Torque convertor and detonation

[smokinnjokin]

Folks,
I have been chasing timing issues with my motor and have come to the revelation that my torque convertor might be the real problem. Here's the background info.

Mild 360 low-comp build, smog heads and XE 262 cam, eddy intake and performer 500cfm carb, full tti exhaust, factory distributor with pertronix. Factory stall convertor (2k?) with 3.23 gears in 727.

Ray (halifaxhops) curved the dizzy for me, I forget the specs offhand but it is somewhere around 12*/24* mechanical, all in around 2500. I can run around 15* initial, 39* mechanical on 91 octane and the car runs like a raped ape. But to dial it back for 87, I have to pull it back to like 10* initial, 34* mech or I get detonation at 2k under load.
So all that makes sense, and before you say, no **** Sherlock, if you want to run pump gas you have to retard the timing... here's my thought, the motor really runs good with the more advanced settings on 87 octane (ideally 15/39*) it only detonates at around 2k-2200 rpm, which is right where the stall convertor puts it under initial load.

So here's my thought, I can either mess around with springs in the dizzy and get timing to come in later, OR, should I stop chasing my tail and get a higher stall convertor? Am I giving up a lot of grunt and fun ripping around on the street (this is a stoplight to stoplight car, no racing) with that factory stall convertor?

Before you respond, understand that

1) I daily drive this car, it will never race or get dyon'ed, I just want it to run really well and have very responsive throttle
2) I intentionally built a low-compression motor to be bulletproof and be able to run 87 octane and still have some grunt, so adding octane is not really an option

What do the pro's think, stick with my stock stall convertor and just adapt the timing curve, or is it worth the $$ and effort to replace that stall convertor... will it alleviate my detonation issue, dramatically increase acceleration? Car does 6.5 sec 0-60 consistently just mashing the pedal in D, no launch.

 

[66Valiant528]

It's a heck of a lot cheaper to mess with the distributor, which I'm sure you know. Sounds like you need to slow down the advance. Heavier spring. Just 1. You can always put it back to where you are now.

 

[oldkimmer]

Try a heavier spring like 66 says. But a decent converter will help u out a lot. It’s the single most improvement bar none. Kim

 

[smokinnjokin]

What is a decent TQ you recommend for a street car to romp around? Should I look for a used one, or is it something I need to buy new from summit or Jegs? I don't know much about TQ's.

 

[RustyRatRod]

Just run premium fuel.

 

[74Scooter]

I'm lazy and cheap... just make 2 marks on the dizzy base and adjust when needed.

 

[OldmanRick]

Any chance to increase the accel pump shot on that carb? Might be enough to cover the initial hit at that stall speed.

 

[smokinnjokin]

I will bump it up one position on the arm and test tomorrow.

 

[TT5.9mag]

The converter won’t eliminate the detonation. Just make the engine run through it quicker. I vote to delay the advance correctly AND put a quality matched converter in it.

 

[MOPAROFFICIAL]

Slow the advance curve if it only detonates at around 2200.. so make it maybe 2-4 degrees less timing at that rpm ..slowing the advance I guess it what it sounds like.... right?
You can have more stall and that will dictate more timing sooner, Sure... but that's not your problem so to speak.

To the comment above my post..
Just a reminder...The later the convertor stalls the later the LOAD is in the rpms..so if its not loading as hard..its not running through any detonation quicker or at all.

 

[TT5.9mag]

Slow the advance curve if it only detonates at around 2200.. so make it maybe 2-4 degrees less timing at that rpm ..slowing the advance I guess it what it sounds like.... right?
You can have more stall and that will dictate more timing sooner, Sure... but that's not your problem so to speak.

To the comment above my post..
Just a reminder...The later the convertor stalls the later the LOAD is in the rpms..so if its not loading as hard..its not running through any detonation quicker or at all.

