71bbc

So I'm getting close to actually drive this thing after 2 years of work and spending a lot of $$$...Using original big block and forged crank, I made a 10.0:1 all forged internals and put a pair of aluminum heads on it and installed this hyd. roller cam:
Duration at 050 inch Lift: 225 int./231 exh.
Advertised Duration: 278 int./284 exh.
Valve Lift with Factory Rocker Arm Ratio: 0.567 int./0.578 exh.
Lobe Separation (degrees): 112

Also reused that torker II intake ( I know, but nothing else clears my hood) was originally on the car and hoped to make some "fair" idle considering that 112 degree LSA. But with my 850 double pumper is asking for initial 20ish degree advance to idle with 13" of Hg. if I lower it to around 15 degree, then It won't be happy and vacuum drops to about 7" of Hg. I checked everything OK 3 times. i just need some input. Is this cam considered big?How this thing suppose to idle? Why is asking for too much initial advance? (has no vac. advance).Is poor idle condition caused by that single plane torker intake or it just normal and I'm expecting too much? Thank you.

zwede

You have enough cam to where it will need some advance at idle. I have a bit bigger cam in my 454 (231/239). I idle it at 27 dgrs. Don't think it will even run at 15.

You really should add vacuum advance. It will let you have enough advance for a good idle without having too much advance for cranking. Vacuum advance will also keep the plugs cleaner.

Grumpy 427

BBC engines tend to like 34-36 degrees total timing,all in by 3000 rpm. My Oval port pump gas 427 made 550 hp and 513 tq had a .585/.585 hyd roller .245/.255 @.050 on a112LSA. Holley strip dominator intake and 850 dbl. Idle was set at around 1000 rpm.

TimAT

I'm running with .671 and 254/260 and LSA 112. I'm slowly working thru the tuneup. 18* initial right now. Every time I change something I bump the timing a bit and it just keeps getting better. 18 is about as far as I can go and stay with a 36* total, so I'm going to have to do a stop bushing.

resdoggie

Your engine likes 20* so let it have 20*. But to tune properly, you need a programmable distributor or modify your existing distributor to restrict the mechanical advance to 16* for an all in at 36*. I originally modified my hei to max out at 12* with a 22* initial. But I wanted to tinker a bit more with the vac adv so I bought a programmable dist'r that allows me to tweak mech'l and vacuum electronically in a matter of seconds. One of the best tuning tools you can buy if anyone is serious about timing/tuning along with an AFR guage.