Tag Archives: research into the science of long runner intake manifolds

I need to write something

Like seriously need to write. The only problem is I have no idea what I’m going to write about. It’s like that old science fiction story by Harlan Ellison, “I have no mouth and I must scream”, except I have to write something etc. etc. Which is where I started this piece about 20 minutes ago.

I guess I could mention what my son gave me for my birthday. The local grocery started carrying Shiner Sausage, a beef log kinda thing made near Shiner TX, where they make the beer. Yes, that Shiner. Anywho, they make the sausage near where the pagans have a campground for celebrating our Big Two holidays. You know how they have Easter and Christmas “Christians” that only show up in church then? Well our two big holidays are Beltain and Samhain. Beltain is pronounced pretty much like it’s spelled but Samhain is pronounced “SOW-wen”, not that that is important to this, but important enough to tell you about. I’m free-associating here, but there is a point I’m going to get to some time before I finish this. Yeah, where they make sausage is the landmark for turning off the main highway onto the little back road that takes you to the gravel road where the pagans’ campground is. I would tell you what the road is but telling you about the sausage factory already gets you too close to finding where us pagans dance naked in the moonlight. Because of my bad hips and knees I don’t actually dance naked anymore, I just kind of shuffle around in the dark and make passes at the lesbians, because they’re the cute ones. Anywho, sausage, birthday, my birthday is Tuesday, and Mrs. the Poet and I are going to go to the Red Robin because I get a free burger, and Mrs. the Poet gets the free one and I buy the one with the half-pound of beef, another half-pound of bacon, and a fried egg on top and endless fries. And a sundae, I also get a free sundae before I hit the meat coma. And that Sausage is a 12 oz. package and costs $7 which just goes to show that when you use local steers and local labor to make your all beef sausage it costs a bit more than commodity beef and overseas labor. I think it’s worth it.

Then I hope I recover consciousness in time to go to my doctor appointment next Tuesday. That part is a joke, because I never take more than a night to sleep off a meal like that. Now I might not be ready for much more than a cup of coffee the next morning, but I always wake up the next morning. Or if I don’t, nobody tells me I didn’t wake up the next day, and it seems like that would be something people would really like to tell me about: “Hey Opus, remember that time you ate so much you didn’t wake up for a whole day?” That kind of stuff, nobody has ever brought it up, so I’m assuming it never happened.

And the overwhelming urge to sit down and write has passed. Mostly. I still wanna write about the paper I found on designing intake manifolds, but mostly I found that if I did the math right I need to make a manifold with 2 plenums feeding 4 cylinders through 2 throttle bodies, and I need to make the runners 180° apart for the whole 720° cycle of the engine. That means I need to have 3 runners from one bank and one from the other bank of cylinders, or I could just have all the cylinders one each bank fed from one plenum and not worry about Helmholtz resonance because otherwise I’ll have an ungodly mess trying to get the runners and the plenum volumes tuned when I don’t have an engine with a 180° crank, which the LS engine doesn’t have. Some of the LT series are fitted with a 180° crank and I could use crossram and also use Helmholtz resonance to get tuned port charge effects, but those engines are like $50k and way out of my price range (free). Well free for the moment, when I start getting Social Security I hope to raise that to $500 for the engine. But yeah, crossram and the injector at the top of the runner to get that charge cooling effect from the fuel getting introduced at the top of the runner especially when I’m using E85. Now I had been considering doing a single plenum like the old TPI system, but the paper reminded me that fuel doesn’t like to stay mixed with air if there are any turns to negotiate. There are a couple of major turns to negotiate if I try to use a single plenum to feed both banks with long runners, unless I make a very tall manifold that doesn’t make the runners cross under the plenum. Even so, there is at least one turn taking the runners from vertical through the ~45° turn to hit the intake ports on a 90° V8.

And now I’m completely out of urge to write, meaning this stream of consciousness has hit a dam.

