TexassTA

Which heads do you guys reccomend porting? What are the advantages of one or the other? Thanks <img src="graemlins/formula.gif" border="0" alt="[Pontiac]" />

11 Bravo

iTrader: (3)

I'm no expert, but I know that 5.3 heads will give you a higher compression ratio. This may or may not be good for you. I could have got a good deal on ported 5.3 heads, but it would have put my compression ratio at like 11.1-11.3. Too high for pump gas imo. Maybe someone more educated in LS1 heads will chime in.

ChrisB

Is this just a heads+cam setup, a stroker, nitrous, FI motor, etc?

What kind of octane can you get in your area, and what kind of camshaft will you be running?

Chris Bennight

TexassTA

Sorry,should have included my sig.I spray a 100 wet shot every once in a while.The highest pump gas here is 93 octane. Chime in guys!!

Paul J.

The ports are identical between the heads, so it really comes down to a compression ratio choice. If you have access to good gas, and plan to run a cam with over 222-224 intake duration, the late intake closing will bleed off some cylinder pressure, especially if the cam is installed several degrees retarded. Basically the intake closing point determines cylinder pressure, and the later it closes, the less cylinder pressure would be developed. It is also the most critical valve event as far as power production is concerned. Ratios of 11:1 are possible with cams having 222-224 min intake duration on these LS1 motors, and will increase engine effeciency and power output roughly 3% for every 1 point increase in compression.

Basically, run as high of compression as you can get away with. This will require less milling with the 5.3L heads although the chambers need more work to unshroud the valves.

Paul J.

LS1derfull

I say no since 5.3 has smaller valves, and BTW the 5.3 exhaust port is smaller than 5.7 port.

Jantzer98SS

iTrader: (54)

Go with the higher compression unless you'll boost the car in the future.

The LS1 heads will flow better in stock form. The ports are the same, but the 5.3 has smaller valves and the valves are shrouded more in stock form. Once they've been ported, the only concern is compression ratio, they'll flow the same.

Scalpel

iTrader: (4)

Janzter98SS. Thanks for your reply! With this info why doesn't everyone just get ported/polished 5.3 heads and get the added benefit of increased compression????? <img src="gr_grin.gif" border="0">

SSBoy

[quote]Originally posted by NastyC5:
<strong>Janzter98SS. Thanks for your reply! With this info why doesn't everyone just get ported/polished 5.3 heads and get the added benefit of increased compression????? <img src="gr_grin.gif" border="0"> </strong><hr></blockquote>


Because us Californians are limited to a max of 91 octane at all gas stations.(cant get higher unless you buy racing fuel) I dont think an 11:1 compression with 91 octane would mix to well... <img src="gr_images/icons/wink.gif" border="0">

Scalpel

iTrader: (4)

Good point, SS. Damn, Cali has it's downsides when it comes to making cars go fast <img src="gr_sad.gif" border="0">

Ragtop 99

iTrader: (7)

[quote]Originally posted by NastyC5:
<strong>Janzter98SS. Thanks for your reply! With this info why doesn't everyone just get ported/polished 5.3 heads and get the added benefit of increased compression????? <img src="gr_grin.gif" border="0"> </strong><hr></blockquote>

more expensive too.

You have a buy a set of heads instead of just trading your stock heads as cores. Many S1 heads use stock valves or atleast the stock valve size to save money. Does anyone know if the porters charge more for the truck heads becuase of the extra work?

Jantzer98SS

iTrader: (54)

You should be fine with 11:1 even with 91 octane if your cam is 222/222 or larger.

It's more work to port the truck heads. More bowl grinding and you have to do work to open up the chambers to deshroud the valves. Where as most don't touch the LS1 chambers.

For boost applications, you want lower compression.

1dirtyZ

iTrader: (1)

so what about the 6.0 heads?? how do they flow compared to stock 5.7 heads??? and i thought i heard someone say that there are certain 6.0 heads that outflow stock 5.7 heads, is this true , and fially , how much compression do these heads drop??? any info about them would be greatly appreciated.....

[ February 10, 2002: Message edited by: 1dirtyZ ]</p>

VINCE

iTrader: (1)

I say try 5.3L's with 11.5:1 compression and 224 plus cam and you will fly..

Scalpel

iTrader: (4)

[quote]Originally posted by Paul J.:
<strong>The ports are identical between the heads, so it really comes down to a compression ratio choice. If you have access to good gas, and plan to run a cam with over 222-224 intake duration, the late intake closing will bleed off some cylinder pressure, especially if the cam is installed several degrees retarded. Basically the intake closing point determines cylinder pressure, and the later it closes, the less cylinder pressure would be developed. It is also the most critical valve event as far as power production is concerned. Ratios of 11:1 are possible with cams having 222-224 min intake duration on these LS1 motors, and will increase engine effeciency and power output roughly 3% for every 1 point increase in compression.

Basically, run as high of compression as you can get away with. This will require less milling with the 5.3L heads although the chambers need more work to unshroud the valves.

Paul J.</strong><hr></blockquote>

Well put, Paul J. BTW, you mention the ports are the same so does this mean they would flow the same as the 5.7 LS1 heads, stock for stock? Thanks.

[ February 10, 2002: Message edited by: NastyC5 ]</p>

horist

TTT

I'm thinking of getting TEA Stage II 5.3 heads....

do they really flow the same (to a 5.7 L head? )

I want 11.1 - 11.3 compression... sounds like these heads will do it.... but I wont have a core, it's only 75 bux to have TEA mill the heads .050 (which I believe raises compression to 11.1).....

thanks

warbird#2

i run 11.1:1 comp. no problems. all the added(higher) compression compacts all the air/fuel tighter giving u more cylinder pressure. this is similar to the way that a blower would work by forcing above normal air(more) + the extra added fuel into the cylinder creating more pressure.that is why u need low compression on a blown motor because u are already have extreme cylinder pressure & with the high compression it would go KABOOM with to much pressure from the explosion. by doing either of these (added compression/blower) it will gain u TQ across the whole RPM range & u can't gain TQ without gaining HP by law.sorry if i am a little off it is 6am & i am tired as well as in a rush for work. i hope that helps u understand a little about adding compression.

Redline-Motorsports

iTrader: (3)

I just cc'd both a set of 5.3L heads and a set of LS1 heads.

The 5.3L heads had a combustion chamber volume of 68 cc's. The LS1 head had a volume of 64 cc's.

IMO the 5.3 can ue some seriuos unshrounding work!

QUASAR

iTrader: (6)

shouldnt the 5.3 have less cc's?

BIG PD

yah the 5.3 heads have fewer cc's then the 5.7 heads. there is less room to compress the air in the 5.3 heads which is why the compression ratio is higher. the same amount of air being compressed in a smaller space is what makes the 5.3 heads better for high compression motors.