New 502 and it sucks!!!
 

My buddy had a 502-525hp. built for his 1992 25ft. Sunsation Aggresser. The engine builder told him with his "formula" it should run about 78mph give or take a few! I dont the specs. but it does have lightning exhuast, MSD ign, new barvo1,1:50:1, 5000-5400WOT. We tested 4 props last night and look at this joke test.

23P mirage....5360 @ 69.0..GPS
24p bravo1....4950 @ 68.1
25P mirage....4980 @ 70.0
26P hydro......4930 @ 69.5

Man is he PISSED!!!!!! not even close! His old 454mag-365hp ran 62-63GPS with 595hrs. on it, and he only gained 6-7mph with a new $11,000 502!! I think he got boned big time!!! Whats this frickin "formula" hes talking about 2 get this speed?? Anybody know??? or isnt there one?? Bring on the input guys! :D......HELP!!!!

Oh, by the way, he didnt have it dyno'd either, its a insurance project from hitting something last fall so he didnt have the xtra cash. Just the word of the builder and he gonna talk with him again with the results!!

Any thoughts guys................john

Re: New 502 and it sucks!!!
 

Your buddy really expected 16 MPH from 160 horsepower gain? Using 20 horsepower to gain 1 MPH as a general rule I've seen many people use, I think he got exactly what he should have expected.

Re: New 502 and it sucks!!!
 

I'm with BGIII

16 mph was unrealistic.

Re: New 502 and it sucks!!!
 

The rule of thumb is that it takes
20 h.p. to gain 1 mph above 60 mph,
525 - 365 =' s 160, 160divided by 20
= 's 8 mph.

Not too far off, IMO

Re: New 502 and it sucks!!!
 

Insurance project yields a higher horse motor and 6 to 7 mph increase does not equal "getting boned" IMO.

What do I need to hit to get new motors?
I need two.

I want in on that. :D

Re: New 502 and it sucks!!!
 

Yeah that certainly sounds good.

I got to agree. For 160 hp gain he got just about what I would expect. The faster you go , the more hp you need to go faster(if that nakes sense).I would venture to say the builder was rather optimistic in his estimate :(
I went from 660 hp to about 1250 and picked up about 25 mph

Re: New 502 and it sucks!!!
 

In that boat, 7-9 mph is about the best for the combo
described.

Sounds like he has something that will give decent power
and last a while. The price is not that bad considered
what everything costs these days.

I would recommend he enjoy it and don't jack with the builder.
He may need him again in the future or if some minor
problems develop.

Good luck,

OR

Re: New 502 and it sucks!!!
 

80 MPH + 29 FT BOAT + SINGLE 525 = FOUNTIAN :evilb:

Re: New 502 and it sucks!!!
 

Based on your "before" numbers, hull efficiency and prop slip (I assumed 23 Mirage @ 5000RPM) are quite reasonable. If you really had 525 HP now vs. 365 HP before the boat should go 75 mph spinning a 25 Mirage @ 5500 RPM. If you can't spin a 25 Mirage fast enough to go 75, either you don't have the HP, or boat weight and drag have changed.

Your top speed now suggests about 450 HP, but think about when the before speed was measured versus now. Changes in temperature and humidity have a significant effect. The prediction of 78 might have been a bit optimistic, but don't kill the engine builder yet, some investigation and more tuning and testing may be required.

Also according to your before numbers, your hull curve requires about 12.7 HP/MPH in this speed range. The reason that rules of thumb like 15-20 HP/MPH are used is because engine HP figures are often optimistic dyno header figures that don't reflect the actual installed HP with marine exhaust, or the richer jets that were installed just before the engine left the dyno. If the engine is really only 475 HP installed and your before speed is the best number ever observed on a cold day with no fuel, then more of the difference can be explained without sentencing the engine builder.

Re: New 502 and it sucks!!!
 

Thanks guys! Keep'm coming!

I did 4get 2 tell u when he bought the boat 8yrs. ago it did go 72GPS with 220hrs. on it with a 23P Turbo. I understand the hp. ratio after 60mph but, he didnt gain anything with an xtra 160hp. Thats where were lost???

How does a 454mag out perform a fresh 502???
And the GPS doesnt lie. :mad: Theres a guy that has a 1994 25ft Aggresser with a 454mag that runs 73-74GPS respectfully around town that will whoop his 502-525hp???? and my other buddy has 500 Bulldog 525hp. that runs 77GPS that i have "driven" in a Checkmate 253 Convincer??!

