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Old 09-08-2008, 07:15 PM
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Cams

Hey everyone. i purchased a new 350 crate motor from jegs for my 75 chevy pickup and i was looking to put in a cam... it's listed at 260hp and 350lbs of torque stock. the current cam has .383/.401 lift and 112 degree lobe separation. im not looking for gas mileage and i want to get the most horsepower and torque as i can without having to completely change out the heads. i'm expecting to have to purchase hardened pushrods but i dont know what else i will need. this is the first pickup i've restored and i'm new to working on the internal engine parts... so if anyone has any suggestions i would greatly appreciate them.

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Old 09-08-2008, 07:27 PM
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I'm bored so here goes.

Any hydraulic flat tappet cam from any reputable manufacturer with specifications as follows........

up to 270 degrees advertised duration int. and exh.
106-112 lobe separation angle
0.460-0.490 lift

You may find a hundred or so cams that fall into this category. My advice would be to stick with an older grind to lessen the need for very stiff springs, and lessen chance of having to deal with valvetrain noise.

Choose your advertising gimmick.


Larry
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Old 09-08-2008, 07:29 PM
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What is the compression ratio?

For your general street friendly-ish build the comp cams magnum 270 or 280 (Or comparable cam from another company i.e. Isky) should work nicely...wont need crazy gearing or converter stall if your using an automatic.

Give you a nice lopey idle and decent power.
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Old 09-08-2008, 07:35 PM
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the compression is 8:5:1... and its a 4speed tranny
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Old 09-08-2008, 07:40 PM
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i found a lunati cam with 227 degrees intake and 233 degrees exhaust with .489/.504 lift... how would something like that work? if i'm willing to purchase stiffer valve springs...
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Old 09-08-2008, 09:44 PM
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Quote:
Originally Posted by 75Chevy
i found a lunati cam with 227 degrees intake and 233 degrees exhaust with .489/.504 lift... how would something like that work? if i'm willing to purchase stiffer valve springs...
You'll need 10.0:1 to run that cam. You can't just reach out in thin air and pick a cam, it needs to be tailored to the characteristics of the motor and the intake valve closing point needs to match up with the static compression ratio of the motor. About 205-210 degrees duration @ 0.050" tappet lift is about all the cam that motor can handle at 8.5:1
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Old 09-08-2008, 10:37 PM
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I built an 8.5:1 SBC once with a 218/224 cam and hated it. I thought I could get away with it in the light car and the converter I chose, but I was wrong. I swapped it out for a 204/214 and was much happier.

You'll also have to consider the head flow. Those stock heads are great for the moderate 260 hp, but will choke things off if you try to squeeze any more out of them.

Everything has to match. Currently the cam, heads, and compression are all well-matched for idle-4500 rpms. Just changing the cam to one that shines between 2000-6000 means that your heads will run out of steam right after the cam hits its sweet spot. Low end performance will suffer greatly, and you won't get much more top end.

GMPP sells the same engine rated at 290 hp and for the most part its the same engine with a 222/222 cam. Many have complained about the lack of torque with the low compression and big cam in the 290hp version, so I wouldn't go that far. Quite seriously, a 350 engine with a 222-degree cam (with a matched set of heads) should be pushing over 350 hp. That should demonstrate how mismatched their combo is.

Now... if you want to up the ante, skip the cam and go straight to a head swap. Even the small (I think its a 192/198) cam in the 260 hp crate engine should make more like 290 hp with Vortec heads and it will be a splendid match. The downside is that you'll need the matching intake to go with it.
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Old 09-08-2008, 10:44 PM
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cams

I agree with what the guys are saying, with that low of a compression, the cam you are thinking is way to big. My 350 is 10:1 with the comp cams 280H, I used 1.6/1 rockers and it gives me just about a .500 lift with 230 duration on intake and exhaust as well as some trick flow aluminum heads, this combo has run really well. I sure would consider a much lower duration with that comp.ration. Good luck.
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Old 09-09-2008, 11:21 AM
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Thanks everyone, i greatly appreciate all of the advice. i'm looking to push 350 to 400hp out of it due to the fact that the stock drivetrain wont hold very much more than that comfortably. so from what you've told me to reach that goal a new cam with a matching set of vortec heads and a different intake is in order... with somewhere around 205 to 220 degree lift for the cam to match the low compression ratio... ?


