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Old 12-30-2003, 10:40 AM
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The cam mistake is running, well, kinda!

Well, its running, kinda

short recap:

Quote:
Originally posted by Jmark
Well, as the saga continues:

My son and I each started building engines back in November. I pretty much left him alone and had him work with the machine shop on the cam selection, along with the heads and pistons. They knew full well that his engine was going in a 5000 pound 3/4 ton 4X4 "wheelin" truck. My son wanted a roller cam and they suggested the Comp "Extreme Energy" 286 cam.

Well, today, I found the cam card and then cked on the Comp web site to see what the cam was all about. They state the following:
"Great for street machines"
"headers needed" ( which we have )
"intake" ( we have the Performer PRM Qjet manifold )
"Gears" ( we have 4.11s with 36" tires!)
"2000rpm stall converter" ( which we do NOT have!)

We converted the stock granny 4 speed to a TH400 with shift kit and 12" stock converter. Are we screwed as far as being able to get this thing to idle at all? Not to mention the AZ has emission testing too!
[/I]





Fired off in about 2 seconds of cranking, so that was good. It sounds healthy for sure, but the cam has to go. Its way to radical for what he needs the truck for.

He's going to run it for a while so he can enjoy it, but for all intents and purposes, its never going to pass emissions or climb a hill. We can get it to idle at about 900 in neutral, but it lopes severly ( sounds awesome un-capped!) but loads up and wants to croak. We don't have the drive shaft in yet so I have no idea how bad it'll be in gear.

I called Comp and they said since I want to go smaller, they can re-grind it for $115. Beats buying another one and scrapping this on. We're also going to have a long chat with the guy at the machine shop too. He knew exactally what the truck was going to be used for and this cam was a really bad choice on his part.

Oh well, sure glad its not MY truck!! LOL

Mark

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Old 12-30-2003, 10:57 AM
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Jmark,
I just wrote a reply to your other thread a few minutes ago:

"I agree you might have made a slight mistake. I made a similar mistake years ago, putting too much cam in a heavy Blazer (350ci) it was a slug. Sure it ran great on the highway, but had very little torque.

You are working with a 400 so it shouldn't be as bad (though your truck is heavier). For your intended use I would think you would want torque from idle to about 5000. We are talking a climbing vehicle not a drag car, you have to build the engine a little different.

I agree with more gear and stall you can make it work. If this is not in the plans it would be cheaper and easier to swap out the cam now (IMO).

Either way let us know how it runs please, this is something we can all learn from."

Thanks for getting back to us. I thought that would be the case. Sorry you had to go through the hassle of installing and finding out the hard way.

Machinist gave you bad advice if you ask me. Heavy trucks need torque not high end HP.
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Old 12-30-2003, 11:01 AM
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Re: The cam mistake is running, well, kinda!

Quote:
Originally posted by Jmark

Oh well, sure glad its not MY truck!! LOL

Mark
Sounds like something a dad would say! Ha!
At least it runs, and the kid can sound cool at the stop lights for now....
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Old 12-30-2003, 12:24 PM
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I have the same cam in my truck, and it idles fine down to about 600 rpm. My engine a 350, so it should idle just as good. You could try advancing the cam, as this usually helps with the low end, plus its way cheaper than getting the cam reground!
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Old 12-30-2003, 01:00 PM
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Well, the machinist may not have been completely off his rocker. I admit, he should have known that you wanted to drive it down the road or in off-idle climbing, but the truck would be an awesome mud machine. Hey, I don't have the number with me, but there's a place in Arizona called Motormachine that will take intake and head flow numbers, bore to stroke ratio, transmission, gearing, and choose a cam that's exactly what you need. They're close to actual dyno specs too. They have a simulation program developed by David Vizard. They're cheap too. I'll get that number for you if you'd like. Happy wheelin'.
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Old 12-30-2003, 01:27 PM
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The comp 268 is what all my friends with 4x4 trucks use and thats what I used in my trans am. I didn't use a stall converter and it still idled well. You shouldn't really have a problem with it. I even went to the performer rpm on my 355 but it's a street car. Still no stall converter but it needs one because it likes to lurch. Keep in mind that the xtreme 4x4 cams that comp sells for trucks have durations of 206/214, 210/218, 218/226, and 226/234 @.050. The 268 has 218/218 which puts it in the middle and it has a power range of 1500-5500. Idled right around 900 in my 355 and about 750 when in gear. It's what I would put in a truck for a mild cam if I had one. But its all up to you. Maybe the 206/214 is better suited for your application. Earlier in this post someone mentioned that you can get more stall from a stock torque convertor??? How would you do that? My paint job dipped into the budget and don't have an extra 300 laying around right now for a nice stall converter.
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Old 12-30-2003, 02:58 PM
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personally I'd keep it, hell I run a solid cam in my mud truck with 260/260 duration, looking to go with a big solid roller for the 400 if I can find one cheap..
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Old 12-30-2003, 04:45 PM
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what size cam was it and is it good for the street truck 78 chevy
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Old 12-30-2003, 06:01 PM
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If you are running the comp 268 like it says above, I would definately keep it. In a 400, I would say that is a perfect cam. I run a 246 @ .050 solid cam in my 400 and it will idle at 900 RPM. It loads a little, but not that bad. It used to really suck before I put the MSD 6A on it. That made loads of differance and kept it from loading up and fouling the plugs. If you have not already, you might also try leaning the idle mixture a bit and see if it helps. The more cam, the less fuel you need at idle due to exhaust reversion. I think you should be able to get a strong snappy idle at 900 RPM with that cam without any loading.

Chris
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Old 12-30-2003, 07:21 PM
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Guys, remember he has to pass a smog inspection as well. I am not sure this cam will pass. I have not personally ran this cam so I don't know. He is also working with a HEAVY truck and plans on climbing hills. Not sure that is the cam for the job even in a 400.

I agree he should be able to get it to idle even with a stock converter but, if it is loading up at all he will fail the emissions test.
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Old 12-30-2003, 08:34 PM
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Yep, it might be tough to get a clean enough idle to pass the test. I did not realize that was part of the equation. If it was EFI I would say it could be done, with a carb it could be tricky though. I have never had to tune to pass a sniffer so I dont have any useful advice there.

As for the hills, I still think it would work well. My Dad ran a comp 268 in a 305 for 150,000 miles in a 5500 lb Surburban. It was not unusually gutless on the low end and idled well in gear with an Edelbrock 600. I suppose the grind could have changed since this was 10 years ago when I put the engine together.

Later,

Chris
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Old 12-30-2003, 09:25 PM
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Sounds like the machine shop had your cam on the shelf and wanted to unload it. Did you ever notice that a shop will recommend a certain cam...and then if by magic they happen to have one.
I missed the previous thread. But, you can buy a flat tappet cam for what they want to regrind yours. Then you'll have something for the future.

My $.02
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Old 12-31-2003, 12:49 AM
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It sounds like you guy need to pick a new machinist. Isn't that the guy you got the Pro Topline heads from?
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