350 EFI TBI Mods, cam, heads, intake, tune, 383?
05-19-2019, 05:39 PM
#111
All right guys. Here she is on the water. The shift switch fixed the tach problem and the boat runs way better. I was still getting just a little tickle of the knock sensor at WOT, with 32 degrees of timing, AFR was 12.5. I took one degree out and richend it up a little, AFR 12.2. It got better, but still get just a spot of knock every once and a while.
I changed the prop from a 17 pitch by 13 3/4" to a 21 pitch by 14 1/2". My RPM's have dropped. Before it would turn 5000 RPM or more, now its about 4500 max. It will peg the speedometer (60 mph) with me in it by myself. In this video there are 4 people in the boat and we had a head wind. I dropped every body off and went out by myself and was able to get more out of it. It also seems like I can trim it up more than I could with the old prop, which I did not do in this video. You can see my voltage gauge blip when I trim it up. Also, do not pay any atention to the wide band read out, its not right. I still have my hand held installed.
Anyway, what do you guys think? Did I make a good choice on the prop? The boat seems to cruise real nice at 3000 RPM. I have thought about putting a 4 barrel TBI on it to get rid of the 2 barrel 95 KPA seems to be about all I can get out of it, which may indicate a restriction, if it won't hit 100 KPA at WOT.
https://www.youtube.com/watch?v=oet9t9Fx0sY
I changed the prop from a 17 pitch by 13 3/4" to a 21 pitch by 14 1/2". My RPM's have dropped. Before it would turn 5000 RPM or more, now its about 4500 max. It will peg the speedometer (60 mph) with me in it by myself. In this video there are 4 people in the boat and we had a head wind. I dropped every body off and went out by myself and was able to get more out of it. It also seems like I can trim it up more than I could with the old prop, which I did not do in this video. You can see my voltage gauge blip when I trim it up. Also, do not pay any atention to the wide band read out, its not right. I still have my hand held installed.
Anyway, what do you guys think? Did I make a good choice on the prop? The boat seems to cruise real nice at 3000 RPM. I have thought about putting a 4 barrel TBI on it to get rid of the 2 barrel 95 KPA seems to be about all I can get out of it, which may indicate a restriction, if it won't hit 100 KPA at WOT.
https://www.youtube.com/watch?v=oet9t9Fx0sY
Regarding max kPa I routinely see 98-99.x at WOT but have a MP setup. Only TBI one I've played with was on a big block and that was running about 92ish if I recall.
05-19-2019, 09:36 PM
#113
Registered
21" pitch x 4500 = 60mph ? i don't think so. unless you don't have a 1.47 geared drive. What am I missing ?
How big is this boat ? Looks small.
How big is this boat ? Looks small.
05-19-2019, 10:25 PM
#114
Registered
05-20-2019, 07:32 AM
#115
Registered
Thread Starter
Man! Wish I had that calculator before I bought this prop....😀
Last edited by Paxtonspeed; 05-20-2019 at 07:36 AM.
05-20-2019, 07:48 AM
#116
Registered
12-14% slip is normal, which puts you closer to 50mph. That's why I am asking what is up. Boat unwilling to go fast ? Engine ? Most 20-21ftboats would be well over 60 and closer to or at 70mph with that power. A few boats would be even much higher.
At 4500rpm with 1.47 gears and 14% slip = 52mph
At 12% slip = 54mph.
What does your same boat mph at with a bone stock 260hp 5.7 ?
At 4500rpm with 1.47 gears and 14% slip = 52mph
At 12% slip = 54mph.
What does your same boat mph at with a bone stock 260hp 5.7 ?
05-20-2019, 08:17 AM
#117
Registered
Thread Starter
12-14% slip is normal, which puts you closer to 50mph. That's why I am asking what is up. Boat unwilling to go fast ? Engine ? Most 20-21ftboats would be well over 60 and closer to or at 70mph with that power. A few boats would be even much higher.
At 4500rpm with 1.47 gears and 14% slip = 52mph
At 12% slip = 54mph.
What does your same boat mph at with a bone stock 260hp 5.7 ?
At 4500rpm with 1.47 gears and 14% slip = 52mph
At 12% slip = 54mph.
What does your same boat mph at with a bone stock 260hp 5.7 ?
05-20-2019, 09:01 AM
#118
Registered
05-20-2019, 09:30 AM
#119
Registered
Thread Starter
05-20-2019, 09:57 AM
#120
Registered
Another bad myth. In fact, Torque loading a drive strugg;ing to get on plane is worse than anything else. ie: too tall pitch, too many blades, too many people, lol, etc... 
i spin mine up to 6100rpm. any other people spin high 5's...few that go mid/upper 6's.
Change gear fluid often and consider using a drive shower,,,that will help the only downside to more rpm....more friction heat.
Why build an engine's peak hp for id 5k, high 5k or 6k and run under 5k ? i don't get it.
but I also don't get why your boat is so slow for the hp/torque as it is. Tuning ? Or the boat itself ? does it not want to move ? I don't know these boats so thus why I'm asking.
Are you still running into detonation issues for the super high compression ?and the knock taking timing out ?
i spin mine up to 6100rpm. any other people spin high 5's...few that go mid/upper 6's.
Change gear fluid often and consider using a drive shower,,,that will help the only downside to more rpm....more friction heat.
Why build an engine's peak hp for id 5k, high 5k or 6k and run under 5k ? i don't get it.
but I also don't get why your boat is so slow for the hp/torque as it is. Tuning ? Or the boat itself ? does it not want to move ? I don't know these boats so thus why I'm asking.
Are you still running into detonation issues for the super high compression ?and the knock taking timing out ?
