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Proper Advancing 1987 Crusader 350 h.p.

J

jumpin

Member
Good morning to all. Here is my question. Wolud not having enough total advance cause my endines to not make full rpm's? I installed new Pertronix distributors in them and I am not sure if I have enough advance available with these distributors. I am using a adjustable timing gun that checks out at idle using the "0" function it reads 10 degrees on both motors and if I dial it to 10 degrees it reads on the zero mark. At 3000 rpm's it reads 22 degrees on the port motor and 20 degrees on the starboard motor. On water wide open is 3800 rpm's on the starboard side and 3600 rpm's on the port side. The boat is a 1987 Chris Craft 427 Catalina and the props according to survey. I did not look myself before putting the boat back in the water (I know that was dumb) 4 blade props 24" in diameter and 25" pitch. The engines start very easy and idle fine. Flame arresters are clean and fuel has Startron in it and is 93 octane fresh fuel. I know I am lugging these motors and feel I may have too much prop. I plan on having someone operate the boat a full throttle this weekend and go in the engine room and listen for detonation as I think this should indicate not enough advance, Right? Any opinions would be helpful, especially if anyone out there has a similar setup. Thanks in advance. This place has the knowledge that can help a person repair and maintain their vessel and I am always grateful for time taken to help me learn. 1987 Catalina 099 THT.jpg
 
Yes, your engines won't make full power if the total ignition timing advance specified isn't reached.

You should have at least 32 degrees by 3800 rpm. Never worked with a pertronix distributor so I can't say what can/can't be adjusted on them. Get the specific model and check with pertronix on what the factory configured advance curve should be before you change anything. Or check the literature that should have been in the boxes. If you plan to use 93 octane all the time, you may be able to increase total advance, beyond factory suggestion, a couple degrees.

You won't hear detonation (at least not for long) and it may be caused by TOO MUCH advance, not too little. Best to make adjustments one-at-a-time and record them so you know what each tweak provided.
 
jumpin said:
  1. Wolud not having enough total advance cause my endines to not make full rpm's?
  2. I installed new Pertronix distributors in them and I am not sure if I have enough advance available with these distributors.
  3. I am using a adjustable timing gun that checks out at idle using the "0" function it reads 10 degrees on both motors and if I dial it to 10 degrees it reads on the zero mark.
  4. I know I am lugging these motors and feel I may have too much prop.
  5. I plan on having someone operate the boat a full throttle this weekend and go in the engine room and listen for detonation as I think this should indicate not enough advance, Right?
Click to expand...


  1. That is correct! (Keep in mind that too much will cause issues as well!)
  2. Look up your OEM ignition advance curve and limit. Have a shop with a distributor machine test each distributor. They can make changes to suit your OEM curve/limit!
  3. I would suggest that you mark off your harmonic balancers up to approximately 35* ahead of the OEM TDC mark. I'd also suggest that you strobe these with a standard timing light, or a digital timing light while in standard mode. This offers you "Real Degrees" in "Real Time", and is what I prefer to do. This eliminates any equipment malfunction and/or user error with a digitally advancing type timing light.
  4. Ah, the ole Catch 22! If your TA is within reason, you may simply be incorrectly propped. I would NOT continue operating if so! You may over-burden these engines, regardless of which RPM you are operating at! In order to do a successful WOT RPM test, all engine related tuning aspects much be dialed in correctly. The test is no good, if not!
  5. Detonation and Pre-Ignition are two entirely different phenomena. We can hear Pre-Ignition in a Marine engine, but Detonation is very difficult to hear. It is also very destructive to a Marine gasser!
In order to actually take advantage of your engine's potential, with regard to TA (total advance), you'll want to know the engine build. I don't believe that the BBC used a full dished piston, but if so, the TA must be held back some. See your OEM specs!

If the engines were built using a quench effect combustion chamber (i.e., LC Q/E or reverse dome), and if the C/R is correct for Marine cruiser use, then the TA can be a bit greater, yet not risk detonation potential.
Either way, a correct TA becomes a fine line between performance, and Marine engine detonation.

I think that you may have two issues here..... props and TA!
I'd get the TA dialed in first!

Here is an example ONLY of an advance curve that includes the 7.4L and 8.2L.
(pay no attention to the original and final graphs.... not sure who altered this)
Note that the vertical scale does NOT include Intial or BASE advance! This must be added when strobing your timing marks while checking advance dynamically.
If Crusader offers a curve like this, that is what I'd use!
171135.jpg


Again, see your OEM specs for this to be certain!

.
 
