454 stroked to 496
 

I just got a new boat (baja) with a 454 stroked to a 496.
It has merlin oval port heads on it, this is the cam specs on the comp cam. I was just wondering what everyone thought.
cb xr274 r-10
valve adjustment intake= .016 exh.=.018
gross valve lift intake= .639 exh = .646
duration @ .015 tappet lift intake = 274 exh.280
valve timing @.015 open intake = 31
exh. 74
closed intake= btdc 63 abdc
exh. = bbdc 26 atdc
duration @ .050 intake= 236 exh= 242
lobe lift intake= .3770 exh = 3810
lobe seperation = 110.0

You'll need a long riser or dry exhaust. My guess is that LSA will probably incur reversion unless your motor has a decent exhaust setup like CMI, Lightning, Stellings etc.

I have the same LSA and have had issues already so am converting to dry exhaust.

That's my thoughts anyway. I'm sure far more knowlegable people than I will chime in too!

I was told the exhuast on it is a gil's dry exhuast, but water comes out the exhuast tips.

Lots of lift and little duration so exhaust means a lot. How do the hoses run on those Gils? Is the water just dumped at the ends?

If they were dry exhaust water would not be mixed with the exhaust. It would run through the pipes to cool them then through a dump. Wet exhaust are fine if you have long risers and the correct cam. I would be concerned with the LSA at 110, does not look like marine specs. Send "RMbuilder" a PM and ask him to take a look at your thread. He is the cam "Guru", you may want to have him grind one to your engine specs. Better safe than sorry.

That engine should be a monster with that solid roller in it.

GILs will have a dump for the ecess water and then mix at the tip.

Some of them have extra holes and just mix at the tip.

Do your tail pipes run solid all the way past the transom or do they have a rubber connecting hose to an exhaust tip.

If they go all the way out the back, then you should be OK.

BTW, that much cam probably makes power to almost 6000 rpms......

How many hp is that engine?

I would guess about 600hp at 5800rpms.

When you guys talk about reversion when does this occur?? With boat off or running?

When you guys talk about reversion when does this occur?? With the boat running? ive heard of it when its off

Idleing.

At idle, a cam with a big lope and overlap will suck water back up the tailpipes.

Would a "silent choice" in the on position prevent that from happening?

Actuallly it makes it worse

It can happen when you pull back on the sticks to fast, It can happen when that wall of water comes back at the transom when coming off plane. It is most common at idle speeds.

I guess if the overlap was really extreme it could happen at WOT, but you would need a lot of duration.

Cam shaft selection is an art form. I leave it up to better trained profesionals rather than trial and error. There is to much money at stake.

I run that same set up its a 420 454 bored 60 stroked with dart intakes and lightning headers its awsome.

If you are running silent choice, then you definatly have the wrong exhaust for a performance cam. Ditch the silent choice and go with long risers, or dry pipes. I use the EMI thunders, there are a set for sale in the swap shop. Looks like a good deal.

Nevermind, I see that was somone else asking about silent choice.

I have rubber connecting the tips to the riser, prolly about 12 inches or so. I will try to post up pictures.

http://i243.photobucket.com/albums/f...thunder011.jpg

What do you guys think?

http://i243.photobucket.com/albums/f...thunder010.jpg

I am not familiar with those exhaust. But that does not look like a dry pipe system to me. If that is a wet exhaust those risers are to short. It does not look like it is set up correctly to me.

They don't look like any gils I have ever seen!!! And that is definitely not a dry system!

they say gils one them. So am i best off switching the manifolds and risers or just risers?

would a manifold with riser such as eddie marine thunders or a header like lightning headers be a better replacement to help from reversion?

Those are early gils with the aluminum risers. you could find dry tailpipes to fit them and use the water dump on top that's blocked off. Or just find a nwer styleof gil pipes to use.

Where would i be able to find some dry tail pipes for it? will the newer dry risers bolt up to the manifolds? Thanks did some searching on the internet but came up with not a whole lot of information. Also if anyone has a set they are looking to sell let me know.

these were the ones I had , dry to the back. The risers usually went bad and tailpipes discarded, so someone has a set . Offshore performance specialites in ft. myers might be a place to start looking. If you get mufflers dump the water directly into them and you will be quiet too. That exhaust is still on the boat after 12years and I bought from aflip over boat in Key Biscayne after Hurricane david. Put an add on WTB swap shop.

I have a similar cam in a 522, the cam is bigger then the heads can flow. I have Lightning wet headers and have never had any problems with reversion and I do a lot of idling, just come off plane easy.