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OHV distributor differences, mechanical vs vacuum advance

84B23F said:
Have you attempted to mount a knock sensor?
Click to expand...

:rofl: flat tappet cam... good luck.

I'm running my B20 off ms2extra, full sequential with LS COP setup, and tried a few methods of knock detection. DET cans were the only way to tell. Even then, its hard to differentiate between cam noise, valve/lifter float, and knock.
 
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cwdodson88 said:
:rofl: flat tappet cam... good luck.

I'm running my B20 off ms2extra, full sequential with LS COP setup, and tried a few methods of knock detection. DET cans were the only way to tell. Even then, its hard to differentiate between cam noise, valve/lifter float, and knock.
Click to expand...

I had some success.

I am running a mostly stock B20E using a Bosch flat response sensor mounted on a stud on the left side of the block just below the head / block mating surface between cylinders 1 and 2. I used a Digilent analog discovery USB scope and the FFT in the Waveforms software to examine the frequency content of the signal. Yes, the B20 generates lots of noise; but, I was surprised to find that most of that noise occurs outside of the characteristic knock frequency of the B20. I will put a caveat on that comment because I did not test for noise in the characteristic frequency range beyond 4000 RPM.

The signal processing board I fabricated used a fairly common architecture. The knock sensor is connected up front to a differential input op amp to reject common mode noise. The output of the op amp is connected to a Max 7490 tuneable switched capacitor filter. The filter is configured as a band pass centered at the what I think he characteristic knock frequency is; but, I can't remember what the band pass roll off is. The output of the band pass filter feeds into a precision rectifier based upon a Max 4253 Op amp. At one point I was experimenting with using a switched integrator on the output of the precision rectifier; but, when I look at my prototype board it looks like I did not use that feature. I think I decided that it was not necessary with the count feature in the MSExtra software. The output of the precision rectifier appears to be connected through a final op amp which provides some adjustable output gain from the precision rectifier. The clock frequency for the switched capacitor is provided by a trinket overclocked board. The trinket allows me to adjust the clock frequency (center point of the band-pass) in software to experiment with different tuning for the knock frequency. The trinket also does double duty as I use its on board power supply to provide isolated power for all the op amps.

I believe I have the clock frequency set to give a tuned band pass somewhere around 3000 - 3300 hz with fairly sharp roll off. I am doing this from memory because I have the proto board in my hands; but, I am not sure where my design notes are.

I did a little testing of the board by cranking up the advance just in the ignition map cells around 3000 RPM 60 - 70 kPa such that I was able to detect audible detonation. The board generated a knock output under these circumstances and I did some initial fiddling with the knock set up in MSExtra to suppress knock. In my non exhaustive testing, the board did not generate extraneous knock outputs.

My MS board is set up with the knock sensor input and the knock sensor has been wired up to the terminals in the MS case; but, I have not implemented the knock sensing feature. My prototype board will not fit in the MS case slots, too narrow and too tall because of the use of breakout boards. The prototype board is also ..... clumsy. I used breakout boards to mount the the op amps and a proto board with a lot of surface wiring. I wanted to have a proper circuit board fabricated to allow direct mounting of all the SMDs with no green wiring required and design the board so that it would fit in the MS case slots.

I returned the ignition map to its pre detonation inducing condition and have not been super motivated to do any further work. The original thought was that a knock sensor might be a benefit in the event of some variable fuel quality. However, that has yet to present itself as a problem. With the current ignition map running 91 or 92 R+M/2 fuel, knock is pretty much a non audible event. If we get another COVID 19 lock down boredom might motivate me to go the next steps this winter - if I can find my original design notes and schematic.
 
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cwdodson88 said:
:rofl: flat tappet cam... good luck....I'm running my B20 off ms2extra, full sequential with LS COP setup
Click to expand...

If this info is true below...then indirectly, this distributor is detecting knock

123 Ignition Explained

Spark Balancing - The 123 ignition analyzes engine performance on a per cylinder basis and adjusts the spark timing and energy levels of each cylinder in order to balance the power levels - optimizing engine operation. This spark balancing function, derived from Formula 1 engine management systems, has not been available for classic cars until now.

I'm not plugging 123, but they do list timing degrees for various engines with a given distributor...scroll down this page to see them....with a cross reference to a given Bosch distributor.

PS Pricing wise, I would shop around, in US and Europe
 
142 guy said:
I had some success.

I am running a mostly stock B20E using a Bosch flat response sensor mounted on a stud on the left side of the block just below the head / block mating surface between cylinders 1 and 2. I used a Digilent analog discovery USB scope and the FFT in the Waveforms software to examine the frequency content of the signal. Yes, the B20 generates lots of noise; but, I was surprised to find that most of that noise occurs outside of the characteristic knock frequency of the B20. I will put a caveat on that comment because I did not test for noise in the characteristic frequency range beyond 4000 RPM.

