Max RPM

[supramariah#1]

Does anyone know the Max RPM of my boat?

Oh and its a 1988 Supra Mariah. 351W. No mods.

I would like to see how close I am to it at WOT. Trying to see if I am gonna get a new prop.

[csuggs]

WOT on a 80's model 351W should be about 4400. My 86 Sunsport with the same motor will only get about 4100 with the standard 13x13 prop - pretty sure she runs out of hp before getting to WOT of 4400. I'm going to try a 13x11.5 and see I pick up a few hundred rpm.

[beast 496]

4200 to 4600 on the ol 351 Fords.

[csuggs]

My '83 351 PCM hits 4500 easily with 20 year old 13 x 13 LH prop.

At 4500rpm what's your indicated speed?

[csuggs]

With GPS, I'm right at 39-40 mph. Used it to dial in the NOS Airguides I just put in.

Good answer, that's what I hoped you would say. Is your transmission 1:1 ratio? If your turning a 13x13 with 1:1 trans your mph should be real close to your speed (i.e. 2000rpm = roughly 20mph and 3500rp = roughly 35mph, of course this can vary with how the boat is loaded/weighted). This rule of thumb has held true for my Sunsport and my friend's Comp with the same driveline - 351W, no modifications, 13x13 prop and 1:1 transmission. I wonder if your 20 year-old prop is worn in a way that makes it spin easier without as much "bite". That would explain the higher rpm and slower speed, unless of course you have a reduction transmission.

[csuggs]

Daniel - I wonder if it has always run up to 4500. You have the same sticker that mine has (or had on the OEM valve cover)

[cadunkle]

It shouldn't hurt a 351w to spin higher than 4400. I've never heard of 351w rods that couldn't take such a low RPM.

Now, interesting question... When did Supra put 460s in these boats? If my 454 ever blows up I'd enjoy building a 545 stroker for it. I guess all that would be necessary is a bellhousing, coupler, and mounts... Mounts being the tricky part I guess.

[csuggs]

It shouldn't hurt a 351w to spin higher than 4400. I've never heard of 351w rods that couldn't take such a low RPM.

Now, interesting question... When did Supra put 460s in these boats? If my 454 ever blows up I'd enjoy building a 545 stroker for it. I guess all that would be necessary is a bellhousing, coupler, and mounts... Mounts being the tricky part I guess.

I think the decal you're reading that refers to the 460 is actually a PCM decal, not a Supra decal. I'd bet PCM built 460's for some kind of commercial utility boats like inboard fishing or crabbing boats? But not for Supra.

[sybrmike]

I've heard of 440's in early Supra's, but never a BBF. I ran a 460 in an old jet - pretty common & lots of marine parts available. You could probably make something work if you really wanted to...

[supramariah#1]

This should answer a lot of questions I frequently see on here about servicing.
Original sticker. Original engine...no mods......1:1 tranny.
Mine goes above max engine speed at 4500 rpm.

http://i740.photobucket.com/albums/xx49/ngavdba/7f5c353f.jpg

Holy moly. I saved that photo. its got a wealth of info all in one easy place. thanks!

[haugy]

Yeah that is a great reference for all those running 351w engines. I've added it to my Supra book.

[mapleleaf]

ditto... thanks Dan great pic.....

[DAFF]

Anyone adding a fuel additive for the leaded unleaded issues?? Never even thought of it until I saw the sticker above!!!

[Hagman]

I remember years ago PCM posted a up date about changing the timing reconditions because of the newer fuels. This could start a hole new thread.

[supramariah#1]

I remember years ago PCM posted a up date about changing the timing reconditions because of the newer fuels. This could start a hole new thread.


Oh I wasnt looking at that. Should I be adding Tetraethyl-lead? I have a lot of it for my old cars. When did they actually install hardened valve guides?

[cadunkle]

Don't sweat it. I've been daily driving 60s vehicles since I started driving, none of which have ever had hardened seals. For a while I was doing 170 miles/day 5 days a week on my '68 Galaxie. Hardened seats are nice but not critical. Most miles I've ever had on an engine without hardened seats and never rebuilt is 302,000 on my first car... A '67 Galaxie with a 289. it ran great when I sold it, but the frame was all rusted out and I wasn't feeling like doing a frame swap.

One thing I have noticed on the few engines I've rebuilt that have had hardened exhaust valve seats... On most the exhaust valves have had to be replaced from being all pitted and in general beat to hell. Hardened seats just more the wear point from the seat to the valve.

If you're really all that concerned get yourself some 100LL from your local small airport and add 3-5 gallons per tank on your boat. Lead content will be higher than leaded gas at the pump was back in the day. I think this is unnecessary though. Don't tell them you're putting it in a car or boat though as they may turn you away. Try not to tell them anything if they ask, but if you must, make up some BS. You have a piper cub or an ultralight, or a gyrocoptor, or you're using it for model airplanes. Whatever sounds legit and passable.

Alternatively go to your local drag strip or circle track and they usually sell 100+ octane leaded racing fuel. It'll cost more than 100LL but they won't ask questions or hassle you. Though as I said, I feel eladed gas is unnecessary for any stock or mild marine or automotive engine where your only concern is not having hardened exhaust valve seats.