Re-curve a HiRev7500 distributor?

[fshd4it]

Hey all-
I bought Ehrenberg's distributor/ecu kit a while back, and I'm working on getting it set up. 18 deg initial @ 700, no advance until 1600; 22 @ 1950, 26 @ 2350, and only 30 deg by 2950 (still climbing slowly, but I stopped there). I'd like to end up at 34 total between 2500/3k, at least for a start, and I'm using FBO's limiting plate.
I have a selection of stock springs, as well as the spring kit from FBO. Has anyone attempted or succeeded at re-curved one of these units? The installed springs are both .035, with one @ 7 turns, and the other @ 11, but no slotted eyelet for the secondary spring.
FWIW, the weights seem to be pretty close to the factory ones, near as I can tell with my scale, so maybe the same spring applications apply as for factory distributors?
Edit: one difference, the pins for the springs are slightly farther apart on the HiRev. So the installed length is .050 +/- longer.

 

[RustyRatRod]

They are almost a carbon copy of the Mopar factory distributor. On those, I use one light and one medium spring and it gets it right on the money "for me".

 

[fshd4it]

Hey Rob-
I edited my post, as I just went and measured the spring pin distances. They'll start off stretched about .050" versus the stock units. Do you used the springs with the long eyes? I've got a few, at least 2 different wire gauges.

 

[RustyRatRod]

Hey Rob-
I edited my post, as I just went and measured the spring pin distances. They'll start off stretched about .050" versus the stock units. Do you used the springs with the long eyes? I've got a few, at least 2 different wire gauges.

I do not use those. You can though. They give a kinda "head start" on the curve. Only drawback is, they are normally much heavier than performance springs.

 

[fshd4it]

I do not use those. You can though. They give a kinda "head start" on the curve. Only drawback is, they are normally much heavier than performance springs.

The lighter spring(s) should bring the beginning of advance down from 1600, right? This is the selection of factory springs I've dug out so far...

 

[RustyRatRod]

The lighter spring(s) should bring the beginning of advance down from 1600, right? This is the selection of factory springs I've dug out so far...

View attachment 1716455628

If you use both light springs, yes, I imagine so. I think two light springs is too light as most times I've tried them, I get advance at idle. You don't want that. I would try the .022 and the .028.

 

[fshd4it]

Thanks man, I'll give that a shot. I expect a few in/outs, but the fewer the better. One nice thing about this distributor, no clip under the felt. Phillips head screw.

 

[RustyRatRod]

Thanks man, I'll give that a shot. I expect a few in/outs, but the fewer the better. One nice thing about this distributor, no clip under the felt. Phillips head screw.

Oh GAWD. I hate those clips. No one makes a tool for it either. You'd figger BY NOW somebody'd make somethin. lol

 

[Newbomb Turk]

Hey all-
I bought Ehrenberg's distributor/ecu kit a while back, and I'm working on getting it set up. 18 deg initial @ 700, no advance until 1600; 22 @ 1950, 26 @ 2350, and only 30 deg by 2950 (still climbing slowly, but I stopped there). I'd like to end up at 34 total between 2500/3k, at least for a start, and I'm using FBO's limiting plate.
I have a selection of stock springs, as well as the spring kit from FBO. Has anyone attempted or succeeded at re-curved one of these units? The installed springs are both .035, with one @ 7 turns, and the other @ 11, but no slotted eyelet for the secondary spring.
FWIW, the weights seem to be pretty close to the factory ones, near as I can tell with my scale, so maybe the same spring applications apply as for factory distributors?
Edit: one difference, the pins for the springs are slightly farther apart on the HiRev. So the installed length is .050 +/- longer.

View attachment 1716455625

30 degrees of timing at 3k is a lot unless you have no compression, the camis too big, your combustion chambers are slow or a combination of any or all of them.

 

[Newbomb Turk]

The lighter spring(s) should bring the beginning of advance down from 1600, right? This is the selection of factory springs I've dug out so far...

View attachment 1716455628

If I could find that .050 wire spring with a closed loop on both ends I’d buy some.

