I've got need of some tech help, I dropped a set of 915 big block heads off at my buddies machine shop, having bigger valves, hardened seats guides & cut them .030 off the deck & .037 off the intake.. Anyway I got a call today & he's concerned about opening the exhaust up enough to put a seat in... Currently the exhaust valve is 1.60 & I bought 1.81 valves, he said he's comfortable with opening enough to run that size valve with out the seat but to put in a seat he's concerned about hitting water.... I thought this was a common upgrade? Thoughts? Thank you for your time & expertise...

Had the same sizes in the same heads without install of the seats, as I had not planned alot of driving-racing. They were still fine after 5000 miles and 75 or so dragstrip passes.

The head should have the same amount of material in that area as a head with a 1.74 valve and other than the open chamber it's the same as a 906 . I have a set of 906's with 1.81's , but I don't remember if I put seats in or not ? Call Dwayne Porter , he can tell you definitively , but the wild card is CORE SHIFT.

Does the shop have a sonic tester they could check the area ?

I've put hardened seats for the 1.81 in both the 906 and 915.

Not really the same but throwing my 2 cents in.
I have 516 closed chambers with hardened seats but only have the 1.74 ex valves. Been on the engine for over 20 years, no problems.

You might see if you can locate Dulcichs' BB porting articles in Mopar Muscle archives. alot of pertinent info that you need to check out regarding port shape/valve sizes/porting benefit differences between early/late heads

All,
R & J performance "Radar" (Hudson, IA) did my BB "915" heads with 2.14 intakes, 1.81 valves & hardened seats on the exhaust valves back in 2004. They have worked great for 8K+ miles 9 years on my 67 440 HP motor.

First off, I seriuosly doubt the seats are any different OD wise for any of the minor differnces in valve diameter being discussed. And, B, odds are you don't even need or want said seats. Why would you think it wise to hog big a$$ holes in your vintage heads and pound in steel rings? Classic case of the cure being worse than the disease. For what it's worth, I'm currently running 2.14/1.88,s in a well hogged out set of 915,s and short of having to do minor bore notching for the stupid big exhausts that some prior owner installed, everything is just fine. Of course this won't work for every set of 40+ year old set of heads but why worry? If it becomes that troublesome, sell 'em and buy new....Just my opinion

Here is a set of my 906 heads with 2.19 stainless valves and 1.88 max wedge exhaust valves. Tell your shop to machine the seats and forget about adding the hardened seats. Just run your carb a little rich and they will last for many, many years.