No, your logic is flawed...
I would guess a possible slipping belt as others have had this problem.Ryephile,
Cool, no offense taken. I appreciate the explanation. I hadn't taken into account that the TB wouldn't be entirely open to rev the motor w/o load.
I'm not advocating this as a viable solution but for discussion; If I was willing to manually open the TB all the way and let the engine rev off of the limiter would I be able to get a boost value in the garage in neutral?
I'm recording about 5psi on my "boost" gauge (just a pressure gauge I've connected to the intake manifold). I've previously recorded about 7psi (I'm at 5000 feet) when the SC was first installed and am trying to diagnose where I'm loosing boost.
I've investigated the belt, which is good and tight, and have done a compression test which yielded ~172 across all cylinders.
This leads me to the bypass valve which I think may not be fully closing. I have manually actuated it (with vacuum from my mouth) and it seems like I can hear it click when it closes 20% of the time. I'm assuming this "click" it fully seating on the hard stop. I was thinking if I could watch the boost while actuating the valve with my hand I could confirm or rule out this condition. I was hoping to find a way to troubleshoot the bypass without removing the SC and intake.
The install was 1,500 miles ago and I'm puzzled how/why the bypass could be malfunctioning (if it's the bypass)? One other reason why I believe it may be the bypass is originally the on/off throttle transition was somewhat abrupt which I attributed to the bypass opening and closing and boost feeding the engine changing the power output. Currently the on/off throttle has been very smooth as well as the power seems low.
I understand I could also be an IM leak or some kind SC damage but I thing both of those are remote. I smoke tested the IM upon installation and the IM bolts are still torqued. The SC is only 1,500 miles old so it would seem unlikely to be the culprit.
Suggestions?
I would guess a possible slipping belt as others have had this problem.
I would also recommend getting an actual boost gauge that is made to show the low pressures you will be seeing under boost accurately. The better ones will record peak boost as well...
PS... Also sorry about my short post last night... Was in a hurry to get to bed when I typed that..![]()
I've been doing 2,3,4th gear pulls on "closed courses" with the boost logged on my gauge and haven't seen any peak levels above 5.5psi.I would highly recommend finding a chassis dyno and doing a controlled WOT pull with a good boost gauge connected to the intake manifold. This would also give power and torque measurements, however such measurements are best observed as deltas from a known state of tune. If you happen to have some good secluded "private" roads in your area and have good datalogging abilities on-board the car then you can do a 2nd or 3rd gear pull [or higher gear if you have the room!] and observe boost, ignition, MAF, and all that good stuff. With simply the MAF reading from the OBDII you should be able to calculate actual horsepower with reasonable accuracy. This would give a good indication if your setup is healthy.
That's my thoughts. Upon receipt I noticed the mounting bracket of my BWR SC had been bent. I installed the SC assuming that the angle I was seeing could have been set that was from the factory and I was being paranoid. After dynoing the car and seeing low boost numbers I realized my earlier suspicions were correct. I uninstalled the SC adjusted the bypass valve and set it up so that the spring tension from the bypass was actually over-stroking the travel and keeping some pressure on the bypass when in the closed state. After this fix the car was seeing peak boost values at ~7.25psi and the power was good.The bypass valve may not be set correctly. In my other current automotive life [MINI's] the factory bypass valve on the Cooper S's are almost never adjusted correctly. Re-setting the butterfly stop set screw usually nets a 0.5PSIg gain [on setups running around 15PSIg], since you're baffling the supercharger better. The bypass valve will almost never lose its setting unless something bad happened.
I've replaced the belt, tried a 1/2" shorter belt and have even tried a brand new ($200) belt tensioner from Toyota, with no change in boost value what so ever. I haven't performed any other mods to the engine.I would also put in a vote for a slipping belt, as the belt-tensioner on the 2ZZ engine is very wimpy and not strong enough to sufficiently tension a supercharged setup. As such, belt slippage is very common. What supercharger setup are you running and what belt size and brand is on there now?
Finally, have you changed or modded anything since the install? [new exhaust and the like?]
I am logging MAF readings... and I've been thinking the same thing... have you worked out a formula to convert MAF into approximate power?...With simply the MAF reading from the OBDII you should be able to calculate actual horsepower with reasonable accuracy...
