Motor out of tune after hard run...
 

Hey folks,

Ran the boat pretty hard yesterday afternoon coming back up the Potomac. Oil pressure stayed consistent (which is always good), temp stayed right at 160* (another plus), and the motor seemed to perform very well. I ran it for probably a 45 minutes at speeds between 4200 and 4800 with some brief slow downs to cruise at under 4000 while dealing with the rules-of-the-road.

Anyway, by the time I made it to the no-wake at Alexandria (about a 25 mile run from where I was), I noticed that the motor sounded a bit different. The idle wasn't as choppy as it had been and I could tell that it was missing slightly (maybe even loading up a bit). Also, I could hear a hissing sound that seemed to be at about camshaft speed. It wasn't down on power too much though I didn't erally push it from that point (seemed to still pull like a train once out of the no-wake area). I went back to the marina to pull it out and found someone using the ramp so I had to wait my turn. While trying to motor around the motor stalled out when going from forward to reverse. It was a mother to start from there, though she did restart (seemed flooded to me). The motor sounded the same as it always did though while trying to start (meaning, it didn't sound like an engine would that was down on compression in one cylinder, etc... which is what was really worrying me, with the hissing noise and all).

So based on the above, and the fact that I have the "black transom" syndrome, I'm thinking that I might have fouled a plug. I think my coil was having some trouble lighting it off at high speed so again I think it's plug related.

Any quick ideas or things to check out? I have not done anything with it since yesterday. I loaded the boat on the trailer and then headed straight over to my folks for my birthday party :D and then dragged it back home afterward. By then it was too late to do anything else so I cleaned up the boat real quick and went off to bed.

Any thoughts or suggestions would be appreciated!

Thanks!

Had a similar situation a few years back, it was a broken valve spring. Also check for a broken rocker stud.

The black transom sounds like carb tuning issues.

What's your setup?

It's a 383 Chevy.

10.3:1
Comp XE 274H
Vortec heads with big valves
Performer intake
750 Q-Jet.

I didn't hear any tapping that would indicate a broken rocker or stud... just the hissing a poor starting. If the plugs didn't show me anything then I was going to yank the valve covers off for a quick look.

Now, just for curiosity sake (and because I'm a worry wart), what would a holed piston sound like? I have had no detonation problems since removing all the old gas and I'm running very conservative timing (32* tops). But the hissing erally bothers me. The motor does seem a bit rough off idle but smooths out as power is increased so I eally doubt it's anything like that, but still I think mentioning it is good.

The best suggestion I have for you is to run a leakdown test. That will tell you right away if there is an internal problem.

Hissing..... have you checked for a vacuum leak? Did insulator blowout of a spark plug?

Sounds like a vacuum leak and or carb problem that created the condition. An easy way to check fro a vacuum leak is to get some aerosol carb cleaner. Spray it in quick spurts at different places on the outside of the carb. If the rpm goes up when you spray it on a spot, thats where the leak is. Also spray it on the intake to head area if you don't find a leak near the carb.

Thanks guys!

I'll probably have a look at it tonight as long as it doesn't rain.

Check Ignition timing, my friends boat suddenly lost power last week and the culprit was a loose distributor.

Rob

Tom, you didnt mention. What kind of speeds you were you running when you were running hard.

I had mine out this weekend and spanked it abit. She sounds really nice. I have a cruise of about 40 at 3000. Around 4200 I was at bouncing at 55-60 on the speedo, which is pretty accurate but I didnt have my GPS. I ran it up to 4800, no secondaries yet, and my speedo pickup flipped up because of the speed, but I was around 65. Those things scream. Ya gotta love SBC's. But I'm still afraid to run them too hard for fear of having them come apart again.

My boat looks somewhat unassuming but sounds fast. I had a punk on a modified wave runner pull up along side while I was cruising at about 45-50. The look on his face when I nailed it and the boat just took off was priceless.

Personally I would check for a cracked plug. Also what jets are you running. I checked mine and they are 68's on the front for the 409's. I didn't check the rears but they aren't coming on anyway. But I get a very light dusting of soot, after running 80 miles over a couple days. I still need to put a set of plugs in and read them at a high cruise and see how rich things are.

Jeff,

I'm still running into issues with props and the fact that I need to spin it to at least 5500 to really make it sing. I have not had it that high yet...maybe 5k or so. Anyway, cruise with my 17P is 33 on GPS turning about 3200 RPM. I have the same problem with my depth finder and speedo pickups getting smacked up when I get into the upper 40s. I still don't have the tune down right so about 50 is all I've been able to get out of it. It's possible, too, that I'm over cammed. Lift and duration are great but the LSA could stand to be a little wider to broaden the torque curve. I haven't seen the dyno specs from this combination other than the peak numbers. Can you run that stuff through the Desktop Dyno again for me?

