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Discussion Starter #1
I’d like to do some experimentation with boost levels on my car and was contemplating disconnecting the bypass valve.

I won’t be driving the car on the street and will just be revving the motor in my garage and logging boost values.

Considering the car won’t be under load and I will be gently progressing the revs up and down can wouldn’t this be an acceptable method of diagnostics?
 

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Do you have a way to create load on the engine? Simply holding an RPM in neutral does not dictate a boost pressure, since you have zero load you need almost no throttle angle to achieve an RPM. You will not be able to see boost beyond revving the engine quickly, and even then it won't necessarily represent full-load boost levels.

Regarding the bypass valve, it's load [vacuum] actuated, so even if you clamp it shut you're still not creating load on the engine, just adding engine drag and making warmer IAT's at part throttle.

What exactly are you trying to figure out?
 

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Discussion Starter #4
Why would I need load to create boost?

Pressure is created by spinning the rotors on the supercharger and as you increase the rpm on the SC you would increase boost. The blower is always making boost if it's spinning.

The reason you don't normally see boost when not "loading" the motor is the bypass valve is seeing vacuum so it's recirculating the boost and not feeding it to the intake.
 

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No offense, but it sounds like you haven't done any sort of datalogging before. Load and MAP are directly proportional. If you try to hold the engine at X RPM when you're in neutral you will discover that you need very little throttle angle once you achieve that RPM, and you'll end up seeing typically around 15 inHg vacuum.

It doesn't matter how fast you spin the blower, if the throttle butterfly is almost closed [which is what happens with no load], the engine is pulling a vacuum. Like I said before, unless you have a way to load the engine, you're not going to get a real-world steady-state RPM boost reading sitting in your garage with the tranny in neutral. Early supercharger setups rarely used bypass valves. They are primarily used to improve fuel economy. Since roots blowers are always displacing air when baffled[poorly at that, with a bunch of heat as a side effect], the bypass valve reduces that heat buildup during part throttle. Supercharger setups without bypass valves still operate in vacuum at part throttle, so please get that misconception that you're "always boosting" out of your head please!

Try it out for yourself and you'll see.

Go down the road and observe vacuum/boost. Cruising down your residential street you'll see 20-15 inHg vacuum. Cruising down the highway you'll see 10-5 inHg. It's not very RPM dependent because you're making so little power when cruising, however the higher the RPM at a steady speed the greater the vacuum since the VE typically improves at higher RPM to a point. Accelerating briskly [about half throttle to WOT] is when you'll see any boost. WOT is the only way to log maximum boost versus RPM, since it's maximum load.

What is the whole point of your datalogging experiment? Chances are there are enough experts here that have already done whatever you're trying to do and we can help.
 

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Discussion Starter #6
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?
 

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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.. :(
 

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When you let the engine bounce off the rev limiter usually the ECU either cuts fuel or retards the ignition timing severely. In either case, you're not making full power all the time, only every few cycles. As such, you still won't get a really solid MAP measurement.

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.

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 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?]

Cheers,
Ryan
 

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Discussion Starter #9
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.



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.. :(
 

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Discussion Starter #10
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.
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 currently don't have any other tools to do any logging from the ODBII port.

What's the likely hood the boost is being affected by something other than the induction system?

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.
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 car had been feeling a little weak lately but I chalked it up to me getting used to the power. A couple of friends went to the drag strip 2 weeks a go and I decided to tag along. I'm at altitude but the car only ran a 14.6 at 95 mph and I realized that it must be down on power.

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'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.
 

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...With simply the MAF reading from the OBDII you should be able to calculate actual horsepower with reasonable accuracy...
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?
 

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Garrett has a simple formula in their Turbo Tech 103:



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
 

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Garrett has a simple formula in their Turbo Tech 103:



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
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)
 

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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.
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
 

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Discussion Starter #16
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
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...

Maybe I'll break out the MiniTab and do a quick gauge R&R. (not really).
 

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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
 

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Discussion Starter #18 (Edited)
Just to clarify, I understand the bypass valve doesn't regulate boost, in the way that a MBC would.

But if the bypass valve doesn't fully close(the butterfly doesn't fully seat and seal) when on boost it will divert/leak some of the pressure from going into the intake side of the motor?


First Attached Picture: (I was seeing gauge pressures of about 5psi)
Example being if the bracket on my bypass valve had become bent and the stroke of the actuating shaft wasn't enough to allow the butterfly to fully close the motor would never see maximum boost pressure because some of the pressure would be leaking past the bypass seal?

The question about bypass in the valve was so I could potentially try to trouble shoot the stroke seal of the valve without removing the intake.

The second picture was after I fixed the bracket and got the bypass to fully seat. (I saw gauge pressures of about 7psi) Was the pressure difference unrelated to the bypass seal?

Phil I know you have a lot of experience with the M62 if my peak boost is down, I've replaces the belts with new and shorter ones, I've replaced the belt tensioner, and done a compression test on the engine where would you recommend I look next? (I'm thinking I will pull the intake and check the bypass valve and make sure it's fully seats when not on vacuum, I'll likely change out the intake manifold gasket at that time too). I've also got a "real" boost gauge on order and (unrelated to the boost issue) I will be trying a different ECU and tune.

Any suggestions would be greatly appreciated, I'm of the opinion the simplest/most obvious solutions are the best but I'm running out of easy answers.

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
 

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Discussion Starter #19
Here'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?
 

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Here'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?
Hi I'm having the same problem with low boost I have a 2.6 pulley with only 6psi of boost
 
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