Here's one for the pros...

[not-a-stang]

Will higher compression (8.4 vs 9.1) and a carbed set-up increase exhaust noise? I say it wont. Fuel injected cars can be loud too, just add some two-chamber Flo's. Me and a buddy got a bet going....

Assuming both engines are factory stock without a big cam ('82 5.0 ho vs '88 5.0 ho)

[Coupester]

Yes, the higher compression motor will certainly be louder, however the difference will not be highly noticeable. The higher compression will move more air through the engine, and whenever that happens, the exhaust rises in decibels. For instance, when you add heads, cam, and an intake to your 5.0 longblock, the exhaust will get considerably louder!

[madmike8]

The higher compression will move more air through the engine,

Hmmm... Higher compression doesn't really have anything to do with how much air moves through an engine... a Higher Compression Combustion does more work for each molecule of fuel burned... it's due to thermodynamic efficiencies... less energy is lost to heat... The Throttle Body/Carb, Intake, Heads/Valves, and Cam would effect how much air you can get into a certain cylinder size...

back to the subject...

To tell the truth I've never put much thought into sounds levels in comparison to HP.... but I'd say it would be louder... due to more power being made... but to what extent... I have no clue...

[f4fntm]

Intruiging - we need to conduct a scientific trial. Anybody need an idea for their doctoral thesis?

Why'd you specify carb vs. FI? Hard to believe that would make any difference...

[bryant99]

same here haven't give it much thought.Don't have stock exhaust all aftermarket.Mine is louder than my brother's 86 stang

[not-a-stang]

I know that "loud" cars are kinda inefficient because the combustion is happening when the exhaust valves are partly open (like at low rpms with a big cam?), and you can hear part of the combustion. Read it in a import mag...so it could be wrong...

[Byrdman]

I know that "loud" cars are kinda inefficient because the combustion is happening when the exhaust valves are partly open (like at low rpms with a big cam?), and you can hear part of the combustion. Read it in a import mag...so it could be wrong...

Stop reading import rags! Everytime you even look at one of those your IQ drops 10 points. :lol:

[not-a-stang]

I cant stop lookin! All the neon colors, the bling-bling, the "NOSS"...its too much fun to see imports like civics that look like skylines or supras or anything else but a civic! And the performance, well makes my 2bbl Capri look fast!



Plus they got some fine ladies in those mags...

[Matt K]

Yes, it will be louder, but you may not notice... I read somewhere that for every point of compression you go up, your back pressure triples! That's why built engines (& diesels) respond so well to bigger headers & exhaust over stock. Those ads that say "this H-pipe or these headers will give up to 35 hp" is true, on a heavily modified engine choked down by stock exhaust. Anytime you increase the amount of airflow it will get louder...I know my car got louder when I swapped from ported stock E7's to Edelbrock Performers, it ran hotter as well!

[Evil86lx]

Yes, it will be louder, but you may not notice... I read somewhere that for every point of compression you go up, your back pressure triples! That's why built engines (& diesels) respond so well to bigger headers & exhaust over stock. Those ads that say "this H-pipe or these headers will give up to 35 hp" is true, on a heavily modified engine choked down by stock exhaust. Anytime you increase the amount of airflow it will get louder...I know my car got louder when I swapped from ported stock E7's to Edelbrock Performers, it ran hotter as well!

Turbo diesels like big exhaust cause of the turbo.. they like no back pressure.

None of my higher comp engines where ever louder than the lower. Thats how you get the sleeper effect, more compression, stock exhaust, same noise..

now if we where talking cam profiles...well thats a different story...

kyle

[Zap's 85 GT]

now if we where talking cam profiles...well thats a different story... \

Definitly. Main things to alter exhaust noise is duration and cam lobe ramp rates. Letting out more exhaust because the valve is open longer and slapping the valves closed faster makes the biggest change in sound. Higher compression promotes faster combustion but doesnt pull in or push out any more or less air then a lower compression does, all other things being the same.

[Evil86lx]

Iv'e been thinking, i know that doesn't happen to often :D

But if you are moving the top of the piston closer to the bottom of the head to get more compression wouldnt you actually be compressing less air.. Not by much, but a little less.

But since you get a bigger BANG from more compression and the piston/crank assembly is moving down faster wouldnt it essentially suck in more air from the extra down force...

wierd..

kyle

[Zap's 85 GT]

You only compress air that is pulled into the cyl as per its displacement. Just because you're compressing it into a smaller volume doesnt change how much is pumped in and out by the displacement of the piston.

Sucking in more air relative to the downward suction/speed of the poston is linear and proportionate to the intake tract and the finite vacuum created in that tract. Compression would play no part of getting more air in. Only once the Air/Fuel is in the cylender will the higher compression lend itself to more efficent combustion which is what actually produces more power. Higher compression will produce more horse power with the same ammount of air and fuel then a lower compression engine will. All other things being equal(octane and detanation issues aside). This will invariatly make the exhaust a bit louder because of the higher ammount of energy in the combustion process. Not much, but a little. I wouldnt think enough to notice unless you have a very free flowing exhaust system or mega compression change over what you previously had. But then other engine components would ba changed to optimize this particular high compression combination and it would not be "all other things being equal".

[madmike8]

Iv'e been thinking, i know that doesn't happen to often :D

But if you are moving the top of the piston closer to the bottom of the head to get more compression wouldnt you actually be compressing less air.. Not by much, but a little less.

But since you get a bigger BANG from more compression and the piston/crank assembly is moving down faster wouldnt it essentially suck in more air from the extra down force...


well... if you installed domed pistons to increase compression ratio.. your total cylinder volume would decrease by the amount of cc's the piston dome is...

[not-a-stang]

So....

Could the roller cam and slighty higher compression (9 vs. 8.5) of the '88 HO cause a CONSIDERABLY louder exhaust compared to an '82 HO (flat tappet marine cam and lower compression)?

[JERSEYGT85]

this comes from good ears....lol my brother has a 93 lx 5.0 fi. and i have a my 85 gt cfi...and my bros car is much louder then mine. but when i put my hand infront of his tails pipes and tell him to rev it up and then did mine my car seems to push more air . same exhaust systems, and both motors are stock,,,so there is my one cent ! :D

[Zap's 85 GT]

I dont know about CONSIDERABLY, but it will be definitly be noticable. I have a B-303 cam in my car and always get complimented on my exhaust sound. Has a nice lope too.