www.the351cforum.com

So as some know, I have asked questions about locking out my Duraspark distributor. I got a deal on a MSD 8577 in the displayed only section at Summit. Got it for $175. So I have already locked it out. I just have some questions/wonders what to expect when I put it in. I'm already planing to put it in 30 degrees BTDC to start with. Here are my questions/wonders:

1) I have heard when you run locked timing it will clean up the idle AFR. This is one reason I decided to do this. Is this true?

2) Does this typically lean out or fatten the AFR and will I have to mess with jets or power valve? I put a 4.5 PV in it already because my vacuum is around 8-10 when idling in gear. I have a 750 Mighty Demon and it has the factory 75/83 jets.

3) do i need to change the plug gap? I run the Autolite AR3924 plugs at .035. Also, does running locked timing eat plugs quicker?

4) Is it bad to idle the engine for long periods of time like this?

5) Have you noticed a change in engine temp either hotter or colder with locked timing?

6) I know it will be harder to start - I have the PowerMaster high tq starter and they say its good to 18:1 compression - guess I will see.

Thank you for any info you can provide me
-Matt

Here's my thoughts, take it for what you paid for it.

Most guys that run locked out timing are race only engines. And those guys don't run power valves or anything else "streetable" on a car. The cars are usually off or on the throttle, and usually in a pretty narrow rpm range. They also tend to be in a scenario where reliability in a timing setup is more important then the little bit of power loss one would see by not having variable timing. Any ignition changes like you're doing should be follow by carb adjustments, as the two go hand in hand. You might need to change jets, powervalves, shooters, etc to get the thing back to running right after locking the timing.

Cleaned up idle afr's is because most distributors run low initial timing at idle. The engine will be more efficient at idle with more timing, which is one benefit of having a vacuum advance. But the transition between idle and off idle can get finicky with wild timing swings, so try to stay conservative with it.

Race cars typically don't run low rpms, so they won't run into detonation issues with low rpm/high load that is a possibility on a street car.

We ran locked timing on all the late model and modified engines. One tip to get them to start easily is to turn on the ignition system after the engine is cranking. We ran high compression and had no issues starting. Good 16 volt batteries, good starters, and a good ignition system are all necessary. If you've got a wop-pause-wop-pause-wop-pause cranking sequence, having high initial timing will make it a hard starter for sure. I think msd makes start-retard boxes, and I know of one guy that ran dual crank triggers, one that was retarded a dozen degrees, selected by a toggle switch. You can look into that as well.

1 - It should, makes the carb a bit easier to tune at idle for sure
2 - no change in jetting, etc. Same 650DP carb settings for the last 20 years.
3 - No plug gap changes. I changed from .040 to .032 because of the potential to run Methanol, not because the timing is locked. Fuel may dictate plug and timing changes.
4 - never had a problem, mine is set at 37
5 - That's N/A with mine, huge radiator and big electric fans.
6 - use a start retard, at least 10 degrees. 15~20 if you can get it. Does not have to be hard to start. The "switch ignition on after cranking begins" is also a way to do it. But most good ignition boxes now should have a programmable start retard, or an optional module that does same.

As for the other comments - it's a race car with tags, I run power valves, The 7AL-3 has a 25 degree retard built in IIRC. I can also crank the car then enable the ignition, since it uses a race car type switch and power distribution setup.

_________________
Chris - Merkel, TX
http://raceabilene.com/kelly/hotrod
"Owner built, owner abused."

Thank you guys for your replies.

When I first got the MSD6AL, MSD told me to run .032 to .035 for plugs. Mine is 11:1 and I run 110 fuel. I was running .032 but with new plugs went with .035.

When it was dynoed he had it at 36 degrees. The last time I was at the Motorplex I ran it 3 times like normal with 36 but then went to 35 degrees and it picked up 1/2 mph. To me that's not a significant increase but I defiantly want to try some lower timing to see if it likes it. I basically just put the engine in as it was dynoed but I know the dyno load and atmosphere are different than being in a car.

