Re: Restoring Rusty
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Uh, no. Complete nonsense. Same thing on the instructions for the 350/290hp crate engine. BTDT, it's wrong. Higher vacuum ==> lower cylinder pressures ==> slower burn ==> earlier spark required for best performance and mileage. Trust me, I've done a lot of research and experimentation on this, and I had a lot of access to people who know what they're talking about. Read this for the real skinny on ignition timing. http://67-72chevytrucks.com/vboard/s...d.php?t=689321 |
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1) the big three used manifold vacuum for 30 years, from 1938 through 1967, and switched to ported vacuum to accommodate pollution-era de-tuning. They weren't wrong for 30 years. And they only switched because additional criteria were imposed. 2) the critical issue is performance in the tall part of the horsepower curve, where SBCs have a peak at 36* BTDC. Set that, and adjust the mechanical advance to get the base timing where you want it. |
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I don't know much at all about it, but enough to recognize that Rich has done his homework and I'd be comfortable trying his recommendations. And that's not a slam against Greg, he's obviously following manufacturer's directions given for the combo he's running. But even on a stock motor you can bump the timing up from the factory recommended number for a little more get up and go, the question is how much. I think Rich may have studied that question a long time and has some good input. At least I think that's what we're talking about. |
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1. mechanical advance should not kick in at idle RPM, be it 600 RPM or 750 RPM, if it does it's a waste. this is when you are setting initial timing and you disconnect the vacuum canister on your distributor and plug the vacuum nipple on your carburetor (be it up top aka ported, or on the base, aka manifold) you don't want vacuum advance during this procedure 2. total advance (a misnomer for sure is really initial plus mechanical, but we call it total, ok what ever, total to me would be initial plus vacuum plus mechanical, but lets not go there, I call that one All In Timing) so anyway total advance for a small block chevy is 36* so that's our upper max, still with the vacuum advance can disconnected you get this reading whilst reving up the engine way high in RPMs like 3500 until the advance no longer advances. (when you connect the vacuum advance you can have as much as 54* of advance and that's ok, but thats a whole other discussion) so there two points to add to your toolbox of know how, this only scratches the surface but I think I am right at least on these two issues |
Re: Restoring Rusty
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alright, nothing to it but to do it
The Three Amigos: Point Dexter, ProForm, and General Mayhem |
Re: Restoring Rusty
Which vacuum cans are on the other two? You could play mix and match to tone that vacuum advance on the GM down. They should all be interchangeable.
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Wow, I hadn't checked on this thread in awhile, I just spent two weeks on the west coast helping my company open a new location.
I have my engine together although it runs it doesn't idle for ****. I didn't get very scientific on the timing, just brought it up on tdc, with rotor pointing at #1 and spun it a bit till it fired and ran. Gonna try and figure out how to properly set a base timing this weekend as well as check for vacuum leaks. Also I'm thinking I should dump the 3" spacer I have, the bottom end is more important and its entirely where my leaks could be. I worry that its going to mean replacing an already too short $60 Lokar throttle cable though. Anyways, glad you found the leak and look on the plus side, you've already got 1 of 8 conrod bearings replaced... :D |
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Set you initial at 12º-14º with the idle as low as you can get it, park brake on in gear with vacuum advance disconnected. GM claims 22º advance in that distributor, you should end up with 34º-36º based on those initial settings. At what RPM it peaks depends on the springs and weight combo. Keep in mind vacuum advance is zero at WOT.
Keep the 41/375 weight combo and install two blue springs from the Crane kit and you will be golden. |
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But for now I just tried the GM recommended setup: 10° Initial + 0° Vacuum (in other words vacuum canister not connected) + 22° Mechanical = 32° Total Truck runs very very good, but not perfect, what I mean by that is the only problem is when I accelerate right after switching to say 3rd or 4th gear, it goes vrooom-vrooooooooooooooooom, instead of just a smooth vrooooooooooooooooooom, forgive me for the childish explanations, I don't know how else to describe it. Not sure if it needs more Initial timing say 12° or even as much as 14° to raise the Total Timing to 34° or even 36° or if I ought to connect the vacuum canister. I think I am going to try baby steps, and report back to you all. |
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The stock(ish) spark plug wires when connected to the HEI cap will prevent you from rotating the distributor too much one way or the other as well, its almost as if they made the thing idiot proof. lol So in other words Ray Charles can stab a small block chevy distributor in with his feet and that rig will run, may not drive good but it will start up for you and allow you to at least check the timing with a timing light and tune it further, so any of you readers out there worrying about taking your distributors out, go and pull them out right now, we'll wait, and set them right next to your keyboards, ha ha |
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All this timing talk has me on the edge of my seat. I've never understood it but there is so much great info here that I am finally learning it. I'm about to fire off my newly rebuilt 350 so I will be putting this info to good use soon! Thanks, Gregski & Rich!!
