Anybody else running a long rod motor? When changing to 7.250 rod length my set up would fall quickly after 31*, I presume because of the extended dwell time near, and at TDC. I haven't tried a retard set-up with this combo, but since I'm bringing it out for the first time since 1997 its worth looking into a little deeper, alot of advancements in timing control today, (no pun intended). Any thoughts?
I run long rod motors,found that et wise 30* seems to be the right total advance. never ran a retard.the dyno may show more advance =more hp but I've found the et was best at 30. gary
We are talking timming I have a 466 that has 6.950 Rods i am running 34 timming on the Mountain mybe i should pull some timming out. Mybe 30-33 mybe a little Faster
I do. Dyno liked 38 total. Made almost 30 more hp from 36 to 38. Hit it with 180 spray and dropped it back to 36. So, 651 at 38 deg and 819hp at 36. Ran 93 oct on the motor and 110 on spray.
Ater reading this thread, other factors that come in to play with the timing numbers. Total spark available, high energy ignitions will have hotter spark to light quicker and consistantly, lesser ignition will need less cylinder pressure and or more fuel. Timing indicators, how many people do an actual piston stop to check for real TDC. Altitude is another one. Higher altitude will require more timing. Engine load, convertor, gears, weight, tire size. Many variables come into play so telling someone they have too much timing may not help there cause, But it is how we all learn. My .02
I have read this tread and one question that came to mind. Does the condition of the combustion chamber come in to play? They are different shapes and if they are polished or rough? Tony
Yes, All of those variables will come into play. A smoother chamber will create a faster flame travel, less timing will be needed. The shape will help or hurt. Also spark plug position and standard or extended tip will have an effect.
Old thread but interesting reading. I'm currently re-vamping my fuel and ignition tables on the EFI and reading up on the subject. Good stuff here. I had always heard the timing pull back was meant for 3rd gear only, ie second half of the track, when the cylinder would be heat soaked and pulling timing is what the A/F would want since more of the heat would stay in the chamber. Now what to do on my ignition advance table......
I tend to be with Gary on timing even though my engine is not as large as his. I have tried several settings and stay at about 32 most of the time. I do have a locked distributor as I have a cranking retard and the ability to change the timing by RPM. I do pull it back to 30 degrees over 6,000 which I only see in high gear as I shift at about 5975. You just have to use what works for you. And the dyno and the track are two different things. Jim Netherland "Mad Torquer"
I like to run 34 deg with a super quick curve that's all in as soon as the motor starts. I used to run locked at 32 but even though my MSD digital 6 has start retard I don't think it always worked. Maybe have to hold ignition on for a second before cranking? I would often get spark knock and slow cranking. With the quick curve and 12.5 comp it starts like a puppy even on pump gas. Also, I take 4 deg out over 5000. I want my motors to last a long time.....
The best way to find optimum spark advance, is with cylinder pressure transducers, and find LPP or location of peak pressure. All internal combustion engines need a LPP of 14 degrees ATDC to achieve max power or MBT minimum spk best torque. If you don't have access to pressure transducers, then a simple spark sweep at a delta of 500 RPM to Delta 250 when your getting close to peak power. A spark sweep @ each speed and load will insure that you find MBT. The limiting factor to this is fuel quality and spark sensitivity. In other words, you will not be able to reach MBT if the engine is knocking.
A few things about total advance. One thing about total advance is that if your using a dial back type timing light you "MAY" not be getting an accurate reading. Most timing lights with a dial back feature are not accurate, I have seen some of these as far off as 25 degrees as compared to a regular light using the marks on the damper. I have even seen a couple of Snap-On digital lights to be off. An overly rich engine usually responds to more timing. Two low of octane for the applications responds to less timing. More important is a combination of all of the above would really confuse the engine. So mark the damper if it is not, use a regular timing light, choose the right fuel for the application, start out with moderate timing, get the fuel curve right and add timing as needed.
Mike, I have 3 different timing lights, a Sears dial back, an older Sears standard timing light, and a digital Snap On dial back. Curiously enough, they are all very close, not exact, but really close. I have tried all 3, using the dial backs set to 0, and using the balancer marked at 34* (2"), and then using the dial back feature. Then using the standard light and balancer mark. The biggest difference I saw was between using the balancer mark and then the dial back feature on each light. It was a few degrees off. I would say it is very important to mark the balancer as accurately as possible, and use as thin a line as possible, as a small error in measurement can result in a sizable error in timing. I run an MSD Digital 6 ignition.
One of the most hilarious things I've ever seen was on Drag Week 2011 in a hotel parking lot Larry Larson was checking the timing on his 6-7 second Nova and had at one point 5 timing lights on his engine at the same time with three different readings, hilarious and tragic at the same time! People just kept bringing over their timing lights to try out and he'd clip them on! :laugh: I would hope a ~2,400HP engine would have the timing pinned down!
If you have an old really sloppy timing chain, you may get some of that top end third gear retard affect. Another way to get some retard at the top is with a dual points distributer. You can cancel out the lead point set and the trailing one will retard your timing. You only want to do this on your last gear. Its not going to put you into the stratosphere or anything but interesting to mess around with. Today its done with cam phasing . As to why , its best to leave that to Jim W or the Wizard, you can really get deep into it with the Vizzard as well.
Ohh , I see well known member Gary , Greatscat already mentioned the dual point deal. Great minds think alike!!
Mine didnt want to go 30' total on the dyno. 13.5:1 comp, 255@.50 cam, 10Amp ignition, 7.1" rod. We have left it 28'
