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Discussion Starter · #1 ·
Hi. Preparing for the DoD delete build. I ordered the GMPP CNC heads from JEGS but they are backordered, so I'm beginning to question my choice. I wanted to upgrade my intake valves, which would also require new seals, and the price of the CNC heads at $1200 just made sense to me. The factory LS3 heads from JEGS are only $700. What do you think? Am I wasting money on my build with the CNC heads? Some day I may want to stroke it or do something more so the cost of the CNC heads at $500 more seem to make sense. But my 6.0 may do better with the LS3 heads. In any event, I will sell my factory heads to recoup some of the money. For those that have the CNC heads, was it worth it performance wise? And since I am not replacing rods and rod bolts will I see enough "safe" rpms to benefit from the ported heads?
 

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I thought the heads in our cars are the same as LS3 heads but with solid instead of hollow valves. If you don't get the CNC'd heads and go the route of the factory LS3 heads from Jegs, wouldn't it just be cheaper to just change the valves you have now?
 

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Discussion Starter · #3 ·
Could be. But new valves at $30 each plus seals plus time it just makes sense to buy the new LS3 heads and sell my heads. And like I said, the real issue for me is will I benefit from the CNC heads. They are sooo cheap it's almost a no-brainer. Unless the additional flow will not benefit my 6.0. For me it's not really a money issue. It's more of making the smart choice given that I'm not stroking yet. Thanks for your input.
 

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every village has one
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Keep your stock heads at this point. Upgrade the valves and get a good valve job.
 

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Discussion Starter · #5 ·
I hear you...but new valves, new valve seals, valve job = new LS3 heads. Are you saying that backcutting the valves and a good valve job would be better flow than the LS3 heads? I'm old school...do they still do 5-angle valve jobs? Because that could be a good move.
 

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LSX Mechanic
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For those that have the CNC heads, was it worth it performance wise?
The answer to this question really depends on you and what you think 25-30 additional HP is worth to you.

The L92/LS3 casting flows extremely well right out of the box so porting gains are marginal compared to a cathedral port head where mountains of CFM can be achieved over stock castings.

I've done 40-50 cammed and/or heads/cam GEN IV engines at this point and the cars with CNC'd castings made a general average of 20-30 more HP than the cam only engines.

And since I am not replacing rods and rod bolts will I see enough "safe" rpms to benefit from the ported heads?
Contrary to what the internet experts will have you believe, you can safely spin an LSX engine in stock form to 6700-6800rpms on a daily basis with no problems. Of course there's always exclusions to the rule on that "one" car that blew up, but I've been spinning stock LSX bottom ends to 7K for almost 15 years. To answer your question, a properly ported cylinder head will provide additional power at every rpm.


Personally, I'd keep what you have and try it with stock castings for a while. It's not hard to achieve 430-450rwhp out of a stock headed 6.0L. The key is camshaft choice (proper valve events), and figuring out how to add a bunch of compression in there without having PTV issues.
 

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Discussion Starter · #8 ·
Thanks Damian. Great post. Just read this article.
http://www.gmhightechperformance.com/camaro_now/sucs_1130_ls3_heads_and_cam_test/viewall.html
Think I'll stick with the CNC heads. Yes, the test was a 6.2 but really not that different from my 6.0. Cam is very similar to my VMS 1.5. They saw a 50 hp jump with the CNC heads and cam over the cam alone with factory LS3 heads. I don't want to tear the engine down again for a while and the cost is just too good. Sell the stock heads and I'm into it for $700. Can't beat that. Thanks everyone for your input.
 

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BOOOOOOOOOOST
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A valve job and a bit of milling are all the heads need.
 

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BOOOOOOOOOOST
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Thanks Damian. Great post. Just read this article.
http://www.gmhightechperformance.com/camaro_now/sucs_1130_ls3_heads_and_cam_test/viewall.html
Think I'll stick with the CNC heads. Yes, the test was a 6.2 but really not that different from my 6.0. Cam is very similar to my VMS 1.5. They saw a 50 hp jump with the CNC heads and cam over the cam alone with factory LS3 heads. I don't want to tear the engine down again for a while and the cost is just too good. Sell the stock heads and I'm into it for $700. Can't beat that. Thanks everyone for your input.
You're reading that wrong.

They saw a 50hp jump from the heads AND cam. They first swapped the heads to the block, THEN added the cam. And then they had another minor 10hp gain with a different set of heads. It's a badly performed test. They should have put the cam in with the stock heads, then swapped heads from there.

Typical GM HTP test.

The 50hp jump is about 40hp from the cam and maybe 10 from the heads.
 

