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Old 07-23-2003, 12:15 PM
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Timing advance with a blower

I've read through about 150 pages or so of posting and have picked up a ton of usefull information, but haven't found an answer to some conflicting infomation I've been picking up lately. First some stats. I realize some of the things I'm going to mention do not necessarily go together, but I just picked this up. I'm guessing the previous owner piece-mealed this together and never planned it to be a blower motor.

70's 350 chev (=030)
9-9.5:1 compression (guess)
Unknown cam - noticeably rough idle.
stock HEI w/ Accel cap and coil
stock heads
B&M 144 with 600 Holley DP
All in an 81 Camero

I picked up from the Holley website and other areas that blowers love initial timing advance. My question pertains to additional vacuum advance at higher RPM in connection with higher cylinder pressures. I understand that some blower motors are actually set up to retard timing advance as pressures increase to avoid detonation. Am I better off disabling the vacuum advance to avoid detonation? Does anyone offer, and/or would anyone suggest going to a distributor set up to retard timing at higher RPM? The car is primarily a stoplight to stoplight runner with a few weekend strip trips.

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Old 07-23-2003, 03:33 PM
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im no expert but your compression seems a little high to put a blower on it. but maybe im wrong.
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Old 07-23-2003, 04:34 PM
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I have a friend that has a Vega with a 671 that has 13:1 compression on it and it runs 10's . He has a MSD that retards the timing under boost ( I think his heads are o-ringed though). I think yours will be ok just keep the boost down.
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Old 07-23-2003, 04:58 PM
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Like propaniac said Keep the boost down, most non N/A motors run 7.5 - 8:1 compression. 4 - 6 lbs boost should be lots. (but dont' quote me do some more research, I've only got limited exp. with blowers and turbos) And yes because of the compression your gonna have to retard the timing at high rpm. Not sure how, but that's what your gonna have to do.

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Old 07-23-2003, 05:19 PM
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The motor will run without it, but to be on the safe side and have it run for a while, I would put a retard on it. Do you know how many pounds of boost you are running? Since you say you don't know much about the bottom end, I would keep it under 5-6lbs. You can run higher with your comp, you would just need non pump gas. BUT, I wouldn't since the bottom end could be stock as well. Too much boost could easily twist it up or melt a pist.

Just my .02
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Old 07-23-2003, 11:13 PM
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well, thats what i meant, not on pump gas. i think, hell i just wrote it down for some odd reason.
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Old 07-24-2003, 06:37 AM
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Thanks for the advice everyone. The blower is set up now to deliver 6 lbs of boost, but I'm already in the process of backing it donw to 4. I'm gathering that MSD offers a setup for retarding timing at higher RPM (I haven't been able to find one so far). If anyone knows of another source, please let me know.

I'm trying to get the most out of this motor through this season. The 4 bolt 383 is on the stand now that will be better suited for the B&M (low compression/ aluminum heads). I'm hoping for a winter heart transplant in the Camero.
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Old 07-24-2003, 08:24 AM
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Yeah, MSD has a retard set-up. I've never ran one, so I don't know if you have to run a "box" along with it.
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Old 08-01-2003, 02:08 AM
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MSD, Crane Cams,,, and other mainstream ignition controllers are 2-dimensional only. To get most out of engine you need 3-dimensional ignition mapping.
There is overwhelming market to choose your ignition controller from. Many boxes hold management for both - fuelling and ignition control. It'll be a somewhat waste of money to purchase such expensive equipment to handle ignition only, and keep carburator. Not that many manufacturers make ignition only 3-dimensional units anymore.


I myself happened to lay my hands on a used Haltech IG5 ignition only computer. It's a fully 3-dimensional direct fire, wasted spark ignition computer.

Have a look at Haltech lineup. They have models to work directly with original GM EFI wiring looms and all. It'll be a somewhat plug 'n' play type of setting up, apart from programming it - of course.

http://www.haltech.com/

Here's a short lesson on 2D and 3D ignition management:
http://www.dbox.demon.co.uk/frame_co...dunnell_3d.htm
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Old 08-01-2003, 03:19 AM
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Cool

howziit guys!

blown, don't worry about vacuum advance higher than 3500rpm. you'll have no vacuum, so no vacuum advance.

FWIW, BDS sells their MALLORY unilite distributor, callibrated for supercharged engines. it has no vacuum advance. give them a call, with your questions.

do you have cast or forged pistons? if unknown, err on the conservative side, and presume they're OEM cast ones.

MSD has a few boost timimg/retard devices, ranging from $165-$225.
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