If what I said was so much BS, then why does it idle better with 42 degrees? If it was BS, then anything above 32 degrees or whatever arbitrary number you come up with would make the engine slow down.

 

rusty70f100, I worked on a bunch of the Bowtie 502s and 540s race motors in the past and none of them ever need 42° of timing to idle much less at WOT and something isn't right if yours does. Physics does not work like your theory on fuel/air burning in the chamber. If it did this information would be out there already and it isn't. If the max of 38° (that's the most I've ever seen published by anyone an that was back in the days of real leaded gas) was BS then the race guys would know it and everyone would be doing it and no one else is.

 

Thats what I ended up running on my 428 after playing around with it. I was as surprised as anybody

Your 511 continues to do the FE boys proud, Scouder

 

well, i guess i need to take one for the team here.. i live at 500 ft above sea level so i'll go ahead and swap you my pristine running 360 for that high timed anchor ya got.. this 360 doesn't burn a drop(it may leak a bit but it'll help you keep the dust down), idles like a champ at 750 rpm's, and the timings totalled out at around 36 degrees... i'll only do this because of the interest in timing figures, and power output of the 511 at sea level. i may be getting took on this one but after all, science and knowledge never come free or without sacrifices...

 

This is interesting to me. When I had my cam built by Comp, the tech and I talked at some length about the effect of altitude. He said that because the altitude causes a slower burn, they typically recommend to open the exhaust valve later in the cycle to allow more time for combustion. It would appear from this that the information IS out there. It is also commonly known that engines running at higher altitude require more advance. (One easy way to look at it is that if an engine requires less timing with boost, it would require more timing with negative boost)

Two other interesting pieces of information that have a bearing on the conversation, relating to total advance:

1. Kieth Craft is quoted as saying that He has run his FE's at 42 degrees.

2. Mark Artis said on the other forum that he has run 44 degrees with his 427.

Both of these guys run well below 7000'.

If the engine is supposed to run with a lower initial timing, what would cause it to like so much?

Personally, I think its just a combination of altitude, big duration cam, large displacement, and nice cool aluminum heads and block. It all adds up to a slow burn. It is also likely that because of the extremely low air density, and slow intake charge speed through the big plenums that my idle mixure is falling out of suspension and forming bigger fuel droplets in the chamber, which also burn slower.

-Scouder

 

How much was the exhaust valve timing retarded? Just curious

Remember, advancing the timing and keeping the RPMs the same causes vacuum to go up.

So with a huge overlapping cam, the more timing the better. Dynamic compression at low RPMs is almost nil, so the higher the better. The "bleed-off" effect, basically.

But to be able to START at 40+ degrees? Jeez...

Either you have a REALLY BIG cam, or you really screwed up dialing it in

Just kidding Scouder ...

 

Hmm... come to think of it, if the exhaust valve timing was delayed that WOULD lead to even more overlap...

 

This is why I don't have much use for timing lights. They're great for stock to near stockers, but once you get into the big custom setups all I ever use is my ear and vacuum gauge and let the motor tell me where she's happy.

 

My 390 idles best at 32degrees. I am at sea level and have a 232@ 0.050 cam.
When the MSD timing computer was being tested I ran around locked @ 32 degrees. It would start fine but it did run on at shut down and the mid range suffered some.
It is happier at 14 init. and 34 total. The idle screw had to be turned up and the idle is a little rougher but over all it runs better this way.

 

My old iron headed 428 ran best with 45 degrees total - pulling out 4 degrees in high gear picked up an extra one MPH with no ET change. That piece went 11.0s for years that way. 650 ft above sea level.

My current 505s - - I have two of them - - make best power with only 28 degrees. The Engine Masters version actually did best with 31 degrees at any level below torque peak and 28 from peak to 6500RPM. The best average was with a locked out dizzy - - no lead changes at all. My EFI version has the same kind of U shaped curve you describe - - controlled by the FAST ECU.
As long as the timing light is right, and the TDC mark is right, and the firing order is right - - it makes no difference at all where the distributor is, or where the plug wires are. I sometimes shuffle them around just for the cosmetics of routing the wires - - or to move the vacuum can back so I can get more room.

I'd still want to recheck TDC related to the balancer as installed on the engine. My ATI was off by over eight degrees when using the stock pointer.

Barry R.
Survival Motorsports

 

This thread is so interesting. I've been reading this and it's hard to understand how some are jumping on the "distributor is a tooth off" thing. I completely agree with Barry_R...if the TDC mark is right, the firing order right, the timing light on #1 then what you see is what you get...and it makes absolutely no difference where #1 is on the distributor. For years as a kid growing up in this stuff I never even knew where #1 was supposed to be on the distributor for whatever engine I was working on because my dad never cared...he'd drop the distributor in when the engine was on tdc and wherever the rotor landed is where he'd start #1 at. Dad almost never used a timing light either...the fact is what's running the best is the best and if you're a halfway decent mechanic you'll get pretty close to puurrrrfect without the light. I'm a little different now...I prefer to match what the factory position was and I usually use a timing light to check.

I also agree I'd recheck the balancer tdc just to be sure something hasn't slipped but my guess is that Scouder's already positive of this.

My house is 15 ft above sea level...I can't imagine what it's like to try to get some air at 7000 ft or what it's like to try to tune an engine up there...

Scouder I'm thinking we ought to see what that thing will do at sea level...I'll volunteer my truck...ship me the engine and I'll email you the timing results...sound ok?????

Tracy

 

Thank you Scouder!

So the Comp Cams tech said high altitude engine require more timing. Ok. Now lets follow this for a bit. High altitude = thinner air. What happens when you close the throttle plates (something that rarely happens on a race engine BTW)? The air in the intake manifold gets thinner! Since the cylinders aren't getting filled through osmosis, it would stand to reason that they could only get the thinner air from the intake manifold. Now, I can guarantee there's a lot more difference between the absolute air pressure inside the intake manifold at idle and the outside air pressure than there is between the absolute air pressure at Scouder's elevation and sea level. So, when you close the throttle, as far as the engine is concerned, it's just like you went waaaaay up in altitude.

Again, we're not talking about race motors (although Scouder's motor would probably qualify as one). We're not talking about WOT timing. We are talking about timing at idle with the throttle closed. What I am saying is, an engine with the throttle blades closed or even partly open, like at cruise, will like more timing than the same engine at WOT.

 

You know the best way to cover a vacuum leak? Advance the timing...

Just kidding! But something to look at.

Yeah, as I mentioned before, the "tooth off" thing doesn't make a diff.

Scouder how much overlap that cam have? I'm assuming it's roller...

 

Barry,

If you are still watching this thread. 28 degrees sounds like a VERY efficient chamber design. Are these by chance Blue Thunder heads?

-Scouder

 

The cam is:
304/310 advertised
266/272 .050
108/104
.685/.695

.050 overlap is 53
Adv overlap is 91

-Scouder