What is the maximum spark advance one can run on the 496HO and 87 octane before you run into engine knock problems.

Are you experincing a problem that you want to alter your timing?? The 496 is not like the 454/502 set up with the distributor. The 496 uses a crank sensor & Ecm.. Jamie

No, no problems. Just exploring what is available for the 496 to increase HP without doing damage. Looking for peolpe who have already played with timing on the 496 and what they found. Timing is controlled by the PCM555 ECU programing which I believe only Dustin Whipple can alter. He does this in his Stage II kit but that also requires you to run Premium gas. Apparently bore notching of the cylinder walls to match up with the larger perimeter of the combustion chamber can reduce the propensity of the 496 to experience knock as it is pushed harder. But has anyone done this and tested its effects on knock sensitivity with more timing, compression, etc?

You may be better of retrofitting to a Mefi system. There is also a kit that allows you to make changes but also requires an ecm & harness change. I can get it for you or AZ speed can get it for you, but it is expensive!! Jamie / Lakeside

Thanks for the thought but I have cast my lot with the PCM555 and to change to the Mefi system now is essentially out of the question.

I am still interested in feed back as regards to the spark advance tolerance limits of the 496HO

I suspect your answer lies in the kits Dustin offers. He's licensed to mess with the 555 (the only non GM source??) and tests (at a higher level of detail??) as much as if not more than anyone

His stage one kit still runs 87 yet barely has any gains indicating (to me) timing is near optimum/safe for 87. The slightly larger gains with the stage 2 kit running premium would indicate that much of the gain comes from the timing room given by the higher octane.

I can't see the Wisdom of going backwards from the 555- seems like the only people pushing it are those who are not capable of working with the 555

That said- Ray at Raylar should be able to add some wisdom here

I suppose if you had talent, a tolerance for risk, and a techmate you could mechanically alter the crank position sensor mounting to gain a couple degrees run it with the tech mate and look to see if the knock sensor is kicking in???

Thats not entirely true. Whipple & merc are to the best of my memory that can get into & alter the pcm555 Mototron/motorolla unit (at least legaly anyway).. So even if you know what you are doing its still basically a no no.. The Mefi stuff or ingenius stuff lends itself to be manipulated more so than the 555 stuff "currently" does..

can you qualify that a bit? Are you saying it's a no-no cause their are no gains to achieve? Or cause you'll likely screw up a good thing?

The mefi stuff is easier to mess with and more peeps have the ability- that's a given. But unless you are doing major things affecting tuning (blower/cam/heads) why would you need or want to mess with the 555? I can't recall the details but I was under the impression the 555 was monitoring more sensors and providing more data/ safegards to the engine mangement system.

I'm pretty sure Raylar has their system (525 at least) tuned and tested to work with the factory PCM parameters

Its a no no because of it being proprietary software/ecm. Not because there are no benefits or gains to be had. If you took the whole legality issue or proprietarty issue out of the equation its' like this : the right person with the right knowledge could improve on the factory preset parameters, it just isn't going to take it from 425hp to 600hp by reprogramming the ecm. Thats what I am saying. If it was proberly reflashed you would only net a little speed increase, nothing in comparison to major internal reworkings or a supercharger done properly. Yes the pcm555 does monitor a bit more and in my opinion on a stock engine is a better way to fly, its just doesnt lend it self to being as easy to having anything done with it as of yet aftermarket wise.. I am sure it is just a matter of time before they do allow more custom shops the "legal" ability to go in & make changes, it's just gonna be like anythiing else. It's gonna cost.. Jamie

All of Raylar's numbers are propritary so no help there.

I have the Stage 1 from Dustin and the Diacom results indicate ~29* max advance at WOT of 5450rpm though around 3200rpm max timing is ~34*. I do not think this is a change from stock but I could be wrong. The Stage 1 is primarily the rpm increase and A/F optimization.

Maybe a better way to ask my question is "what is the max timing anyone has run with the 496 at WOT and an Mefi system on 87 octane?" Hard to imagine anyone doing the Mefi and still running 87 octane but does not hurt to ask.