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PostPosted: Wed Feb 12, 2020 10:26 am 
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TBI Slant 6

Joined: Sun Mar 28, 2004 2:48 pm
Posts: 174
Location: Phoenix, Arizona
Car Model*:
I've received a new cam from Oregon Camshaft, which recommended grind #1461.
It's a cam that provides more power but still delivers a smooth idle for street use.
The slant six is a 1968 225 to be converted to hydraulic lifters. The machinist has not started on the head.
The plant is to "port & polish" the head, shave up to 0.10 to boost compression and install eng bldr oversize valves.

I need your help with 2 things:
1. What valve springs I should order for this application"
2. Are the stock pushrods OK, or do I need to order shorter versions (0.80)?

The cam card contains the following information:

Intake Exhaust
Cam Lobe Lift .251 .274
Advertised Duration
Duration @ .002" Tappet Rise 270 291
Duration @ .006" Tappet Rise 252 267
Duration @ .015" Tappet Rise 237 247
Duration @ .020" Tappet Rise 230 240
Duration @ .026" Tappet Rise 224 234
Duration @ .050" Tappet Rise 205 212
Duration @ .100" Tappet Rise 174 180
Duration @ .200" Tappet Rise 113 120
Valve Clearance: INT: H EXH: H Lobe Diameter: INT: 1.600 EXH: 1.605
Base Circle: 1.319 EXH: 1.311
Checking Tappet Dia.: 904 Tappet Type: Flat Hyd
Cam Timing @ 050" Tappet Rise: Open Close
Intake -6 BTDC 31 ABDC
Exhaust 42 BBDC -10 ATDC
-15½° overlap @ .050
Theoretical Valve Lift (with .000 Lash) with rocker ratio 1.50:1 INT: 422 EXH: 441

Thanks in advance to anyone who can answer these questions.

--Walt Jackson


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PostPosted: Wed Feb 12, 2020 1:51 pm 
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SL6 Racer & Moderator
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Joined: Sat Oct 19, 2002 12:06 pm
Posts: 7401
Location: Silver Springs, Fl.
Car Model*:
I would say the stock replacement slant six/318 valve springs should be fine. They are stiffer then the oem slant six springs. Or you could use stock 340 replacement springs. As for pushrods, the only way to tell is to assemble the valve train, and measure. Too many variables to make a guess. Don't forget to allow for lifter preload.

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PostPosted: Thu Feb 13, 2020 8:41 am 
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Guru
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Joined: Sat Oct 12, 2002 11:22 am
Posts: 3594
Location: Sonoma, Calif.
Car Model*: Many Darts and a Dacuda
Adjusting for the proper hydraulic lifter preload is the biggest concern, especially when machining the head for additional compression.
This will be a 2 step process:
1st, make sure all the valve stems are set / adjusted to the same height.
2. Measure for the needed push rod length plus .020 to .030 of lifter preload.
( I use an adjustable length push rod to take this measurement)

Use the length number to see if you stock push rods will do the job or order a custom made set at the needed length.
DD


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PostPosted: Thu Feb 13, 2020 9:49 am 
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Supercharged

Joined: Wed Sep 17, 2008 6:48 pm
Posts: 2931
Location: Indianapolis
Car Model*:
Quote:
Measure for the needed push rod length plus .020 to .030 of lifter preload.


The hydraulic lifters from the 83 D150 had a lot of internal cylinder travel, almost .090
I disassembled a lifter and verified the travel of the internal cylinder I did that as
before I took the OE valve train off the engine I had marked the pushrods with a horizontal line scribed
on them at the valve cover rail height and then marked a scribe line again after the rocker shaft was loose and free.
The pushrod had moved up about .040

To be safe, I would check to see how much travel the hydraulic lifters that you are using have. Then set the preload a bit shallow of the midpoint
of the overall travel.


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PostPosted: Fri Feb 14, 2020 8:45 am 
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Guru
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Joined: Sat Oct 12, 2002 11:22 am
Posts: 3594
Location: Sonoma, Calif.
Car Model*: Many Darts and a Dacuda
It is nice to see that the special hydraulic SL6 lifter seems to have a little more travel compared to the V-8 (I see around .060 with those)
This give us a little more "room" to work with as far as length variation goes but still, try to get all the stem length as even as possible.
DD


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PostPosted: Sat Feb 15, 2020 9:41 am 
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Turbo Slant 6
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Joined: Tue Nov 23, 2004 6:05 pm
Posts: 614
Location: Desoto Texas
Car Model*: 1972 Dodge Colt
340 spec springs from Rock Auto are pretty cheap.

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