CAI, turbo and surge

Rainman

Member
:
2006 Black Mica MS6 GT + 2007 MS3 (2003.5 Yellow MSP = retired)
With my CAI installed I notice that the engine surges alot with throttle transitions. Jersey explained in another post that it was from air bouncing off the closed TB back onto the turbo. I only noticed this problem after the CAI install and not with the stock airbox. How do you avoid this unpleasantness?

R
 
(lol) The only way to drive.

Seriously though, how do you do it. I'm considering a CAI in the future and don't want any "unpleasntness."
 
On a 550 km drive home from the inlaws I tried to pinpoint when I get the surge. First, I realized that it only happens when the engine is under load and then I mash it. If I used a steady progression of throttle input I didn't get the surge to any noticeable degree. Second, I noticed that it seemed to happen mostly at peak boost. It would surge initially and then I would let off the throttle momentarily. This would be followed by one or two "after-surges" when I got back on the throttle even if I was gentle thereafter. After the boost pressure dropped then everything was normal again.

After thinking about what Jersey previously wrote and about the timing of the surges I now believe that it is a function of the CAI design. Mine I designed by myself so it is a trial and error thing. This may have been explained in the forum previously, but I didn't have a chance to look for it. My thought is that since our BOV is recirculating with a CAI there is limited amount of area where the recirulating port can be located. In all the designs that I have noted, the port has entered the CAI at a right angle. Under load and with WOT, the turbo attempts to spool up quickly. In so doing it reaches its peak turbo outlet pressure (stock = 6.5 PSI). Once this happens the BOV opens and recirculates the excess air, under pressure, into the CAI. Since this air is already under pressure it rushes into the CAI quickly disrupting the streamlined flow of air already present in the CAI. This turbulent air hits the turbo fins and causes a momentary loss of power.

The obvious solution is to place the recirculating bung as far from the turbo inlet as possible. However, the farther it gets from the turbo inlet on such a short length of pipe as the CAI, and the closer it gets to the MAF. I have read on the forums that turbulent air close to the MAF, such as with some aftermarket CAIs, also causes problems. The trick is to find the sweet spot where neither the MAF or the turbo inlet flow are affected. Check out our stock intake and you will find that the recirculating bung is quite far (12-18 inches) from the turbo inlet. Maybe the funky Mazda design of the intake was for a reason...LOL!

I will have to tinker with the design of the CAI to see if a different placement of the port makes a difference. I also wonder if it makes a difference whether the bung enters the CAI at less steep angle (e.g. 30 degrees) rather than the right angle that is typical.

This is my own thoughts about the issue and it may be completely wrong, but it seems to make sense to me. If someone thinks or know otherwise, I am happy to learn.

R
 
Serves you right for putting a cai on a turbo car what were you thinking (lol2)
 
This has been thoroughly covered. The surge isn't any different with the stock box, you just can't hear it as well. Just like your turbo isn't as loud spooling up with the stock box. Its a pretty good sound damper.
 
I thought that the turkey was just the sound from the BOV. The sound I can live with. The stalling was taken care of by recirculating rather than atmospheric vent (since I wasn't going to go right out and do the dual BOV/BPV setup). But the surging is a different beast altogether. I just took it out again and there seems to be two different types of surges. One that comes on right away once into boost with moderate load. Minor hesitation. No real loss of power but it feels as if it just isn't accelerating as hard. The other more annoying surge is the one that comes on with WOT that causes the car to almost buck if I don't let up. This I didn't expect and have never equated with the "turkey." If this is the turkey then I can understand why lots of people don't like it.

If this is the turkey, why are there two different types of surge. Also, does the turkey happen with every car that vents atmospheric?

R
 
The BPV does not cause the turkey sound, but its involved in it. What happens is that the BPV blows built up pressure back into the intake when appropriate (like when you shift, or let off the throttle after boosting). This air goes into the intake and runs into the turbo, which is whizzing along doing its own thing- this causes all kinds of turbulence in the intake as the air runs into the compressor. That's the turkey noise you hear. People don't like it because its not good for the turbo itself. Really won't cause problems at the low boost levels of stock, but would likely become an issue if you raised boost enough.

