The CORRECT WAY to check timing for a mild sbc street motor that has a perf cam like he stated is to not just set the timing for total forgetting about the base timing which isa big mistake/oversite.
Thats an old racers way of checking timing where the motor is not normally run in lower rpms below 3k rpm like a street motor often see's which almost always results in retartded base timing which is esp an issue when running a mild or hot perf cam. Its also what people do when they either dont know how to properly setup a street perf ign timing curve for a street perf motor and or dont want to bother doing it right in the 1st place because it takes more effort.
Significantly retarded base timing results in lost power/poor throttle repsonce-lazy feeling motor off idle and at lower rpms below when total is fully in/poor fuel economy/hotter running motor in traffic /etc with a street motor. Thats not near as important for a strip and or dirt track race motor that doesnt normally operate/spend much time below the rpm where the total timing is all in so the base timing but for a street perf motor its very important.
For example ,if setting timng for total only at 36 deg along with running like in this case where he's running an HEI ign/dist that can often have 28 sometimes 30 deg mech in them from GM the result is:
36 total - 28-30 deg mech = 6-8 deg base timing when on avg aftermarket perf cams need approx 16-18 deg base timng . So that leave's the base timing woefully retarded by up to 10 -12 deg which is horrible for perf esp when below approx 3k rpms befor full total is in & the motor will feel & perf like a slug off idle and in lower range rpms.
So with that said you should be running approx 16-18 deg base timing with a mild to moderate aftermarket perf cam in a sbc along with 20 deg mech all in by approx 2,800 rpms.
Then 16-18 deg base timing + 20 deg mech in by 2800rpms = 36-38 total all in by 2800rpms which will have the motors throttle responce much crsiper/stronger esp off idle and at lower to mid range engine rpms.
For street you also need a vac adv hooked to full to full vacuum all the time that give an additional 12-14 deg timing max or install a vac adv limiter plate to limit the vac adv travel to 12-14 deg max. It also needs to be fully activated at 2" below the lowest idle vacuum in gear with auto trans .
dont forget to set idle low like 600-650rpm max when checking/setting base timing to ensure mech adv isnt partially activated while setting base timing . Vac adv also needs to be unhooked & plugged to when checking base and or total timing.
Then post timing adj reattach vac adv amd then also reset idle minxture & idle speed.
There are people that can setup the mech & vac adv in the dist proerly like i suggest so that what when you get it back all you need to do is set timing for 16-18 base ,hook vac adv to full intake vacuum ,reset idle mixture & speed ,and then your god to go.
You should run 93 fuel to avpoid detoantion when setting this ign curve up and only try ower grade 91 then 89 fuel only if the 93 fuel doesnt detonate .
Good luck.
Scott
