N4cer

iTrader: (11)

I'd like to get some input on this build that I've been considering. Keep in mind that this started as a budget rebuild of my stock cubes until I ran across a couple of deals.

I am unsure what cam to run, so I'm going to use my current cam and see what happens after that. The reason that I think my G5X3 might be okay is that the intake is seen to fall off sharply after 6300 RPM if you've paid attention to the board. So this small cam (small for a 408) will peter out by then. Sound okay so far? Cam gurus, if you think I should retard/advance it any, let me know. Remember G5X3 is 234/242 .598/.610 112+4 on XE-R lobes.

I am building this to be the strongest NA, street driven but mostly race-oriented car that I can build. To put it into perspective, I love the way my car feels with a 3600 stall and this cam/heads that I have now. So slightly big cam but still good in the midrange. With the torque curves I see coming from 408's, I think midrange will be no problem. So I'm not against a bigger cam if that is needed. But give me a reason.

Also this engine will see some nitrous use. Probably just 100 shot when I run spray, but will consider bigger if I go for a faster time. 250hp shot max.

Iron Block 4.030" bore
Eagle 4.00" crank
Callies Comp Star rods
Wiseco pistons -2.2cc (is paying for coated ones important?)
Not sure of rings... make a suggestion on brand and gap
ARP main studs
ARP head bolts
L92 heads (stock but will get some slight work done)
L76 intake
L76 injectors and fuel rail
Still unsure on throttle body... will get whatever I get a deal on
Lifters... LS7? Stock LS1? Caddy?
Rollmaster adjustable double roller timing set

N4cer

iTrader: (11)

Oh yeah, this makes my compression look like this:
Static Compression Ratio 11.91
Dynamic Compresion Ratio 9.17

N4cer

iTrader: (11)

I figure with good pistons, rings, .040 gasket, I can just back off the timing to compensate for the high compression.

Patrick G

iTrader: (14)

The low and mid-range torque will be excellent with a G5X3 in a 408. That will give you the throttle response and street manners of a 224/232 cam in a 346. Retarding the cam 4 degrees to +0 is a smart move for power on motor, but not for nitrous.

On nitrous, the combustion happens much faster and the volume is much greater. A 100 shot will not require too much in the way of special cam events but a 200+ shot will. A 200 shot will want around an 8 degree earlier EVO. If the EVO of an X3 cam at +4 is 57 degrees BBDC and you retard it 4 degrees, the EVO is now at 53 degrees. OK for NA, but not for the spray. Ideally, you'd want your EVO to be at 61 degrees BBBC for a 200 shot (assuming 234/242 112LSA +0 was ideal on motor). Keeping the IVO and IVC the same as the X3 cam at +0, but making the EVO 8 degrees earlier (while keeping the overlap the same (14 degrees at .050) means a cam that looks like this: 234/250 114LSA +2. Same IVO and IVC. Same overlap. Same EVC, but the EVO is 8 degrees earlier. Pretty cool stuff huh?

N4cer

iTrader: (11)

Thanks for the help, PatrickG. Your help is greatly appreciated.

With that info, maybe I'll just go bigger all the way around. 224 manners is NOT what I'm looking for. Having a 4L80e, PY3600, 9", and suspension mods, I'm not THAT concerned with street manners. So basically, if I wanted a cam to act in the 408 like my G5X3 does in my car, I'd need to go something similar to a Trex, only with a greater LSA for nitrous?

Ahh heck, anybody else thinking Futral Godzilla cam? LOL! Just kidding!

Patrick G

iTrader: (14)

For a 408 to have the same street manners and power band as a 346, you'll want to add 10 degrees to the duration. If your intake valve is the same size, you'll be more undervalved which will make your motor want a little more overlap.

Take your 234/242 112LSA +4 and add 10 degrees to it:
244/252 112LSA +4.

Look at the valve events:
14 BTDC IVO
50 ABDC IVC (really good for a 408)
62 BBDC EVO (close to the nitrous recommendation)
10 ATDC EVC
24 degrees of overlap at .050"

Overall a nice cam on and off the nitrous.

N4cer

iTrader: (11)

SO what about the heads?
I have an L92/L76 combo sitting here, and I have my 59cc milled LS6 Livernois heads I can use. I've not seen any good track times yet from the L92/L76 408. Has anybody else?

Patrick G

iTrader: (14)

Most of the L92 setups have been low compression (below 11.0:1). Get your compression closer to 12.0:1 and run at least a 4.03" bore and the L92s will probably walk all over other heads.

N4cer

iTrader: (11)

Sounds sweet to make 500rwhp and never have to spin over 6300... It'll last forever. But at 11.9 SCR, that puts my DCR at 9.17. On 92 or 93 pump gas, can I make that work by using less timing? I know a certain port master on here loves the idea, but what do you think? And who makes a stroker N2O piston with like 4cc reliefs?