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Old 06-09-2005, 07:07 PM
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Setting timing curve with HEI Ignition

I'm wondering if I haven't been running the optimal timing curve for my 350. It has a Mallory HEI distributor, and it came with three spring sets for the centrifugal advance weights. The springs range from having total advance come in at 2800, 3500, and 4200 RPM. I'm currently running the 3500 RPM springs, but I'm noticing that low RPM power doesn't seem to be too great especially considering my compression ratio, and my gas mileage in the city is pretty crappy, even with a conservative foot. I'm wondering if switching to the 2800 springs to dial in more timing early will help this problem a bit, or if I should keep it at 3500 and dial in more initial timing - maybe even do both. I also notice that my car idles around 1,000 RPM and struggles to reach 650 RPM when put into gear. If I tune the idle to a lower setting it dies when I put it in gear. If this is caused by the carb being out of adjustment, I will check into that, however I'm pretty sure my carb is tuned at least pretty close. If this can be fixed with timing, then it may be the reason I have power and mileage problems as well.

Here is my engine setup for reference:

- Chevy 350 .030 over (355)
- Flat top pistons .005" in the hole
- Well ported 305 heads with 58cc chambers (over 11:1 compression)
- Edelbrock RPM Air Gap intake with Holley 650 DP carb
- Comp Cams XE268 cam (224/230 @.050, .477/.480 lift, 110 LSA)
- Evans waterless coolant and octane boosted premium fuel to deal with high compression
- 700R4 tranny with 3.27 gears, stock stall converter

I currently have 16* initial timing, and 36* total timing at 3500 RPM. It may be possible to increase the initial and total timing more because of the high octane fuel I run with (burns slower), however I must be careful to avoid detonation with my compression ratio.

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Old 06-09-2005, 07:34 PM
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what is Evans waterless coolant
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Old 06-09-2005, 07:35 PM
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also with that motor and cam..i would put at least a 2500-2800 stall convcetre in it..that would help a lot..
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Old 06-09-2005, 07:50 PM
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Evans waterless coolant is a Non-aqueous propylene glycol mixture that is used in pure form without mixing water in. It's benefits include a much higher heat capacity and conductivity than water, near zero operating pressure, a boiling point of 375*F, zero corrosion, and near zero vaporization, which really helps in removing pump cavitation and insulating vapor blankets. They say you can run higher compression because it is good at eliminating hot spots in the heads. Here's the link for their site, I use Evans NPG+ version.

http://www.evanscooling.com
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Old 06-09-2005, 09:53 PM
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mmm..sounds fishie to me..but if its true thats cool
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Old 06-09-2005, 10:39 PM
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curve kit

Use the two lightest springs. If you get detonation. Go to one light and one medium.
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Old 06-10-2005, 09:00 AM
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go with the lighter springs for sure. Set the total timing to 34-36 and call it good. If you need more timing at idle, get an adjustable vacuum advance and hook it to manifold vacuum. that will give you a few more degrees at idle but will go away the second you hit the gas. You will have it back at steady cruise but not a mild and wide open throttle. That cam is not that agressive so your idle should be good at 600.
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Old 06-10-2005, 09:38 AM
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i am in the process of doing the same thing with a new 406 right now with an msd system.its all trial and error.you just keep trying spring set ups til you get it to where there is know detonation.start with the lighter springs and maybe middle of the road or small bushing.if you feel you're getting the the springs close but not quite go to the next larger bushing and start again.at that point you may need to go to slightly lighter springs again.you should not need the timing lite til you get it about right then you'll want to see where you are.you may want to use a sharpie to mark your distributor while you're doing all this.it helps when not using the timing lite so you can adv. or retard and move it back if the springs or bushing did not work.you will want to mark the final spot also.this will take some time to get it right the first time.
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Old 06-10-2005, 09:38 PM
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OK, I will try using the light spring set, it should help the 1500-2500 RPM range with a few more degrees. I'm still wondering what is up with the large RPM drop when I put it into gear. I have to set the idle quite high to avoid having it croak when I put it into gear. It gets even worse when I have the headlights on. Is this a timing issue, or is there something that needs adjusting on the carb?

Another thing I need to ask... why stop advancing at a set RPM level? Doesn't the fuel take nearly the same time to burn at 6000 RPM as at 3000 RPM? If the burn rate works out to make the best power stroke at 3000 RPM, then wouldn't it be greatly retarded at 6000 RPM, when there is half the time for it to burn? It just doesn't make sense to me, I know it has to be set this way, I just wonder what anomalies make this a necessity.
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Old 06-10-2005, 09:45 PM
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What's your initial timing right now?

Larry
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Old 06-10-2005, 10:22 PM
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my initial timing is 16*, plus I have vacuum advance connected to the manifold, so actual advance will be much more than this.
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Old 06-10-2005, 10:45 PM
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16*, as long as your vacuum advance can is getting enough vaccum when the trans is in gear it shouldn't fall on it's face.

Hook up a vacuum gauge and take a reading with it in gear, my guess is that the reading drops below what the advance can needs to maintain steady timing.

Larry
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Old 06-11-2005, 01:45 AM
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i'd almost bet your idle problem is from your carb needing tuned for your motors set up.check out for tuning needs.
www.holley.com
www.bob2000.com/carb.htm
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Old 06-14-2005, 11:46 PM
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OK I have been running with the lightest two springs for a couple days now, I do notice a lot more power in the low and mid RPMs, and my idle problems are not near as bad as they were. However I notice some detrimental effects from changing the springs... My engine seems to run a little hotter, even at cruise speeds. I don't know for sure if the timing advance is doing this, however my guess is that I'm running a bit too much timing and not detonating because of my high octane fuel. My exhaust is pretty loud, and it makes listening for pinging or knocking quite difficult, perhaps I just can't hear it. If I am detonating, is it a serious, highly audible knock or ping, or is it something more subtle like a low frequency thud or the sound of marbles rattling in a can? I like the performance improvement from changing the timing, however I will certainly knock it down a peg to avoid detonating. Unless I'm totally sure I'm NOT detonating or running too much advance, I think I will change out to the next spring up.
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Old 08-05-2013, 03:54 AM
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If mechanical advance is part of your 16 initial and dropping it into gear lowers RPM, then mechanical advance will drop some advance out thus lowering RPM even more than trans. Idle Park to In Gear RPM drop should be around 150-200. Carb needs adjusted to keep engine running in all conditions.

I know, "Old thread" but someone will find it, I did.
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