Donzi22zx

I am about to replace my stock manifolds and risers on my 1999 454 MAG EFI because they were shot. I think I will go with the EMI Thunder w/ SS risers, but I have heard that I need to up the fuel pressure and remap the computer? Vortech and Arizona Speed&Marine sell kits , has anyone tried one of these kits, did you notice a difference, speed/power gains was it worth the money. What do you think of EMI headers on EFI engines? I also want to know what fuel pressure to set at . ok last question is the MSD 6M worth the mony as well.
Thanks Bill

Vinny P

I have a stock '99 454 magnum motor in my Checkmate. Last winter I added Gil Wet Offshore manifolds and risers. I also added an MSD6M-2 to the stock ignition system. I didn't re-map the E.C.U. I picked up 2 M.P.H. BUT, what my big gain was a noticably cleaner transom. Very little black soot as compared to the previous year without the addition of the M.S.D. So I would definetly recommend the MSD and the exhaust. Just to get rid of that stock leak prone Merc. junk is enough of an advantage for me. The M.S.D. will not give you a noticable power increase, but it helps burn up the extra fuel these stock motors are programmed to use.

Ric232

Bill,

Save your money. I have a 1998 Baja 232 w/ a 454 Mag MPI (385hp). I installed:

Vortech/K&N flame arrestor
Gil Magnum Choice manifolds
Adj. fuel pressure regulator (set at 48 psi)
ECU re-programmed by Arizona Speed & Marine

Total Cost = $2700
Total Performance Gain = ZERO !!!!!! (oooh, but my transom is also cleaner. Big whoop. Certainly don't waste your money on the MSD.)

Ric

Von Bongo

Same result whe I added it to my FOuntain. Cleaner Transom, no performance gain, cleaner transom, the K&N does have a filter element so that cant hurt anything.

I wouldn't do it again if I had it to again. Maybe the MS6 and the K&N

formula31

And save yourself some breakdowns and use a Crane HI-6 instead of the MSD if you go that route.

26sonic

guys i have a 1998 26 sonic with 502efi . with just the az speed and marine kit i picked up 2.5mph! i went from a 23p mirage plus labed prop turning 5000rpm wot to a 24p bravo 1 4blade running 4850 wot and picked up 2.5 mph top end . noticed at 4000 rpm with 24p vs 23p and with drive all the way down and tabs all the way up running 5mph faster! set the adj fuel reg to 42psi. next year will probably add imco power flow exhaust.

Ric232

Consider yourself VERY fortunate. Results like yours are unheard of. It would take about 40 hp to get a 2.5 mph gain. Much of your gain was likely caused by a change in conditions. The 5mph gain at 4000rpm is purely a function of the prop change.