MS4 110 Lsa First start up
03-28-2007, 05:07 PM
#184
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Here is a good explanation by Tony Mamo, at least I thought so anyway.
Originally Posted by Tony Mamo @ AFR
Is most of you are talking about hydraulic rollers.....the textbook .080/.100 minimums were more aimed towards a solid valvetrain although a properly set-up solid valvetrain could be tweaked tighter.
A hydraulic roller valvetrain at the RPM levels most of us routunely spin them to (7K ish) is always on the verge of valvefloat and in fact all suffer from varying degree of valve control loss at those RPM's. What does that mean....it means the valves aren't precisely following the cam lobe any longer and what started as .076 P to V is now .020 or worse. Many of you are lightly tagging pistons and wont know about it till your engine comes apart and see the small eyebrows in the pistons the valves started forming from lightly tagging at high RPM's.
A high revving hyraulic roller set-up needs more P to V than a similar solid roller set-up. A solid roller has no lifters pumping up and bleeding down with oil creating potential stability issues and also has the benefit of more seat and open pressure to keep that cam lobe (and valve) glued to the lifter and following the exact events the valve and piston have in relation to one another (and making more power by being able to do so).
I also agree that running less piston to valve is a better gamble with an A4 car, but none the less the operative word is gamble. I'm a pretty good manual transmission driver as I have been banging gears as long as some of you reading this have been on the planet and all I can tell you with a manual trans car is stuff happens....I missed a shift trying to pull 3-4 in a nanosecond and hit 2nd instead of 4th....it happens to the best of us with a tight "H" pattern shifter. Needless to say I logged 8508 RPM's and I felt I clutched in and saved it pretty quickly (oooops!). This was with my solid roller 383 I normally shift around 7300....if I had a hydraulic roller and even the textbook minimum P to V clearance I would have bent a bunch of valves if I was lucky or simply grenaded the engine. Morel of the story is you have to be more conservative with an aggressive hyd. roller combination and pushing those tolerances closer and closer just begins to quickly narrow your window for a mishap. And dont think "it wont happen to me"....it will and it's just a matter of time.
IMO if you have much less than the .080/.100 rule, take the extra time to notch your pistons.....its really not that big a deal.
Tony M.
A hydraulic roller valvetrain at the RPM levels most of us routunely spin them to (7K ish) is always on the verge of valvefloat and in fact all suffer from varying degree of valve control loss at those RPM's. What does that mean....it means the valves aren't precisely following the cam lobe any longer and what started as .076 P to V is now .020 or worse. Many of you are lightly tagging pistons and wont know about it till your engine comes apart and see the small eyebrows in the pistons the valves started forming from lightly tagging at high RPM's.
A high revving hyraulic roller set-up needs more P to V than a similar solid roller set-up. A solid roller has no lifters pumping up and bleeding down with oil creating potential stability issues and also has the benefit of more seat and open pressure to keep that cam lobe (and valve) glued to the lifter and following the exact events the valve and piston have in relation to one another (and making more power by being able to do so).
I also agree that running less piston to valve is a better gamble with an A4 car, but none the less the operative word is gamble. I'm a pretty good manual transmission driver as I have been banging gears as long as some of you reading this have been on the planet and all I can tell you with a manual trans car is stuff happens....I missed a shift trying to pull 3-4 in a nanosecond and hit 2nd instead of 4th....it happens to the best of us with a tight "H" pattern shifter. Needless to say I logged 8508 RPM's and I felt I clutched in and saved it pretty quickly (oooops!). This was with my solid roller 383 I normally shift around 7300....if I had a hydraulic roller and even the textbook minimum P to V clearance I would have bent a bunch of valves if I was lucky or simply grenaded the engine. Morel of the story is you have to be more conservative with an aggressive hyd. roller combination and pushing those tolerances closer and closer just begins to quickly narrow your window for a mishap. And dont think "it wont happen to me"....it will and it's just a matter of time.
IMO if you have much less than the .080/.100 rule, take the extra time to notch your pistons.....its really not that big a deal.
Tony M.
