the duke

OMG Chris, this is a first. you and I agree on a cam choice.

SB

iTrader: (1)

Why the 14° at seat ?

cstraub

Exhaust port is not great but it's not to bad either. It needs a nice fat bottom lobe to get the gases out.

SB

iTrader: (1)

I believe I understand where you are coming from, but my thinking is that if you are going to start releasing comb pressure why do it slowly - ie: longer seat to .050" ? You'll get some pressure release but not a whole lot of flow.

If we want max exhaust flow, why wouldn't we get the exh valve to open faster ? Less psi to help evacuate the exhaust at 'flowing lifts' doesn't seem as favorable to me as more psi at 'flowing lifts.'

The pressure decay of a low compression engine (piston going down during power stroke) isn't that fast and the psi itself isn't all that high - compared to higher compression engine.

So, if we decide on this 10 degree split is best for this certain engine, why wouldn't we open it then and get it open as fast as possible to use the combustion pressure to our adavantage ?

Again, the piston is going down here, therefore we are using only pressure differences to evacuate the cylinder.

As we know, the more gases left in cylinder the more pumping losses we'll see as piston then comes up and has to force rest of exhaust out.

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I've studied a lot of wide exhaust seat durations this past year and a bunch of motors + applications will like up to 10 degree seat and at .050" (not all of course - many like lower)spread but I've very rarely seen any respond to say 13,14, or etc spread. Reading on the 12-16 spreads with very high compression and/or nitrous and/or big boost SC engines, has revealed this still causes some power loss (not that much because of higher comb psi - psi decay quicker because of high psi) but is to releive the parts eating heat that would cause problems if exh valve was closed a little longer.

BTW: Studied means I'm still looking at this stuff, and thus why my questions. It's pretty interesting and a pretty deep area of information. Therefore, I'm not poking but just trying to pick your brain - as I'm doing with many others on this subject - to see as many explanations / theories / experiences on this subject. Always more than one way to skin a cat. Poor ol' cat. LOL.

the duke

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the duke

There are a lot of blower motors out there with even more split than this making well over 1000 HP with 540's, and not leaving any power on the table,

You are over analizing this whole cam thing. Its not anywhere near as complicated as your post implies. Changing the numbers by 1 or 2 degrees one way or the other has little effect on a BOAT motor. A drag CAR yes, a boat no.

We all want to get the most HP that we can within reason, but going through all this agravation to gain 10 or 15 HP in a boat is just beating yourself up.

How many hours(months) did you spend building your motor that made in the mid 500 HP range? That same motor could have been built in a week using off the shelf parts, with no agravation. The rest of the time could have been spent on the water.

KAAMA

iTrader: (1)

True, might be splitting hairs, but I guess it could be argued both ways.....and I know I am preaching to the chior here, but I would think that for as much as it costs for HP these days---especially in light of making a boat go faster, that paying a few bucks more for a cam that is a little more suitable for a non-stock engine is pretty low cost wise in comparison. I mean, if you're going to spend the money on a cam (probably the most important component of an engine), then why not spend a few bucks more for a cam specifically designed for a specfic engine??? That is unless of course a person is on a really strict budget. A few HP here and there all add up and boats are hard enough to make them go faster as it is so, depending on what a person wants to do, then every little bit counts....it's usually found in the small details.

So, 15hp here, 8hp there, maybe another 10-15hp from somewhere else you could be talking about maybe 40+ additional HP from a nicely tuned engine that usually will get someone's attention. Now we're talking about something that will make some difference....cuz overall, it all adds up.

Bob Madara provides good cam advice for a few bucks more. He takes all the guess work out of it and you can feel confident with the choice he has made for you. There have been several guys who come on here asking for cam advice because they or some how ended up with the wrong cam selection and causes them all kinds of grief.

A custom cam grind is just an option, nobody says you or anyone has to do it. You can continue to argue it your way if you like, but I usually try to offer it up as an option for guys on here---that's all and Madara has a excellent reputation with cam selections.

the duke

You're correct, when you add 5 different pieces at 10 HP each, you are talking about HP that is worth finding. But I was talking about the HP increase from a cam change only, not a bunch of other stuff. I can change from 1.7 to 1.8 rockers and usually gain hp, and thats a free bunch of power, as I need rocker arms anyway. But you can go the other way, and pay $200 here, and $200 there, and all of a sudden you are spending an extra thousand dollars that you didn't have/plan on spending.

I never said a word about RM builders cam picks. I have NEVER seen a set of dyno numbers for one of his motors compared to a "shelf" cam to tell if they are good or bad. I've not heard bad, so I have to guess that people are happy, which in the marine industry is a good thing.

I try and offer up choices to people that ask questions too. I try and make the choice as simple and straight forward as I can. I can't tell you what cam to use in a 598 blower motor, but I sure can tell you what I know works in the 454's/502's. NA motors. Boats are expensive and confusing enough to people, that when you start giving them tons of tecnical info that doesn't mean anything to them, that they can get confused in a hurry. If I can say call Summit and order these heads, this carb, and this cam, and you are good to go for x amount of HP, I feel that I am trying to keep their life easier, and I know that what I told them to do will give them a dependable motor that will run as they want it to.

KAAMA

iTrader: (1)

I am not in total disagreement with you---just trying to show the flip side when it comes to cam selection.

I guess I keep failing to mention that Madara only charges roughly $50 or so extra for one of his custom cam grinds. So, if one of his custom cam grinds provides an additional 15hp, then if you do the math that equates to only about $3 and some change per 1hp for one of his cams. That's some pretty cheap HP. I mean, if you're looking to upgrade your engine and you want a bump stick that makes more power, then a person would have to ask themselves; "what's $50 extra for a cam that has been custom ground to my liking, and for my application???"

I only mention Bob's name because after working with him on my project he is of the few who can be trusted---especially in light of all the wolves in sheep's clothing within the marine industry and what I had been through before with others who want you to trust them only to find that they are cons---they still manage to show up on here from time to time. Anyway, Bob has proven himself on here with many guys who have needed cam help so, I am only pointing them in the right direction towards someone who I KNOW has the ability and integrity to help them.

Great! So, now that you know Bob Madara only charges about $50 or so more for one of his custom cams, then why don't you join me in offering it up at least as a very feasible and affordable option? I mean, if you're saying you want to try and keep the "confusion" to a minimum, then Bob would be one of the best guys to talk to about cam selection----he makes marine engine life a little easier, and takes out all the worry, confusion, and guess work. However, every now and then I recommend a cam to guys too with 454cid engines that I know have worked well in the past, but usually end up mentioning Bob's name because the cost factor is hardly enough to be concerned with---it's almost insignificant.

the duke

Which is the reason that I said ""I've not heard bad, so I have to guess that people are happy, which in the marine industry is a good thing""


I don't totally disagree with you on this. As I said, I have no experience with Bob, nor have I seen any results of his cam picks. So with that being said, I am not qualified to tell someone that he is who they should call. You have dealt with him, and are happy with his work, so you are qualified to tell people to call him. I try to only answer questions that people ask when I'm sure that the answer is correct, based on my own experience, or results that I have seen myself.