 

[fshd4it]

30 degrees of timing at 3k is a lot unless you have no compression, the camis too big, your combustion chambers are slow or a combination of any or all of them.

I think I have a combination of all 3. This is the motor from the post i put up a few months back, asking about how bad my cam choice was. 360, 9.2-1, stock 1.88/1.60 heads, Lunati cam .480, 230@.050, 107 CL, advanced 8 degrees iirc.

 

[Mattax]

If its the same as the Mopar Performance curve, you are best off leaving it alone. Make small adjustments only unless you have a very specific reason to change it.

lets plot your numbers an dsee what you got.

 

[Mattax]

OK I'm going to take back my previous post!

I don't know 'how bad ' the cam choice is but I think a mopar performance curve would be pretty close.
What you got from Rick is not close. Only good thing I can say is that it allows a good initial timing range for a cammed engine like this.

It should be advancing from just above idle rpm. If you have idling strong at 700 rpm IN GEAR, then advance can start at 750. If this is 4 speed car, then we can't check that way but it still be OK to start advancing above idle.

That looks like tension on the heavy spring when the distributor is at rest.
Those spring perches allow quite a bit of adjustment and this might be his work around to buying long looped springs. Bending in will take the tension off. The long loop spring might be better. But you want it to engage just 8 degrees above intial so set it just a little loose.

Edit: one difference, the pins for the springs are slightly farther apart on the HiRev. So the installed length is .050 +/- longer.

Reducing the the installed length of the primary spring (more coils - lower spring rate) will reduce the initial force from that spring and start the advance earlier. That is assuming there is no tension from the heavier spring.

The installed springs are both .035, with one @ 7 turns, and the other @ 11, but no slotted eyelet for the secondary spring.

Comments about that above.
Spring rate goes up with less coils if everything else is the same.
An important secret in the distributor springs (all springs really) is that the spring force on the weight is not just from the spring rate. Force is from the amount it has stretched times the spring rate.

 

[Mattax]

Just my opinion here.
The lower green line is taken from the factory timing for a Hi-perf 273
The upper green line is from some dynomation simulations . I'd stay below that. In fact there's very little lost in the simulation even when running significantly less timing until getting into the upper rpms (over 4500). And AFAIK Dynomation is based more on dyno and 1/4 mile. For about everything else (street, road race) heat soaked engines will want less.
All that said, it still will want to advance earlier. Timing should be at least where the factory 273 4 bbl was. That was 10:1 engine (in theory) so would need less timing on that front.

 

[Mattax]

The lighter spring(s) should bring the beginning of advance down from 1600, right? This is the selection of factory springs I've dug out so far...

Basically yes.
The .022 looks like it might be a race distributor spring. I can check my notes later.
If you want to do the spring rate calculations, measure the coil diameter (outside), and count the coils.
Rate will change the slope.

 

[fshd4it]

Mattax-
Wow, thanks for all that. I expect to do a few spring changes, bit by bit, unless I get lucky right outta the gate. I'll plot the curves (of course, mine will be on graph paper, in pencil) and compare to the ones you put up.
But... this may all be for naught, as I'm not very impressed with the quality of this distributor (big surprise). Stuff like the reluctor being a bit wobbly, etc. She's kinda rough around the edges. I'm sure it would be a smarter choice to redo one of the stock ones I have on hand, which may end up happening.

 

[Mattax]

Maybe borrow the governor from Ricks?
One nice thing is the points type spring perches allow more adjustment than the round ones.

I should say those Dynomation models were around my lower compression 340 with Hughes split duration cam but its roughly a 230 at .050. That's why I thought it was a useful reference for your 230 cam lower compression 360.

The Mopar Performance race (no vacuum advance) light primary springs I measured were made from .018" and .015" wire.
Their vacuum advance distributor's primary spring was made from .028" diameter wire, and some production ones were similar.

The challenge with many production distributors, and even the MP unit to some extent was the the number of degrees before the second spring engaged. The anti-smog packages from 67 (calif) through about '75 used a retarded initial timing and then a super fast advance to try to get the timing needed for economy and power a few hundred rpms above idle. That's why its often helpful to weld up the inside of the slots rather than stop the advance early (as the FBO plate does). As you play with it you'll see what I mean.

