Engine Dyno vs. Boat
 

Ok, here's the thing. Let's say you have your engine dyno'd and the peak hp happens at, say, 5650 rpm. You really don't want to turn it 5650 in the boat, you want to turn no more than 5200. Do you go to a different cam to bring the peak hp down in the rpm range? Or do you just prop it to turn 5200 in the boat, knowing that you're below the peak hp and probably loading the crap out of the crank? Just a hypothetical question, as just about everyone knows I run stock 330 motors in my tub of a Searay. I'd just like to get differing opinions. Thanks.

why the hell would you build and engine for an application other that yours? knowing it? then dyno the engine, then change the engine configuration? ....i really don't understand???

hp=rpm*tq/5252....play with the #'s yourself.

and yes i have had to change cam timing IN THE BOAT after making a prop change to get optimal performance...could this have been done on the dyno?..yes

additional ?'s????

Regards,
Joseph Allen Skrocki
Engineering Technologist - Phase III Dynamometer Lab
ATNPC Box 38, 35500 Plymouth Rd., Livonia, MI 48150
Phone: (734) 52-35339 Text Pager:(734) 651-2028
Email: [email protected]

To answer your question, if you had for some reason made a poor cam choice for your application I would prob change the cam 5650 to 5200 is a pretty big change and for the price of a new cam/instalation the change would probably be worth it

ursus not sure if i understand???..maybe i do??

the cam for 5600 rpm engine will be very different than a 5200 cam...thus it requires additional spring...thus more heat!...decreased valveterain life.

the dyno is a tool to test and validate what will be used for the application...

i guess i'm still lost to what is the question??

Well as I understood it crazyhorse asked what would you do if you had an engine cammed so peak hp was at 5650 but you wanted to run it at 5200 max, would you leave it and prop it for 5200 or change the cam. I would change the cam.


Perhaps I misunderstood his question, maybe he can clarify correct me if I am wrong :(

Audacity,

I think he's just throwing out a hypothetical question... In fact, I've had the exact thing happen to me. Comp says cam was supposed to peak at 5500, ran dyno up to 5750 rpm and hp still never peaked. Yes, the cam was degreed in, I checked all the cam lobes for seperation, centerline, etc to verify it wasn't a grinding screw up. In the boat could only get 5200 rpm. Started to look for fuel delivery prob.

One issue I see, and correct me if I'm wrong, a dyno works by lightening the load on an engine to let it rev to the next level...in a boat, however, the load is constantly increasing with the hydrodynamics and drag. Seems like apples and oranges to me...

Zack:)

maybe the engine was built prior by someone else and you got it that way?? well if i got it for free then yes change the came and other surrounding componets...if i had to pay $$$ for it,,,for get...how do ya like that answer.


ursus....hey i need to buy you a drink :D

make it a double you got a deal :D

"a dyno works by lightening the load on an engine to let it rev to the next level"....INCORRECT...off with your head!LOL:D

Zack there are a lot of missing facts here...i was not runing the dyna....have no idea what the engine data specs are...what cfm carb are you running...what were the dyno #'s...corrected and NOT corrected!

have at this.....i dailed in a bike to 110 hp on the dyna...to X top speed....at brainerd (fastest corner 1 in north america) we miss calculated the drag CF or frontal area at that speed...guess what we never pulled the top end # we wanted...thus changed cam timing (not gearing) only pulled to 100 on the dyna and our top end # was 15mph higher.

the bottom line is people mess with things and make them slower, or a lot less reliable...i perfer both....

Thanks for the comments guys. Keep 'em coming. This scenario did present itself on KAAMA's engines early this year, as well as SuperV's. I think KAAMA decided to make a cam change while SuperV can (and does occasionally) turn his to 5600. Personally, I think I'd prop SuperV's to turn 5300. I think that would give him a little higher cruise speed, which is what he mostly does now that his wife and young son are with him most of the time. Audacity, I appreciate all your comments, but please understand most of us don't have your background experience. Any chance you might be coming over to the west coast near Holland/ Grand Haven/ Muskegon this year?

i was bro....but we're coming to the races in GH soon....this weekend is the poker run...next is the texas race...then GH....then back to texas....and THEN.....**** i was HOOOOOPING to get this job in cali....time will tell.

hummmmm...i know V...., KAMMA's engine man....well i have never met him but i sure did see a lot of his engines in our shop with his mark on the heads.

Change the cam! Add a dual plane manifold! You're probably giving up at least 30-50 ft-lbs of TQ at the 4000-5200 rpm range. With that additional TQ you will be able to pull a bigger prop and also have a higher cruise speed. You want to maximize your TQ in operating range.

Get a desktop dyno for the computer and play with it. Look what a smaller vs. larger cam does to the TQ curves. They are cheap at Jeg's or summit.

