69LT1Bird

iTrader: (1)

I kept hearing from every cam company, magazine article and every person on the LS forums how the combustion chamber on the L92 heads is 70cc-71cc. I work where I can get the blueprints and they say that the ccs should be 68.4. I finally got my new heads the other day so I thought I would check. The are right to GM specs. I showed about 68.5 on one of my chambers. The magazines keep saying 70 which in my case messes with my numbers. I have a LQ4 with the dished pistons. GM spec, 6.7cc dish, this was also confirmed. So all of the truck engine people, with the 68.5cc heads, +6.7cc dish, .010 piston over deck and a .045 4.030 Cometic head gasket, I show that should be able to get 10:1 cr. Not bad for a street engine and no machining costs.

I just have to pick out a cam now. I have been playing with Desktop Dyno and Quick and Dirty Cam Spreadsheet. I have been recommended cams all of the map from Crane and Comp. After testing a ton of different scenarios in the software mentioned, the best cam looks like this so far. I know if seems low but who knows:
69 Firebird
3.73 gears
4L60E
L76 intake
90mm tb
Z06 MAF
CAI
3400 stall
10:1 CR


Lift = .564 intake
.571 exhaust
Duration:
intake = 220 (advertised 273)
exhaust = 228 (advertised 281)
Overlap=53
LSA 112
ICA 108
IVO=28.5
IVC=64.5
EVO=76.5
EVC=24.5
Timing= +4

This shows 507hp @6000 and 505tq @4500
static compression ration=10.06
dynamic compression ration= 8.04
These are Comp Cams lobes - 3713 3717

If someone can plug these numbers into their software to see what they think I would appreciate it.

03 BUSA

iTrader: (25)

I would say to re-check that overlap number.

69LT1Bird

iTrader: (1)

The overlap is calculate by both pieces of software and they are the same. I have no input into the calculation. What am I looking for?

TurboLark

iTrader: (3)

You may have made an input error. Thats a ton of overlap for a cam that small with a 112 LS.
You probably miss-entered the IVO or EVC. Check and make sure what the program asked for and what the cam card gives(BTDC or ATDC), its easy to mix it up.

69LT1Bird

iTrader: (1)

Nope, that is at .006, if you look at it for .050 it is the lower number.

LS1curious

You could easily do a ton better then 507 flywheel. easily. I see your location is lapeer michigan. Maybe contacting a few local shops working with the engine plaform might have some insight.

69LT1Bird

iTrader: (1)

I did those calculations before I began to understand how these heads work. I have been talking to the guys at Thunder Racing and they have come up with some good ideas.

69LT1Bird

iTrader: (1)

my latest cam choice. Remember, this is a street car, with the occasional trip to the dragstrip.
69 Firebird
3.73 gears
4L60E
L76 intake
90mm tb
Z06 MAF
CAI
3400 stall
10:8 CR


Lift = .581intake
.605 exhaust
Duration:
intake = 222 (advertised 271)
exhaust = 238 (advertised 287)
Overlap=51 @.006 and 2 @.050
LSA 114
ICA 110

all @.050
IVO=1
IVC=41
EVO=57
EVC=1
Timing= +4

heads milled .040
.045 head gasket
.035 quench
static compression ration=10.8
dynamic compression ration= 8.5

ringram

That looks better to me. More split.

Bigchickenhawk

iTrader: (3)

Man you are still leaving a TON on the table...for your setup I would recommend a 112 lsa...lift around .615..on intake and exhaust...and WAY more duration on the intake side ....something like 234 with low 240's on the exhaust

69LT1Bird

iTrader: (1)

Your idea works to a point. The dynamic compression goes down with the bigger duation on the intake side because the IVC timing goes up. Do you have any exact cam specs in mind, I am open to educated suggestions. Just putting the biggest cam in this setup does seem to work from what I have seen and heard. I haven't chosen a cam yet because of this, I want to get it right the first time.

66deuce

iTrader: (1)

i've read on LS2 GTO that those head don't like a lot of overlap,can anyone confirm this?

ringram

Thats what Ive heard too. But you might want to run it by an expert

Gregory

iTrader: (4)

Be careful! I've used DynoSym software to analyze my engine combinations and have always ended up with overstated HP/TQ software computer numbers. I’ve seen numbers overstated by as much as 50HP. Thus, you may need to go with more camshaft than the computer tells you to meet your goal in real life. I'm currently traveling on business, so I cannot plug your numbers into my home computer software.

69LT1Bird

iTrader: (1)

I am just using the destop dyno software to see what happens when you move the duration or valve timing around. I am not using it to build the engine. If you get a chance to run the numbers that would be great.

HSV-GTS-300

Livernois Motorsports Stage II cam that specs out at 232/236 @ .050, .600lift on a 112 lobe separation angle.
Heads un-milled and un-ported. 6 litre LS2 with L92 heads and L76 intake.
"the L92 heads and L76 intake helped the LS2 stomp out 494.9 lb-ft of torque at 5,000 rpm with a very wide torque band. The fact that this combination alsoproduced 546.8 hp at 6,500 rpm seems almost inconsequential."



http://www.gmhightechperformance.com...ads/index.html

89Formulaws6

iTrader: (52)

i'm curious on what cam to go with on my 408 since i wont be reving it past 6400 this cam looks ok above, not sure if stage 3 would be better or not since i have more cubes then a stock ls2

66deuce

iTrader: (1)

did you pick out a cam?just curious what the specs are...

69LT1Bird

iTrader: (1)

The specs in #8 above are the for the cam I had ground.