Total Loss Timing Curve

[springy]

Hi,

I’m looking for some info on timing curves for a total loss ignition system. Before I go any further, I know the general range of values that are safe but these are probably far from ideal. Suffice to say, it’s a freestyle motor running on 95 octane fuel (super unleaded) with the following modifications;

760cc Fully Freestyle Ported (will find out the compression)
48mm Full Spectrum Carbs
Boysen triple stage reeds
ADA Head, squish adjusted for above cc
Total Loss Ignition (obviously)
Factory-B Mod Pipe, bottom and middle closed top open 1.5 turns

I have the ability via a switch on the pole to switch in a second timing curve whilst the engine is running and was speculating that this could help in determining the best freestyle curve. I also understand that the beginning of the curve (low RPM) can be configured to aid starting and the end of the curve (6000 -7000 RPM) can be configured to stop detonation.

Many thanks,

Springy.

 

[Matt_E]

I ran the following very successfully on a similar setup:

29 degrees static
5000 start retard
8000 RPM limit
16 degrees off initial @ limit

 

[springy]

Total Loss

Matt,

Does that mean you run 29 degrees of advance all the way through to 5000 RPM and then start to retard to 16 before 8000 RPM?

Here's what I'm running now;

 

[danjrowan]

you got ure hull yet springy?

 

[springy]

Total Loss

Dan,

Yeah, will post some pics soon. May also see you at Queenford the bank holiday weekend.

Springy.

 

[danjrowan]

wicked, see you soon
Dan

 

[Matt_E]

Matt,

Does that mean you run 29 degrees of advance all the way through to 5000 RPM and then start to retard to 16 before 8000 RPM?

Here's what I'm running now;

It means I run 29 to 5000, then take off 16 degrees gradually, to end at 13 at 8000.

 

[waxhead]

33 degrees till 4500 and pull it out till you have about 17 at 7300

 

[QJS]

For flatwater riders, if you put a tacho on your ski then go set up a wake and see how many revs you are doing as you launch off the wake, this is hard but you don't have to roll it or flip it just pretend. Chances are if your running a freestyle prop you will be doing more than 5000 rpm so if you are backing off the timing at 5000rpm you are loosing hit. I hold max advance till 5750 with no problems as long as you back it off quick from there, this gives a better kick off the wake.
Chris.

 

[Crab]

33 degrees till 4500 and pull it out till you have about 17 at 7300

Wax, how much can you get away with on a K750 with 170 psi cold?

 

[waxhead]

qjs your right

my ski is a race ski with a type 9 so its dynamic pressure is higher once the pipe starts to work

If i run any higher than 4500 i start to lossen plugs and blow o- rings

Crab
on an sxr with 200 psi

we were running 36 down low and pulling it off at 4500 to 15 at 7000 and then kicking some back in at 7300 to help it rev on more

this was a missle but it was a race boat as well

 

[D-Roc]

33 degrees till 4500 and pull it out till you have about 17 at 7300

Wax, after pulling timing down to 17 @ 7000ish do you keep pulling more timing until the max rev limit or do you flatten out at 17 until you hit the rev limit.

i want to run this:
30 static
5500 start retard
8500 rev limit
17 degree at 7000

to get the timing down to 17 at 7000 its calculating to remove 26 degrees of timing at the 8500 rev limit which only leaves 4 degrees when its hitting the rev limiter. is that safe? also when you set the max speed retard it lists 0-15 degrees. is that degress that are taken from static (you could take 0-15 degrees off 30) or is it the actual degrees timing it will have at the max rev limit? (0-15 at 8500) i haven't setup a tl in along time and want to make sure i am understanding what it is i am doing when i flick switches.

 

[masterblaster]

id also like to know the answer to the above ? In reference to what qjs was saying,would it be alright to run a max advance of say 33 to 5750 and then pull it down fast to 15 or so in the top end for surf riding.
The curve some of us were running with the advent on 701-6 that fitzgerald did for limited pump gas was 36 to 5000 ....28 to 5500 and 21 to 5750 continually droped to 14 from 6500 on? any opinions on running something like this with msd tl

 

[waxhead]

I wouldnt keep the timing in for that long its a sure way to a melt down.
I always take it out about 4500-5000
after the pipe stops pulling about 7000 on a limited I start bringing the timing back in it helps them rev on.

 

[masterblaster]

Wax,that makes since for running bouys,but how bout brap brap on off throttle low speed surf riding?Seems Chris had a good point there?Totally diff kinda riding.only down side is the boat is one dimensional if you ever go to flat water and wana do some speed runs.thats where the epic sounds good to me being able to have 2 curves to run on a single switch.

 

[waxhead]

thats what i put om the freeride boats i build
I dont build race boats anymore
two curves you can switch is no good as it changes the mixture requirements of the engine

 

[QJS]

In 2006 the world amateur freestyle was won with one of our ignitions with 36* of advance up to 5750rpm. This ski was run for months like this without any problems what so ever. There are countless others out there and I can honestly say I have not seen any deto or melt down problems, these are all with B Pipes.
Chris.

 

[QJS]

As for switching between two curves, this can be used for many purposes, we have riders that simply want a lower rev limit and people who make subtle changes to see which curve works best for them. For example Spencer Wells found that by lowering the maximum advance on a 10mm stroker slightly he did infact gain more power, this conclusion was arrived at by switching between curves while riding.
If you have to go back to the workshop to change things you won't notice subtle changes and nobody has mentioned a problem with carbs when switching between two curves but I suppose it depends how extream the two curves are.
Chris.

 

[waxhead]

If you change between curves you will find your mixture requirements change, yes i have set a boat up with two curves the same and used one as a lower rev limiter to help get it off the line

I'm happy you have been able to hold that high advance up that high
I would never do it the dynamic compression of the engine at that rpm would be getting very high

Personally i never use seat of pants to check i always use a tacho when it comes to setting max adavance up top.

The reason the stroker made more power is because of a longer rod giving it more dwell time , but no one runs the same timing in a long rod stroker than they do in a stock stroke engine

 

[masterblaster]

Tach tuning for advance isnt gonna make much diff for low end power and response.A dyno curve would be best,but these days that seems like the most illusive thing in the sport.and if anyone ever does dyno it,always hush hush.So arm hanking meter is the next best thing.

speaking of long rod strokers,if you had say 134 long rods on a 5 mill with the longer tdc dwell,what kinda advance to what rpm is best? Chris I was thinking of running the epic on this above setup once fox tests it with his rad fw... if it works im on it