Mopar Muscle Association UK

Good evening all

I'm after some thoughs on running locked out timing on a street car that gets occasional strip action.

I was playing around with today, trying to advance until I find the point the starter kicked back (to establish how much initial the combo can take and improve idle vacuum)and to my surprise this seems to be ~50' advance!

I'm currently running the usual 18' advance stop and got it set to 20 initial giving 38' full.

As the combination seems to like timing, is it worth me just locking out at 36/38' and seeing how it goes?
I can machine some bushings that have less advance but going by the numbers locking it out may work.
It seemed much happier with more advanced at Idle with better vacuum at around 15 and better afr reading though I know afr is never accurate at Idle with a cam like this.
Idle at 1000 or a nats under.

Combination is
440
+030 six pack forged pistons
Crower mechanical level 4 cam (INT/EXH - Dur @ .050” Lift: 236°/246)
10.1 CR ish
Ported 906 heads
Hedman headers
750 holley vac secondary. Set up with the transfer slot square and opening the secondary stop a bit to help idle rpm.
12" vac at Idle
Msd digital 6al
Msd coil
Msd pro billet distributor with one light silver and one blue spring so it's all in by 2300-2500.
2500 sat night special stall converter.

I know I could just lock it and try it but wondering on people's thoughts.
I also have something in the back of my mind telling me the digital 6al has a start retard built in which may explain how it can run with loads of initial timing but I may be mistaken.

Thanks in 'advance'
David

From memory the Digital 6 has the "Starter Saver" that takes 15 Degrees out when cranking?

If you you should probably get away with locking out and still be able to crank the motor.

I think these days 38 degrees is a bit much, most people run 34 degrees all in...

I think that sounds similar to what I was thinking too some sort of cranking retard.
Locked out at 34 sounds like a good trial if nothing else.

I have run locked out timing on the street, and all the race cars have had locked out timing, but have Crank Triggers for greater accuracy.

I've had multiple goes at this over different motor and ignitions. The current motor is the only one I've been able to run vac advance on - but whilst I can see it knocks the idle timing wildly I cant say I notice any driving difference to when its locked in. It certainly aint economical
Anyway - trial and error leads me to conclude 16-18 initial, 34 all in, steepish curve. I dunno. Never had a lot of luck with it really - but this combo seems about right.

Lock it out at 34, that’s enough for a big block. My street driven small block runs best locked out at 36, my ignition retards the ignition by 20 degrees below 500rpm, idle is 900-1000 RPM. The car doesn’t labour starting, runs cool and doesn’t detonate, it has instant throttle response.

Thanks for the replies, I'll try locking out at 34, see how she goes for a bit and report back

mines a small motor but i run 15 initial and 28 total.

it kicks the starter if i lock it at 28 total which is its high RPM optimum as far as i can tell

but i do have the vacuum connected to unported manifold vacuum as a way to achieve similar to what you plan
so as it turns on the starter it gets 15 or so which is nice for starting on a cold or very hot day
as soon at it starts its pulling in 45+ and idles nice.... i used a pulse smoother in the vacuum line
https://www.dellorto.co.uk/shop/vw-carb ... ve-vacuum/

so i get the benefits of the 40+degree idle
as soon as i open the throttle the timing falls back to the mechanical curve
my curve is fast and limited considerably
what i did for a manual that by its nature spins at an rpm dictated by the road and gearbox might not be necessary for motor bolted to auto, that doesn't. you have more freedom with the torque converter in between

my distributor rotor only turns 6.5 degrees on the mechanical advance i.e 13 degrees advance at the crank. much messing about to achieve that

it took me a while to find this Happy place and resulted in a PB.... (more torque faster rpm increase and a clutch set up to slip a bit for the first 1/2 a second.... worked....once at least )

One benefit as i drive my car on the street way more than the track, huge reduction in engine breaking. if i lift off at speed it no longer feels like i hit a puddle of glue. its a 4 speed car so this is very noticable suggest it would be less so with a torque converter

id expect you to notice similar with yours locked at the larger advance but perhaps not so obvious if its auto.

2 ways to achieve the same benefit.. two ways to skin this cat, just going to have to do in the garage what chrysler did with a bunch of engineers and a dyno which is a Pain in the ass

Less use of the accelerator pump on the street, less on off the gas with the flow of traffic on the motorway, and a greater agile feel to the drive, without having to really hit the gas, the car just feels smaller and more ON-IT in circumstances when you are not peddle to the floor, around town on the slip road etc I have to consider the application of the right foot a bit more based on road surface conditions

the vacuum gives you engine load, timing input rather than just RPM based input, it was worth the time and effort for a car that goes down the strip 6 times a year and needs to be a reliable and nice driver on the street

plenty of people don't run vacuum and have cars better tuned and faster than mine they will tell you you don't want or need it

for me though was a good move, made my engine work better at times when i was not using maximum potential, 99% of the time on the way to tescos.

like an ancient version of a MAP/MAF sensor

Dave

Very insightful Dave thank you. Lots to think about.
Like you I dont see much track use so it still needs to behave on the street. I do have a manual valve body on the 727 trans, so no vacuum there or on the distributor.

Lots to try. I can also machine different advance bushes so that is also an option to make a very limiting bush too.

Vacuum advance is handy for pulling in lots of extra idle advance but given the small diameter caps mopars use, if you already have a lot of initial timing it can actually cause a misfire by firing on the next adjacent post. My thinking is vacuum advance on a mildly tuned street car but mechanical only on something a bit lively that gets raced and needs a lot of initial timing.

Agreed, but if you have the right ECU, you can lock out the timing and take that out of the equation, phase the Distributor as best you can (Much easier with a Crank Trigger) and then programme to suit the engine's needs.

I think that engines on modern fuels want as much timing as early as possible, they burn cleaner and run cooler and have better response.

The trick is getting the bugger to crank and start, especially when hot....

Before I had a start retard I used a normally closed push button on the live to the ECU. Press the button to kill the ignition while you get the engine cranking then release it and the engine starts.

I've got everything on its own toggle switch so I can easily crank it over then flick the switch to bring on ignition, so that can be a plan b is she gets tricky to start.
So many ways to skin a cat.