ever notice how some cars shake the ground ?

Compression, cam and ignition timing and exhaust pipe diameter can all affect the sound. If any or all of these are way out of bounds, a good engine will sound like a log truck without a muffler, just a ragged nasty noise. With larger cu. in. blown engines esp., camshafts are built with more duration (and more, and more, and more) LOL This is largely an effort to bleed off torque, at lower RPMs because these engines make so much torque that they require multi disc slipper clutches, or torque converters with little or no multiplication. These are things i've learned the hard way and at considerable expense. Please don't believe that I think I know it all, probably just enough to be dangerous. Anyway, I don't take myself too seriously.

 

What would be considered way out of bounds?; and what's a proven combination?

 

Might also have to do with the motor mounts.I put the engine out of my camaro (regular mounts) into my hot rod (solid mounts) and it will tickle you feet if your standing next to it.When it was in the car you couldnt feel a thing until you stood on it. Just a thought!!!!!!

 

I stood behind an Indy roadster with an Offy when they fired it up. Shook me, the ground, and everything else around it. Glorious.

 

I agree with yoyodyne, Mostly camshaft I'll bet. When you get overlap some of the combustion is actually occouring in the exhaust. Sure sounds great but that would also explain why they're not always the fastest. They're "leaving a little on the table".

There are benifiets to having overlap but since it all depends on the rest of your combination it's easy to use a cam that doesn't "match". Ask me how I know LOL

 

It's basic physics of resonant frequency. Everything in the universe has (at least one) resonant frequency... the point where it will oscillate (vibrate) at a greater amplitude than others. If the motor is generating sonic energy at the frequency that something around it likes to vibrate, then you get this amplified effect. It has practically nothing to do with how powerful the motor is... other than the fact that the motor must be capable of producing the original frequency.

As an experiment to understand resonant frequency, take a small piece of sheetmetal, hold it at one edge, and whack the middle of it with a wrench. Tiiiiiinnnnggg! The energy from you swinging the wrench is transferred to the sheetmetal, which has to do something with it... so it vibrates, producing the fairly high pitched sound you hear. That's a resonant frequency in the sheetmetal when that kind of energy (striking it with a wrench) is applied. Same for when you dump xx brand/size/shape exhaust pressure, which is generating nn Hz sound waves, into this-and-that type of asphalt. Run the exact same car the exact same way on, say, concrete, and the resonant frequencies will change... because concrete has a different set of resonances than asphalt.

 

I went to the Palms Springs CA. vintage road races a number of years ago when they were racing on public roads. The best division was the mid-1960s Trans-Am class Mustangs and Chevy Vettes. When that division started their race you could hear them before you could see them ( what an incredible feeling!!). Then, the earth began the shake and rumble as they got closer but still out of view. Finally all hell would break loose as the cars suddenly appeared around a corner at full racing speed. The sound of the engines, the transmissions shifting and the rumbling of the ground was breathtaking! That was a great show!!

 

I always thought is was just a case of harmonics, just the right ( or wrong ) combination of all things involved. I had a 66 gmc with a 100% stock 351 v6 with a really short pipe and a tractor muffler. It would set off car alarms in parking lots at idle. The patterns it made in idleing above soft dirt were interesting. I eventually put a full exhaust on the truck and all of the rumble stopped.

 

I'm sure its a multifaceted situation.
Sure would like to know the details because some cars do and some don't.

There's a "ground shaking siren " used by some emergency vehicles. Its called the " Rumbler" and shakes the ground 200 feet in front of the vehicle. Supposed to grab the attention of those who miss the near blinding flashing lights and blaring siren. Based on subwoofer technology about the size of s coffee can.

 

One more time in case some scientists want to knock it out of the park with details

 

There's a few of them here at the local cruise night.
Lots of them with a nice lope but hollow and fake sound.

 

This is what it comes down to I think. I don't know what combination of parts will produce the effect but I have stood next to or around stock trucks or equipment that would does this too.

The article a few post back about infra sound was interesting. It mentioned some frequencies would make people salivate. I have had this happen to me. I remember being around big trucks, tow trucks or whatever, that when parked against a wall or something would make my freakin' jaw hurt and my mouth water. Kinda takes your breath away too.

