abv

I have a comptech unit w/ aftercooler in my car and am in the process of putting on a 3.5 inch pulley. ( i am also putting in a AEM EMS, 650 injectors and megan header and test pipe already have a mugen cat back)

The stock blocks are good for about 10psi correct? (no internal mods or head gasket changes)

I hear the 3.5 is in the ballpark of a 9lb pulley please correct me if im wrong...

If im wrong on the pulley "equation" please correct my ignorance and will i need a BOV to bleed off top end boost?

and on another note would that be a good way to go if i kept the engine stock but put say a smaller pulley to get more low end boost and bleed it off with a bov?

thanks

xviper

You seem to have a lack of understanding for what a BOV does and why it's there. It is NOT there to bleed off boost at high rpm. A BOV activates on manifold vacuum. You always tune for max boost of the blower and pulley you've got at redline. What the BOV does is to bleed off all that pressure when you lift off on the gas. When you do this, your throttle body flapper valve slams shut and all that pressure on the upstream side will "hammer" into the throttle plate. The subsequent negative pressure on the inside of the throttle plate can bend the plate, suck out the seal or, in the worst case scenario, suck throttle body parts into your engine.

Sideways

You have it backwards. The BOV releases the pressure at low speed so you don't see boost at less than wide open throttle.

abv

intresting......I told by the dudes over at comptech that you can there are 2 routings on the godzilla BOV one to do as you explained and another to bleed off top end boost...perhaps they are smoking pipe.......wish i had some pipe....


Do you know of any way to bleed off top end boost?

SIIK2NR

The stock Comptech Bypass valve will be fine if you don't want an aftermarket BOV.

xviper

What is the bypass valve set at? If he goes to 9 lbs, will it hold?

For the OP, the Comptech bypass valve works of a different principle as a BOV. Not familiar with the Godzilla unit.

SIIK2NR

Not sure X....

But we had a member who tried and tested a non aftercooled CTSC with 9lbs of boost and it held fine.

abv

SIIK2NR


so you can adjust the bypass valve to various boost settings?

slimjim8201

A blow off valve and a bypass valve are one and the same. It is "sucked open" by the negative pressure that develops in an intake manifold during closed throttle situations.

ABV, I understand what you are getting at with "bleeding off top-end boost", but a BOV/BPV does not function in that manner. You are refering to a wastegate. These are more commonly used to control the maximum flow allowed to enter the turbine of a turbocharger, effectively controlling the rate at which the turbine/compressor spins and thereby the maximum boost/flowrate provided by the compressor. Boost control is managed on the exhaust side of a turbocharged car. (Typically).

Of course, for a supercharged car, the entire system depends on the intake side. You could very easily install a wastegate to your induction system to "bleed off" excess boost. The only downside to this is that your engine has already used a lot of energy in compressing the air that you are now venting off into the atmosphere. Basically, you are throwing power away.

You could install a very high boost pulley and then vent off air once you reach your desired level of boost. This would be terribly innefficient. It is well known that a centrifugal supercharger develops flowrate and boost in an exponential fashion. The power required to drive the supercharger also increases in a polynomial fashion. As you rev your engine past your bleed off point, the percentage of the compressed air that you are using is decreasing and the percentage of the power you are wasting is increasing. This is just a bad idea in general.

Deppenma is going to attempt something similar, but he will be using an axial-flow compressor in place of a centrifugal compressor. While he will still be wasting a portion of the power he used to compress the intake air past a certain boost level, the axial flow compressor is dramatically more efficient and therefore the overall loss is considerably less.

And I'm not sure if any of this is coherrant...

abv

actually quite coherrant too bad though it would seem like such a good idea to be able to control boost up top allowing more boost at lower RPMs while not blowing engine bits up....



Thanks for clarifing