spencnaz wrote ... I was looking at a cam with the following specs
Intake 278
Exhaust 288
Intake lift .420
Exhaust lift .443
Duration at .050 = 204/214
It has a speed range of idle to 4400 RPM which I think will be quite good with the 3.23 SureGrip rear.
I'm not looking to win any screaming drags, just get good solid torque on the freeway for passing and cruising at 70 or so.
I think this cam would have to choppy of an idle to work with the stock converter: the Mopar magnum style cams (268/284))are about all you can run without getting a higher stall converter.
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204/214 @ 50 is a baby cam. What I'd be more concerned with is that it seems to have reaaaaaaaaaaaaaaally lazy lobes with all that duration at .006 but only 204 @50. What brand is it?
The stock magnum cam is not aggressive in any sort of way. If you're looking to not spend very much dough I'd go with that, certainly over the one you've spec'ed in here.
Do you have additional research that points to the usefullness of that offy intake? I understand what the idea was being the design, but the execution doesn't seem to play out in terms of economy or power.
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I have another cam here that is 260/268 with .050 duration of 206/209. Lobe center of 113 degrees.
It's said here in the cam kit information that this cam is a direct replacement for the 330hp 383 cam. A great benefit of this kit I have my eye on is that it comes with everything and I mean everything, lifters, springs, lube, gaskets, the whole smack.
As for the Offy intake, I've used Offy intakes in the past and know that they don't make junk. My research shows that intake velocity is critical for optimum cylinder filling. The smaller primary intake ports provide this rapid intake flow. Sir Harry Ricardo's research on the internal combustion engine showed that an intake velocity of 180 feet per second was the magic number to keep the fuel particles in suspension.
C-bodies are heavy cars, the Offy intake favors torque which is what our cars need. If you keep an engine at peak torque RPM (which means maximum brake mean effective pressure (BMEP)), engine economy is maximized. My goal is to use a stock or RV type cam to get max torque and a good horsepower boost for freeway economy.
I see a Comp Cams kit here. Here are the specs:
XE268H
268 intake
280 exhaust
224 intake at .05"
230 intake at .05"
.477 intake valve lift with 1.5:1 rocker
.480 exhaust lift with 1.5:1 rocker
110� lobe separation
Notice the closer lobe separation angle than the previous cam grinds. This tells me that this cam would be optimized with use of headers. <span class='smallblacktext'>[ Edited Tue Jan 13 2009, 10:16AM ]</span>
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I understand the theory you are talking about for the intake stuff, but I really don't understand how an intake that makes less TQ @ 3000rpm than _any_ other dual plane tested and the same as the _big_ single planes qualifies for your stated goals for the car:
All other things equal (which they were in this test), a manifold that is down on power = a manifold that is less efficient. While they were not posted, I would expect a worse bsfc # from the Offy intake than the other. From the article
wrote ... This intake caused the engine to prefer rich mixtures, with an 11.2:1 air/fuel ratio at wide-open. Anything leaner and the engine lost power.
That intake seems, by the empirical evidence in this test, to be a science experiment that didn't work.
I'll give you a 2nd experiment. I at one time ran the street dominator intake on my 383 with the comp 270H cam and 3.91's and a 750holley. I was very disappointed with the way the engine ran. It would hardly do a power brake stand and would not spin the tires from idle. Later that same year I put the stock 666 intake on and went back to my 3.23's. The car was noticeably peppier off idle, would spin the tires and do a better brake stand. The difference in usable, real world TQ was incredible for only changing the intake AND putting more mild gears in. MPG went up too of course with both changes.
You do as you like, but IMO you might as well not bother with a different cam if you're insistent on running that intake.
<span class='smallblacktext'>[ Edited Tue Jan 13 2009, 02:56PM ]</span>
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also of note, the offy tunnel ram was bad too. The word 'junk' is subjective I suppose, but I don't know how anyone can read both parts of that article and not come away with the BB Offy pieces being junk....
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One mans junk is another man's treasure. My research also shows to have as much manifold vacuum as possible during cruise throttle for economy.
The test that I have for the Dual Port showed that it has a high, consistent manifold vacuum. In addition to the acetone I put in the fuel (2oz per 10 gallons on gas as a surface tension breaker), have been most helpful in the mileage department.
I have been noticing an improvement in power, but of course anything could be better than a 2bbl carburetor on it's last legs.
From what I've read in this article a 256 to 268 duration cam would fit the bill for what I need out of this cruiser.
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you can have all the manifold vac. you want, but if the WOT richness issue with this manifold also translates to it needing more fuel at cruise to not lean surge, you're going to be wasting fuel vs. any other intake substituted into your system.
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I appreciate your help, but I think you're missing the point. This system is being designed as a whole, not just one component.
The combination of manifold, carburetor, cam and exhaust is being designed for good fuel economy and power.
That's why I wanted to know what a good cam grind would be. I do not plan on revving this engine past 4500 rpm, so low to mid range power is going to be the norm.
The Comp Cams XE268H has newly designed ramps for fast valve actuation, and is too much cam for what you want to do with your engine (it loves to rev up above 5500 rpm).
For the torque you're looking for, stick with an RV grind, or the factory 68-69 383 2bbl cam which is basically an RV grind, around 256/260.
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well, I'll for one be very interested to see your mpg, dyno, and bsfc #'s when you put it together. I've got a dollar bill that says a stock magnum spec motor and a magnum type motor with my choice of intake, carb, and headers would beat your system at your own game But hey, that's what keeps this hobby interesting. <span class='smallblacktext'>[ Edited Wed Jan 14 2009, 08:22AM ]</span>