The signal processing board I fabricated used a fairly common architecture. The knock sensor is connected up front to a differential input op amp to reject common mode noise. The output of the op amp is connected to a Max 7490 tuneable switched capacitor filter. The filter is configured as a band pass centered at the what I think he characteristic knock frequency is; but, I can't remember what the band pass roll off is. The output of the band pass filter feeds into a precision rectifier based upon a Max 4253 Op amp. At one point I was experimenting with using a switched integrator on the output of the precision rectifier; but, when I look at my prototype board it looks like I did not use that feature. I think I decided that it was not necessary with the count feature in the MSExtra software. The output of the precision rectifier appears to be connected through a final op amp which provides some adjustable output gain from the precision rectifier. The clock frequency for the switched capacitor is provided by a trinket overclocked board. The trinket allows me to adjust the clock frequency (center point of the band-pass) in software to experiment with different tuning for the knock frequency. The trinket also does double duty as I use its on board power supply to provide isolated power for all the op amps.

I believe I have the clock frequency set to give a tuned band pass somewhere around 3000 - 3300 hz with fairly sharp roll off. I am doing this from memory because I have the proto board in my hands; but, I am not sure where my design notes are.

I did a little testing of the board by cranking up the advance just in the ignition map cells around 3000 RPM 60 - 70 kPa such that I was able to detect audible detonation. The board generated a knock output under these circumstances and I did some initial fiddling with the knock set up in MSExtra to suppress knock. In my non exhaustive testing, the board did not generate extraneous knock outputs.

My MS board is set up with the knock sensor input and the knock sensor has been wired up to the terminals in the MS case; but, I have not implemented the knock sensing feature. My prototype board will not fit in the MS case slots, too narrow and too tall because of the use of breakout boards. The prototype board is also ..... clumsy. I used breakout boards to mount the the op amps and a proto board with a lot of surface wiring. I wanted to have a proper circuit board fabricated to allow direct mounting of all the SMDs with no green wiring required and design the board so that it would fit in the MS case slots.

I returned the ignition map to its pre detonation inducing condition and have not been super motivated to do any further work. The original thought was that a knock sensor might be a benefit in the event of some variable fuel quality. However, that has yet to present itself as a problem. With the current ignition map running 91 or 92 R+M/2 fuel, knock is pretty much a non audible event. If we get another COVID 19 lock down boredom might motivate me to go the next steps this winter - if I can find my original design notes and schematic.
Click to expand...

My experience is limited, but I could see that being beneficial for super ping regions, low rpm, high load + fuel quality issues, but I didnt want to be risking too much by pushing it. Observing the noise at high RPM first hand, and trying to tune freq was beyond my worry at the time. My engine setup was hard pressed to knock before power started leveling out anyway, granted these were 1/8th mile drag pulls in 1st and second, but I noticed it leveling out time slips well before I could catch any knock with detcans. But I can say that 22psi@7k rpm, theres a lot going on. :omg:
 
cwdodson88 said:
But I can say that 22psi@7k rpm, theres a lot going on. :omg:
Click to expand...

My exploration on knock sensing was all below 4000 RPM and 95 kPa MAP. If I could avoid detonation in the 3000 RPM, 60 -70 kPa region I was never able to detect detonation at higher RPM and MAP values and have never seen physical evidence of detonation damage. That does not guarantee that detonation is not occurring. Operation >> 95 kPa MAP would add a new dynamic.

I have read opinions that detonation at higher RPMs is less of an issue because the time is reduced for combustion which provides less time for heating and detonation of the end gasses or the alternative theory that at some magic engine speed the turbulence is greater reducing the end gas issue. I can perhaps buy in to that argument if advance maxes out around 3000 RPM: but, have not been inclined to experiment to see if I can induce detonation at higher RPM by adding more advance. Perhaps on somebody else's engine?
 
84B23F said:
If this info is true below...then indirectly, this distributor is detecting knock

123 Ignition Explained

Spark Balancing - The 123 ignition analyzes engine performance on a per cylinder basis and adjusts the spark timing and energy levels of each cylinder in order to balance the power levels - optimizing engine operation. This spark balancing function, derived from Formula 1 engine management systems, has not been available for classic cars until now.

I'm not plugging 123, but they do list timing degrees for various engines with a given distributor...scroll down this page to see them....with a cross reference to a given Bosch distributor.

PS Pricing wise, I would shop around, in US and Europe
Click to expand...

I don't think it is detecting knock, directly or indirectly. If you have a high resolution RPM signal you can easily pick up the RPM variations between cylinder firing events (crank slows down during compression and speeds up during the power stroke). I have a camshaft driven 24 tooth tach wheel and it is very easy to spot the engine speed variations and the one cylinder that is just a touch stronger than the other 3. I presume that if the delta RPM on one cylinder is different than the others the 123 distributor alters the advance to try and balance out the delta RPM on all 4 cylinders. It might smooth out the engine pulsations; but, I am not sure it enhances power, particularly if one cylinder is a dog because it has bad rings.
 
142 guy said:
I don't think it is detecting knock, directly or indirectly.
Click to expand...

Specifics would be nice to know...send them a question.

I might ask a neighbor, who was a mechanic (top fuel drag racing), but I suspect that's a different world electronically.
 
