427Hotrod

This pic was posted recently by Mark Jones (VortecPro). As I've mentioned before, I've been to his shop and seen his work. Very meticulous and really cares. He makes big power without spending stupid money because he pays attention to details.

I think a lot of people just looked at the shiny valves but failed to look closely at the imprints of the actual seating surface on the valve.

If you look at the intake valve on the right...see how narrow the seat is vs the exhaust valve on the left. Look at the placement of the seat out near the edge. This is a way to "maximize" the size of the valve seat and get as much area as possible with a given valve. If it was lower on the valve...the "hole" for air to flow through would be just that much smaller even though it had the same size valve as a head with a poor valvejob.

Notice the wider seat on the exhaust valve to help dissipate heat which requires it to be more centered.

Some guy hacking with a valve grinder or even an automated machine doesn't guarantee true craftsmanship.

And we aren't even talking about the work in getting the seats/flow correct on the head itself!

Attention to detail makes the difference in an average one and a "Gee Wow" motor when you stuff your foot in it.

Thanks for posting Mark!

JIM

SWCDuke

Those seats look very narrow... may be okay for a race engine that is frequently torn down for inspection and rebuild, but for a long lasting road engine inlet/exhaust seat widths should be no less than .040/.060".

Duke

65tripleblack

Thanks for that Jim!

I see that Mark doesn't back cut all of them inward from the seats. Also doesn't top cut the exhausts. Photo shows top cut on exhaust. Back cut on all 16 similar and on the underside blend back from seat. .040/.060.

MOXIE62

Give me a one piece SS valve and a 3 angle grind and that's all the power I need.

Robert61

And just killed the margins on the exhausts!

63 340HP

Has he tried 29/30 degree seats like the Pontiac intakes to improve open curtain area flow and turbulence close to the head & plug ignition at lower lift?

When I was assisting a Top Gas West car in the early 80's we gained flow playing around with the BBC intake valve seat angles. The car ETs did not change enough to notice, but NA on gasoline we tried everything (to keep the record). Head and chamber design have improved considerably since then so the results are probably untested.

65tripleblack

The seat width is more important, since width is what pulls heat out of the hot valve and transfers it to the head. If you don't have David Vizard's book: How To build And Modify Chevy Small Block Heads then you ought to pick one up and pay special attention to what's on pp 18-20.

68hemi

Yeah, I would think those valves would burn pretty quickly for a street driven car.

Pop Chevy

No, not really. As the seat and valve wear, the contact area gets wider.

Robert61

I haven't read it and don't really care to. I spent 21 years modifying SBCs. No one really cares about my bio including me but in the 70s I spent 10 hours a day grinding race valve jobs. In 76 I did the valve work for a guy with a green Corvette, SS/LA. Dub is rebuilding the car right now, the guy was pretty well known in the Corvette world. After doing several thousand valve seats you kinda get the hang of it.

427Hotrod

If this was a race engine...they'd be a LOT thinner.

This is a 2 bolt main 468" street engine, 10.3 compression, iron oval port GM heads, dual plane intake, streetable solid flat tappet cam with only .560" net lift.

On 91 octane it made 670 HP@6500 RPM

Mark specializes in streetable packages that maximize milder components. AJROTHM here on the board has been running one of his 496's for years in his C3. Cross country driving, 10 sec drag racing all with A/C, PS, PB. There's quite a few others.

Mark has spent years developing ports and valvejobs on those heads. Automatically adding backcuts isn't always a good idea. Depends on if you need an increase in low lift or higher lift flow to achieve the goals, because usually the mod doesn't pickup on both ends. You only know if you test. Same with top cuts....there are folks that play with them considering the overlap of the cam.

As mentioned, interference angle valve jobs are common on some older builds to ensure they seat when they wear in. Same with many race heads use 50* seats....not known to last as long....but they help flow on some ports. I'll say my current heads have them and I haven't had any issues so far.

JIM

427Hotrod

A 3 angle valve job is required to get any sort of decent seat positioning on any valvejob. A single could be done, but the odds of getting it close to correct in positioning and width is minimal...much less the flow benefits of doing it right.

Those heads will certainly run a long time just fine...but there is definitely HP to be gained with attention to the valvejob and valve depths in the head.

JIM