View Full Version : More Power from Engine
Evan Jones
01-14-2005, 08:52 AM
Anyone have any suggestions on how to get more power from a '97 350 TBI in my Prostar 205. It's having trouble maintaining speed for barefooting. I've heard people mention cams, chips, etc for cars. Can you do the same stuff for marine engines?
bradamerry
01-14-2005, 09:04 AM
I would think a aftermarket cam shaft would help. It is a truck motor anyway.
Footin
01-14-2005, 09:12 AM
Before I started spending money on a cam or chip, I would be looking at and testing different size props.
How fast is it now? how much more do you want?
Evan Jones
01-14-2005, 09:22 AM
Top end is fine, it's just maintaining it under load that needs help. I've got a 4 blade stainless on now, but I may go back to the 3 blade Nibral that came with it and see if that makes a difference.
What speed and RPM range is it having trouble with? If it's not WOT, clean the flame arrestor and replace the fuel filter, clean the screen at the inlet on the fuel pump, check the fuel pressure under load, make sure the fuel shutoff valve is open fully and clean the fuel pickup screen in the tank. Also, make sure the hull is waxed and see if there is an updated ECM calibration. If it's just a matter of maintaining speed, you don't need a cam, just a bit of maintenance. How long since the last tune-up, and is there any chance that the gas has water in it?
If you're running constantly at WOT and it doesn't go fast enough, wax the hull, make sure the prop is right for this application and make sure the rev limiter isn't kicking in. Your boat isn't really designed for 'footing although, if you aren't towing someone of my size, it can work.
Footin'- there isn't a replaceable chip in the ECM, just the ability to recalibrate and a recal won't happen if the right program isn't available. There isn't an aftermarket programmer for these like what's out there for cars and trucks.
Jerseydave
01-14-2005, 02:07 PM
Top end is fine, it's just maintaining it under load that needs help. I've got a 4 blade stainless on now, but I may go back to the 3 blade Nibral that came with it and see if that makes a difference.
When I had my 1994 prostar (LT1), I tend to remember that it was a little faster with the 3 blade nibral vs. the 4 blade stainless.
Do you foot faster than 42-44 mph? Your boat should be hitting those speeds, right?
Evan Jones
01-14-2005, 04:41 PM
Top speed is fine. I foot at 37-38. It is the loss of speed which I would like to prevent, which means more power. I think I get more pulling power from the thinner stainless prop, but all in all I wish I opted for the more powerful LT-1 when I bought it. Short of trading up to a new rig, I'd like to soup up the existing motor.
east tx skier
01-14-2005, 05:20 PM
I remember hearing that the torque curve was more favorable on the TBI anyway.
If you can foot at 37-38 MPH, check the stuff I mentioned earlier. A TBI should have no problem towing you at those speeds if it has nothing wrong with it. It shouldn't slow down much when you get up, if it does, it either may have a fuel delivery issue or needs a tuneup.
What is the top speed and at what RPM?
aprgriggs
01-20-2005, 09:36 AM
Ckeck air flow...More air always helps with power
Evan-
That's right. Air flow is critical. In my previous post, the first thing I said to do is clean the flame arrestor. I can't count the number of boats that I have worked on for performance decline that had dirty flame arrestors. It doesn't need to be completely clogged, just restricting the air flow. Try running a 1/4 mile with something restricting your airway. It won't work and a motor near WOT is sucking in a lot of air. If the flame arrestor is dirty and the MAP sensor sees high vacuum, it thinks the throttle plate is closed more than it is and tells the ECM to just deliver a happy amount of fuel, not the increased amount needed under load at high RPM.
Go and get some carb cleaner, spray the arrestor so it's clean and try it again. If this doesn't fix it, then worry about the other stuff. If you can't foot at 37-38 MPH without power loss, either you're really big, there is actually a problem or the boat hasn't been maintained properly.
When you say there is power loss, does it go to about 3500 RPM and start loosing power until you give it a lot more throttle? If this is the case, you have a restriction in the fuel system somewhere. Most likely a clogged inlet screen on the pump. Could it be the filter or pump impeller or a pinched fuel line? Yes, but it's most likely that there are carpet fibers or something in the screen on the pump inlet. You should also do a search in the archives for fuel related issues and look for the other people have been told to do for problems like this. This is hardly the first time someone here asked questions about the same issue you have. Objective, systematic diagnostics is the only way to find the problem. If you don't have or can't get a timing light and fuel pressure gauge, you aren't going to be able to do much on a motor. The diagnostic computer helps and you won't be able to get one easily but MC requires their dealers to have one. If you have a bad sensor, it will show up on the TECH 1.
gene dobies
01-20-2005, 10:21 AM
Jim N. My hat is off to you for all the help and advice you give us here, thank you. You are an asset too this board with your knowledge and expertise. Again, I say thanks.
east tx skier
01-20-2005, 10:23 AM
Jim, would it be more effective to soak the flame arrestor in carb cleaner than just spraying it (depending on the amount of build-up of course). I used to soak mine for a couple of hours per season. With my new one (low profile), I don't expect to have to do that until next fall or so.
