ever notice how some cars shake the ground ?

Why is that?

30 years ago, this guy had a nice chevy II that wasn't exceptionally fast but it was a nice running great looking car. Great road manners just a really nice street car. When he drove by on the road or in the parking lot that SOB really shook the ground. The little pebbles would bounce on the pavement. Tickled your feet. Sounded good but not loud.

I asked him what he had in there and he said it was a "warmed up 283 nothing fancy" .
He said its a real ground pounded but not sure why.

Had another friend with a 318 that sounded really nice taking off and cruising in. His would pound the ground but no where near the chevy. Funny thing is his car couldn't get out of its own way.

Now this summer standing by the return roads at the strip some cars coming by made an exceptional amount of racket but no ground movements, others quieter to the ear but noisier on the feet. I couldn't make a correlation to one or the other being faster.

Also this summer, I've heard some cars go by that sounded awesome but kind of hollow or fake. Some go by and you can feel it . Hard to explain but if you remember the old memorex commercials, you should get the idea.

I've picked up on this riding a motorcycle, your feet are on the ground in traffic.

 

I wonder if it has to do with where the exhaust is directed. A lot of cars in my area run mufflers with turndowns that do that. Otherwise I got nothin....

 

I know just what you mean.

Theres a guy with a GTO who goes to the local cruise in at Marley Station here in Maryland.

That thing just rattles the shit outta anything near it.It just sounds BAD to the bone.

I dont know how fast it really is ,but damn it sounds mean.I love it.

I would like to know why some of these machines pound that hard.

I would think that this GTO is a big inch engine. I"m sure that adds to the rumble.

Oldmics

 

I guess you've never been on the starting line at a NHRA meet when the funny cars come up to run...everything shakes

 

The ground pounding comes from breathing good. Compression, cam, good porting and exhaust. when they breath good you can get the idle low and that'll give them a thump, the thump you can hear in the header tube. when you get really high compression they'll chirp and you canl feel that down in your tail bone.
Its all about the breathing.

 

I don't have an answer for you but i just love that feeling!!!!!!
Gasser Girl

 

Recently I stood beside a real honest to goodness thunderbolt,when they fired it up ,it shakes to ground so hard my heart turned flips . HRP

 

No I haven't , what's that like ? Explain it to me - try anyway.

Last month I saw a field of 42 top fuel funny cars and dragster trying to qualify.
21 consecutive passes, I wanted it to stop. I thought I my body was going to implode. I really couldn't take it anymore. Maybe because it was 99* in the sun all day . It was fucking awesome.

 

I was at the Cedar Falls drag strip with my ATV many years ago, on Friday night test & tune... pretty much everyone runs as they come up... I was 2 runs behind a "1000 hp" funny car... OMG... my back bone was pounded through my chest when that car did it's burn out, & I was 75ft or so behind it... it could have been a jet, but was not smooth, I felt each cylinder fire

anyway it would seem the exhaust & how it's directed would be the most ground pounding effect, but a race cam, or very high compression & radical running ( not smooth ) might transfer that rumble through the suspension & tires ???

 

Its not the turn downs, or cubic inches.

Its something else and its not the fastest ones. I think the more they pound the slower they are. (Top fuel excluded)

 

Also the ones that pound the hardest aren't the loudest.

 

Early exhaust valve opening has a lot to do with it. If you have a cam ground that way, or you advance a 'normal' cam the exhaust opens while there is still a lot of pressure in the cylinder and kaboom out the exhaust. That's sort of why fuel cars are so loud, the fuel has a secondary combustion in the exhaust pipe plus it burns slow so it's got lots of pressure when the valve opens.

Ever notice how Super Stock class cars ratchet and shake the ground in the pits? (at least the older cars) Most of them run the cams very advanced.

 

The first time i went to Indy for the Nationals i was sitting in the stands and when John Force went by it was like being hit by an atomic bomb blast. I loved every minute of it.

 

I have a stock 289 4 bbl in the Fairlane with cheap glass packs. I have turn downs just before rear axle. When it idles down or even when rolling around a show in 1st gear, you can feel it in your chest. Other RPMs aren't really even all that loud, but at certain RPMs it must hit a frequency that makes it sound really mean. The guy across the street (fellow car guy) swore I was running a big block.

