Low profile intake manifold tuned for the 3rd resonance

[SchmidtMotorWorks]

Flap open seems quite good to me, I would choose to avoid the complexity and go with that unless you really enjoy the optimization and can tell the difference.

[ptuomov]

Flap open seems quite good to me, I would choose to avoid the complexity and go with that unless you really enjoy the optimization and can tell the difference.

With the normally aspirated stock car, the difference is noticeable. To the point that people who play with these cars can test drive one and tell whether the flappy is stuck open or not. It's about 15% of torque at a point and the car starts really puling about 800 rpm earlier. As that torque peak happens before my turbos spool, I really want to retain that torque peak and if anything move it to a lower rpm. In contrast, whether the intake is tuned or not tuned at the 4000-5500 rpm range doesn't matter at all, as it's trivially easy to boost the engine to the knock limit at that range regardless of the intake tuning.

[ptuomov]

I am constrained, of course. When I was younger, I had all the time and none of the money to complete projects like this. Now I have all the money but none of the time... So much of this is just speculating and dreaming.

Start with scans and at least be precise with your projects. Contact Faro and see who has a system local to you rather than shipping your chariot hither and yon. I am sure there are individuals or firms that would be happy to instantiate each of your projects and explain the reasoning and physics behind each variant.

Am I just imagining, or are you being slightly critical of my approach here? The approach being fumbling blindly trying to reinvent the wheel on my own? Sure, it's not the most efficient way to make a manifold, but I think I am learning more by thinking about it and talking about it and sometimes doing some high school math.

[Kevin Johnson]

I am constrained, of course. When I was younger, I had all the time and none of the money to complete projects like this. Now I have all the money but none of the time... So much of this is just speculating and dreaming.

Start with scans and at least be precise with your projects. Contact Faro and see who has a system local to you rather than shipping your chariot hither and yon. I am sure there are individuals or firms that would be happy to instantiate each of your projects and explain the reasoning and physics behind each variant.

Am I just imagining, or are you being slightly critical of my approach here? The approach being fumbling blindly trying to reinvent the wheel on my own? Sure, it's not the most efficient way to make a manifold, but I think I am learning more by thinking about it and talking about it and sometimes doing some high school math.

First, I know you are in a position to be able to have this done. It would be a tragedy of some sort if you spent a lot of time (and money) making or having something made that "almost" fits. Second, you are proposing to install what is essentially a cyclically cycled bomb casing on your engine, the safe design and fabrication of which may depend upon a number of details which you or I or other casual readers of the forum may not think of or know to attend to. It might be nice if you stuck around a bit longer in this life.

I love the idea of experimenting and learning but when you are talking about cutting up existing parts to make something that "might" work I think "why?" You can scan in those parts as well and see what you can do with them in a virtual environment.

[ptuomov]

First, I know you are in a position to be able to have this done. It would be a tragedy of some sort if you spent a lot of time (and money) making or having something made that "almost" fits. Second, you are proposing to install what is essentially a cyclically cycled bomb casing on your engine, the safe design and fabrication of which may depend upon a number of details which you or I or other casual readers of the forum may not think of or know to attend to. It might be nice if you stuck around a bit longer in this life.I love the idea of experimenting and learning but when you are talking about cutting up existing parts to make something that "might" work I think "why?" You can scan in those parts as well and see what you can do with them in a virtual environment.

We'll proceed with porting the stock manifold for now. What's the worst thing that could happen? Plus even I can do approximate math to predict the effects of increasing the volume of the Helmholtz resonator chamber and increasing the runner and ram pipe diameter.

If we ever get to making a new one from scratch, I promise someone will model it before it gets tested. None needs to die over this.

[SchmidtMotorWorks]

If you guys are talking about measuring the envelop, a fast cheap way to do it just make some templates out of cardboard and fit them together like the dividers in boxes of liquor bottles but larger. It is really fast and easy to model the carboard pieces in CAD and with some care you can do it within 1/8" quite easily.

