Locked Out Timing and High Compression
 

I've got a 383 running AFR 180E's at about 11:1 compression, 93 octane. The cam is one of Bob Madera's (.571 234* intake .521 240* exhaust). I am using a Nickerson tuned 750 Demon. Nickerson recomended I lock out the timing. My fear is that with so much compression, at part throttle, high load, and high timing it will rattle. I am using a Crane Hi-6m box. I haven't tuned it yet, but I was thinking about keeping the timing low, perhaps no more than 32* of total timing. Should I lock it out? Also, I have only had it in the water for a short time but when shifting into gear, it dropped rpm's quite a bit, making it pretty ornery at the dock (14* base timing). Would locking it out at 32* help this? The crane box does come with a map (#8) for use with high horsepower motors with stalling problems during docking (24* base, 34*max in by 3000rpm). Would that be the better map to use?

On most timing curves, you're going to have total advance by 2500-3000 rpms anyway so locking it out isn't a huge concern. The only thing I might be concerned about would be hot starts. Engine sits and heat soaks for a while and when you hit the starter it wants to kick back. And, yes it will help the manners around the dock.

That #8 map doesn't look bad either and may help with hot starts.

Thanks for the advice. I never even thought about the hot start issue. What is the best way to combat that issue, let it idle for a bit and cool down before I shut it down, or get a hi-torque mini-starter, or both?

I would just use the #8 curve that you listed with 10* of advance.

That does sound like a good curve for hi-po motors. They didn't have that curve in the initial 6-M box back in '05. I had the same problem with bad dock manners - the boat that is!:D

If high initial timing is causing starting problems, install a switch on the ignition at the helm. Turn over the motor with the ignition off and after the motor is spinning flip the ignition on. The motor won't buck the starter with the momentum from spinning the motor over.

Also helps prevent engine damage if your exhaust manifolds start leaking.

Tom

I'm running pretty much the exact combo and love it so far.
385ci, AFR 190's, Holley HP750, RPM Air Gap, RMBuilder 234/240 .580/.568 112+4. 10.0-1 SCR. I'm running an MSD Dist, Merc 22* advance module, MSD 6AL and B3 coil. I'm also at 14* initial @ 36* total. I've been running 87 octane and the plugs look great so far. I've ran 10-1 SCR in the last 2 motors with aluminum heads on 87 and have never had a problem. With our aluminum heads they dissipate heat much more so than iron heads. If you are running 93, I see no reason to worry about detonating the motor with 36* total.
I've been very pleased with the idle quality of the relatively "BIG" cam in the SBC. I have 7HG vac @ 750rpm Neutral hot idle 14* initial. I can idle it in gear down to 650rpms with no stalling idling. Very important with the Alpha drive back there. Have you tried adjusting the carb when hot to fine tune you idle. I had to adjust the idle circuits and fine tune the idle rpm speed. What jets are you running P and S?

I didn't have it in the water long enough to mess with it. It was leaking coolant into the motor from the intake gaskets, and I chased that problem all of last summer. I ended up using double thick intake gaskets to solve the problem. The intake leak may have also contributed to the idle drop, but it wasn't surging so I don't know if it was leaking air too. When I put it into gear, the rpms dropped rediculously low, but it wouldn't stall, but I was afraid it would suck water into the exhaust (my risers are 3/4 dry, they mix water 27 inches back). I checked the plugs and cylinders and there was no water, so I think it is pretty reversion resistant due to the shape and length of the risers. I am completely incompetant when it comes to carbs, that is why I sent it to Nickerson. I haven't touched the carb since I got it from them, but they sent it with 78 primaries and 88 secondaries. I am using a Victo Jr. It had a slight bog when I went to plane off, but again possibly related to the intake leak. It idles on the trailer nicely at 750rpm, and will idle at 650 as well, but I don't know what it will drop to when in gear, I guess we will find out this summer when I start messing with the timing maps and idle circuits.

I think if you adjust it and see what it likes and doesn't, you should be able to dial it in at idle better. I have 22" long riser extensions that go inside my tips. Water mixes inside the tip and only has 3" before it exits. About as dry as you can get. My Holley HP750 has 72P @ 76S right now and seems to like it going by plug readings. When it gets in the summer heat I'll probably fatten it up a tad just to be safe. Holley ships these with 70P, 80S.

Here's mine....

http://www.youtube.com/watch?v=ORkMT3JMWu8