THIS IS NOT LIMITED TO LUDESPEED KITS ALONE.
It's the kit I have and I haven't investigated others.

While troubleshooting some idle quality problems I came upon this important piece of info.

The Ludespeed kit renders your PCV system practically useless. This system is often under-rated by people, but true professionals know that a good vacuum on your crankcase is very important because it helps your rings seal and generates HP. Multi-thousand horsepower engines have vacuum pumps that run off the crank and draw a vacuum on the crankcase.

Eliminating this feature hurts your throttle response, gas mileage and oil consumption.

The Problem

The intake manifold has an attached PCV checkvalve that draws a vacuum on the crankcase and removes oil vapor.

The ludespeed kit has you run a hose from the suction on the valve cover breathers to the suction side of the turbo. The basis for this is that when the engine goes under boost, the check valve will shut and the turbo will draw the vacuum via it's suction. This is an accurate assumption, although the vacuum is minimal.

The problem is that when the engine is in the vacuum region, where it spends most of it's time. The intake manifold is not drawing a sufficient vacuum on the crankcase. It is mearly drawing a large amount of air into the engine from the hose routed to the turbo suction.

This is causing TWO major problems on my car and may be affecting yours too.

It is affecting idle quality by allowing too much air to enter the intake unmetered.

It is reducing the effectiveness of the PCV system drastically.

The Solution

Install another PCV check valve in the air hose that is attached to the turbo suction. Orient this valve so that air can only flow INTO the turbo suction from the PCV system.

This will ensure a good vacuum is placed on the crankcase and will help throttle response, idle quality, A/F ratios, and gas mileage. I noticed an immediate improvement in all but gas mileage because the power increase made me eager to put my foot in it all the time.


If you have been suffering from poor idle quality this may be your cause.


Hope this helps.

Dominic

 

really good write up!!
Thanks

-Brian

 

another way to utilize the PCV is using the exhaust.... My brother in law races pro comp eliminator (NHRA), on his truck, he routes the PCV system to his exhaust this way there is a source of vaccuum. also if there is a chance of oil blow by, through the PCV the excess oil will be burned off by the exhaust.. you would want to do this either behind the CAT, or if you are running catless. Racers have been doing this for years.. although I am not sure how much vaccuum is generated on a suby's exhaust, but on a alcohol fed truck generating 2900hp I am sure there is quite a bit.. has anyone tried this on a suby? maybe I will try this and let everyone know.??

 

Positive Crankcase Ventilation

 

Thanks for the writeup!

 

Suppose I don't have a fitting on my turbo inlet anymore so I have the hose venting to atmosphere. Then where/how would you put the check valve?

 

not sure I understand your setup. Please clarify with pictures/drawing or a futher description

 

How would this relate to those who don't run their breather and pcv valve lines into the intake tract, but instead run them to a catch can that vents to atmosphere (does not touch the turbo intake pipe)?

jonathan

 

well, if you are running a catch can vented to atmosphere then your setup is all goofed up. A catch can is supposed to catch oil vapor from the crankcase and filter it out so it doesn't get ingested into the engine; therfore minimizing the possibility of fouling out your plugs and excessively carbonizing your cylinders.

 

Do you have any sort of vacuum applied to your crankcase at all? You need to utilize some sort of vacuum supply. Well I guess you don't NEED to. However, the best motors usually have a strong vacuum applied to the crankcase; it helps seal the rings good and strong. A lot of motors have vacuum pumps run off of an accessory belt just for the purpose of sealing the rings.

LOL, I said "good and strong" LOL... I'm watching the Nutty Proffessor...

 

I am not running a catchcan, or any turbo components.. yet. The reason that people vent a catchcan to the atmosphere though is because supposedly the can is not capable of capturing all oil vapor, so if you were routing it back to the intake tract, vapor would still be sent back through the turbo, which is not the best thing.

j

 

nah, if you vent it to atmosphere, THERE IS NO POINT IN HAVING A CATCHCAN.

Unless they're trying to minimize the amount of oil vapor they put into the air. But that isn't what it was originally designed for.

I think you may need to look again at the required flowpath of air.

Catchcans are much more efficient if you fill them with something to help trap the oil. Most of the catchcans nowadays (including mine) are made mostly for looks and don't have any baffling or filter media that is required for proper operation.

Putting a handfull of polyfill or cotton would help in trapping oil.