I have a 30 Sutphen motors should be around 525 hp. It has 1.50 TRS drives, I'm running 25 pitch mirage props. I'm working on getting some different props to try. I can only spin the 25's I have to 5100k maybe a touch more if the tanks are empty and I'm by my self. At 70mph it's like I hit a wall.

The one prop does have a few light dings of the edge of one of the blades.

I am only seeing 72 to 73 MPH.

Does anyone know how much this boat weighs and how fast I should be going? BAM's calculator shows around 80. For the weight of the boat and 1000 hp. Which I'm sure I'm over.

I changed the exhaust this year from the old Merc Log Style manifolds. To Gil manifolds and offshore tailpipes. I'm sure this upped my power at least 30hp a motor. But yet I did not see any increase in speed.

I did rejet after the exhaust change.

Here is what I am running.

502 gen V
9.2:1 CR
Holley 850 Manual Secondary’s 90's in front 93's in back. It is a touch rich on the plug readings but I wanted to be on the safer side.
Air gap intakes
Large hi perf flame arrestors
Stock merc fuel pumps. 7-8 psi fuel pressure at WOT
Thunderbolt IV Ignition with MSD coils.
34* Total timing.
Cams are 234 244 564 567 on a 112 LSA

Here is a posting from last year before I change the exhaust. I have not noticed any increase in speed with the new exhaust.

http://www.offshoreonly.com/forums/s...eme+marine+cam

Any help would be greatly appreciated.

Thanks Rob

I don't know anything about Sutphens. Just going by the math, 25's at 5100 RPMs is not going to give you 80 MPH. You speeds don't sound to far off. Maybe 75 tops.

I agree for 5100 speed is right, but I think I should be able to spin the 25's to at least 5600. I'm sure I added power with the new exhaust. Midrange is alot better I can now cruise at 4k out of the 4barrels before cruise was only 3500. So I picked up 500 rpm at cruise but nothing at WOT.

I think there is something restricting me. 2 years ago the boat went 72 with 415hp 502 efi's. I know I'm over 500hp a side now and still no increase in speed.

Rob

What if your present motors are making 415-430hp at the same rpm the 502 MPI's do ? Just throwing that against the wall.

Furthermore,
I'd put smaller pitch props on and see what happens when you let the engine run at proper rpm. I'm guessing (note the guess part) peak hp of around 5800-6000 rpm.???

If the smaller props don't let you get to a higher rpm than you are running now you know the engine's have an issue - either valve spring, fuel, or ignition.

I never actually thought about it that way. Could be but with the exhaust change this year I pick up 500 rpm in midrange but noting in top end. Similar setups are making over 500hp at 5k. Not saying that means mine are for sure but if they aren't I think they should be.

I have had a smaller set of props on one time they were 22 bravos. The lake was too bad that day I could not get a WOT run but the motors did spin up past 5400 speed was under 70. I am working on getting some different props to try.

Thanks Rob

Those are some big jets in your carb. Can you post some pics of your plugs?

I'll take some pictures this weekend. I know I could step them back a little. but 86's and 90's are too lean.

OK here are some plugs from WOT 5100rpm these are from #2 and #7 These plugs were brand new. They were ran for only about 2 minutes at WOT. Then I came of fplane as quick as possiable.

These are with 88's in the front and 90's in the back.

These were #7 and #2 ran for about 4 minutes at 3800. Not in the secondaries. The real dark one came out of #2 on the starboard motor. That cylinder always seems to be real rich. Smae jetting as above 88's front 90's rear.

anyone have any thoughts?