No, your logic is flawed...
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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 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 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..
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
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)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
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.
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.
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