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454 781 heads.........help please.

4

454 blazer

1/2 ton status
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Feb 27, 2008
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bahrain
Hi guys,need help with B block heads the 781s to be exact...i did post here about 5 years ago about what heads to run..and was told wide oval are the way to go so me being a noob was offered some near new rectangle port 088 heads...so ive been running these for years and im happy at around 2.500rpm to 5.500rpm but week at low revs.question is i still have these 781s and im kinda looking for a change so should i put them on and give them a go ? Also exhaust valve rotators ? Do i need these and do i have to make all the valve springs the same hieght i remember this putting me of last time around...is there maybe a kit you can buy like rotators and spring kit ?? Would realy appreciete your help on this one guys:bow:
Cheers Simon.
 
The 781 heads are a much better head for a truck application. The rectangal port 088 and 990 heads are for nothing but top end HP for race cars and i'm surprised you were even happy as low as 2500rpm. As far as rotators on the exhaust are concerned unless you have a very large roller cam with lots of spring pressure I would advise you keep them on the heads. The spring pocket is cut deeper for the rotators so all the springs will be the same height. There should be nothing but a thin (.015" or so thick) metal shim under the intake springs.
 
4X4HIGH said:
The 781 heads are a much better head for a truck application. The rectangal port 088 and 990 heads are for nothing but top end HP for race cars and i'm surprised you were even happy as low as 2500rpm. As far as rotators on the exhaust are concerned unless you have a very large roller cam with lots of spring pressure I would advise you keep them on the heads. The spring pocket is cut deeper for the rotators so all the springs will be the same height. There should be nothing but a thin (.015" or so thick) metal shim under the intake springs.
Click to expand...

Thank you very much for answering sir , i have couple more questions now:
So if i was to buy new push rods , springs , rockers and exhaust rotators which ones would you recomend as i have a 282 comp cam (flat tappet) in there.I would be putting on an edelbrock rpm intake which is wide ovallike the 781s and put my 750 holley dp on there which im running at present.I have long headers also.
Again thanks for your valuble info.:bow:
Simon
 
I would suggest probably the Comp Magnum pushrods and whatever spring Comp recommends for that cam. Remember that too little spring pressure and you'll float the valves early and too much spring pressure and you'll wipe out cam lobes.
 
Thanks 4x4 high.So in your opinion it will be more torquey or maybe a better power curve with the 781s ? I just got a Visa that enables me to enter Saudi Arabia so i am really looking forward to hitting the huge sand dunes they have there 8)
Cheers Simon.
 
from what I've seen of those dunes, mid to high range rpm is common....those 781 ovals should provide plenty for that range. I run the same heads with a comp .570/.550 flat tappet and it moves my heavy K5 pretty good I think.
 
76zimmer said:
from what I've seen of those dunes, mid to high range rpm is common....those 781 ovals should provide plenty for that range. I run the same heads with a comp .570/.550 flat tappet and it moves my heavy K5 pretty good I think.
Click to expand...


Thanks for that 76 Zimmer , did you have any issues with the exhaust rotators i went to look at the heads today they are in great condition but im stumped on were to start with ordering these dam things as there isnt any on them at the mo.
 
454 blazer said:
Thanks for that 76 Zimmer , did you have any issues with the exhaust rotators i went to look at the heads today they are in great condition but im stumped on were to start with ordering these dam things as there isnt any on them at the mo.
Click to expand...

On BBC's the exhaust rotators are UNDER the springs not on top like a SBC and they're about .300" thick but because of the spring pocket being cut deeper you might not think they're there.
 
I bought a set of rotator eliminators for my big block.
They're the same shape as the rotators but solid.
I would recommend them if you have stiff valve springs and an aggressive cam.
There is a small risk that the rotators can break if they see too much abuse,
so I played it safe.

Both intake and exhaust springs should be shimmed to the installed height the manufacturer specifies.
With an old set of heads the installed height of the valves can vary a bit, making that even more important.

And ask comp cams what springs they recommend for your cam.
 
Fred_M1010 said:
I bought a set of rotator eliminators for my big block.
They're the same shape as the rotators but solid.
I would recommend them if you have stiff valve springs and an aggressive cam.
There is a small risk that the rotators can break if they see too much abuse,
so I played it safe.

Both intake and exhaust springs should be shimmed to the installed height the manufacturer specifies.
With an old set of heads the installed height of the valves can vary a bit, making that even more important.

And ask comp cams what springs they recommend for your cam.
Click to expand...

Can you remember what the part number was for the rotators ? The heads are not that old i would say late eighties or so , i really dont have a good garage here to explain all this stuff to so im really after being spoon fed this stuff.On close inspection of my plugs it smoking like a james bond car and the fact that it runs ruff as f$#k it seems i need new piston rings so i want to change the pistons too,this time i really want to get it built right.I want it to be a real torque monster not wanting it to run pass 5000rpm just want to pull hard to that. What would you guys recomend ?
 
I think it was these:
http://www.compperformancegroupstor...re_Code=CC&Product_Code=4779-8&Category_Code=

I can't find your cam shaft at comp cams web site, are you sure it's called 282?
(the one I found was for a small block)
But I would guess from the name and the lift numbers that it's a pretty hot cam.
You would probably be better of with a milder cam.

Comp cams can give you good advice on what cam to use for a specific vehicle, just check out this link:
http://www.compcams.com/Company/CC/CamRecommendation/CamHelpNew.aspx
 
454 blazer said:
Thanks for that 76 Zimmer , did you have any issues with the exhaust rotators i went to look at the heads today they are in great condition but im stumped on were to start with ordering these dam things as there isnt any on them at the mo.
Click to expand...

here's a pic of the CC eliminators on my heads....springs are from K-Motion.

HPIM2453.jpg


I support CC stuff as well, good folks to work with.
 
sweetk30 said:
not saying your wrong but what is that undwer the ex side springs ? and not under the in springs ?
Click to expand...

BBC's use exhaust rotators like the SBC does but instead of being a rotator retainer like the SBC they are just rotators that go under the spring and all of the retainers are the same on a BBC. The intake springs on a BBC use a shim that is about .015" thick under each spring.
 
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