I am running a 19% pulley, GIAC and JCW injectors. Plus the regular intake and exhaust....

I had my car dynoed and got a weird boost graph. I'm now tring to find out why it came out this way. Is it because of belt slippage? Boost leak? Supercharger problems? Or is this how the boost curve really looks like for our cars?



What do you guys think?

John

 

i dont have a graph to back up my statement but when your boost drops off at 2750rpm i seem to have the opposite effect, my car starts to pull at 2500 or so with out a drop off. Being that some people have SC belt issues i would assume that it is slipping.

just my 2 cents

 

The boost also looks on the low side. Assuming you only have the basic bolt-ons, a 19% you should give you more boost... Unless you are in high altitude, which doesn't look like its the case.

I'm no mechanic, but belt slippage or bypass valve issues come to mind as possibilities.

 

I will be changing out my belt tomorrow. Hopefully this solves the problem. I'm still unsure whether which belt to use....the 060535 or the 060539. Helix and Alta are recommending the 060535 while Randy of WMS recommends the 060539 specially for track use. I will be taking my MCS to track on Sunday so I'm leaning towards the 060539....

How do I rule out the bypass valve though?

John

 

I just posted some belt specs on hornguy's "how I removed lots of mods..." thread. I just installed a gates 065353 belt for a 15% pulley and corrected a slight belt slippage problem. I've heard the 19% is more prone to belt problems, but that's not the point... WMS/Helix/Alta have TONS more experience with this than me, so their recommendations should bear some considerable weight.

However, my recent experience with the 15% suggests the 535 is a better fit (at least for my car with the 15%). This probably varies with belt tensioner conditions.

I suggest you read over the last couple of pages of the thread I mentioned above, there is some interesting info and a belt tensioner picture that should give you some points of reference. I don't know what your resources are but maybe you can try both and see which one fits better?

 

Actually, I have read the thread and this is what confuses me. There are mixed recommendations regarding belts for specific pulley's. Some say that the 535 is the belt for the 19%, some, the 539, and then some say that the 535 is for the 15%. Decisions, decisions......

John

 

oops

 

Below is from a Beta BiM-COM data log of my formally 19%/GIAC/380cc injector/stock intake equipped MCS with a ported head, while on a Dynapack. I had a 535 belt which is the correct size for the 19%. It appears there is something amiss as recorded by your plot compared to my log, but anything I say will be thinking out loud.

PSI RPM
09.12 1545
10.30 1914
11.92 2471
12.36 2960
12.28 3474
13.22 3947
13.79 4416
14.64 4924
15.68 5432

 

The start of the graph looks the way it should be....only when rpm's reach 2750 does the graph suddenly dive. So hopefully it's my belt as it would explain why boost is good on low revs then drops off at a certain rev, but still slowly rise as rpm rises.

What items should I look out for regarding my bypass valve?

 

John,

If you change the belt to best one for your SC pulley and it is still showing the drop off, first check the rubber boots on the ends of the intercooler to make sure that they are properly sealed. Then check out Detroit tuned and get some info on thier bypass valve and how that may or maynot help your situation.

 

I'm sure someone else can give a more technical explanation about the bypass valve, but the very basics of it is that it's pretty common for them to loose the ability to close properly. If the bypass valve does not fully close, some pressurized air will escape thru the opening, basically lowering your intake manifold pressure.

 

Right from the horses mouth

The Detroit Tuned Bypass Valve is a re-worked brand new OEM valve that is modified to eliminate the "Yo-Yo" in early year ('02-'04) Cooper S's, but is available for all year Cooper S's. This BPV uses a stiffer return spring, resulting in quicker boost generation, and thus quicker throttle response and transitions. The butterfly assembly is also adjusted to close fully, allowing for maximum boost. Perfect for the aggressive driver or racer. Expect a very minor loss in fuel economy, and a great improvement in throttle resolution and smoothness.

 

my boost tends to be totally throttle body dependant . ex.; i could be at 4000 rpm's and let off the throttle a little and i'll go to vacuum . my throttle's got to be on the plus side to see any sustained boost. no leaks though . vac is at 20 at idle now . 18 -20 . just my .02 .

 

It is not the belt...I changed to a new belt but the dip is still there. I gained 1psi of boost though, seems like my old belt was slipping all through out the rev range.

My By-pass valve has already been aligned, so I don't think that is it. I also ziptied the valve shut but the dip in boost was still there, so I just removed the ziptie again.

