09-03-2007, 07:23 PM #1
- Join Date
- Aug 2006
- Gonzales, La
What does it take to go 80 on the stock ECU?
I've been contemplating my next round of mod's. I don't want to change the ECU because of the higher limiter and required valvetrain mod's, plus added expense. I'd like to explore the option of shooting for 80 with the stock ECU.
The base-case assumption is that you can't use over 42 lb/hr injectors since it will start to run too rich at idle and cruise, keeping in mind the fuel system is not closed loop, so the computer doesn't know when it's running lean. FYI, the next step up from 42's is 46's, but I'm not sure that they'll fit. The 50's we know will work, but I'm sure will mess up the idle and cruise mixture.
Doing injector sizing calc's really gets me nowhere. No matter how you slice it, the 39's don't seem big enough for the stock engine and the 42's don't seem big enough for a mod'ed one. Using a conservative BSFC of .6, I get that the 39's are only good for 195 hp and the 42's are good for only 210 hp. Using a not-so-conservative BSFC of .5, I get that the injectors are good for 234 and 252 hp, respectively. Not that great either way. . .
Soooo. . . I guess we just have to go by experience on this.
Several folks have reached upper 70's by using either an Greenwheel/Akit/RRwheel, or even an S3 supercharger, on a full Stage 2 using the 42 lb injectors. A couple folks are doing 78-79 (speedy and DIGGS) on the S3, while a couple of other folks are doing 78-80 with various versions of the 9 psi wheel (RXP'in in MI, RXP244). But. . . no body that I know of has actually broken 80. BTW, all 4 of these guys are using the 15/20R prop with various tweaks. Seems like a better bet is to do the external intercooler and S3 and try to tweak it to get it there.
The other option is to go the JD1 route and use a RudeCharger on the stock ECU. He's built lots of these and gone over 75 using the stock injectors even, while sticking with the stock air intake and intercooler. I imagine you could upgrade the air intake and up the injectors to 42's and get in the high 70's. This may be a cheaper and perhaps faster route than the aforementioned method.
What are you guys' thoughts on this?
BTW, I'm basically at a Stage 1 + RR wheel and 74.0 mph.
09-03-2007, 07:26 PM #2
If it was me, I would dump the entire engine into a gpr hull and go 82 mph plus, but hey thats just me!
09-03-2007, 07:49 PM #3
09-03-2007, 08:45 PM #4
- Join Date
- Aug 2006
mike,diggs and I were out today and had both boats again over the 78mph mark.Air temp was 87/88 and lake temp was around 82/83.I'm not sure we can reach 80 in the cool temps but should be close
09-03-2007, 10:18 PM #5
your injector calculations don't sound right, what fuel pressure are you using in the formula?
09-03-2007, 10:37 PM #6
another 2 words
09-03-2007, 10:47 PM #7
are you opposed to running the fuel controller? slap 50# injectors on the stock ECU and use the fuel controller to make your idle nice and put the cruise and WOT AFR where they need to be.
is anyone out there running a Rude/B-kit with a fuel controller, External IC, air intake, and more on a stock ECU??
09-03-2007, 11:04 PM #8
- Join Date
- Oct 2005
09-03-2007, 11:20 PM #9
09-03-2007, 11:25 PM #10
80 in the heat? or 80 in the cool? thats 2 diff calls
Jerry has done it
fastest Ive ever seen any of my stage 1+ kits was 78+mph and that was with my new pump mod (released in Oct 07) with out the pump mod it ran 75+mph.
I got full stage 3 RXP's that struggle to break 81mph in the heat heat heat, hot,,,,,,,,,,,,,,,ouch
last customer brought me a Riva I- AI, 14/19, wedge, grate. Watertested 68.5 in the heat before I tore into it. Added a Rude and gave him is ski back doing 75mph in the heat (5+mph gain) total kit:
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