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Author Topic:   SBC engine timing
sledgehammer
Dirt Roller

Total posts: 8
posted March 10, 2003 10:23 PM
I am running a hobby stock with the 9:1 compression. The cam I have has 249 duration at .050 and 508 lift on both sides. Also a rochester 2bbl carburetor. The cam was advanced 4 degrees when installed. What would the best timing be for this setup. Also the track I run on is a 1/4 mile tacky early in the year and semi dry slick as the year goes on.

Thanks

JMillerJr76
Dirt Full Roller

Total posts: 62
posted March 10, 2003 10:35 PM
If it is gas, I wouldnt go over 36*, if it is an alky motor we have run them up all the way to 39* with out a problem, our modifed motors performed best on the dyno at 36*

racer17j
Dirt Forum Champ
Total posts: 1565
posted March 11, 2003 12:34 AM UIN: 54865418
try starting out at 34 and go up or down as needed i but like 76 said 36 would be the max i would run

outlawstock17
Dirt Forum Champ
Total posts: 620
posted March 11, 2003 06:10 AM
timing is determined by the heads you are using. less efficient chambers and port layout require more timing. i used to run 38-40 degrees with my old '69 351w castings. with my new svo "n" heads, 28-30 degrees is all they need. most small block chevrolets with factory heads should be around 32-36 as the others have suggested.

[This message has been edited by outlawstock17 (edited March 11, 2003).]

iowa_dirt_track_girl
Dirt Full Roller

Total posts: 74
posted March 13, 2003 07:13 PM
I almost know what type of motor combanation you are running 35 degrees is excellent for a 9:1 motor it gives it a little longer to compress before detanation sometimes on a heavy track ill make more horsepower at 34 degrees that i will at 36 because of the compression and limited intake on a two barrel setup.

Flatlander
Dirt Freak

Total posts: 310
posted March 14, 2003 12:31 AM
Once again I agree with 17j but I will say if you're not sure make therror to the low side it maylose a lttle ump but it won't puke it guts out on you exper. is the key the more you fool with the better you'll get at knowing what you need

sjakes
Dirt Roller

Total posts: 14
posted March 23, 2003 09:01 AM
When do you set your timing. I heard some set it at idle some set it at a higher rpm? What do you suggest?


racer17j
Dirt Forum Champ
Total posts: 1565
posted March 23, 2003 09:19 AM UIN: 54865418
depends on your set up mine i set at idle becuase i have a welded distributer so it will never change if you have the weights on it still you need to get it up to the advance rpm or it will change from what you set it at so 34 at idle might end up being 38 after advance

BK19
Dirt Freak

Total posts: 285
posted March 23, 2003 10:59 AM UIN: 40696038
i agree with iowa_dirt_track_girl had a motor real close to that and 35 worked the best

sjakes8
Dirt Roller

Total posts: 7
posted March 24, 2003 07:12 AM
Ok, how about this, I have a lock up plate(jr motorsports one) on the distributor, but the weights/springs are still on distributor. Even with the springs etc. on, it should be locked so there should be no advance happening right??

[This message has been edited by sjakes8 (edited March 24, 2003).]

rico 08
Dirt Freak

Total posts: 372
posted March 24, 2003 07:23 PM
The lock plate you described is only for the vacuum advance,the centrifugal advance part (weights/springs)means you will have to bring the motor up to at least 3500 rpm to set the total timing(or at least until it quits advancing).

shadowz
Dirt Full Roller

Total posts: 50
posted March 25, 2003 09:06 PM
how can a person tell when full advance in meet?

SLEEPY GOMEZ
Dirt Maniac

Total posts: 199
posted March 25, 2003 10:33 PM
Just curious here - has anybody ever checked the accuracy of their timing light other than comparing it to another?

Racer17J, PM me with your tel or e-mail, SLEEPY

martnracn_91
Dirt Forum Racer

Total posts: 80
posted March 25, 2003 11:13 PM
No i haven't SLEEPY. Could u explain?

SLEEPY GOMEZ
Dirt Maniac

Total posts: 199
posted March 26, 2003 10:48 PM
I'm working on a simple way to check timing lights but I haven't done the testing yet. You will see it in SCR when I do. Like torque wrenches, I just can't believe timing lights are and stay accurate forever. So far I have found this much: If a timing light is off it will show slow since it cannot anticipate a spark event. Dial back types cannot be as accurate as factory set types. The dial is too small and setting it to an exact degree is difficult to say the least. I'll make some one a deal on a dial back light. It has quit registering above 1800 rpm, I wonder how accurate it is at idle now that I know some of the electronics have gone to visit the great micro chip in the sky! SLEEPY

istock59
Dirt Freak

Total posts: 237
posted March 27, 2003 08:16 AM
Here's how I double check the advance knob of my timing light (Craftsman, I think). Way back when I assembled the motor, I hacksawed another small mark in the harmonic balancer at where 35 degree advance would be. I think Jammin has a tool in the toolbox to help determine the distance from TDC mark. I also paint this mark a different color than the TDC mark, so not to get them confused.

So when I set my timing at 35 degrees, I check it with the TDC mark using the advance dial on the timing light. And then I dial the timing light back to zero, and I should see my second mark on the balancer show up on the timing tab. I also have a second, non-advance style of timing light that I can triple check on occasion.

Of course, that doesn't check that the actual electronics of the light are working properly. But it does tell you if the advance knob circuits are.

SLEEPY GOMEZ
Dirt Maniac

Total posts: 199
posted March 27, 2003 09:30 PM
Good idea, Istock 59. Problem I see on the dial back light is that the printed mark on the dial is about 3 degrees wide. SLEEPY

racer17j
Dirt Forum Champ
Total posts: 1565
posted March 27, 2003 11:29 PM UIN: 54865418
i did the same thing 59 ours is older than i am so i was kinda worried but worked out great

2nd2none
Dirt Freak

Total posts: 368
posted March 28, 2003 11:36 AM
My engine builder does the same thing to my engines, marks the balancer at 36* and zero. Helps double check the light!


RangeRover
Dirt Maniac

Total posts: 174
posted March 28, 2003 12:27 PM
All of the above is assuming that the timing pointer is in the dead nuts TDC, right? How accurate have you guys found the little chrome bolt on jobs that attach to the timing chain cover to be? I try to stay with the covers that have the pointer welded on from the factory. I guess you can find TDC and tweak the pointer if necessary, huh?

Rick D
Dirt Roller

Total posts: 25
posted March 28, 2003 02:51 PM
quote:
Originally posted by RangeRover:
All of the above is assuming that the timing pointer is in the dead nuts TDC, right? How accurate have you guys found the little chrome bolt on jobs that attach to the timing chain cover to be? I try to stay with the covers that have the pointer welded on from the factory. I guess you can find TDC and tweak the pointer if necessary, huh?

after a few unexplained piston meltdowns I check the crank pointer everytime I build. Most are fine, a few have been off 6 degrees. I also mark the balancer at 34 degrees to double check my advancing timing light.


racer17j
Dirt Forum Champ
Total posts: 1565
posted March 28, 2003 04:14 PM UIN: 54865418
thats another little trick i do is mark the pointer so i know it's dead on

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