I like the NAPA carb cleaner. It doesn't come close to being a "green" solvent, but it works incredibly fast. It also removes paint in seconds. On a hot, humid day, it evaporates so fast frost forms on aluminum. Working at a dealership, there wasn't a lot of time for cleaning flame arrestors. A couple of hours was out of the question and even working on things for myself, in a couple of hours I would be done and doing something else. Flame arrestors should be sprayed from the inside toward the outside. That way, the garbage goes out the same way it came in.
If it only takes a couple of minutes, it won't seem like such a PITA and some people are willing to do this more frequently when it's not such an ordeal. In areas where there are a lot of cottonwood trees and dandelions, this should be done more often since the seeds get into everything when they start flying around.
Tom Wortham
01-20-2005, 03:42 PM
Top speed is fine. I foot at 37-38. It is the loss of speed which I would like to prevent, which means more power. I think I get more pulling power from the thinner stainless prop, but all in all I wish I opted for the more powerful LT-1 when I bought it. Short of trading up to a new rig, I'd like to soup up the existing motor.
Evan, Is that a FJ40 picture ON IT'S SIDE :eek: as your profile picture?
BarefootWt
02-06-2005, 09:50 AM
This is a duplicate - please disregard. Good luck with getting more HP.
BarefootWt
02-06-2005, 09:52 AM
The simpliest and most effective ways in my experience have been adjust motor timing (to include tune up), second would be prop change - they can make a world of difference in speed, power out of the hole, wake, and noise. Third, increase air flow can help. See if the motor has a K&N filter assembly available. They are less restrictive. Finally, the motor may have a chip available that can be changed out that will increase HP. All of these items can also be reversed if you decide to sell your boat and the buyer does not want a modified motor (i.e., cam work). Good luck!
Barefoot- read the posts about chips for these motors. They don't exist.
The MEFI ECM(used in marine applications) is programmed with a PC. The aftermarket probably won't have options for this because the software is proprietary and the programs are so application specific. Aftermarket car chips are made for a relative high number of customers and are a lot more general. Any improvement they provide is fairly substantial. That said, a boat owner can check for updated calibrations and if it's an older TBI or MFI motor, there is probably something available from a dealer or by sending the controller to MC or Indmar.
Timing can improve the performance for a carbed motor more than for an injected one. A distributor doesn't have the range of advance/retard and direct control over this like a computer does. You might get 20 degrees of advance from the centrifugal weights and springs, with weaker springs giving you faster advance increase. Increasing base timing another 10 degrees will probably help. The recommended base timing on an injected motor is ECM 10 degrees BTDC. The ECM will provide up to 30 degrees of additional advance, based on load. More than this on these motors with the standard compression ratio/fuel octane requirements can cause detonation and the resulting damage this causes. Also, if the knock sensor hears detonation, the ECM will retard the timing in 5 degree increments until it reaches base timing. A distributor will not do this.
The easiest way to improve performance of a motor is by letting/making it breathe better. If a K&N filter is available, it can be used. It really should pass Coast Guard regs, but I seriously doubt that a K&N will be an improvement over a standard flame arrestor for a TBI motor. The LT-1 used K&N, the LTR didn't, but it uses a different throttle body and I'm not sure there is a K&N for this one. The key is keeping the flame arrestor clean. A new filter will always give a noticeable improvement over a dirty one and a lot of people have no idea when their filter/flame arrestor was cleaned last.
A new prop and a recal should make a nice difference. If the heads are coming off for some other work, that would be a great time to have them "freshened up". If the motor is being rebuilt, a new cam and head work makes sense, along with an intake manifold. Installed during other work makes it more economically feasible.
NOTE: if an injected motor is being torn down and the heads are shaved, the compression will start to noticeably increase after about .007" is removeded. The program for a higher compression would then be needed for a TBI motor with this kind of increase, as well as higher octane gas. The LT-1 is already higher compression and the calibration calls for high octane. They don't have a program for compression that's higher than what the LT-1 has. The MCX is still under warranty- I wouldn't do this kind of work on it till the warranty is over.
Evan Jones
02-08-2005, 04:15 PM
Wow, some great info out here. You guys are all awesome. I can't wait til the ice comes off the lake so I can really try some of these suggestions. I replaced the cap and rotor for the first time since '97. There was quite a bit of corrosion built up on the contacts in the cap. I'm changing the plugs and fuel filters and I'll clean the flame arrestor also. Between all these It will probably seem like a new boat!!
All of the things you said you have or will change are supposed to be done every 100 hours, or annually, if you use the boat a lot. Do you have a list of 100 hour service steps? If not, get this from a dealer. Have you messed with the timing at all? You can't just loosen the hold-down and change it unless the motor has a carb. You need to get it into diagnostic mode first if it's injected.