I called diamond perf today and asked about the KE TnL's and he felt I would most likely need dry tail pipes with that cam.

Anyone got any suggestions on what exhaust to use with the stock cam?

Mechanic has already got my boat in the shop with the engine sitting on the floor next to it. Might be a little late to try swapping cams now.

From where the tail bolts to the ke header to where the outside tailpipes end into the atmosphere should ideally be 19” long. 18”-20” will be okay. This should help with reversion as it’s near an ideal length. Search under my name and the KE Headers and lightning and thunder exhaust. You’ll find sone good info and an example of someone who had reversion until he cut his length to that.

I can’t give you promises but can math thru science and real life data.

+ Just saw Dean Ferry said used same engine, cam, short 6” tail and had non-issues. He’s been-a perf boater and on oso for long time.

X,
I just sent you a PM.
Tx,
Skater Dean

Great info as I too am wanting to repower my 252 Baja Islander...and am torn between a 502 Mag EFI or HP500 EFI, with the goal being to use as much 'stuff', like exhaust...from the 454 that is in it.

I was contemplating getting the Baja 252 open bow, or my Cobalt 252. I like the sporty look of the Baja and the GF liked the luxury look of the Cobalt. Whichever had to have a 454 MAG (385 HP) or a 502 (415 HP) At that time I couldn't find a Baja in good condition, and was very tough to find one with the engine I wanted. (Most were 496 mag with 375 HP) So we got the Cobalt

Well, I can honestly say this has been a learning experience for me. I have the 502 MAG (415 HP) you are contemplating. It's a robust engine and pushed my kinda heavy Cobalt 252 to 63 MPH (4500 lbs dry weight) I did have the fuel injectors cleaned/flowed. Installed the Hardin Marine Seaward exhaust for use with captains call, installed the older style Flame Arrestor and matching Throttle Body as I read that FA flowed the best. New plugs, cap, rotor, wires, and control module. The MPI engine isn't too bad on fuel if you're just cruising. Lots of parts are available for it, but the Achilles heal IMO is the oil cooling system. It's adequate for the stock performance, but needs addressed if upping the HP. If left alone, the engine is supposed to be nearly bullet proof. I've seen some people say about 1,000 hours is achievable before any major overhaul is needed.


The HP 500 EFI is whole other animal. I'm not sure what ignition you have? But most likely will not work with the HP 500 engine. Which I believe is the MEFI 3. So you would need to replace that. The stock exhaust from your 454 would be a MAJOR step back if installed on the HP 500. It came with headers from the factory. It also requires more regular maintenance VS. the black engine.

So I don't think there would be much you could "switch over" from yours to it. It would be more of a remove your engine, and replace it with the HP 500 "drop in ready" engine. (which is what I'm doing)

If you got any Q's just ask. I'm learning the hard way and can teach you what NOT to do.....

Please note that the HP 500 EFI is not plagued with the same problematic camshaft as the engine I am asking about in this thread. They resolved my problem by installing a different camshaft and using the headers for the fuel injected engine

Pretty sure I've already seen what you're asking me to look up. I searched every thread I could when it comes to the HP 500 carb engine. Thank you for sharing that info though. It's something i will be paying closer attention to now.

Yes.
HP500 cam is 222/230 at .050” with 110LSA . Merc installed Gill exhaust

500EFI cam is 230/236 at .050” with 114LSA. Merc installed CMI headers.

Thanks for taking the time to post that...very much appreciated. And I hear you on the hard time finding a boat...I looked for two years to find the one I got, it is PERFECT except for needing a bit more power. Will probably go the 502 Mag EFI route but haven't been able to find a good one of THOSE, either, lol!

In all honesty, your 454 Mag is 385 HP and the 502 Mag is 415 HP That's not worth doing an engine swap if you ask me. Going to 500 HP would be worth the swap.

Just curious, what speed are you getting from that boat and engine combo?

You will have no issues with a stock HP 500 and the KE manifolds. I've run them on several engines: a 439 with a custom cam, slightly larger than a 741, a pair of 454s with 741s, and a set of 509s with 741s. No reversion issues at all. The 439 used the standard short tails, the other two engines used custom through the transom tails.

IMO they are the best option so long as they work with your set up.