New 731 Roller or get a Custom Grind?
 

(1) With this combination would it be worth the time to have a custom cam made for my application? Will I see that much of gain in HP?
(2) I was thinking, when you check for valve to piston clearance with a hydraulic roller cam, what do you use for a lifter. I always used a solid hydraulic to push the pushrod and valve?
(3) Any other suggestions would be great.:D

Stroked 496 MarkIV
9:5: Compression Ratio
Edelbrock Marine Heads, Oval , 110CC
Imco Exhaust
RPM AirGap Intake
Barry Grant 750DP
Currently Comp Cam Extreme Marine 270
224/234 @.050 and .550 lift:(

I only want to spin this setup to 5,300 RPMS Max

Re: New 731 Roller or get a Custom Grind?
 

Jim,

I have several Hydraulic roller (and non-roller) lifters that I have modified for this purpose. I take the lifter apart and stack it full of little washers until I can just barely get the snap ring back in. That way you can check pushrod length at the same time. Solid roller lifters are usually a different hieght and use different length pushrods.

Hope this helps,

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Re: New 731 Roller or get a Custom Grind?
 

Call up Crane and get a 525HP Mercury cam.It runs good in alot of combos.They make the cams for Mercury:cool:

Re: New 731 Roller or get a Custom Grind?
 

There are a lot of posts here that will go into this in more detail but the condensed version is that the 731 and other older grinds have upwards of 10* more duration on the exhaust than the intake. This was done to compensate for the relatively poor flowing exhaust ports(compared to the intake ports) of the stock GM heads. The newer heads have much more efficient exhaust ports and do not need that much additional duration. I have heard many reccomendations in the 4* -6* range. Too much exhaust duration on these newer heads actually will cost you HP. For this reason I had my cams custom ground by Cam Motion based on my flow bench #'s for my dart heads. These cams were not any more expensive and they do a great job. Hope that helps.

Re: New 731 Roller or get a Custom Grind?
 

JC's choice is the choice I would make for max power on a 496. That cam is a Crane 741 on a 114 LSA. Don't go with the myth that says that 8* of split is going to lose HP on modern heads. No matter how well the heads flow, you still need the cam to get the air into and out of them. Your drawback to making HP is the parts that you have. The heads don't flow that much. The cam that you have is very close to the 731 Crane, which is where I would probably suggest that you stay based on the parts that you have now. You will see an increase in HP at higher RPMs, but you have stated that you don't want to turn above 5300, which is limiting you. The last 496 (with a 741 in it) I saw dyno numbers for made 611HP @ 5500, and 645 @ 6000, with a Tq peak at 5000 RPM of 588. This was with ported Brodiz heads flowing near 400 cfm @ .600 lift, which is way way more than your heads flow. Just giving an example of the 741 cam HP potential

Re: New 731 Roller or get a Custom Grind?
 

The 731 has a lot more lift than what he has and is only one size smaller than 741.
The 731 is .587/.610 226/236 on a 112 lobe sep
The 741 is .610/.632 236/244 on a 112 lobe sep

The 731 will probably make more usable power in the rpm ranges you'll be in 98% of the time. The 741 will probably make more power above 5500rpms. I would get with OSO member rmbuilder and see what he recommends with your heads.

Re: New 731 Roller or get a Custom Grind?
 

Thanks all. I am trying to contract Bob M. about a custom cam and the $$$ difference it would cost.

Re: New 731 Roller or get a Custom Grind?
 

Which is why I said that the current cam is "very close" to what he has now. I don't believe that with the heads he has, and the RPM that he wants to run, that changing cams is going to have much if any effect on his HP/top speed.

Re: New 731 Roller or get a Custom Grind?
 

If the Edelbrocks are untouch when it come to porting they are around a 70% IE ratio. You're looking for a cam with 10 degree split at .50" and about a 14 degree at seat.

RMbuilder will take care of you.

Re: New 731 Roller or get a Custom Grind?
 

Cam/brain selection is very important. If you really want a good recommendation on a cam with your combination, then at least one person I would consider is to consult RMbuilder's expertise (Bob Madara) of Marine Kinetics and you will be happy!

Re: New 731 Roller or get a Custom Grind?
 

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

Re: New 731 Roller or get a Custom Grind?
 

Why the 14° at seat ?

Re: New 731 Roller or get a Custom Grind?
 

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

Re: New 731 Roller or get a Custom Grind?
 

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.

=====================
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.

Re: New 731 Roller or get a Custom Grind?
 

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Re: New 731 Roller or get a Custom Grind?
 

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.:D

Re: New 731 Roller or get a Custom Grind?
 

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.

Re: New 731 Roller or get a Custom Grind?
 

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.

Re: New 731 Roller or get a Custom Grind?
 

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. :)

Re: New 731 Roller or get a Custom Grind?
 

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.

Re: New 731 Roller or get a Custom Grind?
 

This thread got interesting.:evilb:

Any suggestions for my application:D

Re: New 731 Roller or get a Custom Grind?
 

Sure...
Merc builds a 500 cube engine that makes about 540HP at 5300rpm, the 525EFI...:D
You are building basically a 500 cube engine with similar parts. Why not use the same Crane cam?:evilb:

Re: New 731 Roller or get a Custom Grind?
 

Hmmm...:drink:

Re: New 731 Roller or get a Custom Grind?
 

Cam choices? Yea, same as above. JC likes the 741. He is way out of my league in building engines, but I think thats a bit much with the heads you have, which is why I said that the 731 may be a better choice. The 525 EFI cam IS a 741, just on a 114 LSa, instead of a 112 LSA, so just a bit "milder"

Re: New 731 Roller or get a Custom Grind?
 

Sprinters like to run, Walkers like to walk....you have to work with what you are given.

Ports the flow air quickly: Give them a lobe that opens the valve quick and shuts it quick.

Ports that flow air adequaetly: Give them a lobe that opens moderately quick but needs some time (duration) to allow the head to fill/evac the cylinder.

Ports that flow air poorly: Give them a lobe that opens the valve moderatly but gives the head alot of time (duration) to fill the cylinder.