That's actually not adjustable runners - that's the throttle blades.

 

That intake is off the C5R Compuware racecar, It has a box that goes over it. If I am not mistaken.


David

 

My mistake

Why put the throttle blades that far down in the runner though? Does it help with velocity?

 

Just like a set of Hilborn mech fuel injection.

 

My guess is that it's for instantaneous throttle response. Very short distance and volume between the throttle blade and the cylinder translate into lightning quick response.

I once had a Dakota RT with the 360 Magnum in it. Those engines have huge, barrel shaped plenums and long runners. You could time throttle response with a sun dial.

 

That's what I thought. Yet again, why doesn't someone build something like that for the LT1? Stupid outdated engine....

 

OK, I've been doing lot's of sketching and calculating on the low and high rpm runner lengths along with chasing down dyno graphs for various intakes (from TPI to miniram and everything in between). Thought of going with a aftermarket TPI system and then connecting shorter runners between the bottom of the plenum and the base, from the calculations for tuned runner length ( 84,000 divided by peak power RPM equals runner length in inches) it looked like this would work pretty darn well. The TPI runner length is about 25" including 6" from the intake surface on the head to the head of the valve. The shorter runner length could be around 15" ( also including the intake port in the head) for a peak around 5500 RPM's and good overrev to 6500 or so. You'd get the typical 35 to 50 ft. lb. torque hump from the TPI length runners around 3K to 4.5K and the shorter runners would come in and optimize the resonant tuning for a very good top end.

Problem is that a stock TPI is about 2 inches too high to fit under the 4th gen F-body windshield cowl. Looks like it would have to use custom runners/plenum to get somewhere around TPI'ish runner lengths (actually would like several more inches than the TPI) and clear the cowl. A simplified description of a workable solution may be to use a LT1 TPI base from Accel and then cut a set of big tube runners in half and turn the upper half 180 degrees so they point out over the heads. For it to work they would have to be cut in at two places and just use about 45 degrees of the radius on each end connected be straight tubing ( to lower the overall height). Then build a plenum, fab the butterflies into the base manifold and connect shorter runners to bottom side
of the plenum.

A considerable amount of mill, welding, layout time would be required so due to time constraints I will probably put the LT1 intake back on right away and tune it/dyno it, and also run some 1/8 mile runs at 1/8 and 1/4 throttle as well as WOT. Then if I get the variable intake built just swap it on one weekend and retune/retest for a valid comparison. The part throttle track runs have delivered some interesting results in the past and I think they give you a more complete picture of how stout an engine feels during average daily driving.

Regards, Michael

 

Sounds like a good plan.

How about a dual plenum intake? Imagine 2 cylindrical plenums, one over each row of intake ports, with short runners to each port. Then long runners to each port on the opposing side, connecting to the short runners in a y-joint. When you are at low RPM the plenums supply air to the heads on the opposing bank via the longer, diagonal runners. When you hit the high band a "trap-door" opens the short runners while sealing off the long ones.

Might work, I'll see what I can do with AutoCad as a rough demonstration for anyone who can't visualize this.

Jeremy

 

I think a stock TPI will fit under a 4th gen cowl, Accel Super Ram will, see the pic on the first page of this post, our intake fits, but it does touch underneath. It is WAY taller than a stock TPI setup.


FOr sure its not 2 inches too high.


David

 

According to Lingenfelter the Super Ram will not clear and uses a different plenum part number for the 4th gen F-body that is shorter by 5/8" compared to the stock Super Ram. I don't have a TPI in hand but came up with what I figured should be a close approximation of the height by scaling a side photo of one I found by the center to center distance on the injectors. I doubt anyone likely see this has a complete TPI sitting around they can measure so I'll check my numbers again and do some more reasearch. Would certainly save a lot of work if a TPI will fit.

Jeremy, you said:

How about a dual plenum intake? Imagine 2 cylindrical plenums, one over each row of intake ports, with short runners to each port. Then long runners to each port on the opposing side, connecting to the short runners in a y-joint. When you are at low RPM the plenums supply air to the heads on the opposing bank via the longer, diagonal runners. When you hit the high band a "trap-door" opens the short runners while sealing off the long ones.

If you play with any drawings I'm looking at something like 15" and 25 to 30" for total runner lengths. Subtract 6" for the intake port portion of the runner length. To get 9" of actual intake runner for the short ones I think the height limitation is going to require a crossing/angled approach coming from nearer the center of the intake. I'm interested in any ideas you have for layout with runner lengths in those ballparks.

Later, Michael

 

I have a TPI on my car with SLP runners. I will measure from the bottom of the base to the top of the plenum. Well with a ruler at an angle and a ballpark figure I would say a minimum of 8" tall and probably 8 1/4" tall. I can bend something up for a more accurate measurement if you need it.

By the way I'm doing what you are trying to do but comming at it from the L98 TPI end of things. I have completely hogged out my SLP runners so that the actual runners start at the intake manifold. So figure 6" for the head and 6" for the manifold that puts my total runner length around 12".

I'm right now I'm building up another long block with all the goodies including ported 200cc heads and an XFI cam and will use my highly modified TPI system on it. Here is a link to my runners and plenum.
http://www.thirdgen.org/techboard/at...settings-owner

By the way I have considered doing some sheetmetal runners. Will just have to see what my latest combo comes up with. Right now I'm at 330RWHP and 370WTQ with an A4. Hoping to bump that up quite abit with the next go around.

I can understand where you are comming from as I like to experiment myself. Good Luck.

 

This project will never happen. . . too complicated, too difficult to fabricate, too many things to go wrong, . . . It would be hard enough to simply fabricate a functional LS1 style intake for the LT1, let alone dual runners and electronic valves.

Seriously, the small gains this will get is not worth the amount of effort it's going to entail. You'd be better off putting in a stroker crank and a Victor EFI intake. It will have more torque and hp than stock stroke and intake throughout the range. It will probably have more torque than a TPI down low also.

How, exactly, will you know you're at 25% throttle for the dragstrip runs anyway?

Man, that Victor EFI sure looks sweet sitting on my motor. . .

FYI, there's about 4.5" of space between the carb flange and the cowl.

Mike

 

Here is a rough idea of what i'm talking about. There are obvious improvements to be made, this is just to get my point across.

There would be butterflies in the runners flush with the inside of the plenum. The long runners would be open in the low range, and short in the high revvs. I included one runner with an arc to show how more length could be obtained.

I'll keep working on the design till I get something I like.

Jeremy

Edit: I think I could control the butterflies on one long shaft running through the plenum, actuate it in the rear with a electric cutout motor, and controlled by a window switch. Might not be the simplest design, but it is made of materials readily available.

 

I'm thinking Billet
Machine all the parts and have it welded to gather.
It would be more like one from Nelsons Racing but it would be better than what we have now.
Just have to figure out how to do the PVC Valve and a few Vacume lines.

 

I drew (rather hastily in paint!) a dual runner system based off the tpi intake a few years ago. Though never having seen a tpi intake in the flesh I'm not sure if such mods would be possible