Think about this. My motor dynoed @ 640 hp @ 5700 rpm with 5.5 lbs of boost.

Once in the boat the boost was @ 6.5 lbs @ 5300 rpm. Why the difference in boost at lower rpm? I have been told that dyno load and boat load are 2 different things.

Ken-- That's exactally why we need an ON-BOARD-DYNO on the boat. Different exhaust, ignition, fuel supply, temperature, load. So how much HP does your engine make at 6.5lbs and 5300 rpm? Don't know!

Exactly!:D

You could also try to advance the cam 4 or 5 degrees. This will increase cyl pressures slightly in the low end and will pick up some low end torque. You will then need to prop for the desired RPM. The best bet is to talk to a good engine builder and get the right cam for your application. Oh ya, running at peak HP may not be the best place to run depending on where your peak torque is occuring. I would try a bunch of props and see what RPM is providing the best performance before making to many adjustments. Just because peak HP is at 5600 doesn't necessarily mean it will be faster or better performing than
running at a lower RPM. Your peak torgue RPM may have more
influence especially in a boat.

A dyno is a Great TOOL is used properly for dyno comparitive testing at a specific facility. Each machine will read a little different, and work different so the numbers are only truly accurate vs. themselves. Next bottom line doesn't matter what the dyno says, it what the boat, or race track says that counts. I know of engines that during a race run in a very short RPM band within say 500 up and down, but change the numbers above or below that (in an area they never see going around the track) and you'll change the acceloration rate changing the performance. An on board dyno is great as a tuning ad for that specific combination, but I don't know that it is the end all be all answer either.

Bottom line a dyno is a great place to break in your combination, and do your baseline adjustments, you can also (if you take the time) try different things so that once you try them in your boat you'll now how close to the line your are going, but you've still got to see what your boat wants. The on board dyno, or some other data aquisition would make this a quicker process.

Interesting, I just had a motor built that peak horse power is @5,600 rpm and I am going to prop it to be able to turn 5,600, I typicaly won't run it that high, but thats where it making the big numbers, engine builder said with a different intake 6,000 would have been the magic number.
Am I making a mistake? This is a fully machined, Balanced & Blueprinted 468 roller motor, 500 hp

What WETTE VETTE said. Advancing the cam timing drops the torque peak. Every cam and application is different but I like to set my #1 intake lobe center at 105 degrees for a 5000 rpm engine. Run Bravos over 5000 rpm for a few hrs and watch them explode.;)

Probably the biggest reason I changed cams was because I felt that on the dyno I saw a lot of rich black sooty stuff in my exhaust which I believe was caused by over scavenging via large tube headers, fully ported heads and too much over lap on the cam specs. I didn't think I needed too big of a cam because the heads were fully ported and thus flow so well that it is causing everything to slip out the exhaust! Now, I know my theory could be TOTALLY WRONG and I could have left the cam in there, BUT I'm the kind of guy who likes a WELL TUNED, EFFICIENT running engine. I don't want to throw any UNBURNED gases out the tail pipes that aren't doing me any good. I want to try and effectively burn all the gas in the cylinder before kicking it out the exhaust. The cam that I had in there on the dyno was 244*/244* duration and .601"/.601" lift on 112*lobes. This cam had about 74* of overlap and made 699hp @5750rpm and 682hp @5500rpm which made very good power with my engine combination. But I have replaced that cam with a 236*/244* .601"/.601" on 114* lobes which brings the overlap down by maybe a few degrees--- 4*? However, I have not dyno'd my engine with this new cam change and one thing that I can NOT stand is throwing unburned gas out the tailpipes...some guys it doesn't bother, but I do NOT like that idea and if it means losing some power then so be it. I'll be testing these new cams in the boat vs the dyno and I also prefer to run the engines at 5500rpm at the most...not 5750, so I will prop it as close to 5500 as possible.

BTW, we degreed in these new cams in at 108-108.5* intake lobe

KAAMA,
 

Do you think maybe your compression is to low for your original cam choice? It sounds like you may have been lacking some heat and that could be why you were getting incomplete combustion. Did you try leaning out the carb to see if it clears up? I am just curious because I run a solid roller 272/280 duration at .050 and have very efficient cylinder heads. My transom is always clean and there isn't any sign of excessive unburned fuel. I am running 13:1 compression which is probably providing enough heat for a complete burn despite the scavenging and valve overlap. What is your compression and cubic inch?

When we work on snowmobiles we NEVER dyno the motors directly. We dyno the power getting to the ground and make adjustments accordingly. You know how many "160 hp" sleds I've beat up on with my 110hp sled because they weren't running the correct rpm?

My point is if I was doing some motor mods I would use a propshaft dyno with my exhaust, ignition, etc.

