locked out timing/any downsides on street cars?

[dieselgeek]

I bet some people on this site know where the scatter really comes from, and probably know if it makes any significant difference in hp.

In my experience, significant spark scatter is usually caused by electrical/noise issue on a distributor position sensor, moving to the crank trigger seems to improve the signal quality going into the ignition controller (or computer).

[twinturbo496]

I hadn't considered that...I am not really smart enough on a O scope to find the noise anyway...

[dieselgeek]

I hadn't considered that...I am not really smart enough on a O scope to find the noise anyway...

I'm no electrical engineer, but I use them pretty often for EFI installations to verify crank and cam trigger signals. What I find is, crank triggers generally provide a cleaner signal when they're removed from the distributor.

What's cool about automotive use of an oscilloscope: we gearheads only need very low frequency coverage, so you don't have to purchase an expensive unit. Some might laugh but, the unit I use is a $140 Parallax scope that comes with one of those introductory "So you want to learn about Electronics" kits! I use this thing all the time, though. Works with my laptop, is small and cheap enough that I don't care if I break it.

Also came with a nice tutorial on how to use it. http://www.parallax.com/Store/Microcont ... roductName

[PackardV8]

Getting pretty far OT here, but these days, the best performance dollar I see is spent getting the distributor out of the ignition business completely.

As mentioned above, the advantages of not having a distributor are so obvious when one is shown the clean, consistent traces from a true crank-trigger with coil-on-plug system, versus the scatter, variation and lag which is inherent in a crank-to-chain-to-cam-to-gear-to-gear-to-distributor-centrifugal-and-vacuum lashup. Add in a high-volume oil pump which drags the drive gears and a distributor just isn't a performance system any more.

I tried to sell the advantages to a customer recently. "Sorry. It just doesn't look like a hot rod without a billet distributor with a red cap."

thnx, jack vines

[Lazy JW]

.....

I tried to sell the advantages to a customer recently. "Sorry. It just doesn't look like a hot rod without a billet distributor with a red cap."......

Can you hid the components inside a dummy distributor?

[PackardV8]

Can you hid the components inside a dummy distributor?

Nope. Most multiple coil systems, whether eight coils like OEMs or four coils like Electomotive, take up more space and aren't shiny like a billet MSD. Some aftermarket guys have a fake rocker cover which hides the GM coil-on-plug. Then, I guess one could run a phony distributor and run dummy plug wires down to the cover, but I couldn't bring myself to do that.

Recently, I was asked about taking a crate LS1, complete with EFI and ignition, pulling off the good stuff and spending another $3000 for carb, intake, distributor, wiring harness and rocker covers. The result will not run or start as well or make as much power or fuel economy, but it will have the look.

thnx, jack vines

[twinturbo496]

I completely agree that coil on plug with a crank trigger is better than the typical distributor setup, but I think more than one time a carb has proven equal or better than EFI, many of the Engine master builders would be better educated than I am on that subject, but I am pretty happy with the LM-1 wide band log from my triple 750 AFB's so far, and they only cost me $100 each.

Back on topic, I can't believe that a "locked" distributor would really make as much average power or torque as the same engine with a proper ignition curve (mechanical or electronic).

[PackardV8]

Yep, we're OT, sorta

more than one time a carb has proven equal or better than EFI,

Yes, at max power, carbs rule. However, most of my vehicles aren't EMC competitors. Cold start, part throttle, fuel economy, passing emissions, idle quality, altitude compensation, it's EFI all the way.

BTW, ask a Cup crew chief if he wouldn't like the fuel economy advantages possible with EFI when there is the need to stretch to the checker. It will be interesting to see what NASCAR finally does with EFI, after years of discussion.

Back on topic, build a, "Just gonna drive 'er to the strip," with too much cam and compression, locked distributor, high stall, electric water pump, and first warm week end the customer will be back complaining it overheated in cruise night stop-and-go traffic and then wouldn't restart.

thnx, jack vines

[MadBill]

...When the piston is going down at the end of the exhaust stroke,it sucks in lots of atmosphere that has O2’s in it and this mixes with fuel from the intake and the rpm goes up.See,the throttle plates are shut so you don’t get much air in from them,but you get it in from the exhaust.The exhaust becomes an intake on the overlap....

Erm...An unconventional explanation to say the least, Greg!
How long does the exhaust system have to be before the engine can no longer draw fresh air from its open end? I've messed with the timing on motorhomes with 30+ ft. systems and they behaved exactly like any other, including ones with open headers ..

Here would be a great experiment: get an old bicycle tube. Cut it in half, tie a knot near one end and stretch the other over the tailpipe. Fire up the engine and observe the result. Does the tube inflate, or is it sucked up the pipe? Unless the latter result occurs, obviously no air is being drawn in through the exhaust.

