Big motor upgrade question.

[wrasse]

Hello. I have a 91 Z24 (basically a black widow) that currently has a 330hp 454 with king cobra outdrive (hump/cone clutch). I'm running around 55MPH right now with 21 pitch prop. I'm looking at upgrade to 509 roller motor that makes almost 600hp at 5000 rpm. It comes nearly complete with intake manifold/carbs/distributor.

I know it's a huge power bump and I have some concerns....

1. Would my transom hold up?
2. Can my hull take it?
3. What prop should I use and what speed can I expect?
4. Boat seems solid but I'm no expert and it's not had a recent survey, how important is a hull inspection by a surveyor prior to undergoing an upgrade like this?
5. It seems king cobra is a pretty stout drive, any weak points I should be aware of?
6. I currently have a 1/2 closed cooling system (cools blocks). Would my current closed clooing system be adequate for the 509?
7. It seems 509 is not used much as 502. Why is that?
8. Would using a differnt iginition besides my stock spitfire be ok? I know king cobra has some interrupter that lowers rpm to facillitate shifting. I wonder if I would need something that would replicate that...
9. Will my huge power give me a heart attack?

Sorry for my laundry list of questions!

[MOP]

You need to know what you can handle before jumping into a very expensive pool! Figured I would hit the last question first!

1. Would my transom hold up?
Transom should be carefully inspected as should the stringers, with that much HP they should be beefed up.

2. Can my hull take it?
That depends a lot on how you drive it.

3. What prop should I use and what speed can I expect?
Trial & error can be expensive.

4. Boat seems solid but I'm no expert and it's not had a recent survey, how important is a hull inspection by a surveyor prior to undergoing an upgrade like this?
I would get hold of a good glass guy to advise you on what may be needed.

5. It seems king cobra is a pretty stout drive, any weak points I should be aware of?
We know the KC will hold 500+ after that it is speculation.

6. I currently have a 1/2 closed cooling system (cools blocks). Would my current closed cooling system be adequate for the 509?
I doubt it.

7. It seems 509 is not used much as 502. Why is that?
Need a finer mind to answer that one!

8. Would using a differnt iginition besides my stock spitfire be ok? I know king cobra has some interrupter that lowers rpm to facillitate shifting. I wonder if I would need something that would replicate that...
Dump the Spitfire it will crap out when you least expect it and they are a bugger to replace. You will need to retain the shift interupter!

9. Will my huge power give me a heart attack?
Return to top!

Phil

[Donzigo]

MOP gave you some great advice...........listen to it.

I won't say I have a good response; but, I'll it's an opinion. I have had a Z-25 & presently a Z-33 from the same vintage. They are wonderful boats and have superlative eye-appeal and their rough water handling charactersitics are legendary; because when Don Westerman designed them and the Genth era factory built them, they were built heavy.

a. By today's standards of light weight materials and stepped hulls, they are not speed demons. I myself have thought of beefing up my 454's and have to tell myself the same things I am telling you.

b. The stringers on these era boats need always be checked. The system of buiding the stringers, materials used, and AGE of these boats dictate that stringers be checked. Most will need some type of rebuilding by this time.

c. I've always heard that it costs a lot more money to chase horsepower with Ford engines than GM engines. (I hope I don't regret saying that.........since, firestorms are common on this board & I wouldn't have it any other way:) ).

d. The hulls, if sound, from this era can take a hella-va-lot more punishment than you can..........don't worry about that.

e. You heart?..........MadPoodle, Buizilla, Cuda, Carter, Lenny and so many others probably discuss funeral plans regularly with their wives along with the planned additional HP added to these bad boy boats.

[ThunderMarineDave]

First, proceed with caution, as this can get expensive and time consuming. I didn't want a boat as much as I wanted another project, so I'm having a great time with mine (25 Widow, 460 Cobra to 496 B1, over a year into it and it hasn't gotten wet yet...)

3. What prop should I use and what speed can I expect?

I will be running a Bravo 1 or Mirage Plus (partially because I get deals on Merc parts, partly because they are good stuff). I don't know what pitch, but I hope to spin a 25P.

5. It seems king cobra is a pretty stout drive, any weak points I should be aware of?

They stop wanting to shift into reverse. Otherwise, pretty stout.

7. It seems 509 is not used much as 502. Why is that?

While we can argue about market position for outboards, when it comes to I/Os, Mercury is king. Not saying they are definitely the best (although I do get paid to say that), but they are definitely the most prominent. Someone has to decide what size motors to build, and Merc decided on a 502 instead of 509, and this has made 502s the reigning big block.

8. Would using a differnt iginition besides my stock spitfire be ok?

Ok is an understatement. Required is probably more accurate.

I know king cobra has some interrupter that lowers rpm to facillitate shifting. I wonder if I would need something that would replicate that...

Yes, you will need a shift interupter (or magnets to retrieve your drive gears from the water).