That's very cool info and data, thanks. My peak MAF reading is 237 g/sec (on a very hot 95 degree day), which converts to 31.3 lb/min... I've got an Exige S with a Gotham265 tune... (and intercooled, of course)Garrett has a simple formula in their Turbo Tech 103:
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However it's worth mentioning that knowing BSFC is more of an educated guess for most of us, about 0.51 for a boosted Elise is pretty close. Also from my experience this formula only works when you use an AFR of 12.
Wa = airflow in lb/min
HP = horsepower at crank [gross, doesn't account for post-supercharger net power]
An example is:
31 lb/min = HP*12*[0.51/60]
HP = 304
This can be reverse calculated with a normal Katana kit running 6psig. At engine redline of 8500 RPM an Eaton M62 needs about 22HP to drive it at 12,500 RPM at 6psig. A Katana'd Elise that puts down 220wHP peak ends up about 250HP net at the flywheel, and 272HP gross. Run that through the formula again and you end up with a BSFC of 0.57, which is a bit inefficient, however the day I datalogged 31Lb/Hr was a very cold day so actual power was probably more in the region of 300 gross HP, so the 0.51 BSFC is a safe guesstimate. If someone has better information [which is likely] please chime in!
Cheers,
Ryan
May I humbly suggest that the PSI gauge may have lost some accuracy as it's been subjected to repeated vacuum outside of its design parameters?I think I've ruled out the belt. I've tried a new belt, a shorter belt and have swapped the belt tensioner, each time with no effect on boost.
I do have a boost gauge on order as I agree it's a useful tool (it will log max boost).
The "psi" gauge I've been using is a good quality gauge that seems to be accurate/repeatable in the positive pressure range and has a small enough range that it provides good resolution at 5-7 psi.
Certainly possible. It will be interesting to compare to the boost gauge once it arrives. Unfortunately, based on performance I believe the gauge has been reading accurately...May I humbly suggest that the PSI gauge may have lost some accuracy as it's been subjected to repeated vacuum outside of its design parameters?
Just an idea.
xtn
Perhaps I'm misreading you, but it looks like you're implying that the bypass valve has something to do with boost... If you're thinking that's the case, it's not... in the case on the M62s and they way they're utilized on our cars, the bypass valve's sole purpose in life is to help with fuel economy and help manage charge temps at light throttle (during manifold vacuum conditions). Disconnecting the bypass valve will only make your part throttle charge temps go up and your fuel economy go down. It will not impact your boost level at all. At a X RPM, the only ways your boost changes in our cars is by modulating the throttle plate, changing the pulley, or changing the VE of the engine (like with the VVTL).
There is such thing as a fancy bypass valve that has a vacuum and a pressure side (for regulating boost). Our TVS blowers have them, although we do not use the pressure side. The pressure side would be used to regulate boost if the need were there using a electronic or manual boost controller (to regulate the pressure to the pressure side of the valve). There's a select few OEMs that use the pressure side of the bypass valve to regulate boost-- sort of like a wastegate on a turbo... I believe that function is only used for a "limp-home" type of scenario though... Not aware of any roots type blower that is using the bypass valve to regulate boost in a performance application...
Hope that helps,
Phil
Hi I'm having the same problem with low boost I have a 2.6 pulley with only 6psi of boostHere's the "progress":
I purchased a boost gauge with high and low tell-tale features.
I did a couple of runs and the gauge shows exactly the same readings as I saw with my home-spun psi gauge 5-5.25 psi.
I also happened to purchase a CharlieX tuned ECU so I plugged it in to see if it would make any difference (I wasn't expecting it to) and the same result ~5psi.
I figured it must be the bypass so I began the supercharger removal process. As I remove the throttle body I notice the transmission mounting bolt looks to be sheared off. I remove the entire SC and sure enough the bolt head is gone.
I examine the bypass and the linkage looks good and appears to be sealing. I decided to remove the "intake runner"(?) so I could visually see the butterfly. And it looks like it's fully seated.
So now I have two questions.
What silicone do I need to purchase to re-seal the intake runner?
And could the broken bracket somehow be the source of the low boost?