Casey Butt

For reference I put 1.94", 2.02" and 1.60" and 1.50" valves in a pair of rusty 601 heads I had lying around, checked clearances on a 305 block bored 0.030" over (3.766" bore) and took some photos.

Here's the 601 head with 1.94" intake valve, which obviously fit in the chamber. Ignore the chamber on the left for now (it has 2.02" and 1.6" valves)...




Here's the 1.94" valve lifted (roughly about 0.450" to 0.500") to show the shrouding by the chamber wall...




The head installed on a 0.030" overbored 305 block (3.766" bore) - the 601 chambers match the bore pretty well...




601 heads on 3.766" bore - 1.94", 1.50" valves opened. The 1.94" intake valve opened to 0.689" lift before contacting the chamber wall; the 1.50" exhaust valve opened to 1.173" lift (which is way past the point of retainer/seal contact with stock length valves).




601 heads on 3.766" bore - 1.60" exhaust valve seated...

Casey Butt

601 heads on 3.766" bore with 1.60" exhaust valve opened. The 1.60" valve opened to 0.881" lift before contacting the cylinder wall...




601 heads with 2.02" intake and 1.60" exhaust valves. The 2.02" valve won't clear the chamber...






However, I did manage to install the head and check for lift before the 2.02" valve hit the cylinder wall. It lifted a very little amount, but had the big valve been able to seat in the 601 chamber the lift would have been about ~0.505" before contacting the cylinder wall.

As a point of interest, the stock 1.84" 305 valves lifted to 1.043" before hitting the cylinder wall (which would be beyond the point of retainer/seal contact).

Take home:

1.94" and 1.60" valves in 305 '601 heads won't contact a 3.766" bore (305 bored 0.030" over) at lifts which can be safely used on these heads anyway - and lifts that would contact the bore with these valves are beyond sane "streetable" setups.

2.02" valves in 305 '601 heads on a 3.766" bore (305 bored 0.030" over) will contact the cylinder wall at about 0.505" lift - if your camshaft/rockers produce less lift than that (plus clearance) then you can run 2.02" valves ...but decisions about shrouding will be your call.

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Atilla the Fun

You didn't specify what thickness of head gasket you used, did you use none at all? Next, on every set of 305 heads I've cut for 2.02" intake valves, (and I've tried it at least a dozen times) I've hit water. But a few times I went ahead, so I could go ahead with porting and flow-bench testing. Even if you don't hit water when cutting the heads for seats to accept the 2.02s, it's not worth it.

Casey Butt

I didn't use any gasket - but it doesn't really matter. The thickness of the gasket will move the contact point up higher on the cylinder, but the geometry is unchanged so the valve lift itself will remain the same. For instance, a zero-decked block with a thick gasket will allow no more valve lift than an undecked block with a steel shim. I should have mentioned that the exact valve lift when contact occurs will vary depending on the valve seats depth in each individual chamber, however.

I personally have never tried to run 2.02" valves on 305 heads, but it is good to know about hitting water. I posted the thread because I'm sure there are people dropping in on the boards wondering about big valves on a 305 bore, and even in 305 heads. I searched and turned up a lot of differing opinions, some based on hearsay, some on experience, so I put this up here to add to the knowledge base.

I did the same fit with Trick Flow 175cc heads as well. The thread is here: https://www.thirdgen.org/forums/tech...5cc-heads.html

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DartByU

Thanks for the info. And due to production tolerances some cylinders of an engine will have valve contact sooner or later, so just because 1 valve makes it to .600 lift before contact the next cylinder may contact at .52 lift, so anyone doing the big valves in a 305 needs to check ALL cylinders before firing it up.

Fast355

iTrader: (2)

EVERY 305 head that I have ended up working, I have installed 1.94/1.60 valves in.

Casey Butt

Did you ever flow bench any of those heads on a 305-ish bore before and after the 1.60" valves were installed. It'd be interesting to see the effect of shrouding with the bigger valves on the small bore.

Atilla the Fun

Shrouding the exhaust valves is something of a non-issue here, but shrouding of the intakes is measurable, but the end result is a net gain, so go ahead and go to 1.94/1.60s if you want to.

Fast355

iTrader: (2)

It is NOT noticeable and the flow actually increases. The highest flow area of the valve is into the open part of the chamber anyway.