I haven't been able to dig up anything good on this. I'm trying to determine what difference enlarging the inside diameter of the runners on the plenum end would have on the effective intake runner length. Here are the details on the setup, brace yourself:

I'm running a Lingenfelter LT1 SuperRam intake, runner length of 15" not counting the cylinder head (add about 5.5" for the head is what I've been told). The tuned length on these runners produces a relatively low peak resonant tuning RPM, somewhere around 3500 to 5500 RPM's. I'd like to bump this up by about 500 RPM's, that would require shortening the effective runner length by a little over 2". The runners have been extrude honed, cross sectional area is about 2.2 square inches currently, roughly 1.7" I.D.

The runner castings are pretty beefy, around 1/4" wall thickness. Wondering if enlarging the inside diameter of the plenum end of the runners by around 1/4" would be able to do what I'm after. This would bump the CSA to about 2.8 square inches. If this would do the trick then the question is how to figure out how deep to enlarge the runners? I suspect it would be a good bit more than 2" if it would work. One other possibility is siamesing the runner pairs a little if that would help. I know some of the siamesed TPI runners don't work well but they are siamesed 4 to 6 inches. Don't know if there is a calculation out there on this stuff without buying software, haven't run across one yet. I guess this amounts to some sort of taper calculation on the harmonics?



Thanks for sticking with me if you waded through all that crap

Any help is appreciated, Michael

 

what type of heads are you running? I think the runner length of lt1 castings is around 3"-3.5".

 

Also, if you are talking about further extruding the runners of the superram and enlarging the plenum I think you could gain a hard won 500 rpm probably not more. That manifold will severly limit high rpm capability but is great for lowend midrange.

 

I don't think it will work.

Rich

 

One of the problems is the intake manifold itself. The CSA at the pinch point is something like 1.7 square inches. This is smaller than most aftermarket heads. That needs to be opened up.

I'm at a loss as to how you got 15" for the runner length excluding the heads. The intake manifold itself is around 6.125" long on centerline. The runners are maybe 4-5 inches"?

 

89TramsAmGTA, I was working off some numbers I found on the web for the runner lengths ( stealthram.com). I just took a rough measurement on the runners with it installed and looks like those measurements were not very close. 6.125" looks about right on the base, the runner pairs are around 5". So total length would be around 11" plus the head.

I found the same numbers you listed on another website. On the CSA pinch point thing, it listed the Accel base manifold runner diameter at 1.75". That would give a CSA of about 2.4". Or maybe you're thinking of a stock tuned port base with the 1.7 square inch CSA pinch point thing? The CSA of the stock TPI base looks to be somewhere around 1.7" (diameter spec for stock base was said to be 1.47").

RRR, I'm thinking that hogging out the entire intake runner is not the best approach. The CSA here should be related to the peak airflow or HP requirements from my understanding. The base has been ported and the runners extrude honed, I'd bet their CSA is not very restrictive for a 375 to 400 RWHP engine.

I'm interested in altering the tuned resonant frequency of the manifold. This resonant effect changes in inverse proportion to the effective runner length. If you didn't know, this tuned length provides a boost or light supercharger effect within a 1500 to 2000 RPM range that bumps the volumetric efficiency up a good bit. You don't get this benefit with the LT1 manifold as it's short runners have a high enough resonant frequency that it doesn't kick in until over 7000 RPM's. Bad design in one respect because it doesn't bulk up the VE anywhere. The long runners on the LS1 intake account for a good chunk of the power improvement over the LT1 motor because of this effect.

Anyway, the more accurate runner measurements make more sense with the dyno charts I've seen. I still want to raise the tuned frequency by about 500 RPM's to better match the heads and cam. With the shorter overall length I'd need to drop about 1.5" from effective runner length to get there.

Any help on whether hogging out and mega-radiusing the entry end of the intake runners ( or possibly siamesing them an inch or two) would do what I want is appreciated.

Michael

 

The runner length is always the dominant spec in determining the shape of the TQ curve. Larger diameters allow that shape to not choke off the motor earlier. That's the jist of it. Your peaks should still be in the same place but it should hang on to the power longer.

This is a good article, read it back when it was free.

http://martelbrothers.com/product.ph...d1e86dc8cc5de3

Bret

 

Let me clarify the choke point on the intake. It starts around the injector bungs going from the head mating surface. There is a pinch point in that area. You will need some telescoping gauges and a vernier caliper for measurements.

