05ls7gto

It's about time for me to delve into a aftermarket camshaft for my GTO, I've gotten a custom grind specified for my setup. The profile that was proposed to me is: 234/230 .625/.625 115+4.

I don't know much about cam profiles so I asked a few local guys for their thoughts on the cam, many of them said it's fairly mild and leaves a lot on the table. There were a lot of comments about the reverse duration profile as well, and I have read and heard that this helps prevent lifting the heads or pushing the gaskets.

Aside from that cam I was looking into the BTR/LJMS Twin Turbo Stage II cam which a lot of my local buddies told me I'd be better off with than the custom grind. The profile of that camshaft is: 226/235 .605"/.604" 114+5

A basic rundown of my setup is:
Forged LS2, Stock Displacement 364ci w/ -3.2cc pistons
LS3 Cylinder Heads w/ LS9 head gaskets
Twin Turbo (62mm, 0.63 A/R)
Manual Transmission
Car is 99% pleasure street use and half mile "racing"

I know we have a lot of very knowledgeable guys on here and would definitely like to get some more thoughts/opinions before making the purchase. Being the ricer I am, the more it chops at idle the better. But at the same time I don't want to sacrifice drivability... I was given the option of another custom spec but haven't gotten that far yet.

Any and all input is appreciated!

Suncc49

local buddies is a dubious recommendation.... turbo cam grinds from BTR are known and proven to make power... why not talk to John B. yourself and see what he thinks rather than local buddies. He is very accessible.

Nathaninwa

I'm no cam guy, but do listen when others and who I use talk. The deal with the reverse duration setup is the lazy port of the ls3 head. Mines ground this way and so far I'm happy with what I've been sent

svslow

Assuming that you are talking about a 62/62 style turbo with a 0.63 A/R T3 turbine, the proposed cam might not be too bad. Those turbos are on the small side for what I would do on a 6.0L, so the cam would help keep them happy with less overlap and shorter exhaust duration.

SLOW SEDAN

iTrader: (13)

Sometimes... except we have local buddies that put forward more facts on Johns products then he did. Brians cams are great for the 85% crowd but a little soft for those wanting to push harder. But will you notice a difference on a low boost street car, probably not.


I agree while the 62's will spool quick I would go larger. I have larger turbos and a bigger cam in my 5.3L and it drives great. Really depends if he prefers a mild street car or is going to crank it up for the 1/2 mile.

I didn't see it mentioned what the planned power level will be?

newschool72

iTrader: (12)

There are those among us, myself included , that thinks short duration (2 teens-220s) is gracious plenty to get a turbo moving air. Once that happens, the turbo should carry you on up the RPM scale, especially on a street car build. That being said, most are single turbos that are larger and the cam helps jump start the boost. With those 62s and the tight AR, you wont need the help of a small cam to light it off on a 6.0.
As a side note, my experimenting with LS3 heads (NA) showed a shorter duration makes them very responsive at lower RPMs, and that the big ports carried the smaller cam up top. 220 IN. duration at .050 spins hard to 7K, but pulls hills at 1600 rpms in OD. The more air you can flow, the less duration you need to make good streetable power.
All that goes out the window if max power with no worries about manners is your goal.

yenkomike

iTrader: (2)

if max power is the goal then you are good to go with those cams but if good street manors and a great average power is what you want keep to the small side and enjoy better low end response. I might be on the extreme side of this but my nova has a 206/212 cam with 528/540 lift and has ran 9.90 at 135 mph on 13 psi boost at 3600 lbs. it has also ran 10.1 at 140 mph on 17 lbs with a soft launch on radials. I keep the rpm to 6200 or so but it will still pull to my 6800 rev limiter.idles smooth . I have seen the difference in a 218 stock48 cam and a stage 2 cam and the power loss at 2800 rpm is about 200 rpm converter stall on my datalogger. some cars I work on have trouble getting a converter loose enuff to get the thing spooling and not blow thru them in boost. if they have any weight to them. jmho.

05ls7gto

The locals I spoke to are some of the hardcore guys with turbo setups running 8's and 9's, not normal street car guys. Some of those have used the LJMS/BTR Twin Turbo Stage II cam with good results. They explained some of the advantages/disadvantages of each cam profile, most of them pushing me towards the LJMS/BTR rather than the reverse duration cam.

I did contact John in the past about a custom cam spec, but I was basically told that I need to get rid of the square port heads before considering a custom cam... I've heard that he is biased against square port heads, so I turned elsewhere.

Correct, it's a 6262 turbo with 0.63 A/R.

For most guys I guess my setup can be considered low boost, 12psi. I've been running the same setup for several years putting down right around 700whp. No real power goal, I just want to optimize the setup and get some chop. I know the LS9 cam I am currently running leaves a lot on the table, that was a poor decision on my part when I assembled the motor... I do have a long term goal of pushing 1000whp just to say I did it, especially since everything in the car has been upgraded to handle power levels past that. I'll eventually get around to hooking up a boost controller.

My car is definitely a pleasure/street car, but I don't want to have poor street manners (bucking at low RPM, poor vacuum, etc.).

At stated above I'm not necessarily chasing numbers and would like to maintain decent street manners. I'm aiming to optimize the setup of the car by tossing the LS9 cam that I know is working against me and have some good sounding lope as well.

newschool72

iTrader: (12)

A short cam isnt going to give alot of rap at idle, that is unless you dont have much in the way of BP with those twins. If your close to 1 to 1 on BP/ boost, you could tighten the LSA up and treat it more like an NA build. All engines are boosted. Turbos just push the boost past the 14 psi that gravity gives us. Back pressure forces turbo cams to widen the LSA out to avoid reversion.

tblentrprz

Talk with Stock48 about a cam for your combo and goals. BTW - is it possible to optimize a cam for power performance and street manners that includes cam sound at idle?

