Discussion in 'Race 400/430/455' started by GS Kubisch, Oct 21, 2007.
What do you guys run for advance?
On my SE motor: 38 degrees total, pulling out 5 degrees at 6200. This ran the best for my combination.
37 deg up to 40 no diff dyno/track
36 pulling back to 30 over 5000.
Track testing backed up dyno testing. My combo likes 32 degrees.
40 degrees with none pulled out - track tested only.
35* with 1 pulled out above 5000
40 degrees,et didnt change from 38 degrees but mph went up...Fish
32 any more than that it would spin the tires....ou:
I'm with Doug, never gained anything running more than 32 degrees. I actually pull it back to 30 over 6000. It will mph a little more doing that. I don't know how you guys are running next to 40 degrees.
36 degress for me
My gse stuff peak torque was at 41 degrees and peak hp was at 36. on track launch at 42 at 6000 rpm pulled it back to 36 that netted me my best 60's and et. The blower deal is totally different.
32 Degrees worked best for my combo also. I have run 36 on launch and pull 4 degrees at 5000 Rpm but that makes tire spin worse sometimes!! If it hooks it helps because I run a tight 10 inch converter!!
About the same here....
And the same questiono No:
38-40 will give seat of the pants feel of more power but it's gotta hurt top end and durability unless you run 116 octane. I run 110 CAM2.
I tine tune to track and air:
1)perfect track, good air......36 back to 30 above 5000
2) perfect track, lousy air......36 back to 33
3) slippery track, good air......26-28...no retard
4) slippery track, lousy air.....32 ...no retard
Aluminum heads seem to like 2-4 degrees more timing at least at my 12.2 compression......or what's left of it. 6th season on motor.......:laugh:
I know on my 525 they have it set at 33 deg and they said they went up while dynoing and it made not noticable difference. so thats where its stays.
OK, not to hijack this thread, but I just gotta ask about what's going on (mechanically) with timing retard at higher RPMs. I guess what I don't understand is how retarding the timing at higher RPM allows for higher mph (and what effect does it have on ET?). It would seem that there'd be less time to get the fire lit at higher RPM, so even more advance would be needed, but I've got a feeling there's a lot more involved, like volumetric efficiency and a lot of other things I'm overlooking. Can somebody explain the concept?
I use 32 on all my engines,even though the dyno may have shown slightly more hp at 35-36 I never found any gain on the drag strip,and to me thats the true dyno.
Jim,regarding retarding,I don't know the reason why it works it just does.Thats why the old hayes set ups worked so well with our BBB's,run 36 then as the r's increase it retards to 28-30 on top end,only ignition I ever found to consistently pick up nearly a tenth in the 1/4.Aslo,Grumpy Jenkens used this trick many years ago to gain mph,he ran dual points then had a switch to short out one set on the top end,thereby effectively retarding the timing.Old technology still works.
What methods/techniques are you guys using to pull out timing?
I've started playing with my MSD Digital 7 nitrous/high-speed retard.
Right now I manually activated for third gear only. Did not see a major change, however have only a couple passes under my belt playing around with it. Have not considered activating for all shifts and any RPM over 6000 grand (or whatever is considered high RPMs)...
I do really like this box over the MSD 6AL and all the associated add-ons I used to run.
Actually it's pretty simple..
The purpose of ignition timing or "spark advance" is to fire the spark plug at the optimum time, so that the cylinder will complete the burn of the air fuel mixture, right when the piston reaches TDC, or just after it.
The problem is that "complete burn" as it's called, is theoretical, as it never really happens in a combustion engine.
At lower engine speeds, more timing can be used to attempt to increase that burn time, and to increase torque, but as the engine speed increases, and the physical time that the piston travels up the bore decreases, creating cylinder pressure too soon (by firing the spark plug early) can inhibit piston speed, and overall power production at higher rpm. This is because there is less time for that early cylinder pressure, to leak out of the cylinder, past the ring gaps and due to reduction in the actual time that the camshaft is in overlap (both valves open).
From dynoing dozens of BBB's from highly modified race motors to stock restoration engines, there typically is a "sweet spot" for the timing, which is the best comprimise between lower rpm and higher rpm torque production. In a cast iron headed typical 455 engine, that is right around 32* of total timing. Aluminum headed engines, and highly modified engines often want more timing, but that need is greatly based on the position of the camshaft in relation to the crankshaft, as well as a host of other factors.
While more timing increases low speed torque, it hurts power at the higher engine speeds, often resulting in a net overall reduction of engine power, in a given rpm range. To counteract this, ignition manufacturers have devised a way to reduce the total timing, based on either a switched input (3rd gear switch, N2O input) or by doing it based on engine rpm.
The attempt here is to get "the best of both" timing settings, thruout the engines rpm cycle.
I have seen very few engines actually make a ton more power with advanced timing, but there certainly are gains to be had, and the more dialed in your race car is, the more you will notice playing with timing and retards.
In all my work, I have seen the "sweet spot" for timing typically right around 32-34*, I can't recall an engine of any description, that wanted more than 35*, to achieve the best overall power output in a given range.
Engines can be very timing sensative.. I know that we picked up about 11 HP and 10 ft lbs, with a 1 degree timing change when we last had Sweesy's 525 on the dyno.. but then again, when your making 850+ to begin with, that's actually not that big of an increase, but I have seen similar results on engines making more like 500 HP.
I have also seen engines that don't care about another few degrees, either way.. My old 437 was a good example.. it made 540 HP, and 560 torque, with the timing set anywhere between 30 and 34*.
As this relates to the car, there are very few race cars out there that can decrease their ET greatly with advanced low speed timing, simply because either the chassis setup, or the racetrack won't allow the extra power to be translated to the ground. What you typically will see is a change in MPH, once you get your timing set to maximize your launch capablities, and then pull it back a few degrees to allow for more high engine speed power production.