Pardon me for my ignorance Excal, but what exactly are emi thunders? Headers, runnered manifolds, tailpipes. Looks like my choice of cams will come down to what I can afford for exhaust.

If I was to do only stainless tailpipes to mix at the transom and leave my stock manifolds, could I use the cam Excal uses?

Can I do nothing to my stock exhaust, use the cam Formula31 uses without reversion problems and get any perf increase. I now have mercruiser stock manifolds with 4" elbows exiting out the transom.

BT

If you use a set of tailpipes that dont put water into the exhaust flow till the transom (dry pipes), you can pretty much forget about reversion problems, so yes, you could use excals cam.

Yes on question 3 but a set of gils or better would help more. Not sure how much.

Its really a matter of all the components working together. Good heads and valves, intake, carb, and exhaust. Changing the exhaust alone has little effect without doing the other things. Ive never tried to do all the other things without doing the exhaust, but as long as you have through hulls you should be OK. The dryer you can keep your exhaust, the more overlap you can have. But remember, big cams need high compression and high RPM's to shine. They will hurt the performance and torque on a moderate 5000 rpm engine on pump gas. Excals cam is not what I would consider too big. Its about right and will make more power than mine with the right exhaust.

Blue Thunder,

My cousin has a pair of 454's with pocket/bowl ported oval port heads, dual plane intakes, a Comps hydraulic flat tappet cam 218*/226* duration on a 110* lobes, 8.6:1 comp ratio, stock Merc Thunderbolt ignition (no ignition box needed) with stock cast cranks turned .010", stock 3/8" rods, and cast pistons and his engines made 461hp @5100rpm and 514 foot pounds of torque @ 3500rpm on the dyno with 32* of timing. But I wouldn't run it much over 5100rpm especially with cast pistons. Of course this was done with dyno tubular headers. If you are using the stock exhaust system then you will still make the 400hp that you are looking for. Just be care of reversion with stock exhausts.

Again, he did this WITH GM oval port heads and they weren't even the 781's or 049's or even the peanut ports----these were another casting of GM's oval port heads. So I think you're on the right track bud!

BT,
EmI thunders are cast aluminum manifolds made by Eddie Marine. they are good for well over 500hp and a lot of guys on the board run them. they are about the same as gills or imcos. i got mine earlier this year from a guy named steve snider who advertises in the exhaust section in the classifieds for $1050 per engine complete. they have a website if you want a better look. i don't know how much if at all they would help you given that you already have 4" exhaust. i ran my motor specs on desktop dyno and came up with around 470-490 hp.

BTW, my cousin had hardened exhaust seats installed in the heads. This is done by a special cutter and then the new hardend seat is installed with a certain amount of "crush" and is pressed into the recess made by the cutter.

Do the hardened seats. I put the bigger valves in a set of 049's without the seats, and the valves actually worked themselves into the head. I started loosing power, and figured it was in the heads somewhere. When I took the valves out, it looked like the valve was a boring bit and worked itself in the head.
mike

Goob... I'll definately do the hardened seats if they are not already there. Thanks.

Excal... I took a look at the emi exhaust manifolds. It looks like the water mixes with the exhaust in the same place as the stock risers. Is that true? If so, I guess it would be ok to run stock exh with your cam grind and setup. Do you agree? How did you know that lsa and duration would be ok with water mixing so soon? Seems on the hairy edge.

And of course excal, the answer is YES... I would love to hear your cams in person. If you plan a run to the C&D let me know. My boat doesn't run at the moment but my truck still does and my cabin is only about 20 mins from there. Better yet... ever try the Nauti Goose?

BT

bt,
i guess that cam is close to reversion but i don't have any problems at all. the stock cams that the 400 hp cyclone engines had (my originals) were 111*LSA also with stock exhaust. the EMI's do mix in the same place as stock so i guess it would be ok for you too.
i will be doing the C&D in the next couple weeks so i'll p.m. you. what is the nauti goose?

Blue Thunder,

In one of my previous posts I gave you an example of what my cousin did with his 454's with cast parts, and the type of parts he used; cams, stainless valves, Harland Sharp roller rocker arms, bowl ported oval port heads, stock Merc ignition, safe comp ratio of 8.6:1, dual plane intakes, etc. Also, he had the complete rotating assemblies balanced. Your base engines are very close to his and those are the mods he did to achieve the results he saw on the dyno---pretty valuable info....especially for what you're wanting to do. Just didn't want you to miss the posts. Have fun.

BTW, back in the mid 80's, we modified our 330's that had the "049" casting heads and when we did all the mods we originally did NOT have the hardened seats installed in them. We were in the learing mode and had to take the engines apart again for another problem. While we were doing this, we checked the heads out and noticed that the stainless valves were pounding the stock seats way into the head just as "goob" has described! I think it was more apparent on the exhaust side if I remember correctly.

Notes being taken Kaama... thank you very much. You have been a tremendous help!!!!! One additional question I had for you was what is"bowl porting". I've never heard of that.

BT