Moon Assad

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).

Moon Assad

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.

Phil's 8

iTrader: (3)

Great, the one I have is piston operated also but seems to be stiffer than the Bosh one and seems to offer more boost. Just checking to be sure that this is OK. Previous ones were the plastic stock diaphragm type did not last.

Moon Assad

Yeh, Roland can tell you all about it.

morkusyambo

Juan, Munche, all those using upgraded bypass valves; How much boost are you seeing on your gauges??

munche187

As soon as I get a gauge I'll let you know.

Hymee

iTrader: (1)

I've been using an "Opcon" supplied billet bypass valve with my Autorotor's compressors since day one.



Cheers,
Hymee.

Charles R. Hill

iTrader: (7)

Try using the Toilet Flapper Valve that comes in the Pettit kit.

marsredr100

iTrader: (1)

Just got the bypass valve today. I will post pictures and test results Friday.

Phil's 8

iTrader: (3)

I need a teenager to come show me, step by step, how to post picturers. I've had people tell me how but it never works for me.

Phil's 8

iTrader: (3)

13-14 lbs currently and it runs like a charm. That is with the stock setting as it comes from the factory.

marsredr100

iTrader: (1)

13-14 lbs

With the stock 8 lbs pulley?

Phil's 8

iTrader: (3)

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).

olddragger

iTrader: (3)

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

Phil's 8

iTrader: (3)

Why get nervous. If you saw the way I drive and the loads I put on this car you would know that if anything was going to happen it would have.

munche187

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.

MazdaManiac

iTrader: (3)

14 PSI with only 300 g/sec of flow or so.
You do the math.

marsredr100

iTrader: (1)

Wish one of these you recommend for the task?

MazdaManiac

iTrader: (3)

I like the colored one.

Charles R. Hill

iTrader: (7)

Racist.

joff

The belt is a 32.5 inch, 5 rib. Its actually the exact same one as the main drive belt IIRC.

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.

Charles R. Hill

iTrader: (7)

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.

MazdaManiac

iTrader: (3)

If you raise the pressure, all that happens is the temperature goes up, so nothing is really "leveled".

Charles R. Hill

iTrader: (7)

What happens when you stuff the same amount of air in two similar displacement engines with their main differences being the intake manifold systems?

joff

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.