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Unread 09-09-2014, 07:04 AM   #1
robco
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which cam to use in a 258?

I know this has been talked about many times but I have to do it again. Im rebuilding a 258 for a frame off scrambler build. It will be bored .060, use the stock head, an offy intake, headers, hei ignition, and im thinking a 390 holley with the avenger mods. It will have 4.88 gears and 35's. Since this is a frame off build it will be mostly street but it will see some 4 wheeling. I was thinking a comp cam but they make several that seem to suit what im doing. Any suggestions on one making more power than another? Thanks.

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Unread 09-09-2014, 07:19 AM   #2
swatson454
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Are you looking for outright, low-end grunt with a smooth idle? You have the gearing for a little more but it's up to you.


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Unread 09-09-2014, 07:34 AM   #3
robco
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Im not worried about a smooth idle at all, im just not wanting to have to turn 3000 for the power to come in.
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Unread 09-09-2014, 07:47 AM   #4
grasmo
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Quote:
Originally Posted by robco View Post
im just not wanting to have to turn 3000 for the power to come in.
I have no idea what those heads flow but look for high lift with shorter duration. if they offer it, a rocker ratio change would help too.
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Unread 09-09-2014, 08:04 AM   #5
swatson454
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Quote:
Originally Posted by grasmo View Post
I have no idea what those heads flow but look for high lift with shorter duration. if they offer it, a rocker ratio change would help too.
They flow about like a straw with a kink in it. But you're right.

Quote:
Originally Posted by robco View Post
Im not worried about a smooth idle at all, im just not wanting to have to turn 3000 for the power to come in.
If it were me, I'd go with a custom-ground Comp Xtreme hydraulic flat profile:

Intake lobe #5442- 262 Advertised duration, 218 @.050, .493 lift
Exhaust lobe #5230- 268 Advertised duration, 218 @.050, .485 lift
106 LSA +4

It will/may have a slightly noticeable idle but will build gobs of torque and you won't have to rev the snot out of it.

The last thing I would do is buy some off-the-shelf "Comp" grind because it very likely wasn't ground by Comp. As I recently learned, virtually none of the name brands actually grind their catalog cams. They're farmed out to someone who simply knocks 'em out to fill orders for internet parts houses and retailers. Accuracy and core quality be damned.


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Unread 09-09-2014, 08:37 AM   #6
gmakra
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Crower still grinds their own cams and they will engage you on the phone they are good people that haven't lost their roots in the corp world.

In response to the stock 4.2 head comments.
The stock head does not flow as bad as people claim it does I once saw the numbers once and I was surprised at what it actually flowed though I cannot remember what the numbers were or were I saw them.
(Shawn not one old guy comment out of you!)

If your looking at doing the build from a numbers aspect go ahead with the custom grind and all that; however once all the dust has settled and your wallet is very thin, think about how many horse power you actually realised.

If you really want to make more power think about boosting your compression ratio a bit. Then go over to jeepstrokers.com and plug your cam numbers into the calculator on the site and see what your dynamic and static compression ratio numbers will be. Cam selection will affect your DCR.
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Unread 09-09-2014, 08:43 AM   #7
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Originally Posted by gmakra View Post
Crower still grinds their own cams and they will engage you on the phone they are good people that haven't lost their roots in the corp world.
Crower was one name that wasn't mentioned so that's good to know.

Quote:
Originally Posted by gmakra View Post
In response to the stock 4.2 head comments.
The stock head does not flow as bad as people claim it does I once saw the numbers once and I was surprised at what it actually flowed though I cannot remember what the numbers were or were I saw them.
(Shawn not one old guy comment out of you!)
I've got them around here somewhere and that's what I used to input the specs into Vizard's Cam Master program awhile back. It's really not that they flow horribly for their size, it's that they don't flow anywhere near what's needed to fill the cylinder below them. And I can't remember my *ss from last Tuesday

Quote:
Originally Posted by gmakra View Post
If you really want to make more power think about boosting your compression ratio a bit. Then go over to jeepstrokers.com and plug your cam numbers into the calculator on the site and see what your dynamic and static compression ratio numbers will be. Cam selection will affect your DCR.
I did all that before I specced the cam. Of course, I didn't use anything from JeepStrokers


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Unread 09-09-2014, 02:40 PM   #8
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If it were me I would go for down low torque......that is where you will feel it most and also stay away from any radical opening/closing profiles, such as the extreme energy line.

It will put undue wear on the valve train parts for your application.......nice easy slow ramps and down low power will give seat of pants feel and offer reliability and a lasting engine.


