question on crane rockers w/sts kit
11-19-2005, 03:03 PM
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question on crane rockers w/sts kit well, i have my sts kit installed. I'm using the stock cam (CA) but had comp 918 springs, Ti retainers and PRs installed to control valve float under boost. Now i'm thinking about putting roller rockers in. I'm interested in the the Crane 1.8 "quick-lift" rockers.
Will these:
1. have enough PTV clearance (stock cam)
2. be okay with comp 918 springs (w/ up to 9 psi of boost)
3. provide a decent hp increase?
It's advertised that they give up to 20RWHP on a stock car. I was wondering if they would give more with a boosted application because of the greater lift or if it would be diminished since the car is boosted and the amount of lift on the valve is not as crucial as a NA motor.
Thanks for all your help!
Will these:
1. have enough PTV clearance (stock cam)
2. be okay with comp 918 springs (w/ up to 9 psi of boost)
3. provide a decent hp increase?
It's advertised that they give up to 20RWHP on a stock car. I was wondering if they would give more with a boosted application because of the greater lift or if it would be diminished since the car is boosted and the amount of lift on the valve is not as crucial as a NA motor.
Thanks for all your help!
11-19-2005, 04:30 PM
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They will work fine with your stock cam and have no clearance issues, they also work fine with the 918's.
As for HP gains, I don't know.. They are well made parts though.
As for HP gains, I don't know.. They are well made parts though.
11-19-2005, 10:16 PM
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1. yes. as i did it on the wife's car for over a year.
2. couldn't say for sure. when using higher ratio rockers, you need less seat pressure to work. but, with FI, you need more spring pressure to control the valve from opening off the seat while under boost.
some tech from Vinci Tech and Tuning Page
3. for me, i got 17 rwhp out of them with the stock cam.
2. couldn't say for sure. when using higher ratio rockers, you need less seat pressure to work. but, with FI, you need more spring pressure to control the valve from opening off the seat while under boost.
some tech from Vinci Tech and Tuning Page
Originally Posted by vinci tech and tuning page
Is Choosing The Right Valve Springs for Supercharged Engines Critical?
Selecting the proper valve spring for any performance engine is important; but it is critical to proper operation of supercharged engines. Consider the fact that when the engine is in a "boosted" condition, the supercharger (or turbocharger) is trying to blow the intake valve open. The boost pressure actually reduces the intake valve spring seat pressure. This is extremely critical on engines with hydraulic lash adjustment. Proper seat pressure (working through the rocker arm and pushrod) is necessary to keep the hydraulic lifter plunger centered in the lifter body to prevent "pump-up." If an engine has 2.25" dia. intake valves, there is 4 sq. inches of backside valve area. Now add 12 (psi) of boost pressure, and you have reduced your effective seat pressure by 48 lbs. (12 lbs/sq.in. X 4 sq. in.). If you started out with 120 lbs. of seat pressure (static), you now have 72 lbs. of operational seat pressure. There is no way that 72 lbs. of pressure is going to control a 2.25" valve!
Selecting the proper valve spring for any performance engine is important; but it is critical to proper operation of supercharged engines. Consider the fact that when the engine is in a "boosted" condition, the supercharger (or turbocharger) is trying to blow the intake valve open. The boost pressure actually reduces the intake valve spring seat pressure. This is extremely critical on engines with hydraulic lash adjustment. Proper seat pressure (working through the rocker arm and pushrod) is necessary to keep the hydraulic lifter plunger centered in the lifter body to prevent "pump-up." If an engine has 2.25" dia. intake valves, there is 4 sq. inches of backside valve area. Now add 12 (psi) of boost pressure, and you have reduced your effective seat pressure by 48 lbs. (12 lbs/sq.in. X 4 sq. in.). If you started out with 120 lbs. of seat pressure (static), you now have 72 lbs. of operational seat pressure. There is no way that 72 lbs. of pressure is going to control a 2.25" valve!