Thread: Heads- which is good?

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Hello, I haven't posted much but have kept eyes and ears open getting educated . Well, I've narrowed my choices down pretty much too DART Iron Eagle 165cc- or 180 cc but not sure which I would be good with. I have a sbc 350- stock rotating- with a mild cam- 204 in. and 214 exh. with lift of 420 in. and 442 exh. but have 1.6 rockers that move it to 442in. and 473 exh.
Would the 165 cc be getting restrictive in the upper rpm range? Rarely break 5200-5500 rpm . Right now I have the stock smogger 624 heads from 1976.
I can get the 165 cc about 2 bills less but will they not be enough head if I go to a little bigger cam in a couple months? Summit has a cast iron head at 165 cc that supposedly is cast by DART for them cheaper but still- too small?
Have studied this but no actual experience with after market heads so will gladly accept any ideas from those who know more than I That means pretty much everybody Thanks to all. Sorry, forgot- have 350th auto and 3.73 gears out back.

Well, my personal rule of thumb for a naturally aspirated street motor is cubic inches times 1/2, so for a 350, 175 is about right. I'd go with the 180 cc heads.

You have me a little perplexed with your mention of changing cams in a couple of months. Normally, a builder would optimize the cam for the static compression ratio that is built into the motor from the git-go. If you make much of a change in the cam, you'll have to change the static compression ratio also unless the motor is optimized for the longer cam now.

What is the present compression ratio of the motor?

Thanks for answering. Sorry to be confusing- long day and brain -frazzled. OK, when I change heads thought about going to a smaller chamber- eithier 72cc or 67 cc to bump up comp. from approx. 8.4 scr and 7.6 dcr to about 8.7 scr and 7.9 dcr or 9.1 scr and 8.3 dcr. this with 72cc or 67 cc chambers, respectively. Quench, which I'm still schooling on, will be a bit high around .045-.055 depending on gasket. No actual choice on cam yet as waiting to see what I end up with. But with the bump up in comp. figured that I could step up cam some, maybe in the low to mid 220* range with lift in .470- .510 area.
Hope this clears things up a bit. A bit more info on motor I'm using a holley 600cfm with vac. sec. and Holley 300-36 dual plane intake. Am I looking in the right direction for setting up a stronger motor? Will be street machine only
and actually seems to run pretty good for what it is. Has good get up and go from dead stop and feels pretty torquey in the lower rpm range.
Back to heads- 180cc sounds like the choice now have to decide on chamber size and figure from there.

I'd use the smaller CC chambers. 9-1 compression is a very streetable ratio especially when using a bit bigger cam. Having 8.7 compression is fine but it is limiting your cam options later. A 220 duration cam will run better with 9-1 compression.

OK, thinking along those lines would a 64 cc chamber workable? Would put scr at 9.5 and dcr at 8.6 . Believe I recall something about for just street car and running pump gas that 8.6 dcr would be a little high considering where I'm at on quench? Would I be looking at problems with detonation?

Using a bore of 4.00", stroke of 3.48", 64 cc heads, 8 cc's in the deck, 8 cc's in the gasket and 7 cc's in the piston crown, I get 9.22:1 for scr. With the KB calculator using 5.7" rods and a cam with an intake closing point of 27* ABDC @ 0.050" tappet lift, I get 8.44:1 dcr. According to everything I've read, somewhere around 8.0:1 is ideal for pump gas, but everyone also seems to think the KB calculator is conservative, so I bump it up a little over 8.0:1 when using the KB. If using a cam with a 30* ABDC closing point @ 0.050" tappet lift, the dcr would be 8.33:1. If using a cam with a closing point of 33*, the dcr is 8.21:1, so somewhere in that area of 27* to 33* should work out. You won't be able to use as much cam as you might think with 9.22:1. Here's an example that would work:
http://www.cranecams.com/?show=brows...tType=camshaft
You haven't said what your piston deck height is, but if the piston is down in the hole very far, I'd use a 0.016" steel shim head gasket to try to get close to the ideal 0.035" to 0.040" squish figure.
http://kb-silvolite.com/calc.php?action=comp2

When finally selecting the appropriate ABDC closing angle, is @.050 the way most CR calculators go to determine DCR?

If so - I see now that I have been incorrectly reading the data sheet and using the @.004 numbers.

No wonder I coudn't find any cams closing near 30 degrees ABDC.

From what I've seen, different calculators use different values. The KB calculator instructs you to add 15* to the 0.050" figure given on the cam timing card, I think to get you from 0.050" to 0.006". They're figuring that there is generally about 30* difference between the 0.050" closing figure and the 0.006" closing figure, 15* on the opening ramp and 15* on the closing ramp.