781 heads

[454 blazer]

HI guys , im running a bb and i have a set of 781 large oval heads, i am at present running the small ovals with a large oval rpm intake, do you think that i will get a substantual power gain if i put on the 781s . And is it something that i can do myself ?

 

[k20]

Yeh those stock peanut port heads are tiny. I have the 049 (basically same as 781's) with 2.19/1.88 valves. I dont recall what size valves come in the 781's stock, but if you wanna bump up to the 2.19/1.88's or even 2.25/1.88s and do a gasket match on the intake & heads you will see a fair power increase over the stock heads. Easy to do yourself, well, except for hefting that heavy mofo in and out of the engine bay.

 

[4X4HIGH]

If you're running peanut port heads with a large oval port intake you will notice a huge difference by swapping any large oval head on since right now you basically have half a wall blocking your air/fuel charge once it hits the obstruction of that small peanut port.

The 781 heads come stock with 2.08"/1.72" valves and those heads flow exceptionally well when they are fitted with 2.19"/1.88" valves and the valve pockets are blended properly.

 

[454 blazer]

Thanks for the info K20, what do mean do a gasket match ? And the valves i assume i can order and just bed them in a usual ? Thanks again.

 

[454 blazer]

Thanks 4x4 high , im looking forward to fitting these heads now!!

 

[dremu]

Bunch of good info from 4x4High, especially about the valves, plus some various grunting noises, in these threads:

http://coloradok5.com/forums/showthread.php?t=202575

http://coloradok5.com/forums/showthread.php?t=213735

-- A

 

[4X4HIGH]

Thanks for the info K20, what do mean do a gasket match ? And the valves i assume i can order and just bed them in a usual ? Thanks again.

You cannot just install the large valves without doing a valve job and then alot of grinding to blend the bowls.

 

[454 blazer]

Oh ok, sorry for being a nooob, unfortunately there are no good work shops were i live at the momment, but from what i hear they are pretty good heads in stock form . So i think ile just put them on as they are .

 

[GMC500]

Oh ok, sorry for being a nooob, unfortunately there are no good work shops were i live at the momment, but from what i hear they are pretty good heads in stock form . So i think ile just put them on as they are .

hello,

where do you find these heads in Bahrain ?
I am from Saudi Arabia and it is very hard to find large oval heads here since almost all old junkyards were bought by local steel factories

and if you want to install bigger valves I can guide you to some good machine shops here

 

[454 blazer]

Hi gmc 500 , i found a set in the garage that built my engine , its in hamad town , from memory i think they had another set ? Are you looking for some ? Im not sure what bowl blending is so its difficult for me to ask a machine shop.

 

[GMC500]

Hi gmc 500 , i found a set in the garage that built my engine , its in hamad town , from memory i think they had another set ? Are you looking for some ? Im not sure what bowl blending is so its difficult for me to ask a machine shop.

how much did they cost you ?
the machine shop will grind/cut bigger valve seats for the bigger valves 2.19/1.88

you need to do the porting/bowl blending your self
or find someone who can do it for you

 

[k20]

gasket/port match would be take the intake gasket, put it against the head and scribe a line around, then use a dremel, or an angle grinder and grind them out to the marks you made. Once you do that, do the same to the heads. You can go back in a little further and smooth out the bumps & ridges left over in the casting. Dont get too carried away though and grind into a coolant passage or something.