I dunno? :confused:

Re: New 502 and it sucks!!!
 

I agree! we thought we could break mid 70's with that combo! Its not a true 525hp then! Read my reply below that i added!
Thanx..tomcat! :D

Re: New 502 and it sucks!!!
 

Beaks don't weigh much :D :D :D

Re: New 502 and it sucks!!!
 

Isnt this really a 26' boat minus the beak & swim platform ? :D Just diggin at ya thats all. :p

Re: New 502 and it sucks!!!
 

I think the new and old speed numbers you are stating sound low. I would think a 25 Sunsation should do 70 with 365 HP. Maybe there is water in the hull? That could explain the loss of speed since it was bought. 8 yrs. ago? was that before people used GPS speeds? If he truly has 525 HP and only going 70, something is not right.

I have a similar hull and I was running 72-74 with 385 HP. I now have 425 HP and running 76-78. I am turning a 28P Bravo 1 to 5000. So, I gained approx. 1 MPH per 10 HP, and that is at speeds over 70. Some of those "rules of thumb" change a little when talking about boats with a 7' beam.

Re: New 502 and it sucks!!!
 

And I can imagine that you spent some serious change, too.

Don't feel too bad Bravo... your buddy can whip my boat's azz and I have twins. :D (26' with 2 SBCs).

The builder shouldn't have estimated so high. He got your buddy's hopes up.
But I agree with those who say "don't kill the builder, you may need him."
Maybe just mention to him that his formula was a little off.

Re: New 502 and it sucks!!!
 

What does the 25 sunsation weight?
72 GPS with a stock 365 is an amazing number.

That's not a stepped hull right?

I'm happy to be at 70 in an older Formula 242 with a 500 HP (crankshaft) motor.

Re: New 502 and it sucks!!!
 

I have a '92 aggressor and it does 75 gps @ around 5200 with a 25p mirage.

Side note: It has a 650 hp. blower motor and I haven't had the balls to hold it out to 6000 rpm where the rev is set :D

The 454 mag it had did 68 spinning a 23p @5000 rpm

Info only.

Re: New 502 and it sucks!!!
 

Did your buddy tell the builder that the boat runs 72 or did he tell him 62? If my boat lost 10 MPH, I be figuring out what the hell was going on. 600 hours on a 454 mag isn't really that outrageous in my opinion. He may want to check some things out with the boat and double check the timing and plugs on the new engine.

Re: New 502 and it sucks!!!
 

My first pull on the dyno with a built NA 509 produced 530hp after about 30 pulls and some changes we left it at 581hp as setup for the boat. Best pull lean and added timing was 600.

Point is.. the internal parts were all there to make the hp but dyno time allowed us to make them work. timing, timing curve, jetting, carb spacers, air cleaner design. All these things make a difference to any motor. In my case we found that the 850dp was still pulling too much manifold vacuum at 5600 so we switched the main body out for a proform HP style and picked up 20hp right there+ going back through all the previously mentioned items got us to the final number of 581. this was with the timing backed off to 35 and with the jets rich to be on the safe side.

Most likely you will be leaving power on the table if you don't dyno a built motor IMO

Dyno time cost $450 horsepower found 51....cheap power

Re: New 502 and it sucks!!!
 

I think what he gained sounds about right. Might want to factor in the hot weather, if it's applicable to your area.

Re: New 502 and it sucks!!!
 

I don't understand, if it ran 62 and now runs 70, he gained 8 mph. That's not nothing.

Re: New 502 and it sucks!!!
 

Remember that 8 years ago the government had the GPS selective inaccuracy and the 72 miles an hour reading could have been while the system was purposely inaccurate. I have seen huge variances in the past with speed readings from day to day with the same boat. The last couple of years the selectivity has been turned off and the GPS's are now accurate at all times.

Re: New 502 and it sucks!!!
 

In my 1995 23 Nova I went from a 7.4/330 to a ZZ502/502hp. Gps speed went from 56-57 to about 68, with a Mirage 25P. 11-12 mph increase = about 15hp per each mph. That's just my boat, every hull will be different.

