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Old 08-01-2012, 02:53 AM
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Rebuild with 186 Double Humps

Before I get started, I understand that there are much better heads on the market. Vortec' and a whole slew of aftermarket heads. I choose to run these, I've held on to them for a while and finally have the 68 SWB that I've always wanted to put them in... Just kind of an old school thing.
They are what they are... But I need some help on the limits of these things. This truck won't see a drag strip, a weekend driver. But, I do want the option of dropping the hammer and smelling the rubber burn!
These heads for their age are in perfect shape! New guides, seals, the springs are Edelbrock 5703 (for the RPM Performer cams) new SS valves 2.02/1.60, they have screw in studs, and guide plates. All the machine work was professionally done by a respected and trusted machinist, beautiful port & polish job finished them off.
They are going on a stock 350ci block. The crank will be turned, the rest will be bought new. ( have not bought the rods, or pistons yet.
The reason being is that I'm not sure where to go from here to make this work. I'd like to run the Edelbrock RPM Perfomer cam with the matching manifold. But with the 64cc chambered heads, I've been told the compression will be too high for pump gas. Will dish pistons lower compression enough to use this cam and pump gas? Is there another way to lower compression besides different heads? Id like to get as much performance as I can out of this set up as possible with these heads. Any suggestions, comments (other than get better heads)? Any advice will be greatly appreciated!

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Old 08-01-2012, 06:24 AM
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I'll try to relate to you in the performance potential of U R double humps and maybe what to do with your compression. I've got a 81 Z-28 with a 350 that I turned into a 383 many moons ago. I'm a very low buck guy (we've got 5 kids) so every penny counted. I used the original 993 open chamber heads...everyone hates them... that are 76CCs not 64CCs like yours. My pistons are cheap cast flat tops that make about 9.3 or so compression...a 383 will make more compression with the same 350 pistons but only slightly more. I put in a XE-268 cam that every one says makes a lot of valve noise but I don't hear anything. I did a home port and polish on the heads and had a cheap 100$ valve job done to them. I don't know if I got lucky and all of the planets were aligned but that motor is a beast. The torque is outstanding and it will pick up very nicely in 4th gear (I'm running 3.73s). So, run your double humps the'll do better than my setup. The reason is you can get a better quench because you have more meat in the chamber..hence the smaller CC size..which is flat and will mate with the piston better....maybe a slight D shape dish piston would work for you. That way you can run higher compression without pinging but I would still run a slight dish piston. The very knowable gents on this forum will steer you in the right direction. As for your cam go ahead and run it but a word of caution...its a high rpm stick. You better have low gears and be ready to zoom the engine up (ie make noise) to give you that thrill. I chose the XE because its got decent vacuum and will pull like a freight train right from the get go....I don't have to make a lot of noise to outrun the little old ladies driving their Toyota Camry's! Anyway good luck, you will be more than happy with that engine..of course, you can e-mail me directly dallam1@hotmail.com if you have any more questions.
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Old 08-01-2012, 09:37 AM
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The edelbrock cams are reboxed mass produced crap. If you want that cam just buy it in the plain white box for half price, its the same cam from the cam factory- edelbrock doesn't grind their own cams.

Flat top 4vr pistons work well with those heads. The rpm manifold will work well. Spend some money for a good cam, something in the 220ish (hyd @.050") range will match that combo well final specs will depend on the rest of the combo.

Since you're getting new rods go with the longest you can, it'll help with those small heads. 6" or 6.125" will work nicely.

Id also get at least a 2500 stall (a good one too no el cheapos), they really make a difference on a street truck.
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Old 08-01-2012, 11:36 AM
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So I take it that, D dished or 4 relief pistons will lower compression enough to run pump gas? if so that's great news.
As for the RPM performer Cam... Ive seen and heard the cam, and was impressed by what i saw. although it was not in the same set up as mine and have been actively looking at others that i think will give me what i want. One of those is the XE268H, the other is the VooDoo 268/276
In my first post, i forgot to mention that the truck has a Turbo 350 tranny, it also has a Holley 650 dbl pumper, the rear end is out of a meteric/disc brakes... the gears are 3.73 i think? thats something I need to check for sure. I know at Hwy speeds its wound up pretty good. it also has decent size headers 1 5/8. that little bit more of info may help someone with more knowledge about this stuff than myself!
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Old 08-01-2012, 11:46 AM
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Either cam will work fine; you probably will get a little more out of the VooDoo line than the XE; whether or not you'll notice it, depends.

As stated previously; the best thing for your truck is a proper, quality converter.
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Old 08-01-2012, 12:03 PM
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I rebuilt my 350 with 186 camel humps,flat top pistons(4vr),rpm intake and a compcam 280 cam(480/480 lift),pulls really well from low down,think it will suit your truck! Always felt it needed more on the top end though! nice lopey sound at idle,ran on pump gas no problem.
Changing to aluminium heads now.....
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Old 08-01-2012, 12:28 PM
How fast is fast enough?
 
