Strange Intake Manifold Sound
 

While the car was on the dyno today, we have been trying to address some of the small problems that have surfaced. We've been able to figure out most but there is one that is baffling us.

There is a sound coming from the intake manifold when you give partial throttle, which sounds comparable to lifter tick in a typical piston motor (but obviously there are no lifters in a rotary).

Also under partial throttle the intake manifold actually expands and contracts, this is partial throttle blips revving to like 2000 if that.

What do you mean it expands and contracts? Like it is swelling up and deflating again? Which part of the manifold is doing this?

Yes, the top of the manifold is.

That's because it is made from a composite. Paul Yaw was going to address that issue on his supercharged race car by building an aluminum upper manifold. He had this same concern.

you mean if you have FI you need a stronger manifold

I know aluminum can handle a good amount of pressure with no issues but what about the new composite upper manifold? A few LS1 guys that have gone to forced induction have cracked the factory composite manifolds on those engines. These are made from basically the same stuff. I'm not saying that it necessarily will crack or break, but it isn't as strong as metal.

The strange thing is that this manifold is flexing at 1500RPM 25% throttle, who knows what will happen at 100% throttle 8000RPM w/ 5PSI going through it.. If it cracks it looks like we will be making a metal intake manifold

Wow, it flexes really soon. If it does break, hopefully it will just be a crack rather than parts flying off into the engine.

Yikes... You paint an ugly picture RotaryGod.. If it's that bad, I would hold off and machine the part...

Better safe then sorry

Do you think the amount of boost would matter. I don't think anyone is going to run much P.S.I. in the RX8 if it is F.I.

You know I wondered about that too. Can the manifold really take much pressure since it's composite. Based on SSR's findings... that answer is apparantly no. It is really surprising that it's flexing at 1500 rpm 25% throttle @ 5psi.

My mistake, that is when we are hearing the sound, but the manifold is flexing under revs with NO LOAD, there is no boost going through the manifold and it is flexing, this is 50-100% throttle in neutral.

SSR, it's time to set yourself up as a site vendor. Please PM me or get in touch with Ryan Scott at advertising@rxtuner.com . Thanks.

I remember from some odd years ago there was an article in a car magazine about using composites for things like intake manifolds. At the time I had wondered about the heat resistance and strength of the composites... now I find myself wondering the same thing again. Maybe this is a mod that someone should look into... replacing the upper intake manifold with an aluminum one.

Yep we've been thinking about making one, however we do not want to incorporate it into our kit, we will see how well the intake manifold holds up.

So did the run ever get done? It sounds to me like you will be trying the dyno run if you havent done it already....

If you happen to dismount the manifold, could you read what type of material it's made of (it usually is written on it for recycling purpose)?

SSR: Take a look at this thread here. Perhaps this could help with finding your noise (unless of course, you already have.)

How does one go about designing a stronger manifold if this one is bound to crack? Should it be similar to the existing one? This is an issue that I am also concerned about, since I one day hope to use force induction. I also have a thread pertaining to the design of the intake manifold. I hope everything works out for you SSR :).

https://www.rx8club.com/series-i-aftermarket-performance-modifications-23/turbo-intake-manifold-design-34440/

I just called the shop in san diego producing this turbo system and they said it's available to the public right now. They have 2 kits. The one that is available does not come with a fuel management system. The other turbo kit that is expected (how many times have we heard that) to be done in the coming weeks will include fuel management for a few a higher price of course.....

He told me they were going to try and dyno the car sometime this week to get some #'s...

I'll call them back later and see how the progress is coming....

:)

Hmmm. Under these conditions, the intake manifold should be under a vacuum. I wouldn't expect it to flex any more than stock. Have you watched a stock car under the same conditions to see if it's doing this?

Having said that, I could certainly see concerns pressurizing a composite manifold that is optimized to work under a vacuum. Composites can be very strong, but they also can be more easily tailored to specific operating conditions than alloys. Moving from a vacuum to a pressurized system could easily put it outside it's "safety zone."