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valve lash

General engine tech -- Drag Racing to Circle Track

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dondon
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valve lash

Post by dondon » Thu Jul 30, 2020 11:01 pm

I watched a episode of road kill and they were dynoing a motor with a hydro roller cam, they later put solid rollers on the HR cam. how would they determine what the valve lash should be. they did pick up about 7 hp. Is this a practical swap as my hydraulic lifters pumped up at about 5800 and the power was still climbing on the first pull at 6000, should of gone to about 6200

F-BIRD'88
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Re: valve lash

Post by F-BIRD'88 » Thu Jul 30, 2020 11:45 pm

The valve lash would be set between .002" and .009".
There are lots of factors as to why your hyd lifters are giving up the ghost too soon... cam profile not stable. weak valve springs. lifter collapse or pump up. . Pushrod instability.
Air in oil. Swapping in solid rollers helps determine what is coming up short. They don't pump up nor collapse, nor are affected by air in the oil. . They tend to be lighter and can take more spring pressure to keep the valvetrain in control.
The lash would be set very tight...

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Re: valve lash

Post by F-BIRD'88 » Fri Jul 31, 2020 12:03 am

Is yours a big block chevy engine?

dondon
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Re: valve lash

Post by dondon » Fri Jul 31, 2020 12:57 am

331 cu. in. sbf, promaxx heads, after market pushrods, elgin hr 224/232 .542/.563, roller rockers,

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Re: valve lash

Post by F-BIRD'88 » Fri Jul 31, 2020 3:00 am

Limited info.. Eliminate the whole ignition system as the cause, first.

travis
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Re: valve lash

Post by travis » Fri Jul 31, 2020 3:15 am

The factory valve springs that come on those heads are a little light on pressure

My427stang
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Re: valve lash

Post by My427stang » Fri Jul 31, 2020 9:43 am

To spin a hyd roller you need to look closely at lobe design and springs, not only open pressure but seat pressure is critical too.

Often a lobe is so quick that it can be noisy and hard to control. However, before I changed cams or lifters, I would look at open and closed height/pressures first. On my FEs which are much heavier, I like 150 closed, 400-ish open. Might be excessive for you, but it's a good reference.

Then be sure you are adjusting preload properly and ensure you are running the correct oil for the lifters, when in doubt, a good racing 10w30 blend should get you there. You may find a Saturday morning spring setup and oil change will get you quite a bit more RPM.
70 Mustang, 489 FE, TKO-600, Massflo SEFI, 4.11s
71 F100 SB 4x4, 461 FE, 4 speed, port injected EFI, 3.50s

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Re: valve lash

Post by mag2555 » Fri Jul 31, 2020 9:59 am

How has your spring pressure changed since that first pull?

Will the motor rev passed 6K with no load on it?

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