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I acquired a used MP62 with an automatic tensioner and 6-rib 100/60mm pulleys. I'm looking for a solution to belt slip/squeal. I've already replaced the tensioner and put on a green Gates belt. Alignment seems decent, and I'm running out of ideas. Would swapping to bigger pulleys with the same ratio help?
100/60 is certainly less ideal than other combos with the same ratio. It is always preferable to increase the crank pulley diameter when possible. 100mm is unusually small.
Alignment is the most critical aspect to a good drive solution. groove to groove (not face to face) should be within 1/8" fore-aft with zero percievable tip/tilt. These measurements usually require a precision edge to verify.
Mounts should minimally be 3 point, preferably three plane.
More details I forgot to include in my original post. It's an older BRP setup, and looks like I have room to fit a 70mm SC pulley before running out of room with the outlet. Here's a picture from a couple weeks ago.
the BRP kit is solid for both the mount and the alignment, assuming it is installed properly. Curious how you ended up with such an odd crank pulley for that kit.
Also, what makes you think you have belt slip? This combo is probably going to be a sub-7psi (intercooled) even at sea level.
Edit: That is not a great place to be sourcing the bypass signal from. It would be much better to route from the throttled inlet, this could be causing your squeal.
If I go WOT at around 3k RPM or so, I can hear a high pitch whine that sounds like belt before I hear the slightly deeper supercharger whine. I need to double check my logs, but the car seems to make around 7-8psi.
Do you get belt dust? I figured you were getting squeal on lift off. Certainly look into changing up that crank pulley so you can get a bigger nose.
In looking around, it appears as if the BRP was maybe offered in a non-intercooled configuration for stock injectors and possibly power cards? I doubt that the 60mm was part of that kit. Somebody probably took the "easy upgrade" path with the snout. This also might explain the bypass signal routing, as evacuating a non-intercooled setup will be much quicker than what you have. With the intercooler, the engine has to pull vac on all that extra volume for that bypass to open, which is going to take time and cause a bark inducing pressure spike.
7-8psi on that setup is suspect, especially if this is as reported by a calibrated MAP sensor. A boost gauge, not so much, as they are frequently approximations.
Hard to say if there is belt dust. Maybe a little, but I just took the car to a track day in the rain yesterday, so nothing is spotless in the engine bay.
You're suggesting running the bypass vacuum source straight to the intake manifold, to where I currently have the pair of unused ports looped together?
You would expect less boost? For reference i currently have a bigger throttle body (I believe its 75mm), BP05 engine, 2.5" exhaust, and an 11x11" core intercooler.
edit: Boost pressure readings are from the MAP sensor. I know autotune was hitting my 150kpa cells, don't have logs on me at the moment.
Last edited by kep; 05-01-2023 at 01:47 PM.
Reason: added detail
no, run the bypass from the volume of space between your throttle and your supercharger inlet. The SC will pull vac in that volume almost immediately on lift off. The volume from the SC outlet to the intake valves needs to be pumped down by the motor to create the vac opening the bypass as configured today. This takes time.
Also, those actuators are not known for handling boost well. As it sits today your are putting positive pressure on the actuator.
None of these things line up with your description of when the slip sound occurs (WOT at 3K). That one is limited really to either the small snout pulley with orbit, or mis-alignment.
I wouldn't get to caught up in what "boost" you are seeing right now. I will say VE table cells are interpolated, so depending on your y-axis scaling your "150 cell" might stretch as low as say ... 135kpa and go as high as 165kpa. You need to look at the actual data to know what your peak manifold pressure is.
FYI, looking at that data should be your first step when trying to diagnose any issue like belt slip.
Took a look at my setup. Alignment was spot on, and I can completely remove the tensioner and the belt will still stay in place on the pulley. I also measured the snout pulley and it was actually only 58mm.
Here's a log from last week. You were right, only 6.5lbs of boost here. Are the oscillations in the MAP normal for a roots blower?
No, that is not normal. Things to check in order of likelihood:
- malfunctioning or improperly tensioned auto-tensioner. auto-tensioner should provide a nearly constant resistance over an angular range of motion with no "hitches". The tensioner should be pre-loaded to have sufficient motion in both directions. It should not be "easy" to install the belt as the pre-load needs to be accommodated via a gymnast like 2-handed process. A well designed kit should have multiple positions to accommodate different belt and pulley combos. If this is the issue the belt needs to be checked for glazing.
- defective/improperly installed/missing IAC/ISC air circuit check valve
- worn out SC bypass actuator linkage. There should be little to no play here.
Tensioner is heavy and smooth. Takes quite a decent bit of effort to move it so that a belt can be installed/removed. I've tried looking into what OEM auto tensioners have more spring force, but I have yet to that data anywhere.
I have an AV23 check valve on the idle bypass. Verified it worked before installing.
I hadn't looked to closely into the bypass actuator. I believe it felt fine when I felt it by hand, will double check next time I'm at the garage.
I've seen a few sites selling MP62 pulleys for Lotus applications. Will likely pick up a 2.7" snout pulley from one of them, and then a larger crank pulley from FFS. Will probably target around a 1.8 pulley ratio
05-01-2023, 09:31 AM
Slipping Supercharger Belt
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