454 mag mpi Horizon builds

[Saltwater life]

Hi Guys
Finaly finished motors after complete rebuild and balanced. So far very happy with outcome.
New Dart heads iron eagle 308s rectangular ports.
Same cam and Crank. Everything else new. Also running new roller rockers.
Anyway you get the drift. And yes im still a complete novice. Just happy that they run and are back in boat.
THANKYOU TO ALL THOSE WHO HELPED WITH INPUT ON STARTING ON STANDS BEFORE BOAT INSTALL.
So this is where im at.... Base timing set 8 deg btd. On port motor with the usual paper clip method. All seems nice. Once finished idle seems to be at approx 650 -700 rpm.
Second motor (starboard) had some dramas setting base timing as i have an idle surge or hunting issue, dont know if there is a difference. But its approx 900 rpm then 1200 rpm then 900 then 1200 and so on. Frequency would be approximately equal to seconds on a clock.
​​​Im in OZ so only just received a couple of IAC valves to see if it does the trick.
Is this the most likely culprit???
I also got a couple od tps,s incase.
on another subject TEMPERATURE
Temps are pretty good 180 - 185 i think they are supposed to be 175. Would the new heads and pistons which have created a higher compression ratio, i cant tell you what it is sorry. But i do know its a bit higher. Does this higher comp transfer to higher running temps???
i am running Premium unleaded over here, which is our best pump fuel.
3rd oil pressures, port motror is approx 40 and starboard motor is approx 30, would this be the surging??? Obviously I will find out shortly if i fix the surging issue.
Guys i did not intend to build higher performance motors but parts are mainly HP stuff here and i got what would work (i think) so i only really wanted good torque and good reliability as they push Sea Ray 34 SD approx 6.5 tonne.
Guys with all this being said am i missing anything here, with the minimum info i have given the changes that have been made. Is 8 deg btd base still correct or would this be better on a different base setting.

Honestly boat runs quite well, but i feel it probably should be better.
3300 rpm doing 23 knots. 1/2 tanks fuel, water was full, 2 adults and our kids. Flat sea.
Im not interested in reving the **** out it, but wonder on settings im using for standard engine.
also this is all on just a 30 weight mineral oil for running in with proper coolant ratio.
Fresh water cooled, V drives.

Thanks in advance
Cheers

 

[Scott Danforth]

you pick the compression ratio when you buy new pistons.

what cc heads? 110 or 119?
which pistons? what CC?
did you have the block decked?
what thickness gasket.

8 degree is tame for a big block, especially running premium. on the one I just finished, I am at 14 BTDC. then again, I am old-school dizzy and carb. I am running 89 octane (R+M)/2 and am running 9.7:1 If I spring for premium, my base timing will go up

the hunting you are experiencing is fully your EFI. the IAC is a good start. (I normally just clean the crud out of them). also look at your pressure regulator. If you changed anything in the combustion mix (chamber volume, runner volume, compression, etc), you WILL have to have your EFI re-flashed to take advantage of it. Stock tune only works on stock motor. going to things like the Dart heads, you probably also went with a different style piston. you will most likely need a custom EFI tune.

oil pressure seems low. which pump did you use? which oil? what were your bearing clearances? did you simply open the box and bolt on the pump or did you go thru the pump and blue-print it? I am using a melling pump, with CNC cut gears and have 60 psi at idle. however I also sprung for coated bearings and verified all clearances.

 

[alldodge]

Sounds like you did a standard rebuild but used some high end (hp stuff) parts. Your idle wonder can be caused by several things including the IAC. After replacing the IAC and if it still does it, connect a vacuum gauge to the plenum with a Tee at the line going to the fuel pump regulator.

Check your fuel pressure at the rail. Oil pressure will not cause surging, and it could be your gauge. Check the pressure with a mechanical gauge which is best. Could also swap the senders and see if it moves. If it doesn't you can also swap the wire connection at the gauge.

Your compression would be slightly higher then original due to boring oversize, but not enough to cause any idle issues. There should be no need to reprogram the ECM. Don't see any need for 92 octane and my guess is 87 will work. Could run 89 if you want a tad more protection, but without more info on your build I would say its not needed

If your motors ECM has code 44 turned ON then there could be an issue with performance if the motor won't reach full WOT. Code 44 can happen when using 92 octane. The ECM checks the knock sensor when first throttling up. This is not your issue right now with idle, and you should not be going to WOT until motor is broke in.

 

[alldodge]

Oh I would also run at least 40WT in the motor

 

[scoflaw]

Agree with Scott, all those measurments matter, that's how CR and octane requirement is figured.