I love my motor, too. I had the same thing happen with a jet ski the other day on the way back. Too much fun! My boat starts to get a little freaky though at higher speeds so when she gets up to 50 it starts to be a handful.

Here's something cool though... we went tube riding behind her on Sunday... man what a blast. I wanted something a little more special from it and decided to unhook the tube and go a drift while my buddy ran the boat to and from me (about 50 yard away from me in a protected area so I wouldn't get squashed by approaching boats). Talk about music to the ears! I'm going to make some changes here and there that'll help the performance appearance some... though the sleeper image has been really cool!

Thanks for the advice. I'm goign to mess with it tonight if it isn't raining.

Later!

I'm also running a q-jet so the two really don't compare as far as the carbs go. I can't remember right off hand but I have it setup a little more on the rich side of things to keep it safe. There may be some power hidden in there. I'm thinking of ordering up a new Holley, though I don't think that the CFO is going to like that one too much. I'm goign to work with the qjet for a little while longer.

Off to lunch! :D

Tom,

I'll put in the numbers tonight. I think I still have your motor. If not I'll modify mine. To match. I'll see what we get. You ported your vortec's didn't you.

This probably more accurate than DeskTop Dyno.



http://www.compcams.com/information/...74H-10_001.asp

Yeah, ported Vortecs with 2.02s/1.60s.

Thanks!

Here you go Tom.

2000 Torque 347 HP 132
2500 363 173
3000 365 209
3500 384 256
4000 397 302
4500 401 344
5000 389 371
5500 366 384


Like you mentioned. You thought you may have to spin it. You don't get your max HP until 5500. Which is at or close to the max for your intake too.

Yeah, that just looks too peaky for a boat combo, ya think??

What cam are you running in the 409s again? I wrote a long-winded question to Comp regarding the specs and how to proceed. There's another post here talking about peak torque vs horsepower and it brought up a good point in regards to efficiency and larger props. I'd like to cut down the RPM needed to reach peak HP and at the same time create a broad, flat-as-a-board torque curve. I have not had any luck spinning my 21P prop though I have not had it on the boat since cleaning out the fuel system (and getting rid of my detonation problem that existed with the old gas.. not to worry though because I was very gentle then). I figure that the boat weighs around 5k pounds with me, full fuel (I always go out full), the wife, and our stuff, maybe a couple hundred pounds less or so but I doubt it. I think that with the 21P prop the engine was not getting into its really heavy torque before the prop was able to overcome the hull (if that makes sense). In other workd, I think that the cam is pretty much wrong for the application (I know that I said I loved it before, but I have now put roughly 15 hours or so on it and can tell that it doesn;t quite work, at least not yet).

Oh well, I'll let you know what Comp has to say. I think they like the duration figures and such but would go with a wider LSA (maybe 112*).

Later!

Tom

Quadrajets are notorious for having sunk floats. This will cause the engine to run VERY rich- fouling plugs, etc. When an established motor/plug/jet combination goes wacky, almost all plug problems are really carb problems.

Did the engine ever backfire or burp??? this can rupture the power valve. Not sure on the quadrajet, but on Holleys there is a power valve that can leak and also dump fuel big time.

If most or all plugs are black and wet, its carb rebuild time.


If the hissing soud drops or goes away when you accelerate, you have a vacuum leak.

Good Luck
Ronnie

Yay me!

Loose plug wire. Seems that all that rough water on the way back (read partially airborne) took its toll on the plug wires. One was "just dangling on the number two plug. That would eplain the "hissing" noise that I was hearing that would not go away. The boot was still attached to the plug, but when I touched it, the wire just fell away. I have not started it yet to check it out but I would have to assume that was the problem.

On a not so good note... Jeannette and I are on the way to the hospital this morning with complications due to our having a miscarriage. As if things couldn't get any worse for us in the baby department, it seems as if there are more serious things happening. Can we ever catch a break here with this baby stuff?? Sorry, had to vent a little.

Tom best of luck to you and the misses in the medical department. hopefully it will just be a quick trip and a false alarm and she can return home soon. take care

Rob

Hang in there Tom. It will get better. I wish you both the best of luck.

