View Full Version : Indmar LT1 Ignition Configuration

09-12-2007, 08:52 AM
I'm trying to gather some info on the Indmar LT1 some of you have in '90s era Mastercrafts (mine is a '98 200VRS MariStar w/ the base TBI engine). I've never seen one live, but I've been looking at engine photos on the boat-for-sale websites. That has answered a lot of questions about how Indmar set up the LT1 for marine use, but I still don't understand the ignition configuration. I see that Indmar replaced the LT1 OptiSpark distributor with the GM Northstar DIS waste-spark system. Did they completely remove the OptiSpark unit? If they did, where does the ECU get the crank trigger signal from? Is there a toothed wheel and sensor on the crank down by the crank damper? How do they block off the OptiSpark drive hole in the timing chain cover if the OptiSpark is not installed? Thanks for any info.

09-12-2007, 09:06 AM
Ummm, I have one, but you are way over my head here...Jim ? Engine Nut ?

09-12-2007, 11:11 AM
My 97 LT-1 had the what I believe is the optispark system. There were two sensors connnected to the engine block that read a notched wheel connected to the harmonic balancer where the timing was taken from.

09-12-2007, 11:16 AM
They use a different timing chain cover and yes, they have a crank sensor. On the cars, they use the cam and crank sensor, IIRC, so they can shut it down when either is in the wrong position. It works very well in the boats. If I wanted to build a vintage car, the marine LT-1 would be a strong contender for what I would use. LTR and 350 Ramjet crate motors would be the other main ones. Probably the 350 Ramjet since it puts out 350 HP and 390 ft-lb of torque and uses the same ECM.

09-12-2007, 12:33 PM
Andy, the ignition system I see in photos of the Indmar LT1 is actually different than the original LT1 OptiSpark system. IMHO Indmar figured out early on that the GM OptiSpark system was going to be a reliability problem in marine use so they switched to the NorthStar DIS waste-spark system. Probably a smart move. The DIS system is the 4 coil unit mounted on the front of your engine with all the plug wires coming out of it. The toothed wheel and sensors on the crank is also part of the DIS ignition system. The original OptiSpark distributor is removed.