05ls7gto

More often than not, no - as with anything you will have to sacrifice one thing which I am aware of. In my case I think it will be "maximum/optimum" power/performance of the cam, which is likely the opposite of a majority of people.

roastin240

iTrader: (13)

Custom cams are typically spec'd based on the combo. That being said they place the valve events approximately where they want them, then the resultant duration is what it is. The lift is rather trivial and known what works well. The LSA is selected based on goals and target overlap for the given combination and then re-indexed to get the valve events where they want them. They then choose an off the shelf lobe that has a duration and lift that is very close to what they determined, and determine how aggressive it should be based on what type of driveability, power goals, and durability is to be expected for the setup. Things that are considered when selecting a lobe profile include valvetrain component mass, spring rate, ramp rate, valvetrain noise, boost pressure, exhaust drive pressure, etc.

This is how I run all my numbers and make my decisions when I spec out my cams for myself and customers engines. I would imagine many of the "custom spec'd cams" are selected in this fashion. Many of them also just know what works based on seeing results of hundreds of combinations. This helps as well. but having a fundamental knowledge of where valve events should occur and why is the best way. Everything else is easy from there if selecting off the shelf lobes (which is what every shop does). Creating a new lobe profile is extremely involved...how much time do you have? I have taken this avenue a few times at work and once for 1 of my own cams on my turbo 5.3 (about to test it soon). Not necessary for almost everyone as the lobe profiles available off the shelf come in many flavors for a wide range of goals.

NOTE - lobe profile does not specify a lift and duration necessarily. The lobe profile is used as a base and then the numbers/profile are scaled to accommodate different target lift and duration. I hope that made sense...

speedtigger

iTrader: (16)

You can learn a lot about what is going on in your current combo by monitoring drive pressure. That information can help you dial in your next cam much better.

pantera_efi

iTrader: (1)

Hi ALL, I was the first to get "turbo" cam timing correct.
I later found the SAME knowledge reported by John Drake, the manufacturer of the MOST WINNING Turbo engine to this day.

My "spec" for your needs is 212/220 with .580"/.612" on a 104 C/L
This spec will provide a GREAT song at IDLE and VERY GOOD SPOOL.
The MAX RPM range will be 6500 though this depends on MAP.

NOW FOR SOME "LS-1 TECH" :

The difference with a Turbo/Non Turbo spec is to ADD about 30 degrees @ .050" to understand RPM Range.
EXAMPLE : A turbo with your spec of 234* will EQUAL a N/A of 264" (234+30)

Would this BE your chosen RPM range for Torque ?

Ten years AGO we tested MANY Comp Cams camshaft at Westec for a Chevy-HI article.
They were similar to other of the "long" spec cams provided by the above posters.

NONE of the Comp Cams camshafts WORKED

We then installed an OEM Z-06 camshaft with a report of 1200 HP@22 .lbs on Pump Fuel.


My IGN-1 Coils AND ECU-882C where the ones fitted, the engine was for Ro M.
The engine ASLO had a 4.1" crankshaft.

Lance

SLOW SEDAN

iTrader: (13)

Then why did COMP get more hp out of a larger cam 4.8L with stock coils then you did out of a fancy stroker on the same westech dyno?

pantera_efi

iTrader: (1)

Hi, YOU STATE NOTHING of your report, could you supply more information?

ONE reason is MAP, RPM, etc.

AS for POWER Brian Hart made 1400 HP with a 1.5 liter turbo engine more that 20 years age.

Lance

SLOW SEDAN

iTrader: (13)

Its a couple of fairly well known articles...

5.3L, 6300RPM, 24PSI, 1308hp.

4.8L, 7000RPM, 26PSI, 1203hp.

kingtal0n

iTrader: (1)

I used to think this way, it makes perfect sense. I sort of tested this theory on a variety of high back pressure small displacement setups over the course of ten years, A couple 2.0L (sr20) and two 3.0L engines (2jz) using the OEM manifold (T-25 flanged) or log-style (cast, thick material with T3) with quite a few different turbocharger configurations (2871r, original T-28, 28rs, T04E 50 trim, 60-1, and other larger Garret as well) And all of them performed better (more cylinder VE, higher RPM capable) with a longer duration and more overlap camshaft (much more overlap). For example one of the 2.0's that was my personal car I went from OEM cam (248* @ 0.00" or 0.05") to a (brian crower) 264 @ 0.05" and then to a 272 @ 0.05" with a healthy lope (by HKS) with significant overlap, and torque still remained high, and increased over the smaller duration/less overlap cams, even with such high backpressure manifolds and tiny flanges.

Maybe it was just the 4-valve/cylinder talking but it sort of shook my theory about cylinder reversion and drive pressure. Any thoughts about this? And fwiw you can obviously look up any of the common "turbocharger grinds" for those popular engines and none of them are short on overlap or duration.

roastin240

iTrader: (13)

^^Yes the go to move for high drive pressure setups is negative overlap (or reduced overlap at least) and opening the exhaust valve a bit sooner to start the blow down process sooner due to higher pumping losses and more time needed to evacuate the cylinder. This has been my observed gains...

Keep the exhaust valve closed longer and your expansion stroke is doing more work on the crank...which theoretically is what you want. But at some point, the pumping losses outweigh these gains. Additionally, turbine response is affected by exhaust valve open timing, among the other parameters of the cam obviously. But I like to set the exhaust valve opening based on the setup and go from there as I march through the process of picking my numbers.