DucatiDon

After a year and a half of fiddling, I am ready to begin tuning my 383 for best performance.

As a refresher, Its a .040 bore 3.75 6" rod 388. 11:1 (10.8 actually I believe) AFR aluminum 195 Eliminators. 237/237 .560/.560 110 roller cam with 1.6 rockers. (.590 total lift). Z28 intake, Holley 750 vac (3310) with mildly ported factory 2.5" exhaust manifolds and true duals. Car is about 3200 lbs with a 5spd and 3.73s. Its in a 63 vette.

Timing is currently set at 10* initial and 26* with mechanical.
I have about 17" of vacuum at idle.
I have a B2 advance can, but don't believe its providing any advance at idle.

The car runs fine as it sits. Spark plugs are nice and toasty brown.

It has tons of torque, but perhaps the throttle response could be crisper?!

Where to start? Timing advance? Jetting?

7T1vette

Save yourself a lot of varying opinions. Send an e-mail to Lars Grimsrud at V8FastCars@msn.com and ask him the same questions. He is an expert tuner of engines and has intimate knowledge on carb tuning. I think he will advise you well to get the most out of your setup.

C3 Stroker

I'd nail down the timing first. Your 383 is similar to the one I had. Mine ran best with 36° total @ 2500 rpm. Dist. was recurved for 14° initial advance with 22° mechanical. Once you're satisfied with your timing, then move to the carb.

drwet

What he said.

DucatiDon

OK. That's my game plan.

calwldlife

6 inches of vacuum?

DucatiDon

Fixed

calwldlife

17, ok that is healthy and very easy to tune

what symptoms are you having. you say it runs good
nice plugs.

DucatiDon

Current timing specs:

12* idle
+24* mech
= 36* total all in by 2500

Vac can B28 which should give me +16 (but is limited by the adj plate to 14* I think...Ill have to double check it)

DucatiDon

Nothing specific. "maybe" could have crisper throttle response.

It could be the characteristics of a vac secondary carb vs a double pumper as well. Nothing a slip of the clutch cant alleviate for tire spinning grins.

calwldlife

hmmm.
at 36 and have another 14 at cruise for 50?
are you pinging?
i know the general thinking is all mechanical in by 2500.
i still have not seen you write anything about
what the motor is doing and what you would like it to do?

lars

With that cam, I would shorten the centrifugal curve from 24 to about 18 degrees so you can run about 18 degrees initial (which will still get you the desired 36 total at 2500 - 2800). This will improve your off-idle and low rpm throttle response, as well as improving your idle quality. I would also install a limiter plate on the vacuum advance to limit it to 10 - 12 crankshaft degrees of advance - e-mail me if you need info on that.

Lars

resdoggie

Lars has given you a starting point but for best performance tuning I would install an afr sensor/gauge and a programmable distributor. This will allow for easier adjustment for retarding mech'l advance and increasing initial advance. I think your initial will end up around 20* give or take a degree or few to get best performance that you seek. Also, try a timing curve with 32-34* total in the range of 2500-3000 rpm.

lars

I agree that the total timing with your heads should be about 32 - 34, not the conventional 36. I just reread your engine specs, and those AFR heads will need less than 36 total.

DucatiDon

I have the vac adv limiter plate.
The task before me is to try to limit the mech advance and increase initial.

Fun fun.

gkull

Modern chamber designs and higher compression create very high pressures with all in mechanical advance at sub 3000 rpm. The so called gurus that tell you all in at 2500 are old lost in the 70's smog motor sub 9 to 1 compression era.


Like other said 18 - 20 initial and max at near 32 especially since you are right at sea level and California 91 max unleaded.

I really don't believe or have not seen a dual plane intake manifold that has the same port size and AFR 195 heads. The mismatch will cause port velocity and fuel atomization problems.