Low profile intake manifold tuned for the 3rd resonance

[Warpspeed]

It's more than that.
Compare the low end torque of a long runner TPI manifold to a single plane manifold.
It's bad enough normally aspirated.
It gets even worse when you block the exhaust with a small turbine housing and a completely closed wastegate.

Flat out with full boost either work great.
It's getting it up onto boost in the first place that is the problem.

[ptuomov]

Here is photo of the Peugeot 205 Group B turbo car that made 700+ hp from 1.8L engine in 1989 Pikes Peak I believe...Those runners must be tuned to the first harmonic at peak rpm?!

I guess second pulse, at about 7000-7500rpm...

The car made peak power at about 7500 rpm. The second pulse tuned length would be about 17 inches, of which probably 4 inches would be in the head. That would make the runner 13 inches long, or 33 cm. Those runners look way longer than that. So that's why I suspected it might in fact be the first resonance, which would mean about 34 - 4 = 30 inch long runners, or 76 cm. The runners really look that long to me.

[ptuomov]

I've seen the intake length / tuning be the deciding factor if a drag engine would manage to spool a turbo or not... so saying that tuned lenghts do nothing because you have boost... ...you have a denser medium, which means you have a much larger difference in potential power (trapped charge) if you're on a pulse giving you an additional 8 psi or in the valley of one (subtract 8 psi)... that's why turbos are usually run with shorter intakes. You want it to tune at 3rd or 4th pulse, so that the "valley" between 2nd and 3rd will not show up smack in your peak hp register.. But first.. negate the backpressure to 1:1 or so at your peak hp rpm. Then you can tune it.. a 3:1 backpressure will kill all tuning at the first hint of IVO, you'd just dump exhaust all the way up to the throttlebody..

In the last test, we were at the exhaust to intake absolute pressure ratio of (32+14.7)/(17+14.7) = 1.5. The new, bigger turbos have already been ordered, not because of the pressure ratio but because the turbocharger speed sensors were reading close 130k rpm which means that we'll sail off the map in the near future regardless. A happy byproduct of the bigger turbos is that the pressure ratio should get better.

I don't know if I mentioned this, but it's a pump gas 93 car. That means that it's knock limited, and there's effectively maximum torque that we can make. Because of this, I don't really care about any N/A torque curve valleys in the rpm range where the turbos have spooled and they aren't yet chocking. I can fill up any valley up to the knock limit by increasing boost back to the knock limit at that specific rpm. Effectively, I really only care about pulse tuning at low rpms where the turbo hasn't spooled yet and at high rpms where we're maxing out the turbo. In between, it's trivial to go to the knock limit with my engine regardless of whether the pulse tuning works for us or against us.

So hence the question is: What is the low-profile intake manifold configuration that allows for pulse tuning at 3300 rpm and at 6600 rpm? My logic says it's a massively long, 34 inch runner in a cross-ram configuration -- but since nobody actually runs those I am thinking that my logic is wrong.

[ptuomov]

Flat out with full boost either work great.
It's getting it up onto boost in the first place that is the problem.

That's right, pulse tuning before the turbines have spooled is the key. In my case, pulse tuning when the turbos have been maxed out also matters.

[Force Fed Mopar]

What about putting the plenum as far down in the valley as possible and have the runners curves come out upwards and curve around into the heads? Like a 90's BMW V8/V12. I've also seen that design in Mercedes V8's IIRC, and Ford uses it in some applications of their mod motors.

[nickmckinney]

I have played with many different intakes on street V8 turbo motors, the torque/HP peaks under boost are pretty close to that found NA. If its a good NA intake in the operating range you like then its also a good turbo intake is what I found. IMHO turbos hate shorter runners on the street because it takes forever to spool them.

BTW - all street V8 intake are compromised because of the hood, resonance tuning is the 2nd criteria to meet, being able to close the hood being the first.

[ptuomov]

What about putting the plenum as far down in the valley as possible and have the runners curves come out upwards and curve around into the heads? Like a 90's BMW V8/V12. I've also seen that design in Mercedes V8's IIRC, and Ford uses it in some applications of their mod motors.

That's one idea on the table. In fact, one gentleman in California is working on a manifold like that. More about the manifold here: http://forums.rennlist.com/rennforums/9 ... tions.html. I lifted a photo for this thread:

DSCF1813_zps0c1f254d.jpg

This is one option I am considering. The main downsides in the design as it applied to the 928 are the following: The runners need pretty sharp short radius turns. The oil filler neck "chimney" in the block doesn't allow one to use exactly the same runner shapes for all cylinders. The plenum may be difficult to configure in a way that distributes evenly. Even with these downsides, this design is definitely on the table.

[ptuomov]

I have played with many different intakes on street V8 turbo motors, the torque/HP peaks under boost are pretty close to that found NA. If its a good NA intake in the operating range you like then its also a good turbo intake is what I found. IMHO turbos hate shorter runners on the street because it takes forever to spool them.

I am also convinced that resonance tuning matters for turbo motors. It's just that with turbos there are often ways to compensate.

Are you using a constant boost pressure in your motors? Because we aren't, we're running boost levels from about 10 psi to 17 psi specific to what each 500 rpm wide segment can handle. With constant boost, I completely agree with your statement that torque and hp peaks don't move much when going from N/A to boost on the same engine.

The three options I am thinking about right now are the following:
1. Intake tuned for low rpm + big turbos that can fill in the high rpm
2. Intake tuned for high rpm + small turbos that spool early
3. Intake tuned for two peaks one at 3000 rpm and another at 6000 rpm + turbos filling any resonance hole in the mid range

[englertracing]

What about putting the plenum as far down in the valley as possible and have the runners curves come out upwards and curve around into the heads? Like a 90's BMW V8/V12. I've also seen that design in Mercedes V8's IIRC, and Ford uses it in some applications of their mod motors.

