Testing the HiRev 7500

[Mattax]

It depends on the type box and how crappy it is. Some actually have high RPM retard designed it to help protect against detonation at high RPM.

It's clear as mud whether any retard was purposely built into HEI or other units, or this was just some BS marketing people came up with as they struggled to explain what was happening. See that link on Speedtalk I posted earlier the thread.

 

[Newbomb Turk]

The next test should be a Pertronix I.. I want to see no spark scatter at 11,000.

I’ve tested a couple of those, but it’s been several years. I know they were not bad but I don’t recall the details.

If I can find one I’ll test it.

I have several Unilite’s sitting around. I can test one as a stand alone and with the box when get a minute.

 

[toolmanmike]

I’ve tested a couple of those, but it’s been several years. I know they were not bad but I don’t recall the details.

If I can find one I’ll test it.

I have several Unilite’s sitting around. I can test one as a stand alone and with the box when get a minute.

That would be great. One magnetic, and one optical. It would be interesting how they perform and compare.

 

[Mattax]

Okay, for us dummies who are struggling to understand this, tell me if this is correct. The timing retard on all these boxes doesn't really become significant until high rpms. 7,000, 7,500, etc. For a motor that only goes to 5500-6,000, it is not a significant problem.

I think the answer to this is yes and no, depending on how the distributor is set up.
In practice, as @GTX JOHN @92b and @MOPARMAGA posted, the effect can be seen 3000 - 6000.

To be clear, the effect being discussed is the apparent retard. Spark scatter and strength is a different matter we can come back to later.
The timing retard seen in the videos is coming from the time it takes for all of the components to react to the signal created in the distributor and the coil releasing high energy. Its the time it takes for each and every electrical and electronic switch to react and do whatever it needs to do. A question raised is whether the type of initial signal is a part of that sequence? For example mechanical switch (points) versus magnetic pickup versus optical (Hall effect). But regardless, most of the time taken is in the electronics.

So, if we locked a distributor, as shown in the videos, then the retard seems to be fairly linear.
Lets say we have a system with slew of 1* per 1000 rpm.
If Joe Cuda sets up his engine timing to be locked at 32* BTC and checks it at 1500 rpm, and then 2500 rpm he may not notice that 1* retard.
His engine won't idle at 500 rpm, so starting at 1500 the engine sees 32, then 2500 it sees 31*BTC, @ 3500 its 30* BTC, and @4500 rpm its down to 29* and by the time its nearing peak Hp at 6500 its 27*.

None of this slew effect shows up on a factory distributor setup.
The mechanical advance rate is more than 1* per 1000 rpm. So when we check timing on the engine, we never see the slew rate until after the advance stops.
When Direct Connection released their electronic ignition race distributors (aka tach drive distributor), the slew rate compensation was built in using a very heavy secondary spring. The explanation in the book may have been slightly off, but the importance was understood even if the bulletin writer didn't fully know why.

The problems with retard mostly show up when the distributor advance is set up to be "all in" at low to mid rpm.

Lets look at a factory high performance timing.
Here's the limits considered acceptable when the inital timing was set to be 10* at 650 rpm.

And this is the timing curve of a Chrysler built MP distributor I measured on my 340.
In this case timing was set at 32* at 2800 rpm.

Whatever retard existed in the ignition system (MSD 6T) is covered or hidden by the mechanical advance.

The problems with slew I ran into with that engine came along when I tried out (a) shortening the advance by stopping the weights early and
(b) using the then new 'adjustable' MP distributor built by Mallory (promoted by the experts as the new trick.)

With the Mallory advance mechanism, the timing was "all in" around 2500 rpm. Early on I started to get timing measurements indicating retard or bounce (or both) about 1000 rpm above the "all in"

^^^This shows advance^^^ its not timing on engine. Add the initial timing to the advance to get timing on the engine that I measured. All of these were measured on the engine, not the Sun machine.

Even after I was able to slow down the YH advance enough to solve the part throttle pinging (another reason no to be "all in" when using vacuum advance), the retard shows up.

 

[Newbomb Turk]

I think the answer to this is yes and no, depending on how the distributor is set up.
In practice, as @GTX JOHN @92b and @MOPARMAGA posted, the effect can be seen 3000 - 6000.

