dyno exhaust ??
 

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.

I think that depends on the particular dyno. I am unfamiliar with how some of them work. The dyno Mike Tkach and I use, can do that. However, like you said, its kind of hard to manipulate the load that the engine will see when installed. Props, hull style, etc can be different.

Where are you located Budman?

I had to ship my engines from VA to Mark Boos (Precision Marine) near New Orleans to get good dyno results. I put O2 bungs in my CMI's so the dyno runs were done wet and with MY exhaust on the engines. Dyno runs were done EXACTLY how the engines sit in my boat.

Wow, how much did it cost to ship two engines that far? Had to be a big hit, plus the cost of dynoing two of them.

Just north of Louisville, KY. Wish I was closer to Chi-town - I would consider heading up there to do it. Cinci is a bigger city and not that far from me. Just don't know any of the shops around there.

Actually only sent one with the computers for both (they were built at the same time so the same program worked for both).

Shipping cost was about $500 but I own a company that ships stuff regularly. Dyno cost would have been the same even if the shop was next door. This way I was comfortable the tune was right, besides Precision Marine has an excellent reputation and I didn't want to deal with someone who "might" be able to tune them properly.

Thanks for everything guys. This dyno shop is at the LVMS race track, he's originally from Florida but here in Vegas he mostly builds street motors but with his experience I'm pretty confident I'll be alright. He uses what ever gas is needed so no problem there. Some of you might recognize what he used to go by, Heads by Rick. We plan on tuning for 89octane so while trailering i'm ok and if I need gas on the water i would use 91 as they only provide 87 and 91 anyways. Some of you might recognize what he used to go by, Heads by Rick.

When I tune an engine on the dyno, for tuning other than WOT I will set the RPM to a steady state, then advance the throttle in increments from light load to WOT, noting the A/F. Then raise the rpm 500 and do it again. For an EFI engine this will cover most of the load points in the fuel map and I can tweak them as needed. On a carb engine you don't have a lot of tunability so it's more just checking to make sure it all falls within an acceptable range.

Bob Lloyd
Full Throttle Marine

One dyno shop I was considering is only taking the A/F readings at each collector. He is not taking any readings for each individual exhaust primary - neither EGT or A/F. Would I be able to catch a lean cylinder using an infrared temp gun? Is this a big concern? I would think ideally you would want to get readings from each pipe to ensure there is not a lean cylinder from inadequate fuel distribution. However, all the guys out there running wideband O2 sensors on their boats are leaving themselves open to the same issue. Thoughts?

I just dyno'd and tuned my motor last week. Ran it with all accessories and the CMI E-top headers. Just hooked the cooling tower to the sea pump and returned the water from the headers back into the cooling tower. The only thing dry was the tails. Worked perfectly. I had previously installed O2 bungs in the tails