Top speed???

[biggsie]

Up north for the week. Took a WOT run last night..... 351 Windsor 13" 3 blade prop.

34 MPH is all she's got at about 3900 rpm. Seem too slow to you guys?


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[Cusefan78]

Yes you have a problem. First you should be turning way more Rpms then that.

[biggsie]

Hole shot feels good, seems to have plenty of power. Overall I'm happy with the performance. 1:1 tranny...., something's fishy huh???


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[2500HD]

What's your pitch?

[biggsie]

Not too sure. Haven't looked into it. All I can read is 13x


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[2500HD]

I would look into a new prop, you probably have an original on the boat.

[crystal waters]

What's your model and year of Supra?
How many hours?
Original owner?

[biggsie]

1987 sunsport. Complete restoration with many many many previous owners.


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[biggsie]

Regardless, should I get more speed?


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[2500HD]

You got a lot of factors here but yes, i run in the low 30's but my elevation is 8500ft. If your engine appears to be running good then i would suspect it is a prop problem, or a tired engine that needs a refresh. Have you rebuilt it?

[biggsie]

Motor is strong, good compression, new ignition/carb Maybe I'll
Just deal with it and call it good.


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[2500HD]

If you don't have a back up prop i would suggest getting a acme 541. Atleast that is what i think it is. Having a spare prop is awesome. It can be the difference between an awesome weekend on the lake or not. Give Nettle's a call, They will get you set up.

[biggsie]

What's a normal top speed? I would like to see at least 40.


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[ckracing]

Even with the stock prop - 13x13 3 blade, you should see more speed and RPMs. My 86 on stock prop WOT with just me was 42 MPH on calm water. When I switched to an Acme 541 I gained top speed (44) and felt a large improvement in holeshot. By far the prop swap was the most notable performance improvement for the $.
Only engine modification from stock I have is an electronic ignition (Petronix), better plug wires, new Holley 4160 carb.
Good luck!

[biggsie]

Maybe I should experiment with a prop swap? Or at least check the # on the current one.


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[SUPRA_ALLEGRO_LANE]

WOT I'm running 46 mph at 3900 rpm. That's with 2 bigger guys in her too.

[lively]

Whooahhhh . So are you for sure it's WOT ? Have you checked the linkage at carb and make sure it's adjusted for full throat ? What about timing ? I have a 351 with a 1:1 and a 13x13 L prop and at WOT on smooth glass 4200 rpm I'm about 40-43 on GPS depending on how much beer and babes are in the back


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[chris young]

I haven't posted my specs in the sticky thread yet because I still have not been able to calibrate my tach since I overhauled it and I'm pretty sure it reads low.

Non the less, Acme 541, 1:1 me alone in the boat 39 MPH smart phone GPS @ WOT. My tach reads 3400, but as I said I don't think it's correct. Basically the same boat as yours, (84 Rider) PCM 351 Holley 4160.

Do you still have your exhaust mod installed? I've heard the factory one takes away one or two MPH and if yours doesn't allow the motor to breath properly, that could cause issues as well.

[biggsie]

I will look into the throttle linkage today. Speed was with no passengers, 7/8 tank of fuel and GPS app on my phone. I do still have the PVC exhaust on, maybe I'll drill out some rivets and try it. Would running without traps or flaps cause an issue ??

Ign timing is another story.... Damn timing light is making me mad, I can set idle timing to 8-12 deg but my attempts at checking the advance at 3000 rpm are not working. Maybe the dist is bad but it seems to run so nice..... I did some on the water timing tuning the other day and I forget where I left it but close to 10 deg.


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[chris young]

Timing makes a huge difference, so if your dist is not working right that could most definitely cause issues. I bought one of these http://www.ebay.ca/itm/E5JL-12100-CA-Ford-New-Prestolite-Marine-Distributor-points-type-Hite-Parts-/280937495742?pt=Boat_Parts_Accessories_Gear&hash=item41692dfcbe&vxp=mtr&_uhb=1 and these guys are great to deal with.


Would running without traps or flaps cause an issue ??

I don't think so, mine's been running with wide open exhaust since I bought it. I'm planning on some type of FAE setup myself so I haven't bothered with flappers or traps.

[Cusefan78]

Yeah you need to see if the carbs open up all the way. Also check to make sure air is flowing into the engine compartment. 34 is barely a skiing speed. The Rpms should be in 4k mark wide open. Something isn't right.

[2500HD]

I did notice a loss of about 200rpm with my exhaust system.

[crystal waters]

Wot I run 46 mph
89 conbrio
351 with new Holley 4160
Acme 541 prop
1200 ft elevation

[SquamInboards]

Wot I run 46 mph
89 conbrio
351 with new Holley 4160
Acme 541 prop
1200 ft elevation

You should add this to the sticky for reference...

OP - my opinion is you should try a new prop before getting too crazy worrying about engine issues. I have seen it make a massive difference in lots of different boats of different ages and conditions...

[biggsie]

A prop purchase seems like an expensive experiment.


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[Jetlink]

A prop purchase seems like an expensive experiment.


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Only if you go out and blindly purchase one without consulting either Nettles or ACME or any of the other recommended prop shops that have already been mentioned.

[biggsie]

Only if you go out and blindly purchase one without consulting either Nettles or ACME or any of the other recommended prop shops that have already been mentioned.

