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Blower Motor Set up and Tune 257 Mirage

Old 10-13-2013, 12:30 PM
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Default Blower Motor Set up and Tune 257 Mirage

Hi everyone ,

Im new to this forum and am looking for help. I actualy own a Hot Rod shop in California www.westcoastautocraft.com and have really good knowledge of engine building and tuning. I have zero experience with blown engines or boats.

I purchased a Mirage 257 trovare with a blown 502. First time out blew head gasket. I had a shop go back through it and now im just getting it going. The shop who has been working on it has done a great job and supplied me with a ton of goodies. Now i just need to make it all work and im a little lost.

What i know about the set up.

502 shortblock with a pretty big hydralic roller blower cam (dont know the specs)
Flat top forged pistons
Everything from here down is brand new.
Dart Pro 1 heads 3 with Dielectric Coating
B&M megablower all rebuilt at The Blowershop with thier front snout and drive. 20% overdriven (should be 6-8lbs boost)
Intercooler with sand strainer
Hardin Marine max volt distributor
Daytona CD-1 Marine unit and coil (running the mercury marine HP800SC program)
Hardin Marine "Hurricane exhaust system"
Quickfuel Marine Carburetors
Holly blue pump regulated to 7lbs pressure
Bravo XR drive
Signature 4 blade 28 pitch prop


So i want to start by saying that i have no issue with any of the mechanics work. He was not quite finished when i went and picked it up. Its been there a long time and i just offered to finish it myself. The day i got there he had just got it running for the first time and it needs tuning. When he started it it was backfiring through exhaust pretty bad. Then he realized that the box was advancing as well as the distributor. Because i was pressing him to let me take it he safety wired the advance in place which stopped the backfiring.

So i finished up a few odds and ends and took it out yesterday. Idle sounds great, throttle responce is excellent with no pauses or stumbles, and boat starts right up. The problem was the minuet i put load on it it has no power and sounds like its stumbling nd or missing. It is maintaining 7lbs of fuel pressure. I put a timing light on it and at idle (800-1100 surging) the initial timing was bouncing around between 13-18 degrees. I figured the bouncing seemed to be from the surging. The advance is all in around 3500 rpms at 28 degres total. I dont know what it should be. Thinking about the timing bouncing i decided to pull cap and check the mechanical advance, and as it turns out the rotor does move a few degrees. There are no wieghts or springs and it is wire tied, but the tie job seems to have loosened a bit. One other thing to note is it also dawned on me that the full tank of fuel is exactly 1 year old (91 octane from pump) and the fuel has been in the boat tank and the boat has always been indoors.


So based on my own knowledge (with naturally asperates engines) locking out the distributor in a more appropriate way and getting better fuel is in order.

Here are my questions.
Do you think the slightly loose wire tie job is causing the problem?
Can the fuel cause this problem?
What timing advance/set up should i run (initial, advance, how much, and how soon?)
Do you see any holes in my set up?
What is the top speed potential of this set up?


Any good advise would really help!

Thank you all in advance.

Chris

Last edited by WCAC; 10-13-2013 at 12:55 PM.
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Old 10-14-2013, 01:31 PM
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Is it ethanol fuel? If so drain it and put fresh gas, it has caused more issues than I've ever imagined. Even with the distributor moving the timing 5* you're still only at 33* total, which is where you will probably need to be anyway.
Air/fuel ratio gauge would be really helpful. With the 420 blower. (I'm assuming) 20% overdriven is a decent amount and may be pulling the power valves open a bit early if they are not boost referenced. Just a thought.
But before getting into any of that definitely drain the tank or try a seperate fuel source, 5 gallon outboard can or some sort.
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Old 10-14-2013, 01:52 PM
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Originally Posted by Borgie
Did you change the fuel filter? Wouldnt think year old fuel would cause any issues unless contaminated with water which is unlikely. Also check the fuel tank vent. Just some initial basics to check. The wire tie job might not be relevant but fix it anyways. Hopefully some others will chime in. Congrats on the Mirage, very well made capable boats made in the Seattle area( no longer in business). I am building and modernizing a 93 232 trovare. Timeless design.


Yes, all new filter, vent, etc. i agree, i love the design.
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Old 10-14-2013, 01:54 PM
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Originally Posted by lil red
Is it ethanol fuel? If so drain it and put fresh gas, it has caused more issues than I've ever imagined. Even with the distributor moving the timing 5* you're still only at 33* total, which is where you will probably need to be anyway.
Air/fuel ratio gauge would be really helpful. With the 420 blower. (I'm assuming) 20% overdriven is a decent amount and may be pulling the power valves open a bit early if they are not boost referenced. Just a thought.
But before getting into any of that definitely drain the tank or try a seperate fuel source, 5 gallon outboard can or some sort.

Im going to drain fuel today. The carburetors are boost referenced.
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Old 10-14-2013, 01:56 PM
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Update.

I locked destrubutor as per Hardin Marines proceedure. I ran it again, same thing. We started advancing the distributor and the more we advance it the better it runs, but it would be off the chart (like 50*) so we abandoned this. We locked the advance all together and set it at 30*, and it is popping out the exhaust pipes.

Any thoughts?
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Old 10-14-2013, 02:25 PM
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Try running a stock Mercruiser dist with the V6 module(less advance).. If it runs well after that you found the problem.. In my limited experience I have found aftermarket ignitions are hit or miss on marine engines..
Get a wideband O2 gauge/sensor for the boat,, personally I dont run any boosted engine without one..
Next running 6-8lbs of boost on a 500cube engine with big heads and cam like you have is pushing that blower..
I wouldnt safely run that B&M blower past 5lbs of boost on you engine setup for any length of time..
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Old 10-14-2013, 03:52 PM
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Make 100% sure you are on the correct mark on the balancer. I've made this mistake before, if you're on the wrong mark the light will show roughly 45-50* when it starts to run right. In all reality you're at 15 or so degrees.
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Old 10-14-2013, 04:23 PM
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Originally Posted by lil red
Make 100% sure you are on the correct mark on the balancer. I've made this mistake before, if you're on the wrong mark the light will show roughly 45-50* when it starts to run right. In all reality you're at 15 or so degrees.
if your distributor is locked out, you can set the engine timing by simply cranking the engine over, no fuel, just ignition, this will give u a correct and consistant reading to get you in the ball park, by doing this you will be eliminating fluctuation of irratic idle, cam movement, chain flex etc... 30 deg BTDC is a good place to start, once you have fuel system dialed in you should be safe up to 34 deg...
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Old 10-14-2013, 05:23 PM
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have you checked the plug wires to make sure they are in the right order,sometimes people will overlook the simple things.i try to follow a satement i heard a long time ago KISS, [ keep it simple stupid],it works for me.
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Old 10-14-2013, 05:35 PM
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I've had bad balancers before that made you think it was timed right but it was not. You might try using a vacuum gage to time it and see what that tells you.
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