b20ricepower

I am wondering exactly how much crankcase pressure is acceptable on a built engine. Since this is my first full engine build I am curious. When I remove my oil cap while idling, I can feel a considerable amount of air coming out and I can actually feel every pulse of air as the pistons move up and down. I have great compression on the engine(180 psi on all cylinders) and brand new valve seals. Piston to wall clearance is .045 with cp pistons. They are a little looser than reccomended because of my power goals. I figured i,d go straight to the drag racing forum because this is probably where the most high hp guys post. Any input on this?

Current setup

84mm bore cp pistons manley rods
cnc gsr head
Pro1 cams
6765 precision t4 top mount man.

Btw I have 4 -10an lines venting the crankcase. 2 on the valve cover and 2 block port fittings all vented to breathable catch cans.

redboost10

Search for a thread on crankcase pressure and catch can setup by Tony1. I believe he logged crank case pressure from the back of the block with the catch can setup he sells and I think saw no more than 0.5-1 psi with up to 40psi of boost.

Tippyman

I can take the hose off my valve cover and feel the air. I work at a honda dealership and if someone forgets to put an oil cap back on, you can hear and feel it. Pretty normal.

ENOXJoe

Blow-by
The best crankcase blow-by number is zero. That is hard to obtain. Our race engines typically attain .2 to 1 SCFM at WOT from 3,000 to 7,500 RPM.

The cause of blow-by is combustion leaking past the piston rings. The top ring seals the pressure in the cylinder. The ring is designed to seal a round cylinder and to the bottom of the land of the piston ring groove. The cylinder must be round and straight. This is a near impossible job, but the closer you get to round and straight the less blowby you'll have. Some piston rings may not be flat enough to seal against the land. The land needs to be square in the piston and perpidicular to the cylinder in 2 axis.

The second ring is to seal the induction stroke. This ring seals to the top of the second land.

The oil ring removes oil from the cylinder walls. Oil on the cylinder walls is your enemy. The tension of the oil ring can improve oil removal at low speeds.

The straight and round cylinder is essential because the rings will not change their shape or size to comform to deviation in size or roundness. Some comformity could happen with the oil ring at low speed, but not at higher speed. This of course can relate to ring tension. The higher the ring tension the more friction the cylinder wall will see and the more heat that will create requiring more cooling. I want to mention that in this part of the engine oil is a coolant. We'll talk about that later as we will about cylinder finish.

Piston ring tension can translate into friction. A farm boy method of measuring this is to use a sping type hanging scale and install the piston upside down in the cylinder with the piston rings inplace. Pulling the piston up by the connecting rods big end allows you to measure the energy required to pull it up. The stock piston ring pack, which includes the top, 2nd and oil ring, tension pressure can exceed 30 lbs of drag in the cylinder.

On the dyno and in our drag race cars we use a 0-5 SCFM flow meter. Our total blow-by is less than 1 SCFM at the beginning of the run or dyno pull and .2 SCFM at the end of the 1/4 mile or dyno pull. Our cylinders are round enough and straight enough that we have reduced our total piston ring drag to less than 5 lbs. This round and straight cylinder will also let the oil ring do its job.

I'll continue later.

twkdCD595

Believe he logged only .1 psi at like 45# of boost and 8900 rpm on his motor at the time.

That was with his 6 line setup t1 catch can... -10AN lines.

ENOXJoe

More #1 on blow-by
Reducing ring pressure is a sure way to reduce losses in the engine. As you attain better ring seal you also reduce losses. Those reductions go to the positive side of performance instantly. With better ring seal you not only keep more of the combustion pressure to push the piston down, i.e. more power, but you enable a better draw on the induction system for ingesting more air and you reduce oil contamination of the combustible charge making for a better, more consistent combustion process. This can change the fuel curve and timing curve. The engine will start better and accelerate quicker. There are some details of engine performance which are difficult to measure. One is engine acceleration. Two engines making the same power can run differently in the car because of engine acceleration. This is not about light weight parts. It's about fixing deficiencies in the current mechanism.

Another thing I would like to mention is the distortion of the cylinder and piston during operation. This distortion can be caused by heat and/or pressure. Any process that relaxes the materials from distortion, such as cryogenic or vibratory processes, the more stable the materials will be and the better the ring seal will be across the power and RPM range. Most Pro's ultrasonic test every cylinder wall for uniformity and thickness.

To verify some of this for yourself, leak the engine down at TDC. Be aware that some leak down tools use 100 lbs and some 50 lbs for the test pressure. The results in % will be different. Then leak the engine with the piston at BDC and again in the middle. To do the middle you should lock the flywheel in some manner. I made a lexan plate for our blocks and could leak the engine down on the engine stand as a short block. You can learn quite a bit. Cold engines should have very small leak down %. If it changes when warmed up, what caused it?

