Helmholtz resonance intake manifold vibration

[TurboRA28]

Yeah that reminds me, I should be repping everyone for their help on this one.. /Joel hands out reps!

[Gold28]

Brett, I'm not sure if the elastic modulus of the material is all that much of a problem here. If Joel can effectively stiffen the manifold, it won't oscillate and won't have the same dynamic energy. Hence it won't vibrate until the manifold brakes.

The static loads on the manifold are nothing. The dynamic loads due to it vibrating are.

You are correct in saying that bracing it to the head would be ideal though. I did think of that last night but I personally don't like the idea of bolting anything to an alloy cam cover. I have broken a few threads on them before.

[brett_celicacoupe]

Re elastic modulus, i was just pointing out that if the manifold is flexing outside the elasticity range during it's side-to-side vibrations, then there will be problems . more prone to fatigue and cracking?

like if the manifold was getting 1mm closer, then 1mm further away, then 1mm closer etc to the tappet cover during its vibration


there is most likely a point (or section) in the runners that flexing quiet a bit.... so maybe you could find it and put some webbing in there. remeber a small amount of flex in the lower part of the runners equals a lot of movement at the top

[30psi 4agte]

its what is called resonance. i just mentioned it in the thread abount the flat spot in the 4ag.
ive had hats crack becase of it. part of the problem when people have half an idea making things is that the things they make for an engine, dont take into account how the engine works.
with out looking at the setup in person etc it could well be a balance problem. make sure you look at you balancer.
have you changed the clutch and flywheel?

Yeah i have had everything balanced same deal as turbo RA ( very rep dealer ) They new that i was going to be reving to 9000+ and the fact that it was a high hp engine so i believe its sweet

Nothing has been changed.

I have tried all of the mentioned ways to counter this prob but with minimal results.

The best one so far is the double solid brace setup. This hasnt completely stopped the vibration/ harmonics but has FOR NOW stopped it from cracking..


This is what i did.




p.s soory about pic quality.

[Celica RA45]

yeah graham does good work none him for 26 years also to let you guys no that the LASRE ,or light and super responsive engine as in 4age and 3sge all have harmonic problems in certain rev ranges ,the race 4age motors used to break things at certain points in the rev range .the problem with these engines ,they use a very short rod ratio which causes whip and also hard on pistons as well ,the old engines like 2tg and 18rg dont have these problems ,only the shit rod bolts that toyota make which are still shit to this day ,ok for std road car s but not to good for race cars

[Gold28]

Gee you really were getting the shits with it weren't you. Nice fab work by the way.

I have a vague recollection from 2nd year uni thermodynamics about most engines being inherently unbalanced. I think a V6 is naturally balanced (or was that I6) but I forgot most of my thermodynamics the moment I walked out of the exam room. I don't have any of my thermodynamics texts/notes here in spain but I'll see what I can track down for you.

[JustenGT8]

Interesting that it's that apparent? I would put it down to the the thickness of the material it's made from. Come the 4th at Wakefield check out the inlet we made for the 3SGTE 22...never had this issue and from what i can see the major difference is the thickness. We used the factory runners up until they point vertically, welded on a 12mm plate for the plenum base and used 3mm plate for the rest of the plenum...curved and tapered. If any engine was going to have harmonic issues it's this one with it's solid engine mounts

[Gold28]

Found it. Engine Smoothness

It may be a little on the technical side but sit down with a coffee and you should be able to follow it.

Basically it is saying that the engine wants to vibrate up and down, not a lot unlike a single cylinder but they vibrate sideways as well.

Maybe the location of your engine mounts, forward/aft of the crank center affects it somewhat. Justins solid engine mounts would help this, particularly if the gearbox mount was solid too.

[30psi 4agte]

interresting !!
I plan to move my engine mounts down the track when i start doing my chassi so i guess ill see if it makes much difference.

[myne]

30psi 4agte : Have you considered grabbing a couple of say...5mm sheets of rubber, cutting to shape to suit the lower mounting brackets (top and bottom) so the brackets effectively have a 5mm cushion either side of them around the bolts. Use studs and nylon-ringed bolts and make the holes a couple of sizes too big.

I dunno if it'll help, but it might provide a small amount of vibration insulation. to prevent the resonance getting too bad.

I'm no materials expert, but I know there's as much strength in flexibility as there is in rigidity.

[Ben Wilson]

If any engine was going to have harmonic issues it's this one with it's solid engine mounts

Soild mounts will change the entire picture, they will effectively make the whole car part of the package, not just the engine.

FWIW - 2lt Escorts are renound for destroying alternators due to harmonics. If you get a cast alloy sump (standard on european RS2000s), the problem is solved. The alloy sump raises the engines resonant frequency out of the usable rev range.

[TurboRA28]

Interesting thread this
I've started to make a brace that will bolt onto 2x of the throttle body bolts and run over to the head and bolt on where the engine hook (to lift engine out) would go.

I'll let everyone know if this makes any difference or not.

[TurboRA28]

Woohoo its fixed!! A brace from throttle body flange across to the head solved it. I'll take some pics of the ugly brace I made was just quickly welded together. I used 2 bolts on the throttle body so it spans a larger area.

But cant believe the difference it made.

Cheers thanks all for your help!
Joel

[JustenGT8]

So the clash of the RWD 3SGTE's @ Wakefield is on!!!!

[TurboRA28]

Yeah baby!!! I'm really keen to see Jack?Jake? sorry.. car in the flesh. Even better we can battle it out on the track