I bought a '99 astro 1800 with a 175horse merc efi last week. It had a 25 pitch laser on, which the motor would turn at 5400 rpm's. I was GPS'n 60.8 mph with a 3.5 - 4 sec. hole shot. I threw a 24 pitch trophy on and turned 5600 rpm's at the same speed with a 4.5 sec. hole shot I felt like the motor was a little bit low, so I threw a 6" slidemaster jack plate on it hoping that if I tweaked it a little, maybe I could turn the laser closer to the maximum rpm (5600). I set everything up in the middle, and ran out to the lake to play with it. I had the motor 3" high of the original mount, and lowered it 3/4" to get the rooster tail about cowling high. What I'm wondering about is that I had a little slower hole shot(1/2 sec.), and it's still turning the same rpm and speed. What's up? I still need to run some more props, and play with the plate some more, but I fully expected some kind of performance improvement. any thoughts or suggestions would be greatly appreciated. If it's only going to run 60, then that's fine, but I would like to get it performing at it's best.

I have a '98 175HP Merc EFI on my Ranger running with a 25tempest no jack plate gps at 65.2mph. It came with a 24trophy but it performed horribly. Waiting to buy a jp sometime soon.

Go with a 25 tempest and have it worked by a good prop guy. Should see mid 60's

Before I put the jack plate on I ran a 25p predator 4-blade. I could only turn it 5200 rpm's, but ran the same speed as the laser. less slippage I guess. I'm going to be trying different props, but I guess my question is why am I not seeing any difference with a jack plate? Thanks for the input guys, and I would appreciate any more.

BKG.....First thing are you looking for a hole shot or top end. Some boats don't like jackplates especially heavy boats and Astro's aren't the lightest boat and ever boat is different because of weight or the contour of the bottom all boats are built with a slight hook and it depends on how far forward or how far back to the running surface the hook is at.I would suggeust setting engine where the bottom of boat is in the middle of the water intakes on gearcase and run a 23 Tempest and make sure the motor is running properly you could be dropping fire on one cylinder and be causing this problem and you are correct max rpm's are 5600 but are you doing all of this testing with the boat empty of all tackle and empty livewells etc when propping a boat you prop it to the high side of rpm range with a empty boat and when you start adding weight you will still be in the range also dont be afraid to turn it 5800 to 6000 I use to turn a stock 94 175 EFI 6200 all day long with a 26 pitch laser on a Skeeter 175.....OPTI

opti, I'm not to concerned with hole shot at this point, because I feel like anything inside of 5 sec. is okay. I'm thinking your comments about heavier boats and jack plates may have some merit. This hull supposedly weighs 1525. I'm not sure what you mean about a slight hook, but this hull doesn't have a running pad. It's just flat hull all the way to the nose. When we started with the jack plate, I was actually turning about 5550 rpm, but with a sky-high rooster tail, and the same speed. The engine seems to be running like a top with no miss, but I am tweaking with the boat fully loaded... my thinking was thatthe only time I've ever run an empty boat was when I was test driving it. Maybe that's the wrong way to be doing it. As far as max rpm's go, a mechanic here in Armadillo told me that the 5600 max is just where the power band is on this motor, and they're all rev-limited at 6200. I did try a 23p laser, but ran it at6100 rpm and only 55mph. Are the tempests a lot better? I know that a lot of boats are coming rigged with them. I am doing all of this stuff at 2600 to 2900 ft. elevation up here in the pothandle, so I wonder if I should see much difference when I go downstate with this efi? I know it makes a lot of difference when you get much above 3000 ft. over in New Mexico, but I'm not sure about going downhill. Are any of you downstate boys seeing much difference when you come up to Henry (2220ft.)? By the way, you must have been hummin' in that Skeeter! Even with a ton of slippage, that would be scootin' on down the lake. Anyway, I forgot to mention earlier, that the jack plate did seem to give me better handling, so maybe that ought to be enough. I appreciate your thoughts.

Lazer is just about my most un liked prop there is, they don't run well on a heavy bass boat.

First, that elevation will certainly affect your motor's performance, high likelhood you'll need a high and low altitude prop.

Did you change any of the PVS plugs on the trophy? That will greatly change the holeshot performance.

That motor is perfectly happy running 5,900-6,200 all day long. There isn't anything internally different than your motor and a 10,000 rpm drag engine.

Get your mitts on a 23 Tempest, and play with the plugs, probably will be your best choice at your altitude.

Pat, thanks for the info. If I can find a Tempest, I'll try it. I was told yesterday that these motors run fine at higher rpm's, but that the oil injection systems have trouble keeping up above about 5900. Any truth to that? I went to Greenbelt (2600ft) yesterday, and turned almost 5600rpm with the laser 25p, but still couldn't break 61mph. We're going downstate in a couple of weeks, and I'll see if I can't find some props to try down there. thanks again.