I got a good machine shop that does good work for me cheap since i grew up around them now my question is can i get the 305 heads off my L98 which would go on my new motor (350 with lots of work done to it) to flow as good as these heads worth $1200. If i did the machine work id put in 2.01 in 1.60 valves have 3 angle valve job done and all upgrades parts screw in studs ect .. What would be the pro's and con's of doing this would i benefit by getting a brand new set of heads or getting this machine work done since i get it done cheap ?

 

Converting to LS1 valves (2.0 intake, 1.55 exhaust) would be relatively cheap as you can get used LS1 valves for about $50 with retainers and keepers. The machine shop could install the 8mm guides for you cheap, and you wouldn't need new seat inserts to fit the valves. Then you just get some good conical springs like Comp 918's like the LS1 guys run. Your machine shop can machine your spring pockets to fit your spring or to give you a certain install height with these springs. They will not need to be shimmed on 305 heads.
If you are unaware, the stock LS1 valves are much lighter in weight and flow much better in a stock iron head than a slightly bigger aftermarket valve would do. They are very good quality, and the beehive or conical spring is superior design not likely to bounce the valve off the seat.

To take advantage of the bigger valves the heads would have to be ported and unshrouded. The porting is a lot of work with iron heads. That might cost you a bit. You'll also want to have the EGR holes in the exhaust ports filled in with steel weld and epoxied over on the intake manifold side.

In the end they will be good street heads, but will not be able to out horsepower a set of aftermarket aluminum heads. You will save a lot of money though.

A good port job would allow about 350 RWHP with no problem. If that's about all you're shooting for (which is very reasonable) then the 305 heads will work.

In your post you mention the 305 heads are from an L98 engine. The L98 is a 350. The 305 is the LB9 usually. What are the casting number on these 305 heads?

 

I wouldn't step up the valve size if I were you . I have been told by a machienist that the shrouding is large !

I got a pic of a 2.02 valve in the 081 casting here



I have been told by the same machienist , that the shrouding there will negate any gains seen by the bigger valve.

 

That is true UNLESS you open the seat up to 90% the diameter of the valve and do a little unshrouding like you're supposed to when increasing valve size. Then the gains are very large.

The shrouding itself isn't a showstopper. Most of the flow goes across the back of the valve towards the center of the cylinder anyway.

The main point most machinists try to make by telling you this is that for most people (who aren't going to do the extra grinding on the heads) it's not cost effective at all to buy large hi-po valves when the gain in flow will be so low. Taken at face value that is true. Without opening the seat up or doing any unshrouding it is actually possible to lose a little flow with the bigger valve.

Bottom line, if it's done right the gains will be large.

 

But all the material that needs to come out ...will it not be over the 4.00 bore ? I mean that unshrouded ... will the flow run into the deck surface ( or head gasket )

Or trying to make a visual aid ... from the side it will look kinda like a mushroom ?

Know what I mean ? Just wonering .....

 

Most people will stay inside the bore-line for a 305 engine, but a few will go further and then chamfer the top of the cylinder.
It doesn't take as much unshrouding as you think. Like I said most of the flow goes across the valve towards the center of the cylinder anyway.

The main restriction to flow isn't the chamber wall, it's the area just below the valve seat. When you go bigger valves and then open the throat & seat area up to 90% the diameter of the valve the flow improves greatly, even with the shrouding on the chamber wall.

Where people mess up is installing larger valves and not opening up the throat and seat area. This would only improve flow up to about 0.100" but then completely kill the high-lift flow.

 

well , nice to know

 

don't 305 heads have a smaller combution area witch would up the compresion two much?

 

305 heads do have a smaller combustion chamber, but not neccesaily up the compression too much. That depends on what pistons you use.

 

i didint think bout the idea of using a dished piston. That would take care of the problem. wouldent that cost more than buying the correct heads and porting them? seems like it would be very expencive to rebuild a entire motor, all parts and balanceing just to use 305 heads. steping over a dolar to save a penny. But i am a rookie so i may be way off.

 

upgrade the heads. 305 heads flow well...for a 305. Less inches need less air to rev to the same rpm...