How fast should I be going?
 

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

Re: How fast should I be going?
 

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.

Re: How fast should I be going?
 

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

Re: How fast should I be going?
 

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.

Re: How fast should I be going?
 

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

Re: How fast should I be going?
 

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

Re: How fast should I be going?
 

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.

Re: How fast should I be going?
 

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.

Re: How fast should I be going?
 

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.

Re: How fast should I be going?
 

anyone have any thoughts?

Re: How fast should I be going?
 

I have a Sutphen 30. Your boat weighs 5800 lbs.

I am running a totally different set up, so I can`t really offer you any comparison.
I have stock Merc 420`s / TRS / 26P Bravo 4-blades. My props are too big for these engines. I can only get 4100 rpm and then it quits pulling. I`m seeing 64 on GPS speedo.

I`d love to try smaller props to get my R`s up. I`d like to see upper 60`s at least.

Good luck

Re: How fast should I be going?
 

I just reread combo and the 34 dgrees total timing just jumped out.

Do you have factory OE heads ?

If so, the total timing on a performance build usually ends up being 36-38 (some even more :eek: ) because of the combustion chamber design.

Bump up timing two degrees, do a run, note performance, and check plugs for any signs of detonation. I'd probably run 91-92 octane fuel just to be safe.

If performance does jump, try another degree or two and recheck plugs.

Some motors don't respond much to few degrees of timing, but some really wake up. Only one way to find out.

Re: How fast should I be going?
 

I will ttry this for testing purposes. I would be scared to keep it that high. The plug readings showed the timing to be a little high at 35 so I backed it off to 34 and the now the readings are almost perfect.

I saw no performance difference between 34 or 35.

I used to run 87 octane I went up to 89 to be on th esafer side. I will try some 91 or 92 when I up the timing.

Re: How fast should I be going?
 

So I can safely say with fuel gear and 2 people Im right around 7k.

I have a set of 22 bravos that would probably be perfect for you. Too bad your in Texas. I wouldn't mind trying the 26's.

Re: How fast should I be going?
 

Plugs look good. I wouldn't lean it out any. Sorry, just wanted to check.

Re: How fast should I be going?
 

I did lean it out you were right it was a little fat. The pictures are from after I droped it down a little. Unfortunatly it did not net me any gain.

Thanks Rob

Re: How fast should I be going?
 

So what jets did you end up going with? THe last set of pictures looked good.

Re: How fast should I be going?
 

The only things that look out of place on your build are the Air Gap intakes. There are a couple of used HP500, Dart intakes for sale in the classifieds. That's what I'd use.

Re: How fast should I be going?
 

I used to have a 30' Scarab with 420's and TRS drives. It weighed 6800 dry according to the factory. It went 70 with 23 pitch 3 blade cleavers. This size boat always seemed to run well with 3 blade props. With almost 100 hp more a side you should be able to spin 25 pitch Mirages. :confused:

Re: How fast should I be going?
 

Any interest in trying a set of 23P Mirage's? It's what I'm running now and would love to swap and try your 22P Bravo's.

Re: How fast should I be going?
 

The primaries are 88's and the secondaries are 90's.

Re: How fast should I be going?
 

That is exactly what I thought. I have been wondering if the props I have have been reworked or are messed up. I have not had any luck finding another set of 25's to try. I found some 24 hydromotives I'm going to hopefully try out this weekend.

Re: How fast should I be going?
 

I would like to try the 23 mirages as well where are you from?

Re: How fast should I be going?
 

You might be hitting the wall with your ignition system. try something in at least one of the engines to see a difference. I have a friend w/ a 1988 sutphen 31 w/ 502 magnums, 410 HP (repowered w/ 502mpi). boat does 78 mph on gps. running 26" hydromotive Q4 labbed. 5100 rpm aprox.

Re: How fast should I be going?
 

Leathl WS6,
It is difficult to tell from the lighting in the photos. It does appear you are a bit cold on heat range and the jetting is inconsistent from cylinder to cylinder. Some of the plugs do not appear to have a full turn of color. Can't see the base of the insulator from the photos.

Perhaps this will help
Bob

Re: How fast should I be going?
 

Second photo

Re: How fast should I be going?
 

That middle plug is from #7. I was thinking of upping the jet on the rear port side of both motors. I am having a hard time getting color on that plug. Keep in mind as well those plugs were only ran for about 2 minutes and were brand new when they went in.

The heat range are you thinkin I should be runnin a hotter plug? Or I should add timing? Won't adding timing will move the mark you are pointing out. Most of the plugs have a reading like your picture for the heat range That one is the worst one. The others are a lot closer to middle of the electrode.

I did notice the jetting is inconsistent what causes that? If I run all 4 jets the same I'm too rich down low or lean up top.

Another thing too those plugs are from 2 and 7 on each motor so those are the leanest plugs I have. Running the Air Gap intakes those cylinders have longer runners.

Thanks Rob

Re: How fast should I be going?
 

I thought the thunderbolt ignition was good to 6k I am only planning on turning it 5400 to 5600 max.

I would be very happy with those speeds and feel I should easily be able to run that.

Thanks Rob

Re: How fast should I be going?
 

I double checked the timing tonight and it was higher than I had thought I'm not sure if the light i used last time was bad or what but timing aswas 36 on one motor and 37 to 38 on the other...

Yikes.

I'm going to try and get back in the water tomorrow.