sorry for all the questions... i'm new at this
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Old 09-09-2008, 11:52 AM
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I'v used the Comp Cams 252H and had good reports back from the customer. Smooth idle, good torque and horsepower. I have also use the 260H, it gives up a little on the bottom, but worked well in the 4WD 3/4 ton chevy it was in (auto trans).
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Old 09-09-2008, 11:56 AM
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Use the performer cam (204/214) with that low cr. Should make around 300hp. Any more cam than that and it will be a dog.

Need to up the compression ratio between 9.5 and 10.0 and use a 230 degree cam to get past the 350hp range.

If you are looking for 350 to 400 hp, then you will need a much better set of aftermarket heads. 64cc chambers (to raise cr to 9.5) and 180 to 195cc intake ports for better flow.
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Old 09-09-2008, 02:56 PM
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Quote:
Originally Posted by 454C10
Use the performer cam (204/214) with that low cr. Should make around 300hp. Any more cam than that and it will be a dog.

Need to up the compression ratio between 9.5 and 10.0 and use a 230 degree cam to get past the 350hp range.

If you are looking for 350 to 400 hp, then you will need a much better set of aftermarket heads. 64cc chambers (to raise cr to 9.5) and 180 to 195cc intake ports for better flow.
I politely disagree. That would be true of old heads, but not vortecs. Keep in mind the RamJet 350 crate engine makes 350 hp with a 206/196 cam. My vortec 5.7 in my boat makes 290 with a carb and a 202/214 cam

9.5:1 is great for a 350-400hp small block. Like 454C10 says, the smaller Vortec chambers should put you squarely on that compression target. For a 350 hp engine (which is a fantastic target for Vortecs) I would use something in the 210/215 duration range, .480" lift, 110 LSA. Couple it with a Performer RPM intake and a 600 cfm carb and you're squarely at 350 or so HP. You can keep a stock rear end ratio and shred tires without having to fill the gas tank every day. You might even be able to keep the stock valvesprings.

For 400 hp I would go with some head work. You can't really easily squeeze 400 from stock Vortecs. You'll need to install stiffer valvesprings with retainers for more lift ability. Most cam companies have them for up to .550" lift without machining the heads. Then install some 2.02/1.6" valves and you might be more in the ballpark. Then you'll have to go with something more like the XR280 or similar; 225/235 duration with .550" lift. You'll be close to 400; probably more like 390... BUT, you'll have to change rear axle ratios, and you'll be giving up low end torque in favor of high RPM HP. You'll also notice a sizeable difference in fuel cosumption. No free lunch. The whole package... and I mean WHOLE package has to match. Things like vehicle weight, intended use, power brakes, emissions, rear axle ratio, etc need to be factored in. Its not just more HP is more HP, its a whole process.

Last edited by curtis73; 09-09-2008 at 03:02 PM.
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Old 09-09-2008, 04:28 PM
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thanks guys. can you purchase a set of aftermarket, non-vortec heads that will match nicely to a 230 degree cam that will up the c.r. to 9:5:1 producing somewhere between 350 to 400 hp and still keep the stock gear ratios and keep it streetable? or are vortec heads the way to go...
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Old 09-09-2008, 04:46 PM
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curtis, I knew he didn't have vortec heads. But yes, vortecs work well and are cheaper but cost extra money to set them up to run more lift and require a vortec intake, rocker arms, and valve covers.

For a normal head setup that uses stock hardware and intake, look at dart iron eagles 64cc chamber and 180cc ports with straight plugs. The edelbrock performer heads would also work well.
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Old 09-09-2008, 05:17 PM
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and those heads will bump up the c.r. and give the ability to run a larger cam and produce my projected hp level like you had said earlier... ?
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