Bauer939

I just purchased a 92 mirage intruder with a mpi 502 when I bought it I recieved 2 props with it one is a 4 blade 24p and the other is a 3 blade 23p prop I took the boat out with the 4 blAde and trimmed out was only getting 58 mph at 4500rpms it seams like it should have allot more. I'm not sure how to find out the out drive ratio but when I bought the boat the guy said the boat will do 72mph and to run the 4 blade prop I was wondering if any one had any suggestions on what to try? The boat has been sitting for two years

3pointstar

Sitting 2 years?-- Not a good thing.

I'm not an expert but I would say it probably is bad fuel - stale gas- almost varnish- Worse thing for an engine is for it to set an extended period without running. I would suggest a good cleaner run thru the engine and change ALL of the fluids. After this I'd also include plugs maybe even wires distributor cap etc. Again, I'm not an expert but the rpm's for this "class" of engine seem a little low-- We have Cobalt 226 with a 7.4 mpi and it turns about 4500- 4600 WOT and top speed is 63 mph. You are in a much higher performance boat and with that engine that sucker should scream!

good luck

3pointstar

gmgearhead454

Fuel filter too! You'd **** if you knew how bad a bad fuel filter and old gas can make a good engine run like crap.

jponfrank

I have a 21 superboat with a 502 bravo 1 1.5. Best speed has been with a mirage non plus 27. 87.1 on the rev limiter. Hope that helps

Pliant

Yes you have a problem as to where that i cannot say, I have a 87 with a tired 330 hp 454 1.47 gear ration turning a 23 4 blade to 55 @ 4000. Time to freshen up that 502..have you done a leak down test, might be a good ideal before you throw a bunch of good money around.