Asmodeus

I want to do this one myself and see how it works (good or bad I can say that I did it). I have been reading a lot in the last couple months, hoping to get a grasp on this.. so here it goes..

Comp Cams (230/234 .612/.598)
Intake lobe - 3016
Exhaust lobe - 3727

Cam events at .050:

IVO - 7 btdc
IVC - 43 abdc
EVO - 47 bbdc
EVC - 7 atdc

LSA - 109
Advance - +1
ICL - 108
ECL - 110
Overlap - 14 degrees

Why I chose these valve events..

IVO - LS engines w/ cathedral port heads like a later IVO, but I have stock size valves.. making me slightly undervalved compared to other head/cam cars, which means I should set the IVO a bit earlier. Also the heads are 227 cc runners which means velocity is lower than stock and high end aftermarket heads.

IVC - My manifold is a aluminum "plastic style" LS intake manifold that I'll be porting.. but those tend to peak around 6300.. so I want my IVC to be "tuned" with my intake manifold to reduce reversion. I have read an IVC of 43-46 is good for this style of manifold. I chose 43 because I want it to peak sooner rather than later.

EVO - I want to open it a tad sooner than my current cam to reduce pumping gas losses and increase low end torque.

EVC - This being at 7 also centers my overlap bias. I'm still not sure what this does.. but I know with 14 degrees overlap, my exhaust needs to be up to task. Should this lobe be bigger since my I/E ratio is only about a 74% average from .300 to .600?

LSA - Vizard's LSA to CI/Inch of valve diameter chart puts my 21.4 at 108. This chart is supposed to be for accurate for 9.0 to 11.0 compression. But I am concerned about PTV clearance and on the high side of his chart so I made it 1 degree more since higher compression likes a wider LSA..

My head flow:

lift --- intake - exhaust
.100 -- 71.4 --- 59.1
.200 - 146.1 -- 118.1
.300 - 212.5 -- 159.7
.400 - 250.3 -- 190.9
.500 - 280.7 -- 206.7
.550 - 291.2 -- 214.2
.600 - 299.8 -- 219.2

Intake should flow close to 280cfm when I am done porting it and set it up for a 90mm TB.

My exhaust is 1 3/4ths longtube headers stepped to 1 7/8ths with a 3 1/2" HVMC into a Y-pipe. The merge at the Y is going to be set-up to a parallel merge with a 4" I-pipe.

Compression is 10.85:1 (They are 243 castings cleaned up to 63cc's with a stock .052 compressed MLS gasket.) I do not at this time plan to take the heads off and mill and flycut.

My Question(s):

What would you change and why (what is effected?)?

Is my thinking way off on my reasoning?

Is any more data required?

5_02ls1

iTrader: (20)

im assuming you have a weiand manifold....that 6300 peak is with a 78mm opening.....open that up to an 85 and watch the rpms move up.....your theory makes sense i say grind it and let all of us know the results

Patrick G

iTrader: (14)

Looks well thought out. I like that you've got your overlap centered over TDC. That should allow your motor to pull nicely past your power peak. I really like the XFI intake lobe. Should make excellent mid-range torque too (although opening the exhaust valve earlier does reduce pumping losses, but it actually hurts low end torque somewhat. It's more of a benefit to higher rpm).

danf1000

iTrader: (2)

i'm with G-man. the only problem with your rationale is the exhaust opening part. with that, consider what you can do differently with that exhaust duration, if you want to emphasize torque.