TylerBurich

Zach, you know your boat is stern heavy so ditching your cast iron anchors for manifolds will always help. You could also just throw people overboard and leave the cooler at home when you want to go fast!!! I guess i just like the blingin looks of the imco's over the stock chit. C ya on the lake this weekend

266ltd

ur damn right u will sat and sunday

TylerBurich

Has anyone on here tried the revolution marine manifold's. I think they would be nice for this application because they are similar to stock except for the dry joint and being aluminum. seems too good to be true for $1k a pair. I called them up when my merc 420 manifolds killed my new motor and they never returned my call.....????? what's up with that?

Smarty

My father installed Gil headers (he has silent choice), with the oversized flame arrestors and had the ECU re-programmed by Tyler Crockett. He picked up 200 to 250 rpms, and a solid three miles per hour (the motors are 502/415 - year 2000)

stevesxm

so.... you really believe that the manifolds, flame arrestor and ecu deal were worth about 75 hp per motor ? or roughly
18 %. because if you are talking about going from 60 mph to 63 mph, thats about what it would have had to be with everything else being equal. thats very very impressive if repeatable.

Pat McPherson

Your boat may need 75HP per engine to gain 3mph, but mine sure does not.
When I had a bone stock 310Hp/7.4MPI in my boat she topped out at about 65mph. I chnage the cast iron exhaust out for Stainless Marine and gain 150-200rpm with the same prop, up 2-3mph on top.
Then I swapped out the 310HP 7.4L for a 415HP 502MagMPI with the same Stainless Marine exhaust.
My boat now runs 75+...
So the 105Hp increase was worth 10mph. If my math is correct, that is 10HP for every 1mph gained.
So I would say that the Stainless Marine exhaust will give you 20-30HP over the cast iron stuff.
I believe, and I'm not alone with this opinion, a better flowing exhaust system is first place to start when you want to increase power...

stevesxm

you are correct. your boat doesn't need that. and your math is not correct. the hp nec to overcome drag is cubed... not linear... you boat needs less because of the vastly less total drag at 60 than , say, mine which is 14 ft longer and probably 5000 lbs heavier. the post i was refering to above is by a guy with a much longer and heavier boat as well... so i scaled my numbers accordingly. my point is that i find the assertions made by some of significantly increased top speed from modifications that, on their face in most cases will buy a couple of % increase in total power more likely to be based on any number of other factors rather than the percieved gains.

and that was the point of this thread... and i still agree w/ griff. on a box stock 502 injected motor, i don't believe that small , non invasive mods will end up being cost effective from a performance stand point. i base that opinion on 30 yrs of doing the work for real and generating genuine and real hard data results. not someone that knows someone that heard about someone that put a MSD box on and went another 50 mph. and sure as hell some oversized flame arrestor isn't going to do anything at all. the exhaust will be worth 10 a side and the ecu will be worth 10 a side MAYBE... and 20 hp on a 34 ft boat isn't going to buy you as much as paying attention and getting the trim right.

Pat McPherson

Hey Steve,
You have told us many times that you have 30 years of experience doing what ever you did.
Well my friend I have been boating for 30 years; the last 20 spent owning some 10 different performance boats. Included on that list is everything from a 900lb Hydrostream to a 9000lb Cigarette.
OK, maybe it took +9HP to push my boat from 65 to 66 and +11HP to go from 74 to 75, I'll give you that.

Read the original post again please...

I would venture to say that a 32' Fountain with twin 502Mags has about the same power to weight ratio as my boat.
Base on my experiences with a 29' Fountain single 502MagMPI, a 24' Pantera 330HP/7.4 and most recently a 24' Super, changing the stock cast exhaust will, "get a few more ponies." Changing the exhaust is about the only bolt on that will reap rewards.
This is what I would recommend to do since the post says, "Want to keep as much stock as possible."

Now for the record, I agree that changing the spark arrestor and remapping the euc will not gain much if anything...

stevesxm

pat,
i just can't argue about this anymore. there have been several threads here dealing w/ the " how much power, how much faster" question, some of which i see your name in so you are aware of them. in those the math has been discussed at length. and the math doesn't lie. AND when the purely theoretical math is comapred to some of the "speed calculators" on various web sites as mentioned in those threads. even those numbers agree within a couple of %... the primary differences being in "prop slip" which the purely theoretical math doesn't account for.

but having said all that, i simply maintain that the math as noted below from one of those earlier threads will

a) give a very accurate estimate of the power necessary

b) show very clearly that to get a meaningful top speed increase is going to require a BIG number that is not likely to be found with non invasive changes.

i investigated this for my boat first hand. the number for me to go from the current top speed of 65 to 70 on my boat meant from going from about 850 total hp to close to 1050 or about 100 per side. and i have the same box stock late 502's.

i don't seee any bolt ons or magic beans that would do that or even come close. so for me it wasn't worth it. when it comes time to rebuild them, ill massage that out of them then without any great strain and that will be that.

the following is from the other thread that you were in.

hp = cumulative drag x V cubed ( in ft /sec)

take what the known top speed of the boat is now in mph ...multiply that times 1.46 to get feet/sec

cube that (multiply by itself and then by itself again ) and then divide THAT number into the total HP you have now... that answer is your cumulative drag figure at THAT speed.

now just work the formula backwards.... divide your NEW PROJECTED hp by that drag figure, and do the cube root of that for your NEW mph in f/sec.... divide that by 1.46 and get mph.... and it will be VERY very close to correct.

or for the example we are talking about here, use the hp you have now vs the NEW top speed that you want ( in fps)... that way you get a direct answer in hp required and don't have to find a calculator that will do cube roots.

Pat McPherson

http://www.go-fast.com/boat_speed_predictions.htm

So what does a 32' fountain weight?
6500-7000lbs
with 830pshp 79mph
with 890pshp 82mph

24' Super
3700lbs
with 310, 65
with 340, 68
with 415, 75
with 445, 78
These are vary similar numbers that I have seen in the real world. 77.8mph is my best top speed to date.
So I guess the exhaust change is worth, "a few ponies"

Steve, you may want to consider changing your cast exhaust. It would give you 2mph...

38' Cig
10,000lbs
with 830pshp 65mph
with 890pshp 67mph


Hmmm...