Timing Engine - To What Degree

[camaro1969]

I am timing my SBC, since it has a lot of aftermarket parts, i cant really go to a spec book and see what i should time it to. I was hoping to get you thoughts.

Engine specs below

SBC 350, Th350 Auto, 12 bolt rear 3.07 gears, 15 inch bfgoodrich t/a radials...

Cam:
Comp Cams #249-CL12-242-2
Xtreme Energy XE268H Hydraulic Flat Tappet Camshaft
Lift: .477''/.480''
Duration: 268°/280°
RPM Range: 1600-5800

Other:
1479H keith black pistons .30
139 piston rings
CLE-CB663P rod bearings
CLE-MS909P main bearings
CCA-817-16 compcam lifters
SLP-260-1000 gasket kit
CCA-981-16 compcam valve springs
CCA-1412-16 compcam roller rocker
ARP-134-6003 arp connecting rod bolt
Non electronic distributor or electronic ignition

[ProdigyCustoms]

We got everything but cylinder head info which is probably the most important info of all.

If it has factory heads, I would time it at 3000 RPM at 38 and then blip the throttle up from these and make sure it is all in at 3000RPM. And then I would see where it is at ldle (14-16 or so it should be)

If it has killer aftermarket heads it may like less timing, mabe in the low 30s.

[ccracin]

I think Franks got it for you. If it's not all in by 3500 for sure work on it. I like 3000 with good gas, but will take 3500 with crappy gas. My .02. Good Luck.

[Vegas69]

My new engine made the best power at 34. I'd error on the side of caution until you chassis dyno. 34-36 total and you won't burn it up.

[camaro1969]

factory steel heads..

since i have a rowdy cam, should i be idling aroud 18-19 btdc?

When i have it too far advanced, my flexplate kicks back, and has already ruined one starter!

My vacuum advance on my distri is plugged for now, until timed

so at 3000 RPM around 38, i should have an idel around 15?

[Vegas69]

Total timing is your main concern. If it has a vaccum advance, you need to detach it from the distributor and plug in off. You need to rev it until it quits gaining advance. Changes can be made to initial timing if you can't achieve a clean idle or have a stumble. I'd go 34-36. More is not always better.

[ccracin]

Originally Posted by Vegas69

Total timing is your main concern. If it has a vaccum advance, you need to detach it from the distributor and plug in off. You need to rev it until it quits gaining advance. Changes can be made to initial timing if you can't achieve a clean idle or have a stumble. I'd go 34-36. More is not always better.

Amen!

[GregWeld]

Vic ---

They've got it right in the above posts -- except I would ADD some info...

A distributor has "X" amount of advance built into it. Since we don't know what you're using and or whether or not it's been modified etc.... "WE" don't know how much advance your distributor has... or doesn't have.

So setting it at 34* or 36* revving the motor up -- to 2500 or 3000 rpm -- will (should) max out your TOTAL advance (minus the vacuum advance since that is not being used at this point).

Okay -- when you drop her back to idle -- you'll note with your timing light - what that is at.

Lets say your distributor is bone stock - and you set it at 36* per the above instructions.... and at IDLE you're at 10* (so your distributor would have 26* of advance built in)..... well.... that might not be enough advance at idle given your "roudy" cam. I'm going to ASSume that your idle is around 800 rpms... This is just INFO that we need to diagnose and to help you figure out what's going to work for you.

An MSD distributor (I'm using this because I'm familiar with them) has advance "stop bushings" that come with them. I personally use the 18* stop bushing in mine... because that gives me 18* of total advance -- so if I set the engine at 3000 RPMs -- at 36* -- then my IDLE is going to be 18* less than that - or idle timing of 18* and that works well with a roudy cam.

NOW ---- there is also the RATE of advance.... and you can build yourself a little chart using a piece of paper showing you the RATE of advance that your distributor has:

Starting at idle - write down the advance
Bump the motor up 500 RPM - check the timing and write that down
Ditto - another 500 RPM - make note of the timing
Go 500 RPMs at a time -- until you've reached the MAXIMUM timing

This is all easiest using a DIAL BACK timing light....

Now with your "chart" you just built - you can see the rate of advance.... This is important because it has a lot to do with how the motor will perform... not fast enough rate and the motor is a dog -- too fast and she'll ping...

MSD's come with different springs -- and they have various charts showing different rates of advance -- you choose a "rate" based on your info of the car - and use the combo of springs in the chart that matches your application. It ain't rocket science and you can get 'er pretty close using some common sense and "our" help.... there's lots of guys on here with the experience to get you going right.

If you have a stock distributor -- posting up your "RATE" of advance -- Your total timing - and your idle timing ---- "we" can look at those results and help to guide you how to best proceed.

But for right now - the total timing has to be set -- because you can damage an engine with too much timing (or too little but too much is worse)... So go do your work and post up the results.... and we'll all be able to see what's going on.

[Vegas69]

I wouldn't be in a hurry to get rid of a vaccum advance. They work great for extra timing and efficiency at cruise. Greg is right, more initial is normally a good thing to increase carb signal. I have a custom bushing in my MSD that nets me 23 degrees initial. That cam doesn't look roudy enough to be a concern. I'd say you have really good engine vaccum and most of this talk should go in one ear and out the other.

[GregWeld]

Todd --

You're right on the cam. I used his description on the "roudy" part... 'cause a XE268 ain't roudy...

But Vic has had "issues" with this motor all the way thru -- or I should say - starter issues and getting this thing running...

Half the time I've helped someone - they've gotten a motor from somewhere - and they really don't know where the balancer came from (what it's off of) - or the timing cover... whether it's been checked against TDC... and they've no idea what the distributor is out of. Could be out of a truck for all they know... so this is the routine I go thru when things are "unknown".

Just had this with a buddy here - couple drunks put a "motor" in - he had more issues than you could write about. Bet he spent 1500 bucks on "tune ups" - and it just was a dog. I finally asked him if ANYONE had actually checked to see if the timing marks everyone was using were indeed what they said they were. They were off about 8*.

I had to do the old --- pull all the plugs -- put in a piston stop. Roll her forward make a mark - roll her back - make a mark - in the middle is 0*...
WAY OFF... Woke the old pig right up getting the timing where it was supposed to be.