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  #1  
Old Jan 31st, 09, 6:42 AM
Paul-ish Paul-ish is offline
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Smile Stock gm/781 heads?

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
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  #2  
Old Jan 31st, 09, 7:33 AM
65lkey 65lkey is offline
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Default Re: Stock gm/781 heads?

maybe if anything just pull them apart and do a little bowl work
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  #3  
Old Jan 31st, 09, 7:59 AM
cwilks cwilks is offline
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Default Re: Stock gm/781 heads?

I've got those same heads and have been told they respond VERY well to an upgrade in valve sizes......go to 2.19/1.88 valves to really wake em up...one of the best street heads out there
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Old Jan 31st, 09, 8:17 AM
Texas70 Texas70 is offline
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Default Re: Stock gm/781 heads?

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Originally Posted by cwilks View Post
I've got those same heads and have been told they respond VERY well to an upgrade in valve sizes......go to 2.19/1.88 valves to really wake em up...one of the best street heads out there
x2
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My combo:496 BBC (454 +.060), Muncie 4 spd, Centerforce dual fric clutch, "781" heads 2.19/1.88, 12-bolt 3.73 Eaton posi, Scat forged rot assm (21cc Wiseco slugs for 10.4:1 CR), Lunati Voodoo billet 60213 hyd roller, Lunati hyd roller lifters, Scorpion 1.7 #SCP1014 roller rockers, Edelbrock Performer RPM, Holly 850 Dbl Pmpr (1" spa), Carter 172 GPH mech fuel pump, MSD R2R dist. #8360, O'reilly Master Pro coil, Weiand high volume mech water pump, 772 stock 7 blade fan, Hayden clutch, fan shroud & Hi-flow 160 deg T-stat, Doug's 2" x 3 1/2" headers
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  #5  
Old Jan 31st, 09, 8:42 AM
bracketchev1221 bracketchev1221 is offline
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Default Re: Stock gm/781 heads?

I have them on a 396 with 2.19/1.88 valves. Without any real porting work on them, they made 500 hp on the 396.
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  #6  
Old Jan 31st, 09, 8:56 AM
tyster tyster is offline
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Default Re: Stock gm/781 heads?

Do the clean-up work and larger valves and you'll be happy. Good torque #'s with theses heads.
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  #7  
Old Jan 31st, 09, 9:23 AM
Rmchevelle Rmchevelle is online now
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Default Re: Stock gm/781 heads?

They are capable of the 400 hp you want with just a stock rebuild.
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Old Jan 31st, 09, 9:25 AM
blasttime blasttime is offline
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Default Re: Stock gm/781 heads?

Spend the cash have them ported best investment for yourself and the econemy.
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  #9  
Old Jan 31st, 09, 12:02 PM
Bryan Maloof Bryan Maloof is offline
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Default Re: Stock gm/781 heads?

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.
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Old Jan 31st, 09, 2:14 PM
85shorty496 85shorty496 is offline
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Default Re: Stock gm/781 heads?

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.
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  #11  
Old Jan 31st, 09, 3:36 PM
Paul-ish Paul-ish is offline
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Thumbs up Re: Stock gm/781 heads?

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.

Thanks for all the help again Paul
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  #12  
Old Jan 31st, 09, 4:20 PM
Tom Mobley Tom Mobley is online now
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Default Re: Stock gm/781 heads?

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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  #13  
Old Jan 31st, 09, 9:21 PM
OutCast OutCast is offline
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Default Re: Stock gm/781 heads?

Quote:
Originally Posted by Paul-ish View Post
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.

Thanks for all the help again Paul
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.
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