how to lock out mechanical advance
I have a blower car and i have been told it might be a good time to set my intial timing to be my total timing and then lock the distributor up so it is stuck at total timing all the time no advance is this true and if so how do i do that
But first lets see if this is what you need to do.
Every setup and circumstance is a bit different.
What are the details of your motor and car and what are you using for timing now? What improvment are you looking for?
Camshaft? compression ratio? carb jetting? shooter sizes.
What distributor make model?
Blower pulley drive ratio? What spark plugs?
Did you check and verify the timing tab pointer accurately indicates true TDC using a piston stop?
If you do lock out the mechanical advance curve, you will want to install a dash mounted ignition power cut off switch to aid hot cranking/starting the engine. Takes the heavy load off the starter mtor on a hot start with full timing. Its easy to do also.
Be sure you have the OEM rear starter motor mounting/support brace/bracket installed on your GM starter motor. If yours is missing go to the GM dealer and get one and install it.
Search my old posts using suitable keywords search terms for the how to's on locking out a HEI distributor.
Most of the aftermarket distributors with the weights on top under the rotor can be done the same simple quick easily reversable way I do it. Many/most others show how to lock out the mechanical advance in the instruction sheet.
Not hard to do.
You can download the instruction sheet for your aftermarket distributor from Summit Racing . com.
It would be nice to also add/reinstall a vacuum advance to your distributor and dial it in correctly to fine tune the overall ignition advance system for your blower motor. It will need specific custom calibration setup also but really helps the overall setup. The stock advance can off a stock distributor will not do. You need an adjustable type.
Last edited by F-BIRD'88; 08-27-2009 at 10:33 PM.
cam is 488 lift
comp ratio is 8.3
not sure on the jet but the shooter are 35
pro comp dist
dont know the pulley ratio
autolite 3924 gapped to 40 thous
its a brand new engine i built on an engine stand so i just assume the timing tab is correct
the car seem to idle better when i advance it but only to and optimum amount of timing i do have lighter than stock springs in the dist currently
heres another question can timing affect overall power
reason i ask is because when i drove the car home high idling when i reached my block i hit the gas a little and the car seem to lurch forward as if it had gain a good amount of power with all that extra timing
is that possible or am i dreaming
First thing to do is to verify the accuracy of the timing tab TDC point.
This is criticial.
Its very very very common for this to be out of wack. Especially if you just assembled it using a aftermarket timing tab and or aftermarket balancer or....
even the factory tabs and balancer TDC mark locations are often wrong
Do not over look this. This is where to start.
Yes the engine will be more responsive with more (idle) timing (than you are used to with a stock engine) at low rpm.
Engines with big(er than stock) cam like a lot of inital timing at idle and low rpm.
Supercharged engines especially. But you got to watch the amount of total timing.
Thats why you need a accurate timing pointer and need to modify the distributor advance to work with the supercharged motor.
What .488 cam?
cam timing specs from the cam card or brand name and grind number/part number.
What is the diameter of the top blower pulley and bottom blower pulley?
i recomend a slightly cooler sparkplug for ypur superchargd motor.
EG: autolite 3923 or 3922 Champion RC9YC
gap at .035"
Install them after the igniton and carb are corrected, but before doing any WOT road testing under boost.
They offer a little more detonation/preignition resistance under WOT/boost
They run a little cooler under power.
You must use the best premimum highest octane pump gas in your that your can buy in your area.
If you are going to lock out the timing, start at 28degBTDC. (after verifying true TDC) Typical spark advance under boost on a blown motor like yours is 26° BTDC to 34° BTDC. using premimum pump gas. Excessive spark timing under boost will destroy your engine. Do not get carried away.
Work in the 26°-28°-30° area until you get it sorted out. More is not better.
Detonation must be avoided. There is a limit on how much timing you can run with boost on pump gas.
You'll probabily need a selection of carb accelerator shooters, jets and maybe a or two larger "50cc pump(s): the larger internal blower+ intake manifold volume need a big(er) shot of accel squirt volume.
What is the carb jetting now? carb model number?
Do you have the holley rear secondary jet extensions and matching notched float?
Highly recomended upgrade for a fast car.
Is the fuel system (pump etc) on your car capable of supplying this motors full power fuel volume requirement at WOT.
engine HP x .1 = minimum required fuel flow requirement (GPH (actual system flow at WOT not freeflow advertized rated GPH on the box)
Last edited by F-BIRD'88; 08-28-2009 at 02:34 AM.
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