HAS ANY BODY TRIED TO RUN A LATE MODEL 87 AND LATER HEI(SEPARATE COIL) IN A PERFORMANCE APPLICATION ? I KNOW THEY WERE ON COMPUTER CONTROLED ENGINES BUT THE ADVANCE CURVE IN PRE-SET IN THE MODULE AND NOT IN THE COMPUTER. I WOULD LIKE TO RUN ONE ON MY B/B JET BOAT BUT NEED A SMALL DIST. TO CLEAR A TUNNEL RAM, THANKS FOR ANY INFO , ROB

Contact Dave at Dave's Small Body HEIs. He knows his HEIs and should be able to answer your questions.

You can e-mail him at: sparkman451@earthlink.net

By the way, you should turn your CAPS LOCK off, in internet-speak it implies that you're yelling, and it is also harder to read.

Good luck.

The timing tables are programmed on the EPROM in the ECM not in the dist. Only initial timing can be changed at the distributor, which has to coincide with the initial value also programed on the EPROM. I'd think at the least, you'd need an ECM, knock sensor, ignition module (the one on the firewall), a map sensor and a throttle position sensor to make one of those work.

The Delco Voyager marine ignition system is built on that basic distributor. It has been discontinued, though.

You are correct. The "limp home" timing curve is built into the module. Mercury Marine (and perhaps delco) sells at least four modules with different curves. You won't have the benefit of knock sensor and the rest of the computer controlled stuff without the whole computer.

The down side is: On a small boat, vacuum advance is VERY handy, yet none of the marine distributors have it, including of course, the '87 and newer small HEI.

I have a pair of crusader 454 marine engine which are using stock looking gm small hei didst., I replaced the cap and rotor with accel parts, this is a very simple setup as this seup uses no sensors of any kind and a 2 wire plug you just unplug,reverse, set base timing, and reverse to run, works excelent, they must just loop the timing wiring, but not sure, but all timing curve is in module, Thanks Rob

That's very interesting. Is this the same dist. used on TBI/TPI as well? How is it wired?

It is the same dist. thats the cap/rotor I used, appears to be a very simple set-up, I don't have a wiring dia. handy, next time I go to the the boat(now pulled and winterized) I'll look in my paperwork and see if the wiring dia. is listed. I always thought the timing curve was in the computer(a lot of others do as well) but thats not the case, was also told by a GOOD parts man at a advance auto parts NEVER buy a aftermarket module for a gm car, as they are one size fits none comprimise unit and performance can suffer.
I am running a h/p kit in a old style hei in my 71 B/B chevelle and that works great, did notice a big improvement over the old stuff I removed(did have a carquest module in it)thats why one of these dist. with the perf. mods my be a slick setup with clearance for a tuunel ram, Rob

I thought about running one with the computer, just so I could reprogram the curve any way I liked with tunercat, and also to program and control the fans. It would aldo provide a programable rev limiter. I have the parts, but it's still on the back burner.

The HEI car computer controlled modules DO NOT have a timing curve built into the module. The computer controls the timing once the engine is started. Whoever told you that the car modules have the timing curve inside them was wrong.

The "bypass" or "set timing wire" is the input to the module to tell it to switch from the module control to computer control. You disconnect that wire so the timing is fixed at the module setting so you can set the timing. Then, when you reconnect it the computer takes over again and adds the programmed advance. When it's not in computer mode the module has a fixed base setting and then it steps to another advance setting at something like 1500rpm. This second setting is to provide enough advance the car will run a little better that with the base 10 degrees if it has to go into limp home mode. So, there is no curve, just 2 different timing settings. If you just disconnect the set timing wire on a fuel injected system, so the computer is still in full control of everything but timing, the engine runs like complete crap. You'd get about the same results with a non-computer distributor by locking the weights partially advanced and disconnecting the vacuum.

The main reasons you were told to buy a GM module is that some of the parts store ones are poorly built so they don't last or they don't have the proper coil saturation circuit so they don't provide the ignition energy the GM ones do. Some could also not have the built in timing advance step but big deal since it's never used in normal operation anyways. It has nothing to do with the type of built in timing curve.

Now, I have no idea if Delco built special modules for marine only use which actually had a timing curve but a car module definately 100% does not. I wouldn't be surprised if there's another small module connected to the distributors of the engines you're looking at that controls the timing. Basically takes the rpm signal from the distributor and adds a set timing curve to it.

Thanks for jumping in Peter, I didn't think it had it either, but I'm wrong usually more than right. While were discussing it, what am I forgetting for running one on an engine without the EFI for ignition and fan control? I would really like to give it a try some time.

It really requires custom programming to get rid of the parts that monitor the O2 and check that the engine is fueling correctly. Otherwise, the computer can go into a fault mode and some things may not operate correctly. It really depends on the computer as to what it does. There is a custom hack for a '7747 computer but that computer doesn't have a rev limiter.

Peter

YES, the computer controlls the timing curve of the small diameter HEI distributor WHEN IT ISN'T BROKEN OR DISCONNECTED.

The newer small diameter module HAS A LIMP-HOME TIMING CURVE BUILT IN that is RPM sensitive, and is activated when the ECM takes a crap, or the harness is disconnected. So, for a no-vacuum-advance timing curve, marine or automotive, all you need is the wire harness that connects the module to the external coil, and the wire harness that connect the external coil to power and tach.

