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049/781 heads

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049/781 heads

Postby Ron Gusack » Tue Jan 15, 2008 10:05 am

What are the differences in the 049 and 781 heads? Is one better than the other for a pump gas 502 in a 2800 lb drag only Nova?
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Postby DOTracer » Tue Jan 15, 2008 11:06 am

The differences are very slight. I doubt you could really see any performance difference from either.

Keep in mind the factory rated chamber sizes are way off and they measure all over the map. My old 781's wound up measuring 122 to 124cc.
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Postby Alan Roehrich » Tue Jan 15, 2008 10:23 pm

Either will be fine, with the proper professional work. There's no real difference between them.
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Postby maxracesoftware » Tue Jan 15, 2008 11:04 pm

the #049 was replaced by the #781
supposedly the #781's cured or fixed exhaust seat cracking
problems across the valve seat and short turn curve on the #049's

what i heard seems to bear out because i've see a bunch more
#049's cracked in that area -than- the #781's.

in fact, i think i've only seen 1 pair of #781's crack there

likewise...its the same reasons for the
#026 -vs- the #990's

Also like DOTracer posted....all the #781's i've ever CC'd
Chambers on were 122 to 124+ CC's
i've never seen #781's less than 122CC's on a Class A Burette
that were in OEM shape with no previous milling or work.

i install 2.250+.100 long or 2.300 +.100 long and 1.880"+.100 long
even +.200" long on intakes most times.
at the same time i convert 3/8 guides to 11/32 for lighter valves
+ much more valve choices

always use at least +.100" longer exhaust valves on #781's
to get enough installed heights..likewise intake valves +.100

the #781's have the most unshrouded chambers of all the OEM BBC
heads ever offered...this makes installing 2.250 or 2.300
very HP + TQ beneficial.

You use the 2.250 or 2.300 to get more material to shape in the
bowl area and valve job area...not necessarily to hog out the Port,
but instead to shape the Bowls and short turn curve better.

the Short Turn areas are critical to making the 2.250 or 2.300
really work great

for maxed out #781's with either 2.250 or 2.300
the short turn curve has to be ported correctly because
there's water jacket waiting for you.
i've made a tool that measures that thickness as i Port the Curve.

if its for general DragStrip use..and not a maxed out application,
just nice gentle short turn curve blending in for the 2.250/2.300
valves will be OK for Cams under .600 or so Lift

for .700 - .820 or so Lift the Short Turn Curve must be
ground more and careful with measuring Tool.
You can achieve 320-340 CFM on Good Direction Ports
and 315-320 CFM on Bad Direction Ports

honest 720 to 740 HP on 468cid to as much as 820 HP on 540cid

don't open up the exhaust port exit..just leave exit mostly stock size,
just internal port mods and bowl porting
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Postby airflowdevelop » Tue Jan 15, 2008 11:20 pm

Ron,
I don't think Larry could have done any better unless he ported the heads for FREE!

I have seen the 781's crack, but only in "severe" applications. IMO, The 781 and 990 head are my favorite vintage castings.

Don't forget Larry the early 26's and fantoms had the eluding broken rocker boss problem also! What a fix that is!!


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Postby Ed-vancedEngines » Tue Jan 15, 2008 11:51 pm

In my opinion after minor mods with valve changes, bowl and throat work the 781 is maybe the best all around cast iron cylinder head that GM ever made for the BB Chevy. I luve them.

Even as stock they aren't half bad but let them breathe with bigger valves and minor bowl/pocket work and they come alive. Also let them run. I have never ever seen any BB Chevy that was happy below 7,000 rpm but I see many trying to keep them down.

GM messed up when they did the Peanut head. They should have just kept what was good. It worked great for economy and for power.

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Postby Ron Gusack » Wed Jan 16, 2008 8:56 am

Great information and very very helpful to me.

always use at least +.100" longer exhaust valves on #781's
to get enough installed heights..likewise intake valves +.100


Larry, my installed height has been 1.900 with my current springs. I also run a rev kit. Would I need the +.100's for an installed height in that range?