Blowing off the pressure to the outside would be the easiest fix, except for one problem- our cars have MAF meters, which only know how much air has passed by them in one direction (toward the engine). If you vent out ot the aptmosphere, you'll trick the MAF into thinking there's more air in the system than there really is, which will cause too much fuel to be delivered. This is why folks who tried venting out to the aptmosphere had no turkey noice, but stalling problems. Folks figured out that the dual system would reduce pressure enough in the intake to get rid of the turkey noise, but still provide acceptable drivability because enough air is recirculating to prevent the stalling. This is still less than optimal, however, because you're still fooling the MAF- it still thinks there's more air in the system than there really is, you've just narrowed the difference in the amount between the two to a level where it runs OK.

The other thing you're describing has nothing to do with what I just talked about. I haven't seen your car to know if there's anything wrong with it, but the hesitation you describe is common and its because the car runs overly rich. The bucking and lash you'll feel through the drivetrain are due to the engine twisting around it its mounts, which are too soft. The more extreme version of what you describe doesn't match my experience, though- do you have the boost turned up? You may be hitting the fuel cut.
 
Yep... I get (used to) get the same thing. It's not turkey related. I'm not sure if you have a FCD, but that's what worked for me. Once I installed and adjusted it, I no longer got those symtoms.



Rainman said:
I thought that the turkey was just the sound from the BOV. The sound I can live with. The stalling was taken care of by recirculating rather than atmospheric vent (since I wasn't going to go right out and do the dual BOV/BPV setup). But the surging is a different beast altogether. I just took it out again and there seems to be two different types of surges. One that comes on right away once into boost with moderate load. Minor hesitation. No real loss of power but it feels as if it just isn't accelerating as hard. The other more annoying surge is the one that comes on with WOT that causes the car to almost buck if I don't let up. This I didn't expect and have never equated with the "turkey." If this is the turkey then I can understand why lots of people don't like it.

If this is the turkey, why are there two different types of surge. Also, does the turkey happen with every car that vents atmospheric?

R
 
If all you "TURKEY" fans read his posts properly you will notice that he is talking about the FEELING of the surges, Not the SOUND of the surges. I'm not trying to start something here, just trying to get this post going on the right track....
I think Rainman has the right idea, but I also get it with my stock airbox just not as predominantly as with your cai. So I don't think it's FCD fixable. That just fixes the fuel cut (or whatever you want to call it) because he said he also got it before full throttle.
 
Yes... I realize that the FCD is specifically to correct the fuel cut, but it also helps with the drivability issues (surges, burps, hesitation...), at least it did for me. Not sure how it does it, but it did. Maybe because it also "tricks" the maf.



Geezer000 said:
If all you "TURKEY" fans read his posts properly you will notice that he is talking about the FEELING of the surges, Not the SOUND of the surges. I'm not trying to start something here, just trying to get this post going on the right track....
I think Rainman has the right idea, but I also get it with my stock airbox just not as predominantly as with your cai. So I don't think it's FCD fixable. That just fixes the fuel cut (or whatever you want to call it) because he said he also got it before full throttle.
 
Different than the lash or the turkey

Thanks Geezer. Let me just say that I am Purple and Proud brother...LOL!

Anyway, the surging sensation is more of the issue here. I will post pix of my setup. At the present I have a custom 2.5" CAI recirculated, a custom 3" mandrel-bent exhaust with single hi-flow cat. I am running stock boost. I have a Joe P MBC and FPR, but have not installed either yet. I am still waiting to receive my FPR from Joe (see my other threads for that story). When I mash it I hit 7 PSI peak and then return to 6.5 PSI steady. I have been flashed, but prior to the exhaust and CAI install. I have reset my ECU twice since the CAI install to try to resolve the issue. I really should have dynoed the car before the CAI install as it is really hard to get a sense of whether I have made any HP/TQ gains. With the surging it almost feels slower, but it is hard to clearly tell. My wife says that it is faster, but that is only because the CAI whooshing and turkey sound scare the s*** out of her....LOL! Of course, while I was on vacation and I took it by Essential Speed to have Ian take a look at it, it never once misbehaved, even though it was hot and humid and we did 4-5 WOT runs. Ian thought I was smoking something or spending too much time in the sun.