[Cubic_Cleveland]

The idea is to increase the plenum volume with spacers and move the "flappy closed" resonance point further down the rpm range. This will hopefully help the engine at the point where turbos can fill up any hole.

I am curious how increasing the plenum volume, will help lower the resonance effect? I was under the impression the size of the plenum will effect the strength of the resonance, and runner length tunes the 'where' it happens? I am keen to learn as I am designing a plenum at the moment too.

[ptuomov]

The idea is to increase the plenum volume with spacers and move the "flappy closed" resonance point further down the rpm range. This will hopefully help the engine at the point where turbos can fill up any hole.

I am curious how increasing the plenum volume, will help lower the resonance effect? I was under the impression the size of the plenum will effect the strength of the resonance, and runner length tunes the 'where' it happens? I am keen to learn as I am designing a plenum at the moment too.

If the plenum is operated in the 180-manifold mode with the flappy closed, it is a Helmholtz resonator. The Helmholtz resonator uses the plenum air as an air spring, a high pressure pulse compresses the spring and then the spring returns the favor by sending a pressure pulse back in the open runner. Larger plenum volume causes it to take longer for the spring to load and release. Works best with 3 cylinder and 4 cylinder plenums with equally spaced pulses.

Heavily caveated, I don't really know what I'm talking about.

[ptuomov]

In case anyone is interested, here's an old article about the Porsche 928 intake and some product ideas by a now-defunct company:

https://picasaweb.google.com/1059510082 ... directlink

The most relevant page in terms of the intake flow (or lack of it):

HeadFlow3.jpg

[SchmidtMotorWorks]

For someone considering buying a 928 for a performance car in So Cal, at 1st glance of the specs, it looks like the later 5.4 models would be the place to start, is that right?

[nickmckinney]

In case anyone is interested, here's an old article about the Porsche 928 intake and some product ideas by a now-defunct company:

https://picasaweb.google.com/1059510082 ... directlink

The most relevant page in terms of the intake flow (or lack of it):

HeadFlow3.jpg

Never thought about carbon fiber for a custom intake manifold, I like the shape of that one. Dude is right on about flowing the head and intake together.

[ptuomov]

For someone considering buying a 928 for a performance car in So Cal, at 1st glance of the specs, it looks like the later 5.4 models would be the place to start, is that right?

The '87 and '88 five speed S4's are I think the most fun per dollar. If you are thinking about forced induction, the '87 and early '88 9.4:1 compression models are hard to beat. Close second would be the '89 - '91 GTs, which are great starting points for normally aspirated projects. The '93-'95 GTS 5.4 liter cars are not much better overall, and a lot worse in some respects, yet priced at a premium. I think it's mainly because of the production volumes.

The 5.0 S4 engine is arguably a better starting point for many projects, yet you can pick up a complete used engine for $2500 while a 5.4 GTS engine with many problems costs triple that. Not because the 5.4 is better but because there are so few of them left, given the low production volumes and the poorer durability of the 5.4 engine compared to the 5.0 engine.

If you are going to keep this thing ostensibly smog legal, you'll be spending a lot of time with that intake manifold.

[ptuomov]

Here are some notes on the intake manifold from one person who has worked with the S4 stock intake manifold and who's judgment I trust:


http://forums.rennlist.com/rennforums/5 ... ost38.html

As another data point, while flow testing the heads to my 6.1 liter engine project, we flow tested the S4/GT/GTS intake. Here is a rough summary of the results.

With the end plates on as OEM, using either the straightest runner or the most bent, the flow at 25" was around 220-225 CFM. Moving the plates out 1/4 of an inch gained about 5 CFM. Moving the plates out approximely 3/4 of an inch took the manifold up to the high 240's with the best runner at 250 CFM... again at 25inches. Only about 5-ish CFM more was gained with the plate completely gone.

