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Post by BrianB on Oct 5, 2004 22:02:42 GMT -5
I have a jet boat with a 540 Chevy. I did not build the engine, so here is the combination (info from previous owner).
Pistons are 10.5:1 for a 119cc head, but heads have 113cc chambers, so maybe 11.5:1.
Canfield heads, castings just cleaned up, previous owner said 365cc (before cleanup) but I only found 350cc on the Canfield site.
Isky cam: grind RR-726/274 RR-726/282 (110deg lobe center).
Erson gear drive.
Super Victor intake, Super Sucker spacer.
1150 Reher Morrison carb and two Holley Blue pumps.
NOS Big Shot about 300hp.
The boat runs 5700rpm on the engine and about 6700rpm spraying. To run faster on the engine, I need to build more power in the 5700-6000rpm range, but not fall off after that for spraying.
I think that the heads and cam (duration at least) are probably too big. I was thinking of switching to some smaller AFR heads with 119cc chambers so I can run pump gas (although maybe I shouldn't spray with pump gas anyway) and a little different profile of cam - my other jet boat has a very aggressive lobe with a lot less duration but is close in lift. Also, I remember Joe Pontiac mentioning a couple times using an intake for a 4150 carb with a 4500 adapter for the lower rpm engines, I can't remember which intake. Also I am going to get rid of the gear drive.
Any suggestions?
Brian
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Post by Maximum Race Engines on Oct 6, 2004 1:01:54 GMT -5
Brian-
I would need to know more information to measure the compression, including deck height, gasket, dome size, etc..Depending on those isues, you could actually have more. No I wouldn't spray it on pump gas. The heads are too big for the operating range that is being used. You will need a much smaller head to have enough velocity to make the power in the lower rpm ranges. I would like to see a 320cc runner or so on there. The heads you have may be ported to 365cc runners from the advertised 350cc Canfield offers. The cam is also very big for what you are doing as well. You will need something much smaller, again more suited to the operating range. Possibly something in the 250's to 260's, with a wide lobe and a little less lift. For marine applications, I like to use short duration, wide lobes with alot of lift for the torque it puts out, with low rpm ranges. That will be more suitable for the lower compression as well. The intake is good as well as the spacer. I hate the blue pumps, and feel you should put one big pump and line in there and be done. The blue pumps do NOT supply enough fuel, even if you have 5 of them. As for the dominator, I would actually use a real nice Pro Systems 4150 based 1,000 HP. Will be alot more responsive with the smaller carb, and pull alot harder. Get rid of the gear drive as well. I like the JP Performance billet roller chains. You are on the right track in thinking you need some changes. What I have mentioned will not kill power up top but will pull alot stronger in the midrange. Hope this helps.
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Post by BrianB on Oct 6, 2004 1:59:51 GMT -5
Joe,
Thanks for the input.
Would you suggest the Pro series or the Nitrous Pro series carb from Pro Systems? Do I need an adapter for the 4150 to 4500?
I was thinking of using the CNC 335cc AFR heads with the large chambers, but since I should run race fuel anyway maybe I'll stay with about 11.5:1.
I've heard you guys say "no blue pumps", and that was another thing I was going to change. Since the boat has two fuel tanks, I'm trying to think of the best way to run the system because they usually don't draw down evenly - with the two pumps I can shut one off while cruising to even out the level.
I've been thinking of pulling the belt drive off my other boat to get rid of the gear drive.
Also, the engine has 60psi oil pressure in the low range but when you get on it a bit, the oil pressure drops about 10psi. It has a Milodon pump and a 10qt Dooley oil pan.
Brian
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Post by Wolfplace on Oct 7, 2004 0:09:27 GMT -5
Brian, You Definitely need to address the oiling problem. I just fixed a 496 boat engine with that flat pan on it & the pickup had come loose in the pump. It did not last to long that way ;D If your pickup is ok then you need some baffling in the pan to keep the oil around the pickup or you will be giving your machinist job security. If you are considering AFR's I would suggest the 325's with the CNC chamber option. They will flow d**n near what the 335 will to about .600 & are a bunch less money. If you email me I can probably save you a few dollars on the AFR's  |
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Post by BrianB on Jan 30, 2005 13:51:33 GMT -5
I'm still trying to decide what to do about the fuel system. Having two tanks makes it costlier and more of a pain to try to run a bypass system. I would have to put on/off valves in both the supplies and returns. I definitely want to ditch the blue pumps though.
How about the internally regulated Mallory pumps? If I run the system like it is now - one pump for each tank, I can run them independantly or both at the same time for running the nitrous, and not have to deal with return lines. Are the Mallory pumps much of a step up from the blue pumps? Engine should be around 750hp plus 300hp shot.
Brian
PS I've seen some that bypass back to a tee in the supply line before the fuel pump, but I've read that will airate the fuel and can cavitate the pump - any thoughts?
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Post by BrianB on Mar 15, 2005 0:21:23 GMT -5
As a follow up to the oiling problem: I finally got the engine torn apart and found that the end of the pickup (circular portion with the screen inside) looked like it was ripped away from the tube. I fished the piece out of the oil pan and couldn't believe that the metal tore like that.
Brian
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