When I first installed the CAI, it was not recirculating. I had the usual stalling issues. However, I also had this surging sensation on heavy load then as I do now. I think that it might have been a bit worse when I was vented atmospheric than it is now, but then again it just might have felt worse as it was totally unexpected then and now I have become a bit used to it. I have had to adjust my driving style a bit to avoid it, but it still does happen. At normal city speeds it isn't a problem, but it is a bit disconcerting when you are cruising along at 140 kmh at the front of a line of cars on an incline and then your car starts to buck when you step on the gas harder. Surging might not be a good way to describe it as it seems to ? "backfire/burp" (for lack of a better description as I do get true backfires that are completely different) and falter BEFORE it momentarily surges.

I also wondered about the fuel cut issue, but with only a 3" exhaust and the CAI that seemed unlikely. The sensation is almost like hitting fuel cut as it is as if the engine momentarily dies, but it is also different as it usually happens 3-4 times very quickly (within 1-2 sec) before it settles when I lift off. Sometimes I can lift off slightly and it resolves. Other times I have to get off the gas completely.

I hear everyone's argument about the turkey sound. This I see and have noticed like everyone else, but here I am talking more about the sensation although it does have a sound associated with it. It is also different than the drivetrain lash that people mention although if you put your car into 1st and depress and release the gas pedal quickly 3-4 times in 1 second you will get a rough idea of what I experience although when it happens in my car my foot is not moving on the pedal. I will try to take a video of it happening so that everyone can see what I am talking about.

R



Geezer000 said:
If all you "TURKEY" fans read his posts properly you will notice that he is talking about the FEELING of the surges, Not the SOUND of the surges. I'm not trying to start something here, just trying to get this post going on the right track....
I think Rainman has the right idea, but I also get it with my stock airbox just not as predominantly as with your cai. So I don't think it's FCD fixable. That just fixes the fuel cut (or whatever you want to call it) because he said he also got it before full throttle.
 

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thunder said:
People get the turkey even when they use atmospheric bovs (ex. Forge bov)....
How did they set it up? Did they plug the nipple on the intake side that the BPV formerly emptied into and vent 100% to the aptmosphere?

As for the bucking stuff being reported, it seems to me that it still boils down to overly rich conditions. Really sounds like the hesitation that folks experience, but worse than most folks get- perhaps due to the combination of mods. I don't think its compressor surge related.
 
Well, there are hundreds (!!) of pages on the subject... One thread explains how to kill the turkey with a dual setup, that is a BOV on the IC-TB pipe while retaining the stock BVP. But it's such a long story.......
Sorry :)
 
there are tons of threads discussing whether or not turkey is really compressor surge or not. Honestly, I don't think it is, but thats just my opinion. I've read that relocating the bov/bpv will do the trick. A friend of mine with a GTI had the same turkey flutter, and he now has a clean "pssht" sound.

plus turkey isn't so bad. all the crazy jdm cars on best motoring vids have it.:p
 
thunder said:
Well, there are hundreds (!!) of pages on the subject... One thread explains how to kill the turkey with a dual setup, that is a BOV on the IC-TB pipe while retaining the stock BVP. But it's such a long story.......
Sorry :)
I've seen most of them. Anyway, I digress. My primary points to the original poster were a two- - that the drivability issues that he's experiencing aren't likely related to the turkey noise and that if you do try to get rid of it, any turkey solution that has you venting air to the aptmosphere is a less than optimal solution.
 

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