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LSX Mechanic
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Thanks Damian. Great post. Just read this article.
http://www.gmhightechperformance.com/camaro_now/sucs_1130_ls3_heads_and_cam_test/viewall.html
Think I'll stick with the CNC heads. Yes, the test was a 6.2 but really not that different from my 6.0. Cam is very similar to my VMS 1.5. They saw a 50 hp jump with the CNC heads and cam over the cam alone with factory LS3 heads. I don't want to tear the engine down again for a while and the cost is just too good. Sell the stock heads and I'm into it for $700. Can't beat that. Thanks everyone for your input.
You're reading that wrong.

They saw a 50hp jump from the heads AND cam. They first swapped the heads to the block, THEN added the cam. And then they had another minor 10hp gain with a different set of heads. It's a badly performed test. They should have put the cam in with the stock heads, then swapped heads from there.

Typical GM HTP test.

The 50hp jump is about 40hp from the cam and maybe 10 from the heads.



And aside from the obvious, GMHTP articles are usually performed on the highest bidders to display an advertising frenzy. I also take magazine articles with a grain as salt. What they did one time in that article I do every single day, 5-6 days a week.
 

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BOOOOOOOOOOST
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Agreed. I love the magazine just as good bathroom reading material, but that test is just laughably poor. They have done proper tests with various heads in the past (not changing cams in the middle of it!!!), but this one is not that. Hah.
 

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HeapBlaster
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if you're gonna spend the money, put a ported cathedral port head on it... If my LS3 heads come off Im putting a ported 243 or a worked over trick flow 235cc head on the car. this giant intake port crap sucks on these little motors.
 

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Hi. Preparing for the DoD delete build. I ordered the GMPP CNC heads from JEGS but they are backordered, so I'm beginning to question my choice. I wanted to upgrade my intake valves, which would also require new seals, and the price of the CNC heads at $1200 just made sense to me. The factory LS3 heads from JEGS are only $700. What do you think? Am I wasting money on my build with the CNC heads? Some day I may want to stroke it or do something more so the cost of the CNC heads at $500 more seem to make sense. But my 6.0 may do better with the LS3 heads. In any event, I will sell my factory heads to recoup some of the money. For those that have the CNC heads, was it worth it performance wise? And since I am not replacing rods and rod bolts will I see enough "safe" rpms to benefit from the ported heads?
I would talk to Rick Crawford (G8-4-Speed) on working your existing heads; I think you will get greater gains for less $$$.
 

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HeapBlaster
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Patrick g that everyone seems to love runs cathedral port heads... if you plan on buying a fast anyways this is the perfect time.
 

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Discussion Starter · #16 · (Edited)
Once again...thanks for all the comments. I cancelled the JEGS order. If I stroke in the future I will look at the heads then. As for my heads, do I really need to replace the intake valves? If I keep my heads as-is, with the steel valves, what is my safe rpm? I will be using LS7 lifters and appropriate springs. The VMS kit comes with PSI sls 1511ml maxlife springs. Spirited street driving only. My ZX-10R answers my need for speed.
 

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LSX Mechanic
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Another frank opinion of mine is, people jumping on the cathedral port bandwagon and saying big port heads are "crap" simply do not have a good grasp on proper valve events that make L92 castings happy.

Cathedral heads are great and will make more low-end snappy TQ than the big square port stuff but a properly built square port headed engine will blast cathedral's from 3600-7000rpms.

Once again...thanks for all the comments. I cancelled the JEGS order. If I stroke in the future I will look at the heads then. As for my heads, do I really need to replace the intake valves? If I keep my heads as-is, with the steel valves, what is my safe rpm? I will be using LS7 lifters and appropriate springs. The VMS kit comes with PSI sls 1511ml maxlife springs. Spirited street driving only. My ZX-10R answers my need for speed.
I love the ZX10's. I was always a Yamaha guy myself having 2 R1's, but I always had a $hit eating grin on my face every time I hopped off a buddies ZX10r.

The PSI 1511ML's are excellent springs, and no you do not "need" lighter valves. Consider them icing on the cake, but not a necessity.
 

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LS3 heads will out-power cathedral heads with a good intake. The problem is people try to cam LS3 heads like cathedral and it doesn't work that way. The heads need compression over cam. I would give up a little up on cam size over giving up compression. The intake port is huge for a 364 cu.in. motor, cam accordingly. If you can make power to 6900rpm with a 223 intake lobe, what is a bigger cam going to get you if the intake wont let you make power at a higher rpm? PTV clearance without notching the pistons is the pivot point on cams....
 
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