AFR Clarification

[SmokinLowriderSS]

10" of vacuum at 3000 rpm in a jet is amazing. 10" is almost like coasting. Didn't think that was possible..
It takes very little throttle opening to get my 454 to 3,000 RPM and I am running a moderately large impeller (A-cut). That impeller only absorbs arround 87 HP to spin at 3-grand.
3,500. aprox. 136HP
4,000. aprox. 202HP
5,000. aprox. 395HP
5,500. aprox. 525HP
Jets demand power on a non-linear curve that increases faster the faster you spin them.
At idle, my impeller demands 2.0HP to spin it.
Per the response at the top, it sounds like Jets are under less of a load that I/O.
At low RPM's, they are.

[ULTRA26 # 1]

It takes very little throttle opening to get my 454 to 3,000 RPM and I am running a moderately large impeller (A-cut). That impeller only absorbs arround 87 HP to spin at 3-grand.
3,500. aprox. 136HP
4,000. aprox. 202HP
5,000. aprox. 395HP
5,500. aprox. 525HP
Jets demand power on a non-linear curve that increases faster the faster you spin them.
At idle, my impeller demands 2.0HP to spin it.
At low RPM's, they are.
At 50 MPH, what RPM are you turning? As I recall, Wes's 21, with a 572 in it, ran on the top at about 76 MPH. Hopefully Wes will chime in here. Every jet boat I've ever seen sounds like it working hard at 50, except for maybe a 19' TPR Shadow or something similar.

[steelcomp]

10" of vacuum at 3000 rpm in a jet is amazing. 10" is almost like coasting. Didn't think that was possible.
3000rpm in most jets is very light loading on the drive, requiring far less power than a prop. 10" ov vac @ 3000 is reasonable. Jets have a completely different loading than any other drive type. It's easy to "assume" that jets see tha same kind of loading, but untill you really have first hand experience with them, (which you obviously don't) it's hard to understand. It's one of the reasons jets require such a different power curve, which most guys don't realize. It's also one of the reasons it's difficult build a "fast" jet boat.
Per the response at the top, it sounds like Jets are under less of a load that I/O which is news to me.
Every drive system has it's power absorption rate. You can't expect a jet drive to have the same rate as a prop of any kind, I/O, V-dr. or direct. Apples and oranges.
Most guys that I have spoken with have stated that because Marine engines are always under a load (0 vacuum)... Very few intke/carb(or TB) systems will show zero vacuum, and then only at WOT. Under load dosen't necessarily mean zero vacuum, in fact, seldom is. You're getting, and repeating a lot of misinformation, it seems.

[Unchained]

V DRIVE DATALOG
http://www.***boat.com/image_center/...talogaug07.jpg

[502 JET]

http://www.***boat.com/image_center/...talogaug07.jpg
Does the data logger monitor the air/fuel ratio?
Why does the data acquisition show the battery at only 12.2 volts?

[Unchained]

Does the data logger monitor the air/fuel ratio?
Why does the data acquisition show the battery at only 12.2 volts?
I have another datalogger that monitors A/F but it does not tell me IAT, inj ms, or what fuel map range it's running on. It is the aux box that goes with the Innovative Motorsports LM-1 A/F unit.
My alternator is a reverse direct drive unit and it needs to be taken to just over 3000 rpms to start charging. It most likely is that I did not run it up high enough at the time I recorded that datalog to start charging.
This Haltech datalog file is from my Daytona V-drive, not the jet boat.
At 3000 engine rpm the prop is turning 3950 rpm.
The jet boat file showed higher manifold vacuum and less throttle opening reflecting less load.
The vdrive runs about 42 mph with 3000 rpm.
The smaller, lighter jet boat runs about 36 mph with 3000 rpm.
My idle manifold vacuum (out of gear) is 14" - 16"
It will actually idle in 3rd gear at a steady 1000 rpm. The EFI really shines at precision tuning. That speed it is too fast for a no wake zone so I use 2nd or 1st.

[Unchained]

JET DRIVE DATALOG
http://www.***boat.com/image_center/...ivedatalog.jpg
Here's a comparison of a jet drive datalog.
I think it's interesting to see that it takes less throttle opening and the injector timing is quite a bit less to get 3000 rpm but the vdrive has more speed with the same rpm. The fuel economy is better with the vdrive even though it's a heavier boat. The prop probably has quite a bit of slip at that speed and rpm. It's an 11" x 15 three blade.
Here's a copy of the other datalogger I have from the jetboat days, http://www.***boat.com/image_center/...talogoct05.jpg
As you can see I'm just taking a picture of the computer screen in the most low tech method possible.

[ULTRA26 # 1]

3000rpm in most jets is very light loading on the drive, requiring far less power than a prop. 10" ov vac @ 3000 is reasonable. Jets have a completely different loading than any other drive type. It's easy to "assume" that jets see tha same kind of loading, but untill you really have first hand experience with them, (which you obviously don't) it's hard to understand. It's one of the reasons jets require such a different power curve, which most guys don't realize. It's also one of the reasons it's difficult build a "fast" jet boat.
Every drive system has it's power absorption rate. You can't expect a jet drive to have the same rate as a prop of any kind, I/O, V-dr. or direct. Apples and oranges.
Very few intke/carb(or TB) systems will show zero vacuum, and then only at WOT. Under load dosen't necessarily mean zero vacuum, in fact, seldom is. You're getting, and repeating a lot of misinformation, it seems.
The only misinformation that have stated was 0 vacuum. The information I have stated with regard to AFR has been factual for Merc EFI Marine engines. Again, the suggestion of running a marine engine with a AFR of 16:1, except at idle or shut down, wasn't a good one. Jets are obviously different that stern or V drives. I have confirmed with more than one reliable source, that propellers are generally more fuel efficient than jets. And your right about me not having 1st hand experiance with jets. Even my Cole, had a prop.
Thanks for your input
JET DRIVE DATALOG
http://www.***boat.com/image_center/...ivedatalog.jpg
Here's a comparison of a jet drive datalog.
I think it's interesting to see that it takes less throttle opening and the injector timing is quite a bit less to get 3000 rpm but the vdrive has more speed with the same rpm. The fuel economy is better with the vdrive even though it's a heavier boat. The prop probably has quite a bit of slip at that speed and rpm. It's an 11" x 15 three blade.
Here's a copy of the other datalogger I have from the jetboat days, http://www.***boat.com/image_center/...talogoct05.jpg
As you can see I'm just taking a picture of the computer screen in the most low tech method possible.
Thanks for posting the data sheets.