Pettit Super Charger Owners
#1976
Its fine to do, it dosnt hurt anything but if you unload the blower at idle it has alot less of a rattle. Also being unloaded creats a little less heat in the charge. It still closes just fine (if your still letting the bypass valve see boost and vac).
#1977
Its ok to try and see if you like it that way. Go ahead give it the Pepsi challenge and see for yourself, it only takes a minute to switch back. Im not asking you to hold a coil so your good to go.
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#1988
Cam came to Vegas a while back (I think late last sumer and worked on my car while I was on vacation. He did change the pulley along with a few other items. I must assume that he did install a 8 lbs one but you know I never asked. Prior to that point I always ran about 10 lbs at maximum. I developed some issues with the car after his visit (not related to his visit) and one of them was with the boost gauge sensor. With all the issues now corrected and with a new boost gauge I am currently showing 13-14lbs of boost at 7800rpm (can be confirmed by those at the Cali dyno meet).
#1989
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13-14 lbs on a 4 port---holy bejeez!! No wonder the Cobb helped you out man---would love to see a dyno sheet on that!
I do not want over 10 lb boost on this 10/1 compression engine. I will be just fine at 7/8 lbs of boost. Now I wonder if that is what I am getting?
Moon do you mean you can inject a little oil in the bosh bbv or do you mean only with the metal type? I am thinking only the metal one.
Yall are making me more nervous about my track day a coming.
BY THE WAY WHAT IS THE SC BELT NUMBER__NEED EXTRA ONE>
olddragger
I do not want over 10 lb boost on this 10/1 compression engine. I will be just fine at 7/8 lbs of boost. Now I wonder if that is what I am getting?
Moon do you mean you can inject a little oil in the bosh bbv or do you mean only with the metal type? I am thinking only the metal one.
Yall are making me more nervous about my track day a coming.
BY THE WAY WHAT IS THE SC BELT NUMBER__NEED EXTRA ONE>
olddragger
#1990
13-14 lbs on a 4 port---holy bejeez!! No wonder the Cobb helped you out man---would love to see a dyno sheet on that!
I do not want over 10 lb boost on this 10/1 compression engine. I will be just fine at 7/8 lbs of boost. Now I wonder if that is what I am getting?
Moon do you mean you can inject a little oil in the bosh bbv or do you mean only with the metal type? I am thinking only the metal one.
Yall are making me more nervous about my track day a coming.
BY THE WAY WHAT IS THE SC BELT NUMBER__NEED EXTRA ONE>
olddragger
I do not want over 10 lb boost on this 10/1 compression engine. I will be just fine at 7/8 lbs of boost. Now I wonder if that is what I am getting?
Moon do you mean you can inject a little oil in the bosh bbv or do you mean only with the metal type? I am thinking only the metal one.
Yall are making me more nervous about my track day a coming.
BY THE WAY WHAT IS THE SC BELT NUMBER__NEED EXTRA ONE>
olddragger
#1991
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Join Date: Apr 2007
Location: Pembroke Pines
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Originally Posted by olddragger
13-14 lbs on a 4 port---holy bejeez!! No wonder the Cobb helped you out man---would love to see a dyno sheet on that!
I do not want over 10 lb boost on this 10/1 compression engine. I will be just fine at 7/8 lbs of boost. Now I wonder if that is what I am getting?
Moon do you mean you can inject a little oil in the bosh bbv or do you mean only with the metal type? I am thinking only the metal one.
Yall are making me more nervous about my track day a coming.
BY THE WAY WHAT IS THE SC BELT NUMBER__NEED EXTRA ONE>
olddragger
I have to second Phil and have Moon and Cam to vouche for me. I push my car hard I have doen one auto X and have had some runs at the Homestead speed way and others that can't be spoken of here on the forum(some of you have seen some of the vids) The only casualty has been the diaphrams. You should be more than ok.
13-14 lbs on a 4 port---holy bejeez!! No wonder the Cobb helped you out man---would love to see a dyno sheet on that!
