I am currently running a 305 with the TBI heads and cam. The valve seals are starting to fail and I occasionally get a puff of smoke on start up. I have read mixed opinions on running the larger valves on the 305. Anyone know if it will be an issue if I swap these. I am also considering tossing a cam in while I have it apart.

 

Valves that large might not fit in the 305 bore. Might crash into the block deck. Even if they DO fit, which is far from certain, they will be shrouded by the bore.

Just change the 305 valve guide seals and save the 113s for a real motor someday.

 

 

Thanks for the response. I am assuming you can't revert the valves once they are increased to 2.02/1.60.

 

Not usually. Kinda depends on how thoroughly they were installed though, and if the seat & throat were cut back (such as with a Serdi) or ported. Which if they weren't, they're just eye candy anyway, and not doing a damn thing besides diverting people off the path who are easily distracted by shiny things strewn along the way.

 

There are a few hotrod articles floating around out there with dyno measurements. hopefully they are reporting real results, not just made up ones. but there is hope for your 305 should you are looking to gain some performance. A real motor would be an LT8, but then, you have lost the soul of what it means to be 3rd Gen. Here is one for example: http://www.superchevy.com/how-to/pro...-engine-build/
https://www.hotrod.com/articles/ccrp...-engine-build/

 

I have 2.02/1.6 valves on a 305 (.030" over) bore. BUT, the heads they are in are the World Products Dart S/R Torquer 305 heads.
Those heads use relocated valve spacing in order to do that. Heads with stock valve spacing will not allow valves that large.
And like Sofa and Orr89RocZ said, they will hit the bore and be severely shrouded. I notched my bores to help with that.
Here is a couple pics of mine: (Sorry, crappy old digital camera)

 

Pontiac did that notching to a few block and head combos.

 

 

 

In my case, it is the proper head. I did not receive what I ordered from RHS 25 years ago. I received 305 class racers heads by mistake. I discovered the 2.02/1/6 valves maybe 5 years ago when I finally took the engine apart to see why it failed. Incorrect, oversized valve seals plus 464 lb/in springs for my hydraulic flat tappet camshaft caused engine death after only 19,000 miles. There was no retainer-to-seal clearance, so while the seals were still soft, they worked. After a while when they became harder, the cam lobes became circles. That shrapnel went through the engine, destroying nearly everything. But, I was able to resurrect it and correct all of the other problems with the good advice I have found here on thirdgen.org.

 

 

 

Yep, correct head casting, but modified by RHS for someone else. I received someone else's heads.
I ordered new 1.94/1.5 valves for them and knew something wasn't right when they fell too deep in the seats.

 

https://www.castheads.com/info/gathe...e-performance/

 

 

wealth of info over here btw on 305/350 heads https://www.thirdgen.org/forums/tbi/...-headflow.html

 

I didn't know you could go that big on 113 heads?

Hows that setup run?

 

 

That's more in line with what I was thinking. I remember years ago in GM High Tech Performance (RIP) reading about a guy with an IROC that had a N/A 355 with 113s running mid 10s. And it seemed like he had 2.00" valves. Heads were done by Lingenfelter.