6carmello8

Hi all,

I'm finally getting around to modding my engine and wanted to know if I can do L92 heads and cam it in two stages. I understand that doing it at once will save me money in tuning and perhaps the spring, retainers, etc swap, but other than that factor, can I do it in stages?

I realize that if I go with L92/LS3 heads first, which I plan on doing, I will need the L76 manifold and other misc. parts at the same time and probably also a basic tune and maybe even TB...I may still be able to use the ls1 TB until I get a 102mm when I get the cam.

If I do cam first, I obviously will want a cam that will maximize performance with a the LS3 heads. That being said, will it work with the stock 243 heads. I understand that I will need spring, retainers etc., and will have to swap them out to the LS3 head if I go this route.

Please advise and thanks in advance.

DavidBoren

Doing them at the same time would obviously be optimal, but may not be financially feasible. You could upgrade your cam now, even to a cam designed for LS3 heads, and still see benefits. It will have a little extra exhaust duration, no big deal. You can still get decent results from a rectangle port cam in cathedral port heads.

If you put the L92 heads on with the cam you have now, you won't see as appreciable gains, in my opinion.

Do the cam first.

6carmello8

That's great news. Thank you for the feedback. I'll most likely go the cam first route. I understand that the LS3 exhaust ports flow almost too well so the cam will have a smaller split than as on a cathedral port set up. I will however port the exhaust only on the LS3 head since the intake already flows enough for a 6.0.

Now, once I get my LS3 heads, can I just swap over the springs into the same location on the new head or will I need new springs. I'm speculating that they may have broken specifically into to each specific "lobe" / "position" on the head.

DavidBoren

Pretty sure the springs will switch right over to the LS3 heads. Depending on how many miles you put on the cam/springs before you replace the heads, you may just want to get new springs with the new heads. Valve springs are a wear item, and some people do not seem to realize that. Good springs will last you a minute, probably 50k miles, but they still need to be replaced fairly regularly for them to continue to properly control the valves.

The exhaust bias ground into cams for rectangle port heads is to carry the pathetic exhaust flow. The LS3 heads are designed, almost directly copied, from NASCAR heads... which are designed to operate at 8000rpms. So they have lots and lots of intake flow, but a lacking and sad exhaust flow ratio. The only way to compensate for this is to add duration to the exhaust to give it more time to clear the combustion chamber.

So, putting a cam with that extra exhaust duration into a cathedral port head, pretty much just allows you to carry power a little further. The cathedral port heads have amazing exhaust to intake flow ratios. The cams for high exhaust flow ratios are usually closer to single pattern, barely any exhaust bias at all, because the exhaust side of the heads flow plenty enough to completely clear the combustion chambers.

Using a cathedral port cam on a rectangle port head chokes the exhaust by not keeping the exhaust valve open long enough to do its job. Any performance cam is going to have more lift, better lobes, and probably more duration on both the intake and exhaust. So even with the cathedral port heads you have now, you will see an improvement, even if the cam you choose is designed to work with rectangle port heads.

Something that hasn't been brought up, but needs to be addressed, is pushrods. Pretty sure that different length pushrods will be required, so make sure you check and measure for the correct length.

The valvetrain is not a place to save pennies, good lifters, heavy duty pushrods, good springs, careful/correct measurements and assembly are key to having a reliable and trustworthy engine.

6carmello8

I figured springs might have to be replaced and of course greatly depends on the miles and the very reason I brought up the subject matter.

Yeah I've heard the exhaust flow ratio on the Ls3 heads can be better and the reason why I plan on only porting the exhaust side and leaving the intake alone.

Ahhh yeas, push rods. Different heads design may change the length and I will look into that, thanks.

Agreed, the valvetrain is most definitely not an area to "save pennies" a cam just spins with little wear. The valvetreain has to deal with a lot more than that.

I appreciate all the feed back and now, I need EPS or BTR to custom grind me a cam or maybe even a proprietary cam that would work best.

Now the next question is very subjective but I was thinking of going with a cam that has better mid to high end power than a typically favored powerband with a flat toqrue curve and a broad powerband. The reason for wanting this set up is for a few reasons.

I have a t56 and want will be running a 3.89's That being said, with this short gearing, a healthy 6.0 will still make PLENTY of low to mid range torque. I will never be at the track or run slicks. In fact, I'm running a 325/30/19. I figure, the gearing will make up for the "lack" of low end and I can take advantage of high end and enjoy acceleration off rolls instead of launches. The last thing I need is more torque which will only spin the wheels. I figure I could sacrafice low to mid, compensate it with gearing and aim for mid to high end power.

What are your thoughts.

Also would you mill the heads to achieve a 10.8:1 ish CR or leave it alone and instead run a higher lift ( within the PTV clearance ) instead. Which route would you go with?

JimmyGTO

I have a great cam spec'd for the LS3/6.0 combo in the for sale section. Spec'd by EDC at FTI. One of the great cam gurus around. It would be a great cam for you. IT's BRAND NEW IN BOX!

DavidBoren

I like compression, personally. And I do not like excessive lift on the cam, due to the wear it causes in the valvetrain. And I agree with the gearing and displacement giving you plenty of torques down low. So you can absolutely get your cam spec'ed for more performance on the upper end.

6carmello8

Compression is never underrated especially when you have more displacement and I do like your take on it. Excessive lift isn't necessary especially on a street car...I will be driving this car a lot and will not be weekend street/strip. Now I got to figure out what SCR the engine can handle on 91 pump here in Cali. I figure is a LS3 is 10.7 so something in that range.

I'm glad you agree with the route I want to go with. Many people forget that a lot of these guys on here are track guys and or running slicks most of the time and traction is not really an issue for them.

I sometimes get lost in "theory vs. practice" and in theoretically, a broad powerband with gobs of torque is awesome but once you start applying it to the real world scenarios, street tires, 4.11's with a six speed, may not be the best route.

I want to be able to enjoy the car more when I am cruising and more than from a dead stop.

Many of the European cars tend to be so much more efficient in acceleration on street tires since the smaller displacement engines with higher redlines is a great balance.

I'll let my 4.11's take care of low end and my cam take care of my high end.

DavidBoren

Sounds like a solid plan. Definitely keep us posted with your decisions and results. My first recommendation always goes to Martin Smallwood for any and all things cam related, but any of the vendors on here will be able to probably spec you a cam that will be a good half way point, and will still work very well with the LS3 heads when you get them. I probably wouldn't go too much above 11:1-11.5:1 static compression with 91 being the highest you can easily find. Using the correct thickness head gasket, and having proper quench will help a lot with detonation resistance.

6carmello8

Yeah my plan is set and had been, just wanted some input from other so thank you.

I have to now figure out was SCR I can go with on 91 pump. Looks like it's all about the cam since dynamic CR is more relevant than just SCR and that will be dictated by the cam I will be running.