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300Deluxe 01-10-2008 12:28 AM

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,

DoubleVision 01-10-2008 01:18 AM

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.

300Deluxe 01-10-2008 05:50 AM

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?


300Deluxe 01-10-2008 06:49 AM


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?

DoubleVision 01-10-2008 07:47 AM

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.

454C10 01-10-2008 11:46 AM

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.

300Deluxe 01-10-2008 11:52 AM

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.....

454C10 01-10-2008 12:12 PM

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.

300Deluxe 01-10-2008 05:30 PM

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.


300Deluxe 01-10-2008 11:31 PM


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?

300Deluxe 01-11-2008 06:27 PM

Bump. I'm getting lost in the shuffle, lol.

300Deluxe 01-12-2008 08:14 AM

The specs for the 1.47" springs are on a card attached to a spring on each head.

F-Bird, I appreciate your help.

300Deluxe 01-12-2008 08:34 AM

One more thing: With this combo, is there a ballpark horsepower/torque figure? Just curious.


300Deluxe 01-12-2008 05:08 PM

Found out about the site a day or two ago. Apparantly it's not 100% functional, but there is a pdf catalog.

roofdawg 01-12-2008 07:01 PM

First I would Like to thank you 300Deluxe for posting this thread. Next I would Like to thank Double Vision, F-Bird'88 and 454C10. I am very very new at this and you guys have answered a lot of questions that I have been asking my self. The four of you have also given me so much to look and thank about. If not for people like you guys my '73 Malibu would be half of what I would like to thank it is going to be. Again THANK YOU so much all of you. RAH!

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