Rapido 5.7 mercruiser remanufactured

[Split Shot]

I bought this motor from Rapido last October. When I ordered he asked if I wanted 300h.p. for an extra $185. I thought great. Now, I am sorry I did. I put about 2 hrs. on it before I put it away for the winter. My mechanic couldn't get it to idle below 900rpm. without stalling out. I fired it up the other day and started right up. Sounds really mean but that ain't going to do me any good, if he can't get it to idle at 600rpm. I am worried about the cam and reversion, that I have read about on here many times. Also the mechanic said that I might have to run 89 octane gas. He told me to run it a few more hrs. and bring it in and he will see what he can do about the rmps. What do you guys think about the cam, reversion, rpm's. Thanks!

 

[Bondo]

Re: Rapido 5.7 mercruiser remanufactured

Ayuh,... I think yer Mechanic needs to fix the carb....

Why does he think you need to run Hi-test gas,..??

 

[Split Shot]

Re: Rapido 5.7 mercruiser remanufactured

thanks for the quick reply bond-o. I know nothing about motors. I have just done that small stuff in the past. Like water pumps in outdrives, bellows, exhaust manifolds, gimbal bearings. that is my very limited knowledge. I don't know why he said about the Hi-test. I have a Rochester 4 barrel carb. It worked great on the blown motor. I am very worried about the reversion issue, since I have read on here about the non-stock cams causing this.

 

[90stingray]

Re: Rapido 5.7 mercruiser remanufactured

I dont think reversion is an issue unless you are running thru hull exhaust, with the chance that water may be injested. Thru prop, i don't think you would ever have enough force to suck in any water. Should be good to go. And yes, larger cams usually idle a little higher. Get her as low as you can, and enjoy that RUMP RUMP RUMP <----- man i love that sound

 

[Split Shot]

Re: Rapido 5.7 mercruiser remanufactured

thanks sting, I know you could get reversion thru the prop, say if your shutters are missing, in another thread one of the top guy's said (I hope I read it right) that you can get reversion thru the risers. I assume, if your valves stay open longer due to taller cam. I am paranoid I guess. I don't want to screw this motor up after all the money I have spent. I love that RUMP-RUMP-RUMP sound also. Sounds like my brothers 66 gto.

 

[dan t.]

Re: Rapido 5.7 mercruiser remanufactured

Find out the specs for the cam, and a manufacturer and part number if possible, I wont go into it now but if that cam is what I suspect it is you dont want it .

 

[Don S]

Re: Rapido 5.7 mercruiser remanufactured

I dont think reversion is an issue unless you are running thru hull exhaust, with the chance that water may be injested. Thru prop, i don't think you would ever have enough force to suck in any water.

Reversion has nothing to do with type of exhaust system, and everything to do with cams.

Reversion happens where the water coming out of the exhaust riser meets the exhaust gas. With excess valve overlap, little bits of water is sucked back into the cylinders. Especially noticeable at idle as the engine starts running rougher until it dies.

 

[90stingray]

Re: Rapido 5.7 mercruiser remanufactured

Reversion has nothing to do with type of exhaust system, and everything to do with cams.

Reversion happens where the water coming out of the exhaust riser meets the exhaust gas. With excess valve overlap, little bits of water is sucked back into the cylinders. Especially noticeable at idle as the engine starts running rougher until it dies.

Don, that makes more sense. It was explained to me as sucking in water from the lake... not the cooling water. But the way you explain it, makes it more dangerous of an issue. Definately something to be concerned about.

Rapido makes marine engines, why would they put in a cam that has too much valve overlap?

 

[Split Shot]

Re: Rapido 5.7 mercruiser remanufactured

Thanks for all the replies. At this time I don't have a reversion problem, oil was perfect. When my mechanic put it together he wasn't happy with the cam that came with it. He said it might be too much cam. I quess the cam was to get me the extra (maybe) 40 hp. So with the threads that I saw about non-stock cams and reversion, that's why I am worried. So, If I understand by one poster, that I should be able to get down to 600rpm. no matter the cam and it probably is a carb problem as far as the high rpm idle is concerned. Thanks again!