350 budget build cam selection

[DoubleD]

Ok guys I know the words budget should not come into play when you talk about performance but it truly is a budget build. I have a 1981 c10 longtube headers with a built th350 with a heavy shift kit running a 2500 stall. I will be locking the rear end and running a 390-411 gear (haven't decided) and maybe a single stage of nitrous down the road. Now the budget comes into play where I bought a running 350 truck crate engine for $250 bucks and put a rpm intake on it and since it had some broke head bolts I got some 64cc aluminum heads from prommax. Not the best but good for price. So should be around 9-9.5:1 compression. I'm looking at using the summit 1105 cam what do you guys think.

[rich weyand]

All those Summit cams are old designs, with 74* ramps.  Ramp time is wasted time.  You've already dumped the pressure, but you don't have good flow yet.  Modern cam designs are more like 44* ramps, and the extra 30 degrees is more compression, more expansion of the charge, and more flow both in and out.  Cam design in general is a compromise, because you only have 720 degrees.  The more you spend in ramps, the less you spend flowing, compressing, or expanding.

With that setup, looking at the simulations, I would probably go with the XE268H, Comp Cams 12-242-2.  415hp at 6000, 400+ lb ft from 2500 to 5000 rpm, and about 250 lbft at 1000.  44/50 degree ramps intake/exhaust, and only .480 lift, which isn't too out there.

This torque curve is pretty:

[rich weyand]

BTW, go to electric fans.  It changes how fast the motor can spool up to that 2500 torque converter if you get the propeller off of there.  Trust me.

When that torque converter grabs, the 12-242-2 will be at 400+ lbft.  That'll be, um, interesting.

Get good rubber.  See what kind of repeat-buyer discounts you can arrange.  :-)

Note: the simulation above was done with similar heads, with the same compression ratio and the same combustion chamber size.  I had a head profile laying around that was close, so I didn't look up the actual flow numbers and build a new profile, I just ran it with the one I had.

[fitz]

Now the budget comes into play where I bought a running 350 truck crate engine for $250 bucks and put a rpm intake on it and since it had some broke head bolts I got some 64cc aluminum heads from prommax.

I would be a little concerned about why the head bolts broke.
I've never run across that problem before.

[DoubleD]

Well just one head bolt broke and this crate motor was sitting in a 79 4x4 that ran for six months then sat. When we tried to pull the bolt it snapped but the bottom of what snapped was rusted so we are thinking it was already messed up and I'll check out that cam.

[DoubleD]

Sorry I think I miss spoke I ment to say an intake bolt broke off into the head not an actual head bolt.

[79 Royal Sierra]

I agree with the guys above. I just sold a an old chevy hot rod that had a well built roller block 350 with the Promaxx Aluminum 185cc heads and xe268 cam. I will tell you that those heads are top of the line. My engine builder only builds racing motors and recommended them. My motor dynoed at 440hp at 5800 and 448 tq at 4800 to the crank with an auto 700r4 tranny. I think with the heads and cam, you can have a nice streetable combo that will chirp the tires.

[DoubleD]

Thanks and Thad what I'm looking for. I think I may stay flat tappet but I'm looking north of 400 so that's good.

[rich weyand]

Flat tappet is OK.  Just run Mobil1 10W30 with a half-bottle of ZDDPPlus in it at every oil change after break-in and you'll be fine.

[DoubleD]

This is suppose to be a budget build motor which shouldn't be bad once I get a cam I should be in around or just under $2k but when I looked at switching to roller I don't think that's gonna be in the budget.

[DoubleD]

Also can anyone help me with my compression ratio. I didn't get to see the Pistons in the motor but I have a 10066036 block that was suppose to be a crate motor that came out of a 79 4x4 and it had 76cc heads on it. I put 64cc heads on it now. Can anyone guess what it is now?

[rich weyand]

Should be about 9:1.

The smogger 350 is nominally 8.5:1 CR, but is more like 8:1.
8:1 CR with 76cc heads gives 102.5cc of combustion space.  76cc in the heads + 26.5cc in the pistons/cylinders.
9:1 CR gives 89.7cc; 9.5:1 gives 84.4cc.
64cc heads is reducing combustion volume by 12cc, from 102.5cc to 90.5cc.
So a bit under 9:1.

Do all the same calculations with the 8.5:1 nominal CR, and you come out a bit over 9.5:1.

Looking around on the net, most people say that running 64cc heads with the dished stock pistons will get you in the 9.2-9.3 ballpark.  It depends on what head gasket you use as well, so you can use that to fine-tune the CR you want.

I found this post particularly helpful:

http://www.hotrodders.com/forum/72cc-heads-sbc-350-crate-compression-ratio-389946.html#post3253098

[DoubleD]

Ok thanks sounds great