What’s up guys, first time posting here so please excuse any ignorance.

My dad and I are building a roots blown bbc and with endless reading here and a few other websites I still have a few questions.

#1 what total timing and what RPM should it come in by?

#2 how many psi of boost should I run for a reliable engine?

#3 is it worth building the engine with low boost psi and timing then slowly adding both as we build confidence? Or is there a safe way to monitor knocking/pinging?



The boat is a 27’ eliminator fun deck with an imco sc drive. The static compression ratio is 7.67:1, we plan on using CA pump 91 octane fuel with some boostane for added safety. We do have a wide band O2 to help us get a nice AFR. We have installed a knock sensor but it is very complicated to tune, I’m using a fluke 123 O scope to listen for detention then will tune the light accordingly. The engine should be assembled in the next few weeks and installed shortly after.



The engine is as fallows

-Merlin iron block 555ci (4.560 bore x4.250stroke)

-10 quart oil pan with windage tray

-Eagle crank

-Eagle h beam connecting rods with arp bolts

-Diamond dished blower pistons .062 quench

-AFR 345cc heads fitted with hydraulic roller

-Local Custom ground cam 245/275 open with 114* separation

-AFR stud girdle

-TBS 1071 Teflon tipped blower

-Boost referenced holly 750s

-msd 6btm ignition

Thank you

I built a similar engine a few years ago and this is what i did. It has been reliable for 4 years now. Ditch the MSD and put on a Daytona Sensors ignition box. It can be programmed to do almost anything you want. I put total timing at 35 deg and started pulling timing at 5000rpm and 5# of boost. Pulled 1 deg of timing for every # of boost over 5000rpm. I ended up around 7# of boost just running and would swing to 9# under hard acceleration. The Daytona box has a provision that will pull timing if you install a knock sensor. It also has an idle stabilization setting built in that will smooth out the blower surge. It can be done without it, but I found it best to install a crank trigger to trigger the ign box and just lock out the MSD distributor and let the box do its thing. The absolute worst thing you can do is lock the timing at 30 or 32 deg like a lot of people will tell you to do. Hard to start, poor performance and if it doesn't have enough timing it will eat the exhaust valves due to EGT's being through the roof. I don't know how much power you are looking to make, but mine made 910hp@6000rpm with a measly 420 blower. Yours should easily make over 1000. Your drive will hate you.

we are planning on going to EFI and either the Daytona sensors or the holly terminator (hopefully an intercooler as well) but that will be this winter. We want to get out on the water ASAP and still enjoy some of the summer.
What knock sensor are you using? And what rpm are you bringing the timing in by? Right now our centrifugal advance brings the full 33 degrees in by 2200 but I was thinking that’s when the boat is trying to come up on plane and most likely to knock so it should come in later maybe by 3200 or so.