I had Throttle Up lab my 25P and gained 2 mph. So, the humble little Nova will do 70 gps on just about any day. Boat weighs 4000 lbs.

================================
Per Tomcat ---

Your top speed now suggests about 450 HP, but think about when the before speed was measured versus now. Changes in temperature and humidity have a significant effect. The prediction of 78 might have been a bit optimistic, but don't kill the engine builder yet, some investigation and more tuning and testing may be required.
===================================

Read what Tomcat says about "temperature and humidity"....

On a hot humid day 69-70 is about my top speed. Late last summer on a day around 70-75* and relatively low humidity I saw 73+ on gps. That's a 3-4 mph difference!

If your bud has his prop labbed, he may see another 2 mph. That's a pretty common gain for a labbed prop. Then suggest that he run the boat on a cooler less humid day. He may see another 3-4 mph. Add the gains up and he just might see another 5 mph.

And as Wobble said, dyno is worth the $$. If he can't do a dyno, be sure it's tuned/tweeked properly.

All in all, I think the builder was too optimistic on the top speed. But it doesn't seem like your bud got hosed.

Good luck

Re: New 502 and it sucks!!!
 

3300lbs.
and no stepped hull............7'-6" beam, no pad.

Re: New 502 and it sucks!!!
 

He did tell him that it ran 62mph. And he did run the snot out of it everytime we went out.

But the boat ran 72mph 8yrs. ago because i got a new GPS and was trying & crying at the speeds compared 2 the dash speedo's. That was a big let down 4 all of us! hahaha :D

Re: New 502 and it sucks!!!
 

How many more things (weight) is he carrying around in the boat now as compared to 8 years ago?

Re: New 502 and it sucks!!!
 

As many have said heat & Humdity play a big roll. Here in AZ we don't have alot of humid weather but we do see the heat (it's a dry heat :evilb: ). Spring and fall when the temps range 85-95 during the day my boat will see around 68 MPH running 5100 RPM, last weekend we were out temp was 116 boat wouldn't move could only get 62 MPH at 4700 RPM. Losing 6 MPH due to the heat, try some testing early in the morning when its cooler and humidity hasn't set in yet.

Re: New 502 and it sucks!!!
 

Sounds about right to me...


Jbravo.. You run the saginaw river/ bay? Thats where I do most of my boating. I run a 18' powerplay with a stock small block :D :D :D

Re: New 502 and it sucks!!!
 

id have to say that i would think the boat should run alittle faster too.
there was a 25 aggressr locally that ran a consistant (not accounting temp and humidity) 73-74. you could count on the boat running 72 all the time!!

talk to sunsation to see what they would expect with stock HP in the boat. then do the adjustments as needed.

im in the same "boat", my checkmate 242 ran 58 with a 330/454, now with a 550hp (dyno numbers) motor in the boat it JUST runs 70-71mph-gps.
i understand that with my exhaust and drive im probably only 500-510 at the prop.......but ive heard that the boat with a factory 502 it runs 68, an hp500 runs 72-73....knowing that and the 15hp/mph rule i should be 73-75. IM NOT!!! but im still tuning as Kidnova said.

Re: New 502 and it sucks!!!
 

I guess after reading JBravo, I am confused. You said the boat ran 72mph 8 years ago and now just before the new motor it only would run 62mph. My math is telling me thats a 10mph decrease before the new motor! What happened to the boat or motor that it slowed that much?, thats a lot! Sounds like there is some missing infor or you are not comparing apples to apples. This is why it is so important when a boater is trying to make speed improvements to a boat that you start with real up to date verified data and then make like comparisons as Tom's post talked about to really get the "black art" of fine tuning a hull, motor, drive and prop combination to its best result. Some boats have bottom and x-height issues that will drastically limit gains as well as other considerations such as CG, prop efficiency. You really can't compare different boats with different hull shapes and forms closely. An actual 525HP (real) out of a good 502 motor is not a big unrealistic number for any decent engine builder to achieve, so if your buddy is smart he won't throw the baby out with the bath water, but get busy fine tuning the whole package. If it ends up an engine builder problem, then deal with that accordingly. If it were easy, anybody could do it!

Be Patient! Good Luck,

Ray @ Raylar

Re: New 502 and it sucks!!!
 

more like a 25' :D

Re: New 502 and it sucks!!!
 

yes i do! and hang out State park beach area.