I see, I mean I have been told by multiple cam companies its that an exaggerated amount of exhaust duration just isn't necessary and may even hurt performance for this specific application. A 48° ivc at .050 should peak at around 6400 rpm and make excellent torque from 3500 and up (where the converter should hit) and still retain good throttle response below 3500 rpm. Opening that exhaust valve earlier would bleed off cylinder pressure faster of course which may not be so bad at high rpm, but at low rpm will bleed off torque which can be felt in everyday driving. Now if this was a track only car then I'd agree this could be useful. Bleed off torque for the launch and make more power up higher but for streetability reasons, this may not be desired. It will also increase emissions and have a much poorer idle quality. Biasing the overlap towards the intake will definitely smooth things out and make more lower rpm power, but we are just compensating at that point.

it can be argued that more exhaust duration is required because of the difference in efficiency between the intake and exhaust ports. But 8 degrees is a lot of compensation.

I'm not saying one way or the other is wrong but it should be open to debate for a street car. A shorter vs longer powerstroke has its advantages for specific applications.

 

All true. And honestly that spec might be too much overlap now that you mention it. It was only a 8 degree split though. Pretty typical of cathedral.

For the the track I would actually go more to a 45 IVC and a 55 EVO. Try to cheat that power band up some. And center the overlap. 48 is getting kind of high if you do not intend to really rev it out. And would definitely need some compression.

Now for a street performance- not towing or hauling - truck, I would try to pull that EVO down to 40 and IVC down to 40 and zero overlap, which would be around 220/220-110 installed straight up. But it'll be done by 5500 in a 6.0.

What makes this hobby fun is the number of things you can do.

 

You will get a loootttttt more acceleration for your money with some gears and a converter. Auto 2.73 is pretty much as bad as it gets for 4th gens. You are way over complicating things trying to spec a magical cam for a very mild combo that all it needs is more gear and a converter. You will get a much bigger difference in your ET with bolt-ons then adding a cam to stock heads and factory manifolds. You're working backwards, and will be making sacrifices on your cam to make it play nice with stock heads and manifolds when what you really need is a stall and gears to get the car moving. A 6.0 will make gobs of TQ by accident, it doesn't need a special cam for it. Of course the cam company will try to sell you a cam - its their job.

I would add 3.73s and a 3200-3600 stall from a reputable company, then have some fun with it and reassess your goals. Maybe throw some ebay headers on it if you want to be cheap. Should be in the 12s and you may decide that it is plenty fun just like that and don't need a cam at all...but if you want more, you will already have the proper supporting mods for it.

 

I believe with ls6 style heads and Intake at 347cui an ivc @.050 of 48 should peak at 6400 correct? That's where the intake likes to make peak power and yo get there we could do a 228/228 .600 .600 114 lsa 114 icl. This would be 0° overlap and make a very flat torque curve. Static compression could be around 11.2:1 for a DCR of 8.3 which is a good safe margin for 91 pump.

 

Guys thanks for all the knowledge and time you have dropped on this thread. I really appreciate the input, tech talk, and recommendations. I always love a good bench race. I can't wait to see where this project ends up.

so here is where I'm at.

Just to reiterate, (I feel like some may have missed or disregarded my original posting) I've got a completely stock and heavy A4 2.73 geared 2002 z28 with a low mileage 2002 4.8 swapped in it with just blue springs, comp 212/218 115 lsa cam, and a good wide band street tune. It goes 14.3-14.4 @ 103-104 mph in 90°f+ 2000+da weather conditions with an appalling 2.35-2.40 60ft time. It doesn't spin at all and it only gets to shift once. It goes through the traps at just over 6k in second.

I was recently gifted an 01' LQ4 short block that needs new pistons. It will be going to the machine shop soon for an overbore and new cam bearings.

I was hoping to get the 6.0 short block fixed up with some budget pistons ( I'm leaning towards 6.7cc dish but that is still open for debate) and then swap the 706 heads and 212/218 115lsa cam from the 4.8 that I already have together in the car onto the 6.0, go and see what It runs and then go from there.

thoughts?

 

If you need it up and running asap and that's all you have then do it, it will drive like stock. Then later on get some new heads and a bigger cam. If you can wait, I'd hold off until you get heads and cam so you dont have to tune twice. You determine pistons based on if you are running Na or FI and how much compression you need to gain or lose to get the desired DCR. You may need a different piston if you get heads with different chamber size and a cam with less cyl pressure. And no "Budget" pistons, get name brand stuff and do lots of homework before a purchase.

