we were tuning my car and I decided to try for a bigger than normal shot for the first time. I sprayed it at 3k rpms and then at 3200 power dropped off (753ft-lbs of torque at 3200rpms). the dipstick blew out along with oil! checked everything, car still had oil press, good idle, clean oil and coolant. AFR stayed good too when it sprayed. after checking for blow-by and vitals we made another NA pull and everything was still good to go (other than a little clutch slippage). I do not have any valve cover breathers or anything on the car, so should I just get a breather and try again, or should I get a crankcase evac kit? is the evac kit okay for a street car? what are the downsides of the breather or evac kit? I know that whatever I do it needs a checkvalve because I had the hose from the valve cover to the TB crack and the car would barely Idle when that happened. (that could have been from air geting to the TB also, not sure.)

 

Good god no breathers I have 2 -10 bungs welded into my valve covers, which vent to atmosphere. That works well for my setup and should be all you need for the street. I also no long run a pcv valve. I think you can see what I did from my picts in my sig.

 

I still have a PCV, but the hose goes directly to the intake from the intake, not sure if that makes a difference. so, breathers are a no-no? you just have those blow off tubes dropping down to the ground? how much oil comes through them?

 

You really can't compare a blower or turbo motor to a nitrous motor... two different issues with regard to crankcase ventilation. I'm not sure why the nitrous should have caused a sudden problem with blowby. Were the pistons and rings selected, located and fitted for the nitrous application? I spray a 275-300 shot on a 381, and use the stock closed PCV system.... no breathers.... no problems.

 

not sure. I have never had a problem with 150 shots or lower, but this 78/41 combo just lost it.....

 

I think all motors should have adequit breathers on it, turbo or not. I've seen this problem with N/A motors alone. I would highly recommend you put some breather tubes on your motor. Either put them into a catch can, or dump them to the street. I recommend the street myself. The reason I say no breathers is because it will fill them with oil and run down your valve covers

The amount of oil that comes out of them is very minimal. Only a small mist if any will come out under a pass.

 

I was thinking about a catch can.

 

Here's one noone has asked yet.. Did you have the motor specifically built for N2O? Reason I ask, is I have a bit of a problem with crankcase pressure as well, but I know why. When I built the motor, it with the full intention of running a 300+ shot of N2O, and as such I had to put in a larger than normal ring gap for safety sake (22 top ring 20 second ring with the understanding that they would open up another .003 to .005 after seating). This allows a little more blow-by on my car, but it was expected under non N2o use. What puzzles me though, is that as you dump the N2O in there and heat up the rings, you would generate LESS pressure, and not more. I would think that if you had the trouble at very high RPM all the time, it would diminish a bit with the tighter end gaps on the bottle..

Somebody hit me if I'm out in left field here...

Dave C.

 

WELL, THE MOTOR is built loose and slaps a little on start up, not sure what the ring gaps were. does this help any?

 

If there is noise at idle that is most likely piston slap until they expand. How much nirtous did you plan when the motor was built? I have a ~.024 gap on both rings. I only experience a little crank pressure under boost. The motor before had a big gap on top with a smaller gap on the bottom. Speedpro did some dyno testing to find a larger 2nd ring gap nets more power on the top end. If you look at all there fill fit rings I believe they recommend .005 gap for every inch of bore on the top ring. 2nd ring is like .006. This is how I did my new motor and the result was a hell of a lot less blow bye.

 

I was thinking about case pressure as well on my car. It is stock but I was looking through the instructions for the blower I have and it says I do away with the pcv system.

I thought case vacuum helped the rings to seal causing less blowby.

Would it be beneficial to me to run an exhaust type crank evac kit? Like I said, my car is a stock LT1, so no custom ring gaps or anything.

 

If people were to look at their '94 service manual, they'd reallize GM has been doing this (a larger second ring gap) for at least 10 years. I'm confident SP has known this, for some time, also.

 

I wonder if vented pistons make a difference here?

I can understand the a larger second ring would allow more pressure to bleed off that gets trapped between the top and second ring, and help to keep the top ring from unseating, but I'm left wondering if the vented piston designs would benefit the same, if at all, froma larger second ring gap.



Dave C.

 

Yes but GM didnt have turbos and nitrous on their cars from the factory. These test were done with FI cars and nitrous. The norm was less gap on the second ring because more heat was related with the upper ring. There recent tests proved this wrong. Speed pro changed their recommended gaps for FI/nitrous cars recently because of this.

All this info was given to me by speed pro