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Stock gm/781 heads?

12K views 12 replies 12 participants last post by  OutCast 
#1 ·
I have a 454 with stock heads...b20/75...836781
so they were made in 75? and 781 is the casting number?
From other post these heads sound ok but im getting my engine rebuilt this spring so should i upgrade any parts or get any work done to them?
This will be an 80% streer car....probable around 400hp.
No sure on the cam yet but rpm performer intake, edel 800cfm carb, msd dis.

Thanks Paul:beers:
 
#4 ·
x2
 
#9 ·
Do the 2.19/1.88 valves, but make sure the machine shop is competent. The increased valve size also needs to have the chambers unshrouded a bit. If you put the larger valves and do not do the chamber work, then the heads will not be anywhere near their potential. Then blend the bowls and you will have a great set of heads. In stock form, the bowls are quite good, but the chances of getting a 3 angle valve job (even 4 or 5 angles with larger valves) are slim to none. The way GM cut the bowls from the factory brought the bottom cut right up to the 45* seat......not good for performance.
 
#10 ·
Paul, i ran a similar set-up in my pick-up before i put the stroker kit in. 454,approx 9-1 CR, stock 781 heads, perf intake, comp 294S cam and 750 eddy carb#1411. it ran 13.7 in a 4200# pick-up and was in the 400-425 hp range i'm guessing. i've now got the same heads home ported w/ the valve upgrade on my 496 and it works well. if you've got it apart and you have the $, have somebody competent do a clean-up on the bowls, gasket match the heads and the intake and go with the bigger valves. you won't be disappointed.:thumbsup:
 
#11 ·
Thanks for all the great advice!! I defenetly have a very good idea of where to go with these heads now....2.19/188 valves and a port and polish.
While i'm at it should i look at better springs?, rockers? any thing i havent thought of.
I'm on a budget but this car is a keeper and i want to do it right the first time.:yes:

Thanks for all the help again :thumbsup: Paul:beers:
 
#13 ·
If you are mechanically inclined at all, and competent with a grinder, you might want to save a bunch of money and port and polish them yourself. I just did my 781's at home with a couple carbide bits, sanding rolls, and an air grinder. However, many have used an electric grinder with great success, also.

For my first attempt at porting, I've received good feedback on the results. It costs big $$$$ to have a shop do it, and rightly so. I spent over 15 hours on mine. I got a smokin' deal on 2.19/1.88 valves installed and unshrouding. If you are going to go with dual valve springs, be aware that you need to get the guide bosses cut down to fit the inner spring. This was only $5 a guide, so not a big deal. I also went to the teflon valve seals at the same time.

My only advice to you is this : Get all the labor and material prices up front. You can get buried cost-wise in head work really fast. Before long, you'll be right up there with the price of a set of aluminum heads. Even without changing valve sizes, I was told you could gain anywhere from 30-45hp on just a good port and polish job. The only reason I changed valves was because I was offered a deal I couldn't refuse.

Good luck. If you want any pics, just ask.
 
#12 ·
use the springs that go with the cam you're going to use. Have them in hand when the heads go to the shop.

Those are good heads, you can get 500HP out of them easy.
 
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