In regards to the cam I'm using, I have the XM262H Comp Cam. I get a flat as a pancake torque curve and max torque around 3200, and HP at 5000.

Well, Jeannette had surgery this afternoon and is now here at home resting comfortably. She had to have the never-ending miscarriage forced to end, and they'll need to run everything through pathology to confirm some things. Basically, her problem is what's called a "molar pregnancy" which can lead to cancer-like cell growth that spreads from the uterus to everywhere else. So, not only has it taken us over three years to be able to properly conceive (after me going through surgery and a very rough recovery period myself), but now we have not only a miscarriage, but a potentially life-threating complication. Fortunately, the doctor said that the tissue did not "look" like that of a full molar pregnancy, but she couldn't rule out a full or partial wihtout tests. Needless to say... I'm praying for it to not be either. Man... what a day. Thanks for the well wishes.

Jeff,

I think Comp is going to recommend a custom grind for my setup (they did before when I ran the 274H by them... same numbers basically with a change in the LSA to 112*). I know that you love those cams. Hmmm... I really don't know what to say (too much going on in my head at the moment). I'm having trouble trying to figure out how this boat should perform. The hull is a deep-vee (rather conservative toward the rear but still a vee, not a a modified vee) and I figure that the weight is somewhere in the 4800 pounds range with full fuel and people (let's say Jeannette and I). I'm running a 1.50 Alpha drive and I'm pushing at least double the power that the old 355 made (seeing as how it was whooped and all). I'm not doing any better so far that the old motor did. Aside from the cam and maybe some minor tuning issues, what am I missing here? I've read up on some hull features and such and feel that I'm "ok" in those respects. Outside of doing some cleaning and waxing of the bottom, and working on the trim, what else am I missing here? Is the cam selection hurting my torque enough where I can't spin that 21P faster than the 4200-4600 RPM that I already achieved? I know that there is some serious speed lokced up in here somewhere... I'd just love to figure out how to pick the lock free!

Thanks!

Tom best wishes with the medical problems, hope it turns out for the best soon!!!!



as for waxing the bottom might want to do a search on that seems it sometimes hurts way more than it helps. some even go to the point of sanding the bottom to introduce air and free the hull up rather than the wax making the hull grab the water.



Rob

I'm hoping for the best for your wife Tom. Like I said hang in there.


Remember that we have two different boats. I have a twin engine hull that weights as much as yours. I'm spinning 22 hydromotives, but need bigger, but my two drives share the load. So far my top end is approx. 65 But I have twice the HP and at the same weight.

Think about a smaller carb. Remember what George said. Torque comes from velocity of the mix. A 650 will boost your velocity. I'm also running a 1 inch spacer that was port mached to the carb, as was the manifold. Which all smooth the mixture stream.

50 is still pretty good in a 5000 lb. single boat. How would it run with the old 350?

Wow, didn't know that a 26ft Wellcraft was so light! I really have no idea about the weight of the boat other than the fact that NADA lists the "net weight" of the boat at 3415 lbs. I'm assuming that, a) the weight is the boat outfitted with the engine and drive, and the different accessories that were "standard" on the boat, and b) the net weight does not include fuel, life saving equipment, food, occupants, and any water that may be in the hull (it's been pretty dry lately and with the heat I think I'm pretty dry in there). If the posted net weight includes fuel then knock off a good 500 pounds or so. Ya know, I may just go and have the boat and trailer weighed and then subtract the trailer weight to get the boat weight.

The 355 was pushing the boat to about 40 or so with the crap heads and Isky cam and then to about 50 (maybe 48, 49) with the Vortec heads and Comp cam. Still, the motor was a DOG due to the fact that it was wore out and consuming oil. So.... something is not right here.

Also, just looked up the "net weight" of the Nova II 26 and the weight comes in at 5200 pounds. So before you figure in weight of fuel, etc., the extra horsepower is still trying to carry an additional 1800 pounds in comparison to my boat's net weight. which equates into about a 2 lbs per hp difference between the two boats with the odds in your favor (net weight of each boat divided by approx. HP at top end... I figured 800 for yours and 400 for mine... granted, I still have not seen the top-end on mine, still about 500 RPM shy if not more). Should that equate to a difference of at least 15 MPH (being that your engines are still not into the secondaries)? That just doesn't quite compute, don't you agree?

Hey Tom,

Best of luck to you and your wife.