 

​​​​​thank you for underlining my dilemma. I've been told that dynamic compression matters more than static and that's why I was thinking I could get the flat tops and still use my 706 heads and retard the cam I have 4 degrees if needed to keep it from detonating if pulling a few degrees of advance didn't work. Don't stock ls2's move heavier vehicles than mine? And they run flat tops with 243's which are only 2-3cc larger right?

Others have suggested that I go dish to be safe for a daily driver but I really want to go flat tops and make what I have work for now if that is possible. Would a custom spec cam really be any better of a bandaid than the one I already have?

 

LS2's were put into Vettes and GTO's; light AND heavier vehicles

 

I would send the 706 heads out to get a cnc port and polish with a good valve job and bowl blend, surface them for a cleanup and bigger valves and then run that cam. Should make power from 2k-6k and have excellent throttle response and idle very smoothly. Static compression should be targeted around 10.7-11:1. It will be a great daily driver.

 

 

Honestly if you retard your current cam to hit your DCR target it will still have a delayed power curve vs keeping the IVC where it is.

 

this causes a loss of low end that is counter productive without adding duration, am I correct?

 

sounds like I'll likely need to use a dish and mill the heads a little bit to get it there

 

Yes sir. You would lose your low end without making it back up in high rpm power.

 

2.73s. Stock stall. Stock manifolds. 2.4 60'. He doesn't need a new cam, he needs supporting mods. There is over a full second left in that car as-is, even with the baby motor. Swap in the 6.0 and fix the current issues THEN worry about changing your build. You have a low 12 second car running mid 14s, and it is not because of the cam. Don't just throw money at it.

You are cooking dinner all over again without tasting it because you didn't like how it looks half way through.

 

I dont disagree. I am just trying to answer his basic cam questions to arm him for the future.

 

Your advice was great, and would make for a killer setup. You are also right to answer the question asked without derailing or criticizing him, and I am sure he is learning a lot.

I just want him to realize that jumping straight into swapping cams is not going to give him anywhere near as much gain as just finishing up what he started. If he is just looking for cheap fun, and has already said that his mid 14 sec ride "runs great for what it is", he will likely be very happy just installing the supporting mods he needs and not even touching the motor again. Just a cheap set of gears would be worth more in the 1/4 than any cam change would bring him, and also make the vehicle a ton more fun while putting around town. Add a stall and headers on top of that and he is likely good to go and will meet all his goals.

Once he launches a geared stalled auto with that small torquey cam and knocks out some easy 12s, I can pretty much promise he won't be happy with 14.4s anymore and may decide to keep his cam...or start thinking about some head work and the cams you suggested to really start having fun .

 

You're dead on. I personally feel one should maximize their bolt ons first. Then when installing a cam, the vehicle is set up to best take advantage of it

 

I love your passion for the LR4, I painted it Chevy orange before I put it in the car just for you. I love these cars too

I have owned a few of them and currently have two. My other one I've had since new and it is also an 02' z but it still has the original ls6# casting ls1 in it. It also has a 10" tci ssf 3500, custom built original to the car 4L60e built by Randy the trans man, 3.73's in the stock ten bolt with a girdle, and a few suspension bolt-ons though it still has stock torque arm and sway bars on it. The engine sports the usual fra, whisper lid, underdrive pulley, pacesetter 1-3/4 longtubes, custom 3in y-pipe w/cutout, and a Magna flow out the stock tailpipes. Internally It is cam and spring only as It also has a btr stage III RV cam with matching blue springs (218/224-113+3) and of course a really good wide band tune. With the idle up at 800 and the cutout closed the magnaflow hides the 46.5° of overlap at 0.006" very well.

I'm very happy with how this car runs but it's my baby so I just start it once a week and save it for the occasional drag strip blast and nice days or car shows. I'm fully aware of the benefits of changing rear end ratios, stall speeds and improving exhaust system efficiency. I learned a lot with that car.

This other car I have with the 4.8 however is a whole different story, it's more of an experiment with a placeholder engine that gets driven no matter what. I'm in this forum to learn more about engines, not chassis stuff.

I think at this this point in my life my idea of a nice daily would be a nearly bone stock looking and driving car with a little extra tq that anyone can drive (in case I get drunk haha) and that's what I'm wanting to achieve with this mild 6.0 and those god awful 2.73's I know the 4.8 would be an animal with a 4k stall and some 4.10's and so would the 6.0 but that's not what I'm trying to do with this car.

 

thanks that's what I thought, narrowed the power band