Very true, but my comment was very situational. We’re not talking 5500 stall here compared to stock. His vehicle is daily driver, 323 gear, low comp, no quench to speak of, non race car status and that puts him in street stall (2800ish) territory. If it rattles now with the timing all in at 2500 it will likely rattle later at the same spot with a 2800 in some driving conditions. So I answered the way I did.

 

[smokinnjokin]

Slow the advance curve if it only detonates at around 2200.. so make it maybe 2-4 degrees less timing at that rpm ..slowing the advance I guess it what it sounds like.... right?
You can have more stall and that will dictate more timing sooner, Sure... but that's not your problem so to speak.

To the comment above my post..
Just a reminder...The later the convertor stalls the later the LOAD is in the rpms..so if its not loading as hard..its not running through any detonation quicker or at all.

That was my thought, the only time it detonates at 2000-2200 is pedal floored, heavy load because thats where convertor puts it… part throttle conditions, even 3/4 no issue at any rpm, nice and smooth. It seems like 2500-3k is where the motor really starts to lay down some power, so my thought is tq alone should fix everything, right? Am I understanding how the TQ works? If so, reccomendations for a quality tq?

 

[smokinnjokin]

Very true, but my comment was very situational. We’re not talking 5500 stall here compared to stock. His vehicle is daily driver, 323 gear, low comp, no quench to speak of, non race car status and that puts him in street stall (2800ish) territory. If it rattles now with the timing all in at 2500 it will likely rattle later at the same spot with a 2800 in some driving conditions. So I answered the way I did.

Makes sense, i will likely need to adjust timing regardless, this issue has just shined a light for me on the fact that this tc is really mismatched to where this motor is making power. Other similar builds (“smog dog dyno flog” almost identical) show good power coming on between 3000-5300. Stock smogger 360 passenger car tc or maybe even original 318 tc with weight welded on, is holding back a lot of potential. It took me this long to realize the tq is what is keeping engine out of its powerband in the majority of daily driving conditions

 

[Bewy]

Engine load, car weight are factors; doesn't ping in neutral correct?
I doubt a smaller c'ter would help & it will use more fuel because of the slippage.
[1] Get the engine running as cool as possible; heat is the enemy as far as detonation is concerned.
[2] Block or partially exh xovers in the intake.
[3] Rig up cold air induction
[4] Slow down the dist curve
[5] Retard the cam 4-6*.

 

[AJ/FormS]

Why does everybody seem to want to run race-timing in a streeter.......
You don't have a race car, no race convertor, no race gears, no race cam. Why race timing? Especially with an automatic and 3.23s?
I agree with what most guys are saying and here is my 2cents;
For 87gas, your low-stalled, hiway-geared, low-compression engine usually needs a two-stage curve, ramp it up from 12* at idle to ~20/24@ stall, then stretch it out to all-in around 34*@ no sooner than 3600; then fine tune it over time.
If she is too sluggish off the line for you, then get more stall.
If you give her fresh cool air, then you might be able to run a wee bit more Power-Timing.
If you run a lot of hiway, then stall it at around cruise rpm; say 2600/2800; which will allow you quicken the timing curve some..
That engine is only making maybe 130psi, so should be able to run 87 all the time: Check your sparkplug heatrange. Keep her cool.

 

[smokinnjokin]

Engine load, car weight are factors; doesn't ping in neutral correct?
I doubt a smaller c'ter would help & it will use more fuel because of the slippage.
[1] Get the engine running as cool as possible; heat is the enemy as far as detonation is concerned.
[2] Block or partially exh xovers in the intake.
[3] Rig up cold air induction
[4] Slow down the dist curve
[5] Retard the cam 4-6*.

Crossovers blocked, car has a hood scoop, I plan to eventually make a sheetmetal airbox for cold air induction (more as a fun project, because it would look badass then for any performance gains)
Why would I retard the cam 4-6* to take care of detonation that only occurs in one small part of the rev range under heavy load?

