Why is my Sutphen so slow.
 

My boat used to run low 70's with stock 502MPI's 415hp a side. I upgraded the 502' with some mild head work. A nice cam Holley 850 carbs 9.2:1 CR. Still using the old Merc Log style manifolds the boat still only went low 70's.

After numerous suggestion to change to a better exhaust last year. I finally upgraded to a GIL offshore pipe and manifold this spring. After rejetting the carbs the boat still only runs low 70's.

I just don’t understand it. The motors should put out about 525hp. That’s 200 more hp and still the same MPH.

When checking BAM's speed calc for my boat weight, hul design and power it claims 1000 hp in my boat should run 80+ MPH. I know I have heard of 30 Sutphens with similar power going in the 80's

I am running a set of 25 Mirage props and can only spin them to 5100. I have tried 2 different sets of the same props with the same results. I put a set of 22 bravos for a test and could easily spin them over 5400 but the speed was not there. So I know the motors are capable of going over 5k.

I have been looking for a set of 23's to try but have had no luck coming across a set. Plus I feel I should be able to easily spin the 25's to at least 5500.

The boat seems to run very bow heavy.

Any help would be greatly appreciated

Rob

Re: Why is my Sutphen so slow.
 

Swap the drives to spin out instead of in. That should give you more bow lift. What kind of drives Bravo or TRS. The TRS will suck up some power.

Re: Why is my Sutphen so slow.
 

They are TRS. but I do remember seeing a few TRS 30 Sutphen's with similar setups running in the high 70's. I also remember Bill (Sutphen30) running mid 80's with 550 or so hp a side and TRS he kept blowing them up and went to Konrads.

I will try switching the drives out. has anyone else tried this?

Thanks Rob

Re: Why is my Sutphen so slow.
 

give Rich Jr a call...201-274-5445

Re: Why is my Sutphen so slow.
 

Thanks Bodyshot i will try him tomorrow.

Rob

Re: Why is my Sutphen so slow.
 

Ck your bottom for a hook.

Re: Why is my Sutphen so slow.
 

dyno the engines.....

Re: Why is my Sutphen so slow.
 

hey you said you still have the log manifolds :eek: , thats whats wrong I think! your chokeing the motors. S/M OR C/M SATIN FINISH HEADERS WOULD CLEAR IT OUT. TRICK MARINE WOULD BE YOUR BEST BET OR SCOTT WHICH I WILL LOOK UP FOR YOU IN A SECOND.

Re: Why is my Sutphen so slow.
 

I'm back its SPEED AND CUSTOM MARINE SCOTT AND CATHY AT 850 875 0381 JUST GOT 380SS K PLANES REAL QUICK AND PRICE WAS CHEAPER BY 300 BUCKS FROM MY FRIEND :rolleyes: AND GPS SET UP :D FREDS # 866 921 4553 so if you have twins you should be able to get prices for 2 sets for under $4,000 I have a pair of S/M DRY HEADERS SINCE 1994 JUST FLUSH THEM OUT AFTER USE IBOAT IN THE OCEAN ONLY. I HAVE A 510 650HP.

Re: Why is my Sutphen so slow.
 

SH!t I MISSED THE PART ABOUT THE GILS :rolleyes: BUT THE OTHER 2 ARE BETTER HEADERS :D BOW HEAVY SOUNDS LIKE HIGH X TRY B1 24 OR 26'S see if the bow comes up.

Re: Why is my Sutphen so slow.
 

I had a 24 bravo on it last week best I could spin it 4800 and around 68mph. I have been looking into prop shaft height now. I think it's way too high. But I'm not exactly sure how I should be measuring it.

Re: Why is my Sutphen so slow.
 

Anyone Have A Pair Of 5 Blades To Try?? If It Is High This Might Help. Or See If There Are Spaces For The Trs's. My Buddys 31 89 With Trs Alwayshas A Hard Time Getting On Plane His Boat Does 72 To 74mph 25p M, 454 370hp's .

Re: Why is my Sutphen so slow.
 

I would love to try a set of 5 blades. Or the 4 blade Hydro's that are supposed to give a lot of bow lift.

I have been looking into drive spacers for thr TRS drives but have not been able to find any. Does anyone know who makes them?

My boat does not come on plane too bad the bow does point high while coming on plane and the props will slip some as well but not too bad.

At slower speeds like 50mph the bow feels pretty light and rides pretty normal. Once I lay into it the bow drops and the boat rides level at best.

Re: Why is my Sutphen so slow.
 

Got some mirage 23's for sale soon let me know if your still looking for them.
USed to work great with the old motors but need a change with the new set up.