Camshaft .006" SAE to .020" Duration Comparison?

[70rcode]

Anyone know how to accurately compare typical 0.550" lift, 250° advertized duration solid flat tappet camshafts rated at SAE .006" lifter check to identical cam advertized at .020" check height for DCR & overlap Calculator uses ? Sometimes, these calculators lose accuracy with .050" input data..thx, ...tom.

 

[BSB67]

You have a "typical" solid flat tappet with an advertised 250° and 0.550" lift....really?

Solid normally use 0.020" or 0.015" lift for advertised. And irrespective of how it's rated, it is the actual lash that will determine when the intake closes. Two SFT cams with an advertised duration at 0.020" will have vastly different actual closing points if the lash is 0.030" verses 0.014".

Some hydraulic, and no solid cams advertised numbers are at 0.006".

That aside, I believe that you have come across the problem with the DCR calculations/calculators. Plus, most people and calculators use the 0.050" intake closing, which is not logical either.

 

[70rcode]

Meant SFT 300° advertized duration in the .550"--.600" valve lift range & how to correct/convert .006", .020" & .050" specs for accurate DCR & other calculator uses..

 

[BSB67]

Let me try an example.

Hydraulic cams are usually measured at 0.006" lift and is usually referred to as advertised duration. I don't know which calculator you are using some use intake closing at 0.050, some use "advertised", some use 0.050 plus 15° (or is it advertised minus 15°?).

SFT cams are usually rated at 0.020" or 0.015" lift and is usually referred to as advertised duration.

Remember it's not what the cam lobe or lifter is doing that matters in DCR calculation, it is what the valve is doing.

If you want to equalize a SFT valve position to a hydraulic valve position that is using 0.006", just use the solid cam's 0.020" number. However, this is only true if the lash is set at 0.021". If your SFT cam is rated at 0.015" tappet lift, it will equal a 0.006" if the lash is set 0.014".

So, said differently, if you simply use the 0.020" or 0.015" number as an advertised number in the calculator, it will be equivalent to a hydraulic measured at 0.006", if the lash is set as described above.

Also remember when using 0.050" numbers when comparing hydraulics to solids that, relative to the valve lift, these numbers are not comparable. A hydraulic cam cam rated at 0.050" tappet lift is actually 0.075" valve lift with a 1.5 rocker ratio. A solid cam rated at 0.050" tappet lift might only be 0.045" lift (if the lash is 0.030"). A rule of thumb is to reduce the the solid cam's 0.050" duration number by 8° when comparing to a hydraulic. The actual could be a couple degrees either way from this.

 

[andyf]

Anyone know how to accurately compare typical 0.550" lift, 250° advertized duration solid flat tappet camshafts rated at SAE .006" lifter check to identical cam advertized at .020" check height for DCR & overlap Calculator uses ? Sometimes, these calculators lose accuracy with .050" input data..thx, ...tom.

There is no easy way to do that since it all depends on which ramps the cam designer used. You have to measure the cam to know what the events are since the information is rarely published and it varies for each lobe design.

 

[70rcode]

Although Crane & others use Solid Flat Tappet .020" advertized duration, the particular Lunati SFT is advertized spec'd at .006", so the obvious SFT correlation attempt for calc's needing seat-seat timing..

 

[PRHeads]

The equivalent checking point for a SFT cam, to compare to a HFT cam that’s using .006” tappet lift as the checking point for “advertised” duration........ is the actual zero lash point......+.006” tappet lift.

In almost all cases, if you want accurate numbers, this would require mocking parts up to determine where that’s actually occurring.

If I’m not mistaken, I believe a variation of that is the SAE method for advertised duration on SFT cams.
Lash point, plus (.006” tappet lift divided by rocker ratio).

 

[70rcode]

Anyone familiar with the actual SAE doccument text # & SAE measurment description ? I've seen "references" to .006" at both Lifter & Valve head ??? ..Cam grinders that use .006" might not using the exact SAE method. Anyone know from the Actual SAE doccument # how the Duration is measured ?

 

[andyf]

You use a dial indicator and a degree wheel.

 

[70rcode]

Hi Andy,...I was trying to duplicate a '65 vintage factory SS cam from their cam card specs..The duration & event #'s look like seat-seat or .006" ....Plenty of event data°, but no reference point (lifter or valve)

 

[70rcode]

The '65 Chrysler cam's spec in question was included in Chrysler's 1966 "Hemi White Paper" presented to the SAE...but I can't seem to locate any historical references to the SAE .006" camshaft measuring procedure as could be measured at lifter or at valve stem..

 

[PRHeads]

With the limited number of Hemi SS engines built....... would it be more likely that the factory ground the cams for them....... or that they had the cams sourced elsewhere?

I’m sure someone knows the answer to that.

If they were sourced elsewhere....... maybe the specs are available from wherever they came from?

I’d call Barton and see if he could shed some light on it.
Plus, he might be able to provide a suitable replacement.

 

[Dodge Bros]

SAE ratings are out at the valve for a solid or hydrualic cam and includes the rocker ratio. The only SAE ratings I know of that get published at the tappet were the .050 and the lobe lift. Did the SAE presentation list the .050? On a solid cam there is a rating difference between the intake and exhaust from the expansion of the exhuast valve. Seems like it is out at the valve and is lash plus .006 on the intake, and lash plus .011 on the exhaust on solids. I would have to look it up for sure, been awhile since I looked at SAE rated solid cams.

Do you have the timing events and the lash from the SAE presentation for the 65 Hemi? Could you post them to see?

 

[70rcode]

Hi Dodge Bros,...Race Hemi Presentation spec'd No duration check measurement method (no mention of SAE or .006" check height) Lift or location point... Flat tappet mechanical, Duration of 312° & Lift of 0.540" at > 7000 Rpm. Compared to the '66 Street Hemi 276° duration at 0.480" solid lifter cam, both were before H. Crane 0.050" duration standardization.

 

[Dodge Bros]

It would not have used SAE rating. The 312* solid cam with .540” lift for the Hemi was ground by Isky in 65. They also did a 300* and .525 in 1965. In 1966 the cam was 324* with .565”. Isky had a big solid roller for the hemi to that made the solid flat tappet cams look tiny. I am not positive, but that 276* cam with .480” may have also originated at Isky too.

We have Isky solid roller cam from that era and, if I recall correct it was rated at .022” tappet. I think the lash was .025” on one cam and .028”/.032” on another. I have a hunch Isky rated the solid flat tappets at the same .022”. But I don’t know for sure, a call to Isky might help if you talked to the right person.

I think Cranes F2 320* (rated at .014”) [email protected] .520” lift solid profile would come pretty darn close to that 312* .54” Isky. Except that Isky would have been symmetrical back in the day, versus that Crane is Asymmetric and slightly short on lift.

 

[Dodge Bros]

The folks at Bullet Racing Cams can look up profiles on the computer and give you specific durations at different lashes. The bigger cam grinders get a little vague when you ask a question like that.

An example is if you had a solid roller lifter running on a hydrualic roller profile Bullet can tell you what the duration is with different lash setting. I usually ask Bullet for the durations at the each end of the lash range on solids. As far as I know they can do that for any cam now that it is on the computer. If you knew for sure a cam had 312* @ .022” and .54” lift, plus a gentle .017” tappet lash ramp design, they could likely look up a profile at that rated lash in a high rpm symmetrical profile, and it would probably be pretty close to that 65 hemi grind. It isn’t all that easy to find a solid with that gentle of a ramp.