Have you seen these?

Post in thread 'lets revisit timing'

Sep 10, 2021

@RustyRatRod @Mattax

Exactly.
Welding the inside , extending the springs into more tension.. ...wtf is he thinking.lol so we want a slow curve?
Putting the spring under tension and into its max resistance..uh no thanks.
The outside is where you would close it up.

Tony is a pants shitter

No. I disagree.
A little more tension on the primary spring is generally no big deal, especially on a non-stock engine where its going to have more initial and little higher idle rpm.
I've welded up slots on the outside only to file them open and redo it on the inside.

If you want less...

• Mattax

Post in thread 'Distributor curve help needed'

Jul 16, 2021

Made a goof in the graphs above (at 3500 rpm) when I plotted out the timing you measured.
Fortunately doesn't change the main point.

In gray is the range where I think the timing ought to be.

So the next question is how to get there.
The first thing to do is reduce the tension of the primary spring. That's the spring with tension when the distributor isn't turning, or turning slow. On a Chrysler distributor you do that by turning the spring perch (circled).

You don't have to disassemble the distributor unless its really stubborn.
You can file a...

• Mattax

 

[fshd4it]

So I swapped out the original 11-turn .035 spring for the .022, and gave it a whirl. Still 18°, but idling in park at 800 now. When warm she drops to 650 in gear... I'll visit that soon. The carb, at the moment, is a box-stock 1406.
I'm using a dial-back gun with a tach display.
Anyway, the new curve is:
Starts advance @1300, maybe a touch later
22 @ 1600
26 @ 2000
30 @ 2300
34 @ 2550
36 @ 2750
And she kept going. At least to 38°, that's when I stopped. I wasn't watching the tach closely, but it was around 3k. So the FBO plate needs to be swapped from 16° to at most 14°. I believe I've had this issue before, more advance than what the plate says.
I'll read those 2 threads (I may have already, in the past) tonight. That's another problem with being a West-Coaster, everyone's asleep when I normally get time to post stuff.

 

[RustyRatRod]

I believe I've had this issue before, more advance than what the plate says.

Purt near everybody has. I've called him about it and he was very curt with me on the phone. Basically, he ain't changin nuthin.

 

[Mattax]

So the FBO plate needs to be swapped from 16° to at most 14°.

Just take it out and use it as a mini-frisbee.

here's the plot

If weights are stopped 14 degrees out, the timing will look somthing like the black line.

My guess is the timing advance measured this evening is a combination of both springs.
The point of using two different springs is to shape the curve.
The goal is quick advance until 1400 to 1800 rpm, then slow it down alot.

You can go step by step testing but I'll tell you what I think should shortcut the testing.
I think that heavy spring alone is too weak to provide good control above 1800 rpm, especially when used with the lighter primary spring that you just tried.

See if either of the longer looped heavy springs in your collection will fit. Bend the tab so the tension begins when the weight pin has moved just a bit in the slot. (You can measure the distance and look at the rough estimates that people have posted, or get fancy with a degree wheel and pointer to see how degrees that will be, but really its not needed. Just eyeball a little movement.)

Like this, or even a little less.

Assuming you can put a heavy spring in to slow the advance, leave the primary spring as is, or install one with a little more tension. I think a stiffer spring like RickE's or the stock one will be best. This one must have tension on it. It will be the only one holding the weights and determining the rpm when advance begins.

 

[RustyRatRod]

Just take it out and use it as a mini-frisbee.

You got that right. Absolute junk. AND if you ever do get them to work accurately like they're marked, they sometimes cause the advance to stick and hang up. Junk.

 

[halifaxhops]

I contacted them how do they work on the advance cams that are over 15 and are slanted. No reply at all.

 

[fshd4it]

Off to work for a bit, but I'll try those combos when I'm home again and report back.
Thanks guys.

 

[Mattax]

@fshd4it my message is box is full. There's a link to my car website under 'about' on my user profile. You can find my email there.