Doug's Headers
 

I installed my new Doug's headers and have a couple questions.

1. By installing the small extension will it have any effect on performance. I know the purpose of the extension is so you can attach exhaust in a street car.
2. For maximum vacuum exactly where to install the evac tube in the collector.

Thanks

I have seen some posts that they cannot install the full size filter with Doug's headers but I have plenty of room to remove the full size filter with 1-7/8 round port.

I'm running the same setup on my 67 Firebird but I don't have a evac tube so I can't help you there. Do you really need it?

Its the next best thing to a vacuum pump. It sucks out the blow by and creates a slight vacuum. Prevents leaks and improves ring seal. The system works pretty good and I have used it for many years. It does not work with mufflers only open headers.

Not exactly the same set-up but close enough. I run shorty headers though. My evac is after the resonator (O2 before). If I hadn’t used the resonators I would have tucked it in a bit closer but probably same effect. The evac has been on a few years. Very happy with the results.

Here is my Evac tube setup. Definitely made a difference on reducing crankcase pressure after they were installed correctly.

It is very important to have the correct angle and depth of the tube in the header. As far as I recall Moroso recommends a 30 degree angle and the tube cutout which creates the vacuum should be at a 1/4" depth.

My evac tubes are 2 inches back from collector flange at about a 30 degree angle approx 3/4in into the collector. I run a 3.5in system with x-pipe and dynomax ultra flows turned down at rear axle. The evac will work fine with free flowing or race mufflers.Big thing is to make sure the breathers fit in the grommets really tight and there are no leaks. I rtv the grommets to the valve cover and also use a ball peen hammer to tap the breather tube a little to expand. I have also found using hose clamps helps. My car runs faster with the X-pipe and evac than it does open headers or extensions. Which is surprising considering the exhaust is almost 65 lbs.

Agree with Mike on the fitment of the breather. I ended up using the Moroso positive locking breather (oil separator for some) 68785. Also, and not necessary, but I had to change from the standard Moroso oil check valve at the exhaust because especially at idle it rattled a lot (didn’t know what the rattle was at first – thought another gremlin popped up). I changed to the Moroso oil check valve 23875 and all good.

dv657172
What is the purpose of the extensions after your collector?

The header extensions are supposed to increase power and torque. I have never checked with them on vs. off to be honest but thats what the guy who was a very serious street racer in South FL recommended after I destroyed the 3" Pypes full exhaust system along with a driveshaft on my first track outing ever. I also had a very memorable 180 rotation at about 1,000 feet thanks to the trans fluid but no damage. Lesson = dont use nearly 60 yr old :eek:stock upper control arms. I'm a rookie at the racing stuff.


Here's some commentary.
https://www.yellowbullet.com/threads...sions.1182330/

Here is a very interesting video on the placement of the venturi tube in the collector for an evac system. This guy did some very cool testing and I was surprised by the result with regards to how to place the tube in the gas stream.

https://www.youtube.com/watch?v=uL4rnN-Sr9M