I do not want over 10 lb boost on this 10/1 compression engine. I will be just fine at 7/8 lbs of boost. Now I wonder if that is what I am getting?
Moon do you mean you can inject a little oil in the bosh bbv or do you mean only with the metal type? I am thinking only the metal one.
Yall are making me more nervous about my track day a coming.
BY THE WAY WHAT IS THE SC BELT NUMBER__NEED EXTRA ONE>
olddragger
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#1996
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Location: Mesa, Arizona
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13-14 lbs on a 4 port---holy bejeez!! No wonder the Cobb helped you out man---would love to see a dyno sheet on that!
I do not want over 10 lb boost on this 10/1 compression engine. I will be just fine at 7/8 lbs of boost. Now I wonder if that is what I am getting?
Moon do you mean you can inject a little oil in the bosh bbv or do you mean only with the metal type? I am thinking only the metal one.
Yall are making me more nervous about my track day a coming.
BY THE WAY WHAT IS THE SC BELT NUMBER__NEED EXTRA ONE>
olddragger
I do not want over 10 lb boost on this 10/1 compression engine. I will be just fine at 7/8 lbs of boost. Now I wonder if that is what I am getting?
Moon do you mean you can inject a little oil in the bosh bbv or do you mean only with the metal type? I am thinking only the metal one.
Yall are making me more nervous about my track day a coming.
BY THE WAY WHAT IS THE SC BELT NUMBER__NEED EXTRA ONE>
olddragger
4-ports should naturally get higher boost than the 6 ports motors if they are pulleyed the same. A positive displacement S/C will eat mostly the same amount of air per S/C rev as it does on a 6-port, but on a AT the blower has to work harder (increase pressure) to force the engine to eat it with only the 4 ports. This may be part of the reason of more belt slippage too on ATs. Once air is ingested at the blower inlet, it has nowhere else to go except through the motor. The twin-screw will steal whatever power it needs and increase pressure if necessary to maintain air in == air out.
I'd predict that this would make the AT Pettit car very similar in power to a 6-port. There will be extra power stolen from the crank by the S/C on the AT and extra heating of the intake charge which might necessitate a slightly more conservative tune on a AT from the increased pressure, but overall I'd predict the AT should be eating mostly the same amount of air as the 6port.
I'd love to do more math with this, but don't have the reliable MAF vs. RPM data and a S/C flow map of the supercharger. Lysholm publishes a flow map for theirs, but its not the same blower as the one we have.
#1997
You're right Jess and I was thinking the same thing the other night with regard to F/I systems in general. A given compressor that is moving the same amount of air in both a 4 and 6 port engine, at the same RPMs will yield higher manifold pressures in the 4-port engine. Thus, the playing field is somewhat "levelled" with F/I. The biggest difference will be IATs but, in Phil's case, he had my intercooler for protection. The question with Phil's car is why in the world did a simple bypass valve yield such different manifold pressures and how much leaking was present prior to the change. This may also be related to the reason why the plastic valves are prone to splitting, at least in two cases I know of, at high RPMs.
BTW, if you're right about the dimensions of that belt I have a racing version I can order for you guys until my damned new blower drive is done. Gates moves SLOOOOW with this stuff sometimes.
BTW, if you're right about the dimensions of that belt I have a racing version I can order for you guys until my damned new blower drive is done. Gates moves SLOOOOW with this stuff sometimes.
#2000
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Here's some interesting math facts:
*) Intake charge temp of 120degF undergoes 10:1 compression at TDC
*) Thermodynamics demands charge temp would go to at least 653 degF with that much compression
*) The autoignition point of gasoline is somewhere around 494degF -> 544degF
Thank goodness for tuning and the latent heat of vaporization cooling of a rich fuel mixture.
*) Intake charge temp of 120degF undergoes 10:1 compression at TDC
*) Thermodynamics demands charge temp would go to at least 653 degF with that much compression
*) The autoignition point of gasoline is somewhere around 494degF -> 544degF
Thank goodness for tuning and the latent heat of vaporization cooling of a rich fuel mixture.