The IC boots look like they're installed correcltly. I will remove and reinstall them again. Hopefully it is that simple.

Is there a possibility that it's my boost guage, or the hoses leading to it? The weird thing is how the boost dips.....it seems at a certain pressure, boost is leaked out and it leaks all the way through th rev range. But below that, there boost is in check.

John

 

watch your boost gauge as you drive . it'll increase in vacuum first at about the rpms you're showing if depressing the throttle slowly. then it'll climb to boost gradually as you depress. if you stomp on it ; it'll jump to boost .

 

How does one know if the belt is slipping because of belt issues or if the belt tensioner is failing under load? Does that go back to the idea of checking how much travel is available in the tensioner? Thanks!

 

It's not the belt coz I've got a new belt on. It's not the bypass valve coz I tried tying it shut but still had the dip. It's not the IC boots as I had check and rechecked it. I ordered a new set of boots though and will give that a try.

Are there any other causes for the drop in boost? Is there a possibility that my S/C's rotors are ruined? I'm using a 19% pulley, so I'm thinking that my rotors clearances may have been compromised by the heat.

Or is there a chance that a ruined belt tensioner may cause a dip in boost? How do I check if my belt tensioner is in good condition or not?

golfersmurf,
I think it's the condition of the belt itself and how much bof the belt tensioner stop is showing. I'm not sure but that's how I go about in replacing my belts.

John

 

Bump

 

How many miles are on your tensioner? I just replaced mine with ~65K on it based on recommendations from LDG. If the tensioner is bad, the belt could be slipping in spite of using the correct belt. If I were you I would call LDG and inquire based on your car & data.

 

I only have 14k miles on my tensioner, so I am optimistic that it is still in good condition. But take note, my pulley installer put in a spacer for the spring of the tensioner, therefore adding more tension to the belt. Could this cause my tensioner to deteriorate faster?

I will try giving LDG a call, but I am from overseas. Anyways, I'l give him a try.

John

 

I have no idea if the problem is related to a failing tensioner, but I do know that tensioners can fail prematurely.

I had two fail in the first 15,000 miles.

The latest one has worked flawlessly for 7,000 miles and several track days.

I also know others who've had tensioners fail early, so don't neessarily assume that you have too few miles on it.

 

How can I determine that I have a faulty tensioner? Is there any symptom that can help me determine that my tensioner is indeed bad?

John

 

While accelerating normal is that when you feel the drop? How about when accelerating hard? Does it go away? My 06 has a low spot in that range but if I accelerate hard it, for the most part, is not noticeable. For me I would have to say it is something in the programming.

 

just for your refrence, I'm at about 10.5 psi at 2000, and its a straight areo from there to 19.5 psi at 7000.

I noticed your graph only goes to 6400rpms. any reason for not taking it to redline?

so like someone else noticed your over all boost # seems low for a 19%.

 

My recent experience with belts and tensioners (on a 16% m7 pulley and with a DT BPV installed as my major mods):

- After adding the m7 pulley we installed a Dinan belt. Assuredly tighter than stock and no slip.
- However, after ~3K miles my belt shredded into tiny bits
- Replaced belt, discovered racket coming from tensioner
- Found tensioner bad
- Replaced tensioner
- Found replacement Dinan belt doing weird voodoo with tensioner and stressing the tensioner to the point of making noise. Too tight...
- Swapped out to a factory JCW belt and life is good. Maybe a bit of slip but overall a much better end result (wearing well, return of performance, and no funk from the tensioner).

Without absolute proof this is my opinion, but I think the tension provided by the Dinan belt was too much for the tensioner. Tensioner fubar'd the belt before giving major signs it was struggling to handle the increased belt tension. In retrospect I did feel the slippage of the belt with a weird flat spot on accel and drop in mileage (from the SC not working its best).

No idea about the math of how small of a belt the 19% pulley should run, but it should prove beneficial to calculate that and see how much variance your belt options have (353 belt vs. 539 belt). Then you could pick the belt that comes closest to matching the calculated diameter and hopefully reduce the occurrence of slip without hammering the tensioner into failure.

My tensioner failure did happen around the 52K mark which also places it in common mileage zone for failure, but I do believe the stress of added tension via the smaller belt on the pulley did the deed on it.

My two cents... Probably worth .0005.

Keep us posted with anything you find. Always interesting to learn about the fixes in problems like this.