Why does everybody seem to want to run race-timing in a streeter.......
You don't have a race car, no race convertor, no race gears, no race cam. Why race timing? Especially with an automatic and 3.23s?
I agree with what most guys are saying and here is my 2cents;
For 87gas, your low-stalled, hiway-geared, low-compression engine usually needs a two-stage curve, ramp it up from 12* at idle to ~20/24@ stall, then stretch it out to all-in around 34*@ no sooner than 3600; then fine tune it over time.
If she is too sluggish off the line for you, then get more stall.
If you give her fresh cool air, then you might be able to run a wee bit more Power-Timing.
If you run a lot of hiway, then stall it at around cruise rpm; say 2600/2800; which will allow you quicken the timing curve some..
That engine is only making maybe 130psi, so should be able to run 87 all the time: Check your sparkplug heatrange. Keep her cool.

AJ, I guess I had the wrong idea here, I though that a low-compression motor would take lots more timing then a high-comp, race motor, not vice versa? And that more initial, like 16-18* would be better... it sure feels and runs better, what gives?
Spark plug heat range is on the hotter side, autolite 985, they are clean with no sign of detonation or overheating, again the problem is only with pedal to the floor between 2000-2300 so I doubt it would show on plugs without a chop.

 

[furrystump]

I installed this for drag week, never touched it. It is very nice to adjust the timing. Just set it in the middle of the range and set distributor where you want it. From then on just dial it in. You do need an msd box i think.

 

[AJ/FormS]

AJ, I guess I had the wrong idea here, I though that a low-compression motor would take lots more timing then a high-comp, race motor, not vice versa? And that more initial, like 16-18* would be better... it sure feels and runs better, what gives? .

Is it working for you?

Spark plug heat range is on the hotter side, autolite 985, they are clean with no sign of detonation or overheating, again the problem is only with pedal to the floor between 2000-2300 so I doubt it would show on plugs without a chop.

Is it working for you?

Your engine does NOT care about any timing until it hits the stall. Below stall, you can make up for some to most of the timing shortfall with Vacuum advance (which can be modified to get 22 to 24 degrees). Sure; you can use timing to band-aid the loss of low-rpm performance due to low cylinder pressure; but how's that working for you? Not very good right? Really, you need more cylinder pressure; your 262 cam actually makes LESS pressure than the stocker.
ExcessHeat in the chamber is the number one reason for detonation. In order from most likely too least, the reasons for this are;
1) too early an ignition spark,
2) running lean,
3) Hot-spots in the chambers ....like....a hot sparkplug electrode ..... for example
4) the Inlet Air Temperature temperature,
5) the coolant temperature

As for #1;
this is a double whammy, cuz if the spark is too early, the resulting high pressure spike may try to drive the piston down onto the crank, POW!, hammering the bearings; instead of driving the piston down the bore.
Then, because the gasses started burning early, they finish burning early, and the pistons end up pushing them out of the chambers, costing you power, twice.
As for #2;
this can overheat the intake valves, cuz the fuel passing over then is one of the ways they are cooled. If the intake valve has carbon on it, perhaps a circumstance will arise that the carbon becomes a hot spot, which may ignite the air/fuel charge before it's time. If the resulting pressure spike is much too early, the expanding gasses may dry to drive the piston back down the bore, on the wrong side of TDC! This type of spontaneous ignition is called Pre-Ignition, and if left unchecked, usually blows a hole in the center of the piston.
As for #3;
This is usually a spark-plug electrode; but could be a hot valve, carbon, or sharp or pointy thing in the chamber
as for #4;
Above hood air, when the car is in motion, is at or close to ambient, in the range of 50 to maybe 100 degrees F.. Underhood air is from rad temp to header temp and higher. Temps can hit over 400*F. How do you tune for air that is constantly changing density due to Inlet Air Temp? Answer, you cannot. So there will be times that the AFR will be rich and times that it will be lean......... all due to the fluctuating underhood temp..... and lean-running is #2 on my list........
Idling, your headers, before the first bend could be running NOT less than ~350*F.. At WOT, it could be triple that. And the air around them will not be much less. That air is about 1ft from the air-filter house. Do you really want extremely-HOT air getting inside your engine?
The air coming thru the rad is gonna be about NO LESS than 15/20*F (average), less than the coolant temp at the stat.
The oil in the pan. the power steering fluid, and the Auto-trans fluid; are all gonna be close to the coolant temp... or higher, and any/all of them could easily hit 200/220 and more.
Heat gets radiated in All directions, but Hot Air RISES...... up, up, up and straight into the air filter house.
This all is just so much bad news to your AFR.
As for #5;
The coolant temp is actually your smallest problem. From 160 to 195 is just 35 measly degrees.

