Where does the engine smoothness come from?

[PhotonFanatic]

Maybe this is something I'm imagining, I'll let yall tell me that. But when an older GM engine is running very well, it seems to be very smooth. Almost as though you're in a vehicle and the engine isn't running. But it is. I've noticed this seems to be even more apparent in with the TBI engines. But it's not limited to just those. You mash the pedal and you feel isolated from the engine and transmission.

It's almost as though there's something dampening more of the vibrations in a vehicle that has a GM V8, than there is in other brands. Does GM perhaps, make better motor mounts? Do they balance the internals better? Maybe they balance the crank, rods, pistons, and everything else better than Ford and Dodge do.

 

[618Syndicate]

As I understand it, NVH comes from material frequency harmonics and balance. Different materials have a variety of natural harmonics responses, so they need to be chosen carefully, and Wikipedia explains engine balance as well as anywhere else:

Engine balance - Wikipedia

en.m.wikipedia.org

 

[Keith Seymore]

Two things:

One - a GM V8 is inherently balanced, not only from a rotational mass standpoint but from a firing frequency standpoint. So there's less work to do, in terms of tuning mounts and adding damping devices then if you were working with a different engine.

Secondly - the GM development community is nuts when it comes to tuning these things. There are entire staffs of people whose full time jobs are to tune shocks, engine mounts, trans mounts, body mounts, add tuned dampers, etc. When we tear down competitive vehicles it is obvious that they do not spend nearly the same amount of time and money with this level of refinement.

*I should say I am thinking of other big three domestic manufacturers. When you get into Lexus, or Rolls Royce and other flagship luxury manufacturers it is a different story.

 

[Keith Seymore]

It's fuel delivery, too.

Fuel injection (especially computer controlled fuel injection) allows you to tailor the air/fuel ratio across the entire map of engine RPM and load. Precise fuel delivery helps smooth the idle as well.

Carburetors are crude, crude devices, and are really just one step short of you riding around on top of the engine and dribbling fuel into the engine upon occasion.

K

 

[PhotonFanatic]

Two things:

One - a GM V8 is inherently balanced, not only from a rotational mass standpoint but from a firing frequency standpoint. So there's less work to do, in terms of tuning mounts and adding damping devices then if you were working with a different engine.

Secondly - the GM development community is nuts when it comes to tuning these things. There are entire staffs of people whose full time jobs are to tune shocks, engine mounts, trans mounts, body mounts, add tuned dampers, etc. When we tear down competitive vehicles it is obvious that they do not spend nearly the same amount of time and money with this level of refinement.

*I should say I am thinking of other big three domestic manufacturers. When you get into Lexus, or Rolls Royce and other flagship luxury manufacturers it is a different story.

Got any tips on making it run even more smooth? If you had to take a TBI 350 and get it to run even smoother, what would you do?

Next question: At what point to aftermarket parts upgrades affect the overall smoothness of the engine? And start to transfer vibration to the driver. I'm trying to strike a balance of upgrading for more hp/tq, but without affecting driveability or road manners.

 

[WebMonkey]

this subject came up awhile back for me.
i took my father in law for a ride in the 85 k20 super double xtra heavy duty.
forest road sightseeing.

he remarked several times how 'smooth' it ran.
now, it RIDES nice and rough but that 350 just hums along.
(even with that poor ol' quadrajet runnin' the show)

'monkey

 

[Turbo4whl]

Carburetors are crude, crude devices, and are really just one step short of you riding around on top of the engine and dribbling fuel into the engine upon occasion.

K

Wow Keith, if that is your description of a quadrajet, I want to hear how you describe a Holley.

 

[Radiohead]

Carburetors are crude, crude devices, and are really just one step short of you riding around on top of the engine and dribbling fuel into the engine upon occasion.

K

Oh, the old "monkeys, dumping in buckets of gas" thing.

A subsidiary of Trunk Monkey Enterprises.

 

[75gmck25]

I have always heard that an inline 6 cylinder has the best inherent balance. In 360 degrees of rotation you have a cylinder firing every 60 degrees of crank rotation and they are all pushing on the same plane. You have to worry about flex of the longer crankshaft, so good support is needed from the bearings.

BMW still uses the straight six, and the older Datsun 240/260/280 engine was an inline six. Not sure of other performance applications that use this layout.

 

[Turbo4whl]

I have always heard that an inline 6 cylinder has the best inherent balance. In 360 degrees of rotation you have a cylinder firing every 60 degrees of crank rotation and they are all pushing on the same plane. You have to worry about flex of the longer crankshaft, so good support is needed from the bearings.

BMW still uses the straight six, and the older Datsun 240/260/280 engine was an inline six. Not sure of other performance applications that use this layout.

Many inline 6 cylinder diesels in medium duty trucks. I have heard the phrase, "Six in a row will go, V-eights sit and shake."

 

[squaredeal91]

Want your engine smoother than already designed? Take your engine to the machine shop and have it balanced. It's usually done with a rebuild. They balance most of the moving parts. Do you already have a roller cam?

 

[GTX63]

About 20 years ago I owned a baby s*** green 69 Impala 4 door hardtop with an L48 350.
Some of the early repairs were replacing the shocks, control arm bushings and rebuilding the quadrajet. I put 4 radial tires on it.
I still remember sitting at red lights and unsure if the car was running or not. The ride was as if I was in a recliner at home. I don't think I have owned anything as smooth since.

 

[Buck69]

I have always heard that an inline 6 cylinder has the best inherent balance. In 360 degrees of rotation you have a cylinder firing every 60 degrees of crank rotation and they are all pushing on the same plane. You have to worry about flex of the longer crankshaft, so good support is needed from the bearings.

BMW still uses the straight six, and the older Datsun 240/260/280 engine was an inline six. Not sure of other performance applications that use this layout.

Their cylinders have to make 2 rotations to fire so actually every 120 deg. A v8 is every 90.

 

[618Syndicate]

BMW still uses the straight six, and the older Datsun 240/260/280 engine was an inline six. Not sure of other performance applications that use this layout.

Both Nissan RB (made famous in the Skyline) and Toyota JZ (of Supra fame) motors are routinely built to 1k+ whp and examples of JZ's with twice that exist.

 

[Bennyt]

I know I am late to the party but there is a lot of talk on various forums that swapping cams to the LS firing order makes SBC run smoother, reduce load to increase longevity, better mpg, and run cooler so you can put more timing in it and increase power and mpg.