Wette Vette,

I'm running 540 cubic inches, Dart Pro-1 fully ported aluminum heads, about 9.7 comp ratio. Also, keep in mind I am running HYDRAULIC ROLLERS, not mechincal rollers. And the figures I gave on my cam specs are @ .050

BTW, I am running #79 size jets on all four corners and BSFC was averaging about 42 which is kinda low and EGT were about 1300* which seems okay, but the BSFC numbers and the EGT numbers just dont seem to jive together too well. It seems that if my BSFC numbers (as low as they are, 42) would make my EGT numbers to go higher than the 1300* temp mark! So It must be that I am throwing unburned gas out the pipes and making my EGT's cooler. It's just a guess, but it seems like that may be what's happening.

Have you done any compression checks with either of those cams? My motor is around 180 PSI cranking. I ran a cam that was on a 114 + 4 installation and the cranking pressure was only 120 PSI. If you did a comparison between your two cams I would be interested in seeing how they compare. I would guess the 114 cen. and slightly shorter intake duration will make for 20 to 40 psi less than the longer 112 cen. Only guessing though.

Again correct, my 114 +5 advanced only reads 115 at cranking speeds. Oh and if anyone decides to try advancing their cam, be very careful of intake valve to piston clearance. Advancing the cam timing reduces this clearance.

Wette Vette,

I haven't done a compression test....but you know, that sounds like it might be a good idea to know what it is and where I'm at with it. We'll test it tomorrow and I will post what we found then. Thanks

Kamma, With your good ported heads maybe you don't need to run a split duration cam. The greater duration on the exhaust is to make up for poor/fair heads or supercharging and it's greater air/burn. You might need a straight 236/236 cam. Look at desktop dyno- it's fun to play with and all this is easily changed.

I built a 12:1 comp 496 and installed a solid roller Erson cam with 268/276 dur at .050 and it had .688" lift. It had fully ported GM 990 rect. heads. I was getting 5600 RPM and the cranking cyl pressures were 240 PSI. Erson suggested a re-grind on the cam and they turned it into a 278/284 dur at .050 and kept the .688 lift. The motor woke up. It was 6100 RPM on top and the low end and mid range didn't seem to suffer to much. According to Erson on that motor 240 PSI would have led to detonation and that is the biggest reason for the re-grind. The longer duration created 170 PSI cranking which Erson said is adequate for good low end torque and low enough to keep the motor out of detonation. Before I did the re-grind I retarded the cam in 2 degree increments a total of 6 degrees. Each time the cylinder pressures dropped slightly, but it was still at 215 at -6 degrees. This gave Erson the data they needed to pick numbers for the re-grind. Both of these cams were designed for 112+4 installation. On smaller motors the 114 lobe centers are for blower or turbos and they lower the cranking pressures. On larger engines 114 to 118 degree lobe centers are good in controling pressures on naturally aspirated motors. I am very interested in what KAAMAs pressures are cranking with that cam. The duration seems somewhat short which raises pressures, but the 114 cen will lower pressure. Let us know what you find KAAMA. I guess 236 dur at .050 on a hyd roller isn't that small. I am used to solids.:cool:

KAAMA

Your BSFC is showing your how much fuel it is taking your engine to convert it into HP. At .42 it shows being a little more efficient than some. If you were cooling your exhaust with raw fuel your brake numbers would be higher. A .42 Brake and 1300 exhaust temp is not that far off.

I really appreciate the responses and willingness to help from you guys----thanks! I'll be leaving for the shop in a couple hours and see if we can do comp test. One of the other things you guys need to keep in mind that I had mentioned earlier is that there is A LOT of BLACK, THICK, SOOTY, RICH exhuast carbon coming from my engine. I had this engine on two different dyno's and one set of headers had larger (2 1/8") primaries tubes on it. I used a Crane Hi6-M ignition box. The second dyno had 1 7/8" primary tubes. Remember, I could be wrong, but I think the exhaust is overscavening the cylinders and pulling raw fuel and I think it's because of too much overlap on the original cam 244*/244* on 112* lobes. It's an Ultradyne cam which usually have aggresive profiles. The advertised duration on this cam is a 296*/296*. BTW, I DO have a Desk Top Dyno and it is close to my actuall and REAL dyno numbers and have been playing with cam specs---more as a reference kind of thing---pretty interesting! The cams I am using now are a Crower hyd roller with a 236*/244* duration @ .050 on 114* lobes and advertised duration of 300*/307*. The guy I spoke to at Crower said that this cam is a "smooth" running cam and is easier going on hydraulic roller lifters. I take it he meant that the ramp speeds on this cam of their's is not as radical as the Ultradyne's. The thing that throws me off is the comparison of the Ultradyne's advertised numbers (296*/296*) compared to the Crower's advertised numbers of 300*/307*----that's that part that I am having a hard time understanding! If the Ultradyne is a more radical/aggresive grind then why are the advertised numbers lower?----ramp speeds??? Jump in, I want to know! And thanks again guys!