More later

redboost10

Awesome. Thank you for the clarification.

b20ricepower

Holy jebus. ENOXJoe had some beastly posts. Sounds very knowledgeable. I'm not sure if my ring seal is as top notch as yours, bit it wàs a reputable shop that bored my block and I set the ring gaps dead on. I was just wondering mostly because of the turbo issues ive been having.
Long story short, I was on my third turbo from precision....WAS is the key word here. Every time I send it back they say it was either intermittent oiling or oil contamination. The first time I believed it and it was covered under warranty. The second time I was a little dubious but figured, ok, maybe I still have something not right. Now it is the third time its went bad and its complete bullshit. My oil feed and drain are both perfect. -4 an line on the feed with an inline filter unrestricted directly from a golden eagle sandwich plate which is filtered oil already anyways. My drain is -10an directly straight down to my oil pan which is a pre tapped moroso. Oil pressure is also rock solid. Im beginning to believe that this turbo is junk. Something is wrong and they arent catching it during the rebuilds.
I posted this because the only other thing that can make the turbo go bad would be excessive crankcase pressure backing up the oil in the drain line.
I have two breathable catch cans with 2 inlets on each and one large breather on top. Both baffled as well. 2 from the back of the block go to one breather and the other 2 from the valve cover go to the other. Only thing that worries me is that the one that connects.to the block fittings fills up rather quickly. If it is full it might block the catch can from breathing properly but I still doubt this is what caused a turbo failure, I guess im just being super cautious.
Anyways, I decided to go with a borg warner s300sx3 because im sick of this precision turbo junking out on me. I just want to be sure that crankcase ventilation is adequate. I mean, 4 -10 an lines should be plenty, right? I even have the stock breather nipple on the valve cover with a breather fitting on it. Anyone else have experience in this matter?

b20ricepower

Also, I wouldn't mind logging my crankcase pressure but im not exactly sure how to do this accurately. I do have spare map sensors I could use but not too sure how to properly log and wire up. A mechanical boost gauge sounds easy but not very accurate and theres no way of datalogging obviously.
If theres a simple way to do this on neptune rtp im game

b20ricepower

Nothin?

luck4rmkc

iTrader: (2)

You could use the hose barb port on the back of the block that usually goes to the "black box" as tony1 did. Run a short vacuum hose from the hose barb to a stock map sensor.

Wire the map sensor to an open 0-5V input on your ECU such as ELD (d10), O2 (d14) then log away.

b20ricepower

I actually did that recently except i spliced.into the stock map wiring for 5v and ground. Signal wire is through input b6. Its datalogging, however the sensor is cutting in and out. It will read fine and then lose reading. Itll do this throughout the datalog. I gotta figure out if its a bad map sensor or something to do with the wiring now. I did a few pulls and the reading never reached above 980mbar but i'm not sure that its accurate until I get a clear signal.

blackeg

i honestly would not run the 2 plugs on the back of the block i find they will fill your catchcan much more than from the valvecover seeing as they are closer to the oil pan.

im also running cp pistons, between .0045 and .005 ptw(i wouldnt run cp at much less ptw than that), 210 psi compression. at 500hp it would fill my catchcan every 2 passes from the back of the block. i swapped to just using two -10 fittings off the valvecover and the can sees considerably less oil now

Turbo-LS

iTrader: (4)

Bestw ay to vent the crankcase is by venting the crankcase. The fitting off the VC really do nothing. Your trying to force crank cressure up through oil passages to the top end of the motor. Your fighting the oil from draining back down and then oil gets stuck in the head which can cause starvation issues. For a mild setup the VC works great when you start getting up there in power other options are nessesary. The fittings on the back of the block arent really breathers they are more for drain back as they are right in the oil galley passages.

One large vent off front of block or oil pan to its own catch can or up to the valve cover and then vent the valve cover seems to be two of th ebest ways to vent the crankcase pressure. But like already stated a proper ring seal drastically reduces blowby and crankcase pressure. I have a only 2 -10 off front of valve cover which shouldnt be adequit enough for my setup but its been working wel. I don't have a lot of blowby in my motor. I will be installing a 1.5" breather off my oil pan for crankcase ventilation though to its own tank.

b20ricepower

I agree that the engine should have more than just valve cover ventilation. Maybe on a stock boosted engine its fine, but not with forged pistons. They contract and expand a lot. Lets more pressure into the crankcase

mrbsponge

as mentioned above, venting the actual oilpan itself has got to be the best form of serious venting on a Honda.

nonvtecallmotor

I run 4 -12's. 2 on the front of the valve cover and 2 from the back of the block. 1 of them I use as a drain back (bottom of the catch can).

DDTECH

That's because u need a drain back. Those block ports are the drainback from the head, the oil runs down that back so, so at wot you will push some oil but with a drain back you'll be fine. I have a breather on my vc, and I vent the two ports on the block to a catch can that's open with a filter and has a drain back. I've not had one issue ever..

HR-1320

Very nice ENOXjoe. Keep it coming. Posts like this will bring me back more than once a week.

blackeg

Personally in all of my ignorance I dont like drain back setup. Once in the can I think it can mix with condensation and then that winds up In your oil pan. Thats just me

nonvtecallmotor

whats in the can is what comes from the motor... Only difference is you don't see it.

I make at least 100-150 passes per year my engine. I freshen it up every year and have never had a bearing that didn't come out looking new.

HR-1320

I run methanol in my motor and the opportunity to drain the the catch can is great to me. I find all the water, fuel and oil separated. Then i can add fresh oil and stay on top of the oil system.