Procharger M1 5PSI has softened My 7.4 MPI

[baronbob]

This is my first season with a used M-1 (5#psi) installed on my used 7.4 Mpi (600hrs). I have 125-135#'s compression in 1,2,7,&8 and 110-1153s in 3,4,5 & 6. I squirted oil in all the cylinders and found aproximately a 10# increase in all cylinders. The leak down however is 50#s/ 80#s in 1,2,7,&8 and 20#s in 3,4,5 & 6. I can hear leak in the exhaust. I also have oil backing up the dipstick under full power. I plan to pull the heads and re-work if necessary, replace the factory gasket with better gaskets designed for blower applications and re check the leak-down to eliminate gasket and valve leaks. If I still have leak problems I will tear down further to the pistons and rings. I was planning to hone, re-ring and replace the pistons with forged pistons. Any suggestions for pistons/rings. If the bearing surfaces are good is it worth the expense to replace rods? rod bolts? and go to a steel crank? I plan to stay with 5#s of boost and keep my rev limiter @ 4750 RPM. The application is a Bravo III on a heavy cruiser.

[blowngas]

be sure and replace the exhaust valves with severe duty stainless----if 5# is good, then 10 should be a thrill!!!

[Partycattin]

How did your 7.4 respond to the Procharger?
I have a carb'd 7.4 in my boat, completely stock except for the exhaust and a 750 Holley. I have an opportunity to buy a recently refurbished M1 Procharger setup with a 6psi pulley(???). Is it an easy install? How did it affect the low and top end performance?

[Wild Horses]

How did your 7.4 respond to the Procharger?
I have a carb'd 7.4 in my boat, completely stock except for the exhaust and a 750 Holley. I have an opportunity to buy a recently refurbished M1 Procharger setup with a 6psi pulley(???). Is it an easy install? How did it affect the low and top end performance?
It won't effect your low end because your not boosting until you start to get some RPM up but on the top end it will make a big difference. And if you boat at a higher altitude some times, you can change pulleys to compensate for that. And you can buy the right pulley for you motor.
Easy to install, At least my vortec was.
Clint

[baronbob]

Install went fine but you should not expect to find all the answers in the ATI manual. I had the good experience of buying my procharger from an exact same installation. It had all the correct brackets, hoses, ect. BIG HELP!!! The intake gasket went out right away and I replaced it after tons of water in the oil. The motor then Ran OK. Top end went from 4400RPM with 22" props to 4600RPM with 26" props and the speed went up in the same proportion (20+%). I now think the bottom end is blowing by as my leak downs are high. I will re-build the pistons/rings/walls & heads this winter. The motor had 500hrs TT when I installed the M-1. Performance change is great and cheep ($1700 for the procharger), but I would reccomend freshing up if you motor has seen some use. I will be doing same after the fact but also after a great summer.