General Category > Quadrajet Carb Talk and Tips

APT adjustment

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Kenth:
350 cui, 9.8:1 CR, 110LSA, 239°/241° @ .050" and only 2000 rpm´s up a steep hill is a fine recipe for ping.

Shift gear and run engine at least at 3500 rpm´s up the hill would place the cam in it´s working range and reduce ping.

JMHO

Cliff Ruggles:
Kenth is correct.  Even though a 239/241 @ .050" cam looks pretty "big" in a 350 build the effective duration is considerably less with flat solid cams.  The "rule of thumb" used to be about 10 degrees @ .050".  The testing I've done shows it to be closer to 15 degrees but will vary some depending on who ground the cam and what lash/ramp they used. 

I'd also add that tight LSA also narrows up the power curve and spikes dynamic compression higher, plus earlier in the RPM range.  So the "recipe" for ping at lower RPM's is certainly there for sure.......IMHO....

jagness:
Yes, I have the cam lashed at .017/.019 (Engle recommends .018/.020) hot because I knew it would be a lot milder than a hydraulic cam with the same numbers.

I just ordered a small cap Progression Ignition distributor. They give you the ability to create timing maps with a smart phone. It has vacuum input, which can also be used as a boost reference. I can let you all know how well it works. I‘be heard good reports so far, and it’s an American company.

We live in rural northeastern Oklahoma with very curvey, steep hills. In some places, it’s easy to kick it down a gear, but it breaks the 275/60 15s loose really easily. So I usually have to kick it down and then quickly feather the throttle. This engine is amazingly responsive, so the carb is working well.

Kenth:
Don´t you have a gear shifter lever for your 200-4R?

Cliff Ruggles:
I've heard good things about those distributors as well.

Even so I've been doing this sort of thing over 40 years and 20 of it full time.  Without exception every single "bug zapping" distributor, module, electronic "conversion" or other aftermarket ignition device that I have used or tested here has eventually failed. 

They will NEVER fail when you are sitting in front of Jegs or Summit Racing, so plan accordingly.

In contrast stock points and HEI distributors have been dead solid reliable and failures are as rare as winning lottery tickets.  There is also not one ounce of power waiting for you IF you know how to tune the stock parts for the engine combination.

I remember decades ago my first experience with an MSD billet distributor.  A good friend of mine broke open his piggy bank to buy one to "upgrade" the stock points distributor we set-up for his race car.  Set to the exact same total timing the car slowed down at the track.  Yes, it ran about .02-03 seconds slower and fell off a little in MPH as well.  We were shocked and couldn't figure it out.  I checked the timing with the engine revved up again and again, but it still ran slower.  An "old timer" at the track overheard our frustrations and walked over and told us that the points distributor by design has a natural timing retard function at high RPM's and it's not uncommon to see a little more performance when using one compared to an electronic unit.

Hum?  I've also back to back dyno tested a factory HEI against an MSD billet distributor with 6AL box and the HEI made more power at every RPM.  Not much, but it was a tad more, not LESS as we are told in all the very well written advertising they do for their products.........FWIW.......Cliff

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