Mine is around 11:1 in my 383. Right now I have a HEI and the Hyfire VI Digital Multi-Strike Ignition Control. My vacuum to the advance is running ported (above throttle plates). This is how it was setup when I got the car. I believe when I changed it to direct it got worse, however I'm not 100% sure.

I'm really at a loss now as to what I can do to fix this. I guess I can buy a MSD setup since everyone thinks that will fix it, but I hate to spend that kind of money when I have the Hyfire already in there.
defsegx2008-02-03 11:17:05

Ok, I got out there tonight and was tested the vac can on the dist. It looks like it's providing about 25 degrees. It is on ported if that matters, but that's what I've come up with using a vac gauge.

From what I've been reading (like on http://www.corvetteactioncenter.com/forums/showthread.php?t=113) that is WAY too much for what I have. With 16 initial, 20-22 from the centrifugal, and then another 25 from the vac that means I'm running about 61 under full load. Does that seem like way too much to anyone?

Like I said, it's hooked up ported, and this problem usually only happens when I'm in 4th and the TC is locked, and I try to give it gas at lower speeds. This puts a lot of load on the engine.

I disconnected the vac can from the carb completely (eliminating the vac advance from the system totally) and it seems like the car is making more power as well, but I'm told this is bad to do because of fuel economy/etc.

So C3VR, what next

If 61 is indeed way too much, especially with my 11:1 compression, should I just buy another vac can and try that? Would changing the vac advance to full manifold help at all?

Thanks a ton
-Josh


Edit: I just took it for a drive on the highway. With the vac can disconnected, I think the pinging is just as bad if not worse than before. I'm totally lost


defsegx2008-02-03 19:19:50

The first thing I would do is verify the timing mark is actually at TDC.  Then I would check the air fuel mixture.  If your headers are glowing, you must be running pretty lean, or are dumping still-burning fuel into the headers.  When you increase airflow through an engine, you usually need to fatten the mixture several jet sizes. 

Independent dyno tests have shown that you don't make any more horsepower with replacement distributors.  The factory unit works just fine up to at least 6,000 RPM.  You tune for power without vacuum advance, then adding vacuum advance improves mileage and cooling while cruising.  Joel is right that when your timing is advanced at cruising, stabbing the throttle will remove vacuum and therefore retard the timing back to what you had it set mechanically.

As far as your lock-up converter lugging the engine, there are kits to control the lock-up by vacuum, or by RPMs, or by throttle position.  You can decide which probably works best for you.

Ok I think I have it mostly figured out. Spent like 4 hours in the parking lot today with a vacuum gauge, timing light, and spring kit.

I have been running gold+gold in my dist for a while (kit is gold/silver/black). I don't know why I never thought about it before, but gold+gold makes my timing coming in early. Early is where I was having problems with being too lean and pinging like marbles in a coffee can. I changed one to silver, and set the timing back to 12deg BTDC and viola, no pinging.

I still need to get a new vac advance, 24 degrees of advance from the can is WAY too much. I am going to buy an adjustable one (tried today, nobody carries them locally ugh). Then I will adjust it down to like 14-16, and I should be able to advance my BTDC to ~16 without pining (I hope).

This is still all running ported manifold btw. I tried full manifold and it ran like butt, I had to retard the timing to almost 0 to get it to not idle 1k RPM.


I'll let you guys know what happens when I get in the new can.

-Josh

Cool! My mechanic buddy was telling me that some like ported and some like manifold seems like it's trial and error to figure out what works best. I'm glad to hear you made progress  79rebuild2008-02-04 21:51:24