That's one idea on the table. In fact, one gentleman in California is working on a manifold like that. More about the manifold here: http://forums.rennlist.com/rennforums/9 ... tions.html. I lifted a photo for this thread:

DSCF1813_zps0c1f254d.jpg

This is one option I am considering. The main downsides in the design as it applied to the 928 are the following: The runners need pretty sharp short radius turns. The oil filler neck "chimney" in the block doesn't allow one to use exactly the same runner shapes for all cylinders. The plenum may be difficult to configure in a way that distributes evenly. Even with these downsides, this design is definitely on the table.

That manifold loooks Verry good.

[nickmckinney]

Variable boost just adds another variable, but that doesn't affect how the intake tunes. One thing I saw on that intake picture was that the injectors look to be spraying towards the floor, IMHO do whatever you can to get them to point where the valve stem meets the head of the valve. We play with injector timing to get the spray to start after the valve has already opened, you want to get the injector to spray right into the cylinder if possible. Bottom feeders are a nightmare to get the throttle body location happy. The Ford modulars tried rear mount, center mount, and multiple access between each runner mount and all have their compromises. They finally got wise and raised the hood height 3" on the 2005 design and put the throttle body over the top of the alternator where it works dramatically better. Big problem with the bottom feed design is that the intake is so cold and the plenum relatively so big any fuel/oil will love to puddle. I have owned every single intake made for the 2V modular which is a close shape to your motor intake wise, here is the sheet metal one I like the best but it requires a taller hood as the plenum is a top feeder, pay close attention to the trumpets at the end of the runners:





Here is a low profile Victor Jr style, problem here is the elbow heights it up there too but both make about the same HP on the top end:




Considering your intake port mounting surface is parallel to the ground like the above modular, you have to put in a sharp bend somewhere or bubble the hood.........................We are taking the Victor intake and bandsawed it for another application where it wasn't intended, we just can't duplicate some of the shapes it has in sheet metal. You could take one and cut it apart to make the beginning of your intake, it has a good short turn bend where it meets the head and the injector is located to the top side of the roof and angled probably pretty close to what you need.

[ptuomov]

Thanks, nickmckinney -- All interesting info.

One note: Although the port surface is machined to be horizontally level, the flow is actually not going straight up but it's at about 17 degree angle towards the centerline of the engine. The intake manifold mounting surface was machined to be level only to make the manufacturing of the intake manifold cheaper. If you would slash cut a pipe at 17 degree angle, then that would give a straight flow path from the head to the runner. Since it starts at 17 degrees, there's only 73 degrees of turn left to be done to get to a horizontal cross-ram configuration, allowing for a bit longer turn radius. It's still pretty steep, I have to admit.

I've been using the modular Ford intake manifolds as a guidance for my thinking. I am big fan of Richard Holdener's writings on the topic. His writings are hugely more data driven (scientific?) than the average hot rod writer's prose. In particular, he had a recent article on a 1000 hp two-valve mod Ford turbo, where he used his own, very simple custom manifold. The article said the manifold was later reconfigured to cross ram to fit under the hood, but there was no picture. Anyone have a photo of that manifold as a cross-ram?

As a side note, the team that designed the modular Ford engine paid a lot of attention to the Porsche 928 32V V8. The design is similar, and I am using some mod Ford valvetrain parts in the low compression engine that is waiting to go into the car.

[nickmckinney]

In all my dealings with modular 2V I have never seen a picture of his intake actually in a car.......................

[ptuomov]

In all my dealings with modular 2V I have never seen a picture of his intake actually in a car.......................

I worked hard on google to find one in a Mustang, but didn't stumble on any photos. Anyone else with photos of the Holdener intake in a Mustang?

The Mustang hoodline I believe is higher than the 928, so I can safely ignore everything that doesn't fit under a Mustang's hood.

[Rizzle]

Have you looked at the vortec 8100 or any of the composite truck/car gm gen III-IV intakes for ideas? The FAST 102 LSXt might also be worth looking at, its similar in design to the IR-common plenum idea previously posted, but the runners cross and would allow a lower total height.

[ptuomov]

Have you looked at the vortec 8100 or any of the composite truck/car gm gen III-IV intakes for ideas? The FAST 102 LSXt might also be worth looking at, its similar in design to the IR-common plenum idea previously posted, but the runners cross and would allow a lower total height.

Vortec 8100 is by my understanding very similar to the manifold I posted the photo of. FAST 10 LSXT is a straigth-runner cross-ram manifold with a large plenum, with the cover giving a misleading impression of what's inside. I think that both of these designs would probably work very well on the 928, I am particularly intrigued by the FAST manifold as it basically uses the space below the runners as the entry point and plenum volume.

One more word on tuning issues. I am heavily constrained on the exhaust manifold design and the turbine size because of packaging. Basically, those have to be taken as given. This will inevitably lead to high average back pressure in the exhaust manifold at high rpms and randomly timed exhaust pulses returning the cylinder. Not a great situation. This is why I am focusing so much on the IVC-IVO pulse tuning for high rpms, if I want to run any meaningful overlap then I better make sure that the intake port pressure is as high as possible at IVO. That's my best, last hope of keeping the intake port pressure above the exhaust port pressure at overlap when the turbos start maxing out. I don't know if this is wise or dumb, maybe it's idiotic and I should focus on IVO-IVC tuning more than IVC-IVO tuning. I am out of my depth on this one, that's for sure.