jamon8

iTrader: (3)

I am putting flattops on a balanced assembly. my heads are mildly ported 081 305 heads with upgraded springs to handle comp cams 08-302-8

gross lift 480 in/ex
264/274 duration
210/220 .05
112 lobe sep

I have headers and 3in, ported manifold and plenum, 21 lbs inj and afpr.

do you guys think it will make a big difference if I went to a 194 valve vs a 184(stock)

thank you

michal_larson

with that camshaft the 1.94's will help
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i also have a set of 081's im going to put on my car, but the 1.84" swirl heads mine came with are suprising me with how the engine runs , but im using a HUGE camshaft though

Sonix

iTrader: (1)

I think it'll help.
I think f-bird could give you a #, cfm, if you were looking for that.

I went with 1.94 in my 416 heads, FWIW.

Fast355

iTrader: (2)

I had the 1.94s cut down to 1.90" and used 1.55" exhaust valves in my 081 buildup.

jamon8

iTrader: (3)

fast 355 I do not understand! you had 194's in your 081's that did not come stock and had them reduced to 190's to put bigger exaust valves in.

let me know the logic behind that move. I am not trying to be a smart @%^ but I am curious

F-BIRD'88

do you guys think it will make a big difference if I went to a 194 valve vs a 184(stock)

Yes you'll gain about 7-10 cfm on a stock port, or one with light porting and as much as 20cfm on a full port job. For a 305 motor I wuld stay with the 1.50" exhaust or do like 355 did and get 1.55" exhaust valves. So a 1.94x 1.55" combo would work well for you. I go with 1.94x 1.60 for 305 heads that will end up on 350's. After deshrouding the chamber around the larger valves and then doing a clean up cut (.005 to .010") on the decks, the last set I did cc'd @ 61cc's (58 stock) So for a 305 to restore the stock chamber size just shave them some more. 2.02's on a 4" bore are possible but hardly needed and I feel they weaken the casting because of the excessive deshrouding nessessary to so a flow gain over 1.94" valves.

I get high 230 to low 240cfm with 1.94" valves with good low/mid flow too.
The exhaust really comes up when done right, to around 170 180cfm from 110-130stock depending on the casting.

Usually the stock valves are finished and need replacement so jumping up in valve size is a no net cost gain.

Fast355

iTrader: (2)

No need to apologize, I should have stated what I had done better. I bought a set of 1.94 valves. I then cut them down to 1.90". I then installed them in the heads that had the seats cut to 1.90" as well. This allowed me to fit in a 1.55" GM exhaust valve by cutting that seat to 1.55" as well. Neither valve was shrouded in the stock 305 chamber too much. I did do some unshrouding work on the intake and raised the CC to around 61-63cc. I then angle milled the heads down giving 57-58cc in each chamber (would not recomeend it due to the crazy thin decks of the 081s). Mine were flowing very similarly to F-BIRD'88s.


Stock 187 chamber with 1.84" and 1.5" valves, the 081 is virtually identical. Notice how close the intake valve is to the chamber?


Stock 193 chamber with 1.94" and 1.5" valves, the 083 is virtually identical and the proportions are nearly identical to the 305 heads. The intake valve is pretty shrouded in stock form.
Notice the spacing between the intake valve and the chamber is much bigger now. This shot is during port/chamber work.