You should not have any problem with piston to valve clearance, you piston is 1/8" (0.120") below the deck at TDC, and as mentioned, duration is what reduces P-V clearance. The maximum lift will occur around 108 degrees after TDC (depending on where you degree in the cam centerline), so the piston will be more than 1/2 way down the bore (well over 1-1/2") at that point.
The two places that lift might be an issue is valve spring coil bind and retainer the valve guide seal clearance. With these small cams (under 0.550" lift) neither of these clearances should be a problem.

If this helps you any, my 1974 FSM lists the following:

400 2bbl/440 std cam
260* intake duration .434 lift/268* exhaust duration .430 lift
intake opens (BTC)18
intake closes (ABC) 62
exhaust opens (BBC) 68
exhaust closes (ATC) 20
Valve overlap 38

400 4bbl/440-HP
268* intake duration .450 lift/284* exhaust duration .464 lift
intake opens (BTC)21
intake closes (ABC) 67
exhaust opens (BBC) 79
exhaust closes (ATC) 25
Valve overlap 46

Thanks Daytona

That does help.

I know this is totally different than what i was looking for but has anyone tried this cam? Would it work with stock springs/valve train? SMC2942BL Hues. Hues says it is specifically made for low compression motors. Don't know how the vacuum would be for the power brakes?

Like I said this is my first time doing this. It seems the options are endless.

Dave Hughes has a good rep. & a cam for low compression would for sure have enough vac for PB, no worries there.

That is the Whiplash cam. It installs at 102 intake centerline (closes the intake early for good dynamic compression) and has a narrow lobe seperation angle which gives it alot of overlap (rough idle, low vacuum.)


It will work with your compression. The Dynamic compression is almost the same. Remember the stock cam 206duration @ 0.050" installed at 112 intake centerline = 7.40:1
The 216 duration @ 0.050 cam installed at 107 ICL = 7.40:1 (108 ICL = 7.37:1)
The whiplish cam 229 duration @ 0.050" installed at 102 ICL = 7.35:1 dynamic compression.

Call Hughes up and tell them what you are doing and see what they recommend.

FWIW I would send it all to FAST 68 and let him do it for you as well as pick a cam.Probably be the best end result for you.

If you use the Hughes Whiplash cam it would be fine with a 4speed, but if you have an automatic, you are going to want a higher stall convertor. I found this out the hard way in a 383 w/727. I have to swap convertors next weekend, because when I put it in gear it lugs the motor down and stalls. Definitely needs a looser convertor.

so one of those cams intended for low comp actually has low vac? I never would of guessed & I woulda thought just the opposite.

You're surprised a cam that specs out as 232/245-107(as per the Hughes site)would have low vacuum?

I would absolutely expect low vac out of that cam...... Especially in a low cr motor.

It's designed to idle rough...... Which is done by dirtying up the idle with lots of overlap.

I didn't see it mentioned anywhere...... But if the "plan" is to retain the OE carb(TQ), intake, and exhaust manifolds, then IMO........ That really narrows down what I would feel are the "appropriate" cam choices.

And if that is how it's going to be run, then I def feel the big valves are a step in the wrong direction.

and then avoid it at all costs ...

Well I ain't a cam guy & I had assumed that a cam that is specifically designed to build/trap compression would have a good vac #. Obviously not & I learned something today.

psh you said the cam had flat lobes , safe to assume you are taking this engine further down ... like completely apart ... than just a bad choice head rebuild?

If you are stuck on stock iron junk then fast68plymouth is the person to see , it's only a 2.5 to 3 hour ride up to his shop.

I still vote for the Crower 267HDP

I know some of you wont like this but I purchased the KC661 kit. I Know I know. It mimic's the original.

Cam Lift Exhaust (Inch) 0.3090
Cam Lift Intake (Inch) 0.2990
Cam Series Pro-3000
Cam Type Hydraulic
Duration @ .006 Lift 292/309
Duration @ .050 Lift 214/225
Engine Family Big Block
Exhaust Duration 225
Exhaust Lift (Inch) 0.4640
Exhaust Lift (MM) 7.849
Exhaust Valve Lift 1 (MM) 11.786
Footnote Code (050) Duration at .050 Lobe Lift
Intake Duration 214
Intake Lift (Inch) 0.4490
Intake Lift (MM) 7.595
Intake Lobe Center 110
Intake Valve Lift 1 (MM) 11.405
Lobe Separation 115
Manufacturer Chrysler
Overlap 46

Thanks again for all of your input.

Nah we're good with that! post how it acts when the time comes.

I have the same car

35000 mile 74 Roadrunner with a 400/auto.

My car is stock except for a 3" TTI exhaust and 3.91 gears.

The no. 5 intake lobe went bad and I had to replace the cam.

The cam that's free is right for me, so I wound up with a 274 comp.

This is not a great selection, rough idle noticeably less low end torque. I'm not happy with it.

I was going to make the same post, so this is what I need to know.

I look forward to seeing how it works out for you.