Timing Question

[78Eliminator]

I have a Chevy 468 with dual 750s on a tunnel ram setup. My question is: where should I start my timing at? 15 deg BTDC? Please let me know. I have no friggin idea.
Justin

[HM]

Justin,
depending on the curve, that could be right, but you usually go for what full advance is. For cars, full advance is usually 28. On boats, you can get away with A LOT more, up to 38 on pump gas depending on your compression. I would take it out to the lake/rive and play with it. If it predetonates (ping/knock) then turn it back a touch, and test again.
I got a great low cost tip for timing here on the boards, that will give a more power on the bottom end. Lock out your advance - so you get no advance(there may be a screw already in the dist for doing this, or you may need to add one). Set the timing at 38. If your starter can't turn the motor over with this advance, run a cut-off swith on the power to the coil. With the switch off, turn the motor over and when it is turning at full speed, turn the switch back on and vroooooom. Again, test the advance for knocking and pinging, and dial it in. You can try some octane additive (prolong makes one that is about as good as they get).
A more expensive route is to go with an MSD. You can get a start retard and knock retard built in, but you have to pay for it eek! . That was the route I took.
I am sure you will get a lot more tips on timing.

[gnarley]

Anywhere from 12 to 16 should be a good range to start but what's your total?

[HM]

Justin,
you are going to the CBBB? I will be there and we can play with it there and probably get a few other people to pitch in with some other tips.
Frank

[78Eliminator]

HolyMoly:
Justin,
you are going to the CBBB? I will be there and we can play with it there and probably get a few other people to pitch in with some other tips.
FrankYep, I'll be there. Send me a pic of your boat so I know who the hell you are :)

[78Eliminator]

78Eliminator:
HolyMoly:
Justin,
you are going to the CBBB? I will be there and we can play with it there and probably get a few other people to pitch in with some other tips.
FrankYep, I'll be there. Send me a pic of your boat so I know who the hell you are :) Never mind, I just saw it in your profile....

[78Eliminator]

gnarley:
Anywhere from 12 to 16 should be a good range to start but what's your total?What do you mean by "total"?

[Jordy]

You shouldnt be running any vacuum advance, but what about mechanical? You know, the weights that are under the rotor in your distributor? Those control mechanical advance. On an MSD you can change out the springs to control how fast rpm wise the advance comes in. As you pick up RPM, the mechanical advance puts more timing in. Say you have 20 degrees of mechanical advance built into the distributor. You add that to the 16 degrees of initial timing that you have the distributor set at idle for 36 degrees of total advance.
Jordy :D

[HM]

jordanpaulk:
You shouldnt be running any vacuum advance, but what about mechanical? You know, the weights that are under the rotor in your distributor? Those control mechanical advance. On an MSD you can change out the springs to control how fast rpm wise the advance comes in. As you pick up RPM, the mechanical advance puts more timing in. Say you have 20 degrees of mechanical advance built into the distributor. You add that to the 16 degrees of initial timing that you have the distributor set at idle for 36 degrees of total advance.
Jordy :D This is where I started until I went fully locked out with no advance. I run at 40 locked out, but am running some very nice $$$ race fuel.
I forgot to mention the amount of power you gain aby running locked out is PHENOMINAL! Ask anyone who runs locked out. The advance is really to allow the stock starter to turn over the motor and prevent pretonoation at low RPM in combo with WOT. Boats, becasue of the cooler running temperatures get away with a ton more in regards to timing. It is only a matter of time until some of the veteran tuners see this post a jump in with similar and better ways to run locked out.

[gnarley]

78Eliminator:
gnarley:
Anywhere from 12 to 16 should be a good range to start but what's your total?What do you mean by "total"?Total refers to the initial timing or "lead timing" that is added to the amount of advance that the distributor allows to occur. So say in your case 15 degrees initial + 21 degrees advance = 36 degrees total timing. You can adjust both of these numbers to come up with the right curve & total for your own special needs or do as others suggested & just lock it down with an ignition on/off switch for cranking.

[canuck1]

Holy Moly
locking out your timing only works if your rpm is constantly above your timing dial in point. it works for you cause of the fuel you run but for most lake boats(heavy and loaded up) they will get major detonation if they try it.
I agree with you on the power thing but my boat is lite and doesn't have to work to get on plane

[HM]

canuck1:
Holy Moly
locking out your timing only works if your rpm is constantly above your timing dial in point. it works for you cause of the fuel you run but for most lake boats(heavy and loaded up) they will get major detonation if they try it.
I agree with you on the power thing but my boat is lite and doesn't have to work to get on planeOpinions are all over the map regarding this. I just try it and see if it works. It is really cheap low end power and I have seen it work in most cases on pump gas(91). Actually, I have not seen it not work - even locked out at 28, you still make a ton more power - and it is basically free!
Now if you run 87, you will start to have some predetonation and should have your boat taken away from you!
I am not sure what you mean by timing dial point? When it is locked out, you set the timing while it is idling - no need to rev it as there is no advance.

[canuck1]

dial point
the rpm that your total advance comes in at on a non locked dist....sorry

[Froggystyle]

Not to be contrary, but I just added a mechanical advance to PTL's boat, and got far improved starting, much better idle manners and no noticed performance decrease. I don't have mine locked out either, and it idles and behaves like a stocker.
In a blown application, I agree that the locked out advance brought in early is a major good deal. It works better and the blower motor likes it. I had that on my Daytona.
Jerry and I are running better gas than we need to. I just have not seen the performance increase to warrant the low rpm issues.
Squirts up!

[Bahner tunnel]

Would the "locked out " set up work on a motor with 12.5 comp. as long as you were running high enough octane gas ? It seems it would be more likely to detonate with that much timing off of idle because of the high load a jet boat motor sees when planing out . This sounds pretty trick if it will work in my application .