What are they capable of? HP/ cfm flow with porting and bigger valves. Im considering using them on my 350 build. thought I would get some oppinions from the pros first!

 

Not sure of the year of the heads or even the flow numbers. However 1987-89 305's with tuned port injection had heads that flowed well or decent for that setup. In other words if you have the those piticuler heads with larger valves installed 2.02/1.62 along with a bowl and port job(three angle cut)... you will have a good set of heads to throw on a 350 with the performance of a set of $500-600 heads for about $200 dollars of machine work. Sry that I don't have numbers to post. Hope this helps. Kinda remmber those 305 heads having around 64cfm-174ccm stock and around 220-230 with larger valves installed and machine work maybe more. I bought a set of heads for about 500 dollars that came with roller rockers strengthend rods and the larger valve size of 2.02/1.62 that have less flow at around 52cfm but allow plenty of air power and cam I chose with the valve size increase alone. Just the route I took. Could have saved a little money having work done to the 305 heads and had slighty better numbers...but the new heads cam with all the stuff I was going to have to shop for.

 

If you try to go to 2.02" intake valves in most 305 heads, you'll hit water, so stop at 1.94". this is good for about 215 cfm with good porting, and the 2.02s won't give you any more peak flow anyway. If you just run #416 heads, you'll get 180-190 cfm. Even with 1.94" valves and good porting, they're done by 5500 rpm, and they're behind Vortecs as low as 3000 rpm. Don't go any bigger than the GMPP "HOT LT4" cam. Otherwise you're giving up low end and midrange torque without getting anything useful back in exchange.

 

first off, thank you for the information. i have a set of 416's on my 305 at the moment, so i was going to use those for the build. would Comp cams Xtreme Energy XR276 Hydraulic Roller Camshaft be a good choice with the ported/polished 416's with 1.94'' 1.5'' valves? I've heard that the gain from going up to 1.6'' on the eghaust is very minimal. This would be going on a stock 350 shortblock until i can build a a stonger bottom end.

 

Dont bother. You'd have a better starting point if you use someone's cast-off 350 L98 iron heads and spending the money on those. Some better 1.94/1.50" valves will drop right in (such as Manley part numbers 10721-8 and 10722-8) with no extra work to cut up the valve pockets. They also have larger intake runners and larger combustion chambers so you will flow more air and not have too high of compression that leads to knocking and pinging.

 

What kind of hp/tq difference would there be from the 416's to the l98 heads? I'm hoping for 350 flywheel hp/tq for this engine, would this be attainable with the 416's or l98's? I'm planning on porting/polishing either set too.