Why are some car engines so loud?

[mender]

Good cars, fun and quick, no major issues that I remember (was an M-B shop foreman); anything specific that you're wondering about?

 

[Ranger Mike]

no problems Mr Mender...it has 62,000 miles on it...i know original lady owner...anything i should do mait wise with the milage?
any mait on the blower?

 

[Danger]

Oh, wowzie woo! This just brought on a flash memory (a tiny one). I remember decades ago seeing a movie on TV, which I'm pretty sure starred George C. Scott, set in Europe. He was driving some German car which (crucial to the plot) had a gear-driven supercharger that was turned on or off by a shifter in the cab. Is that what you have, or is yours "always on"?

 

[mender]

Nothing comes to mind, Mike, just check the service records and make sure everything is up to date. Most M-B owners are pretty diligent about that though!

Danger, the compressor on the SLK should have an automatic clutch only, no shifting or switching (a la Mad Max!) required.

 

[Danger]

Thanks, Mender. I can't remember Mad Max, even though I've seen them several times.

 

[HowlerMonkey]

All of my cars are whisper quiet.

All of my cars are turbocharged.

 

[462chevelle]

I'd say that it's worth quite a lot given your history with cars.

Since Coconut wrote "If they produce so many noises...", and everyone has focused exclusively on exhaust, I'm just going to briefly mention some of the others. I refer here to Detroit Iron, not rice-rockets, because that's what I'm familiar with.
Lsos and, to a lesser degree, Nugatory touched upon the subject of intake, but didn't really address it. Most musclecars incorporate some sort of free-flowing intake such as open-element foam filters, velocity stacks, etc., which create a very noticeable "whoosh" and sometimes whistling somewhat similar to a vacuum cleaner. If the car is running a blower, you can multiply that effect significantly and add in the distinguishing whine of the gears and buzz of the drive pulleys (or turbo whine, if that's the way you swing).
Lots of "tuners" prefer mechanical lifters, which can make an annoying racket. Personally, I'm willing to forgo the potential performance increase in order to avoid the hassles of spending half of my life under the hood with a wrench. Anti-pump-up hydraulic units for this boy...
Timing equipment, be it double-roller chains and sprockets or dual-idler gear drives, contributes to the overall under-hood ambience, as do the various accessory drive belts and pulleys for such things as the alternator and water pump. Even airflow through the radiator can be noisy. Piston slap can be annoying, and can be good or bad depending upon the reason. (My Roadrunner sounds like a coffee can full of rocks because the pistons are mounted backwards for increased efficiency. It only adds about 35hp, but that's still worth the auditory assault.) There are more factors, but that covers the most predominant ones.
Some of those things increase the power of the engine, and some rob from it, but the robbing ones are necessary for streetability.

edit: I made a somewhat misleading statement regarding the pistons. The decrease in frictional losses due to them being installed backwards accounts for about 35hp. Because of their design, though, doing so also kicks the compression ratio up from 12 to 12.5. That's worth even more.

putting them in backwards cannot change the compression ratio. no matter how you put them... at tdc and bdc they take up the same volume in the chamber. I have actually heard old people talking about putting them in backwards and the only advantage I could think of is if the piston had an assymetrical dish that you would put the flat spot of the dish to the flat spot on the head and the dished spot to the valves.

 

[Danger]

Putting them in backwards reverses the wristpin offset, which is where the initial frictional benefit comes in. It also alters the geometry of the pistons relative to the bore at both the top and the bottom of the stroke. It gives essentially the same effect as lengthening the stroke.

