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Bracket Talk Bracket Talk Forum Tech Talk - by Abruzzi Determining pushrod lengthGo | New | Find | Notify | Tools | Reply | |
| Determining pushrod length | Login/Join |
DRR S/Pro |
Needing to determine pushrod length for a SBC with stud mount roller rockers and a solid flat tappet small base circle cam. I've read articles, posts and watched Youtube videos. It looks like there are 3 schools of thought, the center of the valve tip, the narrowest sweep pattern and the 90* at mid-lift. What method has worked for determining the length for you? | ||
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| DRR Sportsman |
I used to have a builder local to me whose engines held records in nearly every nhra sportsman class and won many bracket races. “ center the pattern on the valve and don’t worry about the rest of what you read. “ That is how I’ve done it for thirty years and always works for me. | |||
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| DRR S/Pro |
I would agree with this. If you aren’t centered then you will start putting side load on the valve stem all though it may only be a little it adds up. | |||
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| DRR Top Comp |
Depends on the spring pressures in play, the complexity of the build. Compromises. | |||
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| DRR S/Pro |
Your missing the whole picture here, valve stem side load comes from a lot more than where the roller hits the top of the valve! Why do you think they make needle bearing roller tips? If max lift from a given lobe is the goal, then the rocker needs to be at 90 degrees to the valve stem at half lift due to the circular motion of the rocker tip. If it's not you will loose some lift. | |||
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| DRR S/Pro |
This is why I started this discussion after reading a lot. I even broke out my old Smokey Yunick Speed Secrets book. He stated as long as it's not rolling off of the valve and within .020 of the edge it was good. | |||
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| DRR S/Pro |
My first thought as to why they make needle bearing roller tips would be to eliminate the wear created by the stock style lifter sliding back and forth on top of the valve step. | |||
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DRR Elite |
Not mentioned, but after you sort out the tip contact desired, using a mild spring and a full build mock up using an adjustable push rod is how I found the length. Once that length is measured for intake and exhaust and you have verified all 16 valve tip heights are same, order the custom length push rods. 2005 2000lb 4 link dragster home brew 582 BBC Dart 355 1.058 2.98 4.629@149 6.094 7.310@185 | |||
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DRR Sportsman |
https://www.lunatipower.com/ho...-valvetrain-geometry This is the simplest method I have seen. 72 Nova "Hooptie" | |||
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| DRR S/Pro |
The Lunati link is interesting in the fact I have an old Lunati catalog. They show and explain their formula for mid-lift method. Interesting how there isn't much about pushrod angle to rocker arm discussed. | |||
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DRR Sportsman |
I bought a used motor built by a rep. builder, the sweep was backwards, (started near exh. swepted up towards intake) but lasted 300+ runs w/o problems. Yes, I corrected it... | |||
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| DRR S/Pro |
OK, what method did you use to correct it? Was your sweep wider or narrower on the stem? | |||
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| DRR Sportsman |
That link to lunati refers to exactly what I quoted in my reply earlier. Very simple and works well with stud mount rockers. | |||
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Bracket Talk Bracket Talk Forum Tech Talk - by Abruzzi Determining pushrod length
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