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  #31 (permalink)  
Old 02-16-2009, 10:35 AM
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Quote:
Originally Posted by curtis73
These are all great discussions, but something I want to add that I don't think we mentioned...

Overlap is one of the big determining factors with MPG. You didn't list LSA numbers for those cams, but its possible that a cam with a longer duration, wider LSA (and therefore less overlap) can make better MPG numbers than a smaller cam with more overlap. But its also not usually advisable in a naturally aspirated engine to go with a big duration and a big LSA in search of power and mileage. That usually leads to disappointing dyno numbers.

Otherwise, I second the vortec recommendation. Their chambers are very nice; much more inspired than anything before them. They allow for much more compression on cheap gas, and the fast-burning characteristics mean you only need about 32 degrees total ignition lead. That means 9.5:1 on 87 octane depending on cam.
I don't mean to turn this thread, but this is getting into the focus of what I was really getting at. What would my compression be with a 64cc chambered head. I was told 11-12:1. I do not think it will be that high.

On the cams, they are all on a 112lobe center. The grinder mentioned he can put them in a 110 for a little lope we like, but said something about still not enough duration to get the nice sound. What would changing to a 110 on the first cam do.

Lastly,
Regarding part of your comment here

"but its possible that a cam with a longer duration, wider LSA (and therefore less overlap) can make better MPG numbers than a smaller cam with more overlap. But its also not usually advisable in a naturally aspirated engine to go with a big duration and a big LSA in search of power and mileage".

Can you give me examples of such numbers. I am learning what this duration stuff is all about. I think once I get it, I can pinpoint how I want this thing to behave on the streets/hwy.

The grinder said that I needed to be in the 220's and up to get the nice lope, but now that's way up in duration and poor gas mileage right. There's something I read here about not going over 219 on a daily driver. Look at the camshaft paragraph here http://www.sun-engineering.com/prod02.htm

I think my problem is I want the best of both world, but am NOT willing to sacrifice sound for drivability.. so what do you do.. build two cars/motors...

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  #32 (permalink)  
Old 02-16-2009, 12:28 PM
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Quote:
Originally Posted by Carlos9
On the cams, they are all on a 112lobe center. The grinder mentioned he can put them in a 110 for a little lope we like, but said something about still not enough duration to get the nice sound. What would changing to a 110 on the first cam do.
if they're all on a 112 LSA, then adding duration will always add overlap, which has a tendency to reduce MPG. Reducing LSA to 110 would very quickly increase overlap and most certainly reduce MPG.

Quote:
Lastly,
Regarding part of your comment here

"but its possible that a cam with a longer duration, wider LSA (and therefore less overlap) can make better MPG numbers than a smaller cam with more overlap. But its also not usually advisable in a naturally aspirated engine to go with a big duration and a big LSA in search of power and mileage".

Can you give me examples of such numbers. I am learning what this duration stuff is all about. I think once I get it, I can pinpoint how I want this thing to behave on the streets/hwy.
Sure. For example, Let's take a look at two cams.
214/224 duration, 110 LSA yielding -1 degree overlap @ .050" lift
218/228 duration, 113 LSA yielding -3 degree overlap @ .050" lift

The second cam has more duration, but the wider LSA gives it less overlap. There is no real way to predict MPG, but there is a good possibility that the second cam in this example would produce better MPG... at the expense of a potentially less desirable torque curve. Excessively wide LSAs just suck, especially when you are trying to use them as a crutch. Anytime you try to pick a cam, pick the RIGHT cam. You will most likely be disappointed if you try to add duration in search of more power and then reduce your overlap with more LSA.

Quote:
I think my problem is I want the best of both world, but am NOT willing to sacrifice sound for drivability.. so what do you do.. build two cars/motors...
You absolutely can't get the best of both. You can have some of both, but as you increase lopey-ness, drivability and MPG will suffer. As you do things that increase MPG and streetability, the lopey idle goes away. There is no such thing as a lopey-idle, high mpg V8. Lopey idle by definition means intake reversion, which means that torque and HP peaks will occur higher up in the RPM range. Any time that happens, you are working your way toward a purpose-built, narrow RPM range race motor.

Its possible to get lope for the street, but heavy vehicle + lopey idle = FRUSTRATING to drive. Many people do it because they so desperately desire that lopey idle that they'll put up with anything to get it, but you also probably notice that you only see them at cruise-ins instead of regular daily-driver commuting. Anyone can put up with a cranky engine for one weekend a month.

Last edited by curtis73; 02-16-2009 at 12:38 PM.
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  #33 (permalink)  
Old 02-16-2009, 12:53 PM
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My point exactly.. This guy I deal with is a race head.. and can't seem to slow down/program his mind to help me build a good street driver. I am thinking about adding link bar rollers also so I can go roller. If I do not do it with the initial build, can I add a roller later (by adding roller cam and linkbars) do I need to change the cam bearings.. or will a roller cam use the same bearings with no problems. I say later because it's really not in the budget right now.

I know he will be mad as hell (not going 270) but to be honest.. you think I give a.. Will the idle be totally smooth with the first cam. What type of idle will I have. I know I am probably doing overkill to the 3rd power on this post, but I know what I want and just want to do it right the first. Torque is king.

Seriously thinking about the vortecs. I am starting to finally BELIEVE they are better than the ole irons. I guess the port design/chambers is what makes them. And they do really well at lower lifts.

On the fist cam would you recommend advancing the cam 4 degrees or run it straight up. Thanks for the explaination on duration. There's still some gray areas there, but reading back thru the post helps a little. Someone mentioned earlier about me not seeing it with the smaller cam, but I was just trying to figure out what would a little bit more do to me (the second cam). I still think the 2nd cam is on the conservative side. With both cams it depends on how you drive, but you will have to be a bit more cautious about driving styles with the second.

Last edited by Carlos9; 02-16-2009 at 12:59 PM.
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  #34 (permalink)  
Old 02-16-2009, 05:58 PM
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build 2 cars/trucks

alot of us have 2 cars, for the reasons you described!
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