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madman
08-18-2010, 01:47 PM
I was wondering if anyone knows what rpm my 351 should be turning, 93 ps190, also what should max boat speed be? prop is a 12.5/13/4 blade oj .90 cup. thanks, kevin

east tx skier
08-18-2010, 01:53 PM
The 351 HO did 4,600 rpm. Roughly 45.5 mph with a 13x12 3 blade acme. Drop a mph for the 4 blade is my guess.

The 351 did 4,400 rpm. Guess 43--44 mph (one less with a four blade).

madman
08-18-2010, 01:58 PM
How do I identify which 351 I have? She only pulls to 4000rpm, possibly connected to my carb problem???

Luv2Ski
08-18-2010, 02:16 PM
The 351 HO did 4,600 rpm. Roughly 45.5 mph with a 13x12 3 blade acme. Drop a mph for the 4 blade is my guess.

The 351 did 4,400 rpm. Guess 43--44 mph (one less with a four blade).

Don't mean to threadjack here, but I have essentially the same question.

88 Prostar 190, standard 351 with a 1:1 transmission and a 3 blade 3x13 prop, I think it is original . Presently WOT will get me ~43 mph (gps verified), which seams to be appropriate; however, the engine is only turning 3,650 rpm.

Is this normal? Based on the searches I have performed, it seams WOT should be around 1,000 RPMs higher.

east tx skier
08-18-2010, 02:28 PM
Check the knowledge center link at the top of the MC home page. Look at the manual for 88. The rpm WOT should be listed. For 91--93, it was 4400 for the 351 and 4600 for the 351 HO.

DooSPX
08-18-2010, 02:40 PM
the HO meant the standard 351 w/ GT40 can tell by the number of vertical bars on the front of the head.
the standard 240hp 351 had 2 raised vertical bars
the GT40 has 3 raised bars

Luv2Ski
08-18-2010, 02:58 PM
Check the knowledge center link at the top of the MC home page.

Good call. Manual states max is 4,600 rpm at ~45mph..... How is it possible that I am so far off? From hooking up a external tach during tuning, I know the gauge is good at lower RPMs. Guess I will start by verifying it is correct at high RPM. After that, I guess my prop has somehow been reshaped (no vibration or obvious damage)... Will check into it and start a new thread if needed (sorry for the threadjack Madman).

east tx skier
08-18-2010, 04:12 PM
You're right. Sorry about being off on the rpm. Should have just checked the manual myself. Mind must be going.

GuitsBoy
08-18-2010, 05:33 PM
Im chasing the same problem in a similar boat (92 205 HO). Turning about 4300 RPM on perfect pass (only 3700 on tach) at about 36 or 37 MPH.

You said you didn't see or feel any problems with the prop and shaft. If your carb is in good condition and the secondaries are opening fully, then I would suspect ignition. I recently replaced all the normal tuneup stuff, the coil, and the electronic pickup. My next thing to check is the timing.

How do your plugs look? Are they a light brown / tan color? Too white and you're starving for fuel - carb problem.

turn1andburn1
08-19-2010, 12:05 AM
the HO meant the standard 351 w/ GT40 can tell by the number of vertical bars on the front of the head.
the standard 240hp 351 had 2 raised vertical bars
the GT40 has 3 raised bars

Are these the raised vertical bars? Looks like mine has three? Very center of the picture.

http://i704.photobucket.com/albums/ww44/turn2andburn2/photo7-1.jpg

east tx skier
08-19-2010, 12:27 AM
3 raised bars is the GT-40. 4 raised bars is the GT-40p IIRC.

Bert
08-19-2010, 12:38 AM
Check the knowledge center link at the top of the MC home page. Look at the manual for 88. The rpm WOT should be listed. For 91--93, it was 4400 for the 351 and 4600 for the 351 HO.
I have a 13x13 OJ stainless on mine Been on there since the day I got it in 91. I have always had all the juice I needed but have never been able to hit more than 4000RPM. Elevation doesn't seem to matter, I run in lakes between 1000' and 4000' above sea level.
Hit about 43MPH but haven't verified with GPS. Old school here and set my speedos by timing through course. :D
Now I wonder if a different prop might get a little more performance.

east tx skier
08-19-2010, 12:45 AM
My wife even took notice of a 13x12 acme over a 13x13 stock OJ.

Bert
08-19-2010, 12:46 AM
My wife even took notice of a 13x12 acme over a 13x13 stock OJ.

Uh, what did she notice?

turn1andburn1
08-19-2010, 12:46 AM
I don't think so. More traditionally, it's this:

http://www.fordmuscleforums.com/attachments/all-ford-techboard/8451d1244382194-gt-40-heads-gt40p-head.jpg

I see three raised vertical bars in your picture, am I wrong:confused:

85 stars an stripes
08-19-2010, 09:08 PM
I put a demon carb on mine it will only 4200 speed o doesn't work .
but my motor does need a rebuild

DooSPX
08-19-2010, 09:32 PM
that picture is of the GT40P heads... my 2 bars seem to be in the middle like the pic., but on yours, thats the only 3 bars I see on that head unless you can get a different angle.

madman
08-19-2010, 09:42 PM
Only 2 bars on my heads, going to the lake for 4 days starting tomorrow, bringing external tach and gps to verify actual rpm/speed. boat seems to run great on the top end just wondering if 39mph as indicated on the 1 working speedo and 4000rpm is correct or not. Side question here....boat came with a barefoot boom, how fast do I need to be going to try putting my feet down?

madman
08-25-2010, 12:00 PM
Ok, went to the lake, GPS indicated 41 mph top speed and tach says 4400 rpm. I guess that should be about right. Thanks for the help everyone, will replace the carb this winter and that should take care of the problem at idle. Boat ran great all weekend.

east tx skier
08-30-2010, 11:17 AM
Sorry for the confusing picture. 3 = GT40; 4 = GT40p.