I doubt that 123 is much more than a programmed centrifugal advance, I don’t believe the one I had my hands on had a vac reference. Maybe it’s available. IMHO at the tune of $300, megasquirt it and just don’t do anything with the efi if you want carbs.
 
cwdodson88 said:
123...had a vac reference.
Click to expand...

I know nothing...but what I read

- two centrifugal advance curves
( 500 to 8000 rpm )
- two vacuum-advance and boost-retard curves
( 0 to 200 kPa or -30 inHg to +15 psi )
- two MAP-start fields
- two rev.limiters ( advanced random spark stealing )
- real-time tuning under keyboard-control ( ideal for working on a rolling road )
 
There’s been a bunch of research (years ago) on detecting knock by looking at spark plug discharge rates, maybe that’s what 123 is doing?
Even the simple 123 distributor is an upgrade over a stock setup. I’m really impressed with their quality and function.

If looking at distributor advance curves, they are usually based on distributor RPM and not crank RPM.
 
culberro said:
If looking at distributor advance curves, they are usually based on distributor RPM and not crank RPM.
Click to expand...

"Nevertheless, a potentially confusing aspect of ignition tuning on pre-electronically managed cars is that distributor centrifugal advance curves, as well as the amount of any vacuum advance, are often described in terms of distributor degrees.

As the distributor rotates at half the speed of the crank when installed in the engine, just multiply by two to get crank degrees. For example, if a tuner put 11 degrees of centrifugal advance in the distributor and set the initial (base) timing to 14 degrees BTDC at idle on the crank, the total advance when the centrifugal curve fully "comes in" would be 36 degrees at the crank [(11 2) + 14 = 36]."
 
culberro said:
...detecting knock by looking at...
Click to expand...

123 - Simple 2 wire hookup - one to the coil positive and one the coil negative


If 123's microprocessor can "see" how much energy was consumed by the coil, then it would 'know' each spark plug's load consumption. Note...on a 4 banger, a single coil will work fine.


Spark Balancing - The 123 ignition analyzes engine performance on a per cylinder basis and adjusts the spark timing and energy levels of each cylinder in order to balance the power levels - optimizing engine operation. This spark balancing function, derived from Formula 1 engine management systems, has not been available for classic cars until now.
 
So the 123 is pretty much like a pertronix setup but with more brains built in and I could hook it up to my laptop?

If so that sounds like a pretty neat solution that will be on my radar when I eventually finish grad school and start making some money.
 
spock345 said:
...123...hook it up to my laptop?
Click to expand...

Correct...and modify timing curve

An existing Bosch distributor (point system with a functional distributor, and set correctly) will work fine. With a point system, points and condenser must be replaced over/over, somewhere around 15,000 mile interval. It's not a PIA to do, but you need a feeler gauge, and a timing light.

I've seen replacement parts with high/low prices, and cheapest I've seen currently is around $21.00 via eBay HERE. Seller says Bosch no longer makes points...which would not be unusual for Bosch to quit making them.

If distributor is mechanical only or if a mechanical/vacuum advance, and is working to specs, either will work just fine if your coil/wires are up to specs. If distributor has vacuum retard, I would not use it.

If an engine was near OEM specs, 123 unit might be installed for peak performance...but for around $50.00, I'd buy this product for a mechanical only distributor, which replaces points/condenser. If I had a mechanical/vacuum distributor, I'd see what a new OEM spec'ed vacuum pot cost, and then evaluate distributor...most likely, I'd just buy a 123 distributor.

If I installed a 123 distributor, I would keep the Bosch distributor in the trunk...as a backup when I leave my home area. Any electronic part can fail on new and old vehicles...I prefer to have a plan B when replacement parts are not available.
 
spock345 said:
So the 123 is pretty much like a pertronix setup but with more brains built in and I could hook it up to my laptop?
Click to expand...

You need to look at the 123 product listing. 123 offers distributors with fixed spark maps, distributors with user selectable pre set spark maps and distributors with spark maps that can be user configured / screwed up on a lap top via a USB connection.

The 123 is not like a Pertronix "but with more brains" because the Pertronix has no brains - period. It is a simple Hall effect controlled bi polar transistor switch. All the 'brains' are provided by ancient mechanical devices (centripetal and vacuum servo).

If you are looking at a B18/B20 you are looking at a distributor that is at least 45 years old. Forget ignition point wear. The more significant issues are that the centripetal advance mechanism wears out, the vacuum servos get stiff or leaky and the shaft bushings on the distributor wear, all contributing to ignition timing error. Switching to a Pertronix module will not fix those problems. On my 1971 B20E, ignition timing was stable until just under 3000 RPM at which point it started bouncing around in about a 5 deg window according to the timing light. Ditching the distributor fixed that problem!

Volvo used to sell rebuild kits for the distributor bushings. I think rebuild parts for the mechanical advance and some of the servos may now be un obtainable. If you are willing to throw enough money at it, there are specialists who will rebuild your vintage Bosch distributor if you need to remain vintage. However, if you don't need to remain vintage I can guarantee you that a replacement 123 distributor will have a much lower cost than a distributor rebuild. That is the biggest performance advantage for 123!
 
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