To be clear, the effect being discussed is the apparent retard. Spark scatter and strength is a different matter we can come back to later.
The timing retard seen in the videos is coming from the delay in all of the components to react to the signal created in the distributor and the coil releasing high energy. Its the time it takes for each and every electrical and electronic switch to react and do whatever it needs to do. A question raised is whether the type of initial signal is a part of that sequence? For example mechanical switch (points) versus magnetic pickup versus optical (Hall effect). But regardless, most of the time taken is in the electronics.

So, if we locked a distributor, as shown in the videos, then the retard seems to be fairly linear.
Lets say we have a system with slew of 1* per 1000 rpm.
If Joe Cuda sets up his engine timing to be locked at 32* BTC and checks it at 1500 rpm, and then 2500 rpm he may not notice that 1* retard.
His engine won't idle at 500 rpm, so starting at 1500 the engine sees 32, then 2500 it sees 31*BTC, @ 3500 its 30* BTC, and @4500 rpm its down to 29* and by the time its nearing peak Hp at 6500 its 27*.

None of this slew effect shows up on a factory distributor setup.
The mechanical advance rate is more than 1* per 1000 rpm. So when we check timing on the engine, we never see the slew rate until after the advance stops.
When Direct Connection released their electronic ignition race distributors (aka tach drive distributor), the slew rate compensation was built in using a very heavy secondary spring. The explanation in the book may have been slightly off, but the importance was understood even if the bulletin writer didn't fully know why.
View attachment 1716384260


The problems with retard mostly show up when the distributor advance is set up to be "all in" at low to mid rpm.

Lets look at a factory high performance timing.
Here's the limits considered acceptable when the inital timing was set to be 10* at 650 rpm.
View attachment 1716384264

And this is the timing curve of a Chrysler built MP distributor I measured on my 340.
In this case timing was set at 32* at 2800 rpm.
View attachment 1716384265

Whatever retard existed in the ignition system (MSD 6T) is covered or hidden by the mechanical advance.

The problems with slew I ran into with that engine came along when I tried out (a) shortening the advance by stopping the weights early and
(b) using the then new 'adjustable' MP distributor built by Mallory (promoted by the experts as the new trick.)

With the Mallory advance mechanism, the timing was "all in" around 2500 rpm. Early on I started to get timing measurements indicating retard or bounce (or both) about 1000 rpm above the "all in"
View attachment 1716384273
^^^This shows advance^^^ its not timing on engine. Add the initial timing to the advance to get timing on the engine that I measured. All of these were measured on the engine, not the Sun machine.

Even after I was able to slow down the YH advance enough to solve the part throttle pinging (another reason no to be "all in" when using vacuum advance), the retard shows up.
View attachment 1716384277

This should be a technical sticky. OUTSTANDING.

Also, I’ve never seen a real linear retard. I’ve seen them start at 1500 and I’ve seen them start at 6k.

On average the retard can be 1-2 degrees per 1k rpm. That orange box hanging on the wall is more retard per rpm than 2 degrees per 1k rpm.

 

[Mattax]

after all doesn't matter what happens before as long as the spark arrives at the right time

Exactly!

probably explains why the advance curve set in a points distributor from the factory differs so from the curve in an electronic...

Maybe.
Without having access to internal memos and documents its hard to know if any changes in the curves were due to performance goals or simply response to changes in engine design and emissions goals.
Got to go to '67 for US 49 state non-emissions timing curves in the shop manuals (or Sun cards, etc).
Electronic ignitions came in mostly 1972 and 73 model years.

Here's a couple of comparisons that are interesting.

 

[Newbomb Turk]

The first 5 min was enough or me.
What the gentleman ignores is that it could be the electronics in his m/c that is causing the retard.

The only true way to see if the ign is retarding [ or advancing ] is to watch the ign trace on a dual trace osciloscope, where you can see the initial generation of the spark v the spark being delivered on the time axis. Once you have the time difference & rpm, you can calculate any retard.

After a two and and a half hour conversation about this, my answer is correct.

The operation of the Allen machines are different than a Sun machine. They are from two different eras.

The answer is my machine is fast enough that is isn’t skewing the results.

As the video shows, the ignition is the same as it would be run in the car.

 

[Newbomb Turk]

I'm not saying that boxes don't retard but I have seen timing retard go from 6ish degrees of retard to 1ish degree with the same box and two different types of distributors. On running engines not a distributor machine. I don't know for sure but I think the results will be the same on a distributor machine. Most test including this one are done with the same type of distributor. Self generating ac signal.

Exactly. But that’s a different issue and it has zero bearing on my testing.