As for other;
As for slightly late timing, below stall, there are two/three downsides;
1) a really TINY bit of WOT power-loss.
2) The engine may run a little hotter as the fuel may not finish burning in the chambers. In your case with a 262 cammed 360, probably not. But if that happens; the burning AF charge will pass heat to the water-jackets just above the ports.
3) A noticeable drop in throttle-response. This is what you can really feel. But with your very modest cylinder pressure, this is to be expected, expected, expected.
> IMO: You are trying to make something from what is not there. You can just get a piece of it, and then you get detonation. You cannot normally hit the low Power-Timing number at stall that I mentioned, when starting from 16/18 at Idle. If you had a computerized timing control, then you could do that.... but you didn't mention having such a tool. Besides, there is NO GOOD reason to run those numbers at Idle in your set-up; it will just mess up the Transferslot to mixture-screw synchronization. You will end up fighting a tip-in hesitation, which you may be able to cure with excessive pump-shot, which you will activate every time you step on the gas, burning vast amounts of fuel. In a Daily-Driver, you want to tune the pump for as little activity as possible.
>As for slightly late PowerTiming;
At peak power, if you are within 2or3 degrees of optimum, you might experience a loss of power in the range of, 2% to maybe 4% ; so on a 250hp 360 maybe 7or8 horsepower; probably less. In most cases you will never know this by seat of the pants; because in Second gear, with 3.23s, the power may not peak until near or over 80mph. In First gear, you are burning thru the power peak in just a couple of seconds, so no way to tell. The only way to be sure, is to do a timed run from say 4500 to 5500 rpm, and you will need a datalogger.

That's the best I got.

BTW
At Idle, your engine may like 25 to 30 degrees of timing ...... But with the factory advance mechanisms, you cannot drive it like that, because as soon as you put a load on it, it will begin to detonate. Want proof, just pull the timing in until the rpm quits going up, then reduce the idle-speed; then put a Timing-light on it.
But it will take 10 or 12 at WOT right off idle. Now if you V-can has 24* in it you can access that beginning at about 1600rpm on the sparkport with no load on the engine. If your mechanical is up to 16* by 1600, that would total 40 degrees. If by stall of 2400, the mechanical is up to 22*, then 46* , until the vacuum starts to drop out, with load. That's how you get your PartThrottle-Timing back.

 

[MOPAROFFICIAL]

I'll say it again, torque convertor match aside... slow the curve so that full advance is a few hundred rpm later,aka less timing @2200 rpm.

The timing is the issue, regardless of if the convertor isnt just right... that fixing it would only be an indirect fix or by byproduct.. but it's only cause you would delay the full load to a higher rpm.

Making it way too hard...but if you really want to buy a convertor... go ahead. Please. Do that..THEN come back and ask about your tune issue.

 

[smokinnjokin]

Understood. Current curve is suitable with 12* initial, 34* total so I will just dial it back and stop trying to get this motor to do something its not built for. A new stall convertor will be a nice upgrade, separately from this issue. It's funny, you talk about this motor like it is a dog based on the compression and mild cam, but to me it feels great with tons of power, its all relative I guess. I am satisfied with what I have, just want to tune it properly.

 

[G70464]

What is a decent TQ you recommend for a street car to romp around? Should I look for a used one, or is it something I need to buy new from summit or Jegs? I don't know much about TQ's.

