I installed a new cam and i am not sure how to determine what the timing should be. Advanced how many degrees??

I had the pistons dished so the compression is now at 10.2:1 as compared to 11:1 before. Also here are the specs on the new camshaft.

Lunati Voodoo part number 60103

Duration @ .050 IN/EX: 227/233
Gross Valve Lift IN/EX: .489"/.504"
LSA / ICL: 110/106

RPM Range: 1800-6200

Thanks!

 

Have you had any distributor work done? Do you have any idea how much total advance the distributor will kick in at 2700 RPM?
If the answer is you don't know a good base timing is 12 degrees total timing should be 38-42 depending upon cam.

 

Ask 10 people and you'll get 10 answers. The short and skinny run 12-14 initial 36 total all in by 3000 rpm.

 

I'm with Wish.

 

No idea what total advance the distributor will kick in at any RPM and have no idea how to determine that. I guess i will need to get it to a DYNO to figure it out.
I also have the petronix kit that eliminates the points.

So how do you figure out the base advance?? Timing is an area that has always been strange to me. I broke the engine in last week. I got lucky and it fired right up on the first try and ran well enough to break the engine in. However, i can tell that it is not perfect.
Thanks

 

You need to find someone with a sun machine as this is the only way to curve your distributor. Doing it on a dyno is expensive. You set you initial and your springs determine your mechanical advance is the simple answer. The vac advance can needs to be selected based on the vac you have available.

 

You may have trouble finding a sun machine, unless you know a shop which deals in older cars. I use my uncles, excellent machine.

oWEN

 

Oh well, i guess i will just attempt to get it running as good as possible setting the timing with my light as suggested somewhere between 12-14 degrees.
thanks

 

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An old engine builder/hot rodder that I know says that if you don't know the correct timing specs from the manufacturer the easiest way to time the engine is to take it up to 2000 rpm or so with vacuum advance disconnected. This should get the full centrifical advance in at that rpm. Turn the distributor until you hear the engine start to run as free as it can. You'll know it when you hit it as the engine will sound like it is purring with no labor. If you go past it the engine will pick up a lot of rpm's and you may start to get backfire through the carb. Back it down to where it runs free. Lock the distributor down and forget it. Whatever the timing is, it is. Once you lock it in and put the vacuum to it, you'll have to back down the idle. You can hook up a light to it and check in case you ever have to re-time it. This is an old hot rodder trick.

Steve

 

Just be sure you are not using the stock style vacumn advance. I don't recall the number of the alternative but you can research it here.

 

cobra
if you aren't familiar with timing adjustments, how to determine what your curve it, how to set it up, etc you should read JohnZ's timing tech articles. They are great and will not only explain everything clearly but also take you step by step thru the process of setting it up.

I have both articles hosted on my website tech articles page here:
http://69.253.166.197/corvettes/tech/vettetech.html

scroll about 1/4 way down or so and look for the two articles called:
Timing101Article.pdf
by John Hinckley
MAPPING ADVANCE.pdf
by John Hinckley

 

golf tees make excellent vacum line plugs,are cheap and are plentiful.I believe one disconnects the vacum (and plugs) to set initial timming with a light.Use a yellow crayon (lowes sells a pack of 5 yellow lumber crayons) or white,to mark the timming grooves/numbers.use number 1 cyl plug wire.

 

If you have a dial back timing light, disconnect and plug your vacuum advance, set the light for 38 degrees, point it at the timing tab, and start increasing engine RPM until the timing mark stops moving on the tab. Note the engine RPM when it stops moving. Ideally you want all the timing "all in" by 2800 or so RPM. If it comes in later than that you can get lighter weights and springs from any performance shop. More on that later . . .

Keeping engine speed at that "all in" RPM from above, rotate your distributor until the timing mark lines up with 0* on the tab. Now you have 38* centrifigul timing. Let the engine return to idle, and turn your timing light dial until the timing mark and tab again go to 0*. Note the timing on your light. This will be your initial timing w/o vacuum advance. Reconnect the vacuum advance and once RPM stablilze at idle you can again play with the dial to get your initial tming w/vacuum advance.

Next take the car out and drive it. If you get any detonation you will likely need to retard the timing by 2* until the detonation stops. Conversely, if you have no detonation under load, you can advance it by maybe another 2*.

A note on centrifigul advance: try to plot an advance curve by adjusting your timing light and RPM to determine what advance is in at various RPMs. If you have a stock cam, you will want your advance map to be the same as it was from the factory. If it is non-stock, see if the mfg has recommended timing specs.

Hope this helps. There are other ways to do this, but this method is easy and has worked for me.

 

Also, make sure you have the right vac can on the distributor. Find your idle vacuum reading and then select the right can (Duke & others have a chart somewhere, I only know what I need).

 

The info from JohnZ referenced earlier rocks! And just do what he says and it will turn out just fine.