Trouble holding boost - Big 16G and Comp 200's

[andymoraitis]

Howdy All,

I've been banterting back and forth with Mike and Jon at Slowboy and also with my fellow wisemen about an issue I'm having with holding boost on my Big16G since the Comp 200's went in. Prior to the cam install, I had shimmed the wastegate actuator and she held 26psi like a champ. With the same shims in place, boost now reaches a max of 25-26 and then bleeds down to 20-21 in second or third. I've leak tested to 28psi and she's tight. Additionally, the A/F and timing are spot on perfect.

I'm not overly concerned since I know that the small compressor wheel is not able to supply enough airflow to meet the motor's demands. This is a given. Nor am I disappointed that I added cams since she pulls like a beast in all gears. I'm also not worried about meeting my goals of running 12.20's since fellow wisemen have picked up huge gains on cams even with falling boost.

My question is this though. Are there any strategies that I can use to try and hold at least 23-24 at redline? I've adjusted the MBC almost all the way down and while it creates a quick spike, boost still bleeds down. I've removed the shims and there's no difference. My setup is currently unported and I'm wondering if this would help.

Suggestions and feedback from the cammed 16G tuners out there would be appreciated.

Thanks,

Andy

 

[NewB2dsm]

I had this problem with my small 16g and comp cams 100s'. Granted i was having the problem before the cams.

I think what is happening is the turbo can supply enough air in the upper RPM to hold the boost where you want it. So the band-aids would be shimming which you have done, or pull the wastegate line all together and let it run as much boost as possible, if it still drops well you know its the turbo.

But really, I wouldnt worry about it. I was dropping boost down to 19psi from 25 on the small and i still ran a 12.12@112 i think if the damn thing would have held boost i could have crossed into the 11's but the evo 16g seems to be doing to trick so far.

Only thing i can think, perhapds try and shim again, although personaly i dont like that idea at all. Or Tear into the acuator and put a tuffer spring in. I did that but was scared to test it out. I have one at home with a 14.7psi spring in it.

 

[andymoraitis]

Kyle,

Thanks for jumping in. I've always admired your times and you've done great with the S16G. Interestingly enough, I may not have been seeing the boost I thought I was in the first place. My boost gauge has been erratic and I replaced it today with a new unit. I now show 21-22 dropping to 18-19. I'm going to re-shim the wastegate and see how much she'll take. Three washers was getting me around 26 psi and four washers puts me into to the 28-30 range. Considering how much it bleeds down, I'll try each and see what happens. I know it's a bandaid, but I know she was doing better with the shims in place.

I appreciate the help,

Andy

 

[40oz]

Boost pressure is essentially related to the accumulation of air mass inside the intake system. Since the 16G turbo can only provide so much air, the pressure will not be as high in the intake now that more "volume" is available per revolution. You'll probably have similar power even at the lower boost levels, but the short of it is that it's time for a bigger turbo. You could even risk hurting something if you try to flow too much through the 16G, although, I'm not sure just how fast you'd have to spin a 16G to make something bad happen. Basically, what I'm saying, is that there is a point where you could weld the damn wastegate shut, but you will NOT see higher boost, because your engine is "outflowing" your compressor.

 

[Syndicate13]

I was having the same symptoms on my small 16g and FP1's. Would hold 25psi until 5000 and then drop to 19ish at 7000. I largely sttribute it to the cams but I did notice 2 cracks around my wastegate flapper when I removed my 16g. Before the cams I did not have this problem but I rarely ran higher than 20psi.

 

[CanadianTSi]

This is what Happens when you raise VE

I doubt that there is really anything you can do that will make the turbo hold boost up top, although porting may help to an Extent, I would give it a shot

 

[andymoraitis]

We're basically reiterating what Mike from Slowboy mentioned in the first place. The turbo is the next thing to be replaced and I'll be sure to choose something that flows well with the rest of my setup (50 trim/20G, etc).

In the meantime, I'm going to do what I can to maximize the setup and get it to hold steady boost in the area of 22psi. If it will, I'm confident that it will hold up long enough for me to meet my goals and make it through the season.

Thanks for the input everybody.

Andy

 

[dsm-onster]

We're basically reiterating what Mike from Slowboy mentioned in the first place. The turbo is the next thing to be replaced and I'll be sure to choose something that flows well with the rest of my setup (50 trim/20G, etc).

In the meantime, I'm going to do what I can to maximize the setup and get it to hold steady boost in the area of 22psi. If it will, I'm confident that it will hold up long enough for me to meet my goals and make it through the season.

Cogratulations on actually maxing out your turbo!!!! Maximizing your setup will probably only include more traction control or better cooling (so that you can advance your timing).

All that you can do to hold 22 psi to redline is stop modding!

Second gear is a real good gear to tell you what your potential is (if you're not breaking loose). You state that you are dropping to 21 psi in this gear. Then, this is your limit. You're simply flowing more throught the block than the turbo can deliver at a higher boost. You cannot do any more to increase this other than drop your cams or clamp something up.

 

[jo1]

i'm having the same problem with my evo316g, the boost keep on droping after 6000rpm from 25psi to 22psi. After checking for boost leak it was found out that the BOV cannot hold the pressure long enough. After changing the BOV the car run happily until 29psi without any problem.

 

[90blacktsiawd]

Andy i'm sure you've already thought of this but i don't see it listed so i might as well throw it out there. Is there a possibility that you wastegate is blowing open at the higher boost and rpm's? I wouldn't be too surprised if over time, running those washers to tighten up the arm lead to it prematurely wearing out. Like I said probably not it and you've probably thought that already anyways.

 

[andymoraitis]

Andy i'm sure you've already thought of this but i don't see it listed so i might as well throw it out there. Is there a possibility that you wastegate is blowing open at the higher boost and rpm's? I wouldn't be too surprised if over time, running those washers to tighten up the arm lead to it prematurely wearing out. Like I said probably not it and you've probably thought that already anyways.

Acutally, I only shimmed the wastegate about 3 weeks ago to see how it would hold. I think the real issue is VE on the cams that I have. I'm going to re-shim sometime this weekend and see what it does. I'm not sure about it causing additional wear on the wastegate, but the simple fact is I just can't flow enough air through that wheel to supply what the motor wants.

I'll try a few things and see what happens. Thanks for the suggestion,

Andy

 

[andymoraitis]

i'm having the same problem with my evo316g, the boost keep on droping after 6000rpm from 25psi to 22psi. After checking for boost leak it was found out that the BOV cannot hold the pressure long enough. After changing the BOV the car run happily until 29psi without any problem.

I have a crushed 1G that was holding well on my boost leaks tests, but I may replace that with a Forge unit on the 24psi spring and see how it does along with a wastegate shim.

Andy

 

[90blacktsiawd]

I agree that it's probably not your problem, but it's easy enough to try a different actuator just to test the theory out. As for the washer wearing out the actuator. If you were only adding a washer i wouldn't think that would be an issue. But depending on the thickness of the washers your using i could see them putting additional strain on the actuator. I mean that's what that little mod is supposed to do. But i doubt after 3 weeks you'd have a problem.