I can do a fair bit with some guidance, but the fine tuning seems to elude me. I replaced my old Ford distributor with a new MSD unit, new plug wires, and 10W40 Royal Purple instead of the 20W50. I'm thinking 0.1 sec faster ET. Nope. Consistent 0.3 slower, and 1.95 60' instead of my usual 1.8 seconds, even with fast air (40 deg F). Here's the technical stuff. It's a carbed 87 roller 302, 280HR Comp cam (2500 - 6000 RPM), 2500 stall Hughes, 4.56 Locker on 28 inch tires. I haven't touched the carb, so it shouldn't be one of the variables. I've got 16 deg initial timing and 20 deg mech, all in at 2300 RPM. I hope that's enough data for someone to give me some ideas. I know a 3000 stall would help, but I want my 0.3 seconds back first.
My first guess would be to look at the base timing and at the advance curve in the distributor. Oops....I see where you posted your timing stuff.... Did you check TDC on the balancer before setting the timing?
I was getting good burnouts and no slippage of any kind. The 9.77 sec '69 Camaro wasn't having that problem either. Lots of grape juice on the track.
what was the timeing like on the old distrubor? do you have a msd box or just the distrubor? did you change spark pulgs? did you run the same gap? could the carb be to lean for the "good" air?
20* of full advance timing is not very much. Or is that 36* total? Are you running race fuel. I would bump (+) 2* timing every pass until the car doesn't improve or slows down or until you start to spark knock. My car with locked out timing ran best at 38*.
I run an MSD 6AL and the same plugs as when I shut it down in October last year. Weather was about the same as then with a little less humidity, so the carb tuning shouldn't be a factor right now. I'm not saying I won't work on the tuning. I just don't want to introduce more variables right now. Timing on the old distributor was similar It was set at 16* and the mechanical advance gave me 18*. Would those 2* more mechanical on the new distributor give me that much difference?
That's 36* total. I'm running 92 octane premium fuel. I heard about "locking out" the timing and that the MSD box could take timing out to ease the load on the starter. How does this work?
the timeing being taken out by the msd box is only possible if the msd has that opition on it. my digital 6 has it. theres a knob on i that you set to the amount to take out when the motor first turns on. once the rpms get high enough it stops the retard. its really hard to figure out what caused the loss of time. it could be bad fuel. could the brakes be draging now? I would sugest takeing the old dizzy to the track and try swaping them between a couple of rounds.
Depending on the heads, 36 is quite a bit more timing for a SBF. Mine doesn't like anything more than 32 but the chambers are really efficient, compared to stock iron heads. Locked out timing isn't a great idea on a gas engine. Alcohol it's ok but gas sometimes tends to kick back more, which is not good on flexplates and starters. And bellhousings. Mine is on alky but it isn't locked out....I just pulled one of the springs off of the flyweights. All in by 1200 (30 deg total). Idles kind of weird unless it's set to 1400 or more because the timing jumps around from 1000-1200 due to the mech. advance trying to advance the timing based on RPM.
If you have a later model gear reduction starter you should be fine. You can buy a timing retard for the box to do that but shouldnt need one. I would start with the timing.
My timing on my 306 i had which had stock heads liked 36 but my 347 with world heads likes 32. Definetely, the combustion chamber shape has alot to do with timing.
timing is another one of those: "it worked for me"....."but not for him" deals. I played with my timing for 13 straight passes. Mine runs best at 38* It did not pick up a thing with more timing than that and lost .2 at 36* (felt like a snail). I do have a START/RETARD box, takes 15* out when starting, then goes to full advance once it hits 900-1000 rpms, then a module controls the amount of timing taken out at high rpm. MAVMAN is right, locked out timing can be very demanding on starters and flexplates. But there are ways to help....it just cost money
The only issue I see with a start/retard box is that I have seen them in the past make the timing act weird. They generally also retard the timign above 4000 RPM, IIRC. Dad's does. It pulls a total of 4 degrees IIRC. We have it set up at 38 total (locked out) and it pulls that 4 out and it's back to 34. Works good for excellent throttle response (as if that is a problem already on an alky injected lightweight 347) for good reaction times, yet still have that top end charge. His runs nice. We used one of those HP calculators online and came up with 470 HP, which ought to be pretty good considering that its a STOCK 302 block and running untouched performer RPM heads. That little turd is impressive, IMO. Ran some 6.30's at I think around 110 mph at 2850 race weiight. One other thing to consider about timing. If you're on the ragged edge of block or crankshaft strength (like in my case making nearly 700 HP on a stock 351w block), ideally you'd want to start off VERY conservative and creep up on the timing until MPH doesn't change anymore. I start at 24. Make a pass. Then 26 and make another pass. At 32 it doesn't change ET or MPH. So I pulled it back to 30 and lost a tiny bit of ET (like .02) and MPH didn't change any. I use MPH to gauge it because ET can be skewed by too many things. Track temp, tire spin, oil temp, trans temp, jetting, air quality (HUGE differences in ET with air quality alone!), etc. Excess timing can lead to detonation, which is extremely hard on cranks and main webs. It doesn't even have to be detonation...just too much timing. When the burn starts too early it tries to push the piston back down the hole, which if you consider how fast things are happening inside a running engine at 7000 RPM for instance, it causes the crank to flex (twist) and the block to take the brunt of the crank trying to be forced out of it's bearings. So be careful, especially if you're making a ton of power on a stock block. Really its not any different than a top fuel car running a "race" tune....they will usually lift the heads right off the block, bust rods, break crankshafts, etc. We just don't have quite that much cylinder pressure to deal with.