Any 6000 series or 9100 and down series, pre electronic compensator are good.
Plenty of guides to tuning. Need to fix the primary well seal with JB Weld Marine.

Or you can get the 750 street demon with composite fuel bowl.
Your car is way under carbed.

 

[smokinnjokin]

Yeah the super cool shop that rebuilt my motor insisted I didn't need a bigger/new carb... but charged me $350 to "tune/rebuild" my 500... that had not a damn thing wrong with it... stupid me. It does run fine and seems appropriately tuned to the car. Still, we can all agree a 750 would be more appropriate. I have a 650 on the bench that I could slap on the car and tune, just haven't got around to it. Seems like the TQ is king though. Might not be worth getting a spread bore intake though

 

[OldmanRick]

Any chance to increase the accel pump shot on that carb? Might be enough to cover the initial hit at that stall speed.

Did you every try increasing the pump shot with your current timing? Just curious.

 

[Ironracer]

I'm lazy and cheap... just make 2 marks on the dizzy base and adjust when needed.

Old School Cool! Yep, map it, Ya wanna run, add Hi Test, ans Spin!

 

[AJ/FormS]

It's funny, you talk about this motor like it is a dog based on the compression and mild cam, but to me it feels great with tons of power, its all relative I guess. I am satisfied with what I have, just want to tune it properly.

Yes it is relative.
Here's the thing;
At a compression ratio of a true 8/1, and with the 262 cam your cylinder pressure is predicted to be ~130psi. And the V/P index is expected to be ~115; read about V/P here;
V/P Index Calculation
Now; at split overlap, and at sealevel;
1) A stock 9.0Scr 318 is predicted to make a pressure of 161@133V/P
2) A stock 8.0 smoggerteen.................................... 138@114
3), A stock 8.0/360 with 360 stock cam..........................139@130
4) Pumped up to 9.0 with stock 360 cam ....................... 154@138
5) Your 8.0 360 with 262 cam in at 109 .................. 128@111
6)for comparison, my alloy-headed [email protected] .....193@167
So compare your combo, to some of these numbers; Your engine has the least amount of predicted pressure, which leads to the least amount of V/P which is a measure of low-rpm performance and is directly comparable no matter the engine.
>Compare 2 and 3. Notice they both make about the same pressure; one is a 318, the other a 360. Notice the 360 is up 6% in V/P; that's the cid
Compare 1 and 4. The 360 is - 4% in psi but +3.8% in V/P; again the cubes
>Compare your 360, to the smoggerteen.
Now you know the rest of the story.
The V/P difference is most noticeable at low-rpm, and diminishes with rpm, and eventually, beginning at somewhere between 3000 and 3600 is no longer meaningful. But with a 2000 stall and 3.23s, you can see where this information is useful. And you can see that getting the timing right, down in that never-never land, is a pita.
Find your stall rpm. Then determine your maximum stall timing.
Then build your low rpm curve to the stall rpm to be as fast as possible.
Then find your max PowerTiming at say 3800. Then connect the two parts of the curve. This usually requires a two-stage curve because the two lines are rarely climbing at the same rate. And that takes a fat-wire one-long-loop spring, which you adjust to slam the brakes on the high-rate low-rpm spring. Followalong on some of @Mattax 's diagrams, and you'll get the idea.
After this you can experiment with bringing the PowerTiming in earlier, and or increasing it.
But the Big Deal is to sneak up on the Optimum Timing and not worrying about not being able to get it right on. Without a Dyno, and without a Distributor-machine, or without a dial-back timing module, AND without a knock-sensor; it can take weeks to months to get it dialed in just right.
And the idle-timing always gets the chit end of the stick.
Getting the timing right is easier with a stall that is closer to where the V/P has decreased to being meaningful, cuz like I said, your engine doesn't much care about the low-rpm timing until it hits the stall-rpm, AND you cannot give the engine the Idle-Timing it wants, anyway, in stock configuration; and if you could, you would lose the idle-lope that everyone is so keen to have.
Happy HotRodding