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The 268 voodoo should work well for you but make sure you get the right springs, have good lifter bores, use the right oil for the cam, and follow good break in procedures. The aggresive lobes need extra attention to last.

On the pistons, make sure you get ones with the right compression height to match your rod length.

Don't skip the converter and take it to be tuned by someone who knows what they're doing, many "tuners" don't know how to properly tune a holley.
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Old 08-01-2012, 01:01 PM
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Thanks guys... ill start looking at converters, what brands and types should I start with? TCI?
I've got some good feed back to kind of re think what i've started on this re build. Still have some work to do before I start turning wrenches, want to make sure im putting parts that will work togrther and match to perform, then buy'em!
Keep the advice coming!
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Old 08-01-2012, 02:23 PM
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heads up

I am running these same heads, 202/160, heavy springs, guide plates, roller rockers, slight port job done professionally. I have a 60over 350 4 bolt, Keith Black /flat top pistons, pink rods. steel crank yada-yada. I used a competition cam about 455 lift if I remember, about 10-10.5 compression. The engine ran good but not great. I started with a Holly 650 #4150 carb, found out that was too much carb, went to a Edlebrock 500 cfm. Much better low end performance now, using a aftermarket Al manifold dual plane. Good luck. sc
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Old 08-01-2012, 02:32 PM
How fast is fast enough?
 
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Quote:
Originally Posted by sportcoupe View Post
I am running these same heads, 202/160, heavy springs, guide plates, roller rockers, slight port job done professionally. I have a 60over 350 4 bolt, Keith Black /flat top pistons, pink rods. steel crank yada-yada. I used a competition cam about 455 lift if I remember, about 10-10.5 compression. The engine ran good but not great. I started with a Holly 650 #4150 carb, found out that was too much carb, went to a Edlebrock 500 cfm. Much better low end performance now, using a aftermarket Al manifold dual plane. Good luck. sc
The holley 650 is far from too much carb, BUT it may have been way out of tune, which is more common than not. Edelbrock carbs are idiot prof and reliable as long as they're clean though. They're my favorite carb for start ups of new engines as they usually work well with a near stock tune and are easy to quickly retune.
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Old 08-02-2012, 11:58 AM
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A somewhat similar set-up, so here's about what you can expect:





331 CI, pump-friendly 9.5:1 CR
K&N 14"x4" air filter, Corvette drop base and lid
Holley 600 dp, choke horn milled and blended, Primary - 69, Secondary – 74, Squirters - 21
1/2" Aluminum open spacer port matched to manifold, exterior polished
Edelbrock Performer RPM, port matched, exterior polished with all extraneous castings and lettering removed
Homemade lifter valley splash shield to keep hot oil off manifold bottom
Camel hump 1.94/1.50 heads hogged out to 2.02/1.60, pocket ported, port matched, pump-friendly hardened seats, 3-angle valve job
Cylinder bores clearanced to unshroud the valves
Comp Cams 1.52:1 roller-tip rockers
Crane Cam Vintage Muscle 327/350 hp cam, 222 degrees @ 0.05, 0.447" lift (with 1.50 rockers)
Doug Thorley headers, dechromed and ceramic-coated
2.5" mandral-bent exhaust (including tips), 2" cross-over just before rear axle
DynoMax stainless Ultra Flow mufflers
Millerspeed 1-1/2” Gilmer under drive belt drive system
Mallory Hyfire IV CD ignition box triggered off Accel points
Mallory high voltage chrome coil
Mallory spiral-wound coil wire
Mallory solid copper plug wires, ends soldered to wires
Champion plugs
37 degrees total ignition advance
Carter high volume fuel pump
Melling high volume oil pump
Open breathers
Polished aluminum high flow water pump
160-degree thermostat
Flex fan with polished aluminum spacer
Polished aluminum one-wire 100 amp alternator
Header Power Bracket
Keisler TKO600 5-Speed
Hurst shifter
3.70:1 positraction
225/60/15 Firestone Firehawk SZ50s on 7”-wide Western 30-spoke Turbine Wheels
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Old 08-02-2012, 12:45 PM
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I don't know where you got your info on compression but if your block is not decked and you are going to run 4 valve relief pistons with 64 cc heads you will only have a true 9.8:1 compression ratio or approximatly 170-190 psi per cyl. this is basic and you could run any pump gas easily I have ran a zero decked 2 valve relief 62 cc chamber 350 in my work truck for years now on 93 octane pump gas specs are as follows 98 chevy c1500 ex cab 3 door 350 vortec block .030 over stock rods and crank crane 2050 compu cam aries alum heads 210's 2.05int 1.625ex 62cc 1.6 roller rockers cfi intake cold air intake full lenth flowtech headers single roller timing chain cam is hyd roller set up and I have a sct program installed in the computor for a whopping 375 rwhp 425lpft at the rear wheels block is zero decked 2 valve relief flattops "manley silver light pistons" comp is a true 11.5:1 or 200-220 psi per cyl and have not had a problem other than burning the plug wire boot on #5 cyl in 6 years
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