We did not do any steady state pulls. We will when the engines go back on. Although it seems all these pulls could have been done better and provided more detailed and accurate info, their purpose was just to see where power was going with each comb and I guess that was accomplished. The engines are going back on again and they will be swept slower and run steady state. As far as sweep rate, I was just curious as to why someone that builds all manner of boat engines would set the rate so fast. Even completely stock black motor rebuilds that come in from the marina get run before they are returned to verify they have no problems and those customers likely don't even know or care that they were run. He runs the piss out of this dyno and should know it like the back of his hand. Might just be bs but he claims about 14k pulls and he knew exactly where each combo would peak before it ran. He doesn't lack experience, that's why some of this just doesn't quite make sense.

IMHO: Set it for the 300rpm/sec rate.

Reason for acceleration rate options on a dyno is to try to match what the engine's acceleration rate is actually in the vehicle. Example: think how fast the rpms climb when you go WOT in a chosen vehicle.

A boat will accelerate less quickly thru it's rpm range then a, say 4000lb car, vs a 2800 tube frame Camaro, vs a rear engine dragster. Again, this is reason why you can choose different acceleration rates on dyno. To better match how engine will accelerate thru rpm's in real life.

I want to add in my post above, any time I see a BSFC (how much fuel is used per horsepower uncorrected) in the .300's to alomost .400, a red flag goes off in my head telling me that the corrected hp is going to be a lot higher than as measured. So, with my above post, if the fuel use is lagging behind because of the huge acceleration rate, this may make the corrected hp % (not actual corrected hp # ) look higher than it is.
Edit in: I slept on it, and saw I was headed in wrong direction. Lagging fuel flow reporting will not change corrected #'s.

Sorry, hard for me to write/type some things down. Hopefully someone will understand what I'm saying here. LOL.

Sometimes I forget what info I've posted and it gets more confusing because I've also been exchanging emails and texts. All the pulls were between 800-1000 rpm/sec. One of them exceeded 1000. I understand why the dyno is capable of different sweep rates, still wondering if there is a reason one would sweep a boat engine that fast. I'll just ask him next time I go. I haven't been there in over a week and sort of lost interest in talking to him due to serious health issues of immediate family, but the show must go on.

I just noticed another parameter titled: Inertia- ft lbs- sec. This was in the same area where he input hi-low sweep limits etc. What would that be?

Just for kicks I went to the go-fast website and plugged in some numbers for different boats and their calculators have the same mindset I do. I plugged in 1600 hp for a heavy v-bottom and then plugged in 1760. There was a 4mph difference. I said sometimes there's only 2-3mph, so I was 1 mph off on my guestimate using their calculator. Then I used a 50 hp gain (25hp each engine) and it netted only whopping 1 mph gain in a heavy v bottom. Lastly, on a fast cat with a 300 constant factor the increase of 160 hp netted 6 mph.

Site disclaimer: "There are so many factors that affect boat speed that it is hard to make accurate estimates of what the real top end will be. Mercury Marine uses the following formula to estimate potential top end, this calculator uses this formula."

To support what I originally posted. Even when using the speed calculator, there's no magic formula to say that X power increase results in X mph increase. case closed. :-)

I think the steady state pulls are really nice because you give the engine a chance for the EGT to level out and it better simulates how the engine will run in the boat. I like seeing steady-state pulls at 4K, peak HP and even peak torque.

I plugged in 840hp (stock 420s)total in a heavy vee weighing 8500lbs like donzi matts boat. Said 71mph. I plugged in 80hp per side more for 1000hp total, said 77mph. I then plugged in 25hp per side more, 50hp total , and got 73mph. Seems like his assumption of a 2mph gain equating to around 20-25hp per side, is a heck of alot closer than 80hp per side than his engine designer claimed. At least in that application.

What about when you swap your cams for custom ones, and lose several mph? Theres quite a few who have experienced that. Lose 3mph, how much HP is lost is their question, rather than gained

It depends a lot on the speed range in question. It is easier to gain 2-3 mph at a max speed in the 60 mph range than the same gain on a boat with a 100 mph top speed. Also there are speed barriers to hull and drive combinations. Once you hit the wall it takes huge horsepower gains to find speed. It is usually easier to do some setup or rigging changes to gain performance.

We're actually speaking the same language here but for some reason there's still a disagreement. You gave one example, I gave another and I still say that it's really hard to tell what speeds a boat will gain by stating who much HP increase etc.

