Please Vote: RV Cam - Team Camaro Tech
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post #1 of 11 (permalink) Old Feb 5th, 08, 08:19 PM Thread Starter
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Please Vote: RV Cam

'73 Chevy 3/4 ton 2wd with occational towing. Here is the setup:

'73 454 with stock rotating assembly
Performer 2.0 intake
781 heads
Performer 1411 750 carb
HEI ignition
TH400
Gears are 3.54 to 3.73



1) Crane Energiner 266 duration .499 lift
2) Comp High Energy 260 duration .475 lift
3) Comp High Energy 268 duration .485 lift

All cams are single pattern with LSA of 110

Where I get unsure is the relation of duration to lift. Some cams will have less duration to lift than others and vise versa. Just not sure what more or less duration does for an application and the same for lift. Thanks!


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Last edited by dubs68camaro; Feb 5th, 08 at 08:52 PM.
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post #2 of 11 (permalink) Old Feb 5th, 08, 08:47 PM
 
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Re: Please Vote: RV Cam

Funny you ask. I used a COMP XE268h in my fresh 74 454 Vette. (automatic) CR = 8.25/1 It ran great, but the idle was too rough, especially since the wife drives it quite a bit. It made good power and sounded great, but I just didn't like the way the car felt.

That XE cam has less than 400 miles on it and is now for sale along with the matched lifters.

I replaced it with a COMP HE260h...your #2 choice from above.

SMOOTH idle and MORE power than the 268. CRAZY torque through about 4400 rpm. Noticible better mpg than the 268. I love the way this motor runs now. No horror stories about "wiped lobes" with the older ramp design as compared to the "more aggressive" ramps on the XE models. All around I think the HE260 is more dependable and streetable.
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post #3 of 11 (permalink) Old Feb 5th, 08, 08:51 PM Thread Starter
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Re: Please Vote: RV Cam

Thanks....I would not go with an extreme energy cam at all. Everthing above is in the high energy line.


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post #4 of 11 (permalink) Old Feb 5th, 08, 09:35 PM
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Re: Please Vote: RV Cam

http://store.summitracing.com/partde...0&autoview=sku

Hard to beat the price tag on the little Summit cam kits. This is their towing BB cam. Split pattern to help exhale.

Duration is how long the valve is open. In a perfect world the valve would only be open 180. But engines don't see things our way and we have to keep them open longer to move the power band around to suit our useage. High duration cams run like **** down low because the valve is open when it really should be shut, until RPM comes up(and time decreases) and things smooth out.

In a towing application your rpm will be low most of the time but the load will still be high. You need your engine to not act a fool down low, so you need less duration because in addition to having the valves closed closer to ideal, less durastion minimizes overlap or the period when intake and exhaust are both open. High overlap is what causes our lopes we love in hotrods but also makes em weak down low. So less duration = less overlap and gives an engine a better low rpm air/fuel intake charge.

The relationship of lift to duration in most apps is limited by how aggressive they want the lobe to be. With less duration they get less time to open the valve. Opening the valve further is a good thing in most applications until they break the speed/acceleration limit for the particular lifter style and get the edge of the lifter too close to the lobe and it barfs

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post #5 of 11 (permalink) Old Feb 5th, 08, 10:27 PM Thread Starter
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Re: Please Vote: RV Cam

That was a nice explaination Tim. I guess that's why those 8,000 rpm strip SBC's have so much duration in them. One thing that confuses me though is that I thought I read some posts from that guy Harold or Harvey or someone (sorry, but I can't remember his name) that did a lot of cam designs for some of the major brands.......It seemed that he was shying away from split patterns in my application. I will say this though: I had a Crower 260/266 in my 460 (which is in my SWB now) when it was a tow application, and that thing had retarded amounts of torque (retarded being a good thing)


P.S. Does UCHAROLD sound right? The guy that is?


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post #6 of 11 (permalink) Old Feb 6th, 08, 04:27 PM
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Re: Please Vote: RV Cam

The cam guru's use dual pattern or single pattern for lots of reasons, but usually it has something to do with compensating for low lift or poor head flow to get more exhaust out of stock heads or heads with a low intake/exhaust flow ratio. I think they like i/e ratios up close to 70%. You could go to Stan Weiss' site and see if he has the flow #'s for your heads....
http://users.erols.com/srweiss/tablehdc.htm#Chevy

UDHarold, Harold Berkshire. Ultradyne, Comp, Lunati

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post #7 of 11 (permalink) Old Feb 6th, 08, 05:14 PM
 
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Smile Re: Please Vote: RV Cam

Please consider this UDHarold cam.

272/272, 217/217, 112/? .515"/.515" lift hy-cam.

Harold said back then that it was the best cam for pulling trailers, car-hauler or boats.

"Excellent bottom end and mid-range torque. Works power accessories. 1600-5500 rpm."

I don't know if he has created a better, modern version of it or not?

pdq67



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post #8 of 11 (permalink) Old Feb 6th, 08, 05:36 PM Thread Starter
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Re: Please Vote: RV Cam

Quote:
Originally Posted by pdq67 View Post
Please consider this UDHarold cam.

272/272, 217/217, 112/? .515"/.515" lift hy-cam.

.......I thought a tighter LSA (like 110) increases your torque? That just seems like a lot of lift for a stock, daily driver. I was hoping that if I stayed in the .475 lift range, I could get away with my stock springs. This is a $1,000 vehicle and I would just as soon my $$$ go toward one of my other products.

LOL...this seems to be getting more difficult.....not easier!

The truth is that I probably would have trouble really "feeling" the diffs with any of these cams.


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post #9 of 11 (permalink) Old Feb 6th, 08, 05:40 PM
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Re: Please Vote: RV Cam

Quote:
Originally Posted by dubs68camaro View Post
.......I thought a tighter LSA (like 110) increases your torque? That just seems like a lot of lift for a stock, daily driver. I was hoping that if I stayed in the .475 lift range, I could get away with my stock springs. This is a $1,000 vehicle and I would just as soon my $$$ go toward one of my other products.

LOL...this seems to be getting more difficult.....not easier!

The truth is that I probably would have trouble really "feeling" the diffs with any of these cams.
Hard to beat the little 100 buck Summit cam kit

Here's what Harold told this guy

http://speedtalk.com/forum/viewtopic...ghlight=towing

Tim Smith
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post #10 of 11 (permalink) Old Feb 6th, 08, 05:57 PM Thread Starter
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Re: Please Vote: RV Cam

You know Tim....one thing I forgot to list was that I will have 1 3/4 inch long tubed headers with dual exhaust and an h pipe. Will that cancel out the need for the split duration and lift???? Thanks again to you and PDQ


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post #11 of 11 (permalink) Old Feb 6th, 08, 06:57 PM
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Re: Please Vote: RV Cam

Ain't gonna bull**** ya Dub, Idunno. The headers would have to help it feels like to me because of freer flow. But compensating for an i/e port flow imbalance doesn't feel entirely true.

All our work trucks had manifolds...the old man didn't want the noise after working in noise all day. I am the same and not the least ashamed of it. Gimme quiet after being around screaming behemoths all day. But you could damsure feel the difference in an RV cam and a stock cam. Especially in a big block but man that was a long time ago. Hell, I've been running diesels 20 + years I realized the other day. Even my personal truck.

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