Your thoughts on replacing the stock heads on a 2007 C6 A6

Currently have VR intake, 160 stat, comp cam package from DTE, UD pulley, LG long tubes, 3.15 gears

I was planning on having a Midwest tuner replace my stock heads and intake with a L92 / L76 package but it looks like I have to look at options. My local tuner has a lot of experience with high performance cars but is not deep in Corvette experience so I need to guide him.

The car is NOT a daily driver. I want to maintain the low end torque it has now, idle is good (a slight lope) at 800 rpm in gear. I do run ¼ mile runs at the local drag strip once in awhile but other than that, just quick on the street is what i want. My goal is 435 RWHP. I am at 390 RWHP at 6,000 and 371 RWTQ peaking at 5,800

I need some recommendations from anyone who has made a L92 swap or to other heads that are mild in design. This is not meant to be an all out street racer.

What intake / exhaust values should be considered?
Anyone know the cost of ZR-1 values as they are the same size and are the lightweight titanium.
Dual springs instead of the single spring from comp cams that came with the cam package from the tuner?
These heads as you know require off-set rockers on the intake. Are the stock L3 rockers fine or is there a better option?
Any thoughts on retainers?
Is milling the heads to increase compression ratio a good way to go or use Cometic head gaskets a better way to go? I have read getting compression to 11 (up from 10.5) helps with low end torque.
Injectors – what would be a good choice to replace the stock? What pound per hour?

Intake is the L76 – should it be ported? If ported will I sacrifice any low end torque?

Any thoughts are appreciated - youout

 

Okay, just to make a short reply. I have an 05 Mn6 Z51. I recently installed the L92/L76 package. The heads are completely stock but I had Texas Speed mill the heads at .020 instead of .030....I used the stock GM gasket. The VaraRam and Melrose 1 7/8" headers were already on the car. My initial dyno without tuning the VaraRam and headers was 344/340, with the tuning 369/352, and with the ported intake/tb 378/366. Now with the L92/L76 package mentioned above 440/405. Don't even bother with the ported L76 intake....the horsepower did not increase, just a difference in the throttle response. Remember, the heads are completely stock, no porting. The cam installed is a 224/228 LSA 114 .581/.588. My car idles steady at 850 rpm with a noticeable lope which I think is "nasty" Now, if I had to do it again, I would have opted for the ported L92 heads....already to go from Texas Speed & Performance. PM me for further if necessary.

 

Very similar here, L92/L76 package from slp - milled .020 and using cometic gasket, single springs as supplied, 224/228 @ 114, using 1 3/4 arh headers and added yella terra rockers. 452/418 thru 4.10's. Idles at 850 rpm, no bucking, best 1/4 11.6 sec on 1.85
60' times @ 123mph. Love the combo.

 

I gained 11/11 to the wheels with the Cory Harris ported L76.

You will gain about 30/30 with the head swap and the stock cam.

A .040" cometic with a .020 mill is about 11:1.

DO NOT use a stock GM gasket with .030" milled heads. Milling hurts flow so always exhaust thinner gaskets before you get to milling.

The heads work fine with small cams and will have more TQ with the stock cam especially at 2700rpm. You will need to throw a lot of timing at the 3k-4k range to offset their performance in that range. GM has this timing curve in the LS3 for the same reason with as much as 7 degrees more timing in that range. With this in mind they are good heads for the price but dont hold a candle to their higher priced cathedral aftermarket heads. Guys have swapped them out to make gains of 20/20 with 2400 dollar heads after the fact.

Enjoy the bump in performance and dont waste money on porting them. As they approach 2000 bucks ported you may as well get a good cathedral head that isnt shrouding the intake valves. This will allow bigger cams later if you so choose to use one without flycutting.

When the FAST for the LS3 arrives I suspect the L92 head's potential will be extended quite a bit. The L76 holds them back. The L92's performance may have to be re-evaluated at that point. You can see how this can be a big issue as the best cathedral heads are held back if not used with the FAST manifold.

 

thanks guys. this really helps.
what about manley stainless steel valves? need an affordable suggestion for valves. i have read that the new ZR-1 valves made from titanium could be used.

any need to change out the fuel injector size?

 

any thoughts on which values could be used other than stock

 

You may be better off calling Texas Speed Performance. They could give you technical information on their products. Here is the website: www.texas-speed.com. Good luck!

 

I have the L92/L76 combo, 450/405 to the wheels and 11.3 @ 125+ mph 1/4 mile times...on stock converter and PS2 tires. Great combo, very reliable and consistant, although my set up varies from Spin's , both intake and heads are unported and I did mill .030 and used stock gaskets, but have seen no ill effect. I totall respect Spin's experience though, and his way may be the way to go. I too am looking forward to the new FAST, but want someone else to be the test subject this time, lol.If it doesn't give a minimum of 18-20 rwhp and 10-15 rwtq, I'm just gonna stay with the stock L76.

 

What is the thickness of the stock head gasket?

 

There is no 'ill effect' other than you left some power on the table (likely not much). The flow is hurt by milling. I have seen 470-480rwhp with a 228 cam four times now with box stock heads. One was 462 through 4.10's and another was 471rwhp/435rwtq through 4.10's. You have an auto and its not comparable.

You also lose the benefit of decreasing the quench area between the piston and head. I'm not sure what effect you would see other than not having as much immunity from detonation due to your increased quench distance (not debatable).

Its difficult to get compression up (more TQ) and thinner gaskets increases the compression 30% more for each .001 you take off the gasket compared to milling the same .001".

I'm not sure how the 'ill effect' can be seen. The car that ran the 471rwhp through 4.10's was on 91 octane.

 

Yeah, the way I went probally left some HP on the table, no doubt, but it has been super reliable and what matters most is if the end user is happy with the results. The o.p. asked about our experiences with the L92s, so I posted. The ill effect, or lack therof , that I mentioned, was just that, no ill effects have been noticed from the way my setup is installed, just throwing that out there, not meaning to step on any toes or to debate who's way is better. I have no problems saying, if you're getting 20rwhp and 30rwtq more than my set up doing it your way, then that's a better way to go.

 

If you don't mine me asking, what cam do you have? I really think I should have gone with the .030 mill and stock gaskets as you did. Instead, I opted for the .020 and stock gaskets....probably left about 10 hp out there. Hence, I have a MN6 compare to your auto. I made 440/405 and my cam is 224/228 LSA 114. Thanks in advance.

 

Well, I know it burns alot of people with me saying this, but the cam is my tuner's custom selection for this set up and I've told him I won't give out the specs. If you want, PM me and I can set you up with his number and he can tell you the specs. In all reality , the varience of our numbers (10rwhp) could be in the dyno, not the setup. It does seem like you'd have more TQ than me, since you have a M6, but again, could be dyno-varience. I will say this without saying too much, your cam is close to what I have.