Wierd stuff...

 

Late to the party here, my first answer was compression and the way the exhaust was built. After reading other answers I think cylinder pressure is a better answer, and what I think of as harmonics. In the 70's a friend of my brother had a 67 GTO with twin turbos. It did not rumble or shake the ground, but it would screw up the TV reception from a block away. Very specific exhaust tone, and un godly fast. A combination of several factors I suppose.

 

Well, I just read the entire thread, although the Winged Express at Pomona makes my heart feel funny and makes my knees go weak and all the other good explanations , examples and other theory offered is interesting 31 vickys opening remarks in #1 refer to those cars which are just sort of idling by, and not all the real radical racey cars, I have come to realize I want my Merc to thump the ground with its tailpipes, I have a 1965 425 nailhead with headers and when I revved it up for my son and daughter in law she said it feels like something was pounding her chest, now I have to put an exhaust system on it and after reading this thread I'm thinking single chamber mufflers but I can't put turndowns on it cause they won't look right . I hope I can get a good thump rather than a rap. I used to work a mechanic at a bone yard in the mid seventies when muscle cars were slightly old and easily written off and part of my job was to test the engine and by far the loudest was the small block fords, 289 302 , these without exhust manifolds would rattle the eardrums the best.

 

No, your reasoning is incorrect. They are only firing down in the pipes at LOW RPM. The only way they are "leaving a little on the table" is if they are trying to make peak power at 2500 rpm...

 

bore x stroke, exhaust system resonance, timing, cylinder pressure remaining when the exhaust valve(s) open. Mainly bore x stroke, not nessesarily more cubes, but the way the bore width and stroke length make a unique and sometimes ground shaking noise. We have a switch truck at work thats just so slick when moving but will rumble your ballz off when idling. International with DT466 (SAM-small ass motor)

 

So what's the magic bore/stroke ratio

 

Okay, to throw a wrench into all of these guesses: I had a 1971 Grand Prix SJ with the original 455, rebuilt to factory specs except for a Ram Air cam, with original intake, carb, manifolds, and factory-style dual exhaust with stock-type mufflers. The car was not especially loud but driving at low speed you could hear it rumble from a block away. Not a loud sound, but a deep lovely tone that just traveled like crazy.

No radical cam, no exhaust turn-downs or special mufflers, not high compression (1971 was something like 9 to 1?), but just delicious deep-tummy rumbling that wasn't all that loud in the car.

There were a couple other Pontiac 455s running around at that time and they did not have that exact same sound. A neighbor had a 400 1969 Grand Prix and it did not sound the same. But there WAS a lifted 4x4 truck in town that sounded almost exactly the same but it had headers, short exhaust pipes, and a Chevy or Ford motor. (Can't remember which one.) When we drove near each other we could modulate the frequencies with our gas pedals to either harmonize, double, or clash. I liked the clash, he liked to harmonize. We never spoke to each other or even met, but whenever we heard the other's vehicle it would catch our attention.

 

A friend of mine and I had the opportunity to help Connie Kalitta work on his funny car, the "Bounty Hunter" one winter night when I was 17 years old. After putting the left bank of the engine together we rolled the chassis out onto the snow-covered driveway. Connie started that sucker up. There was a full 55 gallon drum of oil next to the car with a case of oil on top and the whole drum started moving around the driveway in a bouncing manner. My guts rumbled when he revved the beast up!! One of my happiest childhood memories.

 

Dont know about the ground shaking but when the top fuelers and funny cars take off it makes my nuts vibrate!

