Hello guys!

Having a bit of trouble here. My 454 c3 ran good over summer, then over night it had a different tone to the engine and when driving it, i noticed the engine characteristic were completely different.

As i went on troubleshooting, i found out that the clamp that holds the distributor housing were really crooked, and i believe this caused the ignition timing to change radically by the movement from the engine.

The engine should deliver 500-550(with headers and aftermarket intake) and is as said 454 cui with an hydraulic roller cam, forged pistons and some stuff including 9:5 compression ratio. I am running with original exhaust manifold (will put 2 1/8 headers on it) and 2:79 rear axle ratio. XR288HR-10 is the name of the camshaft - (see below)

Duration @ 0.050": 236° / 242°
Lobe Separation: 110°
Intake Centerline: 106°

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Questions:

1. How much timing should a mild/high performance 454 have? Something tells me about 12° advance idle and 36° advanced total. Am I completely off with these numbers?

2. How does one set two different idles (idle and total) with only two options to rotate the distributor housing? Do you guys know what i mean?

If i am correct, i could set the idle by two ways. I either let it idle and adjust the housing so that the timing gun strobes at 12° advance, or i could idle up to 3500-4000rpm and set the timing there at 36°? How can i regulate both idle and total timing when rotating the housing affects them both?

3. What is all this about vacuum advance? I dont seem to have any vacuum advance thing on my distributor, and i use a Holley 4DI Projection TBI which i dont know much about, should i ignore all this about plugging the vacuum advance if i dont seem to have any of that on my distributor?

Thanks guys, i really hope some kind soul out there could help me out with this one.

 

this should clear it all up for you, it's quite a read but well worth the time.
http://forums.corvetteforum.com/c3-t...long-post.html

 

Thanks for the link, should have used the search function before posting.

I think i know what do to now, but i have one question that i cant find the answer for. I dont seem to have any vacuum advance thing on my distributor, i took this picture to know what way the rotor was pointed at when taking it off. Should i ignore all this about vacuum advance?

 

I don't recognize that distributor, not stock, maybe some one else will be able to help. Are there any numbers or brand name on it that will help to identify it.

 

I think the DI version of the Holly system controls spark timing with the ECM. Check your documentation for the unit. You would still have to set the initial timing of the distributor. A new rotor and probably cap is called for after seeing all of the carbon on your rotor.

 

With the Holley fuel injection, did it come with a complete distributor and ignition? Not sure what distributor that is but if it doesn't have a mechanical centrifugal advance, that will be built into the electronics as well as the vacuum advance.
Btw, if centrifugal and vacuum advance is controlled by the ecu, the procedure to set timing in the link is unlikely to work.

 

1. You have an ECU-controlled aftermarket distributor, so you cannot set up for total timing. Set the distributor for initial timing per the manufacturer's setup instructions and then use your laptop to set up the ignition map in the ECU.

2. Don't use any of my papers that are posted anywhere on the Internet, including on this Forum. Posted papers are obsolete and outdated, and should not be used. If you need any of my papers, e-mail me directly so you receive and use current data and information - the stuff posted in the referenced post is years old, and completely outdated. You cannot use my timing papers for your setup, however - it does not apply.

Lars
V8FastCars@msn.com

 

Right, I havent been online for quite a while so i havent been able to check my responses on this thread.

Thanks for them, though. When buying this car i recieved an old laptop with the mapping software installed, and i have floppydisks supporting my injection system so i will take a look on that.

I will first off need to lower my idle since it is way high and i cant set any proper initial timing with this high idle. Do you guys think this is done by a computer or a screw on my throttlebody?

I´ll take some time reading through the instructions for my injection system.