Cooldude5231

iTrader: (6)

so im at a crossroads with my build. looking for some insight.
keep in mind the car will be a street car. not a track car. itll be a daily for about a month just cause i want to drive it. itll see the track. but the purpose for this build is for it to be a street car i can drive where ever i want to go

build: 98 t/a
lq9, stock bottom end with arp main studs, and rod bolts (also arp head bolts)
brain tolley stage 4 cam (235/242 620/593 111)
ported ls2 intake and 92mm throttle body
double roller chain
lunati .660 springs
th400 with fti 3500 stall and MVB
8.8 with 3:27's
28" tall tire.

i plan on spraying a max of a 250 shot. 2 seperate kits. probably a 100 on the first kit then another 150 comes in after the 60' if needed.
my confusion is in the head setup.
im looking to get the optimal CR (compression ratio) for my build.
stock lq9 CR with 317s is 10.4:1
lq9 CR with 241's is 10.6:1
lq9 CR with 706's is 11.4:1
car will be on 93 pump gas with a 1GAL cell of 116 for the nitrous.
from what ive read from brian (really hoping he chimes in) is that cam likes 11.3ish CR.
im worried about having too much compression with the amount of nitrous i plan on running, or not having enough timing in it (due to the compression) and making it a pig on motor.

i wouldnt call this a MAX effort build but im putting as much into it as possible with the amount of funds i have available.
if i go with 706's ill have bigger valves put in (if yall find it necessary since 241s flow 227 @ .600 lift and 706s flow 226 at .600)

GO!

HCI2000SS

iTrader: (2)

So what is your question, or are you just making statements?

Cooldude5231

iTrader: (6)

which head choice is the best for my setup and amount of spray i plan on using

HCI2000SS

iTrader: (2)

From my understanding those heads will be very comparable in terms of flow and power once worked over. If it were me I'd go with whichever ones are cheaper and/or more readily available

svede1212

iTrader: (3)

Some milled 243s

Always2Slow

iTrader: (8)

With nitrous your going to want the extra cross sectional area of the 243 heads. Even stock they will be good enough for what your looking to do without spending much money. Just clean them up and hand lap the valves in and check the guides for wear.

1FastBrick

iTrader: (16)

Your compression ratios don't add up.

A stock LQ9 is rated at 10.02:1 with 317 heads figured at 71cc

The same formula with a 241 head at 66cc is 10.59:1

The same formula with 706 heads a 61cc is 11.26:1

Combustion chamber CC from casting to casting will vary but those are pretty close to the general stock numbers.

As far as flow goes the factory numbers are all pretty close, but the 862 heads were done with a 1.89 in intake valve. a 2 in intake valve will change the numbers slightly.

Pick the compression you're after, do a mild clean up in the bowls, get a good valve job, and let her rip.

I can't find any of the old stuff about casting info but luckily I copied it over to the truck side of the forum and it got stuck in the Sticky Section. http://www.performancetrucks.net/for...g-info-434396/

redtan

iTrader: (5)

I'd rather have ported heads with bigger valves than OEM cast heads. Good head porters can re-shape the runners and combustion chambers for better flow. Also, those would have valve job done to them too which further helps flow and power.

There have been some pretty sick numbers put out by properly ported 5.3s. Not gonna get the same numbers out of stock 241s.

BLINGOLE

iTrader: (5)

My gm service information page shows a stock 2004 silverado lq9 is this "Compression Ratio 10.08:1" Not that .06 really matters.

I say 706 heads with big valves! MOA SQUEEZEEEEEE

1FastBrick

iTrader: (16)

Yeah you will get different readings between different parts. It all depends on the block, Some have a taller Deck height than others. Same with the combustion chambers. All depends on the casting and the machine work done after.

I based my calculations off some of the engines I have put together. It's only a base guide to go by as each one will be different.