Thread: 355 sbc question about exhaust sound (need some help here!)

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Tie

I'm not much on U Tube videos for analizing sound of engines running as the recording capability and then my playing the sound over cheap PC moniter speakers don't do it justice----------but I will tell you what the change of the exhaust sound is the result of (in my opinion) and its hard for me to be forward and state this as the info about what is on your set up is difficult to believe ( I am not saying your fibbing) because I can't see it and you haven't proven it--------the sound change that your hearing is coming as a result of changing timing and mixture complicated by tuning length of exhaust headers as they reach tuned rpm length and same as you back out of it.

On a small block chevy, if the builder used roller rockers, he probably also upgraded the entire valve train to where it should easily be capable of 7000+ rpms------again , as your talking 5000 rpm I think some timing curve, carb tuning and utilizing tune length of the exhaust should make things sound better and rip on up to a much higher number.

Originally Posted by jerry clayton

Tie

I'm not much on U Tube videos for analizing sound of engines running as the recording capability and then my playing the sound over cheap PC moniter speakers don't do it justice----------but I will tell you what the change of the exhaust sound is the result of (in my opinion) and its hard for me to be forward and state this as the info about what is on your set up is difficult to believe ( I am not saying your fibbing) because I can't see it and you haven't proven it--------the sound change that your hearing is coming as a result of changing timing and mixture complicated by tuning length of exhaust headers as they reach tuned rpm length and same as you back out of it.

On a small block chevy, if the builder used roller rockers, he probably also upgraded the entire valve train to where it should easily be capable of 7000+ rpms------again , as your talking 5000 rpm I think some timing curve, carb tuning and utilizing tune length of the exhaust should make things sound better and rip on up to a much higher number.

could you go in more depth about what you mean by "the sound change that your hearing is coming as a result of changing timing and mixture complicated by tuning length of exhaust headers as they reach tuned rpm length and same as you back out of it." i dont understand what you mean by the tuning length of exhaust headers or what tuned rpm length is.
also about the rpm issue, it may be able to go higher then the 5000 i shift at. I have never been in or around another car like mine in real life so i have no idea what it should feel like when driving. I was just always afraid to go higher then 5000 rpm because of 2 things. 1 the tach red zones there (now that tach is for the stock 305 that would have been in it) and 2 its sound and feeling changed when you got to that higher rpm. its hard for me to explain but thats the best i can do. and on top of all that im the one tuning the carb because the only garage around me says that they don't know how. and because i self teach i took what i knew about some engines and some info i got from the web and did the best i could to tune it.
thanks
tie

No big deal Tie, have a nice day.

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Tie-----first to clarify some terminalogy--tuning a carb doesn't mean turning a couple idle screws---------the mixture changes with throttle opening, seconaries opening, power valves, venturi velocity/pressure/vacume changes, fuel level in the float bowls---------timing changing occurs from varying vacume from throttle opening causing changes in carb and manifold vacume which changes timing in the distributor. Also, centrifucal advance in the dist causes change in the amount of timing related to rpm----when you apply or let off the throttle as in your video , this varies from one EXTREME to another with total range variance of components.
Headers are created to tune the exhaust flow pulses to help vacate the spent gases out of the cylinder (and helps pull in more new unburnt on the overlap) and they do create a HIGH FLOW range according to the RPM pulse tune length.
Now add the header tune to the carb/ignition and you should see what I'm talking about

Originally Posted by jerry clayton

Tie-----first to clarify some terminalogy--tuning a carb doesn't mean turning a couple idle screws---------the mixture changes with throttle opening, seconaries opening, power valves, venturi velocity/pressure/vacume changes, fuel level in the float bowls---------timing changing occurs from varying vacume from throttle opening causing changes in carb and manifold vacume which changes timing in the distributor. Also, centrifucal advance in the dist causes change in the amount of timing related to rpm----when you apply or let off the throttle as in your video , this varies from one EXTREME to another with total range variance of components.
Headers are created to tune the exhaust flow pulses to help vacate the spent gases out of the cylinder (and helps pull in more new unburnt on the overlap) and they do create a HIGH FLOW range according to the RPM pulse tune length.
Now add the header tune to the carb/ignition and you should see what I'm talking about

so if im understanding correctly the sound is caused by the headers when the fuel goes from flowing wide open to being cut off to almost nothing. (extremely watered down just want to make sure i got the jist of what your were saying about the sound) as for tuning it is like i said i have a very very very basic understanding of it, mostly just what i know of small engines. so i just set the screws on the carb to the point when i idled it sat low (can't remember what exactly but i think it was 6 or 700) and when you punched it it didnt fall on its face.
But thanks alot for the info you shared i will need to look over it more in depth later.

try cell phone photo of those areas

Tie, the numbers on the back of the block are big, ~3/8" tall in a string 2.5" to 3" long towards the back of the block. No one is saying that they are easy to see - you may need a telescoping mirror and a good bright flashlight to read them, and they may be covered over in grime. The casting number is generally biased to the drivers side off of center, but on some crate engines it's biased to the passenger side, just off center. You may end up laying atop the engine to get the angle to see them.

