Is there a modification required to the crankcase ventilation system when running a blower? I am pushing 8 psi in an L98 (with other mods) and during the dyno-tune the technician disconnected the vent hose coming out of the passenger side valve cover from the throttle body. He then capped off the throttle body tube and left the hose coming from the valve cover venting to the atmosphere.

On the driver's side I still have the factory pcv valve plumbed into the side of the intake. Is this arrangement satisfactory? If not what mods should I perform to make the crankcase vent optimally?

90Indy

 

 

Yes, the instructions that came w/ my ATI unit had me REMOVE the PCV from both the lower intake & from the throttle body. They two lines were T'd together & then vented to the air filter on the blower. If you leave the PCV in the intake, when boost occurs it will also be applied to the crankcase if you leave it hooked up as normal & you could blow oil etc out of various seals...

Ps. the two fittings (manifold & TB were capped off).

 

Make sure the brake vacuum lines are rerouted too, or at least a check valve is installed, otherwise you have pressure instead of boost, and you'll find it very hard to stop!

 

In my blower kit (L98) from Blowerworks, Greg included some parts to modify the crankcase ventilation system to work under boost. Check out www.blowerworks.net, I think you can get an idea about the design by looking in the C4 catalog (downloadable), it´s also possible to purchase these items separately from him.

 

Great advice. I certainly appreciate the input. I will contact Greg @ Blowerworks and get his system. I hadn't thought of that.

90Indy

 

Funny, never had that problem or heard of anybody having that problem. I don't have a check valve for mine.

 

How much boost are you running?

There may be a check valve already.

 

10psi. When I let off the gas and go to the brake the throttle plates close and engine builds vacuum. Vacuum opens the discharge valve between the blower and throttle body releasing boost between them. I don't have a check valve between the booster and manifold. Checked my Blowerworks instruction manual and parts list and it does not suggest a check valve for my LT1. On the L98's it suggests a check valve in the PCV hose but that is all.

 

The factory brake booster has a check valve installed, that is how it holds vacuum after you shut the engine off.

 

Good Morning Guys, couple of comments. I like to maintain the functionality of the PCV system, especially for our 'garage queens'. The PCV system removes crankcase contaminants. All PCV valves will leak a little boost into the crankcase under WOT, therefore a positive shut off checkvalve in series with the PCV valve is a must. For LT1's I make a billet PCV with integral checkvalve that is a direct replacement. Older IG's for my kits do not mention this.

The brake booster has its' own checkvalve but I often install an additional checkvalve for high boost applications in order to protect the booster checkvalve from blowing out.

You can never have enough crankcase ventilation. I like to vent both valve covers, but on L98's I use a breather with a "low cracking" pressure on the PCV side in order to maintain the integrity of the PCV system. Without the checkvalve on the breather the PCV valve will draw its' fresh air from the same side breather thereby defeating the purpose of the PCV system which is to draw fresh air thru the crankcase.

It's also a good idea to check the HVAC checkvalve and make sure it is working as well.

All of the above assumes the engine does not have excessive blow-by. The only fix for that is an engine re-build.

Finally, even with a good engine I often find the engine oil dipstick needs to be replaced as the seal on old dipsticks is shot.

Best regards,
Greg