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Thunderbolt IV timing question

87concord

Regular Contributor
I've got a thunderbolt IV ignition with the v8-24 module. At what rpm is the advance all the way in so I can check my total timing?
 
I've got my idle at 900 to help with the possibility of reversion since I have a larger than stock cam. That's why I need to set the total, can't do it by base
 
You are a wise man for wanting to not only set/check BASE or Initial, but to also see what your TA is doing.
According to the Ignition Advance curve being shown for the V-8 24 system, it is showing being FULL IN at 3,700 rpm, not 2,500 rpm.
32* Full In at 2,500 rpm (for a non-Q/E built engine) is asking for potential Detonation trouble, IMO.
Sorry Chris, but I happened to catch this, and though it would be important to mention. :)

When viewing this curve, take note that most advance curves will be minus BASE or Initial.
So BASE or Initial Advance must be added in order for your actual strobing to be meaningful.

While this curve is being shown for the BB engine, I'll guess we assume this to be correct for your engine.

If you are of the old school type, you'll want to mark off your harmonic balancer, and strobe this as to see spark lead in REAL TIME/REAL DEGRESS, as am I.
This removes a potential element of equipment error and/or user error when using a Digitally Advancing Timing Light.
This is just too dang important, IMO.... and I know that you guys love your DA Timing Lights.

You do not mention which drive you have...., but if the A drive, your idle speed of 900 may cause issues with coming from gear, back into neutral.... perhaps not!
Just an FYI on that.

.
 
I've got my idle at 900 to help with the possibility of reversion since I have a larger than stock cam. That's why I need to set the total, can't do it by base


NO WAY CAN YOU RUN A MERC AT 900 rpms for idle with a ALPHA DRIVE!!

And while I am at it there is no way you have a cam needing 900 rpms at idle in a marine engine in a pleasure boat.

If you can not get good idle under 750 rpms you have another issue (s). PERIOD!!

Oh and please define reversion for me???

Reversion would cause in my opinion a severe back fire when decelarating or possibly on acceleration but unlikely.

The only way your "cam" could possibly contribute to reversion is if it had some outragous lift and or duration...........

So What cam are you running anyway?
 
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Cam specs are as follows

218* intake
228* exhaust. @50
.525 lift with 1.6 roller rockers

112* LSA

Stock merc manifolds and risers
 
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I have always been under the impression that reversion occurs at idle when the cam is overlapping. At the low rpm the gases aren't moving fast enough to keep the water from sucking back into the motor
 
That is a nice cam but what outdrive are you running? What motor? small or big block?

You are also correct in your understanding of the effects of reversion in some cases......Merc bigblocks (HO) had this issue from the factory years ago and was forced to run a aftermarket exhaust manifold to overcome it. (Gill) I believe but I actually forget, been awhile..

If you have the room under your engine cover you may be able to add some 3-4 inch riser extensions to increase the distance but the ultimate fix is a better exhaust manifold where the water being introduced is father down stream (at the end of the elbow). In my opinion.
 
I have always been under the impression that reversion occurs at idle when the cam is overlapping. At the low rpm the gases aren't moving fast enough to keep the water from sucking back into the motor
That is correct in some scenarios...., and is exactly why lobe seperation is important for most pleasure boats.

On another note.... the Mr. Gasket decals are great, but we must purchase the decal for the diameter of the balancer.
Otherwise, the degree numbers will not be correct.

.
 
It's a 350 SBC, VORTEC heads, performer rpm intake, demon carb, forged flat top pistons, decked and balanced, roller cam. It runs good but I'm needing to set my timing to keep from detonation. I'm thinking 32* total advance is all the vortecs will want. Correct me if I'm wrong but to check total you run the engine to 3700-4000 rpm and twist the dizzy till it's at 32*? it was set once but it was at base and I really need the total. On another note it will idle smoothly at lower rpm but I set it 900 and have had a little difficulty shifting back to neutral. Think I would be safe around 750-800?