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Thanks Jake, I am so close I can feel it
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good luck to you bro, take your time, don't be skierd, and you'll get it, with every turn of a bolt you will get that much more confidence so just keep turning them |
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Side Note & Fun Fact: Whilst adjusting my timing advance I was controlling the RPMs using the idle speed screw on my Holley carburetor and I learned that the highest RPMs it can get up to with the screw all the way in was only 3500 RPM, which is fine cause that's not what it is meant for, we usually idle below 1000 RPM fer sure. However in my case that was not high enough to get the total timing yet.
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Yes, obviously that was far an auto, it slipped my mind you had a manual.
If you like your curve the way it is, then leave it. I like all in somewhere around 3000 and the blue springs with those weights and center plate provide that. |
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I tested the GM distributor and it is spot on to the specs they gave but I could not get more than 32° of Total Timing out of it just out of the box even North of 4500 RPM[/QUOTE] That's all you going to get if initial was at 10º. |
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Yeah, you can dial the initial up to 14, but not if you keep that advance can. The vac advance will be too much and hang on too long and you will ping like crazy. Dial the initial up to 14, put the adjustable can on it, dial it back to 12-15 total vac, and keep it 0 advance at maybe 5-7" of vacuum. Vac advance ought to be all in at 12". That ought to get you where you want to be.
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First is to check what advance can you have. It is probably poorly suited. Get an AR23 equivalent (see my post about 20 posts up), or you can get an adjustable one and spend a lot of time to tinker with it, but you're just going to end up in the same place. |
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Truck Runs AmazeBallz!!! |
Re: Restoring Rusty - DynoMAX Mufflers
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so now that we took care of the big exhaust leak I can actually hear the new Flowmaster 40 Series exhaust, and I'll be honest with you, it needs some work
first it has a drone sound, around 1500 RPM it sounds like you are driving in a 4 door car and your kids rolled the windows down in the back, whoa whoa whoa... annoying to say the least so it pays to have car buddies, I convinced my Mopar buddy Seth to loan me his brand new DynoMax mufflers for a test run (on the account of his Dodge truck being sidelined do to an enjin rebuild) Notice how you can see right through the DynoMax mufflers, they have that straight through design, you can't see through the Flowmasters like that, some will argue that they flow better than the FlowMasters, I can't say either way. Also I've been told these are not directional, you can mount them offset in front or offset in the rear, there is no Input and specific Output. so since these be 2.5" like mine they just bolted right up, and what's the verdict? Well, they do sound different, these have a much more raspier sound, he calls it 60s muscle car sound, but more importantly they drone as well, so I am convinced that most if not all mufflers will drone unless you tune your exhaust system (more on that later) |
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so how do you get rid of the drone exhaust sound? how do you tune an exhaust? well shoot I don't know, lets find out together
first I believe you can try these salamis called resonators or as I call them baffles, so lets take a look at these bad boys inside them there are metal holes or notches in the inside pipe and they are stuffed with fiberglass, hence the nick name glass packs, you can mount them one of two ways I recon, I went with the quieter way which is against the grain if you will I wish these were bigger than 9" but for $20 bucks thats all they had in the 2.5" pipe selection |
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ok so to mount these and try to keep my bolt on exhaust system as leak proof as possible I had to notch the muffler ends and any flared ends, otherwise these pipes are a joke and leave air gaps for the exhaust gases to escape, in some places a single notch did the trick, in most it was two 180° apart, and yet in some it took as many as 4 notches, your mileage may vary
eventually after I have the exhaust setup that I really love I will weld it all up, that's the only way to ensure air tightness in my opinion |
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here is are some sound samples of what the truck sounds like, not the best quality, and I apologize for filming the ground, I don't know how or why I did that
Flowmaster Series 40 Dual Exhaust With 9" Resonators Short Sound Sample Flowmaster 40 Series Dual Exhaust Sound Sample |
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