Header evac system

[lust4speed]

I read the post about the evac pump but didn't want to hijack the thread with a question for a friends street/strip project. We're building a nice 467 with Butler ported Edelbrock heads and all the good stuff. It will retain the stock PCV valve off the valley cover. Can we also install the header evac system? Will the system work somewhat with running through the mufflers? I know that when we get to the track and uncork it will be of value, and just wondering if there would be a down side to installing it for the street driven portion of the running.

[Brian Baker]

It'll still pull vacuum with a corked up exhaust. Lose the PCV valve, and run the EVAC to the headers.

[ponjohn]

I kind of butted in on that thread also. I am going to do exaclty what Brian suggested with an AP valley cover. 90% street driven.

I bored a hole in the front runner of the rpm for the PCV and it is pulsed and eventually wears the vacuum tube out and then it begins to whistle.

John

[RAIV55]

Just for what it's worth I have used a PCV valve with header evac on a race only engine. It caused me no problems and somewhat eased a combustion chamber oiling issue with the engine running at low RPMs. This was due to very low tension oil rings and no second rings. The eventual permanent cure in this particular case was a vac pump.

Can't tell you what would happen on the street with capped up exhaust, but I'd consider it worth a try. It's not a big deal if it don't work.

If you are running an aftermarket valley pan, the PCV could be in direct contact with oil spray and create issues of it's own.

[suprchikn]

Can't comment on effectiveness with corked exhaust, but on my street car it pulls a definite vaccuum at idle. Lots of overlap in the cam, 2" headers, 3.5" pipe from collectors through Flowmaster Delta Force mufflers and exiting out the side well before the rear wheels. Probably 0 backpressure but with all the overlap I was very surprised.

Ray

[Tim Corcoran]

I have used the header evac system on a drag car for years and it works great. I tried it on the street with an exhaust system and had poor results. For street use I recommend using a factory PCV system and a hose from the valve cover to the air cleaner like a factory system. You could hook up the header evac system for track use only and switch back to PCV for street use.

Tim C

[JoePapa]

I think someone posted a while back that for a street driven car you need some type of one way valve type fitting so that you don't let positive pressure into the crankcase. I'll see if I can find it but the basic idea (if my old brain is remembering correctly) was that at low rpms (stoplights/signs/idling) you don't have enough force and that exhaust could come up the tubes and pressurize the engine. A one way valve would prevent this from happening.

It looks like the Moroso kit may have that built in?

http://store.summitracing.com/partdetail.asp?autofilter=1&part=MRG%2D6002&N=700+115&autoview=sku
and
http://store.summitracing.com/partdetail.asp?autofilter=1&part=MOR%2D25900&N=700+115&autoview=sku


Heck, I may have to inquire about that for my car...

[lust4speed]

Yes, the Moroso, Summit and Mr. Gasket evac systems all have the check valve. I kind of figured that for this reason there wouldn't be any harm in running it on the street, it just might not do that much good. I have been running it on the drag car with open headers and it has worked excellent. Sounds like we will go ahead and weld in the bungs in the collectors - sure can't hurt anything, and a lot easier to do with the headers out of the car before we bolt everything together.

[ponjohn]

I don't have time to look now - I wonder if you can buy the one way valve seperate as my wife just bought me all the fittings (from summit for my b-day) to weld in to the header, along with O2 bungs.

John

[Brian Baker]

I ran the evac with the exhaust corked up (if you want to call 3.5" pipes dumping into Flomasters and then out "corked up"). Never had an issue.

Jeff Kipe ran a full exhaust system in his 11 second street driven Firebird with an evac and never had a problem. It pulled all kind of vacuum.

Placement of the evac tube in the collector is key, I suppose. Wouldn't matter if the exhaust was corked up or not, if it's in the right spot, a low pressure wave will be created over the orifice, which will draw a vacuum. Wehere to find the sweet spot? I have no clue.

[screamingchief]

I don't have time to look now - I wonder if you can buy the one way valve seperate as my wife just bought me all the fittings (from summit for my b-day) to weld in to the header, along with O2 bungs.
Yep,bought a pair of moroso valves just a while back,part #97800.

$20.99/pr. @ summit,ships today.

These are nothing more than GM air pump check-valves,can be sourced through many sources,but you need to watch the applications as different OE applications used differing calibrations for the check-valves.

I just buy the moroso units,a couple of bucks is'nt worth it too me to try and deal with the morons often found behind a parts counter...

Bret.

[steve]

yeah, but will an evac system work well enough on a street car to be able to ELIMINATE the pcv ?

[screamingchief]

Placement of the evac tube in the collector is key, I suppose. Wouldn't matter if the exhaust was corked up or not, if it's in the right spot, a low pressure wave will be created over the orifice, which will draw a vacuum. Wehere to find the sweet spot? I have no clue.
I use the same method I've always used for finding the right collector extension length on open exhaust cars.

Paint a stripe along the outside of the header collector/extension and watch where the paint burns off to,any place where the paint is burned off still sees a strong wave pulse as this keeps the exhaust temps up and will burn off the paint.

Any place the paint remains the gasses will have cooled and expanded and the wave will be a lot lower in strength.

DO NOT use a real high temp paint,just a generic paint or standard temp engine paint,and dont paint it real thick either,the idea is it should burn off easily.

[ponjohn]

I ran the evac with the exhaust corked up (if you want to call 3.5" pipes dumping into Flomasters and then out "corked up"). Never had an issue.

Jeff Kipe ran a full exhaust system in his 11 second street driven Firebird with an evac and never had a problem. It pulled all kind of vacuum.

Placement of the evac tube in the collector is key, I suppose. Wouldn't matter if the exhaust was corked up or not, if it's in the right spot, a low pressure wave will be created over the orifice, which will draw a vacuum. Wehere to find the sweet spot? I have no clue.

I run full 3" including tailpipes. 40 series flowmasters.

[NHRASuperStock455SD]

Dont be afraid to run the evac tubes down the center of the collector between the 4 pipes. I drill a hole in the center of the 4 tubes in the tube sheet, then stick the evacuation tube in the same direction as the 4 header tubes in the exact center of all 4.

It gets a bit trickey if you have a Burns Collector. (Besides getting up enough nerve to drill on a set of $850 stainless collectors). Make sure you have it clamped down in a VICE! It will get caught in the drill and spin the whole thing if you try to hold it by hand. Very dangerous so be safe!

I use either alum or copper tubing to bring the evacuation tubes past the header tubes straight out the front. I then attach a braided hose.

Pulls much more efficiently than a hole in sideways. There is a huge draft just beyond that tube sheet where the tubes merge. Take full advantage of it. We saw significant numbers on the dyno, and it takes no moving hardware(HP) to run!

Lynn

[steve]

yeah, but will an evac system work well enough on a street car to be able to ELIMINATE the pcv ?



no takers ? my pcv is still sucking a little oil into the base of the carb so i would rather do the evac BUT i am mostly on the street now...........