just as the topic says, I am planning to install a TPI onto a stock 260HP carbureted Mercruiser 5.7l engine. I think this will be a great combo since the max recommended RPM on these motors is 4500-4800 rpm anyway. Took me a while to find the cam specs: "269/280 adv and .394/.403 lift. What surprised me is when I plugged all of the stock motor parameters into dyno 2003 and it was very close to factory HP specs: 255hp@4500 and 334tq@3500 with 304tq@2000. I changed just the induction to Tuned Port and the new numbers are 252HP@4500 and 340tq@3000 with 318tq starting at 2000. Not really any measurable gains but I bet it will save some gas in the longrun and run very smooth. I will be using a 727 ecm mounted under the dash to keep it dry. Here's the questions: how in the world will I fine tune the ecm? It will of course be running in open loop since there are no O2 provisions on the manifolds.. not so bad but I will need some kind of feedback to know what the engine is operating. Then I thought of a method they used in the old days.. using a vacuum gauge. Could this be an (ok) tuning aid? Should I start with a stock 350 $8D prom? I would also think only a limited number of VE cells would need to be tweaked since the load will be pretty much linear for a boat. What about AFR and Timing? Any thoughts, comments or suggestions would be greatly appreciated. I will be sure to post back pictures if anyone is interested. Thanks

I would run some sort of compute rlike the ram jet that does not use closed loop. If your motors ar elike ours, I believe they run a 130* stat. Cant use 02 since water is in the exhaust manifolds as well. I would talk to some people on the boating forums and see how they ahve done it.

Something from the DIY-EFI mailing list a while back. You'll might find it interesting.

http://home.hiwaay.net/~davida1/boat.htm

that was intersting.. I at first thought about TBI, but after finding out the 727 couldn't drive two low imp. injectors the only other option is to port inject it I've always wanted a TPI anyway, and it would definately look cool in a boat. Should I post a thread in the DIY/ECM board on tweaks that would needed to be made to make it work correctly in this application? A little off topic, any recommendations on priming and painting the TPI to make it corrosion resistant? Thanks

I dont think the aluminum would really corrode, but you could always powder coat it.

I thought abt installing a modified TPI on my boat, but decided aginst it for the same reasons you have found.

For the AFR, abt all you can do is a lot of plug reading.

I've heard abt cyl head temp gauges that monitor each cyl using a special washer shaped thermacouple that goes under each spark plug. Not sure how well they would work with a boat cooling system.

For the timing you could either monitor the ECM for knock counts using a laptop or build a stand alone knock detector (I use both in my Camaro).
As for optimum timing, that will be realized thru perf testing.

I've tried tuning with the vac gauge, but had little suscess.

I'd love to see some pics of it in the boat.

Good luck..

vac gauge = MAP sensor. as where you read a vac gauge and adjust accordingly, the computer reads the MAP sensor and tunes accordingly. - is the ECM you are using MAP or MAF? (I don't know the ecm #'s) what exhaust is on the boat? stock? if you ran the later model mercruise risers(cast over stainless exhaust passage), you could punch the O2 in the top of one. The exhaust doesn't see water until right at the hose hook up. Up until then the water is around the exhaust(cooling purposes) in a seperate passage. Several riser designs are dry on the top of the riser....

p.s I worked at a marina for 5 years....

I've been saying mercruiser the whole time but its actually an OMC cobra 260.. same motor really.. ZZ28ZZ, I do have access to an ostrich so my thoughts on the vac gauge was to tune the VE in the cells throughout the rpm range for the best possible vac.. I can make a few runs on smooth water and hold the engine at different rpms and try 5%+/- on the VE to see how that works.. I also thought about making a small spacer between the manifold and riser to install the o2 in if only temp for tuning.. I also have access to an LM-1 which would really make tuning simple with the ostrich.. I will have a closed loop cooling on the engine and manifolds so I don't need to pass water into the riser from the manifold.. what do you think about this?

the thing is you would have to tune for different loads/ water conditions. 2500rpm w/ 2 people is very different than 2500 rpm w/ 4 people and a skier(different engine load changes vac at the same rpm)...Yes, OMC/mercruiser, basically the same engines. - still same senario on exhaust. You could also look into some custom stainless risers with provision for the O2...probably not cheap, but do able...

thats a very good point about the load conditions

is your ecu MAP or MAF? if its MAP you can dial it w/o the O2, but it'll be a longer learning curve getting the various load conditions tuned in properly. In our race applications, we work w/ the tune and try to eliminate the O2 sensors. Not that thy're not easy to run/use, but for ideal power your better off w/o it, forcing the computer to run within the user-set programming. i'd still look into a good aftermarket exhaust that you could drop the O2 into. A lot of the aftermarket systems run the exhasut dry all the way to the back of the boat(thru-hull). The water stays in a seperate passage around the exhaust passage, just to cool it. Then (if stainless or aluminum) you could drill a whole to put the O2 though, and weld a bung to the exhasut pasage, and simply weld around the O2 to the water jacket from the exhaust jacket to form a small spot for the O2...use the O2 bung itself to weld to both the liner and the jacket to seal the water around, but allow access to the exhaust...

how about this approach... just for tuning install an old dry manifold with O2 boss just for tuning purposes with the exhast dumping up and out.. without the engine cover of course. use the LM-1 to do some logging then dial in the VE tables as needed? I know the theory of tuning but have not actually done any myself for my efi vehicles.. what would be the best way to go about this?

even w/ no motor cover I'm not sure you'd want that much heat in the engine bay. You have to realize that boat motors create higher exhaust temps due to the continous load. Unlike a car, boat motors never free wheel. Tha's why you can't get by w/ near as much cam, you have to pull that prop ALL the time.
not sure how I'd go at it. Probably like you said before, make a little spacer between the riser and the manifold with a procision for the O2. Use a solid plate and take the water from the manifolds through a hose to the riser(usually have plugs in them that you can remove and put a barb in). possible w/ your exhaust?

You could always run some temporary headers:

wanted to give everyone an update on my project.. my motor and parts are painted up and ready for final assembly.. have the harness finished, AUJP prom and a custom tune from pcmforless ready.. won't be much longer I hope

lookin good!