KAAMA you are right.
 

The ultradyne starts to open the valve slightly later, but then opens it faster than the Crower. That is the explanation of the Ultradyne being a more radical cam. For more comparisons it is also good to look at dur @ .100 and .200 lift. Below .050 lift there really isn't anything happening and the lift rate is a major key in determining how hard on parts a cam is and how much HP can be made.

comp test...
 

We're not able to do a comp test yet today, but we will. Well, the headers, bell housings, couplers and "Drive Savers" are all bolted up to the engines now. We keep having to do little modifications that slow us down. Anyway, the engines are now ready to install and that will happen on Teusday evening. The wire harness/bracket need a few wire mods. We should be making noise by Thursday---I hope!

Maybe you will have it ready for the water in time for the Hardy Party? Hopefully there is a good turn out and not a lot of Barney Fifes.:p

Oh hey dude, IF everything is running smoothly, I am DEFINATELY going to be at that HOT BOAT weekend up at Hardy Dam for sure! Just don't you worry about it---ol' KAAMA is gonna be there! Just listen for that sweet rumble-----or HOWL of my Stellings-----depends if I'm idling around or on plane. :) You coming up for it?

I plan on being there. I plan on pulling the motors out this fall and fixing the leaking tiller arm seals, sand blasting the drives from the transom back and painting them with IMRON, going through the motors to freshen them up and do some more TINKERING. I am planing on installing big hyd. roller cams at the very least . I plan on using a rev kit with the cam since this seams to make the lifters last longer.

Hey Steve, glad to see you'll be there----it was a good time up there last year eh?

KAAMA, compression test coming soon? It'll be interesting to see what the numbers are. I'm still thinking I'd like to see SuperV turning around 5300 rpm instead of the higher numbers he can reach right now. Besides, he'd have a higher cruise speed than he has now. It was good to hear that his drive looked like brand new inside. Over the years he's run the boat pretty hard and he's always been able to turn around 5600 with it.

I am planning on going to Hardy and look forward to meeting some OSO dudes and seeing their boats run. I plan on taking it easy on the WETTE VETTE the next couple of weeks so she should still be in one piece and in working order. I think we will have a convoy of 4 or 5 boats from LaPorte. Hopefully my buddy will have his Obsession 234 running strong after some hull repairs. This 23 footer has an 860 HP 540 blower motor and did 99 MPH earlier this year on radar. While he was getting the hull fixed he added a short bravo which I think will really help. We have 1 22 Velocity and a 24' Check coming along that are still stock, but not for long.:D Which day is better on this weekend? Hopefully the weather is good (75 and dry = heavy HP :D ). Sounds fun!!!

Hey Kamma,
I don’t know if this info would be of any help to you but I thought I’d throw it out there anyway. Can’t have too much info I suppose. The first variable is that I run at 4000-6000 feet of altitude and built the motor with that in mind (i.e. smaller cam, oval ports, compression etc..). It is a 540 c.i. with an Ultradyne HR 232/240 114 .600/.600 straight up. The heads are fully ported and polished Edelbrock (Chapman Racing) ovals and my compression is 9.3:1. Fuel management is handled via a Holley MPI system. Boat idles very smooth at 750 rpm.
You would think that this would be a 5000 rpm motor:confused: Read on……
These are real on the water GPS results with Bravo 1 props in back to back test:
Boat is a 4800 lb. 28 foot single engine stepped hull with raised X dimension.
At 4250 feet elevation I can turn a 28 4600 and 64.6; I turn a lab 26 5100 and 67.7 and I can turn a stock 24 5500 and 69.8.
At 1250 feet elevation I can turn the 28 5200 and 73.1 and the lab 26 5600 and 74.3 and obviously I didn’t try the 24.
If peak speed is function of peak hp then it seems that even this smaller cam likes the higher rpms. The prop feels very torque loaded with the 28 and then everything seems to free up with rpm. Hydromotive told me that you want to be at least 1250 rpms higher than the peak torque so that you unload the torque on the prop to achieve optimum speed. Seems to be true I suppose.
I’m not sure how, but this must tie into the dyno vs. the “in the boat” comparison somewhere.

Sorry to change the subject but I was just curious about an earlier statement in this thread about turning a Bravo over 5000 being detrimental to its health; from a mechanical view, I would think that you’d much rather spin a Bravo 5500 that isn’t loaded up vs. 5000 under massive amounts of torque load. To a point, gears and bearings are impervious to rpm; throw side load and stress on them and you start having problems.
I will be adding a M3 ProCharger over the winter and I think I still want to turn 5300-5500 for this reason.
Any thoughts on this?
Dave
:confused: :)