Large Cap HEI Conversion

[trlrider]

Morning All!
Has anyone converted a Large Cap (Coil in Cap) HEI to be used with the 8625/7427 ECM's?
Maybe a mid-'80,s Corvette distributor? Trying to remember how my boss' 1984 was set up. Hmm!


Trying to clean up the engine bay a bit and despise the divorced coil setup currently in the truck.

There was a right up on this online, but cannot find it.

Thanks!

[Fast355]

Morning All!
Has anyone converted a Large Cap (Coil in Cap) HEI to be used with the 8625/7427 ECM's?
Maybe a mid-'80,s Corvette distributor? Trying to remember how my boss' 1984 was set up. Hmm!


Trying to clean up the engine bay a bit and despise the divorced coil setup currently in the truck.

There was a right up on this online, but cannot find it.

Thanks!

Vettes used coil in cap HEI through 91. Easy to do even with a roller cam. I would use one for an 85 or 86 Camaro TPI or CCC Q-Jet application if you have a flat tappet cam in that TBI. Just a matter of swapping the connectors and using the matching latency table for the distributor in question. Ran one in my G20 van years ago.

I used the 3.4 DIS with the 7427 in my S15 Jimmy years ago as well. Was a little more complicated to setup though.

[trlrider]

Vettes used coil in cap HEI through 91. Easy to do even with a roller cam. I would use one for an 85 or 86 Camaro TPI or CCC Q-Jet application if you have a flat tappet cam in that TBI. Just a matter of swapping the connectors and using the matching latency table for the distributor in question. Ran one in my G20 van years ago.

I used the 3.4 DIS with the 7427 in my S15 Jimmy years ago as well. Was a little more complicated to setup though.

Thanks for the reply and all you do for the community!
Yes, the new engine in this truck is a flat tappet.
May be a route to take with the Camaro unit, would just have to source one of those distributors.

I have two new big cap dizzies sitting in boxes on the shelf, and was studying a way to use the small cap module. Sure it is possible just not sure I want that headache. LOL!

[trlrider]

Update:
Converted a standard big cap(Coil in Cap) HEI to work with my TBI!
In theory!
Took guts out of the large cap except for the Stator, locked the advance and extended the stator wiring.
With the help of a couple of diagrams/schematics relocated the Module from the small cap to the firewall with a big heat sink attached.
All the wiring and mounting is done.
Still need to finish up some other work before firing it off, but according to everything I have found, this should be good for starters.
Some timing table adjustments will probably be in order due to possible latency delays due to the larger cap.
Found a few old post on various groups/forums where this worked, so I am keeping my fingers crossed.

I always have a couple of new dizzies on the shelf if all else fails, and if I get really frustrated this pup will get a carburetor and straight HEI until I can work out the other issues.

Between the weather down this way and work, it has really stalled progress.

Edit: due to the taller intake, carb to TBI spacer and additional spacer the fuel lines and linkage were in the way of mounting the divorced hei coil in its normal position for a TBI. Mounting it on the firewall looked stupid, would interfere with the cold air box for the hood mounted scoop,
and would require a longer coil wire which would require purchasing another plug wire set. Modifying the Coil in Cap distributor made perfect sense!
Yes, I had other options, but those option required spending funds on more parts.
At this point to the engine swap in the '93, I am done spending funds that I need for my 6.0 upgrade in my '04!

Constructive advise very welcome.

Thanks to all those that came before and have left a wealth of knowledge on this forum and others.

[trlrider]

Update: Finally finished all the needed changes and modifications and fired this project up yesterday afternoon.
Had a nasty miss and intermittent backfire and the injectors were not flowing as clean as I remember.
Made a parts run to pick up some exhaust tubing parts to modify the exhaust to fit the shorty headers and let the engine cool down before searching out the miss. Also needed a timing light since we could not find the one I have not used in several years. Picked up a can of Berryman also to put in the fuel tank to try and clean those injectors a little.

Got back home, had some lunch and back to the project we go.
Embarrassingly found I had crossed the number 5 and 7 plug wires. Fixed there and she ran nice and smooth.
Set the time at zero as required and hooked the wire back up.
The large cap conversion is working this far.
Today our son had a shooting sports competition out of town, so it was late afternoon before I could take the Sub out for a test drive.
Cold it has a random backfire.
Once it warmed up the backfire was gone, but it is low on power.
Going to need to do some logging to see what is going on. Really feels like a timing issue, which is quite possible. We did double check the tdc mark on on the balancer and point and it seems to be correct.
The injectors seem to be spraying better today also after the 2 short 5 mile runs we did.
Checking the headers with my FLIR, all 8 cylinders are within 10 degrees temp of each other, so that is good.
Sometime this week I may get time to rebuild my spare TBI and install the fuel pressure gauge.
Hope to get some logging time tomorrow after work if it does not rain.