Hi Guy's,

I've done a few searches but haven't found anything conclusive on this yet. As many of you know I have got my little project car registered and am in the process of ironing out the bugs. One thing I wanted to quiz was how to cure the drone or from the exhaust, it definitely sounds like a drone rather than loud exhaust noise).
Entire floor is sound proofed in Dynamat equivalent. Then underfelt, then carpet.
I find that at low revs or when the engine is straining a little, the exhaust tends to resonate quite a bit between 1500 - 2500/3000 RPM. Seems to die off at highway cruising at 100km/hr + when under less load.

I've tried to keep this thing as quiet as I could and I don't want to spend a small fortune on the exhaust of the car but wondering if anyone has any tips on how to keep this bloody thing quiet. I'm not keen on going back to the exhaust shop after it has now changed hands and the new owner charged me extra to fix the issues the last exhaust guy did... So I figure I'd do the rest myself as unpleasant as that job is...

Originally it has a 3" S/S turbo back exhaust, high flow (magic) cat into a large "Super Cat" muffler something like 14"x9" with a dump tip. Has terrific note from the SR and met my DB restrictions, but It was touching the spare wheel well and I thought it was resonating in that dead space, so took it back to the exhaust shop and they tweaked it a little ($$) so it was missing the spare wheel well and got them to install a 14" xForce resonator after the cat also (doesn't have much muffling) can justify the $$ on that.

Anyway, cut a long story short, the exhaust became marginally quieter outside, next to no difference in cabin noise or resonance, and if anything the low end became even beefier, so that was one test that didn't pay off.

Exhaust guy thinks it could be because its going through the rear cross member which is causing it to resonate, and he suggested we drop it below it, which to me sounded like complete nonsense. Also he didn't brace the exhaust along at the back of the gearbox and I noticed that it might be able to be braced on the back of the cross member through a hole thats conveniently located there, using a Cotton Reel mount.

I've also looked into making a Side Branch resonator. But figure that will be last effort attempt.

Can anyone offer any suggestions?

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Current Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
Daily: MY98 Subaru Impreza RX (my workhorse)
Previous Car: Restored Green 1972 Datsun 510, Hot L18

Just turn the music up louder.

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Datsun 1600 CA18DET 185kw @ 16 PSI Engineered
http://ozdat.com/forum/viewtopic.php?f=59&t=6322&start=135

varex?

take the 3 inch exhaust of and put a 2 inch one on

Hey Ross,

In my WRX's I used to go 3" off the turbo and 2.5" at the diff to reduce the noise, didnt really impact the power figures all that much. Not sure if that will help you.

Cheers,

Trent

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1600 Build: viewtopic.php?f=59&t=22694

That should help keep exhaust gas flow ok too as it will have cooled slightly by then.

The forester guys do same as wrx ones

Does your car have the hole in the crossmember pumped full of space invader to fill the gap between the exhaust and the crossmember? If it is your car I'm thinking of, I'd start by removing that stuff.

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My names Travis and I have a Datsun problem.

Thanks guys. Why would going to 2.5" through the cross member make a difference though? Obviously I'm not going to 2" that's just ridiculous. The drone is caused by sound waves resonating at a particular frequency, causing the pipe to vibrate and transfer that energy into the cabin. That's why I was wondering if there was a nice place for installation of a side branch resonator.

Travis, mine has got packing inside the cross member, did you look at it at the exhaust shop? Its been siliconed in with exhaust rubber I think. To try and stop it rattling and vibrating or hitting the cross member. Maybe I should take it out and see if it helps. Shouldn't be hard to replace it. Maybe thats why the exhaust guy suggested going Under the cross member instead of through it?

The other thing to do is try and make the exhaust heavy to stop the sounds vibrating. Not my favourite option. Maybe some lightweight soundproofing between the muffler and boot floor/car body might help also.

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Current Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
Daily: MY98 Subaru Impreza RX (my workhorse)
Previous Car: Restored Green 1972 Datsun 510, Hot L18

If the exhaust is made right then it shouldn't need the packing in the crossmember hole, nor should it vibrate or contact it. Do you have any other mufflers you can borrow to see if it changes it? Even if they don't fit on the car properly, just to bolt it up and give it a few revs to see what changes?

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Fitting the exhaust thro the Xmember & touching the brake cables are where most exhaust shops FAIL.
If the exhaust is too solidly mounted resonance will result.

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A little knowledge is a dangerous thing.
www.datsport.com

It may have been mentioned but is yr rear xmember hole enlarged to fit the bigger 3" exhaust? Pretty sure fitting a 3" through the standard hole would be a very tight fit.

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Its enlarged yes. Its a Datsport item. I'll try and remove the packing and see if that helps.
Strange that having the exhaust to solid will cause extra resonance though. Would like to know more about exhausts!

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Current Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
Daily: MY98 Subaru Impreza RX (my workhorse)
Previous Car: Restored Green 1972 Datsun 510, Hot L18

I think I spotted it the day you got the wheel alignment done. I'm thinking that's what the exhaust guy would of been referring to.
I was just thinking that might be the couse of it because we fitted some super pro bushes to a ba falcon a few years back in the rear crossmember and the noise from the diff transferred through the car so bad, so we swapped them back to the factory rubber type and the noise was gone. It's not quite the same thing as your experiencing but I'm sure your crossmember is fitted with a similar style solid bush to transfer the vibration from the exhaust through the crossmember and into the car. It's worth a try anyway!

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My names Travis and I have a Datsun problem.

Definitely worth a try. I started it the other day and jumped underneath it and the resonance from the muffler from being underneath it was incredible. It was so loud even though its not overly loud outside. It could be transferring that. First to rebuild my brake booster. Its shagged too and was taken out on the weekend for a replacement that didn't fit!

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Current Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
Daily: MY98 Subaru Impreza RX (my workhorse)
Previous Car: Restored Green 1972 Datsun 510, Hot L18

The joys of modifying cars!

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My names Travis and I have a Datsun problem.