The mainifold runners gained slightly with mild porting, but not as much as hoped for. Using a simulated 3/4 inch spacer for the end plates, re-shaped horns to the runners and mild porting got the best runner to 280CFM and the worst to 265CFM.

With all the test porting and flow work done on the OEM manifold, I am now looking to making some sort of new setup before proceding further on my 6.1 engine. I say this as my heads flow 340 CFM at .425" of lift. Restricting such nice heads with the OEM manifold would be a huge waste !

http://forums.rennlist.com/rennforums/1 ... ost41.html

About 4 years ago, I worked with BC Gerolamy Co. in Rancho Cordova to develop a pair of 928 4V cylinder heads for a "hot rod" project. Using a flow bench and lots of experience and information from BC Gerolamy, the modified heads flowed quite well, but tested using a bellmouth at the manifold connection face. The flow data was relevant for the success of the port / valve work, but did not matter much if going to be mated to a S4 manifold. In short, the whole intake system has to work together, not just the heads.

At this point, we spent several hours doing flow bench tests on the S4 manifold and learned some interesting things relative to this thread.

1.) The flow and velocities through each runner varied enough to suggest creating inconsistent combustion in each cylinder... not acceptable for a batch fire injection engine.

2.) For a stock set of heads, the manifold was "not bad", but if you work the heads, the manifold needs work hand in hand with the heads.... bad results if not worked as a matched set !

2.) Simply "extrude honing" the manifold MIGHT improve one or two of the runners, but would definitely make matters worse for other runners, especially the tight turns ones.

3.) The runner bellmouths on #5 and #8 become restricted with the manifold plenum end plates are mounted. Flow does not significantly improvement with spacers less than 5/8 of an inch. Some smaller amount of spacer thickness helps, but not as much as thought if you are trying to get best flow from the stock cast manifold.

4.) After several hours of hand porting and testing, the manifold was able to flow around 285-288 CFM @ 25inches, but did require some welding to maintain wall thickness in some of the tighter corners. Welding the Mg manifold is tricky given the need to purge the air from runner being welded. Plumber test plugs work well to plug one side of the runner for purging

5.) Even at 288 CFM, the manifold was never able to flow for possible long block HP. The runner area / length models better than observed results. In short, getting the heads to flow is much easier than creating a good working manifold.

[SchmidtMotorWorks]

For someone considering buying a 928 for a performance car in So Cal, at 1st glance of the specs, it looks like the later 5.4 models would be the place to start, is that right?

The '87 and '88 five speed S4's are I think the most fun per dollar. If you are thinking about forced induction, the '87 and early '88 9.4:1 compression models are hard to beat. Close second would be the '89 - '91 GTs, which are great starting points for normally aspirated projects. The '93-'95 GTS 5.4 liter cars are not much better overall, and a lot worse in some respects, yet priced at a premium. I think it's mainly because of the production volumes.

The 5.0 S4 engine is arguably a better starting point for many projects, yet you can pick up a complete used engine for $2500 while a 5.4 GTS engine with many problems costs triple that. Not because the 5.4 is better but because there are so few of them left, given the low production volumes and the poorer durability of the 5.4 engine compared to the 5.0 engine.

If you are going to keep this thing ostensibly smog legal, you'll be spending a lot of time with that intake manifold.

IN CA it is best to by something you will be happy with stock. What model in that case?

[ptuomov]

If you are going to keep this thing ostensibly smog legal, you'll be spending a lot of time with that intake manifold.

IN CA it is best to buy something you will be happy with stock. What model in that case?

In my opinion, 1989-1991 GT is the best value stock. It's fun stock with 5-speed transmission and something like 325 hp at the crank and 270 hp at the wheels.

The GT is a good starting point for a little California hot rodding, too. Here's a dyno run with cams, headers, cat back, and hours and hours of fuel and ignition mapping by one guy who lifted way too early on the dyno:



Oh, and buy the car in the best possible condition with everything already done by someone competent. Way cheaper in the end.