One last example, that is exactly why I asked him what kind of boat it was. But it wasn't made clear to me. You seem to know, but I don't.

Agreed! I've had the unfortunate pleasure of hitting those barriers before.

The minor detail about going from 600 hour to completely fresh motors in my scenario seems to be getting left out also. Not to mention one of the motors had a cracked head between the valves and was pulling water. Boat ran 67-68 GPS like that before the refresh.

Did this happen in the boat in your profile pic? (Cafe Racer)

Sorry for the omission. 87 Formula 311SR1 with 420's and TRS drives.

A friend who has a 353SR1 recently spoke with me about upgrading his 420's to 500's. For the amount of work I had to do and the money involved for not much of a gain, I suggested to him that it probably wasn't worth the money to do the upgrade. Especially since I could not guarantee how much he would gain.

He told me that he was looking for a bigger gain than I guesstimated so I suggested he go in a completely different direction and do further upgrades to make more power. The more we spoke about it and he realized ho much it would take that boat to go 10-15mph faster, he decided to keep it stock. I think he made an informed decision! I didn't get the business but that's just how it goes.

In your case, are the TRS really deep? If so, it's going to make speed gains more difficult. Did you pick up acceleration with the new setup vs the old? If you picked up acceleration but not much top end, there could be more gains realized in your setup than in the engines IMHO.

TRS runs very deep, gains only go so far without raising X, the deep drives limit speeds more then power or hull in a TRS boat, a buddy had dyno [proven 830HP's in a 34 ScarabIII still only went 82... and its lighter boat then a 357, I assume you meant 357 not 353...

311 with 420s and TRS drives should run 72mph.

68 ish GPS

. 72 on factory speedo..

Yes, I meant 357.

Stinks about your buddys boat!

I saw that happen on a friend's Baja Force. He went from the 420's up to some 540" 750's and the boat ran no more than low 70's. My Scarab Panther was faster then it with much less power.

it's ok that was 20 years ago, he has a 125 mph 43 Nor Tech now with 1600's

BCK I get what you are trying to do, would be nice to see your different carb and intake combo power difference. problem is on here there a lot of experts that always chime in to tell you what you are doing wrong but never have any real world dyno numbers of there own to compare what you are trying to do. only tell you what you are doing wrong, what wrong cam you have in, your wrong heads, your choice of intakes suck, the dyno you use sucks and so on. thanks for trying to compare carbs.

I agree somewhat. But its also good to hear others opinions. Theres a few guys who posted some good info on this thread. Horsepower1 , haxbyspeed, panther, matt, and some others tried giving out some insight. Whether or not its liked, it is a tech forum

Did you get around to running your 540s with the 325s and madera cams yet ? What kind of power did they make?

I didn't reread this thread and I honestly forget what transpired in it. I did end up dynoing with several different combinations of carbs/ intakes/ spacers. 3 different dominators, 1 4150, 2 intakes, 3 spacers, iirc.

The summary was:
Swap a cam + 15 hp
Swap a intake + 10 hp
Swap a carb + 10 hp
Add a spacer + 5 hp
Add another spacer + 5 hp

you are correct there are some good points made you just have to read between the lines a bit. I am close to being complete, took a little more time because I don't have an open check book. builder has motors about 2 weeks from being complete. then off to dyno. just got complete ignition, still up in the air with carbs, I have 4150's with merlin intakes and have a set of 1050 dominators with no intakes? guess I will leave it up to Brad Nickerson to send him the 1050"s before the motors and buy new intakes or go with the 4150 and intakes I have? it will be his call on price vs gain. thanks for asking MT.

what 4500 intake worked best? how much difference between 4150 and dominator?

I don't know how it would apply to your combo, but using the dominators was an improvement for me even with using an adapter and 4150 intake. My 4150s actually flowed 986 cfm, so its not like they were small.

Unfortunately I couldn't test different 4500 intakes as I was just using what I could borrow. I just tested a 4150 Vic Jr vs a 4500 Victor. I think I picked up 10 hp and a decent amount of tq by putting the 4500 on top of the 4150 Vic Jr. It's all posted in a couple threads on here.

Dont forget, there is power to be found in porting these intakes as well.

thank you for posting what you found. I am not 100% sure which direction I will end up as far as carb and intake but I would be glad to post what my results are from my completed engine project.

I went with Brodix HV2000 intakes this round, 4150 style... supposed to be a great intake, we will see

what was the old manifold/carb combo?

I have merlin intakes #063034 and Nickerson 4150"s flowing 980. this ran very well on 502's