Suggest a cam for my /6 build.

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timk225

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I'll be improving the /6 in my 1973 Duster a bit, but nothing too extreme. I'd like to cam it a little better, but it probably won't be too far from stock specs, so I'd like to get cam suggestion ideas for what I plan to end up with.

Intake - OEM iron super 6 intake, Holley 350 2 bbl, basic air cleaner. No nitrous or turbo.
Head porting / valves - cleaned up stock head, probably stock size valves, head cut about 0.060" to compensate for the thicker than stock Fel-Pro head gasket, and then a little more. Stock valve springs, maybe something slightly better.
Block - stock, maybe decked to blueprint specs of 10.68" for a 225. Stock oil pump and stock pressure. Oil holes in block and crank maybe drilled a bit. Half or full groove bearings. Mild oil pan mod to keep oil from rushing to the back of the pan on acceleration. Maybe a crank scraper. Double roller timing chain.
Exhaust - stock manifold or maybe Clifford 55-0010 headers 3 into 1 type, 2-1/4" exhaust pipe.

Transmission - stock 904, stock converter.

Rear axle - 2.76 or maybe 2.94 gears. 205-70-14 tires.

Whatever cam I get, I definitely don't want anything from Comp Cams or with Chevy lobes. Something made for our .904 lifters. It'll be a weekend car, so I'm not trying to get too crazy with it, but would like to improve it somewhat. Maybe an extra 30-40 horsepower.

Way back in about 2002 when I built a /6, it was a big valve ported head, Offenhauser 4 bbl intake, Holley 450 mechanical secondary, stock torque converter, the 904 had a wide ratio gear set, and 3.21 rear gears. I used a 268 Purple shaft cam. It was WEAK until about 3000 rpms, then it'd pick up and run ok. It ran mid 16's in the 1/4. I couldn't afford any torque converter at the time, I think that's most of what held it back.
 
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timk225 said:
was WEAK until about 3000 rpms,
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Pretty common with a modified Slant. I drag raced my Slant, actually many of them.All had that then pulled like gangbusters at the 3,000 mark. Gear ratios ranged from 2.76 TO 4.30. I ran a 3,000 stall converter and was same as a stock converter. Ordered a 4,500 NOW YOU ARE TALKIN'.
timk225 said:
I couldn't afford any torque converter at the time, I think that's most of what held it back.
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Yep.
It's been awhile, I believe Hughes Engines have some slant cams that spec out quite nice.
Maybe they still do.
 
timk225 said:
I'll be improving the /6 in my 1973 Duster a bit, but nothing too extreme. I'd like to cam it a little better, but it probably won't be too far from stock specs, so I'd like to get cam suggestion ideas for what I plan to end up with.
Click to expand...

Dutra RV-10RDP, grind № 2106R from Oregon Cam.


timk225 said:
Head porting / valves - cleaned up stock head, probably stock size valves, head cut about 0.060" to compensate for the thicker than stock Fel-Pro head gasket, and then a little more.
Click to expand...

Measure your combustion chambers rather than just guess at an amount of head milling. Also, split up your milling between head and block.

timk225 said:
Exhaust - stock manifold or maybe Clifford 55-0010 headers 3 into 1 type, 2-1/4" exhaust pipe.
Click to expand...

You'll hear the name "Clifford" come up, but be very careful before you decide to spend any money with Clifford. They have a long and ugly reputation for being a bunch of clowns; see for example here, here, here, here, and here. Much of what they sell is inaccurately described, and a lot of it is not even slightly cost-effective.

Pick between a stock manifold or a Dutra front-3 casting with a cut/capped stock manifold for the rear three cylinders, either option with a thoughtfully-configured exhaust system like this


timk225 said:
Transmission - stock 904, stock converter.
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TransGo TF-1 shift improver kit

timk225 said:
Rear axle - 2.76 or maybe 2.94 gears. 205-70-14 tires.
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I'd go 2.9s, if you have the choice. Either way, this reinforces the cam recommendation above; it's a torquer grind, which is what you want with a tall rear axle.
 
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For the RV-10RDP, what valve springs are recommended? It's not a lot more lift than stock, would stock Slant 6 / 318 replacement springs be fine? I don't want to use more spring pressure than necessary, putting extra load on the valve train.
 
What they said.... Block decked 0.060, head cut 0.020, OEM steel head gasket, Oregon Cam 1206, Dutra Duals with the Y back at the transmission cross member for peak torque at about 3000 RPM, over sized valves, very slight cleaning up of the ports with an Offy dual one barrel manafold with two 275 CFM carbs.. It is a hoot to drive.

 
Change to a 3.23 gear and it will feel like it has 40 more horsepower compared to the 2.76! 2.xx gears are a dog on take off. Are you doing a lot of cruising at 70 mph with the car, or what are your goals?
 

They are close enough that you probably won't notice the difference. The only thing I don't like is the extra lift. Doug did a lot of head testing and found that stock heads don't do much over the 0.446" in the RV10 other than put more stress on the valve train. I don't know if the 0.483" will be enough to need stronger valve springs or not. Have to ask Hughes. The RV does have another 6 degrees of exhaust, again probably can't tell in the real world.
 
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