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Old 06-29-2010, 12:59 PM   #1
88GTBLACK
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Default 1.6 rockers vs 1.7

http://www.summitracing.com/parts/TFS-51402000/

im considering getting this cam with a stock block and these heads
http://www.summitracing.com/parts/TFS-51400004/

if i get 1.7 rockers will that change PTV clearance with the cam?

That seems like a decent cam for my setup so far i just need to decide rockers and lifters...parts i have now is

75mm TB 75mm MAF calibrated for #24 injectors trick flow upper and lower intakes, full length 1 5/8 headers....what do you think of the setup?
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Old 06-29-2010, 02:34 PM   #2
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1.7 rockers basically make the cam act like it has a bit more lift and duration. Remember that cams are spec'd at the camshaft lobe and not at the valve. The bigger advantage of using higher ratio rockers is that you can run a milder cam lobe and still good good valve action...and since the lifter has way more mass then the rocker/valve, it can help with high rpm stability and prevent valve float. That's why a lot of high rpm pushrod engines run larger rocker ratios.
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Old 06-29-2010, 05:36 PM   #3
87 T TOP GT302
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It will definitely change PTV clearance.With the 1.7 rr it will change lift on the intake from 499 to 530 and on exhaust from 510 to 542.The way you get the lift numbers is divide the lift by 1.6 and that will give you actual cam lift. 499 divided by 1.6 =311.88.Take 311.88 multiply by 1.7 and it give you 530.40
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Old 06-29-2010, 08:42 PM   #4
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as long as you check ptv 1.7 will be your best bet, most dont have clearance problems but all engines are different
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Old 06-29-2010, 09:01 PM   #5
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Quote:
Originally Posted by 87 T TOP GT302 View Post
It will definitely change PTV clearance.With the 1.7 rr it will change lift on the intake from 499 to 530 and on exhaust from 510 to 542.The way you get the lift numbers is divide the lift by 1.6 and that will give you actual cam lift. 499 divided by 1.6 =311.88.Take 311.88 multiply by 1.7 and it give you 530.40
SWEET!!! I'm still running speed density as we speak...i switched back i couldnt get it to run right are you still running stock injectors with your setup??? I see your sig doesnt list new injectors was wondering how its running
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Old 06-29-2010, 09:07 PM   #6
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Total valve lift has nothing to do with the possibility of PtV issues. If a setup clears with 1.6 ratio rockers, it will clear with 1.72 rockers 96.9% of the times. Total valve lift happens at 102°+ ATDC, when the piston is over 1.9" down he hole, how can they become intimate? It's during the overlap (exhaust-to-intake changeover) TDC cycle that they can hit the piston.

Here's a comparison using the X-303 cam with both ratio rockers.....

Click the image to open in full size.
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Old 06-30-2010, 12:20 AM   #7
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I wish I knew as much **** about a ford as this^ guy
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Old 07-02-2010, 12:08 AM   #8
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I think there won't be a problem with the rockers.
But
If you are using headers that are 1 5/8 O.D. they are only 1 1/2 I.D.
You'll need 1 3/4 O.D. headers for the new heads with 1.60 exhaust valves.......
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Old 07-02-2010, 01:04 AM   #9
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I doubt you will be able to tell the difference between the two.
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Old 07-02-2010, 01:04 AM
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