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-   -   what rpms should i run??? 540ci NA..... (https://www.offshoreonly.com/forums/general-q/243781-what-rpms-should-i-run-540ci-na.html)

TxHawk 12-10-2010 07:11 AM

Make sure it has plenty of fuel at 9.5:1 with iron heads.

Rookie 12-10-2010 07:15 AM


Originally Posted by jeff1000man (Post 3271153)
If you deck those heads, you are going to loose a lot of valve lift that you really need to get those engines to breath.

Could you explain this to me? I see that your valves will be closer to the piston but the lift and rocker ratio is still the same. The mechanics that lift the valve are the same.

PatriYacht 12-10-2010 07:29 AM

Those cams are awful. They have less duration and lift than a 415hp 502 efi. Most rv cams have more lift and duration. A good cam for stock rectangular port heads is the Crane 651. It is 244 int. / 256ex. duration @ .050, .630 / .630 lift. this cam will make 575-600 hp and rev to 5400-5600. For any more hp, you will need aftermarket heads.

Rookie 12-10-2010 07:31 AM


Originally Posted by Rebel_Heart (Post 3271113)
Jim Valako is the man when it comes to porting aluminum heads. He did a great job on my Dart Pro Ones. I'm running 1050s on my 540s.

You will appreciate the new castings. This will be the Marine/Street Strip head that he has wanted to cast for years. He has a couple heads out there on some boats and a couple on some weekend drag cars. He finally got some poured a few weeks back, they are at Dart getting the machine work finished now. Hopefully he will get them back before Christmas and I will post some pics and info.

jeff1000man 12-10-2010 09:13 AM


Originally Posted by Rookie (Post 3271217)
Could you explain this to me? I see that your valves will be closer to the piston but the lift and rocker ratio is still the same. The mechanics that lift the valve are the same.

You are correct, what I meant was that he will loose the ability to put in a higher lifting cam because there will not be as much clearance.

302Sport 12-10-2010 09:22 AM

you guys are helping me a ton. thanks for all the info.

PatriYacht 12-10-2010 11:32 AM

The piston to valve clearence with those pistons is quite large. Easily enough for any cam you would want in a marine engine. To answer the original question, I bet the hp peak would be 4600 using the parts specified. And I would guess that it makes about 450 hp but about 700 ft.lbs. of torque.

302Sport 12-10-2010 11:35 AM


Originally Posted by PatriYacht (Post 3271404)
The piston to valve clearence with those pistons is quite large. Easily enough for any cam you would want in a marine engine. To answer the original question, I bet the hp peak would be 4600 using the parts specified. And I would guess that it makes about 450 hp but about 700 ft.lbs. of torque.

going to talk to with bob on monday when he gets back. needed new intakes anyways, but most likely going to have him grind me a diff. cam than what i have. also heads are at machine shop for valve job w/ new valves and spring.

Griff 12-10-2010 11:38 AM


Originally Posted by PatriYacht (Post 3271224)
Those cams are awful. They have less duration and lift than a 415hp 502 efi. Most rv cams have more lift and duration. A good cam for stock rectangular port heads is the Crane 651. It is 244 int. / 256ex. duration @ .050, .630 / .630 lift. this cam will make 575-600 hp and rev to 5400-5600. For any more hp, you will need aftermarket heads.

Look at the actual specs on the cam card, not the top description. Its a .595/.612, 242/252 on a 110lsa.

PatriYacht 12-10-2010 11:38 AM

I just looked a second time at the cam card. The cam card doesn't match the wording above it. A bit of confusion in that catalog. The cam card looks better.


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