Hi. I have a 1991 Chevrolet Camaro Z28 with a stock 350 tpi motor. I have been to different car shows and cruises and lot of these are high horsepower motors. When I listen to them their engines crank right over within 1 second of cranking. Their engines sound "strong"(responsive to throttle pressure)- no delay on revving and no vibration at idle or high rev. The thing too is that they sound "quiet" (no engine noises) such as rattling, or tick noises coming from the valvetrain or even worse from the rotating assembly. My father has a brand new (new block, rotating assembly,heads, etc.) 377 performance stroker motor in his mustang and has 3,500 miles on it and it is very noisy inside the engine-has loud clattering at idle and increases when the engine is revved. Even though it is a Mustang, by no means I am not trying to stir up anyone because this is a Chevrolet only forum but I am using it as an example because it applies to my question of a noisy engine. So, that poses my question: What are the key components to making a qiuet and strong running performance engine?

 

Find out what he's running for a cam. Maybe it's solid lifters over hydraulics that others may be running which would account for the chatter.

 

Hi AM. Nice to see you again.

I've also noticed how the new more powerful engines sound so quiet. So it's funny he posted this because I've been wanting to post something, but I didn't feel it was pertinent to our cause, lol. But...

I was at my local dealer this week to order some parts, and naturally a sales person grabbed me as soon as I got out of my car. So I let him show me Chevy's new SRS. Wow! What an awesome and fun vehicle that is! Very cool, very retro, lots of tricks and goodies. If you get a chance to see one, check it out.

It had an awesome sounding exhaust, like a big block, but under the hood was a smooth quiet 5.3 liter V8. Nice engine--very beautiful! And it ran so smoothly and quietly that it sounded like a little japanese 4 cylinder. You could hardly hear it running.

Anyway, that's it. I just wanted to tell that, lol. It's only relevance to the fbody is that the 5.3 liter might very well be the engine of the future Camaro/Firebird when they come back out.

 

Ahh, the 5.3 is the truck version of the 5.7 LS1 that has been used in Camaros & Firebirds since 1998.

 

I think a lot of the noise (or lack of) is due to the tolerances between the moving parts. A race motor built to survive high RPM might be built loosely compared to a stocker rebuild.

Forged pistons require loose tolerances to allow for more expansion from their higher density, and valvetrain noise from lash designed in to the components. Older production engines are somewhat 'thrown together' compared to a carefully built engine that has had all the tolerances and balancing checked by a machinist during assembly.

The strong throttle response and quick starting that you speak of can be due to the high compression designed into a performance engine and effective cylinder filling from a good combination of engine parts.

I know that Ford has a large engineering department (NVH) that deals only with noise, vibration and harshness. GM and the others probably have something similar. They will re-engineer an alternator bracket to change it's resonance characteristics to reduce noise/vibration. They claim that aluminum oil pans stiffen the block and reduce noise too.

 

If the car "chatters" theres probably something wrong like the valve lash is incorrect. A solid cam sounds kinda like a sewing machine. Just a steady light tickity noise - NOT chatter.

Typically a "performance" engine is the exact opposite of what you say. By performance I don't mean high-tech LS1's. I mean all out race motors. A typical high compression, huge solid / solid roller cammed motor with loose valve lashes will be pretty damn mechnically loud - The thing is you just cant hear it over the exhaust. Also most motors like that have a lot of initial timing which doesn't make them exactly easy to start either.

 

I'd guess the main reason most people at such shows have really nice sounding engines (no clicking, clanking, chugging, or variations or such noises) is because the vast majority of them have tons of money into their cars and a good portion of them know a thing or two about tuning their cars and having them run right.. IE: no noises that they shouldn't be making. As far as the new high tech fancy 6- bolt main aluminum head/block LS1 being nice a quiet.. yes they sure are if they are left stock.. hell I can't even tell if mine is running sometimes.. overall its a really decent setup but the exhaust system leaves a lot to be desired (not quite as bad as our third gens..) but everytime I shut the car off you can stand in back of it for about a minute or so and listen to the exhaust hiss until it finally runs out of pressure.. and the ****er pulled a 13.2.. almost as fast as my third gen but twice the gas mileage.. but IMHO my third gen is so much more fun and better looking then my TA.. even tho her front end is flat black primer (can you think of a better color?!?).. I dunno I fell in love with em at a early age and honestly can't find an F-Body styling I like more.. (well maybe first gen) and no she doesn't make any strange noises... she shakes a tad and is extremely loud if your standing in back of her.. but from the engine compartment.. nopers. As far as starting right up first crank.. she wasn't too good at that with the initial timing and the 11.1 comp ratio with the stock starter, but the high torque mini starter solved that.. and emptyed my bank account quite effectively...Ok I've been drinking and I have no idea how this post got so long or what my origional point was, I apologise in advance. :lala:

 

I've got a little question on this note. I'm sure there's nothing to worry about, but I'd like to be even more sure.

I just finished building a 441ci SBC, with relatively loose valve lash on a 0.630" solid roller setup at 12.5:1 compression. This is the first high-compression big-displacement motor I've built, so I'm not as sure what to expect.

Anyways, it's when the RPMs dip down below 950 or so. The car won't idle below around 1000 comfortably, but that is expected.

So especially when I shut the motor down, it sounds like something is just relaxing. Almost the sort of sound you'd hear if you took a small handful of nuts or bolts and tossed them gently into a plastic bucket or something. It's almost like the motor kinda fights itself a little to shut down. Sort of a shuddering feel.

Any idea what I'm hearing here? It seems like it's definitely mechanical. I know on a 383 10:1 SR that I built, I don't remember hearing it have these shutdown noises.