Has anybody measured actual vacuum from a header evac system?

[cjshaker]

Before I order my FE Power valve covers, I was considering getting the caps machined for the AN fitting to use for a header evac system and was wondering if anybody had measured actual vacuum while under WOT? Or if anyone had measured actual power increases on a dyno? I know a vacuum system can add power, but not sure how well a header evac system works. I see plenty of rails and tube chassis cars that use them, so they obviously must do some good.

[blykins]

Doug, if the engine is sealed up well, you will see a couple of inches vacuum from them. 

I like using them when I can.  It's a good "compromise" for when you need a little help, but you don't want to pay for a vacuum pump and all the fixin's.

On all of my engines where I pull vacuum with a header vac, I usually use a fitting on each side where it will suck from and then an additional fitting that will take a small vacuum gauge so I can see what it's doing on the dyno.

[wowens]

How about with mufflers, does back pressure of mufflers negate any vacuum

[blykins]

It depends on the muffler.  It's hard to get them to work with mufflers, unless it's an extremely unrestricted one. 

[cjshaker]

Brent, I realize you were only running one side for measuring purposes, but wouldn't it increase the vacuum reading if there were one on each side? Is the sole purpose of running vacuum to be able to use low tension rings? I'm under the impression that a depression in the crankcase also helps windage and has less piston pumping losses. I'm just trying to figure out if it's worth doing or not. I don't want to go the pump route because of cost, complexity and space issues. And thanks for your response.

[blykins]

Doug, I pull off of each side.  My post wasn’t very clear and I will edit it.

And yes, every reason that you gave is the reason for pulling vacuum on the crank case.  Obviously a higher tension ring produces more drag and you lose that if you use a lower tension set. Unfortunately if you use a lower tension set you don’t always get the oil control that you need.

Last 1/1/2mm ring pack I used netted a 7 lbft rotating torque on the short block.

[blykins]

Are you running open headers or will you be using mufflers?

[Barry_R]

Ran one on one of the EMC engines a few years ago when they were legal.  Only saw maybe 3 or 4 inches.  Did pick up average power - maybe 5 or 8 HP gain.  Mufflers would probably negate most of that.

[Falcon67]

You'll get the best draw with the collector tube in the center of the collector and turned so that the open end of the tube (with the 45 degree cut) is facing out, not laying parallel to the air stream.  My "measure" has been no more than holding the motor at 2500 or so and putting a thumb over a hose pulled off the valve cover.  If you feel suction, it's working.  You'll also want quality one way valves.  My experience with the Moroso parts is that they don't last very long.  There is a NAPA part number but I don't have it handy.

Edit - https://www.napaonline.com/en/p/CRB229000

[cammerfe]

Does anyone have a comparison of the header set-up as opposed to using a dry sump system?

KS

[cjshaker]

Brent, it will probably be a combo of headers with a cutout, for times like Drag Week, and open headers for times like the FER&R. Either way, it'll be free flowing enough to take advantage of the combo.

Chris, thanks for that diagram. That's a big help and saves me a bunch of research.

Ken, if I remember correctly, some of the combos I've seen that were optimized for the use of a full pump system will generate as much as 15-20+ HP. I haven't gone back to look at Jay's dyno experiment, but I believe it was in the 20 HP range. I realize it's not exactly apples to apples, but if Brent and Barry can see a 5-8 horsepower or torque gain on a somewhat milder engine, I'd think that's a fair enough comparison to assume that, while it's certainly not as good as a full pump system, it does generate at least a 1/4 or more percentage of that. Maybe even up to half as much on comparable engine builds. Of course the header evac system is only functional at higher RPMs, but I'm not talking about low RPM use anyway.

Thanks to everyone for your replies.

[blykins]

Does anyone have a comparison of the header set-up as opposed to using a dry sump system?

KS

Ken, with a sealed engine and a good name brand dry sump pump, I can pull 7-8 inches at idle and can pull enough vacuum at WOT to deprive parts of oil....15-20 inches.

[Tommy-T]

I have run a Moroso PanEvac set up on my blown 427 (454) for several years. While I have not measured actual vacuum, you can absolutely feel vacuum with the "thumb method" at idle with a 3" exhaust going into Hooker Max Flow mufflers.

In my situation, it seemed open breathers or the Pan Evac were the only options. Pretty happy with the results as the car does not blow oil out the exhaust at full throttle or build up pressure in the crankcase.

Use at least -10 lines to the collector. Bigger would be better.

[Heo]

The Volvos in the 70-80s had no airpump for the air in to the exhaust..emission stuff
Just a tube in each exaust port in the manifold to a collectortube to a oneway valve
and with a restrictiv stock exhaust  it gave quite a suction on the tumb ...