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Discussion Starter · #1 ·
Is this Comp cam a good choice or not? 660/666 and @.050 254/260. Part #XR292. 13 to 1,Victor Jr,RHS 320 heads,850,ATI 9" 4000 stall,4.56,29" Hoosier,3900lb/driver. I wanted a 714/272 SR but there is varying opinions. It had a SFT 600/620 and @.050 266/276 with GM rectangle ports. The car has 25 gal of fuel put through it a season on the street. There is only a few SR BBC cars here so I would appreciate your thoughts. Thanks .
 

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With the 13.0 compression..I'd be looking for a lot more cam...and for sure in the .700+ lift range.

I'm assuming that .600/.620 was the old Crane flat tappet. It's definitely old school, but I used it in my 540 for awhile (still have it on the shelf) and it runs a lot better than you would think. But with your heads I'd surely look for some lift.

JIM
 

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Discussion Starter · #3 ·
It will have T&D shaft rockers too. Would a 1.8 ratio be an option or stay with the 1.7 and more lift on the cam?
 

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I have been dealing with the same issues. You have none of the problems I am trying to contend with, I only have 440 cubes and 10:5 to 1. the #XR292 would be a great street cam. But with the 456 gears,4000 stahl 320 heads you do not have to worry about bottom end. You will be @3500 rpm most of the time. So in your case go bigger. The#XR292 would be a good choice for my combo. It is more streetable, 373 gears 10:5 to 1, 3500 stahl. As far as the shaft rockers they are the way to go. You may want to look at Cranes. I think I am going to go with them. As far as a 1.8 ratio rocker they will put a lot of added stress on the valve. The thing is you will be moving the valve at a much faster rate and it will depend on the ramp speed of the cam. If the cam has a fast ramp as most of todays cams do, the valve is going to bounce off the seat and want to float. You will have to run higher spring pressures and that is harder on the valvetrain components. I would try to find a cam that has the specs you want with 1.7 ratio. I hope this helps.
 

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Is this Comp cam a good choice or not? 660/666 and @.050 254/260. Part #XR292. 13 to 1,Victor Jr,RHS 320 heads,850,ATI 9" 4000 stall,4.56,29" Hoosier,3900lb/driver. I wanted a 714/272 SR but there is varying opinions. It had a SFT 600/620 and @.050 266/276 with GM rectangle ports. The car has 25 gal of fuel put through it a season on the street. There is only a few SR BBC cars here so I would appreciate your thoughts. Thanks .
I do like the fact that you want to run the 1.8 ratio T & D shaft mounts.
You have the comp. ratio to run the larger cam.
The only thing I see is your car weight.
With the weight of your car I would like to see a little less cam than the .714/.714,272 at .050., but if you have it I say run it.
 

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i have a 12.3-1 468 and i tried quite a few cams and ended up using a cam with 272 278 on 112 with 708 lift. i think this cam would work great with 1.8's on the intake. this setup made awesome torque in the 5000 rpm range and max power at 6800-7000 rpm
 

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Discussion Starter · #7 ·
No, I don't have the cam yet. The only two SR BBC cars around this area use a 1.7 ratio with the larger lift. Both also have 10.80 time slips with full weight cars. I thought this new top end combo would be good for my car too. This is new to me but I see the results of the others and I hate not to trust the engine builder. This is his first SR BBC street build also. He makes great power on the dirt tracks though.
 

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No, I don't have the cam yet. The only two SR BBC cars around this area use a 1.7 ratio with the larger lift. Both also have 10.80 time slips with full weight cars. I thought this new top end combo would be good for my car too. This is new to me but I see the results of the others and I hate not to trust the engine builder. This is his first SR BBC street build also. He makes great power on the dirt tracks though.
Does this car have a trans. brake?
 

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Discussion Starter · #12 ·
No trans brake and 100% race fuel. I also don't want to give up that much duration from the FT to SR. 7000 rpm is what I'm looking for and the cam seems like it might come up short.
 

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that cam is too small for that combo from what you have listed although i would probably go a little smaller than what i would use for an application with a brake. i would go atleast 10 deg more than what you have
 

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A few things, some already mentioned,,
First. that is a cast core POS cam unless it was ordered as a custom so you do not want it in your engine
Second is it is too small for your compression
Heads are a little on the large side but if you have them for sure you want more lift
But they will be excellent when you decide to build that 500+ inch engine you will soon be wanting,,,, :D :D

Plan on 7500-8000 with that head on a 468 & cam accordingly
This means about another 20 degrees & I would like to see .800 lift on the intake about 750 exhaust
This is also assuming you have the compression you think you have
The T&D's are an excellent idea

As far as ratio there seems to be some misconception above,,
The higher ratio does not put more stress on the valve
I does put slightly more pressure on the lifter & lobe but with what you should have you need a bit of spring anyway, in the area of 300/800 would be a good place to be with the rest of your stuff

I would stick with the T&D or Jesel rockers I do not like the Crane "quick lift" stuff
Here is a thought
Cam designers go to a lot of trouble to slow the valvetrain down when the valve is closing
Now assuming they actually do what they say they do,,,
why in the hell would you want to defeat this by installing a rocker that is purported to do just the opposite, open (and close) the valve faster at the very point you want to slow it down
I can see it on the opening side but what you do to this side with the rocker is going to mirror on the closing side,,,,
And no a 1.8 rocker does not do the same thing.
It increases lift & it increases the duration & acceleration only slightly but over the complete curve
Assuming you adjust your lash accordingly you will not change the seat timing, you will "gain" a couple of degrees at the valve at .050 & a little more at .100 etc but the biggest difference will be in lift.
 
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