JS

iTrader: (4)

U look a these new GM heads and the runners CC is BIG...Now why is the 205 stuff sooooooooo great when GM who has more money than Davey Crockett they went to a BIG BIG BIG RUNNER and BIG BIG BIG VALVE?


I guess on a 3.90 bore the 205 might be king but on a 4in bore or larger I would think the min would be 225CC????I also realize u would need the proper camshaft too with these new heads L92/LS3/LS7 to make the proper power but again whats everyones talk on this stuff..

I could play devils advocate and say most of the L92 stuff I see isnt any better than say a ETP 4in Bore LS6 CNC/ETP 215CC/AFR 225CC on something smaller than 420CI but bigger than a 364CI?

Thoughts????

ringram

I think emissions control has a lot to do with the new valve sizes etc. Ive seen a few comments that older engines were retired because they couldn't meet newer emissions requirements.
Perhaps its the best way to get the most power while controlling emissions.
Not sure on the theory side, except that small valve timing on the large valve will work the same as larger timing on the smaller valves. Lets you get more air in without overlapping valve events too much and you cant have a large valve with a small port as flow characteristics would be fubar. Exhaust ports are much the same size as before.

LSwonderfull

Exactly, but thankfully we can add valve timing and have it aLL! Valve area is the limiting factor to max power, port dimensions must support the large valve sizes to keep everything happy.

Beast96Z

iTrader: (21)

I think you should play advocate. I still haven't seen many great results from the bigger stuff. If the LS7's were all they were cracked up to be, they'd be common place by now, however, you see people laying down the big numbers with the cathedral heads most of the time. They may have their time once the cams are figured out for them, but for now, I would gamble on what works.

ChucksZ06

iTrader: (9)

Apparantly you think that the ls7 z06's that have 550 rwhp and are totally streetable are not immpressive. One off the reasons for the high velocity theories is that companies producing aftermarket heads do not want to spend money on retooling. A lot of folkes are stuck in the carb era thinking that you have to have air velocity to break of the fuel dropplets out of the venturis. Get the most air you can in and out of the cylinder and have the computor spray the correct amount of fuel in and make some power.

KillerZO6

iTrader: (-1)

gm is going to be selling a LSX head's that well be based off the c6 z06. They haven't released much info on them yet except there going to be released in the spring. U can google it and find a bit off stuff about them and some pics

JS

iTrader: (4)

I think on the bigger motors they shine but on a something under 400 inch I dont think there nessessary....

JMHO

KillerZO6

iTrader: (-1)

i dont think they will work on any thing under a 402

66deuce

iTrader: (1)

i had this thought about the L92s while driving to a friends house yesterday...

everybody talks about how the exhaust port flow sucks compared to the intake,or how weak the exhaust port is...and how GM put a lot more dur.on the exhaust lobe of the cam to help crutch the exh. port..
then i thought,maybe we are all looking at this backwards..

GM made a big int. port with a big valve,so they could keep the dur.of the int.lobe smaller than what they used with the LS1/2 head to hit there HP/TQ goals.in other words,they didn't crutch the weak exh.port with more dur.on that lobe,but made the int.dur smaller just because they didn't need to because of the bigger valve/port,and better flow..

does this make sense?or am i way off here?

Beast96Z

iTrader: (21)

Impressive, sure. Any car that lays down 550 rwhp is. However, 550 rwhp is becoming common place with big cubes these days. It just seems the square port heads are still a gamble at this time. I've seen results going both ways. Eventually it will get figured out.

vanilla89

iTrader: (8)

Yes,a big head and small cam will make the same power as a smaller head with bigger cam with more power under the curve

$750 L98

iTrader: (7)

It has to do with parts matching, always has - so what if GM goes big. Look back at the TPI, big engine, little airflow.

On the same cube engine say: 346
Small runners = High velocity / shallow high end breathing
Large runners = Low velocity / low end torque suffers

A 346 will only pull in so much air NATURALLY disregarding the cam, And a 402+ will pull in more air because of extra cubes...so obviously the larger the motor the more air it wants hence GM going with progressivley larger heads for the new BIGGER motors.

That doesn't mean that a 346 will like big heads unless you wrap it to 9,000rpm

1CAMWNDR

iTrader: (21)

And Gm doesn't even make a 346 anymore. You go from the 327 5.3 to the 378 6.2. Maybe this means all performance motors will be larger for the forseeable future...............
Maybe the 327 5.3 will get dropped also. Then you have the economy 4.8 for the trucks and lower power cars (Monte Carlo, Impala etc) and the 6.2 for everything else (Monte SS, Impala SS, Camaro, G8, trucks) .

black_z

iTrader: (4)

The 6.2 is ~378 CI. The 6.0 is ~364 CI.

merriman44

iTrader: (4)

I highly doubt they'll get rid of the good ole 5.3. It seems to get better gas mileage than the 4.8 and they are strong little mid-range engines. Just my opinion.

jay_lt4

iTrader: (4)

they are keeping the 5.3, it will be an option for the 2009 chevy colorado


http://www.autoblog.com/2007/06/07/v...eup-expanding/


article says 2008, but it was just released that gm is holding out till the 2009 model year


.

1CAMWNDR

iTrader: (21)

Thank you for the correction.
They should make the 5.7 the little motor---5.7, 6.0, 6.2, 7.0 .

66deuce

iTrader: (1)

but remember,GM is putting these heads on 6.2 liters,not a whole lot bigger than a 346,and their going in big *** SUVs.and suffering no low end TQ problems..goes against the big runner low velocity theory..

JS

iTrader: (4)

6.2 in a much bigger bore than the 5.7...IMO u are wasting money if u already have 243 castings on your LS2...I would have ET do there CNC program to them,I believe this to be the best bet going for a 364CI LS2 H/C setup..

66deuce

iTrader: (1)

i'm not looking to buy heads,at least not right now..just talking theory..and your right,the bore on a 6.2 is a lot bigger,4.060 if i remember..
just stating how these new heads and cam combo's for the LS3/L92s are going against traditional thinking when it comes to velocity and low end TQ..the LS3 in the new vette has plenty of low end TQ,as an example..