View Full Version : comments and questions from a newbie


1 2 NV
11-28-2010, 11:48 AM
i suppose i better give a little background on myself. i come from a pretty extensive honda background. built a civic from the ground up to run low 11s all motor. it wasnt a street car but still decently fast for being all motor.

i sold the car and now i have a boat. ive had my boat for 2 yrs and looking to build a different boat. im researching what would be cost effective way of me building my own motor and adding my own fuel injection to it.

in the marine industry they currently use GM products. i have a small block
383 in my current boat but looking for more power in my next boat. the next boat should weigh about the same as my current boat but i think if i make more HP the motor wouldnt have to try as hard to push the boat, thus making it more fuel efficient. i know there is a point of diminishing returns regarding HP and fuel efficiency.

what limits rpm in marine motors is the impeller (jet boat).
for example:
gm 350 325hp max rpm 4100 2.8kW impeller
gm 383 340hp max rpm 4000 3.4kW impeller
gm 8.1HO 425hp max rpm 4100 4.0 kW impeller
gm supercharged 6.2 550hp max rpm 4600 3.4 kW impeller

so with that said the actual RPM range of running on plane in a jetboat is about 3000-4000rpm. if you have more HP the RPM range will increase.

as i was saying the next boat will be 1 foot longer and structurally should be a little heavier. im looking at a L9H (L92?) due to its availability, all aluminum construction and good heads. there is a possibility i might stroke it to a 427 right off the bat but for the time being im looking for more low end grunt. i could change the impeller to a lower kW rating but usually you decrease efficiency by adding RPM. hence the reason for the possibility of stroking it.

hopefully some of this makes sense, its long and drawn out and ive read a ton of stuff on here. some of it foreign but for the most part im understanding just fine. do you guys have any suggestions regarding my low end HP/TQ? the only real solution i see is stroking the motor right from the get go.

im also thinking i might do a FAST EFI system. depends on budget. id like to put the ECU up front where i dont have to worry about it getting wet. so the harness would have to be about 25'+/- long. im familiar with ECU tuning just never done a GM. realistically it should be pretty simple due to the constant load of the impeller on the engine.

also when RPM does the VVT turn on? probabl right around the max RPM id be running is my guess. id probably be looking at doing a VVT delete as i dont think there is any functionality for it on a jet boat. i could be wrong.

looking forward to your replies.

Jimbo1367
11-28-2010, 12:39 PM
Try a SEARCH. There are a few LSx boats in the CONVERSION section. You could keep it stock EFI and use a vendor ( www.speartech.com ) to supply the extra length harness. There are other harness vendors, but Speartech seems to be the BEST

1 2 NV
11-28-2010, 01:20 PM
those boats are sissy lake running boats. my boat is a heavy guage aluminum rock stomper boat. designed to run big whitewater, bounce of rocks and hopefully continue down the river.