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Need opinions on this cam-

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Shawn, Sep 6, 2000.

  1. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Ok, before I buy this sucker with new roller lifters, springs, pushrods, roller tip rockers, what do you guys think? I think it may be a little lopey for a small block but I was told by a few engine builders that big blocks can take more of a cam without being too lopey. I like lope but not for crawling on the trails. I'd like to stick to a roller setup so if anyone has another suggestion, I'd like to hear it.

    Comp Cams Hydraulic Roller
    Xtreme Energy
    XR270HR
    270 in. dur
    276 ex. dur
    218 in. @.050
    224 ex. @.050
    .510 in. lift
    .510 ex. lift
    110 degrees lobe separation angle
    RPM= 1600-5400

    This is going in a 454, 4 spd, GM 049 heads milled .020 for 9:1 fitted with 2.19 in. valves, flat top pistons, headers, 1000cfm Holley MPFI w/ Holley ECU, 450hp injectors, 4.88 gears, 36" tires

    Shawn
    87 K5
    few mods
     
  2. Andreas

    Andreas 1/2 ton status

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    I think a little lope is OK too. When you´re on the trails you have 4wd low going in your t-case, right? Low gear makes up some for an unstable idle. Not to mention you run a manual tranny. You can always clutch a bit and rev the engine if you notice your engine is stalling.
    I´m going with a Comp cams 270 too (smallblock), but a hydraulic one. That, or a 260 with 1.6 rockers.

    Andreas

    406cui of pure sh*t[​IMG]
     
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I've got the Comp cams 260HE in my 350 and I have a pretty smooth idle, you can tell it has a bit of a cam and thats about it. I have the 4 speed, 3.73's, and 35" tires and frankly I think I could easily have used the 268HE. A 454 is going to need more cam than a 350 anyways.
    Did you talk to the boys at Comp Cams? They have a pretty good tech-line and should be able to tell you if that is more cam than you want.
    In my opinion I think this would be a great cam for the 454. (I'd like to see the difference on the dyno)
    Rene

    [​IMG]
     
  4. Thats a very good cam for a 454,a 270 is a little lopey in a 350 but you wont hardly notice it in a 454.The tight lobe seperation cuts down on the lope also,very good vacume also.
    Sounds like a good cam choice to me.

    IF IT AINT BIG IT AINT BAD!!!!!!
     
  5. Donovan

    Donovan 1/2 ton status

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    Hey Bigbad82 I think that the wider the seperation the better the idle. It don't put the valve in overlap. That causes rough idle when the valves are in overlap. I think that cam should be fine for a 454. Look at this place http://www.elgincams.com. They have a great explaination of the cam and how it works. Shawn read this page and see if this cam is to big.

    Donovan
     
  6. Donovan

    Donovan 1/2 ton status

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  7. realsquash

    realsquash 1/2 ton status

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    Lopey? That cam will sound like a stocker! Honestly, that cam will idle smooth and run like a million dollars if you never want over 4500 rpm. If I was going to spend the money on a roller, which I am thinking about doing this winter (hibernation season in WI), I would go bigger than that, maybe an XR276HR, http://www.compcams.com/speccard/11-423-8.txt And with this cam, stronger full-roller rockers would be a good idea. But my truck surely get's used differently than yours, so YMMV.

    I ran a flat-tappet XE268 with 9.5:1 and pocket ported & port matched 049's and was happy, but it ran outta go-power at 4500, seriously (because of the heads, not the cam).

    With a roller cam, you can run more duration/lift due to the steeper opening/closing ramps made possible by the roller lifters.

    Squash
    http://www.trailrunners4x4.org/users/realsquash
     
  8. realsquash

    realsquash 1/2 ton status

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  9. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Thanks for all the comments guys! I did talk to Comp Cams tech dept and the guy didn't sound he knew what he was talking about. First he suggested the 276 then he changed his mind and suggested the 264 (both rollers). It sounds like the 270 will give me good power with a smooth idle.

    Shawn
    87 K5
    few mods
     
  10. Donovan

    Donovan 1/2 ton status

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    Why I say stay with a smaller cam is because of the altitude. You loose so much compression at are elevation. You should stay on the small side up here. Think of it this way 9 to 1 compression with atomspheric pressure at our altitude which is around 12.2"of HG. Multiple the 9 (which is your compression) times the 12.2 and then divide by sealevel pressure 14.7 and you come up with 7.47 to 1 static compression. This is why I say stay on the small side on the cam. I hope that makes sense.

    Donovan
     
  11. realsquash

    realsquash 1/2 ton status

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  12. Donovan

    Donovan 1/2 ton status

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    Sorry it is not " of Hg it is PSIA (pounds per square inch Absolute).You are compressing 9 times what your air pressure is. Here in Denver the air pressure is 12.2-12.4psia. Static compression would be 9 times 12.2 which is around 110psi in the cylinders. Simple math. Take 110 and divide it by sealevel pressure and you get 7.48 to 1 compression. This is what we are really seeing here in Denver for compress. Same thing with blowers up here. People will put on a 9 pound pulley and they will only see 7 pounds of boost. This is because of the head pressure on the blower is not the same as sealevel. You have to install a 11 pound pulley to get your 9 pounds of boost. It just really suck to build a engine up here and try to get them to run good.

