barchetta1

It definitely sounds more like a carberated 70s car with the idle low. kinda like it.

barchetta1

Specifically where did you change the advance? Im changing mine under the spark table and using the table called " Closed tps spark advance" and not notcing anything at all. Do I need to disconnect my battery for awhile so it doesnt have to slowly make the change?

Tom400CFI

I've never messes with timing on my LT1....I've only played with it, and noted the change in exhaust note on older cars with a conventional distributor, where I can simply "crank the distributor" one way or the other, while fiddle f'ing with the throttle (minimum air) to keep idle speed about the same. If you didn't hear any change to the exhaust note/sound, I'd say that somehow, for some reason, you didn't acctually change the timing. I'll go make a quick vid of the 'vette kart and hopefully it will illustrate the change in sound. Give me a bit and I'll post it up, here.

Tom400CFI

"45 minutes remaining"...on the vid upload. Crazy, the vid is only maybe a minute and 30 seconds long or so.

Tom400CFI

Finally! Turn on the Bose surround and listed to the Kart go from bubbly "mustang" sounding....too ye old boat.


EDIT: Sorry, IDK what that rattling sound is, but it really interferes with the actual sound. Try to ignore that, whatever it is.



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barchetta1

What you are doing is lowering the idle by reducing timing. In an lt1 that has not been messed with the computer maintains the idle no matter what timing is set. I assure you, retarding the timing has little to no affect on the sound, it is the idle speed that changes the sound.

I definitely have been able to get more of a 70's idle sound by lowering my rpm to 550. Funny, in drive that is stock anyhow, its only in park that the idle is cranked up to 750. I think this is to meet emissions requirements at idle in park. Just a guess.. I have a very slight hunt as well.. which I think I can tune out.

Ive noted that oil pressure is fine at 550 by the way.

84 4+3

if you get the actual timing at zero degrees, including base, it will change. At zero degrees quite a bit of the combustion will happen when the exhaust valve is opening and will make it sound different. At least it does on every distributor I've owned. The opti may not allow for that though.

Tom400CFI

What ^this guys^ said. He "gets it".


Ahhh....did you watch the video? The idle did drop initially...but then it came back up (just like the LT1 would do). I even throttled it a little. The sound is, I'd say, "dramatically different". Much more rough and you can hear each cylinder firing much more clearly. When I advance the timing, it mellows way out, gets smoother and the cylinder sounds run together, leaving just a smooth 'bubbly' V8 sound (which I prefer).



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cv67

Agree with the "less bends" statement.
Id go so far as to say any crossover will dumb down that strong sound guys are looking for especially if theres a cam in it. Any glasspack type muffler really accentuates it.
Obviously compression and the right cam profile will really do the trick but if its stock one can only pull a little timing and add some fuel to fake it.

barchetta1

Ahhhhh; I did watch the video and I never heard the idle come up and stay steady, I only heard you throttling it and it sounded like a v8 on 4 cylinders. So we may have a difference of opinion in what sounds nice. Where you didnt move the distributor on the way back it sounded like a missing v8.

I cannot go below zero degrees with my software. Its possible you are going below zero. I dont hear any significant difference, I will throw my timing light on it to confirm Im changing the advance.

Tom400CFI

10-4. I didn't check timing (as you could see) but I bet it was way "below zero", or ATDC. The 4 cylinder sounding part....I kind of thought that's what you were looking for. That's is basically the sound I thought you meant by the "individual cylinder firing".

barchetta1

I think Id like a little bit of that Im going to play around some more and see what I can do. There might be a way to force it below zero. there are like 16 zillion parameters on that damn computer.

GREGGPENN

750 might also be a "countermeasure" to insure it doesn't die when dropping it into gear?

I agree with the assessment idle can't be forced by rotating a distributor. The ECM is programmed to hit a specific RPM. You can't change that except reprogramming. Rotation of a distributor will retard timing but do so at all loads/rpms. I question the "wisdom" of retarding the timing (especially severely) for the goals stated in this thread. I might not be as skeptical if the change was ONLY for idle -- which may be the point? Otherwise, retardation of timing would lead to less responsiveness (esp. off-idle) while risking premature failure of CATS or overheated manifolds. All of this in exchange for gettting a "cool sound"? Really?

The addition of an "H"/"Y" pipe doubles the pulses coming out of each dual pipe. That's why it smooths sound....more pulses. More bends may do the same but who picks more bends -- which would translate to more restriction? Has ANYONE said how cool "Side Effects" sidepipes are -- which all their bends? Looks maybe....Sound maybe...but overwhelmingly forum users would question the wisdom of installing a (presumably) more restrictive exhaust in exchange for sound/looks. This statement comes from someone who "gets" looks/sound as a criteria -- in addition to performance.

Ironically, this thread seems like a debate between the appeal of individual pulsing of an aggressive V8 muscle car vs the more sophisticated? "Euro" sound of fine sportscars. I would add that diameter, length, and muffler contribute heavily to the overall sound. Even in the comparison of a LS Vette vs. GTO, I didn't see anything mentioned about mufflers used. Or converters for that matter.

I'm all for chasing all the intrinsic aspects of owning a sportscar. Maybe we all want something a bit (better?) or different all the time. With 2.5" piping and lots of bends, mine might be more the sound Tom likes. I've liked it for a long time. I also wonder how much different, enjoyable, aggressive it might be with straight-thru 3" exhaust. Any change is fun for a while. I just wouldn't change timing to get it....especially to the extremes suggested here.

mrodoc

That's the sound I'm chasing. Any hope of getting that in an LT1?

barchetta1

You can come close with a cam.

mrodoc

I have an LE2 build. Cam is 227/234/ .575/110LSA. At Idle it sounds great with open headers. With straight pipes and magnaflows, it sounds like crap? I may just delete mufflers and go straight pipes.

barchetta1

You should consider posting each or at least the config you are running on youtube and send the link here.


I dont know enough to say what those cam specs mean, Im sure someone will chime in.

Can you describe "crap" please?