Isn't it roughly $2,000 for part's and labor to rework 781's? Could I achieve the same, or better, performance with some out of the box Brodix Racerites for just a little more money.....and save some weight?
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Postby Speedbump » Wed Jan 16, 2008 9:39 am

I'm getting ready to do a set of the 781's for my 55 Chevy PU project so this info is very interesting to me and I'll be asking for lots more info/opinion as I progress.
For now, the engine is a tall deck 505 inch with a CC roller that's good for 6.5K. I'm using an old school 2x4 weiand tunnel ram and have hooker 2"x34" into 3.5 collectors. It may not all match exactly but I want a look and a sound as well as performance.
The question: I have 2.190 and 1.88 3/8 stem stock length valves for this project. After reading the above, would it be worth my money to get 2.250's and change the stem to 11/32? I'll be using 75* bowl hogs for size and hand blend the bowls, topped by 60, 45, 30 seats. I have an old winnona guide and seat machine and Serdi style cutters as well as a complete set of Sioux stones so the machinework will cost me nothing but time. Should I get new valves and save these for another project and what suggestions, if any for my plan so far? Thanks :D
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Postby maxracesoftware » Thu Jan 17, 2008 3:34 am

Ron Gusack wrote:Great information and very very helpful to me.

always use at least +.100" longer exhaust valves on #781's
to get enough installed heights..likewise intake valves +.100


Larry, my installed height has been 1.900 with my current springs. I also run a rev kit. Would I need the +.100's for an installed height in that range?

Isn't it roughly $2,000 for part's and labor to rework 781's? Could I achieve the same, or better, performance with some out of the box Brodix Racerites for just a little more money.....and save some weight?


the alum Brodix RaceRites would be better choice in long term + short :)

1.900" is the very least i use.

normally always running .800" lift cams
to sometimes as much as .900" lift with these #781's on more serious
engines..thats why i like at least the +.100" on exh and sometimes
+.200 on intakes

when you install new larger OD valves,
the valves tend to setup higher in the Chamber now...
another reason for +.100" long valves

also be aware theres a bunch of water around the exhaust valve guide
and its cooled by internal passage across the exh guide boss

also the OEM exh guides fit in only one of 2 directions
those exh guides have slightly different OD's along their length.
there were a few versions that had the OD cuts reversed in direction

for the above reasons don't replace the entire OEM exh guide if at
all possible,...instead install Liners in the orig OEM guide.
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Postby maxracesoftware » Thu Jan 17, 2008 3:39 am

Speedbump wrote:I'm getting ready to do a set of the 781's for my 55 Chevy PU project so this info is very interesting to me and I'll be asking for lots more info/opinion as I progress.
For now, the engine is a tall deck 505 inch with a CC roller that's good for 6.5K. I'm using an old school 2x4 weiand tunnel ram and have hooker 2"x34" into 3.5 collectors. It may not all match exactly but I want a look and a sound as well as performance.
The question: I have 2.190 and 1.88 3/8 stem stock length valves for this project. After reading the above, would it be worth my money to get 2.250's and change the stem to 11/32? I'll be using 75* bowl hogs for size and hand blend the bowls, topped by 60, 45, 30 seats. I have an old winnona guide and seat machine and Serdi style cutters as well as a complete set of Sioux stones so the machinework will cost me nothing but time. Should I get new valves and save these for another project and what suggestions, if any for my plan so far? Thanks :D
Speed


the Bowl Hog @ 75 deg is just OK if you have a 60 deg you are
transitioning it with.

where theres ton of HP waiting is in the Short Turn Curve
on those Heads after you've installed the larger intake valves.
need to at least blend in the 75 cut in gentle curve into short turn.
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Postby WAWA » Thu Jan 17, 2008 12:06 pm

If you do a search, Darin Morgan mentions that he has never seen gains going over 2.19" on those haeds. I don't mean to dispute the other posts, and I would be interested knowing what cam profile guy's are using with these heads and their combo's. Cheer's.
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