Can’t stop thinking

And you can get back out from under whatever sturdy object you got under when you read that headline, because this is (relatively) harmless. I have been thinking about applying lessons from Richard Holdener’s TPI manifold test especially the part starting at 5:11. You notice that the manifold that made the most average power was the one with the standard TPI length runners and the biggest ports, with 534 ft-pounds of torque and 460 HP at widely separated points on the RPM curve and not much sag between those points.

I have been looking at the runner lengths of the various LS manifolds and nothing was even close to the old TPI intake 21.5 inch runners, the best being the Dorman truck replacement manifold at just over 11″. To go with that the runner cross-section seemed to be a lot smaller on the long-runner manifolds. This is 180° out from what the Holdener tests showed, that to get both high low speed torque and high peak power you needed long runners that were as big as you could make them so they would flow at high RPM and jam mixture in at low RPM with the ram tuning effect. So, I was thinking about how to get a TPI manifold for the LS series engines, and what I came up with was fabricated aluminum from sheet and milled base plates or these base plates.

Now the problem with the LS series is there are basically 2 different engines with many parts that can be swapped between the two generations, with the biggest differences for the intake manifolds being early engines had a smaller “cathedral” port and later models getting rectangular ports, and intake manifolds could not be swapped between the two. This means that before I build the manifold I have to know which kind of head I have on my engine, and before that I kinda have to have an engine to build the manifold for. But that’s basically for the part that bolts to the head, there are basic design parameters that are going to be the same between the two engines. As can be seen by the shots of the manifolds in this video by Richard Holdener the driver side intake port is slightly ahead of the passenger side. So what it comes around to is building the same manifold half twice to bolt against the two heads and then bolting them to a common plenum after snaking the runners between each other. So installing this manifold would be a 7 step process, driver side head first, then passenger side head, then plenum bottom half, plenum top, throttle body, injectors in the plenum top (because charge cooling from fuel evaporating in the intake runner, something else I picked up from Richard Holdener), then plumb and wire like a normal LS intake. I just have to be sure the flanges that bolt to the plenum are small enough to pass between the runners when the runner assemblies are bolted to the head. Now what would be cool with this would be if I could make either the front or back runner from clear plastic so we could see exactly what the fuel was doing in the runner, was it puddling anywhere (unlikely), did it flow down the sides or bottoms of the port, what happened when the runner made the turn from the plenum back to the head, that kind of stuff.

Also as I’m thinking about it, would having the sides of the plenum at an angle so the entrance to the runner was more of a straight line before turning back to the head would make that big a difference in peak power. I already know from stuff I found on the TPI manifold that vertical plenum sides did not hurt torque as much as too abrupt a radius on the port entry did, but I can’t find anything on peak power and plenum shape vs runner profile. Speaking of runner profile I know from stuff I read a long time ago that I need to make the runner cross section smaller as the runner turns from the plenum to the head to keep the flow attached to the runner walls, and hopefully keep the fuel droplets in suspension instead of splattered on the runner walls. That would be something else to look at with the transparent runner on a running engine. I could do stuff like this every day if I had the stuff to make the things to study, and the facility to make the tests to find things out. I have so many questions, like did the fuel that falls out of suspension just drip into the cylinder past the intake valve, or evaporate back into the charge, or what? I mean we are talking about a system that has one way in and one way out, so where does the fuel go that falls out of suspension? It has to go into the cylinder somehow, but in what state does it get to the cylinder? These are the kind of things I think about when I think about intake manifolds. Now granted intake manifolds are not something I think about often, but I think about them intensely when I do think about them. Just like everything else I think about, I go long periods of time not thinking about them, but I think very intensely about whatever they are when I do think about them. At rare intervals I can come to an earth-shattering conclusion about something, but mostly it’s a draw of doing something meaningful before I lose interest again. That’s what makes building the Sprint-T so cool, there are so many things to maintain my attention, when I lose interest in one thing, there are dozens if not hundreds of other things to hold my attention while still getting something accomplished on the car.

And my word count tells me I need to temper my enthusiasm for this and go ahead and put this stream of consciousness to bed before I get burned out. Again.