well my vortec heads are in the shop getting the works done to it like a 3 angle valve.....valve guides being cut down......and also bigger valves...i was wondering how big of a spring could i use can i use dual or tripple spring....and also what is a good lift?? i really dont wanna run anything over a .550 lift wit 1.6 roller rockers....just give me your input because this is really my first engine build and i want my motor to be strong and fast

 

I understand larger valves don't help Vortecs. Perhaps some of the 'sperts could verify that.

When the guides are cut, have the spring seats cut as well so something like Comp 981 springs will fit.

 

I am no exspert but when I was getting info from different engine builders up here it was this. The vortec heads are a very good flowing head . The newer performance designs have the bigger valves. To take an older style of vortec heads with the smaller valves you do not have much work to flow as good as the newer style with the bigger valves.Mine now have 2.0/1.55 .You do not have alot of port work to do. Do a search on google and you will see some of the flow rates with a little port work and the bigger valves , you will be amazed. They are flowing alot better then alot of the aftermarket heads and can get them at a good price.


I ended up getting my motor built in the USA , I wanted to buy an aftermarket head, money was not the problem. I could not believe the builders saying why these vortecs are working real good with the right work done to them.

 

Larger valves dramatically help the vortec heads, especially on the exhaust side at the lower lifts.

 

True for the exhaust side. hard to go wrong with the bigger ex valve. The intake side is a little more involved.
If you won't be porting the intake ports don't go with 2.02" valves.
The head will flow less than stock with just the big valve installed.
If you'll be porting the intake port and need more than 240-245cfm then go with a larger valve than stock. The chamber needs a little work too when going to larger dia valves in the L-31 Vortecs.

With stock ports and valves .480" to .530" is plenty lift.
Full porting and larger valves helps the high lift flow. thats where .550" and higher lift can be of some benefit.

The cam manufacturer can recomend the right valve spring for your cam. Cylinder head machining will be required, reguardless.
Triple springs are for full race roller setups.

 

correct me if I'm wrong, but wouldn't too much exhaust flow create an issue if/when there's a valve overlap?

the stock 305 cam has no overlap if I remember correctly, but most aftermarket cams do, and if that's the case, wouldn't there be a point of no return on the exhuast flow?

this of course is assuming that you still want to pass emissions, or have a cat...or save the planet...

 

i guess theoretically there may be a point where exhaust flow could be detrimental but you wouldn't be anywhere near it with 1.6" valves...

http://www.nastyz28.com/forum/showthread.php?t=56505

a great thread about vortecs pretty much all you need to know

 

I've got a set of Topline Vortec replacements. These were pocket ported, an2/02/1.6" valves and a good valve job. All by Creative Flow Mgmnt. Here are the before and after flow #'s.
Intake Exhaust
.1 71/72 66/78
.2 127/128 119/135
.3 186/188 139/170
.4 226/231 143/183
.5 239/258 146/187
.6 236/260 146/191

The bigger valves didn't seem to hurt these heads. Really make a difference on the exhaust and at high lift.