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Old 01-10-2008, 01:28 AM
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New Engine Combo - Your Opinions

Hello All,

I'm currently in the process of upgrading a few components of my mostly stock 350 in my Chevelle. I'm curious to see what you all think of my combination.

It has a virtually stock bottom end. The engine was rebuilt well over 10 years ago, but has been run very little. This is a mid 70's smog engine with dished pistons.

I'm replacing the unknown aftermarket cam with a Voodoo 60102. I've purchased a set of Summit brand aluminum heads with 200cc intake runners and 64cc combustion chambers along with 2.02/1.60 valves. I also have a set of Comp Cams Magnum roller-tipped rocker arms (1:5 ratio).

The engine will be topped off with a Weiand Stealth aluminum intake and a 600 cfm Holley carb with vacuum secondaries. I also have an aftermarket HEI distributor to install.

This all will be backed by a TH350 trans. with some stall to it and a shift kit. I still have the factory open differential (I'm guestimating it at approx. 3.73 ratio, originally a L6/glide car).

I realize that my engine's downfall (in my opinion) is the dished pistons. It's just not economically feasible at this time to purchase flat tops. I have yet to get new head gaskets. I'm still studying to figure out what thickness would be best for my application... Any suggestions?


So.... Would any of you be so gratious as to give me your opinions on this setup? Criticize/compliment at will. I know this is far from the ideal engine combo, but it's what I've got to work with. My funds may allow a few changes here and there, but not much. What kind of power would you expect to get out of this combo?

Any and all info is appreciated.

Thanks in advance,
300Deluxe

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Old 01-10-2008, 02:18 AM
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200cc heads are too big, it'll be rather soggy in the lower RPM ranges. 180 would have been far better. the smaller 600cfm carb will make up for some of it, but not much. Since you dont know for sure your rear gear I'd find out, as it will be a big influence on how it performs. I always use GM head gaskets that are .028 in thickness, the 64cc chambers will give you a ratio somewhere in the 9:1 area even with the thin head gaskets depending on how far down in the bore the pistons are. rest of the combo looks good, but I think you have a bit too much head for it.
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Old 01-10-2008, 06:50 AM
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Thanks for the reply DoubleVision.

I've also been under the impression that the heads are a bit much for the rest of the components. My line of thought was that they would give me room to grow when I decide to go more radical with this or any other engine. Plus when comparing prices at the time I purchased the heads, they weren't much more than an iron counterpart.

What would be a desireable rear gear ratio? 3.73? I plan on eventually replacing the stock differential with a 12 bolt.

I *think* that my pistons are .025" in the hole. Can anyone confirm this of a 70's era 350 with dished pistons? Does anyone know of a set of piston's being further in the hole from the factory?

Also, with a .028" thick head gasket, would I need to be concerned about piston to valve clearance issues?

Thanks,
300Deluxe
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Old 01-10-2008, 07:23 AM
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To maximize the cr using a dished pistons and 64cc heads use a thin .015" felpro 1094 head gasket. retorque the head bolts after inital breakin. Remove the inner valve spring of the 1.47" dual valve springs that come on those heads. Reinstall the inner spring after 500miles of break in.
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Old 01-10-2008, 07:49 AM
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F-Bird,

I've been under the impression that the springs that came with the heads are too aggressive for my cam (see my other thread on valvesprings). I don't know the specs right off hand, but I do remember the tag on the springs mention a roller cam (I'm running hydraulic).

Sounds like you're familiar with these heads. Will the springs be suitable for my cam?
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Old 01-10-2008, 08:47 AM
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I wouldnt even consider roller cam springs on a flat tappet cam. But then again, my belief is always run the springs that are matched to the cam.
The cam companys say do not use flat tappet springs on a roller cam, machinists will tell you the same, same thing applies to vice versa. With todays crappy oils that are killing flat tappet cams and a roller springs pressure, it wouldnt take long to eat the lobe off.
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Old 01-10-2008, 10:04 AM
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Quote:
Originally Posted by 300Deluxe
F-Bird,

I've been under the impression that the springs that came with the heads are too aggressive for my cam (see my other thread on valvesprings). I don't know the specs right off hand, but I do remember the tag on the springs mention a roller cam (I'm running hydraulic).