I think that my boat is a pretty good comparison. I have a 1989 Mach 1, MV 2450 CC Magnum. I dug out the old literature, and here are the specs:

Centerline Length : 23'8" I'm not sure but I think this includes the swim platform.
Beam : 96"
Weight (7.4/Bravo): 4025 lbs
Deadrise : 22 degrees

I haven't been out this summer, but last year I was running a consistent 53-54 on gps at 5000 rpm.

I'm running the same cams as jr in my 406. I had it dyno'd last year before I put it back in the boat 'm going to try and attach a scan of the dyno sheet. Max power was 360 @ 5000.

I think that you're making more power than that with your cam. I'd give that 21 another try now that you've got some of the bugs worked out with the engine. This is just gut feel, but I would think if you can get on plane then you should have plenty of torque to get up into the power band of your engine.

The only other thing you might want to think about is are those heads to much for your the rest of your systems? I'm running stock Vortecs. I know yours are ported and use bigger valves, but if you don't have a good breathing flame arrestor, and free flowing exhaust, you could be having some problems.

I'll try and post a pick of my boat below for your reference.

Mike

pic from 1989 literature.

Mike, Your pic didn't make it. ;)

I guess I need to find out exactly what the boat weighs to be able to accurately predict the top end. My boat is slightly smaller than yours and that makes sense when looking at the posted weights of the boats.

As for the heads... they have not been "over ported" just opened up some (especailly on the exhaust side). The guy who ported the heads does the same work for guys running Vortec-based motors in IMCA racing (the engines are for the most part stock to keep the fields even). So, I have the big valves, blah, blah, blah which basically turned the heads into iron versions of the Fast-Burn aluminum head, flow-wise. I think they work OK.

I'm going to try out the 21P again this weekend to see what happens. But I'm still interested in finding an explanation to the above info that I posted regarding the comparison between my configuration and jr's.

And another thing... watching my boat from the water\ (tubing, sidelines, etc.) I noticed that a lot of the hull is still in the water even planing. maybe I need a way of getting the stern out of the water more.

Thoughts... ideas?

Thanks!

Mike, what are you running for an intake?

Tom, I looked up an old spec sheet on my boat. It goes 5200 lbs, plus 108 gallons, plus 200 lbs of me, and misc. crap. So I'd figure 6300 easy. Now also figure in the rolled on bottom paint. Now if that isn't like trying to drag a non slip surface through the water I don't know what is.

After looking at Mikes numbers, I feel I'm pretty accurate around 425 HP probably give or take 15.

Do you know what the heads flow at different valve lifts. Hope the wifes better by now.

edelbrock performer rpm - vortec intake
Aluminium

Turbo,

I talked to the builder today and got the head flow numbers:

Lift Intake Exhaust

.100 63 60
.200 129 118
.300 184 149
.400 223 164
.500 235 171
.600 236 175

Jeff,

I'm probably over-estimating on fuel (I keep getting different numbers for the weight per gallon). So at 70 gallons with the weight being 7.0 pounds per gallon, that makes the weight with a full tank of gas 3905 (please tell me if I have the weight of gas wrong). Add me to the mix plus misc stuff and at best another 300 pounds. So about 4200 pounds. Not bad. So where is my speed?? ;) There's got to be something else going on here.

On the cam front.... I ran some info through Wolverine's old CamSelect program. There was a utility in there that applied to boat engines called the Marine Engine 60 Percent Rule. In order to acheive maximum HP at 5800 RPM (which is where my max comes in according to the desktop dyno), I would need at least 388 foot pounds of torque at 3480 RPM. I'm guessing that the 3480 is the 60% throttle setting which would be cruise. Any thoughts on that?

I think I'm still going to run that other cam. I might just run it like it is though for the rest of the season, and work on some other things that'll help get the boat flying (some weight savings, less fuel, etc.). I think I need to work on some trimming as well. One thing I noticed with the 17P was that it would cavitate with aggressive trim angles (Mirage) while the older 21P Quicksilver would not (I don't even think that the trim was working right when I went out... another problem). So many variables here...

Later,

Tom, are those flow numbers before or after porting? I can put those numbers in to desktop dyno and get a more accurate number. I can probably get them Sunday sometime. I have to go out of town so I'm be away from my tube.

I always figured 8 lbs for fuel. I know that is too much but I rather over estimate than under. I agree at 4200 you should be faster.

Yeah, those are the numbers after porting.

I'm going to work on some things over the weekend and see what it nets me.

Thanks!

Tom I put in the flow numbers in for your heads and you get an increase of 9 HP to 393 and 8 LBS. to 409. The curve stayed the same but just moved up abit.

Hope this helps.