Noise under hard acceleration?

[Claus Poulsen]

I have used the search option but came out empty handed.
My newly acquired 1979 911 SC has an irritating growl drive train noise under hard acceleration (4k and above) but the weird thing only occurs when I have passenger(s) in the car because of the extra weight I guess. Its barely noticeable (if there at all) when its only me in the car.
I suspect the drive train or could it be the engine?
Timing is spot on and all head studs are there. Recently changed to SSI's and Dansk 2-2, but it was the same with the old original exhaust.
I suspect worn CV joints, wheel bearings or the 915, but again I'm a rookie.
Any advice?
Thanks in advance.

Here are a few photos of my oak green SC.

[rusnak]

Slipping clutch? Can you replicate it by taking off from a standing start in 2nd or 3rd? The engine should die in 3rd for sure.

[Claus Poulsen]

The clutch is not slipping. Acceleration performance is fine apart from the growling grinding noise.
The harder I punch it, the more noise I get.
Maybe I should tell my spouse to hit the slimfast ;-)

[Rich Gas]

Claus, are your passengers heavy? Rubbing tires...squatting while hitting the gas

[Claus Poulsen]

The tires could be it. Good Year eagle F1's. Seems to be worse uphill.
Wife claims to be around 60kg last I dared to ask.

[DRACO A5OG]

Welcome aboard.

If you like your life don't ask wife her weight :-o.

If CV joint it would always make noise for the most part.

Check the wheel bearings, fronts are straight forward. Grasp the top of the wheel a 11 & 1, tug and push. If slop you bearings are loose and may be the culprit.

Next, what are the condition of your transmission mounts, if worn it can cause vibration. while you are at it check the motor mounts. I would replace to have a fresh start on those mounts.

F1's are noisy, I use to have them loved them on autoX but they are horrible in the rain.

[rusnak]

Wheel bearings would make noise all of the time, and you could hear them when coasting. CVs make more noise when turning, and the sound is more of a clicking. I concur regarding tires. You might check the tire pressures and gear oil level.

[Uncle Enzo]

If the tires are rubbing there will be marks on them. If not and you still suspect them, put some white tape on the lip and go for a spin with a passenger and see if u have some rub marks on the tape.

[Claus Poulsen]

Thanks for your replies.
915 is full of new Swepco 201 and no wheel bearing play can otherwise be detected.
I will start with renewing motor and tranny mounts which I planned on doing anyway.
If this doesn't do the trick I will have a good excuse to disperse some Good Year tire tread on the local roads before trying out another brand of rubber.

[pjd131]

One more thought. Could it be the shifter linkage vibrating in the tunnel. When I took mine apart the donut like bushing had basically disintegrated. On higher revs it would knock and vibrate. Congrats on your car too Claus. It looks great.