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540 BBC

Old 09-08-2003, 09:49 AM
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Monty, desk top dyno is not very accurate on the torque numbers below about 3500 RPM. Seems like I remember reading that it can't calculate in that range so it just plugs in numbers. I've found it to be very accurate at higher RPM. I've simulated several engines that were actually dynoed and pretty much confirmed the lower RPM torque numbers are way off. The 731 will definitely give you a lot of torque though. I would expect peak HP to be right around 5000 RPM in a 540 with a dual plane intake.
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Old 09-08-2003, 10:31 AM
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That seems to be true from my experience as well. I used DD2000 to "mock" up the last few engine's I've built and then subsequently dynoed them on Fast Times Motorworks' Superflow and the actual results were within 5hp/tq across the board, but unfortunately, most of these were relatively high performance engine's and the dyno would "grab" below 4000 rpm or so. As a result, I can't say for sure how accurate DD2000 is at low rpms either.

Last edited by Monty; 09-08-2003 at 10:41 AM.
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Old 09-08-2003, 06:33 PM
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hey budah the spec sheet that came with my cam said 130lbs for my 139741 should i change i have the heads at the machine shop so now would be a good time to change
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Old 09-08-2003, 06:56 PM
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Monty,

You need to go back to my first post within this thread and read what a REAL DYNO TEST did with my 540's and the cams I used that are identical almost to the "T" compared to the 741 cam and fully ported aluminum heads with a Dart intake. In a heavy boat like a Cigarette I would definately use a good dual plane intake manifold. You are being wise and I respect you that you are at least considering the smaller cam---- it seems everyone always wants to install the largest cam they can get away with in an engine when they don't need it. I like the way you are really thinking taking into consideration of all your engine components---especially the cam! Your mindset is that you want reliability and dependability, good idling and drivability around the docks FIRST---not just speed and horsepower----although I will say that a 741 cam is still considered a somewhat mild cam for a 540 inch engine.

I have seen many guys who put really BIG NASTY cams in their engines that require high idles, fouling out plugs and can't even shift without the engine dying and they have ONE HECK OF A TIME when trying to manuver around the docks, boat traffic, wind and river currents. They suddenly don't look so cool anymore because they operate their boat with panic mode movements and over compensate...i.e. while trying to shift into reverse the engine dies and the boat is still moving forward towards another boat, seawall or other object that they are trying to avoid hitting. With the cams in my 540's (identical to the Crane 741 on 114* lobes) will idle at 800rpm in nuetral and what is really nice is that they will idle at 600-650rpm in gear for long periods without dying.
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Old 09-08-2003, 07:10 PM
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Hey Mark,
My big ol nasty cam idles at 700 in gear with no problems !

Now getting lifters to live is a whole other story !
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Old 09-08-2003, 07:21 PM
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Kaama,

Thanks for the reply. I'm new to boats, but I've been hot rodding for several years. I know I'll never be the fastest guy on the lake with the Mistress, I just want to be able to have decent performance reliably without all the headaches. To be honest, I'm wondering if I woulda' been better off just building a pair of decent 454's since even my mild 540's will probably push the limits of the TRS's. I'm even considering using the stock cast iron intake manifolds to intentionally detune(choke) the engine, as well as ensure it all fits under the stock hatches. If I am able to fit an aftermarke tintake, it'll definitely be a dual plane (although a pair of custom Hogan's sheetmetals would be trick - got one on the Vette). I've already got a pair of Performers that Too Old gave me.

One of the reasons I'm leaning towards the 371 is that the boat came with Stainless Marine manifolds and risers and I'd like to be able to use them for now. SM recommends cams with less than 230* duration in order to prevent water reversion. I haven't called them yet, that's just what they have in their FAQ's. I'll probably call them and see if they have an overlap recommendation rather than just duration. Their recommendation is probably based on a 110 or 112 LSA. A 114 LSA would generally provide a relatively broader and flatter torque curve while allowing a little more duration with less overlap compared to a narrower LSA cam.

BTW, I looked back over your first post as you suggested and noticed you've got a "hole" in your torque and hp curve at 3500rpm - at 3000 it is 614tq, 3500 is 598, then 4000 is 662, and your hp makes a 105hp jump from 3500 to 4000 rpm. Was that a typo or just tuning? The math works out, (598 x 3500)/5252 =398.5, so I was just wondering. Big mechanical secondaries coming on, or just eh dyno starting to grab?

Last edited by Monty; 09-08-2003 at 07:24 PM.
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Old 09-08-2003, 07:21 PM
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Chuck,

I am mainly speaking about guys I would see back in the 1980's who didn't know better back then or who were ignorant about cams durations for marine use and just wanted to go fast. You on the other hand have done your home work and know better.----Besides, if your cam is idling at 700rpm then I think most would agree it really isn't too big and you have made a good selection for your engine!

Last edited by KAAMA; 09-08-2003 at 07:24 PM.
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Old 09-08-2003, 07:32 PM
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Mark,
Thanks for the complements. And I thought I just got lucky !

Hopefully with Budah's help and a new camshaft I can get the valvetrain a little more reliable. As I've learned snowmobiling and now finally it's sinking in on the boat , RELIABLITY is the key word.
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Old 09-08-2003, 07:37 PM
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Originally posted by Monty
Kaama,

BTW, I looked back over your first post as you suggested and noticed you've got a "hole" in your torque and hp curve at 3500rpm - at 3000 it is 614tq, 3500 is 598, then 4000 is 662, and your hp makes a 105hp jump from 3500 to 4000 rpm. Was that a typo or just tuning?
Monty,

NO---that was not a typo! Actually/honestly, I was going to go with a smaller hydraulic roller cam too---BUT Crower accidently sent me the wrong (larger) cams! I originally ordered a pair of 232*/240* cams from Crower, but they sent me the 236*/244* cams by mistake and my engine project was WAY BEHIND so I knew they would still work well,------I almost sent them back because I was a little HOT about it, but I decided to installed them anyway.
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Old 09-08-2003, 07:44 PM
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BTW Monty,

I think if I would have had a dual plane intake on my engines instead of the Dart single plane that hole in the torque would have not even showed up!

Last edited by KAAMA; 12-03-2004 at 08:39 AM. Reason: I made a statement that I shouldn't have
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