I will look at the MSD start retard box. I really dont want to buy a new CDI box but i will look at pricing and what is available. With the old motor I wired up an ignition interrupter switch. It had Aussie 2v heads and only 10.25 compression or so but it loved some timing. Full advance was 42 degrees but it had a stock balancer so who knows if it spun a little. I do know the stock replacement 5.0 starter was not a happy camper turning it over though.

My older 9~9.5:1 open chamber motor had like over 40 total. The dragster 393 with 11.5 and the AFD 62cc chambers liked 28 so I didn't even wire up the 7AL-3 retard. The 351 in the Falcon is 10.5:1 and is set at 37 with the 25 degree wired up. I've noticed that this older MSD box doesn't always engage the retard so start is typically crank then ignition on. I bought a new box for the dragster and the current 7AL-3 uses a chip to set the amount of retard. That's a nice feature I might never use LOL. I've run locked for a long time - the older Mallory 685 box had max 10 degree retard so I'd be cranking with 27~28 initial and didn't have any problems. Everything uses a PMGR starter from Summit Racing.

PS - I love my crank trigger setup also. Makes things even easier to set.

_________________
Chris - Merkel, TX
http://raceabilene.com/kelly/hotrod
"Owner built, owner abused."

Falcon67

Crank trigger would be cool but unfortunately I can not race enough to justify the cost

The reason I changed from 36 to 35 was because my buddy was like "that seems like alot of total timing for a modern aluminum head" He is a 385 BBF guy and Cleveland guy. I might lean towards a new box with a retard in it. Tomorrow just might be a trip to Summit

I forgot to note about my dyno pulls. When I went to Rick's shop to see the last pull (in August) it was over 100 degrees outside. Not sure if you know of or have ever been to his shop - Metroplex Machine shop in Balch Springs but Rick is my builder/dyno. He doesn't have one of them HorsePower Tv dyno cells with A/C etc.. Nope, his shop doors were open and it was every bit of 110 inside his shop. So like he said, when mine made the 521hp/450tq - he guarantees it will make 30hp or more on other dynos. So in reality the atmosphere was Tx heat during the pulls.

I've never noticed any difference in plug wear from locked to unlocked.

I have always done the "get it spinning first, then hit the ignition" to start mine with the locked timing. Doing it that way, the stock 5.0 replacement starter from O'Reillys has no issues starting the motor, even with 13-1 compression and a big roller cam.

I wouldn't be surprised if a new plug pulled after a pass would show your motor wanted less timing, probably something around 30-32*, but I'm just guessing here.
Ignition timing is a weird thing to me. My 377 before this last rebuild, ran best with 35*, and that is what the plug showed it wanted. After this last rebuild, using all the same parts, it ran best with 38*, and that was what the plug showed it wanted.

Thanks again guys for your responses. I looked at Summit and these start-retard boxes are not cheap but probably were a better price a year and half ago

I think I will wait to either buy one of those or bit the bullet and get an upgraded ignition box after I see how it starts after I put the distributor in. In theory I have good things going for me - high tq starter, Optima Red battery, big welding cable for all the positive and grounds, Flaming River high current cut off switch and an Accel Ultra Tork starter solenoid "part #40200" in case you want to look it up. Also if it makes a difference I have a TCI SFI flexlate. Maybe it will want less than 35 degrees timing , so that will help a little too.

Agree with KV - that's the big difference between the old iron and the AFV aluminum - timing. I said 28 but I think now I meant 26. I started at 30 and went down - per Brent - until the heat mark was at the curve of the plug electrode. Yes, none of the timing stuff was ever "inexpensive". MSD especially is high. The new 7AL-3 was over $700. Combine with a coil, crank trigger distributor and the crank trigger setup there's close to $1500 just in ignition.

_________________
Chris - Merkel, TX
http://raceabilene.com/kelly/hotrod
"Owner built, owner abused."