My ZZ4 has Made in Mexico and GM 5.7L on the drivers side, and 10243880 off center towards the passenger side, seen easiest from just above the right rocker cover rear. The pad up front is stamped ZZ4. You can read the casting numbers if you want to bad enough, but it may not be that big of a deal for you. The suffix number up front could have been machined away if the block was decked.

As for taking the engine into the 7000 plus rpm range, you'd probably be fine, but for me I'd want to know what's inside before I went much above 5000 to 5500. You can build a SBC to turn 10K, but pushing one too far without knowing what you've got is a crap shoot at best.

Originally Posted by rspears

Tie, the numbers on the back of the block are big, ~3/8" tall in a string 2.5" to 3" long towards the back of the block. No one is saying that they are easy to see - you may need a telescoping mirror and a good bright flashlight to read them, and they may be covered over in grime. The casting number is generally biased to the drivers side off of center, but on some crate engines it's biased to the passenger side, just off center. You may end up laying atop the engine to get the angle to see them.

My ZZ4 has Made in Mexico and GM 5.7L on the drivers side, and 10243880 off center towards the passenger side, seen easiest from just above the right rocker cover rear. The pad up front is stamped ZZ4. You can read the casting numbers if you want to bad enough, but it may not be that big of a deal for you. The suffix number up front could have been machined away if the block was decked.

As for taking the engine into the 7000 plus rpm range, you'd probably be fine, but for me I'd want to know what's inside before I went much above 5000 to 5500. You can build a SBC to turn 10K, but pushing one too far without knowing what you've got is a crap shoot at best.

K thats where i thought the casting number was on the block (that little ledge where the tranny and motor meet on the drivers side). the mirror idea is genius tho i will have to give it a shot next time it warms up because its -18 here and the garage isn't heated. as for the suffix number i could see it have being machined off if they had to deck the block when they put the edelbrock heads on it for some reason. and as for rpm that was the reason i shifted at 5 grand, i knew it wouldnt blow no matter what at that!

I just want to add that the fuel pump could very well be an efi type pump. Keep in mind tbi engines never see over 11psi stock and if the overage is returned to the tank, there wouldn't be an issue and the stock in tank fuel pump could be retained. Tie355, nice car and welcome to CHR! I for one am glad to see a young man working to earn and build his ride. Not something you see very often or get much credit for these days it seems.

Originally Posted by 40FordDeluxe

I just want to add that the fuel pump could very well be an efi type pump. Keep in mind tbi engines never see over 11psi stock and if the overage is returned to the tank, there wouldn't be an issue and the stock in tank fuel pump could be retained. Tie355, nice car and welcome to CHR! I for one am glad to see a young man working to earn and build his ride. Not something you see very often or get much credit for these days it seems.

thanks man!

Subjectively speaking, Tie, your engine sounds pretty good to me, nice gurgle and growl to it . It obviously has a relatively healthy cam in it, probably coming into it's power band in the RPM range of 2000 to 2500 and running out at somewhere around 7000 to 7200. With the headers being tuned to a specific range, when the engine gets into the power band, some will call this "getting up on the cam", it will tend to sound like it smooths out, thus the change in the sound of the exhaust note. Depending on the combination of components in it, it will sound different at different RPMs.

Here is a link to a Wikipedia writeup on early (First Generation) Chevy V8s; pretty good basic info.

https://en.wikipedia.org/wiki/Chevro...l-block_engine

From it, you can see that there have been a lot of iterations of the same basic engine design, from 1955 all the way to 1992. Because of this, one could build a 265 cubic inch engine from 1955 for example, with the right combination of parts, and it would sound and look just like the one in your car, and from an external point of view, only a person with a very intimate knowledge of the genre could likely tell the difference from the one you have. That 265 could be passed off to the uninitiated as just about anything. This is why you need to find out the "numbers". Read up on this, ask cogent questions, and if I were you, I'd not mess with that engine too much, unless you can definitively say there is something wrong with it.

One more thing: a few of us on this board have been messing with Chevy V8 engines since they came on the scene some 60 years ago, and have seen and done just about any and everything that can be done with them. We are getting somewhat long in the tooth - that means "old", at least in years, and often times, us "Old Guys" are somewhat short on patience with young folks; it's just the nature of the beast. Think of some of us as if we were your Grandfather; I'm 74, and have grandkids from twelve to almost twice your age. So if you get barked at and it bothers you, back up and take a look at what happened, and come at it a bit differently. We're not really old ogres, we just sometimes forget what it was like to be young and impetuous.

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