 

[Ranger Mike]

Not quite true on the offset. It can not change compression ratio nor can it add or subtract from stroke.
All production pistons have pin offset to the right or toward the major thrust surface of the piston ( on typical clockwise rotation engines; marine engines rotate CCW).
Pin offset is to load the thrust surface against the cylinder wall to keep the piston from rocking as it moves down the bore, thus preventing piston slap and noise.
Think of what happens when the piston pin is centered in the piston. When the piston reaches top or bottom dead center the rod is straight up and down. This places a huge load on the rod. The crank must rotate past TDC or BTC in order to get the piston moving again. This robs both power and RPM's from the engine. Now off set the con rod pin. The piston pin is offset to one side of the piston. When the crank is at TDC or BDC the rod is not straight up and down. This in turn allows the crank to rotate with much less resistance giving the engine more power and speed. Now reverse the offset and you have even more advantage mechanically.

You can reverse this with flat top piston only..no eye brows ( valve reliefs and definitely no pop up piston domes). It can add slight mechanical advantage by increasing the dwell time of the piston at top dead center and getting more power from the same amount of fuel air mixture at ignition because of better leverage on the crank shaft. This is the same trick we used to do using a longer connecting rod with custom piston. We had stock bore and stroke but much more power. When you reverse the pin offset you will suffer from increased piston wear and more noise. Not worth it for the small mech advantage.If you are taking down the engine to this level of disassembly I got more power trick that will give you significantly more power than trying this and sounding like you are ready to throw a rod every time you drive it.
I picked up attached diagram off the internet and it shows advantage of reverse offset ...not my math on the angles..simply shows lever advantage..smokey yunick was first to pioneer this and rumor had it the trick was worth 5 h.p. per cylinder...take it for what it is worth

 

[462chevelle]

its nice hearing the engineering thought that goes into things like tha

 

[Danger]

Mike, I'm still quite ill, and so can't really get into this now, but you have given me something to think about.
I was going by what my engine builder told me (his specialty was pulling tractors). Still, the leverage factor puzzles me. When I get better, I'll think it over some more.
For the record, my pistons are "race only" forged aluminum 12:1 TRW's with 1/16" double moly rings running .008" gaps in a .030 overbored 440. I was warned that the rings would be good for 10 passes in the quarter, but I got 50,000 km out of the first set. Good thing, too, because I was on vacation when I had to get the engine rebuilt and it was a hell of a lot more than 2 1/2 miles home.

 

[Ranger Mike]

Danger

sorry to hear you are feeling down...on the plus side..it sounds like the engine builder is way low balling the run time. First of all, the custom piston you have now already have been designed for maximum leverage factor. I would not order custom pistons with huge pin offset in a class that is wide open..if rules were super restrictive..maybe I would do it..number two rule in racing behind the number one rule..tires, Tires , TIRES..is you have to finish to win and the longevity you have in a proven design far out weighs the mechanical advantage.
In my opinion with little empirical data, is the fact that Heat is the biggest killer of piston rings, number two being lack of proper oiling.
I would brush up on proper procedures for leak down test and would thin of rebuilding once the numbers stated to fall off. Compression test does not give you as much data as the leak down test will.
Finally, 1/16 rings are the standard now..the old 3/16 rings are way to heavy and parasitic drag is too great...I would run the 1/16 rings for a season,,,all round track engines I built had these and we ran 165 miles a season.
I would stroke that 440 block to 510 cubic inches, stick a .610” lift cam in it and run it for a year!


anyway...get well soon

 

[462chevelle]

older rings were traditionally 5/64, 5/64, 3/16 oil

 

[Danger]

Hey, guys. I'm feeling a bit better, but still not enough to really participate. It's only a matter of clogged sinuses, but that prevents my oxygen from being fully effective and thus makes me groggy.
Mike, I'm not sure now that you realize that the Roadrunner was my everyday street-driven vehicle, not a track racer. The #4 rod bearing spun out while I was on vacation (a 440 oiling problem), and the piston collapsed with accompanying damage to the bore. I had to get it rebuilt to get home, over 400 miles away. The tires were always L60x15 Goodyears on the back and G60x15 Tiger Paws up front. Those were replaced with the equivalent size all-season radials when I moved back to Alberta.