Extreme opening/closing rates and higher lifts require stiffer springs which starts to put loading on the valve train........it will wear guides/seats etc at a accelerated rate........longer durations require rpms to kick in, which equalls more wear.

Unless you have a specific need, I would shoot for the broadest torque curve at the lowest rpm possible........with eveything all done by 4000 rpm.


Ideally you get the head flow numbers, compression ratio and find a good cam program/virtuall dyno and start playing with cam profiles untill you find what you want.

I would say 89 percent of beginer cam choosers go atleast one size too big, to several sizes too big.

Here is a good primer to get you started....http://www.popularhotrodding.com/tec...mshaft_basics/
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Unread 09-09-2014, 02:48 PM   #9
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So what would you spec for his application?


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Unread 09-09-2014, 03:41 PM   #10
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No?

Robco, the cam I specced peaks right around 4,000 rpm, carries the peak to 4,250 and is on its way down before 4,500. It should be making ~250 ft.lbs of torque at 2,500 rpm and peaks around 275 ft.lbs at roughly 3,250 rpm.

If you keep your compression ratio to ~9.0:1, no more than 9.25:1, you'll have a dynamic compression ratio of ~7.5:1 which is A-OK on mid-grade fuel. I also factored in your 4.88 gears and the fact that it's mostly a street rig. Does that sound like what you're looking for?


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Unread 09-09-2014, 05:38 PM   #11
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I am not up on his engine at all,or that type of egine, I have no idea of the valve sizes or flow rates etc.....

I have only built a few engines completly myself.......played with a few cams etc.

But I have talked a lot with many builders and done a lot of reading on the subject....from reputable sources.

I was just pointing out some attributes to shoot for in his engine build .....

To be honest, I have no idea what to spec out for actuall numbers in his application......I am just not that experianced.
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Unread 09-09-2014, 06:08 PM   #12
robco
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Quote:
Originally Posted by swatson454 View Post
No?

Robco, the cam I specced peaks right around 4,000 rpm, carries the peak to 4,250 and is on its way down before 4,500. It should be making ~250 ft.lbs of torque at 2,500 rpm and peaks around 275 ft.lbs at roughly 3,250 rpm.

If you keep your compression ratio to ~9.0:1, no more than 9.25:1, you'll have a dynamic compression ratio of ~7.5:1 which is A-OK on mid-grade fuel. I also factored in your 4.88 gears and the fact that it's mostly a street rig. Does that sound like what you're looking for?


Shawn
That does sound like what im after. Im building a pretty well stock motor with the bolt on mods to get the most out of it. I thought about working the head or doing a 4.0 head and all the other thing that come into play when the ball starts rolling on a engine build. Ive been down that road and I like the power and all that goes with it and i know how i am, its best with this one to stay on the drivable and stocker side with just the easy mods on this one. With that said, matching the ports to the gaskets and cleaning up the ports may not be a bad idea. The custom grind does sound like a good idea too, but if the money is a lot more than an off the shelf cam, with this build I'm not sure that the gain would be worth the dollar. Is that a wrong way to see it? Im not stuck on comp cams either, I could go another way just as easy. I do appreciate everyones help and ideas and I like hearing them.
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Unread 09-09-2014, 06:27 PM   #13
swatson454
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There are lots of options, bud. We could always drop down in hydraulic intensity, like Unretarded mentioned, and use High Energy lobes, we can go to Bullet cams, etc.

The real challenge in doing things the way I do is that it builds a lot of cylinder pressure early on; which is where you get your brutal low-end from, but the 258 head seems to be pretty knock prone so we have to be careful with where we close the intake valve.

Going custom, at least from Comp anyways, doesn't cost any more. Even if it did, that's money well spent over common shelf grinds.

Why don't you find out how much needs to come off the head deck and block, we'll get a better idea of your compression ratio and go from there. Some D-dish pistons will help us out in that department. I'll check out some Bullet lobes but they're more expensive than Comp. Probably better quality, though.


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Unread 09-09-2014, 08:51 PM   #14
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I have a custom grind comp in my 258 and it comes on low, and thinks it is a small V8 up till just shy of 4K on the tach (258 with a 4.0 head). It is grind# A6 5440/5406 H 114.0
.462 gross lift and .206 duration@.050-- intake
.484 gross lift and .214 duration@.050-- exhaust

This runs on MPFI and pump gas. I think Comp has pretty much started making this cam as a standard order part so you can compare the specs but I think you will be happy with anything in this range. You can call and talk to them to compare.

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Unread 09-10-2014, 02:08 AM   #15
grasmo
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Quote:
Originally Posted by robco View Post
headers
keep the primaries small for torque.
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