[blubiu65]

Contemplating a cam change. Current combo is a 428 with ported 670 heads, Performer RPM intake with 850, Turbo 400 with 3400-3800 Continental convertor, 4.10 gear, 28 inch tall tire. Cam is a Crower HFT 524/540 246/254 at .050 on a 108. However I run a 1.65 rocker so lift is actually higher.

I have a cam that I would like to try. It is a SFT with 555/555 260/260 at .050 on a 110. I would also run the 1.65 rockers on this.

Do you think that I would see much improvement? Is it worth it? I know the new cam has more lift and duration but going from a 108 to 110? Thoughts and opinions please.

[Stan Weiss]

Originally Posted by blubiu65

Contemplating a cam change. Current combo is a 428 with ported 670 heads, Performer RPM intake with 850, Turbo 400 with 3400-3800 Continental convertor, 4.10 gear, 28 inch tall tire. Cam is a Crower HFT 524/540 246/254 at .050 on a 108. However I run a 1.65 rocker so lift is actually higher.

I have a cam that I would like to try. It is a SFT with 555/555 260/260 at .050 on a 110. I would also run the 1.65 rockers on this.

Do you think that I would see much improvement? Is it worth it? I know the new cam has more lift and duration but going from a 108 to 110? Thoughts and opinions please.

While the SFT cam probable will have more intake duration, there is a good chance it will have less exhaust duration. What is the lash setting for the SFT? Can you paste the cam cards?

Stan

[Scott Stoneburg]

When I ran my 428, ported 62s, Torker I manifold, Holley 830 cfm carb. I swapped a few came, never seen a lot of difference. Cam changes...
Comp HFT 292H cam. 244 dur@.050- .501 lift. - 110 lobe Sep.
Comp SFT. 306S cam 260/260 Dur. @ .050. - .555 lift. 110 lobe Sep.
Comp SR .288R. 288/288 adv dur. .555 lift. 110 lobe Sep.
It did run better with each change but marginally. I probably needed better springs for the roller but do not recall if I changed them. I was 18 and did not know enough then. If i recall it may have been a tenth faster in the 1/8 mile.

[steve25]

The end result of the center line change would hinge a lot on how much your heads now flow and the overall Intake to Exh ratio up the peak valve lift that you are running.

Why don't you do a pre test and retard your current Cam 2 degrees ?

I would also try running your current Cam with just the 1.65 rockers on the Intake and then only the Exh and the result of that would for sure give you a clear indication if a single pattern Cam would help or not.

[pastry_chef]

Not specified that your solid cam is from Comp Cams but the posted numbers line up with Magnum Solid Flat lobe 6003
306-5
260 @ .050
164 @ .200
.3700 lobe lift

I did not have a hydraulic flat lobe on file close to your intake lobe specs so I generated one, it is symmetrical. The lighter trace is the solid flat lobe 6003, .020 valve lash. Both using 1.65 rockers. The plots are using the same lobe centerline.

[Stan Weiss]

Mike,
I would guess this is the cam he has. Looks like lash is 0.022"

Stan

[tc]

Comparing a HFT to a SFT cam, kind of a general rule is to subtract 8-10 degrees of duration, at .050 lift, on the SFT. So these two cams are close to the same duration at .050. Also, subtract the .020 lash on the lift number for the SFT cam and the SFT cam lift is close to the HFT cam.

[pastry_chef]

Originally Posted by tc

Comparing a HFT to a SFT cam, kind of a general rule is to subtract 8-10 degrees of duration, at .050 lift, on the SFT. So these two cams are close to the same duration at .050. Also, subtract the .020 lash on the lift number for the SFT cam and the SFT cam lift is close to the HFT cam.

How the relative duration numbers compare depends on the solid cams designed ramp height and how aggressive the lobes are. I think the Magnum Solid lobes are early 80's designs, using a fairly tall ramp height.

In post 5.. those lines represent about a 6 degree gap at .050 net valve duration.

[Steve C.]

This might be of interest.....

On the Speed-Talk website, this question was asked of Mike Jones, of Jones Cam Designs.

"Mike, you may have already tried to explain it, but why the added duration for a solid lifter cam vs the same spec hydraulic cam?"

Mikes reply:

"If you want the valve lift curve to be the same, the solid(Mechanical) lifter cam will be bigger at .050".
That's because with the hydraulic lifter you start opening the valve at around .004"-.006" lifter rise, so .050" lifter rise is .044"-.046" above the point the valve is opening. Now, with the mechanical lifter you start opening the valve at the hot lash point divided by the rocker ratio(normally around .012"-.016" lifter rise), so .050" lifter rise is only .034"-.038" above the point the valve is opening. So if you only look at the lift above the point the valve is opening, you're trying to compare the duration @ .045" on the hydraulic cam, with the duration at .036" on the mechanical cam."



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