 

Shit, Steve... I'm willing to bet dollars to donuts YOURS makes the ground shake a l'il beneath the old feet. The car in your avatar is one of my all-time favorites. Yours is one of those cars I'd give up a body part to be able to take it for a cruise for a day. Love it.

 

Short answer- Compression and cam timing.

 

I don't know what causes it, but the end result makes me smile.

 

That's it... Exactly.

 

Turn it up.....http://www.youtube.com/watch?v=wFOmGkv6Dn8

 

Local guy who had a wicked 455 in a 70 Trans AM .....it would regulate your heart beat.

 

While I was in shower contemplating this , I had the same thoughts. Early exhaust valve opening. Early intake closing builds more cylinder pressure and the early exhaust valve opening let's some of the boom out.

It has to be some physics. The energy released to the ground should be used to move the car. That might be why the hardest pounders aren't the fastest.

What pounds harder , funny car or dragster ? What's faster?

 

Don't know yet, 421 cid of blown hemi ought'a do something
Maybe I need to advance the cam.

 

Bingo. Big cam, VERY narrow lsa, lots of noise down in the pipes. And smaller motors "rax" harder, bigger motors have a softer, "lazier" sound. Bigger motors also tend to like a wider lsa. I have built otherwise similar motors under 450" and over 500", the smaller motors sounded much nastier at idle.

 

Those are pretty big compared to a 283 that would tickle your feet and make the pebbles dance. Would the same hold true for an engine of that size?
It had a noticeable lope but nothing really radical. Nice cruiser built 30 years ago.

 

Also add hi octane race fuel into the mix...

 

Maybe solid motor/exhaust pipe mounts? Sort of turns the whole car into a speaker?

 

What about mufflers and pipe size? Can too big a pipe and nothing breathing through it, sound lousy?

 

I agree that cam timing and compression certainly have a big effect. I also think cu inches has an effect. The larger engine has more volume going through, so it is noticeably more. Go to your local drag strip on test and tune or regular Sat night. After a while you can usually tell what cars are big blocks vs small blocks. It is not loudness, but the quality of the sound.

I do think cam timing and being advanced has probably the most to do with it. Turn downs on exhaust help the sound echo back up emphasizing the feel.

 

Back in the early 80's, when I was in high school, I was walking down the hallway after school let out. I was a little later than everyone and the halls were mostly empty.

As I was walking past the lockers I noticed an odd buzzing sound. I looked around trying to figure where it was coming from, then realized all the locker doors were vibrating. I wondered what could cause that. Some sort of machinery some where?

As I continued down the hall I began to notice the floor was vibrating under my feet. The closer I got to the exit the stronger it became. The exit had a double door air lock, as I opened the inner door I could hear an engine running outside, and realized that must be the source.

When I got outside, what I saw was a Ford C-600 delivery truck, idling at the curb. To my ears, it just sounded like an ordinary engine. A little louder than typical, but nothing extraordinary. No loping idle, just steady and slow. What stopped me in my tracks wasn't the sound I could hear, but the sound I felt. The sidewalk was shaking under my feet, I could feel air pumping in and out of my lungs, vibrations through my bones and guts. I looked at the truck to figure why it sounded so bad-ass. It had about a 5" dia. pipe feeding into a muffler the size of a 30 gallon trash can. Typical big truck stuff.

Those truck had the old Superduty gas engines, 401, 477, or 534. Nothing near a radical cam or high compression. As best I can figure, the idle speed just matched the natural frequency of the exhaust pipe. Like an old fashioned church pipe organ that shakes the rafters on the low notes. I've never heard anything quite like it since. I've heard loud, radical cars that come close, but nothing like the quiet, smooth, rumble that could be felt so strongly from such a distance. It obviously stuck with me as a vivid memory for nearly 30 years. My goal is to duplicate that sound someday.

 

I think it`s header design.I remember a Z11 Chevy in AZ driven by Bob Sanders also he built the headers.It had a high pitched buzz to it.Havent heard the sound since.