Valve spring upgrade with gt40p heads

[Mamigacz]

I put a new cam in my boat this fall. Currently, its a 351W with stock GT40P heads. When I say stock, it has the stock valve train components as a 2000 ford exporer. The cam I chose is made by cam research (they said its an awesome cam for ski boats). The specs are:

intake lift .49
exhaust lift .49
intake duration 278
exhaust duratation 282
Intake duration @.050 216
Exhaust duration @ .050 220
lobe separation 112
recomended seat pressure 95lb
recomended open pressure 295lb

I want to use the stock gt40P valves which have an installed ht of:

Intake 1.780"
exhaust 1.690" (without the exhaust rotator)

The stock gt40p springs don't seem to satisfy the cam requirments. The stock gt40p springs yeild:

intake seat pressure (@1.78") 76lb
intake open pressure (@1.29") 227lb
exhaust seat pressure (@ 1.69") 67lb
exhaust open pressure (@ 1.20") 208lb

Has anyone done the GT40P/cam upgrade and changed valve springs? If anyone used a simular cam as I have chosen, what springs did you use? I have set in mind, but reinforcement from others would help me out alot.

[DanielC]

What RPM are you going to run the engine up to? If you are still going to run basically stock RPM's (about 5000 WOT, with rev limiter kicking in at 5200).

By the way, do not trust valve spring specs by what is written on the box. I had access to a valve spring height/pressure tester and found out the used valve springs on an engine I was rebuilding were actually better (close to factory specs) than the new valve springs that were sold to me. The new ones got returned to the store.

[Mamigacz]

Currently, I have 13 X 12 ACME prop and the boat can barely get past 4000 RPM. I'm in the process of putting a rebuilt engine in the boat. I'm hoping the rebuilt engine, cam, gt40p heads, Edelbrock performer intake will get me into a power band that will push the boat faster than 40 mph. If it gets close to 5000 RPM I might consider a differant pitch prop, but for now anthing over 4000 RPM is fine with me.

Good advice on checking the springs. I will check them out after I receive them.

[Mamigacz]

I should probably mention the boat is an 1986 so there is not rev limiter. Also, its 19-1/2 feet long, open bow and weighs close to 2800lb. I'm not sure what RPM to expect out of a boat this size.

[DanielC]

I would expect the engine to run to about 5000 RPM. That is a reasonable, pretty safe RPM.
By hot rod standards, it is really not that high.

What kind of boat is it?
That weight seem heavy for a 19' 6" boat. Is that based on sales literature, or did you actually weigh the boat?

[Mamigacz]

Its a 1986 Ski Centurion, Concourse Skier (kind of rare). The weight came from specificatons from NADA. No, I never weighed the boat to see if it was accurate. The Concourse Skier was wider (8 ft beam), deeper, 6 inches longer than the typical closed bow Centurions of the 80's. I think the standard closed bow, Tru Trac Centurions weighed about 2300 lbs.

[Zach@n3]

My 86 2001 has about 600 hours on the rebuild. Acme 540 (13x12). Bone stock rebuild other than a .030 over bore. 4500 RPM and solid 45mph on gps. Sometimes it will scratch at 46 if its cold out. Dry weight 2300lbs.

[Mamigacz]

Zach@n3, thanks for the speed feedback.

Do you have gt40 or gt40p heads?
Do you have a nonstock cam? If so, what is the lift and what valve springs did you use?

[Mamigacz]

Whoops, I missed that you said bone stock.

[Zach@n3]

Just a stocker. Giving you some baseline numbers. I'm also considering GT40P, cam, and intake in the future. I would expect yours to run a tad bit faster than that. Howmany hours?

[Mamigacz]

I'm in the process of putting a rebuilt engine in right now.

The hour meter reads 1200. It could have more depending on the previous owners ethics (disconnecting the hour meter).

[Zach@n3]

I'm sure you will be very happy with the P heads and that cam. I think thats the cam another member at CCF.com is running in his 90 SN and it screams.

[bhectus]

My 86 2001 has about 600 hours on the rebuild. Acme 540 (13x12). Bone stock rebuild other than a .030 over bore. 4500 RPM and solid 45mph on gps. Sometimes it will scratch at 46 if its cold out. Dry weight 2300lbs.

I've got a '87 BFN w/the 351w with exact same prop and I'm pulling almost identical performance numbers to yours. That's a great prop.

[Zach@n3]

I stand corrected. Tim's cam is a different grind being that his engine is standard rotation. Still a good cam choice.

B, The 540 is a boss.

[TRBenj]

I stand corrected. Tim's cam is a different grind being that his engine is standard rotation. Still a good cam choice.

B, The 540 is a boss.

Its a 1986 Ski Centurion, Concourse Skier (kind of rare).

Dollars to donuts says he has a LH engine and an Acme 541 (LH version of the 540).

As a general rule, I think it is wise to allow the cam designer to spec the valve springs for you... and ideally you'd buy them right from the same shop at the same time. The cam guy has a vested interest in that cam working as designed (both performance and reliability wise)... and should you ever have problems down the road, its one less variable that they'll be able to pin on someone else (or you).