rev limter
 

have 96 , 38' cig top gun. two , 100 hour 502, mag mpi box stock. bravo 1's with 24 props. am new to the boat and have just gotten it together and doing sea trials. everything works like its supposed to. however 54 mph ( gps true) is as fast as it goes trimmed out in perfect conditions.... the motors get to 4500 and just stop there. are these things rev limited ? the reason i ask is that even in less then perfect conditions it does the same thing.... doesn't seem drag limited.... seems to repeatable for that....

Re: rev limter
 

Rev limiter are at more like 5200rpm.
Those engines make max power at 4800-5000rpm.
Does seem a bit slow, ask over on Cig. forum if you've got the right props.

Re: rev limter
 

thx...will do

Re: rev limter
 

check ignition timing

i had my motor rebuilt last year (single 502) and was still only getting 59 mph out of my 27 fever. i bumped the timing up 2-3 degrees from stock and picked up 2 mph. I think i need to play with the carb now, the plugs looked pretty rich when i winterized it.

Re: rev limter
 

these motors are efi... but for the record, running your motor rich is the single worst thing you can do to it. the extra fuel ends up in the oil and dilutes it, washes the oil off the cyl walls so they don't seal and won't make power any way... bumping the timing picked up the combustion chamber temps a bit and got rid of some of the extra fuel so that " increase " you saw wasn't real.... it is just masking the symptom that will ultimately junk your motor.

Re: rev limter
 

Something doesn't add up. If it were the wrong ecm, it could limit it to 4600, however, it would have most likely burnt it up as well. Tachs could be wrong, or someone could have altered the ecms. See if you can get a checksum number off of the ecm or have someone get the checksum number out of the ecm.

Re: rev limter
 

maybe can do... THINK local dealer has the computer interfaces to read the boxs however... these motors were takeouts and where absolutely complete and factory when i got them. every single nut bolt washer screw and tie wrap is factory so i am convinced the boxes are correct. also... they run great. start instantly make real power , accelerate f;lawlessly... checked the plugs before i reinstalled the motors and they were perfect....

just gets to 54 mph 4500 on both tachs EXACTLY and stops right there... like it had a soft limiter that i couldn't feel... and i don't mean 4435 or 4511 revs... i mean the needle SPLITS the 4500 line on both tachs... and stops rite there....

i want my other 600 revs.

Re: rev limter
 

Maybe you have taller ratio drives and 4500 is all it can spin them. You asked for help, I gave you some advise to clarify ecm info which is the only thing that controls the rev limiter on a stock 502 efi/mpi and the title of this post is rev limiter.

Re: rev limter
 

I'm sure that your advise is appreciated... :cool:

Try smaller props.
If they still don't spin past 4500 then there is another problem besides not enough power...

Re: rev limter
 

Smaller props. You may be lucky to see 58-62 mph. Takes a lot to move a TG.

Re: rev limter
 

not certain what i said that implied any and all advice not appreciated. any and all advice IS appreciated. was trying to offer more detailed infomation that might assist those more knowledgable than myself in coming to a conclusion.

suggestion was made that boxes may not be correct and is, of course a possibility.... was just pointing out that llikelyhood of that , given the physical evidence, less likely than more and that problem , if any, may be elsewhere.

for the record you are talking to someone here that has , essentially zero experience in the marine industry but 30 yrs experience in the race car engineering and manufacturing industry.... am asking questions and posing problem in a technical scenario/forum and simply applying my own engineering logic to any proposed solutions.... thats what discussion and problem solving in an engineering sense are all about....

i thought.

Re: rev limter
 

Take a look at your hull. Using a 4-5' straight edge, make sure there is no hook or rocker in your hull. I have seen the exact same thing when a rocker developed in the hull about 4' forward of the transome. Right where Myco left a space for lifting straps.

Re: rev limter
 

The info provided was to eliminate one possible cause and to address your title and problem as stated of hitting the rev limiter. Nothing but the ecm controls the rev limiter.

You can eliminate that from your list of potential issues 100%by following the suggestion.

Another way is to do as another suggested by putting smaller props on and seeing if it revs more.

Look on the drives and see what gear ratio is stamped on it and then turn the engine over and check it.

Re: rev limter
 

Did you ask what props to run over on the Cig. forum or at Prop talk?

I'd try a set of 23p Mirage or Mirage+.
Spin then out, then try spinning them in.
I realy don't think a 38' Cig is much more than a 60mph boat with twin 415HP/502s

Re: rev limter
 

lets talk about the props for a minute..... people keep saying " less prop"
and that was the first thing the local guru here said as well and im not argueing.... im looking to understand this at a basic level. now on the cars that is analagous to shorter gears... which will improve acceleration but not necessarilly add more top speed ( unless you were geared very bady to start with) . now a 22 prop is about 8 % less prop than a 24 which means i would need 8 % more revs to break even... which for the sake of this discussion is about 375 revs.... so that gets me to 4900 give or take for the exact same speed. question... has anyone actually see a dyno sheet for one of these motors ? is there so much more power at 4900 to then allow the boat to get thru the drag limitation then there was at 4500 ? serious question does anyone know what this power curve really looks like ?

Re: rev limter
 

Don't compare your 11,000+lbs boat to a car. Compare it to a tractor-tailor going up hill.
Yes, dyno testing would indicate that a stock 415HP/502MagMPI makes about 400HP at 5000rpm...
Yes, assuming your engines are 100%, you absolutely need smaller props!
Prop the boat to max out at 4800-5000rpm; at 4500rpm the engines are lugging.
If you want to stay with 4 blade props then try 22p Bravos; you will get the motor to 5000rpm and gain 1-2mph.
If you want to go 3-4mph faster on top, then run 23p 3 blade Mirage or Mirage +.
And like I said in my earlier post, test spinning them out and spinning them in.
You may loose some mid range speed with 3 blades, but the boat will go faster.

Re: rev limter
 

i am sure i can get my hands on some 22 x 4 to try and will do that for sure. please educate me on the rotation issue.... whats the concept about spinning them to center or away ?

Re: rev limter
 

update.... prob was pilot error. due to inexperience was running with drives full down. cig forum members suggested trimming drives out and that was the magic trick. boat now has lots of revs and 62 mph at first go at dialing it in.

learning more by the minute... and thx