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Rootsy
07-25-2001, 08:50 AM
All you Chevy guys out there have any opinions on total ignition advance for slightly modified motors? I've always thought that right around 34 or 35 degrees was optimal for a sbc. seeing how the thunderbolt V ignition module on my motor will only give me 30 total by 4200 rpm i'm wondering how much i'm being hurt now that i've added more fuel and valve lift. Do the 98 - 2001 model ignition modules allow for more total advance than the 1996 - 97 210 hp 350 version? anyone have a part number?

Thank ya!

RickR
07-25-2001, 01:28 PM
I do not know what total should be on a SBC. But you can set any total you want. The easiest way is to use a timing light with a manual advance setting.
Of course this will change your initial advance also. Too much initial will make the engine hard to start.
When setting timing on a Thunderbolt V make sure you ground the knock sensor lead (purple/white) on the ignition module..

Rootsy
07-25-2001, 02:18 PM
Rick,

Got the timing thing with the timing light down pat, you can trust me on that one... have an adjustable retard dial on my light. I ground out the knock sensor (put it in base mode, turn key on start motor) and the initial i have set now is 14 degrees. I had it at 10 which is stock and was getting 30 total. Turn it up to 14 and i still get 30 total. Makes me wonder if the circuitry isn't setting advance by rpm regardless of intial timing, ie a preset ignition curve. My first thought was that there would be 20 degrees of advance in the module.. set initial and just stack 20 on top of it to get total. I dont think this is so now that i've played with it some. I could quite possibly be wrong though... when i bought the boat i did notice that someone had probed the tach and knock sensor wires with a test light at one time or another.. but i got no service history with the boat.... i should try the dealer and see if i can get a service record, they probably did the work. PLUS i Figured i'd try to get a hold of a module from a newer engine that has like 24 degrees of advance, i'm sure that stouter motors use different modules than mine. retarded full advance lowers cylinder pressures at high rpm which in turn creates less HP. It'd be nice to just have an infinitely variable setup, i'm just not quite prepared to dish that kinda cash out at the moment.. heck i'd love to do that but if i am gonna i might as well go crank trigger and a 6M-2 Box and a soft touch and keep the stock distributor, it's a tad cheaper but not much.

RickR
07-25-2001, 03:19 PM
Sorry, :confused: I haven't messed with my Thunderbolt V much since soon I'll upgrade to MSD.

Just out of curosity have you checked the timing with 93 octane?

Here is a quote from Bobby Moore's BBC Marine Performance that explains why you are still gitting 30 total.

"Thunderbolt V
Idle speed is maintained by the ignition module at 650 rpm by advancing or retarding the ignition timing. Therefore to adjust the idle mixture screws on the carburator or set the initial ignition timing , a purple/white wire in the ignition wiring harness must be grounede bfore the engine is started. By grounding the wire, the timing will be locked into place. Then the timing is set, the idle mixture screws are adjusted and the idle speed is adjusted to 650 rpm.
When accelerating an engine with Thunderbolt V, the ignition module will advance the timing at different rates depending upon how fast the rpm's are increasing.
At high speed, the Thunderbolt V will search for optimal ignition timing, the ignition module will advance the timing small amounts and wait to see if the rpm's increases, and continue to advance the timing until there is no more increse in rpm. If the ignition module senses an rpm drop, it will retard ignition timing.


He recomends going to a Thunderbolt IV for more control over the timing.

BigGrizzly
07-25-2001, 07:35 PM
The actual correct timing of the engine depends om cam size (lift, lobe center split, advance or retard and duration) compression ratio and carb size. My units range from 30 to 37 deg. In my Corsican each cam had its own timming depending on the advance or retard of the cam. the rest of the engine internals remained un changed.
So play with it untill you get the best results. I would not suggest going past 37 in any case

Randy
Randy

Rootsy
07-25-2001, 09:44 PM
Interesting Rick,

i get that oh so huge income tax check back and maybe i'll plop it down on an msd.. but then again i need a prop... decisions decisions... and all i ever run is 93 Amoco... or Sunoco 94. probably a bit overkill but if ya run something hard the last thing ya want is any spark knock. and i agree with you Randy, just have to play with it til you reach the point where you begin to slow down then back it off. Just have to watch for that Ping. local merc mechanic told me tonight that the Thunderbolt V is capable of 29 degrees total advance.. so who knows... i'll play with it.. we'll see... thanks for the input guys

Classic Razorback
07-25-2001, 10:45 PM
I just put a 502 in my 22 and I am working on that also. I think we need to convert our thunderbolt V back to IV which means remove the detonation sensor from the block and the V modules from the back of the distributor and get the Thunderbolt IV module with the advance curve you want and plug it in.
If you would like a copy of the advance curves and part no.# e-mail me a fax number or give me a call 501 927 9324 or get the HP book BBC MARINE PROFORMANCE by Dennis Moore #1-55788-297-5 this stuff is on page 188.
GREAT BOOK !!!
hope this helps
chris