My motor will be going to dyno shortly hopefully. I am running an aftermarket EFI setup and keeping it open loop. Everything will be the same as in the boat except for powersteering pump and the stainless marine manifolds with long risers. How much consideration should we take into account for these things not being on motor as will be in boat? Intake breather and all will be on same as in boat. Its a small block also

your exhaust may make it a tad richer but not enough to be concerned with.jmo.

Mike will it be enough to really be concerned with or should it be tuned slightly lean to compensate for the richer change with manifolds? Also should i also tweak timing once in boat also?

You'll want to tune for the way it's set up on the dyno. When on the water after a trip or two out you can always lean down a little after some plug checks. You never want to tune it lean to compensate.

I'd recommend you educate yourself a bit on having the dyno operated in a manner consistent with the way the engine will be run in the boat, particularly as it applies to sweep rates to get the most accurate and useful information. As I'm just discovering this myself, I'll let others provide information. Fwiw my builder went out of his way to tell me to keep my damn hands off the timing when it leaves his shop.

i normally go 1 or 2 jet sizes leaner in the boat but i recommend a/f readings in the boat as well as a quick look at the plugs.i am not the one to give advice on efi tuneing as i don,t know squat about it but with your exhaust system i don,t see a big change from the dyno headers.

In a perfect world all would be hooked up and hunky dory however this is pretty basic here probably more so to run the engine, wind it up, ck for leaks and make sure EGT's and BSFC are good to go and go boating.

If you wanna start drilling some holes in your exhaust manifolds and have compatible probes welded inside and out to get temps go that that route. Better yet maybe your dyno shop just might have a set there already to go with probes in all. Doubtful but hey you never know. Or just use the supplied exhaust and be done with it. Like mike said worse case sinerio reject to actual conditions or in your case remap your fuel injection if need be. I doubt you'll be fouling plugs in the boat.

tune on the dyno and get your timing right and give you a nice number.then once tune the boat,monitor your afr's and adjust accordingly.I've never gone from the dyno to the water and not had to make some type of corrections.
who's efi system are you running?

I am going to try a FuelTech system