow. The only thing I like better about it is that I now have a slight whistle at idle, and it revs better in neutral. It will now rev to 3400rpm without popping when warm as upposed to about 3200rpm with the 16cm housing. But like I said... The 16cm is going back on first thing tomorrow, and it will be there to stay. I have abn 18.5cm off a 1st gen laying around... Maybe I need to try that? Naa. I just figured id like the 12 a little better all around, but I dont. Just figured id let everyone know my experience, and see what you all think about it... Anyone else noticed the same when switching?

Eric

STACKED

can you tell me whats better, wastegate open with less boost, or blocked with most boost. got a stock hx35 i can see about 38 psi with wastegate blocked would it run better with adj elbow?

rockjeep73

drop it down to 32-35psi

cumminsdriver635

They say about 32-34psi is the best for a stock hx35 with 12cm housing. It keeps them in their efficieny range. Much over 34psi and you are just pushing hot air. That said; I think 38psi is fine, but I wouldnt go over that. You can buy a manual boost controller on ebay for pretty cheap which would be better than the elbow because it has more adjust ability. You wont notice any increase in power by putting it down about 4psi, but possibly just barely lower EGT's. I personally wouldnt worry about lowering it from 38psi. Hope this helps

Eric

rockjeep73

cumminsdriver,

the 12 housing should spool up a lot faster as long as the wastegate is holding shut at lower boost levels and with the drilled divider it should flow as much if not more than the 16 housing.

Artsi_L

I'm surprised by this find.
Could the 12cm housing have wastegate creep present, or wastegate flapper not sealing properly?

cumminsdriver635

Believe me guys... I thought it would spool a lot faster too. I can tell a little difference in spoolup, and cruising boost is higher; just not what I expected...I think the wastegate is sealing fine because once it gets boost it holds it fine. I think maybe its just that my torque converter is so tight it is keeping it from being able to spool very fast.

Eric

SHARPMACHINE

635,


Seems like I remember you saying that the 16 seemed worse than the 12 when you first installed it? I would look closely to see that your gate is working right. Maybee some of the well versed guys in turbo knowledge will chime in.

Artsi_L

At the end of an office day I made a few calculations for fun.

How to check wastegate for creep at half way point to a boost build up to a max of 35psi.
We have two forces acting on opening the wastegate flapper, the actuating mechanism, and straight head on exhaust pressure against flapper gate.

A conservative assumption for drive pressure is 1,5 times boost pressure. Let's assume the wastegate flapper bore is 20mm's (i.e. 0.78"). This will net us 0.47 square inches of surface area.
At half way point of boost build up to designated 35psi, we have 17.5psi of boost. By a fair 1,5 time drivepressure assumption rule of thumb, we have around 26.2psi of pressure within turbine housing. This pressure is pushing our flapper open through that 0.47sq inch opening, causing around 12 pounds of force to jimmy it open.

By my assumption, we could check out wastegate operation on a workbench by attaching a spring worth 12 pounds of pull to the very center of flapper itself, and leading 17.5psi of pressure (from a spare tyre for example..) to the wastegate operating actuator.

If our wastegate can still hold flapper closed - we're in the clear, and wastegate is in mint condition.

Above situation was at half way point to max boost build up. Ideally wastegate should remain absolutely closed until max boost is reached, and then open up to vent off excessive exhaust gasses.


I guess practical real world measuring method could include installing a mere electric switch onto wastegate actuator arm. This switch could light up a small lamp/buzzer when actuator arm moves more than 0.1 inches.

Time to go home and do something productive...

cumminsdriver635

Yep. You are right. When I first put it on I was pegging my pyro doing a 0-70mph or so WOT run. I put the 16cm on hoping it would cool it down a little. I noticed spoolup was just a bit slower, and that I had lost no EGT's so at the time I didnt like it as well. Keep in mind this was with the stock torque converter and timing... I advanced the timing to 16*, and my EGT problem went away. When I put the Goerend TC in; that is when my spoolup got hurt. Almost any turbo will spool fast with a stock torque converter They are so loose that it allows them to spool quick. So now I put the 12 back on thinking it would make a big difference in spoolup, but it doesent, so..... I dont know. Im pretty sure my wastegate is holding closed fine. I had the cover off the wastegate, and it seemed to work fine with no binding up. I also took my buddy a ride in it, and he agreed it doesent feel like it has as much power. Either way; it just doesent run as good, or spool up that much better, so I am swapping her back out today.

Eric

STACKED

thanks for info but i am understanding right your wastegate can still open if it is completly blocked off at the turbo. and if you have your wastegate hooked up or not blocked it may spool faster.i see 38 psi but spoolup dosn't seem that fast, mine is completely blocked. i dont know if i just want more power or what.