Rick,

I have basically the same size boat/engines and also top out under 4K rpm's. I wanted to know what bad things happen when the engine is over-burdened besides burning alot of fuel and assuming it is not detonating , I don't see any harm. 36/38 is fairly close to 40 (didn't say if accurate tachs)
Also if Jumpin is set at minus 10 and seeing plus 20 at higher rpm, then doesn't he have about 30/32 which is close to spec? I am not dis-agreeing but really want to know (I'm in the same boat). Tim
 
Tim, not sure that I understand your "36/38 is fairly close to 40"! Are you speaking of ignition advance numbers as in "degrees"?
Total Advance numbers must always be accompanied by an RPM. Any TA spec, w/ no RPM, is a worthless bit of information.
BASE or Initial is always set at idle RPM, so this is never really an issue.

BTW, if those are Total Advance numbers, and if corresponding to an RPM range at/near 3,200/3,400 RPM, those are way too high for a Marine gasser, IMO. The engine will very likely undergo detonation if using those figures. Just the nature of Marine engine loads.

Also if Jumpin is set at minus 10 and seeing plus 20 at higher rpm, then doesn't he have about 30/32 which is close to spec?
Click to expand...
Again, not sure that I understand you regarding "minus 10", and I have not seen an OEM ignition curve for his exact engines.
Again, keep in mind that Total Advance must be accompanied with an RPM.
IOW, to bring in a TA of 30*/32* @ 3,400 RPM is one thing............., but to bring in a TA of 30*/32* @ 2,400 RPM may be a recipe for detonation damage.
Conversely, to bring in a TA of 30*/32* @ 4,400 RPM may leave performance on the table.

I did not catch that Jumpin's Pertronix were EST. If they are EST, then the procedure changes somewhat.... however, his TA should not!

********************************

I am fully aware of how well the guys love their Digitally Advancing timing lights, I just prefer to do this dynamically and in real degrees/real time, and eliminate any risk of error. Call me "old school" if you want to! :D

.
 
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Rick:
Pretty sure the 36/38 close to 40 refers to the rpm achieved.

BD2:
The issue with the overpropped situation is the ease that the engine will overheat. Overheated engines can detonate very easily. Usually, it's only an issue at the upper end of the RPM band; if you don't go there, you should be ok.

The "-" on the 10 degs at idle is a bad inference.
 
You may be right, Mark.
Peresonally, I did not know if degrees or RPM were being discussed!

If 36/38 or 40 is to mean 3,600 / 3,800 to 4,000 RPM, then the short cut for this can be 3.6k, 3.8k to 4krpm.... for example. Hardly worth saving a few key strokes for!

Pertaining to certain criteria, it can be important that we all speak the correct language on this stuff. :D

.
 
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Rick,

Sorry for the very poorly written question, even I could not understand it after re-reading.
So what I really meant to say is; Jumpin says he has 10 degrees BTDC at idle, then at 3,000 rpm he has 20 degrees - port and 22 degrees strb, so a total of 30 port and 32 strb. For his engine he appears within specs. Crusader calls for 4,000-4,400 max rpm at wot. So if he is turning 3600 rpm port and 3800 rpm strb, he is fairly close to the recommended max r.p.m.. He also did not say how he got the rpm (off the boat tachs or with a more accurate gauge).
My question was given the numbers Jumpin is currently seeing; what harm is being done by over-loading the engines?
I have the same engines and same numbers on my boat. With gas price what is it, I doubt anybody is spending too much time with the throttles on the wall attempting to push 14 or so tons boat around. So why get smaller props that are only going to change a top end rpm that you rarely use?
I apologize again. After re-writing, it still sounds like a stupid question. Tim
 
bluedog2 said:
Rick,
Sorry for the very poorly written question, even I could not understand it after re-reading.
So what I really meant to say is; Jumpin says he has 10 degrees BTDC at idle, then at 3,000 rpm he has 20 degrees - port and 22 degrees strb, so a total of 30 port and 32 strb. For his engine he appears within specs. Crusader calls for 4,000-4,400 max rpm at wot. So if he is turning 3600 rpm port and 3800 rpm strb, he is fairly close to the recommended max r.p.m.. He also did not say how he got the rpm (off the boat tachs or with a more accurate gauge).
My question was given the numbers Jumpin is currently seeing; what harm is being done by over-loading the engines?
So why get smaller props that are only going to change a top end rpm that you rarely use?
Tim
Click to expand...
Tim, understood! I too have to proof read my own at times! LOL
And there are NO stupid questions!

As for timing..... if he is using a digitally advancing timing light, he may not be understanding the procedure. This is just one reason why I'm so Hell Bent on using a standard mode strobe light, and using "Real" degrees marked off on the Harmonic Balancer. It is as simple as falling off of a log, and removes any margin of error from the equation, IMO. (real degrees/real time!)

Tim..... IMO, he is short by 400 to 800 rpm of his recommended WOT RPM.
And just to be clear.... it may NOT be a propeller issue! It may be state of engine tune!