[GREG K]

When an engine is idling there is a lot of vacuum that sucks in whatever there is to suck in.
If you lean the idle fuel out and advance the timing,then the exhaust is not full of fuel anymore so it can suck in O2,where as before it couldnt with rich retarded settings.
The only test you need to do is grab the dizzy,turn it and lean the mixture screws.now your engine runs smooth and rpms go right up.keep going if you want,2,000--3,000---4,000 rpm sometimes.
You havent opened the carb,its shut,so you know that you are sucking in O2.
The tire tube test wont show you.
Tuning engines shows you.

It doesnt matter how long the pipe is.

simple,isnt it.

[Troy Patterson]

I just changed from a MSD street distributor with vac and mechanical advance (12° initial, 22° mechanical, 20° max vac) to a crank trigger & crab cap with 30° fixed timing. I was very concerned about starter damage and hot start problems, the setup already had ignition switch separate from the starter, but so far it has started just fine, pump throttle twice, spin starter for 2-3 seconds and hit the ignition, even on 87 octane.

However, the engine is a 8.5:1 CR BBC with a 14-71 blower & a .680 solid roller. Perhaps big cam + low compression = acceptable option

That said, the only reason I did it was because I couldn't fit a real distributor under the blower, if I could, I would still go back to the street distributor setup.

One interesting side note: Even with all new parts, the conventional setup (with plastic thrust button) had significant spark scatter, but it is completely gone with the crank trigger, I wonder if the scatter was from the timing chain, distributor gear backlash, harmonics in the mechanical advance...???

I bet some people on this site know where the scatter really comes from, and probably know if it makes any significant difference in hp.

There are a number of sources of spark scatter. Four that come to mind right are... 1) bad wires; 2) very high resistance at the plug; 3) running non helical wires with a hot coil / ignition system in close proximity; 4) loading the distributor intermediate shaft against the oil pump

Troy Patterson TMPCarbs.net TMP Carbs

[Adger Smith]

I haven't spotted this in this thread so:
One downside to locking out any Dist. advance is the accuracy of getting rotor/dist terminal alignment correct.
That one thing can make or break the deal as to how good the results become.
Get it a little off it can work, but miss it and Wow, talk about spark scatter and pooting and popping.....

[torquefan]

When an engine is idling there is a lot of vacuum that sucks in whatever there is to suck in.
If you lean the idle fuel out and advance the timing,then the exhaust is not full of fuel anymore so it can suck in O2,where as before it couldnt with rich retarded settings.
The only test you need to do is grab the dizzy,turn it and lean the mixture screws.now your engine runs smooth and rpms go right up.keep going if you want,2,000--3,000---4,000 rpm sometimes.
You havent opened the carb,its shut,so you know that you are sucking in O2.
The tire tube test wont show you.
Tuning engines shows you.

It doesnt matter how long the pipe is.

simple,isnt it.

it was my impression when one advanced the ignition timing at idle, it actually helped combustion because of the lack of mixture motion and cylinder filling. go figure. so, if o2 is being drawn in the exhaust, wouldn't it be of benefit to run a siphon tube from the gas tank to tail pipe? pay attention, madbill. time to learn something.

[rabbit]

lots of info here to digest, i appreciate it.

Further to this, why would i "need" any mech advance curve if total timing is achieved before the convertors flash stall (as is the case with my engine), and shouldnt more timing, earlier, be a better thing for low speed/low load street cruising (especially if UNDER the rpm where total timing is reached)

so why even use an advance curve at all? (remembering I dont have vac advance on this distributor)

a stock convertor, 2.xx rear gear and WOT at 2000rpm might not like locked timing, but what about 4k stall and 4.33 gears under the same conditions?

[RednGold86Z]

When an engine is idling there is a lot of vacuum that sucks in whatever there is to suck in.
If you lean the idle fuel out and advance the timing,then the exhaust is not full of fuel anymore so it can suck in O2,where as before it couldnt with rich retarded settings.
The only test you need to do is grab the dizzy,turn it and lean the mixture screws.now your engine runs smooth and rpms go right up.keep going if you want,2,000--3,000---4,000 rpm sometimes.
You havent opened the carb,its shut,so you know that you are sucking in O2.

If the engine can get up to 4000 RPM without changing the throttle angle, and just leaning and advancing, it means the initial point was way too rich or way too retarded and needed a very open throttle just to idle or just wasn't pulling fuel in well. It's not getting O2 from the atmosphere through the exhuast, unless there is a leak within a few feet of the head, or if you count misfiring. Getting more O2 from the exhaust isn't a good thing, either, unless you're already rich. O2 doesn't burn. O2 + vaporized fuel burns. If you're leaner than ~lambda 1, more O2 cannot help make RPM higher.
AFR and Spark affect power, such that at idle you need say 8hp to keep that speed. You can get 8hp by many ways - stinking rich lambda .65 + open throttle + late spark; or lambda .9 + much less throttle + near MBT timing; or Lambda 1.2 + open throttle + near MBT timing; or lambda .8 + a little open throttle + near MBT timing; and so on.
The power required to keep idle speed is not affected, but the efficiency is. If you do something to change only one part of the equation, the RPM will change, without getting O2 from another source. If you change 2 things both towards better efficiency, of course the RPM will increase, but doesn't mean it's from the exhaust.