Stock 781 BBC Heads - Max rpm? - Team Camaro Tech
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post #1 of 5 (permalink) Old Jan 8th, 20, 03:13 PM Thread Starter
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Harris
 
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Location: Hannover, Germany
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Stock 781 BBC Heads - Max rpm?

Hey guys,
do any of you know about the common limit rpm-wise with these heads in stock config?

Im tryring to figure out, till which max rpm i should design my valvetrain to be stable.

No point in an 8500rpm valvetrain, if the stock valves limit to e.g. 7500..

Heads: 336781
454, 73-85, oval-port, open chamber,
113-119cc, 256-258/114-116cc ports, 2.06in 1.72ex

Thanks in advance!

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post #2 of 5 (permalink) Old Jan 9th, 20, 07:11 AM
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Frank
 
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Location: South Bend, Indy
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Re: Stock 781 BBC Heads - Max rpm?

Quote:
Originally Posted by Harris Roc Malouda View Post
Hey guys,
do any of you know about the common limit rpm-wise with these heads in stock config?

Im tryring to figure out, till which max rpm i should design my valvetrain to be stable.

No point in an 8500rpm valvetrain, if the stock valves limit to e.g. 7500..

Heads: 336781
454, 73-85, oval-port, open chamber,
113-119cc, 256-258/114-116cc ports, 2.06in 1.72ex

Thanks in advance!
I would check with Chris Straub @ Straub technologies, he would probably know
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'68 Camaro 454, 4sp
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post #3 of 5 (permalink) Old Jan 9th, 20, 10:26 AM
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Dave
 
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Location: Tampa, Florida
Posts: 4,700
Re: Stock 781 BBC Heads - Max rpm?

If your valve guides can keep the valves centered then it will be the valve spring that limits the RPM of the head. Recommend replacing the rocker studs with ARP studs, using PAC springs and a Rocker Arm Stud Girdle to maintain that high an RPM. A CompCam rev kit wouldn't hurt either, but it limits your choice in lifter bodies. The lighter you get things like valves (Ferrea titanium intake valves), with CompCam titanium valve retainers, and either hollow stem 21-4N steel alloy or sodium filled exhaust valves (depending on a power adder raising exhaust temps or normally aspirated) the more stable your valve train will be and the higher the engine can be spun and still make power. If you are not making power why spin it up?

You will need a solid roller cam to hit that high a goal and I recommend a minimum of a 7/16th inch diameter chromoly push rod with an adjustable guide plate to fit. Also the '781 had an exhaust valve rotator that has a deeper seat machined into the head; so you will need a spacer to fill the hole before you set the correct spring height.

Big Dave
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post #4 of 5 (permalink) Old Jan 10th, 20, 02:11 PM Thread Starter
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Harris
 
Join Date: Aug 2019
Location: Hannover, Germany
Posts: 36
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Re: Stock 781 BBC Heads - Max rpm?

NEWS!

I talked to Chris Straub, he recommends with fully stock 781s, if:

1.) valvetrain is high-rpm-stable and all those parts are capable of these rpms --> lifters, 7/16s Pushrods, roller rockers, dual springs, light as possible remaining parts

2.) Bottom-End is up to that task:

7000 rpm bullet proof,

7400 absolute limit

so now we know!
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post #5 of 5 (permalink) Old Jan 10th, 20, 06:23 PM
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Dave
 
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Location: Tampa, Florida
Posts: 4,700
Re: Stock 781 BBC Heads - Max rpm?

With what I recommended above I used to twist my tunnel ram two fours with vertex mag to 7,800 RPM all the time. never lost a bottom end. Ate a lot of valves figuring how to make everything live at high RPM, but discovered all it took was money to buy premium parts.

Big Dave
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