1.5 to 2 inches.

depending on the cam, you could about grind them completely off with a 5.9L.

 

I am prolly gonna go 1.5. I don't see how anybody could do 2. I don't see how anybody could grind them all the way down either. I would like to see a pic of that if anybody has.

 

it's not a straight 2" all the way around, it's more off the front of the runner than the rear wall. I've seen a few that are ground down to just about comforming to the curve in the top of the keg.

 

Has anybody seen a difference in MPG? In my 5.9L is it safe to take the runners all way down?

 

The easy answer to that is YES. There is a difference in MPG. HOWEVER, members almost always do this mode while doing the plenum fix. So it's hard to say if your getting better MPG's because of the kegger mod or because you fixed the plenum. As far as grinding them all the way down, I'd go no further them 2 inches off the runners. 1.5 inches will do you just fine.

 

So glad I found this thread!

I ordered the Hughes Plenum fix and this will be a nice freebie mod! Due to my inexperience of grinding down metal - I wonder what a machine shop would charge to do this mod for me and port / polish the inside for me? Hmmm.....

 

Because it is aluminum, it really isn't that hard to do it yourself. Soft metal is easy to work with, just don't get crazy. Machine shops tend to be kinda pricey in my opinion.

 

SilverDodge - forgive me if this is beating it down, but with my 5.9 some are saying you can cut all the way down but 1.5" down is recommended. Then do I determine the angle to cut from the outside edge of the runner to the mark 1.5" down - then cut away? Right?

I don't do much off roading or towing - its a weekend driver and here in Phoenix I do mostly city / suburban type driving. I'd like to see more mid to high rpm power for passing.

I have Spectre cold air, Magnaflow cat back duals and Superchips (until I can buy SCT). I'd like to get the H&S 1.7 RRs later this summer after some vacation funds are built up.

 

Silver_Dodge = you weren't kidding. Places are quoting 100-200 and up to 1 week to trim the runners; true it up with a port and polish.

 

Right, usually people with the 5.9 just cut the exposed part of the runner all the way off. If they do the 1.5" cut though, they mark 1.5" down from the edge of the runner (that is the edge closest to the center of the intake where the runner is most exposed), and then mark parrallel to the runner opening so that the cut is 1.5" down on all four sides of the runner. Notice however that I took a different approach with my cut. I cut it at an angle instead of parallel to the original runner opening. I did this for several reasons. Mainly, so that the back wall of the runner was still the full length, but also so that my cut basically opened up the mouth of the runner (effectively making it a larger opening) and turned the opening angle more towards the center. In air flow dynamics, there is a term know as the funnel effect, or funneling. Basically, all it amounts to is the tendency for air velocity to increase as it flows from a wide opening to a narrower passage. That's what I was going for. My hope is that by making the opening mouth of the runner larger, the air velocity will increase as the air flows from the wider mouth of the runner into the narrower runner itself. Increase air velocity in the runner means you will have a better "inhale" of air into the cylinder on the intake stroke.

Did it work as I intended? Who knows. In my garage, I can't really do the type of testing needed to determine if air velocity with this design is better then with the stock design. Since noone out there has really done much scientific testing on the kegger mod other then dyno tests and seat of the pants tests, I figure all I can do is apply what I know and give it a shot. I've always been happy with the results though, but as others have stated, when you are driving with a blown plenum (which I was at the time I did the mod), anything is going to feel better then it did when you where sucking in oil.

I think I shared with you all the dyno result posted by a guy on another forum. His summary was that the mod made about 7 less horsepower from 3000 until it hit 4000 then made 14 more from 4000 until 5200. As for torque, our engines hit max torque at under 3000 rpm. On the dyno, the modded kegger produced less torque (10 ft lbs) at the point where torque is first at its max, but produced more torque from that point up to 5200 (so basically, the torque curve didn't drop off quite as fast from 2900 on up with the modded kegger as it does with a stock kegger. So the jist of this is, it basically gave both torque and HP increases in the upper rpm range, but decreased the max torque and HP at low (3000) rpm range. I once spoke with a guy who had done several modded keggers and dynoed them all, and his results where similar. It wasn't until he started filling the kegger that he saw the max HP and torque numbers come back up, essentially giving the best of both worlds (higher max HP and torque, and less/slower drop of torque as rpms increase).

By the way, this completely confirms generally accepted understandings of the relationship between long runners and torque. The longer the runner, the better the low end HP and torque. HankL used to post often about this relationship.

So if one is wanting to gain more HP and torque at high rpm (and have a flatter torque curve from 3000 on up), this would seem to be a good mod for them. Just know that you might notice a slight decrease at lower RPM. But that could be restored or overcome with other mods that focus more on low end power.