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Discussion Starter #1
What exactly is involved with installing larger valves in a SBF head? I'm specifically looking at increasing the valve sizes in in pair of 1968 302 heads from the factory 1.78"/1.45" to ch*vy 1.94"/1.60" (after attempting to port them). It seems the valve seat would have to me modified to accomidate these larger valves but the archives make it sound like it's a quick switch? So is this a project an ambitiious novice should take on at home or would I have to pay a machine shop to redo the valve seats? Also, how much grinding should I expect to do with respect to modifying the shroud in the combustion chambers? Will the loss of compression be significant?. Thanks.




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<font size=-1>[ This Message was edited by: Wildcat on 2/12/02 7:55am ]</font>
 

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I had the 194/160's installed in my 289 heads. I did most of my porting before I took them to the shop. The machine shop cut in the new valves seats and did the deshrouding in the chamber (no quick switch). I don't think you could do it at home unless you had the right tools. They can assure good chamber size consistancy as well, mine actually went from 54.5 cc's to 53.5 cc's because the bigger valves sit higher in the chamber.

The stock length springs wouldn't work anymore with the new valves so I had to get different ones (no big deal).

I did the rest of my bowl blending after I got them back, then installed the valves and polished the chambers a little more.

It was actually kind of fun...
 

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Discussion Starter #3
That sounds about right. Where you happy with the performance difference? If you don't mind me asking, about what should I expect to pay to have the deshrouding and valve seat work done? Did you port out the exhaust side as well and gasket match everything? I think my casting will have a thermactor bump, yours might be too early.
 

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I have not ran the engine yet... might be awhile too


Valve grind (included deshrouding) $100
Install hardened seats $56
Resurface heads $70
Stainless Valves $130
Hardened Seats $40

Hope that helps
 

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Has anybody ported the heads without increasing the valve size to see if it makes a difference ?? I remember somebody on this forum ported theirs and got 0.5 second reduction in quarter mile times. Anyone else?
 

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Discussion Starter #6
It's my understanding that porting the heads will significantly increase the flow on the exhaust side but has minimal change on the intake side. The larger valves seem to be the best way to increase intake flow. Check the archives on the FM site for the exact numbers.

But all the flow numbers are just theory, I'd like to hear some real results. It seems that larger valves would have a similar effect as a longer cam duration. Both allow more gas/air to flow by. Of course doing both should have even more flow -- in theory. Again, I'd love to hear if anyone has just done valves and seen a significant increase in power.
 
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