What exhaust does everyone use, the shop provided exhaust or can you run marine exhaust dry for dyno purposes?

Depends on there set up,we use there marine exhaust and water cooled tailpipes more real world results and end up with a better tune,most auto shops can only do dry exhaust but shops that do a lot of marine work might be set up to do both

Here in Vegas there is only an auto style dyno. He provides exhaust for dyno. I was wondering if I could run my merc 496 exhaust dry, something tells me probably not.

the manifolds need water going thru them or you will damage them

I thought so just looking for confirmation. Thanks.

Well, on the plus side, if you are dynoing with dry headers and then going back to wet exhaust manifolds, your tune should end up being on the rich side rather than the lean side due to the increased backpressure. You sure don't want to run it lean on the water.

Can he run it on pump gas? I had one shop right down the road from my office that would be super convenient for my dyno service, but he won't run anything except racing fuel because he is afraid the alcohol in pump gas will damage his fuel delivery system on his dyno. I'm going to have to drive two hours out of my way to find a shop that will run my motor on pump gas.

Try to be realistic about the fuel you will be running on the water and set the tune up for that type of fuel. You don't want to tune for 93 octane and then end up out on the water somewhere and find out 87 is all that is available.

dont know what shop you are talking about BUT,if he wont run his dyno on the pump gas you will run in your engine,run forrest run,they are not the dyno shop for you.

I agree. I never understood why one would want to dyno a pump gas engine on race gas.

With carb engines, I feel its always a good idea to recheck AFRs once installed in the boat. Most dyno shops do one style of pull, and thats Full throttle. Thats just fine for wanting to know what your tune up is like when your throttles are pinned to the dash from 3500-6500RPM, when the power valves are opened, along with the throttle blades. But one must consider, the tuneup, when the engine is at 3000RPM CRUISE, where the power valve might be closed, and the throttle blades are not wide open. A race car doesnt really car much about that scenerio, because they dont sit there and put a partial load on the engine for an hour at 3000RPM.

Chances are, if your AFR's are just where you want them on the dyno, they will be heavily rich in the boat (carb setup), when setup with the marine exhaust, closed engine compartment, etc. For us midwestern guys, we mainly dyno our engines during the winter/spring. The air is good and cool during the dyno session. Not exactly the hot humid summer air the boat will run in.

He does almost exclusively racing engines - rarely ever puts a street engine on the dyno, apparently. I'm going to go with a different shop, even if I have to travel. As I stated before, I'm going to run it a little while on a startup cart first, just to make sure there are not any little clusterfuq's waiting to spoil my day on the dyno.

MT, is there anything that would prevent me from just running the engine in a loaded state at 3000 RPM's on the dyno just to check AF readings at those speeds? I realize it would be a different load than the boat would provide, but I would think it would at least tell me if I had a problem at those speeds.