Dumb Question, but I gotta ask...

[Test4echo]

What is it that causes our 3.4 DOHC's to sound so raspy and what is with that rat-a-tat-tat when giving WOT from 1st to second?

It can't be muffs or tips, cause I've been through 3 sets of each and the characteristic noise is still there. (Yes different brands as well)

I'm asking for details on why it sounds like it does.
Intake design, Geometry of the 60*V6..etc....
And, is there anything you can do about it?

It just sounds so Ricey to me from 1st to 2nd.

I mean, it sounds GREAT at idle or doing 40 or 50MPH, especially with the new CAI I just put in.

For example,

I saw a camero that had a V6 in it the other day, 2.8L I think.
Why does that 2.8 have that really awesome growl and our 3.4's sound like crap compared to it?

Thanks,

[pocket-rocket]

I think it might have to do with intake or exhaust geometry. I think Ben said some thing about the VE (volumetric efficiency). I know that the point where most stock exhausts start making that noise, my gutted intake gets quieter, then when the rpms where the noise stops, my intake gets louder again. All of this while getting on it partially.

[Test4echo]

A Secret....

Humm,

I really expected a few comments on this issue.
I know all 3.4 DOHC owners know what sound I'm talking about.

Oh well.

Thanks for the input pocket-rocket.
Appreciated very much!!!!


Test,

[brian89gp]

The LQ1 is just like that, both cam profile and a larger exhaust then the pushrod cars.

[dohcfiend]

it's b/c it is DOHC, all the 2.8/3.1 are pushrod engines. like when u rev it up and let off of the gas u get that kewl ass growl(if u have a gutted cat or high flow one it is more pronounced) u don't get that with a SOHC or DOHC.

this is the 1st DOHC engine i have owned but to me the 3.4 DOHC begs u to rev it higher but sounds like crap when u stop.

i am not a hardcore tech so i don't know why i just know that it is.

if it makes u feel better his 2.8 might sound better but u would blow his doors off. hell i have beaten quite a few 80's muscle cars with mine. it was quite surprising the 1st time it happened.(this excludes the buick gn i am not crazy enough to run one and the peeps that own them that i have seen baby them)

[SappySE107]

It has to do with the exhaust pulses, and given that each bank fires back and forth, the front bank takes a little longer to route around the block, and these pulses interfere with each other at the RPM you hear it get raspy. Adding a resonator will help remove those high pitched frequencies, and i suspect going with a single exhaust would help as well. I have the single outlet but no resonator so I still have that raspiness...but I dont think its as annoying on mine (but what do I know). Its only shitty when the muffler is cold.

Other factors are the larger diameter exhuast pipes which are meant for the higher RPM throughput, but it allows the exhaust pulse to cool and lose velocity at lower RPM. Yes, its a lot of different aspects that give us this sound. Perhaps on a RWD setup with each bank being equal distance to the muffler the sound wouldn't be there, or moved to a different RPM.

[bvr775]

yes the ehaust setups creats and odd pulse that will give you the bugfart sound but you can counteract this sound by useing differnt metals in the exhaust system. it takes some exsperimenting to get it right for your own personale taste.
remeber this stainless has a higher pitch than steel mufflers. The thickness of the metal will also affect the sound.
Check your cat to see if rattleing. It's common for the honeycomb to breakloose on engines that viberate like the 60ds. All you have to do to check for this is hit with a soft mallet on your fist and listen rattleing.If you have a newer vortek style are anything GM newer than 97 engine you already have a highflow cat so don't waste money on HFcats.
i personaley don't use stainless on exhaust systems because of the ricy sound they produse. If fact I bought a brand new s-10 last year and had all the stainless from the cat back replased with aluminized steel pipe and a 40 before it even hit 1000 miles.

One more thing gutting your cat will turn it into an exspansion chamber this can cause increased backpresior and I've seen alot of blown head gaskets because of it. If you must bypass the cat take it off completely.

[Test4echo]

Awesome guys!

Thanks for the info!

I had to know cause I did change my exhaust from my catback and I still had people askin me "Whats wrong with your car? Or, whats that sound?"
Now I can tell them why it sounds like it does, and be right about it...lol

test,

[jmgtp]

I chopped out the stock resonator and put a glasspack in its place. No rasp and rattles at all for me.

[SappySE107]

"It's common for the honeycomb to breakloose on engines that viberate like the 60ds."

?

[Anonymous]

It has to do with the exhaust pulses, and given that each bank fires back and forth, the front bank takes a little longer to route around the block, and these pulses interfere with each other at the RPM you hear it get raspy.

So if I had made my headers TRUE equal length to each other, the rasp would be a lot less?

The headers made the rasp like 20X worse, but it is mainly from 2-3k, nothing on the high end really.

[SappySE107]

Headers have that unique quality of making exhaust systems sound like ass. Its a V6, so its not going to have the exhaust timing intervals of a V8 which would smooth it out some. How is the rest of your exhaust after the headers?

I did say its a lot of factors though, and the efficiency of the motor at 2-3k is not what it is at 4k and above. You could probably alter the cam timing and move that sound to a different range, which is what I think I have done. Its more lik 2500-3000 for my car.

[Anonymous]

The headers did that quite well

The rest of my exhaust is good and new, Magnaflow mufflers, cat, and resonator and 2.5" mandrel bent.

I am not going to mess with cam timing yet, probly not at all. In the long run tho, I'll probly buy reground cams at W41 specs.

[SappySE107]

I take it you are running fake duals out the back then?

[bvr775]

"It's common for the honeycomb to breakloose on engines that viberate like the 60ds."

?

yes gm 60d and 90d V6 engines viberate bad at mid to high rpm range. It's because of the splayed design of cranck shaft.(ford,dodge and yoda V6s do it to) Those with older cars that don't incorparate a balance shaft and the newer designs of engine mounts and body mounts to counteract some of the viberation know all to well how bad they viberate after a few thousand miles. It was a major consern when the first Carbed 60d came out because it would shack the linkages loose on the carb(look at the original Duojet carbs that were used on the 2.8s and the refined versions used before fuelinjection became a standered) It was know as the 2.8 shake in my days at the dealership, but it wasn't isolated to the 2.8s we were consantly replaseing broken mounts, and fixeing loose plug wires on all the 60d and 90d engines. As Gm begian to relase more and 60d engines 3.1/3.4 and my favorite the 90d 4.3(good engine now,but crap when first relaesed in the late 70s) they bagain to figuer out how to keep the vibration from transfereing to the driver and passengers but not to systems like the exhast that were bolted directly to the engine. They were however sucsseful in reduseing the vibrations.

Even the new 60d dohc engines(probaly the most stable of all the 60Ds) still viberate, you just don't feel it any more and engine componets are made to handle the viberation better than the older cars, but i'm still seeing allot of cars with less than 20K with bad cats because the honeycomb broke loose. The bad part about that is the honeycone can turn sideways and block flow. it'll run great one day and like crap the next. Most people don't even know their cat is bad untill they blow their donuts or worse a head gasket.