Just wondering if it sounds like I have to much Maximum Spark Advance..My mods are in my sig. I had a piston break after the car was dyno tuned, just after an engine build..It came apart for about 1 1/2 x 3/8 along the outer top edge of the #4 piston. I was on Keith Blacks web site and it seems that this could have been cause by an improper ring gap and the pic of the broken piston on there site looks EXACTLY like my bad KB piston.. I had another friend tell me he thinks I have to much "Maxium Spark Advance"-it's set to 43.95..Is this dangeriously high??? I keep hearing you should never go over 40??Whats the stock setting for Max Spark Adv?? My base timing is set for 17.93

 

What are you using to tune, I mean where / what RPM ranges are your highest SA values, and what are they? What's your engine compression? IMO 43 degrees is pretty high. Also curious, what was your ring gap, do you know?

 

well I had takin it to a speed shop and had it tuned on a Dyno Jet dyno...So he tuned it...as far as compression I have brodix 200 Ik heads 64cc and Flat top KB Pistons... Someone told me that makes 11.4-1 but that seems high.. I have no Idea on the ring gap

 

I'd ask whomever the tech was at the dyno, if you didn't pay for tuning, then they didn't do any. If they did, I'd want to know from them, what they used to tune (software), what they set the tables too for spark advance. 11.4:1 isn't high depending on what your intentions were for the car but in case you don't know, stockish compression is around 9.75:1. I'd really recommend talking to whomever built your engine if you didn't and get some info from them. When I've had engines built in the past for me I'd know everything right down to the guys kids names, LOL.

If you did the buid, there's plenty of calculators out there on the web that will give you a decent approximation when you enter gasket thickness, deck height, stroke, etc. Those are all numbers you should be able to get from the different part manufactures.

FYI, a good performance gap guideline is bore dia X .0045"

 

sorry forgot to say it was tuned via The Prominator/tunerProRT

 

so if I'm running 18* base timing and 44 maximum spark advance does that mean my total timing is 62*? think I read some where that u add them together to get total timing??? I also read that u shouldnt go over 36* total timing in a chevy so whats the deal??..thanks

 

well i just built my own 383 and only has about 13miles onit... i did alot of research on my piston ring gap before i did it myself. KB hyperconetic? if they are hypers then ring gap on those is suppose to be way high. i gapped mine for .020 1st ring and .022 second ring i believe but i was using SRP forged. my gap is alittle large and is specd by SRP/JE for mild nitrous/forced induction. otherwise it would have been .018 1st ring, and .020 second ring.

I read somewhere that KB hypers need alot of gap something like .036 or something insane(call them and ask to be sure). the reason being hypers expand alot more esp the KBs due to the silicone content i thought i read. when the rings arent gapped enough when the rings/pistons heat up the ends will butt together and just destroy the piston/cylinder walls. Forged are wayyy better. If you were still able to pull a piston out i would, pull the top ring and 2nd ring off. space one about 1" into the bore of the cylinder and check ring gap with a feeler gauge. then do the same thing for the other ring. that way u kno for sure incase that was the reason.

other things to consider is your base timing at the engine. 18 is by no means low... my 383 with HSR and XFI280 cam (got some lope to it ) is only set a 8 degrees. most ppl dont go over 12ish. i kno ur cam is not much larger than mine if any and im runnin .576/.571 lift! i would back down ur base timing to like 10. u gotta remember that the ECM can only take off so much timing when it detects detonation.


no it does not add 18 to 44. wat ever is in the timing table is the MAX timing the motor can give. so if u have a value of 44, that means the computer minuses -18 from 44 to be 26, so your ECm will add 26 degrees of timing to get to 44 at that given RPM/LV8. i would back max timing to 43 0r 41 on the BIN. i think mines at like 41.8 or something but 43 wouldnt be to bad, u gotta remember that distributers have a MAX mechanical advance of about 45 degrees. i would also have the tune REDONE! ASAP! max timing will not be 45 or close to that. prob be around 38 or so depending on what the motor likes. also make sure they tune the chip for the BASE timing u set it at. so they have to set the BASE timing in the BIN for 18 if thats what your leaving it at so that way the engine/ECM are on the same page and can make the correct changes.

ive been messing with my timing tables and i think mine is MAX at 37 but it ran fine with like 33/34 max. even tho my MAX timing is set in the BIN at 41.8 total. I for one no longer trust anyone to work on my cars, had my trans rebuilt and the guy didnt increase the clutches in the 3/4 clutch pack so it was stock (which is weakkkkk) and he also put my lockup weather pack connector in wrong so my converter wasnt locking up FOR OVER 2 YEARS!!!! AUGH. i just rebuilt that too and swapped in my fresh rebuilt ford 8.8 by me.

 

Suggested reading:

https://www.thirdgen.org/techbb2/sho...hreadid=317768

RBob.