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Old 11-08-2011, 12:16 AM
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Timing help ported vs timed. Mallory Dist

hello,

I need some timing help please. I have mallory distributor and I am not sure which port to run it on. I ran it on the ported vacuum (on carb plate) yesterday and set the initial timing to 8 deg. When i connected the distributor to the vacuum port the timing advanced 4-8 deg (15 deg). I ran it like that and it ran awesome. but the car was stumbles or backfires off idle and low RPM if I put my foot in it.

my setup:
- +18 domed forged pistons
-990 open chamber heads 118cc
-holley 850 double pumper
-cam xe274h-10 (flat tappet)
-9:6:1 compression
-mallory (mech and vacuum adv)

My questions:

1. is it okay for my timing to be that far advanced (can i go farther). Does my setup require more/less advance?

2. any idea why I cannot accelerate hard from idle or low RPMs? I am using a Holley 4150 double pumper. Is this difficult to tune?

3. If i run the distributor off of the ported vacuum port, will have to run my transmission (TH400) vacuum lines of the timed port? or Can i run "T" and let the tran and distributor share the ported vac port

4. my rockers make noise is this normal?



THANKS in advance for your help!

ben

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Old 11-08-2011, 06:49 AM
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Quote:
Originally Posted by bendiesel
hello,

I need some timing help please. I have mallory distributor and I am not sure which port to run it on. I ran it on the ported vacuum (on carb plate) yesterday and set the initial timing to 8 deg. When i connected the distributor to the vacuum port the timing advanced 4-8 deg (15 deg). I ran it like that and it ran awesome. but the car was stumbles or backfires off idle and low RPM if I put my foot in it.

my setup:
- +18 domed forged pistons
-990 open chamber heads 118cc
-holley 850 double pumper
-cam xe274h-10 (flat tappet)
-9:6:1 compression
-mallory (mech and vacuum adv)

My questions:

1. is it okay for my timing to be that far advanced (can i go farther). Does my setup require more/less advance?

2. any idea why I cannot accelerate hard from idle or low RPMs? I am using a Holley 4150 double pumper. Is this difficult to tune?

3. If i run the distributor off of the ported vacuum port, will have to run my transmission (TH400) vacuum lines of the timed port? or Can i run "T" and let the tran and distributor share the ported vac port

4. my rockers make noise is this normal?



THANKS in advance for your help!

ben
The best answer is run it where it runs best. I have always had the best luck with it on manifold vacuum but every application is different.

As far as the transmission modulator, it should be on a direct source of non ported vacuum. T's are not recommended for transmission vacuum.

Your initial timing is a little low, at a minimum you should start at 12BTDC and work from there. I would try to get it dialed in without the vacuum advance first and once you get it working ok, bring the vacuum advance into the mix later and do final tuning.
You say you cant accelerate, exactly what does it do.

If you can give a description of the car and all the engine specs, they all matter, you will have a better chance of getting some help. You gave a break down of some of the parts but not the actual displacement or what kind of car it is in.
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Old 11-08-2011, 08:18 AM
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My bad. The car is a 70 chevelle and the engine it's a 468. Running 3:42 gears in the rear
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Old 11-08-2011, 09:06 AM
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You are running on manifold vac, not ported, like you stated. Ported vac does not come in at idle.
1. You probably need more timing. Your Mallory should have adjustments to llimit your total, without vac. I would start at 38 total and have it all in around 23-25 hundred rpms with the auto trans. If you have a degreed balancer, rev the engine up, using the timing light until all the advance is in. Set it at 38 and let the initial be what it is.(at least 12-15 without vac) THEN
your cam might like the vac at idle. If you can set the idle speed with vac to your liking and it idles OK when dropped in gear, then great. The biggest problem with using the vac at idle is the engine wanting to stall when put in gear because it looses the advance when the engine is loaded. If it tries to stall, set idle without vac to cure the problem and run true ported vac vor mileage.(should be the port on the metering block, most Holleys)
2. You can adjust the pump cams for the leaner position, but this is probably happening because you don't have enough timing when the vac drops out.(see above)
3. Trans wants manifold vac, either from manifold fitting(most common) or the big port on the back of the carb.(usually power brakes)
4. In my experience, the Comp XE cams are somewhat noisy for hydraulics. My best results are 1/4-1/2 turn past zero lash and know they might be a little loud at startup. You can go a full turn past zero and get rid of the noise usually but, IMO, the cam performs better at less. Cam guru's will tell you the ramps ground on this particular line of cams is what can make them noisy. (You didn't actually say you're using Comp, just making a guess)
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