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Old 06-03-2004, 05:56 PM
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sbc 400 cam choice

i posted a thread similar to this in the intro. section but didn't get much info. i have a 73 sbc400, performer intake, 327/350hp cam, q-jet, full length headers, auto, with around 2.80-3.23 rear gear. i'm looking for a cam that will provide great torque and response and have a nice choppy idle to it. i plan on dropping the gear ratio to a 3.73 posi by the way. im looking at a comp cams 268h cam thats 218 duration and .454 lift. some people have said its better for torque but has a fairly smooth idle. does anybody know any cams for a 400 that provide good torque and have a good choppy idle to them? also what duration and lift numbers should i look for to make torque? thanks

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Old 06-03-2004, 06:17 PM
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Torque and choppy idle are on the opposite ends of cam selection. Low end torque= smoother idle. Choppy idle= no low end. Basic Laws of engine physics are at hand here.

Anything over 225 @ .050 will be plenty choppy but to get any low end you have to have about a 114 degree centerline. Most of the cams ground for street Chevies are around 108 centerline. This will give you the sound but no bottom end. The 400 should be large enough to cover a lot of the lower end loss. More so with a decent rear gear.
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Old 06-03-2004, 06:18 PM
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If your going for a cam thats got strong low end torque then why would you want to raise the rear end ratio?

Why dont you stick with the rear end you have and cam the motor to match. If not and you want the higher rearend then get a cam to match. What transmission do you have? If say you got a 3 speed (TH350, 400) and you want to run a 3.73 than why not shoot for a cam around 280-290 duration, make sure your heads can breath and get a single plane intake to take advantage of those high RPMS?
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Old 06-03-2004, 06:38 PM
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Re: sbc 400 cam choice

Quote:
Originally posted by camino_man
im looking at a comp cams 268h cam thats 218 duration and .454 lift. some people have said its better for torque but has a fairly smooth idle.
I am curious about this cam you mention.

Evidently Comp Cam offers more than one cam with the 268H designation.

I previously ran a Comp Cam CS XE268H-10 Part # 12-242-2.

The gross valve lift for it is .477 intake .480 exhaust. The duration at .006 tappet lift is 268 intake 280 exhaust. The valve timing at .006 is intake open at 28 degrees and closes at 60 degrees. The exhaust open at 74 degrees and closes at 26 degrees. Lobe separation is 110 degrees.

This cam is supposedly the hottest cam recommended to be used with the stock torque converter. It has a slight lope in a 350 and idles very well at 750 RPM. Begins to 'come on' at 1500 RPM.

I consider it to be an excellent cam for a slightly warmed over engine and performs very well with stock heads and small valves. The rear gears that I had at the time I used this cam were 3.25-1.

Your rear gear choice of 3.73's sound excellent.

There is another thing that you can do that will begin the torque curve about 200 RPM's lower. If you have a crank sprocket and cam sprocket with three keyways; use the 4 degree advanced keyways. Be sure to check the valve to piston clearance though. Your ignition timing will be the same as you would normally use.
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Old 06-03-2004, 07:22 PM
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Bob and Frisco are right on. Listen to what they said. Also wait for someone that has actually used the comp 268 and their COMBO . That would be the best advice. I hear that the 268 is a great street/stip cam. I would use a higher stall convertor.

I went 2 cams bigger, the 274. And that cam was TOOO BIG as far as I was concerned for a street/strip vehicle. It sounded GREAT!!!! I even had 3:73`s and aluminum heads, with a 9:7 to 1 CR. The cam was very lumpy but the car moved at 4000 rpms. That`s too late for a street car. I sold that cam and am in the process of going to the chevy ZZ4 roller cam...the power is alot earlier and has better lift on the exhaust. IF I did not go with the ZZ4 roller cam I would of went for the 268!!

Good Luck!! Keep it fun!
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Old 06-03-2004, 08:01 PM
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thanks you guys, this is exactly the info ive been after. frisco your right, comp cams has a high energy 268, and a extreme energy 268. the high energy is a single pattern while the extreme is a dual pattern, which would be better the single or dual? and what is the centerline of a cam? also i have another set of stock heads that im going to have pocketed ported and have a multi angle valve job performed.
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Old 06-04-2004, 03:59 PM
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comp cams xe284 would be good in a street 400. I used a xe274 in mine but the idle is not as choppy as you would think so I would go a size bigger if I had it to do again.they make tons of torque across the board.
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Old 06-06-2004, 04:55 PM
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ok fellas, some people say the 268 cam is to small, they say it would be like a stock 350 cam. others say to use a bigger 270 or higher duration cam. ive found a lunati cam that id like yalls opinion on. its adv duration 276/286, .050 duration 221/230, lift .454/.454, lobe sep 112, centerline 106. lunati said its a big street cam for a 350, popular in 383-406, lopey idle, will work power brakes, and makes power between 1000-5800 rpm. do you guys think this cam will work well in my 400, and will have to go to a stall converter? thanks, hopefully this will be my last question on my cam issues
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Old 06-06-2004, 05:16 PM
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For street and occasional strip I'd suggest Comp Cam CS XE268H-10 Part # 12-242-2.
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Old 06-06-2004, 06:19 PM
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frisco, did you use the xe268h in a 350 or 400, most everyone that ive talked to that has used put it in a 350.
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Old 06-06-2004, 07:14 PM
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I have the XE284 in a 406" sbc. 750 holley and a RPM intake. 13" of vacuum at 850rpm idle. 3.73 gears and a TCI converter flashes to 3300 or so depending on traction.

I like it ok. I wish I'd built it with less compression and used a smaller cam or one with a wider LSA for better vacuum and a lower idle speed.

Larry
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Old 06-07-2004, 03:22 AM
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Quote:
Originally posted by camino_man
frisco, did you use the xe268h in a 350 or 400, most everyone that ive talked to that has used put it in a 350.
I used it in a 350 but would still suggest it for your 400 for the street. The lift specs are the reason for my suggestion with your combo. If it were my engine I'd go one step higher than that cam and use a 2400-2800 RPM stall, but then you begin to lose some streetability as a daily driver. Much more fun though.
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