Agreed but I worry that even with a new prop I still won't have the rpm/mph that I should. I have a hard time thinking it's the prop, like stated before 34mph is hardly enough speed to slalom ski, my prop looks great and I'm almost sure it's the factory pitch.


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[biggsie]

Confirmed throttle linkage is not the issue :(


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[chris young]

I wouldn't be going for a prop just yet either. I was sitting almost exactly where you are now, (I think I was 35 or 36MPH) with a brand new Acme 541 which was the prop Acme recommended for my needs. I adjusted the timing to 10 deg (it was way too advanced by the PO) and gained 4 MPH.

[lively]

Timing .... Timing ... Prop would be the last thing I would replace . I have the same set up as mentioned and pushing 42 knots


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[Supra-in-steamboat]

I second what Lively and Chris Young are telling you. Jetlink has stellar advice as well. Do your research. I have 4 props. At sea level a very aggressive 4 blade CNC Nibral sent my 87 to 46mph quickly. At 7500ft that prop would take 30-40 seconds just to get on plane with no weight and 1/4 tank of gas. Add a .60 cup 3 blade 10.5 from Acme (ballast prop an older acme 913 -new ones are.80 cup) and it will rip the rope out of your hands and do @39mph at @4100. Is it possible there is some crap in your power valve?

[Blackntan90]

For info I run WOT at 42 mph and 4400 rpm- Just as it says in my manual with a stock 13x13 prop at less than 1000 ft elevation. I have added alot of weight to her over the years in accessories(tower, tunes, misc. crap), and my bimini acts like a sail and probably slows me down a bit.

[carlossa]

I would check your timing first. Cost you nothing to throw a light on it. Flyweights in the distributor could be frozen and not advancing through the rev range.

[SquamInboards]

I would check your timing first. Cost you nothing to throw a light on it. Flyweights in the distributor could be frozen and not advancing through the rev range.

While I may have just come out saying "get a prop," I completely agree with this. A new prop can really transform a boat, but it does have to be running right to begin with. As far as the cost, you can work with a shop that will let you try one, and if it doesn't perform the way you want they'll give you a different one until you're happy. Not all shops will do this but some that have been mentioned certainly will, and maybe someone near you would do it for you too. But definitely checking timing is a good idea since it's FREE if you can get your hands on a decent light.

The more info you have and the more confident you are that the engine is performing properly, the better experience you will have looking for a new prop to take you the last 10% of the way to excellent performance. I've seen boats with new (repower) engines gain 2mph @ consistent RPM with a CNC prop over the old one. So once you get in the neighborhood, the right prop can really dial you in.

Good luck, and keep us posted with what you find. There's a lot of collective engine knowledge here to steer you in the right direction.

[cadunkle]

Check for full timing advance, you want 32*-38* full advance around 2500-3000 RPM. Check that your secondaries are opening, if vacuum it could have a ruptured diaphragm not opening or not fully opening.

WOT RPM should be ~4500, give or take a few hundred depending on prop. My Saltare does ~44 MPH with a CNC Acme 13x12 and with the original cast OJ it did ~50 MPH.

[biggsie]

Timing light has been erratic... Works ok at idle but cuts out and acts funny at 3k rpm. New dist going in this afternoon. Funny thing is that the boat seems to run great.


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[lively]

Get a new timing light ?


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[biggsie]

It is a very new digital unit that works great.

Just pulled the old dist and the guts are all rusty and crappy looking. Fingers crossed.... New one goes in soon.


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[lively]

Pictures ! I wanna see !


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[biggsie]

Too late for pics, it's gone to the core charge gods.

New one installed and set timing to 10*. Instant gain!!!
40mph and 4200rpm. Not too sure what the factory timing curve is but I may just leave it be.


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[SquamInboards]

New one installed and set timing to 10*. Instant gain!!!
40mph and 4200rpm. Not too sure what the factory timing curve is but I may just leave it be.


That sounds a LOT better. Good to hear! I'm going to sound like I work for Acme, but now you could try out a prop and really dial it in. If you plan to run ballast or anything, you will probably want to get WOT up at least to 4400 or maybe slightly over, with no ballast, so you can get up and go when you DO have the extra weight.

But anyway, go enjoy the boat for now and play with props another time. It sounds like you solved 95% of your issue.

Cheers!

[biggsie]

Now if I could stop my oil filler/vent from puking hot oil under high RPMs I'd be all set ;). The power is great, it feels like a new boat!


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[lively]

Sounds like you got a solution ! Should be 36*-38* full advance at 3600 rpm

[SquamInboards]

Now if I could stop my oil filler/vent from puking hot oil under high RPMs I'd be all set ;). The power is great, it feels like a new boat!


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The oil filler, I believe, should be sealed with a rubber o-ring, no? There should be another way for positive crankcase pressure to escape. Not the dipstick, and not the filler.

[chris young]

IIRC you said you had no PCV on that motor, that would be your next stop. Mine has none either for this season since I put the wedge spacers in, and it smokes a bit out of the filler cap but no oil. I'll plumb my spacers for PCV this winter after I pull the boat out.

[biggsie]

I installed a 1" spacer with the PCV port and plumbed it all properly. Must just not have enough "pull" to keep it under control.


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