 

I have always thought that it was compression, cam and exhaust to get that ground shaking feeling, more feeling than sound. It also makes me remember when I was a kid the sounds you could feel from the steam powered Great Lakes freighter ships that pass by our city here. I remember being woke up in the middle of the night by the ships, you could "hear" them coming out of the Lake Huron into the St. Clair River on their way to the lower Great Lakes. Although my parents house was about a half mile from the river you could feel the ships engine as it approached and passed. This was in the house in my bed. They made a steady THUMP, THUMP, thump sound. My dad explained they had triple expansion steam engines that used the steam pressure three times in three different sized cylinders before it was exhausted. You didn't really hear it as much as felt it, probably like the ground pounding cars, just the right frequencyto feel more than hear. Those ships would have been built before WWll for the most part, the "modern" ships are mostly steam turbine powered or deisel/electric and dead silent as they slip by without a sound. Even some of the straight diesel powered vessels done make a sound you can feel. I wonder how those sailors slept or functioned on the old steamers....

 

Me too! I had a '64 Fairlane also with a stock 289 with stock exhaust manifolds, dual pipes with mufflers right at the ends with down turns ending just in front of the diff. It sounded like a tuff big block and when driving around shopping mall car parks, it use to set off all the car alarms - way cool in my book. -H.R.D-

 

Thats another thing I like about my modified it sets off car alarms. Stock longblock pontiac 400 with a edel p4b & 650 carb with home fab'd cone headers.

 

I have an OT vehicle (2006 Jeep Grand Cherokee SRT-8) with a Late model 6.1 Hemi srtoked out to a 392 with a cam with little overlap and a wide LSA to pass emissions and through a set of long tube headers, cats, mufflers, and tailpipes out under the rear bumper. It pounds very hard at idle, it constantly sets off car alarms in parking lots etc.. but is relatively quiet. I love leaving it idle when filling up (something I always seem to be doing) as someone always comes up to ask about it.

 

Update

Well I got my small cube (307), high compression 10.5 :1, XE 262 cam fired up.
After the break in and tune I started messing with the exhaust.
First is long tube headers into 2.25 pipes, H pipe about 24" back. That all stayed.
This is mandrel bends no bends over 22.5 * 4 per side and those were used as offsets with about 24" between bends.

I started with summit turbos and then purple hornies louvers open toward the engine at the very end for resonators with a 12" tail pipe at the bumper. Very nice sound, mom wouldn't mind driving it and the neighborhood would know any different.

Next I turned the purple horneys around and that didn't make much difference but it was a touch louder.

Next took the PHs off and swapped in a straight pipe. Didn't care for that sound much so I didn't mess around much.

Next I took the turbos off, swapped in the PH and piped it back to the bumper. Louvers open to engine. Now were getting somewhere but has that glasspack sound at acceleration. Sounds like a really big zipper .

Turned the PH around and that made it worse.

Next I put the PH back at the end with 12 inch tailpipe. That sounded much better and started thumping some. Much lower note and a smaller zipper.

Next turn the PHs around and the zipper got bigger . Some high pitch sound came thru that sort of annoyed me.

Not much left so tried no mufflers, just 12 feet of pipe. That sounded pretty good but rough. Thumping pretty good but kind of too abrasive. It be fun for couple miles not couple hundred

So at this point I'm thinking the very first way would be best but no pounding..

Over in the corner I had a 2.5" bassani x pipe. I re finagled the pipes and put it at the very end with 12" tailpipe. Now that sounded good. Took away the obscenity of open pipes. Thumping like a freight train going by but we could talk at normal conversation right at the bumper.
Quiet as can be at the front but massive low rumbles out the back. Throttle was perfect sound level. Mom wouldn't mind driving it but people would be looking at her funny. Neighborhood would know you are leaving but not wake up the baby.

I'm pretty happy and think any hotrodder would be it sounds like it means business and to quote my buddy " beast"

I'm not sure why the "X" pipe made such a difference.

 

Nothing like the '60's cars. High compression, 12 and a half to 1 compression. All had good exhaust, would shake the ground right out of the factory. Cars are running stock 30/30 Cams.Most of the motors nowadays don't even compare, at least what I've seen here on the H.A.M.B. a lot of flathead guys that don't go fast. Hell, that's what hotrodding is about.

 

many moons ago, Seattle International Raceway had a yearly event called "64 funnycars". The only time I ever went, they put all 64 on the line and started them simultaneously. I could hardly breathe and my heart felt like it was going to come out of my chest. It is still one of my most memorable moments.