9. Will my huge power give me a heart attack?

Only if you start it.

-David

[MOP]

David!! I like the way you think!

Phil

[wrasse]

Thanks for the advise. Given the feedback, I think I'll look into a tappet 509 instead of roller 509 to make the power increase more reasonable. I'll be looking at 450hp or so at 4800 rpm instead of near 600hp. I'm still hoping that my 1/2 closed cooling system will be sufficient. Any hints on if I can check the transom/stringers myself before commiting to the power upgrade or should I just bite the bullet and pay a professional? If I can get close to 70mph with that setup, I'd be really happy!

[Donzigo]

I had a Z-25, which is what mold they used to make the Z-24. It had a 454 and top speed was 55 MPH. You say you want 70 MPH, a 22% increase in speed. PLEASE check those stringers and transom. The boat was designed by Don Westerman and he never meant for it to do 70MPH. It will handle the strain, for sure; but, be sure you have a sound boat.

How do you check? Take a small ball pinned hammer and tap near the bottom of the stringers where they meet the hull. Also tap all around the transom in the same way. Especially check the transom around the housing that holds the outdrive. If you don't have any problems, with this vintage boat, you'll be the first one. If the boat was stored inside it's entire life and the owner took the plug out every time, then you've got a great chance it's OK. If the boat was stored in any other way, hig n dry, trailer outside, rack outside, covered or not, I'll bet you've got at least some stringer rot somewhere. Check the gussets to make sure they are sound. Any light colored fiberglass means that it has delaminated. This happens a lot with gussets. Ok, you're not finished yet. Check the front cabin area. Take up the carpet and tap on the floor. Take all the inspection plates off and tap. Check the bulkhead in the front of the engine room. Ok, you're done.

[wrasse]

Wow, thanks Donzigo. Maybe I should just keep the boat as is and just enjoy it huh? =) The motors fine and it runs great. Sounds like I should save the cash (which will I'm sure will be over 8K when all said and done). Thanks everyone for putting things in perspective.

BTW, I was told by the shop that serviced the outdrive recently that my oil cooler has a leak.

It's a 91' 454 OMC. OEM OMC replacement is $350. Can I pick up one of these from ebay http://cgi.ebay.com/ebaymotors/Marine-Oil-Cooler-12-X-1-25-X-375_W0QQitemZ320103989683QQihZ011QQcategoryZ50442Q QrdZ1QQssPageNameZWD1VQQcmdZViewItem
or do I need a OMC one?

Are they fairly easy to replace ?

[Pismo]

Almost 600hp means about 550-575, so actually in the boat with marine exhaust 500-525ish at the drive so you are putting a single Merc HP500/525 equivalent in a 24' boat. Not really that big a deal. As long as there is no rot in the transom and stringers it should be fine. A 509 is a 502 bored 30 over, so this block has been used and rebuilt. The Cobra is stout, should take it ok if not abused. You will probably need a bigger oil cooler, can always be added later. You are also entering the world of non-stock performance motors which means MUCH more frequent problems/tweaking/tuning/adjusting/rebuilding. Be prepared. 70mph, probably if the hp rating is true.

[MOP]

Quote: wrasse
BTW, I was told by the shop that serviced the out drive recently that my oil!

Ebasic Power has a decent rep, you need to see if that cooler will fit your app.

Phil

[Cuda]

Hello. I have a 91 Z24 (basically a black widow) that currently has a 330hp 454 with king cobra outdrive (hump/cone clutch). I'm running around 55MPH right now with 21 pitch prop. I'm looking at upgrade to 509 roller motor that makes almost 600hp at 5000 rpm. It comes nearly complete with intake manifold/carbs/distributor.
I know it's a huge power bump and I have some concerns....
1. Would my transom hold up?
2. Can my hull take it?
3. What prop should I use and what speed can I expect?
4. Boat seems solid but I'm no expert and it's not had a recent survey, how important is a hull inspection by a surveyor prior to undergoing an upgrade like this?
5. It seems king cobra is a pretty stout drive, any weak points I should be aware of?
6. I currently have a 1/2 closed cooling system (cools blocks). Would my current closed clooing system be adequate for the 509?
7. It seems 509 is not used much as 502. Why is that?
8. Would using a differnt iginition besides my stock spitfire be ok? I know king cobra has some interrupter that lowers rpm to facillitate shifting. I wonder if I would need something that would replicate that...
9. Will my huge power give me a heart attack?
Sorry for my laundry list of questions!
1) If it's solid, yes it will.
2) Yes
3) You'll have to wait for the swap to figure
4) I would check it myself, your mileage may vary
5) Keep good oil in it
6) I would think so
7) It's a punched out 502 (0.30 over)
8) I'm unfamiliar with the shifting of a KC
9) Check with your doctor before going on this treatment. :)

Go for it!