John/Duke_ setting lash on LT-1 cam

[Steve D.]

I'm following the cold setting procedure. Starting at TDC #1, set #8 exhaust and #2 intake. At TDC #1, the #8 exhaust lifter is exposed about 1/4", but the top of the #2 intake lifter is flush with the bore. Is there anything amiss here? I expected both to be flush if they are sitting on the base circle of the cam at this point.

Steve

[Joe C.]

Re: John/Duke_ setting lash on LT-1 cam

You are at TDC of the exhaust stroke. You must be TDC compression stroke, where the rotor points to the tower of the target cylinder.
John and Duke developed a more accurate lash setting procedure than the Service manual shows. They will certainly be here to show it to you.

[Steve D.]

Re: John/Duke_ setting lash on LT-1 cam

Joe
Thanks. I rotated the crank 360 and all appears well. Duke sent me the cold setting procedure, and that is what I'm trying to follow.

Steve

[John Nuzzo]

Re: John/Duke_ setting lash on LT-1 cam

Would be interested in knowing if John/Duke's procedure would be applicable to a C1 (098) cam as well?

[Steve D.]

Re: John/Duke_ setting lash on LT-1 cam

John

A comment in the procedure write up says that it is applicable to all solid lifter cams. If you don't have a copy of the procedure, send me an email and I will return it with the procedure attached.

Steve

[Joe C.]

Re: John/Duke_ setting lash on LT-1 cam

I don't think that it applies to the "Duntov" cam. It applies to the "30-30" for both intake and exhaust, and the LT1 for intake (exhaust?) only. The "30-30" uses identical lobes for both intake and exhaust. The engineers liked it so much, that they borrowed the "30-30" intake (exhaust?) lobe and stuck it onto the LT1 shaft. The exhaust (intake?) doesn't have as steep a ramp, and so responds well to the more conventional setting procedure outlined in any manual showing lash setting procedure.
"Duntov" doesn't have the steep ramps either, so same applies.

[John Nuzzo]

Re: John/Duke_ setting lash on LT-1 cam

Thanks all............I have the standard proceedure Joe.

[Duke W.]

Re: John/Duke_ setting lash on LT-1 cam

You can adjust each cylinder's valves (both of them) at TDC of the firing stroke on the Duntov cam, but that won't work for the 30-30 or LT-1 cam, The Duntov can also be set using the procedure for the latter two.

The procedure also has "factored" lash settings that take into account actual rocker ratio at the lash point.

E-mail me and I'll sent you the Word document.

Duke

[Duke W.]

Re: John/Duke_ setting lash on LT-1 cam

The procedure applies to any mechanical lifter cam, but since the Duntov is shorter duration from the beginning of the opening clearance ramp to the end of the closing clearance ramp, both the inlet and exhaust are on the base circle at TDC of each cylinder. Both lobes of the 30-30 are NOT on the base circle at TDC. The LT-1 cam exhaust lobe is NOT on the base circle at TDC. The inlet is, but just barely.

I use the term "ramp" for the clearance ramps. I use the term opening or closing "flank" for the portion of the cam above the clearance ramps so as not to confuse these two very different portions of the lobe.

In terms of dynamics, all these cams are very mild, but the 30-30 is the mildest with peak acceleration of 3000E-6 inches/cam degree on opening. The Duntov and LT-1 inlet lobe are 3200. Since the Duntov lobe is symmetrical its closing characteristics are a mirror image of the inlet. The other lobes are asymmertical. Peak closing acclereration for the 30-30 lobe and LT-1 inlet are 2500E-6 and 2600E-6 respectively.

The LT-1 inlet lobe is the L-72 lobe (both sides of the L-72 cam have the same lobe), and as previously mentioned, the exhaust side of the LT-1 cam is the 30-30 lobe, but it is advanced 4 (crankshaft) degrees relative to the 30-30 cam.

The Duntov cam has the same lobe on both sides, with the exception that the exhaust side clearance ramp is .004"taller. The opening and closing flanks are identical for both inlet and exhaust.

The bottom line is that all SB and BB SHP mechanical lifter cams are made up from three basic lobe designs. The LT-1 cam, in particular, was not a new design in the sense that it incorporates two lobes that already existed, but the exhaust lobe point of maximum lift was advanced to 122 BTDC versus its 118 BTDC indexing on the 30-30 cam. The inlet lobe is indexed at 110 ATDC - same as the 30-30 inlet, but retarded two degrees relative to the lobe's indexing on the L-72 cam. The net result relative to the 30-30 is an earlier opening exhaust valve, less overlap, and an earlier closing inlet. This yields better low end torque with about the same top end power. More cam doesn't help top end power because the heads are choked at about 6000 revs. With massaged heads the choke point moves up to about 6500 and at this point the SHP inlet manifold is limiting flow and power to about 360 gross at 6500. FI will improve power with massaged heads, but doesn't help much with the OE machined heads that are the limiting factor on inlet flow.

A 327/375 FI engine with the 30-30 cam in OE configuration will make close to its advertised gross power rating, but if you rework the heads and install a well designed racing exhaust system (headers and side pipes) it will make about 450 gross at 7000 where the heads choke, and more cam won't do much. In this configuration the 30-30 cam's overlap really helps, where it hurts on the OE engine with manifolds, and the FI system manifold is essentially a "tunnel ram", which offers very good flow characteristics. This would be an excellent configuration for vintage racing engine as the valvetrain could be completely OE with excellent reliability. Only a good set of connecting rods is required. All other internal engine parts could be OE.

Duke