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I dropped some ported c heads off at a shop to get cut and a fresh valve job. He said the seats are to far gone but he thinks he can save them going with a slightly larger valve. Wondering what my options are for valves larger than factory large valve. I’m sure the typical 1.7 exhaust will work but what are my options for intake valves, hoping to find stock diameter/length stem with larger head.
Keep in mind that a 2.125" intake can only be used with a stock size exhaust valve in iron heads and even then it would be marginal due to the loss of material between the valves. You could cut those 2.125" intakes down to 2.110" which would be safer next to the stock exhaust. Also, most of those replacement race type valves have 0.3415" stem diameter (Chev. and Ford small block size) so you end up with sloppy valve stem to valve guide clearance which is only corrected by new valve guides! Good luck!
Keep in mind that a 2.125" intake can only be used with a stock size exhaust valve in iron heads and even then it would be marginal due to the loss of material between the valves. You could cut those 2.125" intakes down to 2.110" which would be safer next to the stock exhaust. Also, most of those replacement race type valves have 0.3415" stem diameter (Chev. and Ford small block size) so you end up with sloppy valve stem to valve guide clearance which is only corrected by new valve guides! Good luck!
Hmm not entirely true.
The new Edelbrocks have 2.150/1.68’s with room to spare. If you do the math it’s the same. Knowlton does all their heads with 2.170 intakes.
2.125’s will fit with either 1.68’s or 1.71’s, although there’s no real performance reason to go to the 1.71’s.
And 11/32 is 11/32, it really depends on the manufacturer as to how they decide to machine the stems. Some build in extra clearance, some don’t.
Last edited by cutlassefi; Nov 6, 2024 at 02:38 PM.
Hmm not entirely true.
The new Edelbrocks have 2.150/1.68’s with room to spare. If you do the math it’s the same. Knowlton does all their heads with 2.170 intakes.
2.125’s will fit with either 1.68’s or 1.71’s, although there’s no real performance reason to go to the 1.71’s.
And 11/32 is 11/32, it really depends on the manufacturer as to how they decide to machine the stems. Some build in extra clearance, some don’t.
If the valve seats are gone why not just buy a different set of C heads. (They are plentiful and cheap) If not going for matching engine there are other good Oldsmobile heads you could use to.
I don’t have any money in them currently and they are already ported and filled, I’m willing to spend some money on them if it doesn’t get out of hand.
I picked up my heads the other day. With the valves out it looks like the seats overlap but the shop owner said he got them all to seal. With both valves installed they appear to have plenty of clearance from each other.
these are 2.125 intake 1.68 exhaust