Sounds like you're familiar with these heads. Will the springs be suitable for my cam?
These heads come with a 1.47" dual coil valve spring suitable for a Hyd roller cam and a aggressive flat tappet cam. They are not for a solid roller tappet cam unless the max rpm is kept to a point that the springs can handle. Mild street solid roller cams with easy opeing and closing ramps and modrate rpm are ok up to .575" lift and under 6500rpm. No race rollers. If you don't understand this, don't play. A roller tappet and camshaft can easily be damaged by "valvetrain crash" if you float the valves/lifters from exceeding the rpm capility of the springs.
This spring is the max you'd want to use on a Hyd flat tappet cam.
For easy break in wether hyd or solid flat tappet on any dual type valve spring it is highly recomended that you first run the motor using the outer springs only until the cam lobe and lifter face get nice and friendly (break in). Break in the cam and motor in for a good week of driving and then if you want maximum rpm limit capability out of your hyd cam reinstall the inner valve springs using compresseed air to keep the valves closed and a simple lever type valve compressor tool to compress the retainers.
For initial cam break in (on the outer springs only) muck up the cam lobes and lifter bottoms good with Isky rev lube. (moly disilfide grease). Add 1 bottle of GM EOS + 1 can of Moly lube to the oil and be sure to keep the rpm up on the motor above 2500rpm for the first 1/2 hours of running. Do not excessivly crank over the motor and do not idle. if the motor is not right, shut it off and fix the problem and then restart, again keep the rpm up.
Drive the car around for a good week with the mixture of break in stiff in the oil. Do not let the engine idle for long periods and do not try to exceed 5000 rpm until the motor is fully broken in and stabilized, You've changed the oil and filter, reinstalled the inner valve springs and reset the valve train adjustment. Continue to add GM EOS to every oil change and the cam will live a very long happy life and rpm to its full potential. If max rpm capability is not a priority just run the outer valve springs only. Should be good for 5500 5800rpm . If thats all you need for max rpm then running just the outer springs are fine.
Remove the valve covers and look at the pushrods while the motor is idleing ( after its all broke in.) If all the pushrods are spinning,the cam and lifters are properly broke in and the cam will live a long life. If the pushrods will not spin even when you rev the motor, you got troubles and the cam and lifters will soon fail or are already failing.
The extra pressure of these 1.47" "Hyd roller/flat tappet type dual springs" is only a issue during the critical initial break in period. Sometimes in some situations, I use a stock SBC springs without shims when breaking in a new motor's flat tappet camshaft. On cams up to .510" lift.
During flat tappet cam/lifter intiial break-in, less (spring pressure) is definatly better.

You can read about Moly engine oil supplement and break in lube
here.
http://www.mrmoly.com/ It does much more for your motor than help ensure easy cam break in.
Its best to premix the Moly break in lube first with the engine oil, then add it all to the oil pan so its instantly ready to go to work when you first fire the motor ,eliminating metal on metal scuffing, reducing friction and aiding successful engine break in.

Last edited by F-BIRD'88; 01-10-2008 at 10:37 AM.
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Old 01-10-2008, 10:32 AM
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The Lunati Voodoo 60102 is not that radical and won't need much more than 5500 rpm for best performance. Try just running the outer springs.
if that not enough spring pressure for the rpm you want to rev it, install the inner springs too and give'er.

If you were running one of the bigger duration higher rpm voodoo cams I'd surely use both outer and inner valve springs for best rpm capability after first doing the initial break in on the outer springs only.

Last edited by F-BIRD'88; 01-10-2008 at 11:01 AM.
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Old 01-10-2008, 12:46 PM
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Just running the outer springs will cause harmonic issues. The inner and out springs have different natural frequencies so they dampen each other. Therefore, I would recommend you buy the correct single spring with dampener for your new cam. check with Lunati.

I think a 2000rpm stall should do it. I would think you could even run the stock converter. Again, check with Lunati.

Why did you select a cam with so much more exhaust duration? Do your new heads have poor flowing exhaust ports?

Good luck keeping that cam from going flat. Those voodoo (lunati) and xtreme (compcams) cams have very aggressive lobes tend to go flat quickly. Sure, they make more power but not worth the damage that a flat lobe can cause.
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Old 01-10-2008, 12:52 PM
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The cam was suggested to me form another member on another forum. Being as the bottom end of the engine is basically stock with dished pistons, I didn't want to get too radical of a cam. I'm not knowledgable enough with valvetrain geometry to specify a particular duration for the intake/exhaust; hence I didn't get a custom grind. I was under the assumption that this would be a decent cam for a mild build. Was I wrong? I'm beginning to doubt the cam selection now.....
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Old 01-10-2008, 01:12 PM
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Yes, it will make a good mild cam. However, it has very aggressive lift rates which often can cause lobes to go flat.

When selecting the cam, the intake/exhaust flow ratio should be considered. A stock GM cylinder head typically has a poor I/E ratio (65 to 75%) so it does well with a cam with more exhaust duration, like the one you have. However, after market heads tend to have good I/E ratios (>80%) so a cam with the same intake and exhaust duration should be used.

