Isuzu 4BD1 Vs. 300tdi sound check

[abaddonxi]

I finally found the dB meter and thought I'd better see which is the louder.

I put the meter in the cubby box tray, that pretty much covers scientific rigour.

The Isuzu -1988- has insulation on floors and firewall, but none under the hood. 300tdi has standard Defender mats, etc.

Isuzu warm idle at about 66dB
Isuzu driving 72-80dB

300tdi warm idle 64dbB
300tdi driving 64-84dB

[Rangier Rover]

Intersestig results there.:)

I recon the road noise is louder in my 120 than the Zuzu at 80 kmh on anyway.

The idle is a different story though:angel: Had to bump it up to 900 as I got sick of putting new pop rivets in the rear bulkhead:twisted:

[Captain_Rightfoot]

That's very interesting. :) Good work.

Can I ask about the DB meter? Has it been calibrated? Without calibration these figures are only really of use for comparing to one another.

[abaddonxi]

Cali-what? I might have dropped it once if that makes any difference.:D

Nuh, picked it up off the bargain table at Tandy a few years back and took it out of the packet for the first time for this thread.

And how's this for an interesting one?

I changed the oil a few weeks ago to Shell synthetic 5w40. Dunno if that's the right stuff for an Isuzu, but there you go. From the first drive afterwards I thought it was noticably quieter. Went for a drive with the meter today and it was 2db+ down on last time.

Wonder if it's just the oil really needed changing, or if synthetic is magic oil.

[Offender90]

That's very interesting. :) Good work.

Can I ask about the DB meter? Has it been calibrated? Without calibration these figures are only really of use for comparing to one another.

I'm happy to measure in-cab noise levels with a calibrated professional sound level meter if I can get access to a 4BD1 and a 300Tdi in Perth. Would also be interesting to compare a 4BD1T against the two above. I think I already have a volunteer for the 4BD1T.

Cheers

Bojan

[rijidij]

And how's this for an interesting one?

I changed the oil a few weeks ago to Shell synthetic 5w40. Dunno if that's the right stuff for an Isuzu, but there you go. From the first drive afterwards I thought it was noticably quieter. Went for a drive with the meter today and it was 2db+ down on last time.

Wonder if it's just the oil really needed changing, or if synthetic is magic oil.

My 4BD1T always seems quieter immediately after an oil change. I'm not using anything special, just 15/40.

Murray

[isuzurover]

I'm happy to measure in-cab noise levels with a calibrated professional sound level meter if I can get access to a 4BD1 and a 300Tdi in Perth. Would also be interesting to compare a 4BD1T against the two above. I think I already have a volunteer for the 4BD1T.

Cheers

Bojan

Ready whenever you are ;)

Wind and tyre noise seems most prominent on the highway. Might need to fit a set of AT tyres for the test???

[Dougal]

Interesting, I got a chance to drive a 300tdi powered 98 disco yesterday head to head with my 4BD1T powered 85 rangie.

The disco was much quieter, but I don't know what levels of sound insulation they have and this is the very last of the 300 tdi's. It also appears I missed a piece of sound foam when putting mine back together last week. Sounds like there's a window open to the gearbox.:angel:

[Offender90]

Ready whenever you are ;)

sweet... next weekend perhaps?


Wind and tyre noise seems most prominent on the highway. Might need to fit a set of AT tyres for the test???

Tyre noise (externally) usually becomes dominant at ~ 70km/h and above. Internally it may start dominating even earlier, as the rear wheelarches are very thin so there is little to stop noise entering the cab.

Any volunteers with a 300TDi / 4BD1 in/around Perth? I work in the city and live south of Freemantle, so anywhere between the two is good for me.

Cheers

Bojan

[Offender90]

OK, 4BD1T noise test results are in. In-cab LAeq (energy averaged) noise level summary:

50 km/h, windows open - 85 dB(A)
50 km/h, windows closed - 81 dB(A)
70 km/h, windows closed - 83 dB(A)
100 km/h windows closed - 86 dB(A)

The measurements were done with 5 people in the car and a bit of talking from time to time, but nothing to significantly influence results. In addition, there were some in-cab noise sources (chiefly a boost pressure gauge rattle), which I've tried to filter out (by discarding some of the high frequency data).

At higher speeds (70km/h+) tyre noise became the dominant source, while with windows open, it was engine noise at low speed, and aerodynamic noise at higher speeds. With windows closed, the dominant transmission paths (subjectively) seem to be through the door seals / lower door panels at higher speeds (tyre noise) and through the firewall / floorpan at low speeds (engine noise). When open, most of the noise came through the windows.

So, if you're planing to quieten your 4BD1, it's pointless to do so without having a good air-con! I'll add some thoughts on how to quieten later once I've had a better look at all the data.

Cheers

Bojan

PS - Anyone in Perth with a 4BD1 / 300Tdi wishing to volunteer 1/2 hour of their time in the name of science, send mea PM.