But let's say he is tuned correctly. The potential harm caused by NOT being able to reach WOT RPM, may be excessive cylinder heat, and heat that may contribute to gasoline engine Detonation. Depending on the engine work load (hull design, size, etc.), some engines may have a greater detonation potential right at/near this lower RPM range. That would be my concern, since detonation is not exclusively caused by excessive ignition TA alone!
(other causes: High Cylinder temps, poor combustion chamber design, poor grade fuel, incorrect F/A ratio, excessive C/R, excessive loads, etc.)

The entire Pleasure Boat Marine Industry (as per engine model) will offer a specification for WOT RPM, as to determine if a given boat is geared and propped correctly.... and this includes higher altitude operation, anticipated load, etc. The equation does not allow for any deviation due to intended lower RPM operation that I am aware of! (IOW, they still want us to reach this prescribed spec to ensure that no over-burdening is occuring)

An explanation of Marine Propulsion loads is way over my head to even attempt. I put my faith in these engineers that have 50-100 years of research to call upon! :D

******************************************

As for Detonation, I could type a few pages on the topic, and end up boring you! If you were to do a search on "Detonation", you'll find many good articles on this. Many relate to "automotive", but the phenomenon is not exclusive to either. High Performance auto engines may pass through this rpm range quickly, whereas the Marine engine may sustain an rpm where this potential is greater. For the gasoline Marine engine, it can be dangerous at the lower 2.5K to 3.8k rpm range (example only). So basically, it is not necessarily a high RPM phenomenon.

All too often ignition TA is not given enough consideration, IMO. I've seen/heard of well seasoned marine mechanics who will set BASE advance, and then walk away, not even considering checking TA.
We'd be hard pressed to find an OEM gasoline marine engine that was not accompanied with a prescribed ignition curve to follow. Sadly, it's all too often over-looked!


OK, nuff said.... I'm starting to repeat myself! :rolleyes:

.
 
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I have been reading the posts and I can tell you I think my engine tune is good. New distributors, new plugs, clean fuel filters and clean spark arrester. Is it true you add the 20 degrees to the original -10 degrees BTD to get total advance? If so, I think I go to the props next. Have a diver going to clean running gear next week and I will find out what the props have stamped on them and hope it is correct. Have had two different prop shops say they think a 24" diameter by 21" pitch is what I need. Will keep you posted bluedog2.
 
jumpin said:
...........
  1. I think my engine tune is good.
  2. New distributors, new plugs, clean fuel filters and clean spark arrester.
  3. Is it true you add the 20 degrees to the original -10 degrees BTD to get total advance?
Click to expand...
Jumpin, as you can tell, we're all in your corner, and are trying to help you. But some of this may come across rather harsh..... no ill intensions, OK?

  1. Thinking is one thing....... You need to know this!
  2. I know that you said New Pertronix Distributors. Were these Pertronix conversion kits to existing used distributors.... or brand NEW Distributors? Mechanical advance? Can you clarify for us please?
  3. Not exactly! I think that you may be misunderstanding this!
To help understand, a basic mechanical advance ignition system is not capable of adding any spark advance during low rpm start and idle rpm. We give the engine "BASE" (aka "Initial") spark advance by changing the postion of the distributor housing relative to the crankshaft/camshaft only! We set this, and lock it down. The engine then starts and idles on BASE advance.
Actual Ignition Advance is what occurs as a result of any Mechanical advance (or EST system advance) that will be added as RPM increase beyond idle RPM and "Initial" advance. This is progressive!

So think of your "Initial" or "BASE" spark lead as being PRIOR to any Mechanical (or again, EST system) Advance at Low RPM.
And think of progressive advance as being a result of adding both together as RPM dictate! This progresssive event occurs from above low RPM to higher RPM until TA is reached.

So what ever your specified OEM advance curve ends up being...... it may NOT include BASE.
If it does not, then the BASE number must be added to Mechanical (or EST system advance) for the timing light and markings to make any sense to us when we time for TA.
Checking progressive advance is done through the RPM range up to the point at which no more advance occurs! This is called TA (aka Total Advance)! TA may occur @ 3,200/3,400 RPM (your OEM specs will call this out) This is referred to as the "limit" or "full in" RPM.


You also mention having a diver clean the hull.
A dirty hull can play HELL with achieving the correct WOT RPM..... even with properly tuned engines, and perfectly matched propellers.


.
 
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Thanks Rick, Complete New Distributors, Mechanical Advance and I am looking in my Crusader manual for TA Specs. The reason for the diver is two fold. First, I totaly agree that no testing can be conclusive without a clean bottom and running gear, and second I think I may have different props than the ones listed on the survey. The personI bought the boat from in 2009 called me not long after the sale wanting to sell me some refurbished props that were just by chance the same diameter and pitch as the ones on the survey. I think he may have hit something with the originals and may have replaced with whatever he could find that was close. Thaks again for your time and efforts in your posts.
 
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