Do a search on this site for "flat lobes" or "bad cam" or the like and see how many are voodoo or xtreme cam grinds.
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Old 01-10-2008, 01:35 PM
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Quote:
Originally Posted by 300Deluxe
The cam was suggested to me form another member on another forum. Being as the bottom end of the engine is basically stock with dished pistons, I didn't want to get too radical of a cam. I'm not knowledgable enough with valvetrain geometry to specify a particular duration for the intake/exhaust; hence I didn't get a custom grind. I was under the assumption that this would be a decent cam for a mild build. Was I wrong? I'm beginning to doubt the cam selection now.....
The cam you chose is a good one for you. it will work just fine with a stock torque converter. It likes a bit of gear, dual plane hi rise and good heads and exhaust (headers) always helps. The break in on the Voo doo and Comp extreme cams is critical. Reread my recomendations. This is the exact procedure I used on my 400 with the Comp Extreme XE28H-10. I use lots of spring pressure. 130+ seat pressure. These fast action "Voodoo/Extreme" cams require a bit more valve spring pressure than most are used to using cause they move the valve faster. Therefore you must follow a strict break in procedure without the inner spring and including both the oil additives I use and recommend.
They both use tried and proven anti-wear anti-scuff Moly and Zinc chemistry. Both have been around for years.
You can maximize the cr you get with dished pistons by selecting a thin .015" head gasket.
Your 200cc heads will not have a "soggy bottom end". Your only problem is going to be keeping tread on the tires.
Pull a valve spring off, measure the retainer installed height and then measure the spring seat and open pressures on a spring tester and go from there. Post some pics of the ports and valve bowls when you get the heads torn down for inspection, spring shim set up and final cleaning and prelubrication of the valve stems.
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Old 01-10-2008, 06:30 PM
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Guys I certainly appreciate your input.

I've read horror stories on various forums of cams failing prematurely. This is why I'm trying to go about this build as meticulous as I can. I've read about cam break-in procedures at-length and hope to follow the guidelines provided here and elsewhere.

There seems to be differing opinions on the valvespring issue here. Here are the specs of the springs provided with the heads:

1.47 Dia

Intalled Height (Intake): 1.88 (Exhaust): 1.88

Seat Pressure: 130

Open Pressure: 320

There are various check boxes with the different types of cams on the spring card with "Hyd Roller" checked.

Lunati's recommended valvespring specs:

1.266 Dia - single spring

Installed Height: 1.75

Installed Pressure: 108

Open Height: 1.25

Open Pressure: 339

Coil bind height: 1.060

Spring rate: 462 lbs/in

I realize we need to compare apples to apples here, but the above info is what I found on both springs.

Judging by the numbers, the provided springs are obviously heavier. So F-bird, do you think that these will be OK for my cam? My line of thinking is the fear of having too much pressure on the lobes. You suggested removing the inner springs. What are the specs of just the outers? Are they similar to Lunati's recommended specs?

454C10, you recomment NOT removing the inner spring, right? What would your alternative be?

I apologize for the redundancy. I just want to be confident before I start assembling anything.

You all have already been a big help.

Thanks,
300Deluxe
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Old 01-10-2008, 07:18 PM
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The Lunati 73943 1.26" springs that are on the Lunati 60102 cam card are the minimum spring requirements for that cam. They are good hi perf stock diameter drop on springs and work very well.
The spring specs that you show for the springs on the Summit heads are on the upper end of what you'd use on a agressive hyd flat tappet cam or a fairly agressive street strip solid flat tappet cam. or most of the hyd roller cams you'll likely use on a street car. They are just right for what you are doing.
But you do want to remove the inner coil as I recomended for the initial fire up and cam break in. Give it about a week of driving around. Get it all broken in and then reinstall the inner springs using compressed air to hold the valves shut, readjust the valve lash and change the oil and filter. Add another bottle of GM EOS on every oil change and you're good to go.
As long as your spring installed height is the same or very close to as speced they are well within the recomended pressures used on high performance hyd flat tappet cams. They are not too much spring for you.
If you're just not going to sleep at night with 130LBS seat pressure, change the valve locks to +.050" to reduce the installed spring pressure. about a $30 cure.
Where did you get the specs from for those springs?

Last edited by F-BIRD'88; 01-10-2008 at 07:30 PM.
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Old 01-11-2008, 12:31 AM
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F-Bird,

I got the spring specs from both Jegs and Summit's product description on their websites. I want to say that I looked them up at one time on Holley's website as well. I'm guessing that they can't be found there anymore.

It's a relief knowing I won't have to purchase new valvesprings. I just wanted to be certain.

What about pushrods? I plan on purchasing a length gauge. I was told that the stock pushrods wouldn't work. I've read that with the proper length, that the tip of the rocker arm should be centered over the pushrod. I *think* this came from article on Comp's website. I may have to dig up the link. Is this something you eyeball to see that it "looks" centered? Or is there a more precise way of measuring?

Also, I'll pose this question again: With such a thin head gasket, do I need to be concerned with valve-to-piston clearance?
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