Id like to get some Expert advice on this issue,rather than wearing my car out on the dyno experimenting,with base timing changes.
I remember that Ski posted that the correct total advance made a 6mph difference on his SuperRam set up thur the 1/41

 

Going off of memory, I believe it is 36° total.

 

It will be different on EVERY engine combination/mileage and condition.

heck with my original heads I ran 50-52degrees total without detonation. Can only get by with about 44with the new heads/compression.

 

Ski

would you share your experience on this,with us?

 

Every engine combo is different. The main issue is chamber design and static compressio ratio. An engine with more compression typically does not need as much lead as a engine with with less compression. I just tuned a 440 inch SBC and total timing on that engine was set at 36 degrees. That engine has a 13:1 compression ratio, and as logic would have dictated I would have set the timing to 32 or 34 degrees. But in this case this engine liked 36. If this engine had different heads with say a GM fast burn head rather the AFRs that are on it. I would think that the advance would be no more than 34 degrees.

Some lower compression engines would take about 38 to 40 degrees of lead. So its really dependent on your engine combination. 36 degrees is a good starting point however if your engine is prone to detonation I would start with more conservative numbers. I was working on a 426 SBC with individual stack EFI and brodix heads. His combo involves a large road race cam profile with 265+ duration at .050 and .730" lift This engine is controlled by a GM MEFI4 controller which is the same as what is controlling the RAMJET series GM Crate engines. This 427 is tuned on the conservative side with a total timing set at 30 degrees. His static compression on this engine is at 10.5:1. Even with this rather mild timing map, this engine made nearly 700hp on the engine dyno at 6500 RPM

 

Every engine is going to be different in some way. Don't ever ever ever take a # for granted unless you're talking about stock engines (even then be careful) or else you could end up with a big repair big.

 

snake.

Yes timing plays a HUGE role from what I have seen in these EFI cars. In every setup I have track tested the timing made more effect, in small incriments, than anything else.

I would suggest that you get to the track or the dyno and get a baseline at 4* base timing, depending on what your total timing is set at???? Is it stock tune or aftermarket? Do you know what the total timing is.

Anyways, I would start out low at 4* base, then incriment up in 2* incriments until the power falls off or the MPH drops back, then back it up to the best position.

I played with my 406 on the dyno and knew ahead of time from track testing - that the timing was dead on. I mainly went to the dyno to see what my AFR was before I got a WB02 - and moving the AFR from 10.5 to 13.5 yielded only 12.5hp difference. During that time if I moved the timing at all, from the position I had it at, the car would drop off 40hp! At the trach it would loose as much as 6 mph.

My 434, exhibits basically the same behavior.

 

Are you guys talking about total timing at WOT? Or at cruising speeds?

 

I realise different combinations require different WOT advance,
My question was based on My Combo as outlined in my question.
Ski,s response is for a very similar combo.
I have owned a Jim Formato chip since 1993 & Ive had Diacom since then.I used to talk with him alot,(he knew every little nuance about TPI
setups)having take a stock 1985 from a 15.0 performer to a 420 MiniRam mid 10 car,with ac driving back & for to the strip.
I noted that he programmed in 32 degrees WOT( 350,383,406 )on my chip.
He remarked to me one day that he had just finished,tuning a JL
420 SuperRam that only needed 26 degrees to "pull your ears off".
Currently my chips have either 36 or 34 @wot,LESS,what the knock
retard pulls out,which makes hard for me to determine what "It Wants"
I have found it difficult to (quickly) advance & retard basetiming on the Dyno. Does anyone have a shortcut for that?

Mike