Idle speed
 

What speed do y'all have your engines idling at ?

My engine seems to idle good at 700 RPM..
If I set it to 650 RPM, the IAC is at 0% and it seems to hunt a bit..
Wondering if it's worth trying to close the throttle blades more or is 700 RPM going to be ok with a Bravo drive ?


THANKS !!

Doug

650 RPM idle..


700 RPM idle

700rpms is fine with a Bravo.
Above 900rpms will start causing drive issues

700 should be cake with a bravo

I have mine set for 750 cold start and 700 hot. 598 cubes

Merc in 1997 has a Service Bulletin for all -- the HP 500 / Hp 525SC yes a SB for the 525 SC thats not listed in the manual / 540 / 600 SC and few others to raise Idle speed to 750 RPMs in the water totally warmed up -- in fwd gear using a accurate shop tach . So anything 800 or below should be ok for a bravo outdrive.

Have to ask how are you monitoring rpms -- Scan tool ? or the rpm gauge on the dash ? I would not trust the gauge on the dash. Have no idea your engine set up nor any engine scan adaption. Maybe its just me but IMO the 2nd video sounds higher than a dead on 700 idle rpms.

My cammed up big blocks always idle around 7 to 800 rpm's. If not they are loading up or stalling when going into gear.

Never knew about the SB, but I had my 525SC idle set to those exact specs. It was just above 800rpms in neutral. It would stall sometimes if it was set below 700rpms and with add on hyd steering, it kept more PS fluid moving. The drive had almost 300hrs and never had any issues.
I think they did it with carbed HP500's to reduce reversion issues.

At 850 it sounds like a stock 454 mag idling.. lol
I may see how it sounds at 750 RPM.
Cam isn't all that big so I likely don't need to worry about reversion at lower rpm anyways
( .644 in .629 ex. Lift. Duration 239 in 246 ex 555 cid)
However I DO have two O2 sensors to keep dry..

It's running Holley EFI.. It's certainly NOT steady at 700 RPM as it's continually adjusting the timing and IAC to compensate some for the cam lope


have to apologize for the video.. held my phone the wrong way after I climbed in the boat... LOL

Merc racing service bulletin 97-4 for the idle rpm fwd gear warmed engine using a shop tach. That also included the 800 SC and the 900 SC as well. It was for water reversion for all the models I mentioned and to change the 850 rpm in fwd gear that many listed in the service manual including the 525 SC.

there was 11 Merc racing service bulletins that year ( 1997 ). I would nt except non dealers and or boat owners to know much about them. One reason of many, that OEM dealers can be a huge wealth knowledge and info.

Just passing on for whomever over the course of the 525 SC there was at least 10 to 12 related SB 's. Keep in mind that engine used Fire Power ignition for the first x amount years then went to T bolt IV. There was a few related SB's there.

Yeah, you are probably going to need 750 or 800 RPM to be able to shift into and out of gear without causing IAC to surge.