Any motor heads still hang out here?

Any motor heads still hang out here?

Timberwolf
Timberwolf

July 23rd, 2012, 12:23 am #1

I picked up a 2001 GM crate 350 with 40k miles. Roller cam motor, but it was a TBI setup, which I'm not going to mess with. So those heads will be hitting craigslist along with the fuel injection setup. In the meantime, I picked up a set of 062 vortec heads.

I've read I can use LS3/LS6 valve springs, Comp Cams retainers, and Dodge Daytona turbo 4 cylinder valve seals. This will give me up to .550 valve lift before coil bind (stock limits were .490 I believe). I am going to run an LT4 hot cam and 1.6 GMPP roller rockers which give me a max lift of .529.

My question is, is there any reason to go to the larger valves (2.02/1.6) or will the stockers be ok for my setup?

Also, I've read conflicting opinions on whether to do any porting or cleanup. Some say the vortec heads really benefit from bowl blending and opening the exhaust port around the valve guide, others say not to touch them unless you're going over 425hp.

What say you?
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Hans
Hans

July 23rd, 2012, 2:15 am #2

I'll start with a few questions, which I always pose to an engine build query....
What's the engine going to be doing?
What vehicle?
What useage?

It's been a while since I've really dug into cam numbers, but .529 is a fair sized lift IIRC. What kind of duration is the cam? What's your target powerband? Just based on the little bit of cam numbers you're showing, I'm guessing you're looking at a high RPM powerband. What's the compression ratio going to be?

I'm not familar with those heads, but can they support the extra flow that the 2.02 valves will allow? Or are they narrow valve heads that you're just going to cut bigger seats into? Do your pistons have the clearance for the cam/valve combo you're looking at?

2-bolt or 4-bolt block?

I'm not a big fan of randomly slapping engine parts together and seeing what they do, I find things work out so much nicer if you start with a target performance level and build to match that.

-Hans



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Timberwolf
Timberwolf

July 23rd, 2012, 2:29 am #3

Well, I'm not one to slap things together either. I've been building motors a long time, but this is my first build using GM's vortec heads. So my question is based more around them than anything else. Was just hoping someone here had some experience with them.

As far as the build, it's going in that stepside Chevy truck I posted a few weeks ago. I'm not sure if it's a 2 or 4 bolt block, but honestly, I'm not building it aggressively enough to matter. For what it's worth, I'd always go 2 bolt over 4, in favor of the thicker webs, then I'd have it machined for splayed caps. That is, of course, if I wasn't going to use my favorite...the LS based motor and its 6 bolt mains

The cam is actually 525 lift at the valve, I misspoke. 112 LSA, and a split duration of 218/228 @.050. RPM range should be in the 1500-6000 neighborhood. I plan for a 2500 stall torque converter in the 700r4, and 3.73 gears.

Compression will be right near 9.75:1 assuming a .010 piston-to-deck clearance and a .040 head gasket. Cylinder chambers are 65cc on average.

I'll use a small base HEI ignition with a slow advance curve to keep detonation to a minimum. Fuel will be fed by a Holley 650 vac secondary carb or a barry grant (haven't decided 100%) and the intake will be an Edelbrock Performer RPM Air Gap. (unless I decide to go for looks instead and do a dual quad setup with a couple 375cfm holleys)

I am figuring the combination should make right around 380hp at the crank and break into the 420 range for peak torque, averaging 395 or so across the RPM band.

I know the heads will support the larger valves, but I am not sure if my intended power levels and rpm range justify the expense.
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Maker of Toys
Maker of Toys

July 23rd, 2012, 4:07 pm #4

so, my take is, if you're not planning to terrorize the dragstrip with this thing, (it's a truck, after all) and all other things being equal: The smaller intake valves will give better port velocity, leading to more in-cylinder tumble, swirl and turbulence effects; and smaller exhausts promote velocity across the ports for better scavenging. . . all of which will make for better transient response and better part-throttle manners.

(for those just joining us: turbulence in the intake side will tend to improve charge mixing, which is where carbs (and TBI) tend to fall down a bit. That'll do good things for mileage and tend to keep carbon deposits at bay longer. . .)

I've no opinion on your carbs; my experience is more in the Weber and Solex line. The only carbed V-8s I've dealt with were severely smog constrained, (Yay california) or in work vehicles. I did some messing with Q-jets, which was mostly down to fiddling with the secondaries and kick-down linkages and trying to keep things from going really lean at low RPM and WOT so the engine would give good service under the sort of abuse that field techs give a vehicle.





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