73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Performance => Topic started by: Skunksmash on June 08, 2009, 03:15:56 pm
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Hi all I just wanted to ask what the biggest cam was that you could have, before you got a rough idle. This would obviously be considered a mild cam, but i understand there to be varying degrees of mildness. Im sure there are ones with taller lift durations than the factory ones, that would just barely be under what starts to give a rough idle. Anyone know which one would be the best for this? I want the most performance i can squeeze out, but i want the idle and ride to be smooth. There is sort of a line you can walk if you do it right.
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http://store.summitracing.com/partdetail.asp?part=SUM%2DK1102&view=1&N=700+
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"Rough idle" is a relative term. I've heard people (not me) refer to the Comp XE268 cam as having a fairly smooth idle. Others consider cams in the size range that Vile posted above as having a mild lope.
If compression is 8.5:1-9:1 this is my idea of a good entry-level cam: http://store.summitracing.com/partdetail.asp?part=ISK%2DCL201264&autoview=sku
But I plan to use a cam like this one with a decent idle (slightly smoother than XE268): http://store.summitracing.com/partdetail.asp?part=ISK%2DCL201271&autoview=sku
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maybe i should have put it this way: Is there a bigger cam than the factory one, that will run as smooth (or close to as smooth) as a factory cam?
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The one I posted
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I have this....
Hydralic Flat tappet Cam
Advertised Duration is 280 Duration @.050" 214 .295" cam lift X 1.6 = .472" Valve lift
Ground on a 110 Lobe center.
I have 1.6 rockers --2.02 int; 1.6 exh
I love this cam. It is considered an RV cam, taking advantage of lower rpms for higher torque down low for my 383 stroker. She has a very slight lopey idle, just enough to sound fun. My wife always thinks its getting ready to cut off. She alway asks "what's wrong with it?" I laugh. She knows nothing about engines.
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maybe i should have put it this way: Is there a bigger cam than the factory one, that will run as smooth (or close to as smooth) as a factory cam?
The one I posted
Yeppers
The ones I posted would both make for a "noticeable" idle but not a rough idle.
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Thanks. I want it to be on the lower end of noticeable. If it's noticeable at all, it should be just barely. Pretty much hard to tell it's not stock. What about a roller version? I was considering converting to a full roller motor due to the increased efficiency of them.
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I was talking to a buddy and he was talking about a cam he just got. I think he called it a Thumper cam, sounds radical at idle but the power band is 2200 on up. He was talking it is about the same lift as a stock cam and there is a web site that you can listen to it. Supposedly meant for a stock engine.
http://www.compcams.com/thumpr/default.asp click a listen...
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What about a roller version? I was considering converting to a full roller motor due to the increased efficiency of them.
From a performance perspective, the difference between flat tappet cams and roller cams in that size range is minimal and not worth the investment. Move up a few notches in size and the roller cam begins to really shine. From a durability perspective the roller wins, but with such a mild cam I wouldn't expect problems, unless you neglect to break it in properly or run high spring pressure.
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I have a Comp XE268 and it's noticeable idle for sure without being rough, (rought meaning it has to idle above 1000 just to not stall and still shakes the heck out of the car). Mine can idle around 700 in Drive and it shakes around nicely but smooths out when I put it in Park and the idle goes up to 900 or so. If you are looking for stock-style smoothness, the XE268 would be too much. The XE256 might be more for your liking.
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Yeah i am looking for stock-like smoothness in all RPM ranges. I just thought that ya might be able to go slightly larger than stock and still have the stock smoothness. You know how they always leave lots of room for improvement...
But now that we have established the cam, what would be the best most efficient set of aluminum heads to go with such a cam? There would come a point where i could overpay for heads, and not get the benefits out of them due to the mild cam.
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If you're gonna use a mild cam like that don't waste your coin on aluminum heads.
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Go with 170cc ports and no larger. And I'm with Vile; no reason to waste money on aluminum. Vortec L31 heads would be a really nice choice. With 8.5-9:1 CR and that cam, you'd have the makings of a snappy little 87 octane motor.
Though, if you are dead set on aluminum, I like the Edelbrock Performer RPMs or their E-tec 170s. Also if you can get a set of good used Corvette L98 heads, those would be perfect. Their flow numbers, while not spectacular, are good and they have tremendous swirl characteristics. Perfect for making the most out of mild cams.
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Thanks. Though i doubt i will ever be able to come across any vette heads for any kind of decent price. What about a roller cam for this type of desired application? I would like a full roller motor if i can...
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Thanks. Though i doubt i will ever be able to come across any vette heads for any kind of decent price.
You might be surprised. Their are complete Corvette L98 pullout motors out there for the taking. This would be the best way to get aluminum heads, roller cam, and fuel injection all in one (late model LSX swap, of course, would actually be the best way).
What about a roller cam for this type of desired application? I would like a full roller motor if i can...
I answered this question above. I've heard Vile advise other members that same way. Maybe you want to hear directly from him first though. But if you really want a roller cam and have about $500 for retrofit lifters, go for it, as they certainly have advantages over flat tappet. Just not enough performance gain to justify the cost in this size range, IMO.
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Oh. Well i just thought it would help with power and efficiency a little. All new motors are full roller, so i figured it would still help out. Although i must admit i am not sure what you mean about retrofitting or whatever. If i had new aluminum heads (i am set on aluminum) then they should not need anything special for roller setup, correct?
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Although i must admit i am not sure what you mean about retrofitting or whatever.
These (or some like them) are the lifters you would need for a pre-'86 non-roller block: http://www.summitracing.com/parts/CCA-853-16/
These are for a '87-up roller block: http://www.summitracing.com/parts/NAL-12371042/
Notice the price difference. Also, if you are retrofitting a roller cam into a pre-'86 block, you must use some sort of thrust button to control camshaft endplay or you'll have some erratic ignition timing.
If i had new aluminum heads (i am set on aluminum) then they should not need anything special for roller setup, correct?
Yes, there are different requirements if you are buying assembled aluminum heads. Rollers need more spring pressure both on the seat and over the nose. So make sure that the heads come with springs that match the requirements of your cam.
Unless you want to try your hand at some cheapie Pro Comp heads, I really like these: http://www.summitracing.com/parts/EDL-60979/
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Well that raises another question for me. How can i determine if my 87's engine is one that came with rollers, and not flat tappet?
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I'm sure there is someone who can decipher engine casting #'s, but the most sure fire way I can think of to determine which lifters you need would be to pull the intake manifold. If if has a row of three raised drilled/tapped bosses down the center (to bolt down the sheet metal spider that retains the lifter guides) you have a roller block.
Also I might not have mentioned earlier, if you have a roller block the actual camshaft (and timing chain for that matter) is different. Roller blocks use a bolt on plate to control cam thrust and the cam must have a "stepped" nose to accomodate this plate. Retro-fit cams will have a nose like any other flat tappet cam and, like I mentioned earlier, require a thrust button.
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Hmm, so it's best to buy a roller block if you are building a roller motor. Anyone know where exactly i can find my engine's casting numbers? It is still in the truck, so please bear that in mind heh
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Look on the back of the block near the transmission on the drivers side.