Those numbers look much better. Depending on what head you wind up using you are looking at something in the 15 to 16 inch range for total runner length. You will need to decide what runner length you want depending on the desired peak power and torque rpm.

You can fine tune the runner length by siamesing the runners on the Superram. If you do I would suggest a round divider versus a sharp divider.

I'm in the process of doing a similiar project but with a highly modified TPI. Right now it looks like a 15 inch total runner length will be the ticket.

Thanks Bret for the link.

 

So from what you're saying the accel base (this is an older one so it may be the accel vs the Edebrock) has a 1.7" csa choke point around the injector area? If so that's pretty lame when the base manifold entry CSA goes well over 2 inch CSA. My heads flow 280 on the intake side so if you're correct here I definitely need to do some work. If needed I can do some welding to open this area up. Already welded above the ports so the intake gaskets would seal. Do you know if welding is required to fully eliminate this constriction? On the siamese treatment, I remember seeing some dyno results on the stock length TPI runners that were siamesed. Seems like they moved the peaks to a higher RPM but lost some peak torque and lost area under the curve. Wonder if this is bcause they are siamesed well down into the runner pairs vs. right at the plenum? Thanks, Michael

 

Read through this thread. It will answer your questions concerning the intake manifold.

http://www.thirdgen.org/techboard/tp...-manifold.html

 

grammerman, I gave this a quick look-see, I think you will find it very informative. Hopefully, it's just what your looking for. But I have to ask, what happened to the idea of a dual purpose intake that you mentioned some months ago? Did that get put on the back burner for now?

 

IIRC, the effective pipe length is also dependant on the diameter of the pipe. I think its 50% of the diameter? Correct me. So a 10" long 1" pipe open on both ends will resonate like a 11" pipe at 50% (0.5" on both ends).

89TramsAmGTA is correct on the injector bung choke point. The smallest runner cross area will set the choke for the entire runner. I'd start there before you try your original idea.

 

OK, the "choke point" around the injector on my particular Accel high flow TPI base is around 2" of cross section. Height in the injector area at the narrowest point averaged about 1.65" and width was 1.28", that gives an area of 2.112". Once you allow for the corner radius that should still be way over 1.7". I'll probably open it up some while I'm in there, doesn't look like very much trouble to get it up in the neighbor hood of the 2.4" csa of the runner entry end. 2.25" CSA should be easy.

In the other post I noticed that you expect to have a 500HP hybrid TPI soon. If the intake has enough cross section to flow that much air I don't see why not. There are probably better ways to do it as far as average power ( area under the curve), a modified Stealth Ram, Super Ram or single plane conversion come to mind. From what I've seen the siamesed TPI runners usually drop significant peak torque, the reflections bouncing up and down the siamesed portion of the runners probably chokes things off some I'd guess.

Z-RATED94, the intake manifold idea had to be shelved for the time being. It took way too long to finish the build even using the SuperRam setup. Later when all the details are worked out and I'm bored maybe it will pop back up. A company I used to work for developed supercharger kits in house and had castings made for some of the parts. Wouldn't it be neat if someone offered a mid-length (8" to 10") intake for the LT1 engine? Might talk to them sometime about developing one, certainly wouldn't have any competition. They are working on some aftermarket heads for the Jeep 4.0 engines right now, maybe I can make a little suggestion for the next project

I know the SuperRam intake is a pain. Takes like 3 or 4 hours to install it, most of that is tightening the runner to plenum bolts. They are a BASTARD to work on and too expensive, not to mention that the LT1 version has been out of production for years

Later, Michael

 

Thanks Grammerman. You may have a better manifold than the Edelbrocks we were testing.

The First Fuel Injection TPI intake manifold flowed 301cfm out of the box. I'm going to open the "choke" area up to 2.2 square inches. That should get me 310cfm. I plan on tapering the runners in the manifold from 2.68csa at the runner down to 2.2csa at the head mating surface. Hopefully that will do the trick as the 2.2csa is still larger than the pushrod pinch point in the heads.

 

Yeah, I was thinking about the taper on my base too. No need to have a half inch more CSA than the pushrod constriction a couple inches upstream.

I had a TPI motor a good while back in a '88 IROC with Brodix heads, Arizona Speed & Marine runners and chip and a 230/236 cam. Damned fun engine to act up with. Had to go to Micky Thompon Street Slicks eventually, the car just wouldn't hook with street tires. With all that HP kicking in suddenly at 2500 RPM's I can't imagine why

Good luck on your TPI project.

Michael