375stinger

if we have bbc with intercooled m3 prochargers..what would be the benefit of runnin 6 or 7 pounds of boost as opposed to 8? the motors were new dynoed at 643hp before, then we lowered compression from 10.3 to about 8.9ish...we figure around 950 hp each at 8lb of boost. would there be a very noticeable difference in reliability/ engine wear from runnin 6or 7 pounds? is the 8lb of boost only made at the high rpms? i take it that at lower revs there is not much a difference anyways. what would be the most boost you could safely run of 91 fuel with this setup? were dynoing asap, and need to decide how much boost.....thanks

articfriends

iTrader: (1)

I'd run as much boost as your octane can support. I made 942 uncorrected hp w/540 w/m-3 and 9-10 psi boost on 93 octane. By pullying motor up to make more peak boost you will make more tq from boost coming in earlier which will make your boat feel torquier.Your going to need some serious innercoolers,cylinder heads and cam to make 950hp on 7- 8 psi of boost on 91 octane,Smitty
If your dynoing soon ask what your correction factor is and WHY,there have been too many guys with 10-14 % correction factors getting bs'd by their dyno guys. Make sure your blower belt is real tight on dyno runs too,especially if your running 8rib.I couldn't get enough boost from my m-3 with 8-rib drive on my 540,had to go to 12 rib driveand when you go smaller than 4.0 inches on upper pulley they slip unless real tight.

375stinger

they sent us 8ribs, but we sent back for 12 rib pulleys, thanks for the comment about the tightness, and correction factor, ill be sure to ask. did you run the innercooler from procharger that came with the m3 kit to hit those numbers? thanks for pointin out thatstuff

Ratickle

It's nice to see someone who understands the bs behind correction factors. The best builders don't fudge the numbers.

cobra marty

I think that your 950HP numbers are a bit optimistic. What is your combo? CID, heads, cam, intake, CFM card, or EFI, size intercooler, CR.

375stinger

thats just what we were told from procharger with 8lb of boost. 555c.i., brodix heads(dnt no nething else about em), merlin 4150 intake, modified bg marine 750, dnt know cam specs, aw-504 intercooler, whihc is the same procharger uses with their m4 and m5 system.

articfriends

iTrader: (1)

I used the aw540 inercooler (normal for m-3),I was at about 10 psi of boost at the manifold and although I didn't measure it that time probably 12-13 psi above the throttle blades. At 600 ft sea level I had a 3.85" 12 rib pulley on blower to get the 9-10 psi of manifold boost. I also tried a 3.70 but I only saw 8-10 more ft lbs of tq. If you look at my dyno curves the lower power numbers are what my 540 made 3 years ago with 6 pi of boost and merlin heads,I was expecting to make 750 hp but made 620 hp/695 ft lbs tq,I was less than thrilled,Smitty

articfriends

iTrader: (1)

I recently saw 2 dyno sheets,1 for a 740 hp motor that actually made 665hp with a 10% plus correction factor at SEA LEVEL ON A 62 DEGREE DAY with afr's that would melt the pistons in 30 seconds and another one for 800 hp that actually made 730hp with a 10 % correction factor at 600 ft above sea level in 55-60 degree weather,its not like these guys are dynoing their motors at pikes peak or something,Smitty