How to get my timing curve set up!

jenkins71 said:

Hi guys. So, I just built a 440 and 4 speed for my 71 Charger. Cam break-in went well, and I am now just seating the rings and trying to get a good tune out of her.

Engine stats are as follows:
2266 TRW Pistons, 9:1 CR
952 heads, port and polish job using the Mopar templates
Holley street dominator intake
Holley 750 carb
Comp Camps XE274 cam
Hooker Super Comp headers
Factory, stock, unmodified Mopar distributor with Accel Wires, Orange Box ECU, MSD Blaster 2 coil.

Centerforce clutch and 4 speed, rebuilt.

So using the vacuum gauge on manifold vacuum, trying to get the highest vacuum reading by advancing the timing, (vacuum advance at dizzy disconnected) it appears that it likes about 25* of initial timing! That to me seems like quite a lot, so I've backed it down to about 15* initial, but it idles worse and RPM drops at that setting.

It's a pig off-idle, and you kind of have to rev it up to keep the clutch from staling it out! Keep in mind, it does at this time have a set of 2.76 gears until I rebuild my 3.55 set up.

Can someone guide me through the process of setting up my ignition timing? This will be the first time I attempt to mess with ignition timing on a true performance motor, and trying to create a good curve other than just setting initial.

I do want to continue using my vacuum advance, to increase MPG hopefully.

Also, my dizzy is the old weld-up-the-slots style.

THANKS!

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747mopar said:

I'll be interested to read all the advice because I have a setup much like yours. Mine likes 36 with no advance, I've put 5,000 miles on it like this and it runs great. I've tried mechanical advance, vacuum advance and toyed with the curve too and it just likes 36 degrees. I know it doesn't sound right but it runs 185 degrees all day long and runs like a top?

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Cranky said:

What's your cranking PSI?

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Cranky said:

The 2266 piston usually give less than 9-1 compression. Even with an open chamber head that's been milled to 85cc, it will only give you about 8.8-1 on a .030 over 440 with a stock deck height and using composition head gaskets. If your heads have been milled just to clean up, they are still pretty close to 90cc....88-89 is more realistic after a clean up depending on how much material was removed. If this is the case, it's most likely why your engine likes 25 initial and will probably like more than 38 total. I've had the displeasure of tuning on two different engines and after checking true TDC and using 3 different timing lights, we ended up with a lot more initial at idle and 50 total! Both cars kept going faster in 1/4 mile until we got to 50 degrees and at that point, we didn't even care what the initial was so long as it didn't back up against the starter. One was a 7.8-1 318 and the other was a 8-1 440. Both had long duration cams and neither one showed any signs of detonation. Spent a lot of time on the first engine because it just went totally against the grain but it ran well like that and then here comes this small block a couple of years later displaying the same mess but spent much less time tuning it after finding out what was in it. Told the second guy that I would rebuild it if it burned a piston after he was skeptical about my method and he finally said ok. Just wasn't about to spend as much time on it as I did the first one! It too ran well.....heck, it ran like an ape with it's butt on fire.

Never did get a good ET number because of excessive wheel spin but the 318 Demon was knocking down 13.50's and the best the 440 powered Coronet was a 12.30. I hate low compression engines. It's so easy to build a 10-1 motor and run pump gas and have a conservative tune on it not to mention they take up less time to get em tuned up....and yes, your 2.76 gears are killing you. Get the 3.55's in it as soon as possible.

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