Glad I changed camshafts

[threewood]

So I swapped cams in my GTX in May. Not because it was running bad, but because I wanted a bit more duration. Old cam was a Hughes STL3842 with Hughes supplied edm lifters. And I always used either VR1 or Driven oil.

So I started looking at the cam and noticed crown was gone on several lifters and cam lobes had taper worn off. It appears they were all still spinning somehow as the wear is uniform. One cam lobe pictured is shorter and rounder than the rest.

That cam was in 9 years with a few thousand miles on it. No troubles.

 

[threewood]

 

[davek]

couple thousand miles on it , that sad.

 

[Kern Dog]

My Lunati looked like that after a few thousand miles. I pulled it in 2014 to run a smaller cam....that lost lobes in 2022. I put the Lunati back in and it runs fine.

For having a cam so wild, the engine runs as smooth as ever.

 

[threewood]

In any event, I'm sending out those used lifters to get reground so I have something for the next cam swap down the road. That's the only reason I was looking at them.

 

[68-500]

Can I ask what where your spring pressures?

 

[threewood]

Can I ask what where your spring pressures?

Hughes springs #1128. I used the same springs for the new cam. I'm hoping that the rate will be a little less than when they were new. Both cams were broken in without the inner springs.

 

[Geoff 2]

No FT cam is going to like a 436# spring rate, new lifters or not....

 

[Kern Dog]

Whoa...I missed that. Holeeee ****, really? I have 130/330 with this flat tappet Lunati with just shy of .600 lift. (1.6 rockers)

I agree, you need to REthink that spring choice. TWO things are considered to be leading causes of flat tappet cam failures...improper oil and excessive spring pressures.

 

[BSB67]

Hughes always recommends stupid high valve spring pressures, IMO. But they’ve been doing it for 30 years.

 

[PRHeads]

I guess no one ever read the DC/MP engine manual and looked at the spring chart.

They had some FT springs with rates higher than 436lbs/in.

 

[threewood]

Hughes always recommends stupid high valve spring pressures, IMO. But they’ve been doing it for 30 years.

What rate would you recommend?

 

[BSB67]

My mistake. My comment was to HFT cam.

 

[Krooser]

I guess no one ever read the DC/MP engine manual and looked at the spring chart.

They had some FT springs with rates higher than 436lbs/in.

Not for daily drivers... great if you change cams often

 

[PRHeads]

The cam needs what it needs for spring load to maintain control of the valvetrain, within the parameters it’s operating in.
Max rpm, rocker ratio and valvetrain weight being the key elements affecting how much spring is needed to get the job done.

A spring rate of 436lbs/in, with a seat load of 145lbs and .600” net lift will put the open load at a bit over 400lbs.
While that’s not crazy high for a high intensity cam in a race car, it’s not ideal for something where you’re hoping to rack up a bunch of miles.

Less spring is easier on the cam & lifters, but will result in the valvetrain getting unsettled at a lower rpm.
That’s the trade off.

If less spring will still allow the engine to rev as high as “necessary” for the application, then it’s a viable option.