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will it be over cammed?

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Rusty68, Jan 25, 2003.

  1. Rusty68

    Rusty68 1/2 ton status

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    I just recieved a pair of full roller rockers that are 1.6 ratio for my Bday. The current cam I have has 450 lift and 224 duration at .50.. If I add these rockers I think my lift will go up to like 480 somthing. Not sure how much duration will increase. Anyway, I have a th475 trans with a RV type converter and 3:07 gears running threw 33 inch BFG all terrains. Will this kill all my power or have running/idle problems with my converter?
     
  2. Topdown

    Topdown 1/2 ton status

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    Let me state right off the bat, I am FAR from anything even remotely close to an engine expert... /forums/images/graemlins/thumb.gif Having said that... The 1.6's shouldnt kill your power, but you may lose some of your low end and push up the high end power. Also, you may want to check clearance inside the valve covers, I know the 1.6's I am getting wont fit in stock covers, I had to get tall ones. Also, you will probably need to make sure that your valve's and valve springs and whatnot can take the extra movement. Those are my thoughts anyway... Hope it helps a little.

    -Ryan /forums/images/graemlins/k5.gif
     
  3. Stroked72Blazer

    Stroked72Blazer 1/2 ton status

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    I think mosr stock valve trains are good to .500 lift so you should be good there. As for power I agree with the abouve statement and regardless of useng those rockers or not you should change those gears as soon as you can afford to. Something in the 411 range would be nice.
     
  4. chulisohombre

    chulisohombre 1/2 ton status

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    you will definitely have to change the valve covers to tall ones.i have a stock cam and 1.6 roller rockers and they put a hole in my valve covers.i changed to some chrome ones for 20 bucks and they work good.just get the rubberized vasle cover gasket because it definitely seals better than the stock cork ones with aftermarket covers.
     
  5. Sandman

    Sandman 3/4 ton status Author

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    Your converter might start the get upset getting up there. I would suggest looking around for a different gear combo. The power increase of going to like 3.73's would make the rocker upgrade look like a wast of time.
     
  6. Rusty68

    Rusty68 1/2 ton status

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    I already have tall valve covers, so thats not a issue, and my valve springs are rated to 540 lift. The biggest concern was the torque converter. I like to be able to idle in gear and take off without funny bogs etc. I think I am going to drop in a milder cam shaft. That way I can take advantage of the roller rockers. I may be the only person that likes 3:07 gears with 33 tires. I do not do any heavy rock crawling, or mud pit bombing. Just like cruising the log roads etc. If I end up going to 35s then I will more then likely go up to 3:73 gears.
     
  7. '72brett

    '72brett 1/2 ton status

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    yea. I got 3.07s I have never come acrossed a time when I didnt have enough power. I like my 3.07 due to the fact that I drive 10 miles to work and 10 miles back. When, if ever I need more power, I will use 4-low. We got plenty of 373's and 411's behind the barn, but they arent in my plans as of now. I dont have 33's either tho, I got 31's and I am planning on a 2" body lift. Then, when my tires wear out, I will got to 33.
     
  8. ben427

    ben427 1/2 ton status

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    have your valve guides been machined down? usually stock valvetrain is good to .480-.490, but after this it will bind coils and hit the valve guides.you could put a pair on and rotate the engine by hand to make sure they wont bind up. Also does your engine have flat top piston? they may cause a clearence problem between valves and pistons.Your gears are also a little high too, you will want a 3.73 at least, 4.10s would be better yet.
     
  9. Steve_Chin

    Steve_Chin 1/2 ton status

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    Don't trust the claims as to what lift a given valve spring is worth. I've seen too many engines messed up due to incorrect claims or incorrect installed height. Put a dial indicator on the valve spring retainer and move the valve until you have 0.050" between each coil. This is considered minimum safe clearance. If the reading is higher than the actual gross lift you will have at the valve, you're OK. If it is equal or less, you need a different set of valve springs or yu need to change the installed height by cutting the seats, installing longer valves, etc.

    WRT the duration, 224 degrees at *0.050"* (not 0.500") doesn't seem too aggressive. BTW - is that on the intake or the exhaust? I'm running a cam with 225/230 duration 0.454"/0.463" (@ 1.5:1) and it is not lacking terribly in bottom end. Obviously, it must be degreed in properly and all of the other engine systems must be tuned to function properly with the chosen grind. Oh, s general rule of thumb when using camshafts of less than 245 degrees of duration at 0.050" lift is to increase the 0.050" duration by 2-3 degrees when moving from 1.5:1 to 1.6:1 rockers.

    That said, an automatic will probably require a torque converter with a stall speed in the range of 2300-2600 RPM and will flash at about 2200-2400 RPM. I haven't a clue as to what your "RV" converter may satll or flash to, since so many seem to call anything that's just a little hotter than stock "3/4 race" or "RV."

    Now, all that extra lift may or may not do a thing for your engine, depending on the cylinder head port design you have. Many cylinder heads simply don't flow any more once the valve lift exceeds a given point where the head is most efficient. Some actually lose some flow. You can't tell without using a flow bench.
     
  10. Rusty68

    Rusty68 1/2 ton status

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    Some interesting points there. For heads I am running the 461 casting fuely heads that have just recieved new seats and guides, and 1.94/ 1.6 valves. The springs are Elgin Z28 style suposedly good to like 530 lift. However I will and always have checked for coil bind. I just ordered the edelbrock performer cam from summit. It has much milder duration figures and the small improvment of lift should help without over whelming my converter. I was told that going to a 1.6 rocker would only effect the lift and rate the valve opens not duration. This does not make sense to me as if the valve is opened further then the stock rockers then the duration should also increase no? How would I figure this? My pistons are a flat top but have valve notches machined in so I shold be cool there. I dont think my cam bearings are bad. This motor only has about 3000 miles on it since I built it.
     
  11. Steve_Chin

    Steve_Chin 1/2 ton status

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    Gross duration is not affected by rocker ratio, but duration at or above 0.050" is affected due to the increased rate of acceleration that the higher ratio offers.

    I don't know howthose heads flow, but I would guess that running lift about 0.480"-0.500" wouldn't be detrimental.
     

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