1984raw

I need some help i have SBC 355 can someone help me i live in Colorado which is 6800 feet my primary jets are 92 and the secondary 95.also my intail timing is 12 my cam is XE268 480 intake and 477 exhaust i have not check the total timing which shouds my tuning be at if someone could help me thank you

midias

Need more information
How is the bottom end built?
What heads are on the car and are they modified?
What is the top end(intake, carb)?
What is your ignition system?
What tools do you have to help tune (AFR gauge, Vacuum gauge)?

sofakingdom

iTrader: (1)

Nobody is going to be able to give you "numbers" that are "right" somehow. EVEN IFFF your timing marks were right, for example, which they're almost certainly not. Just not the way to go about tuning.

I wouldn't bother with "check the timing". "Checking" it won't make the engine run any better. That will require adjusting it. Set it to where the engine runs the best. If your dist has adjustable centrifugal advance (springs & weights, the weight cam, stops, etc.), adjustable vacuum advance, etc., then you'll have more handles to tweeeeek it with. If not, all you can do is twiddle it in the block.

Same with jets. At altitude, you will typically need to jet leaner than at sea level, because the air is thinner (less molecules) butt occupies the same volume; and since a carb responds to volume, not air mass, the same amount of fuel will be drawn out as if it was at sea level butt there won't be enough oxygen molecules to burn it properly. Buy abuncha jets in the range you seem likely to need to move to. Like, if it runs rich now, buy jets that are leaner. Swap em out and find the size that makes the engine run the best. Like the dist, whatever carb you have may have other "handles" for tuning; air bleeds, power valves, etc.; if so, be prepared to change those out as well until the optimum combo is achieved.

Key here is, ignore the "numbers", and make changes until the engine runs the best. THE ENGINE couldn't care less about "numbers"; all it cares is, if the spark occurs at the right point of piston motion, and is the right amount of air & fuel coming into it for all (or at least, as many as possible) situations and circumstances that it finds itself running in.

1984raw

I have found more info on the 355 sbc my Total is 34 and i dialed in the Carb and now it's time to have fun

1984raw

I have found more info on the 355 sbc my Total is 34 and i dialed in the Carb and now it's time to have fun

T.L.

What kind of carb is it? 92/95 is an outrageous jet size for that altitude. Should be more like 72 if it's a Quadrajet. Smaller than that if it's a Holley...

midias

On a 355 with a cam that runs out before 6K and what I'm guessing are vortec heads because 34° Max I bet with those Jets it looks like he's rolling coal

sofakingdom

iTrader: (1)

So the total timing you have your 350 set to, "is" 34° after you've verified the "mark" and "tab" system, or your builder recommended that as a good starting spot?

So what happened when you changed it to 32°? to 36°? How DO YOU KNOW (a) that this "recommendation" is the be-all end-all; and (b) that that's what your "timing" is REALLY set to? When you tweeeeeked it a little bit one way or the other, did the engine run better? worse? you DID tweeeeeeeek it, didn't you? Don't lie; either you did, or you didn't. Don't lie. Either the engine ran better, or worse, or there was no change.

Keep in mind, "better" and "worse" are ENTIRELY subjective. YOU, as the car owner (and I presume, driver) get to decide that. Among most of us, the things we look for include more power, better fuel economy, cooler running esp on the freeway, quieter exhaust (YES timing affects that), crisper throttle response, and maybe some other things that you get to discover as you travel along the path of TUNING (finding out what THE ENGINE wants) instead of worrying about "numbers" that are horse plop. Things we avoid might include pinging, hard starting when hot. YOU get to decide what the order of priority of those things is.

OK, I thought so. Go out there and tweeeeeeek it NOW. I suggest advancing it from wherever it now is as the first tweeeeeeeek. Since at high altitude, the cyl fill is MUCH less than it would be at sea level, the A/F mixture in the cyls is MUCH thinner as well, meaning it takes longer to burn, meaning it needs to start burning earlier to reach max cyl pressure at the right time to extract the most energy from the hot gases that result, meaning engines usually LIKE more advance up there.

As I've posted countless times before:

"If it RUNS good, it IS good".

Don't outsmart yourself over something SO SIMPLE. Let THE ENGINE tell you what it wants. It knows, better than any "number" ever will, what makes it happy. Give it that. Don't be afraid to TRY IT. Don't come on here and tell us "I set it to this 'number' that I (or my builder) concocted out of thin air and now it's 'perfect' and here's what it does wrong although I'm too scared to admit that it's because it's NOT 'perfect' otherwise it wouldn't be doing anything wrong".

We call it TUNING. It's a very different process from "number".