    Donovan
     
  13. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Ouch! My brain is starting to hurt! Good theory Donovan. Doesn't the altitude also have an effect on a larger cam which would mean it doesn't require as much compression? I'm trying to get as much oxegen in that motor as I can and I'm thinking a larger cam will help. When I switched to a larger cam in my old 68 Camaro, I actually had much better times at Bandimere (no other mods done). True, you can have less pressure with a blower or turbo and thats why I can run a smaller 3 inch pulley on my Grand Prix GTP and it's fine for Denver but soon as I take it to sealevel, it will have too much detonation. Sometimes I hate this altitude... Thanks for all the comments!

    Shawn
    87 K5
    few mods
     
  14. Donovan

    Donovan 1/2 ton status

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    If you read the Elgin cam site it tells a lot about how the cams work. We have been fighting a cam problem in my brother race cars for 3 years and I think we have a handle on the cam and how it works. I did say I think we have a handle on it? Basicially how it works is your engine will has a max. piston speed and that occurs at 75-80 ATDC. Your engine will not use anymore air than there is at max piston speed. Lets take my brother engine. It is a Caddy 500 engine and the heads flow 275 at .600" of lift. His cam has .630" lift on the intake and it is a solid cam. We take the lash out of it which is .025" so the brings use down to .605 lift and the cam will get this lift at 110 atdc. So we came up with 30 degrees before that (which is max piston speed) we have the lifter lower on the cam. We came up with the lift on the lifter at max piston speed is only around .520-530". His heads flow 250 CFM. There is a formula that converts that to hp and it should be around 580hp with that much flow. But it we look at his heads they flow all the way up to 275 that means that the engine should be making 650hp but the cam says it will not do that. These HP figures are at sealevel. Since we are at 5000feet we lose 10-12% because of the altitude and 10-12% going though the drivetrain. So we use 20% lose just running up here and that come out to be 464hp at our altitude. His car was dyno'd at Dyno Pro and it made 470 hp at 5000rpm. The times at Bandimere is 11.76@115 in a 3700pound car. All of this figures out to be right on the numbers. So I say don't get real wild with the cam because it will hurt you somehow. It might run real well but have a bad off the line starting or the other way around. Talk to the elgin cams guys and see what the would recommend, they have the same thoughts on cams as I do and it sound like they win a lot of races with there cams.

    Donovan
     
  15. Mudzer

    Mudzer 1/2 ton status Author

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    Re: I can give you your HP and TQ

    Shawn,

    Tonight I will input your specs into my Engine Dyno program and give you an approximate HP/TQ reading. After I get this info put into the computer, we then can play with camshaft selections to find the best one for you. We can get all the cam specs from Comp Cams website.

    Neil

    Mudzer 1978/91 K5
    <font color=blue>www.mudzer.coloradoK5.com</font color=blue>
     
  16. realsquash

    realsquash 1/2 ton status

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    Actually, you are compressing the *volume* of the cylinder. Your equation would mean that a blower raises compression ratio, which it doesn't. Also that would mean when it's cold and humid out that the compression ratio goes up. I understand your point, but the math is wrong.

    Squash
    http://www.trailrunners4x4.org/users/realsquash
     
  17. Donovan

    Donovan 1/2 ton status

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    Why couldn't the static compress raise if you have denser air? Please tell me why you don't have the same compression up here as you do at sealevel. Why do cars run 1 second slower up here? So you are saying that I am compression the same amount of air in Denver as I do at Sealevel?

    Donovan
     
  18. 6.2Blazer

    6.2Blazer 1/2 ton status

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    The compression ratio inside the cylinder will always stay constant no matter what altitude you are at. The only way the compression ratio can be changed is if some dimension physically changes inside the cylinder, such as changing the displacement of the cylinder (shaving the heads, different pistons, etc) or if you somehow increased or decreased the stroke length of the piston.
    I do agree that the total maximum pressure built up inside the cylinder is different due to the altitude because of the lesser dense air, but the "ratio" will always remain constant.
     
  19. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Re: I can give you your HP and TQ

    Ok, talked to another guy at Comp that seemed to know his cams. He suggested the 276 roller so I think I'll be going with this one:

    COMPETITION CAMS CAMSHAFT SPECIFICATION SHEET

    PART # 11-423-8
    GRIND NUMBER: CB XR276HR-10
    ENGINE: CHEV BIG BLK 396-454
    INTAKE EXHAUST
    VALVE ADJUSTMENT HYD HYD
    GROSS VALVE LIFT .510 .510
    .006 TAPPET LIFT 276 282
    VALVE TIMING OPEN CLOSE
    AT .006 INT 32 BTDC 64 ABDC
    EXH 75 BBDC 27 ATDC
    THESE SPECS ARE FOR CAM INSTALLED
    AT 106 INTAKE CENTER LINE
    INTAKE EXHAUST
    DURATION AT .050 224 230
    LOBE LIFT .3000 .3000
    LOBE SEPARATION 110
    THIS CAM SHOULD USE SPRING # 911-16

    This is the hyd. roller Xtreme Energy 276. I'd like to stay with Comp but their rollers are very limited. The Magnum series seems too radical for the trail.

    Mudzer-
    I'll email you about the dyno software.



    Shawn
    87 K5
    few mods
     
  20. realsquash

    realsquash 1/2 ton status

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    The air is less dense, less O2. You still compress the cylinder's contents 9 times it's original volume. But there is less O2 requiring less fuel, which lowers output. Look up some aviation engine stuff onthe net. Aviators must know this stuff any time they fly. Turbos and such compress the air, making it seem like your running at -5000' altitude. This is also why turbocharged deisels work better at altitude than NA ones.

    Squash
    http://www.trailrunners4x4.org/users/realsquash
     

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