At what point in a mild chevy sb rebuild does the need for the 2.02 valve come into play. Is this a case of too big aint good? :D
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At what point in a mild chevy sb rebuild does the need for the 2.02 valve come into play. Is this a case of too big aint good? :D
IMHO, as soon as you said mild!:LOL:
WHY ?? Think reliability thgose 202 1.6 heads are more prone to cracking than the 1.94 1.5 heads. Also the bigger valves dont just end there, you will have to get the bowl area machined out to match. So that you get the increased flow.
It gets pretty deep when it comes to valve size.Others will give more info,but bigger is not always better.Valve shrouding also comes into play.The way I get it is that for lower rpm engines with torque in mind you will want smaller valves.Higher rpm horsepower engines (less low end torque) a bigger valve will probably work best. I dont know that bigger is always better though,another way I see it is that a smaller valve with more lift will flow pretty good .A smaller valve will not block the flow as much.I am not even close to being a expert on this ,this is just my two cents.Good question though,I would like to see where this goes.
I.M.O,If you are wanting to jump to a bigger valve size you might as well go to an aftermarket heads because of all the work that will go along with it.Quote:
Originally Posted by jimmyjeep
In other words why put all that time, effort,money into old castings.If you do decide to use the old castings.I would say after 4,500 and about 300 hp I would look at the larger valves.
I really don't have a magic number but after 425 hp it becomes much easier with aftermarket heads.
All sound thinking, but still I'm just wondering if you had the basic 350 warm over, +.030 bore, .450 lift cam (oh hope I didnt stub my toe there), aftermarket intake and vanilla flavored 4bbl holley wth headers, and you had two pair of heads to work with, one with 1.94's and one set with 2.02's, would the mild build favor the smaller valves, or would you bolt on the 2.02's. I know there is a well established formula for carb size, but what about valve sizing? We talk alot about compression and chamber cc's here, but how about the valve sizing speech. If there is a good thread on this subject, I just havent found it yet, cuz I know you guys got it down cold. Pardon my ignorance, just trying to learn from those with the knows.:D
Hard to say.... IMO it would be more important what the flow numbers and flow charachteristics of the heads are.... Around this part of the country, there are some very fast Wissota Super Stock circle burner that are limited to 1.94 intake cast iron heads with a cast iron 5 barrel intake NON PORTED and running a 500 cfm 2 barrel carb.....
With the wrong combination of cam and heads, maybe the bigger valves will help, but on heads done right, especially on a street engine, I doubt there would be much difference at all in the performance between the two valve sizes... The valve size is just one part of the equation.....
A case in point that valve size is not the whole answer is given in this blurb from Chevrolet about the L31 Vortec heads with their smallish 1.94"/1.50" valves:
Small block Vortec heads, the head with huge performance gains that everyone is talking about.
This production Vortec iron cylinder head was first used on the 1996 pickup truck RPO L31 with fuel injection. The intake and exhaust port are very similar to Corvette 350 LT1 heads. America’s favorite high performance cast iron small block cylinder head offers big power and bigger value. The Vortec cylinder head's fast burn combustion chamber and high velocity ports combine to produce big horsepower out of the box. The Vortec head can be mildly ported for additional performance and can be milled up to .040” for increased compression ratio. This head includes 1.94” intake valves and 1.50” exhaust valves, springs and retainers, and pressed-in 3/8” studs. This head with compatible valves flows more air than bow tie head P/N 10134392, but the casting may not be as durable. It is a 20 to 40 horsepower bolt on increase over earlier cast iron small block heads. The water passages are the same as the original 1955 small block design. The eight-holt intake bolt pattern is totally different than the early model V8 12-bolt design. The Vortec head REQUIRES a Vortec style intake manifold due to its improved manifold mounting flange and gasket design and raised intake ports. It is not recommended that the heads be modified to accept early design intake manifolds (They will never match up right.). Use new manifold P/N 12366573, 12496820, 12496821, 12496822, or any others that we have listed below for correct matching to the Vortec head. Vortec heads fit all small block engines produced 1955 to present, excluding LT1/LT4 reverse coolant flow engines and current LS1 style “GEN 3” engines.
Technical Note: The valves seats in these heads can be machined to 2.02” intake and 1.60” exhaust. The rocker arm studs can be pinned or drilled and tapped 3/8”. These heads require the use of self-aligning rocker arms. (Casting P/N 10239906 or 12558062) (65 ft./lbs. head bolt torque)
Please Note: The casting number myth debunked:
The myth is that there is a difference in the head performance produced by these two castings.
This myth was started by some Magazines that didn't do their homework before publishing their articles.
This is the truth the whole truth and nothing but the truth. So sayith the Grand Wizard GM and his Apprentice Wizard GILBERT CHEVROLET.
10239906 casting has one large single hump.
12558062 casting has 3 small humps.
If either of these two castings have not been altered by GM and the part number changed from 12558060 or altered by someone else (previous owner, etc.), the heads produced by either casting will be identical except for the external cosmetic difference. Both castings are used to make the 12558060 Vortec heads which are the true unaltered Vortec heads.
Heads from both castings come out of their cast IDENTICAL except for the minor cosmetic external differences!!!!!!!!