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.

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