Side note: my timing light has and advance knob on it
 
That is a nice cam but what outdrive are you running? What motor? small or big block?

You are also correct in your understanding of the effects of reversion in some cases......Merc bigblocks (HO) had this issue from the factory years ago and was forced to run a aftermarket exhaust manifold to overcome it. (Gill) I believe but I actually forget, been awhile..

If you have the room under your engine cover you may be able to add some 3-4 inch riser extensions to increase the distance but the ultimate fix is a better exhaust manifold where the water being introduced is father down stream (at the end of the elbow). In my opinion.


I plan on upgrading to better exhaust next year but it is out of the budget for the moment
 
If you are running an Alpha out drive you will be replacing the lower also next year if you continue to shift into gear at 900 rpms.........just so you know.

750 would good!!! 650 would be better!!

According to the pdf posted above the 350 timing module is at max advance at 4600-4800 rpms and 32 total degrees is the spec.

All of this info is for not because you are not running a stock motor. You really need a performance ignition, one you can tweak.


Do the base timing method, reduce idle rpms to 700 and set it at ~8 btdc and forget it. Then if need be, readjust idle back up.

The demon carb is a great carb and is very tricky to tune... it is awsome though.....

Do you have a knock sensor? If so that should help with the detonation but will reduce performance....A little.

When you did this motor What did you set the squish to? typical optimum is ~ .030-.035". what was your piston deck hieght? if you used a standard head gasket then you may have a minor issue with too much squish if you are having detonation.
If detonation is an issue then you may want to reduce you initial timing a couple of degrees.

If all this fails then getting a different ignition with an adjustable timing curve would be best.
 
That is correct in some scenarios...., and is exactly why lobe seperation is important for most pleasure boats.

On another note.... the Mr. Gasket decals are great, but we must purchase the decal for the diameter of the balancer.
Otherwise, the degree numbers will not be correct.

.

Jegs has them and they are taylored to the damper diameter that they intend to be used on.
 
ok so i set idle at 700, set base timing at 8*btdc. when i run the motor to 3700 rpm its only getting like 25* total advance. its a v8-24 module. is it possible that the module is faulty or do they not have this kind of failure, or is it possibly that its not all in until 4500 or so? the chart for the v8-24 is showing 3700 and the v8-24S is showing 4500 or so.
 
I am not currently on my pc so i can not look at the pdf with the graph.
From what i remember when i looked the other day it said 4400 + until full advance.
Did you go past 4000 rpms to see if the timing continued to increase?
 
I just fired up the puter and looked.

So you have a big block timing module.......................lol

the 24S is for the "high output" models especially SKI boats......

If that is what you have then according to the chart you should have a full 24 degrees by 3700 rpms......+ 8 initial would = 32 total.......

The fact that you reach 24 degrees says the module is working.

one more thing did you remove the jumper when you check the total? The only thing that comes to mind is if you have a knock sensor and that is the reason to jump the module to ground to begin with (to eliminate the timing changes caused by the knock sensor) then maybe it is detecting KNOCK and holding the timing back.......

I am not 100% sure how to defeat the sensor or eliminate it and if you were to do so what efect it would have on the ignition.

my suspision would be to remove it (plug the hole it came out of) and bundle it in some towels away from the motor so it can not detect any knock and see if the timing advances correctly.

I personaly have never messed with a knock sensor so I am unfamiliar with its function in electrical terms....and what signal it actually sends to the module.

Not sure what to tell you at this point.......
 
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There is no knock sensor, I'm getting ready to take it to the boat shop so we can hook it to the dyne and I can put it under load and runthe rpm higher and see what's going on. I'm also hoping they have a a SBC module I can try as well. Post back shortly with results
 
Ok I'm stupid so if any new guys read this take note. Last night when I was revving the motor I had the distributor loose and when I would rev it up it was retarding the timing. I figured it out this morning after repeatedly checking base and total timing. After I got the base set to 8* I tightened the distributor and got 32* full advance. It's a simple mistake but I should have known better lol. Thanks guys for all your help!!!!
 
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