More HP or Torque
 

Trying again with a new thread: Formula PC27 single 502 weighing 10000 pounds. Need more of something to get me out of the hole. WOT at 4700 RPM doing 45 MPH 1/2 tank fuel reading with a GPS, normal cruise at 3600 RPM at 32MPH. Put six folks on the boat and other stuff and it has a heck of a time getting on plane, turns 3750 RPM to do 32 MPH. Have a 2:1 bravo 3 drive turning 22 degree pitch props. Do I build/buy a 540 or do change out rectangular port heads for oval port (oval port heads suggested by another offshore member). I'd like to go through the engine this fall and have it ready for spring.

Fixx
 

cheep fixx would be a procharger or a side mount whipple..

option 2 pull the 502 and and sell it, change stringer arrangement and drop a pair of 6.2 mpi's in it and reuse your gimball and drive and add another..

option 3 sell the boat and find a 28ss and save a ton of money on converting your current boat..:drink:

That is a HEAVY boat for a single engine. You can build more motor......but set aside enough $$$ for another drive, you'll be buying one of them soon. Best bet is to drop pitch to get the RPM's up. I'm assuming you have the 502mag (fuel injected) which should have a recommended WOT of 5,000 rpms. Prop the boat to get to that and you'll likely have enough "umph" to get on plane when loaded down.


Actually, you should probably have your props sent out with instructions to tune them to acheive what I described. A good shop should be able to work them and if they have any damage what-so-ever, you shouldn't loose any performance.


BTW: HP makes you go fast, TQ will get you out of the hole.......but TQ is what breaks drives!! (I know, made 700 TQ and busted a couple XR's)

What is the peak rpm on that 502t? 4700 seems low. The cheapest thing you can do is to pitch down in props. Your hole shot will be better with the lower pitch and top speed should be better at optimal rpm (what ever that is...I would think over 5000rpm).

It will be a drive busting mofo if you put any real power to that drive with a 10k boat. I would just have the props labbed or drop down in pitch.

One more thing:drink: you said
"I have a heck of a time getting on plane"
Are you using the trim tabs to help getting on plane?

Ideally you want to be able to spin 5000 under WOT and a normal load. So having your prop set tuned for that is likely the cheapest option. You will probably give up 2-3 mph at cruise, but at least you can get there.

Probably should have mentioned my WOT use to be 4800 RPM but forgot about some of the slime that builds up. I have four sets of props and tried verious things just to get it up quicker, different rakes and cupping. Matter of fact I mis spoke I currently have 24 pitch props on it. When I run 22's it creeps to close to 5000 and I'm turning 3700 to 3800 to stay on plane. When I'm up that high I start getting in to the major fule burn issue. The 3600 RPM range gets me about 1 MPG. With the wife and I it does OK and I know it's not a runabout but I'm looking for what is the best choice. I do have trim tabs and they are all the way down, without them I don't stand a chance of getting up unless by ourself. If I can just figure out the right way to go.

Fixx
 

remove the outter trim ram pin,their should be a white trim insert where the pin slides through,try noving the insert to the rear of the pin hole..this will tuck the drive closer to the transom and hopefully this may help you get on plane quicker..

# 30 http://www.mercruiserparts.com/Show_...nd+Drive+Gears

I'm willing to try anything but a 1/2 inch change on the out end of the drive (maybe .25 degree change) could make that much of an effect on coming out of the hole?

send your props to brett at bblades or post this in prop section.

There should be very little, if any, difference in fuel usage between 3600rpms with a 24" prop vs 3800rpms with a 22" prop. Unless you have a flow scan, and have figured out your exact mpg, you are just guessing at that. Chances are the throttle is pushed to the same exact position. The engine just has to work harder to spin the 24.

You may be right but I do the same thing most every trip. Get up on plane go out 9 miles anchor. 4 to 5 hours later come back the nine miles. When I'm turning the 3800 plus I have to get gas every other trip (never fill up I don't like carrying all the weight, about 40 gal each time), if I turn less RPM I get gas every three some times four trips.

Maybe a 540 and an XR drive is the way to go but would sure like to find someone who has gone down the same road.

Fixx
 

it only takes 10 minutes if that to swap it. i read somewhere it made a differance,,its worth a try.

How are your props timed? looking at the skeg the lower part of the props are not soppose to be aleigned, inner prop @ 6:00 and the outter prop @ 12:00

1/2" could make a big difference. It's all about leverage.

Maybe but forget I changed the position and lift the drive all the up and maybe bust the drive against the ginble, might be worth a try but don't think I would leave it their.

If you are at all worried about fuel economy, this is not the answer. It will probably use twice the fuel and be even harder to get on plane. A Bravo 3 is about as good as its going to get. Any significant power increase is going to break the drive.

Not to mention, it makes no sense to spend 20k on 25k boat.
You'd be better off to buy something different with twin small blocks.

Like everyone has said , a 27ft cruiser weighing 10K is seriously underpowered with only a single 502 ....

45mph for that setup is not bad at all..

Not to worried about fuel but still don't want to throw it away money away either. Formula screwed up in 94 because they don't sell the boat without twins anymore. Twin 350 would put out 260HP each yet weight about 1000 each equaling 2000 pounds and 520HP. One 502 puts out 415HP and weights 1210. 800 pounds more for 105hp and more drag. Net sum gain might be a bit more but not a lot. Spend 20K on a 25K boat may be worth it if it cost 100K to replace it with a few year old used one, new one is 206K.

I've made two calls to Bblades and have not connected yet, but will keep trying. Willing to spend some money to get the boat running like I want but do understand to differences.

May wind up with another boat but have to make sure it's worth the funds. There is a 2008 370SS at a local Formula dealer with twin 525 but he wants 299K.

Fixx
 

You can give the guy that does my props a call,he knows more then most and is almost half the price..
Read his background before you decide..

http://www.dahpropellers.com/

Will do thanks

Fixx
 

ask for john sr.. and he will return your call ;)