longhorn262

Just purchased my first boat for a restoration project since I just finished restoring my 1976 280z. Had fun building up the car and thought maybe it was time to learn something new so I bought a boat.

I have already pulled the motor and it is at the machine shop. My goal is to get as close as I can to 400hp but anything over 330hp is fine.

So far purchased/plans for the motor:

22cc dome speed-pro pistons .030 over (should be around 9.3 to 9.4:1)
120cc Peanut port heads (slight port and bowl work being done by machinest)
Edlebrock Performer intake manifold
Stock mercruiser exhaust
Rotating Assembly fully balanced

Only thing I have not decided on is the cam selection. What cam profile would be best for my build?

I read of someone on here running the isky 270/280 mega (221/232 @.050 on 114 LSA) with the stock exhaust and no reversion...

longhorn262

May also go with 049 heads over ported peanut heads which would lower the compression even more.

longhorn262

Thank you. From my searching I have seen both of the people you speak of on this forum.

I don't necessarily need 400hp but the motor needed to be rebuilt and I hate going back completely stock when I know there are some things I can do to give her more pep without breaking the wallet.

I would really like to keep the stock exhaust for now as that is the most expensive upgrade for this motor. I was just hoping to raise the compression (I will be running premium 93 octane at all times) put in a mild cam do some port work on the peanuts so that I could retain a ton of torque. Supposedly the peanuts with a mild port can do about 415hp and over 500 torque from what I have seen. The only reason I would swap to the 049 heads would be to lower the compression a little bit as I fear it may be a little too high.

So in short what would be a good cam to use while retaining the stock exhaust with the above mods?

wannabe

Longhorn- There may be some people selling using HP 500 intakes and carbs- these are well worth it if they arenty asking too much. A 454 with a good roller cam HP 500 intake and carb will make 400 hp no problem if the heads are worked on a bit.

I have Merc 400's (454) that have been bored 60 over has CMI headers- Iron eagle heads and roller cam, HP 500 intakes and 800 cfm Holley- MSD ignitions- dyno 475 hp each.

EDIT: Member Rbesola has HP 500 intake and carbs.

Check the other threads in this section. BTW exhaust will be your limiting factor very quickly as the factory merc manifolds are really only good to about 370 hp. and reversion is an issue if you put much more lift and duration increased.

GOOD LUCK

Wannabe

longhorn262

So basically if I keep the stock manifolds I should just go back with the stock cam and stick with just the ported peanut heads and increased compression for my boost in power probably 350 hp.

BTW please stop recommending things I do not need. My final goal is about 400 hp which can easily be made with the peanut heads along with gobs of torque. I only have a bravo 1 drive so no need to go over 400 hp or I will be breaking things I cannot afford. The quadrajet is a great carb and will do just fine if tuned properly so no need for a different carb. Also I don't need to spend 1200 dollars on a roller cam setup (especially if mercury can make 400hp on a flat tappet)
Also doesn't the 400 hp 454 have the same log manifolds as the 330hp if so your 370hp rating on the logs is completely wrong.

longhorn262

http://www.offshoreonly.com/forums/g...h-power-2.html

Here is a peanut making 422hp/500tq

wannabe

Longhorn- You definitely want an upgraded cam, springs and new lifters. Don't go crazy but whatever RMBuilder suggests.

Wannabe

mcollinstn

You'll be better served with flattop pistons and deck the block to keep your squish around .036-.040"
Since the motor is already at the machine shop, all you need to do is compute where the deck needs to be.

Peanuts heads are around 116cc or so. You can deck them and drop that a bit if needed.
At 116cc, and a Marine FelPro gasket (.039 thick/4.37 dia), if your pistons are true "flat" (0cc), then you'd deck the block to stick the pistons out of the hole between 0.000 and 0.003". This would give you 8.4:1 actual CR.

120cc Peanut heads and a -22 piston would put you at 9.70:1 at .036 squish. That dome will increase flame travel distance, needing a little more ignition lead. It might be a little ping-happy unless you run a lot of cam.

Something with a -12cc dome at .036 squish would give you 9.0-9.1 CR, KB pistons do a good job of taking squish into consideration.
Or if you're getting a raging deal on the Speed-Pros, then they have an .030 over piston with a -10.5cc (8.9:1) and one with -13cc (9.03:1).

So, unless you are going to go with big heads, just do some work on your peanuts, match up a good cam (I honestly don't have a good recommendation for a peanut cam, but there is a very inexpensive Speed Pro cam that mimics the Merc 420 cam - but that's for rectangle port open chamber heads and I wouldn't necessarily expect it to be the best bet for your peanuts - dunno, though.. somebody may have some experience with that).

Center riser Merc exhaust manifolds are out of gas at about 450hp. A 350hp motor won't benefit at all with a swap from Merc center risers to aftermarket exhausts (both thru hull of course). A 400hp motor might or might not see an improvement that is noteworthy. A 450hp motor will certainly be at the upper limits of the Merc exhausts and would benefit from better exhausts. There's your rule of thumb.

Crank - no problem as long as you keep your revs under 5,200.
Rods - please put in ARP rod bolts if you plan to keep your stock rods. Period. (any rod bolt change requires resizing the big end).
Carb - your stock carb will support 400hp. Just rejet and put a less restrictive (taller) flame arrestor on it.

MC

longhorn262

I've talked to Dennis Moore and he suggested a 224/230 duration cam on a 110 LSA. I also don't know where people keep getting 9.7:1 with -22cc dome pistons and a 120cc head. If you do the math correctly it only comes out to 9.4:1 assuming .020 piston to deck clearance. Only way I could get 9.7:1 would be if i decked the block to zero which I am not.
Also you are off on your 8.4:1 calculation with flat tops if i put in 116cc with .003 over the deck with flat tops I get 8.55:1

Im also fairly certain my math is correct as I don't have an engineering degree for nothing...

Also true peanut port heads are between 119cc and 121cc from the factory and are listed as 120cc. If your seeing a peanut with 116cc then it has been milled.

Thanks for everyones responses.