MSD vs Thunderblot

[Sam]

I have been told that the Mercuriser Thunderbolt ignition will perform as good as an MSD unit on small blocks. What's the difference between the two and if you switch to MSD do you need to replace the OEM distributor.

THX
Sam

[Rootsy]

Sam,

as far as electronic ignitions go, the thunderbolt has little over anything else in terms of energy delivery... if you want more energy you need to go with a better coil with more windings. If you want to put an MSD box and rev limiter on it you will need to replace the distributor since the Thunderbolt is a fixed shaft (no mechanical advance). The thunderbolts advance curve is controlled by the computer module. A distributor with a mechanical advance will let you modify the advance curve by replacing springs and weights etc depending on the distributor. YOu cannot change the advance curve in a thunderbolt ignition unless you replace the module which are made for different engine models. The thunderbolt V is different for the IV in that it constantly varies the ignition curve depending on what you are doing.. it'll increase advance until it sees no performance gain then it'll drop back a bit.. it also adjusts idle so that it remains constant. The IV has a straight ignition curve and advance. The MSD ignition box claims multiple fires per combustion cycle but this only happens up to approximately 3000 rpm then the time between firing on the same cylinder becomes too short and it reverts to a single spark. The multiple spark helps keep the cylinders clean at lower rpm's and improves fuel milage by helping complete combustion to occur.

[BigGrizzly]

Putting all the techie stuff aside. I have not heard anyone who would go back to any thunderbolt after using the Thunderbolt IV or V ignition, ask Rick if he would go back--not.

Randy

[Sam]

Randy, how do I tell what Thunderbolt ignition I have.

Sam

[RickR]

Thunderbolt V has two solid state modules attaached to the Distributor. The second one is for the knock sensor. T IV has one module.
Is your SBC stock?
If not, how does she idle?
What grade of fuel do you use?
What is your Max RPM?

Modules cost a couple of hundred bucks. Thunderbolt is fine for a close to stock engine. But a MSD is much more versitle to adjust advance curves and total advance.

MSD will not increase top end power but it greatly improves idle and off idle performance.

[Sam]

Rick, Up until a few weeks ago it was stock 350 2 brl and idled very well. At present it is undergoing a top half upgrade IE cam,heads,intake and carb. I usualy run 89 octane fuel. As far as RPM we are targeting 5200ish. My builder who is a Mercuiser mechanic said that my currrent ignition is just fine. I guess come Monday I will find out what series I have. He has been very up front with me and knows his stuff. Beyond his mechanical abilty he is also an avid performance boater but it can't hurt to ask.


Sam

[Rootsy]

Randy has a valid point... actually my thunderbolt V is now a IV... I've never personally had nor in my 5 years as a marine mechanic in the midst of the thunderbolt IV era did i ever experience any problems with the thunderbolt IV... my experience with the V on the other hand...... well lets just say... that module is somewhere about 30 yards off my dock in about 20 feet of water... after i bought my boat i noticed that the wires into the module had been probed and it never did want to idle very stable... then last summer after a good run she just wouldn't run period... basically the ignition was breaking up terribly at anything above idle. so i went to a fixed curve IV module from a 350 mag which works just ducky for what i'm doing instead of shelling out the 800 or so bucks for an MSD... although it's on my wishlist... maybe this year.

actually do you have the plastic flame retarder cover that came on the motor? it'll tell you what ignition series you have on the sticker... or like above you can look for the knock sensor... or you can check the part number on the module attached to the distributor.... basically merc changed over to the V around 1994 or 95.... my boat is a 97... HAD a tbolt V...

[Sam]

James I happen to have the plastic cowl you spoke of but there is no mention of the ignition on the label. Looks like it will have to wait until Monday.

Sam

[jwright]

Hi Sam,

I have the MSD ignition on my boat. I installed it to replace my original points ignition. It has worked well overall, except for a problem a year ago that was hard to trouble shoot becasue it was intermitent. I ended up replacing some parts, but it my have just been a bad connection.
I have never had fouling issues with it and the engine starts great. I am not sure if it is worth the cost on anything but an extremly high performance engine. As I said, I was replacing points. If I already had an elcetronic ignition I am not sure if I would spend the money.

[RickR]

I am not a SBC guy but if the cam, heads and compression is not too radical I'd suggest 32 degrees total w/89 octane.
If she starts and idles good at 32 total with the Thunderbolt I'd keep it.

[Sam]

For what it's worth I found out today that I have the Thunderbolt V ignition. As far as the major up grade components they are all in. I should be ready to go in a week or two. Then I just need some open water to begin break in and prop testing.

Sam