GM sold variations of the small diameter HEI as the "Voyager Marine" ignition system, as a retro-fit to older points-style distributors for V-8, V-6 and 4 cyl engines, using, of course, different distributor bodies 'n' pickup coils for the different engines. Unfortunately, those units seem to be discontinued. My Delco manual shows the p/n to be:
2.5 and 3.0 four popper: 10457090
4.3 V-6 10457091
5.0 and 5.7 V-8 10457092
7.4 and 8.2 V-8 10457093
The external coil is the difference in part numbers between the small block and big block. They use the same distributor, 1103799.

You would need:
ANY V-8 small diameter HEI in good condition. Note that these units are known for crapping out the magnet on the mainshaft. Choose wisely, my child.
Ignition coil p/n 1115498 (small block) or 1115499 (big block) I have NO IDEA why or how the coils are different, and I bet you could interchange and never see a problem.
Wire harness p/n 12097982
coil pigtail p/n 10486134
special harness used to defeat the electronic advance and lock the timing in order to set initial timing and idle speed: p/n 10486133
IF these numbers are still good, you'll need to go to a AC-DELCO outlet, not a Chevy dealer.

Of the numbers listed, so far as I know, NONE of them are "special" for marine use, except the one used to lock the timing, and that's only for tune-ups, you disconnect it and put it in your timing light case when you actually run the boat. (This special connector plugs into the same "port" in the module that the computer would plug into, if there was a computer. Since the whole point of this exercise is to get by WITHOUT the computer, that port is normally "empty".) On a stern drive (NOT a jet) you would plug in another special harness to the "computer" port. It has only one wire, and is connected to the shift interrupt switch. I think the purpose of this harness is to kill RPM and power when shifting between neutral and forward, or neutral and reverse, to protect the outdrive unit. The part number for this harness is 10486135. Again, Delco, not Chevy dealer.

You should be able to scalp all of this stuff off of any junkyard refugee, except for the special tune-up wire harness and shift select harness.

I was wrong, there is only one advance curve for the small diameter HEI. The Mercury Marine modules I referred to in my first post are different. According to the chart in HPBooks: Big Block Chevy Marine Performance, pg 189:

"THE ADVANCE CURVE"
11 degrees advance at 700 rpm
12.5 D A @ 750
13 DA@ 800
15 DA@ 1000
16 DA@ 1250
16.5 DA@ 1500
17.5 DA@ 1750
18.5 DA@ 2000
19.5 DA@ 2250
20.5 DA@ 2500
21.5 DA@ 2750
22 DA@ 2800 and higher

I guess that means you need to set the initial timing at around 10-16 degrees with the special harness in place. If the engine idles higher than 650 RPM, you're gonna have a lot of advance! This could be beneficial to smooth out a rumpety cam. Considering the "dirt cheap" cost of this ignition system, "try it, you'll (maybe) like it!"

On my v-drive, vacuum advance is good for about 30% decrease in fuel use. I don't know if a jet would see that much improvement, but I bet there'd be some.

Last thought: I HAVE NOT researched this. I wonder if you could take that shift select wire harness, and connect it to a knock sensor...

Thanks, I knew there was in fact there is a timing curve in the dist. in the crusader engines, i was pretty sure i saw a gm part # on the module when I was tuning the engines a while back, I can also tell you if you don't reconnect the timing connector back to "run" the motor has no power(imagine that)I was thinking of using one of the new engine works or simular h/p dist., if this set-up give you a lot of advance down low after starting that might work out very well, and we don't turn these boat engines much above 6k, may have to see what modules crusader has for replacements, I know they used this ign. setup thru the 90's at least, Rob...

You'll need to research this a little further to find out what the part number of the module with a timing curve is.

In my research on car systems I've never heard or read of a timing curve in the module before, only the 2 steps. I've read a little info written by hackers on how the GM code for trucks of those years worked (87-91 trucks using '7747 computers) and there was no mention of the computer compensating for some type of base curve in the distributor module. I've actually looked through the code and I know there is no table with "the advance curve" in it. If the module had "the advance curve" in it, the computer would have to know what it was so it could properly adjust the timing to it's programming. I've programmed simple timing curves into the computer with only a few different advances so that I could check that I was doing it right and the numbers I put in were what the timing actually was. So, the GM engineers didn't just modify the timing table in the computer to account for "the timing curve" in the module. I've put the computer into limp home mode and there was no timing curve coming from the module but only the 1 step that I mentioned. The computer only stores the base mechanical timing setting. To sum it up, I've read and done all kinds of things with the efi system that uses a small cap computer HEI and I've neither read about or found an advance curve in the distributor, during either normal operation or limp home mode.

In the above I used "the timing curve" to represent the distributor module curve Schurkey mentioned so it's not confused with the programmed computer timing curve. I'm not saying a module with a timing curve doesn't exist but just that it's not in the module used in the truck application (which was compatible with every other small cap GM road vehicle application). As I've said, it's got to be a marine part.

Peter

I will check it out further on the marine side, I have worked on both mercruiser and crusader engines and merc used there own dists. w/ there own module, the crudader XL engine are the only ones I've run across with the "stock apearing" late model gm dist, I was amazed at the simplicity or the setup, I don't know the timing curve that they use as I do not have timing tapes to ck total advance at rpm, but when set in the run position, the timing mark is off the tab at idle, stay tuned film @ 11 Rob...