BBC cylinder heads limitations

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prairiehotrodder
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BBC cylinder heads limitations

Post by prairiehotrodder » Mon Dec 10, 2018 12:25 pm

I'm trying to decide if i should run the heads i have or sell them and step up bigger. I'm wondering if any dyno guys have experience with these heads and how far they will take me ?

Many of you have followed my 540 BBC threads and the new version of the engine is coming together right now.

I purchased a set of Mahle 4.560 dome pistons that will put my engine at 12.9 CR and 555 cubic inches. A new Erson custom grind cam thats .730 / .760 280 / 288 112 and degreed in +4 at 108 ICL and 69 intake closing. The intake is a weiand tunnel ram with a pair of 750 holleys.

The heads are untouched AFR 335 CNC heads. I'm not a head porter by any means ( i've done lots on cheap iron heads) and wouldn't feel good about touching these heads myself.

The car is an 81 malibu with a 5500 convertor. It went a best of 9.72 at 137 if i remember correctly with the old low CR motor. Shifting at about 6900 or 7000 and falling back to about 6300 and crossing the line at maybe around 6700 ( can't remember all these numbers very well but i did check them on a data logger at the time) I'm thinking the new cam is going to raise the whole rpm range a few hundred rpm. (old cam was 274/283)

Am i at the limit of these heads ?

Brian
The Word of God is quick and powerfull
www.therocketshop.blogspot.com

prairiehotrodder
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Re: BBC cylinder heads limitations

Post by prairiehotrodder » Mon Dec 10, 2018 12:28 pm

BTW - the next step for me would be the AFR 357 heads, as they are accessible for me and i allready have the right length of pushrods.
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PRH
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Re: BBC cylinder heads limitations

Post by PRH » Mon Dec 10, 2018 4:04 pm

We’ve made over 900hp with those heads on a single carb 565.

Low 8’s in a S/G corvette roadster.

IMO, your intake is the cork in your combo.

If you want to run a TR, you need a “better” one.
Somewhat handy with a die grinder.

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Re: BBC cylinder heads limitations

Post by Newold1 » Mon Dec 10, 2018 6:16 pm

Where do you think you expect to get with the car and this engine as you are finishing the build? That is going to determine how much engine you ultimately need and whether the heads , cam and intake system can get you there.

With the package you are talking about now I think you should make about 980-1000HP at 6900rpm if you go with 1.8 ratio rockers 115% VE

The AFR's are pretty much done there at about 400cfm at .750 lift. Bump valve lifts up around .850 and there is a little more there.

Just my best calculation and guess.

If this gets the car where you want it you pretty good to go. You should dyno in my opinion for a base tune.
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stokerboats
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Re: BBC cylinder heads limitations

Post by stokerboats » Mon Dec 10, 2018 11:05 pm

I suspect with the 335 you can gain good port flow with some good porting. Tony managed over 405cfm on my puny 300cc rovals @ .700 lift and a respectable 320 on the exhaust at the same lift. Those 335's should best that by a good margin.

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Re: BBC cylinder heads limitations

Post by 67 Nova » Tue Dec 11, 2018 9:44 am

Brian, there still is some in the heads, but comes down to cost vs returns? It just might not be worth the cost for minimal returns. You could be further ahead by selling the AFR 335's and getting a set of RHS 320's and having Abbott Racing Heads do them. No two ways around it, Abbott's RHS 320's will absolutely KILL a set of AFR 335's. And most all the AFR line too. BUT it's a custom ported head, so there's that.

I agree with the intake being the choke point. The straight runner Edelbrock is a good intake that's not killer $$$ too. Cam could be on the small side too.

Good luck, John

prairiehotrodder
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Re: BBC cylinder heads limitations

Post by prairiehotrodder » Tue Dec 11, 2018 10:02 am

ok thanks for the suggestions guys, i believe i will stick with the parts i have for now. Once i am running and racing i may change the heads or intake if the car seems to run out of steam. My intake has been heavily ported inside by a previous owner and it kept going faster last summer as i tried different things so i'm not yet convinced i've reached its limit. Also i've been told the motor would like more lift but for some reason i just can't bring myself to go bigger due to the fact the car gets a tiny amount of street driving every summer.
Brian
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www.therocketshop.blogspot.com

Newold1
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Re: BBC cylinder heads limitations

Post by Newold1 » Tue Dec 11, 2018 12:57 pm

Lift won't disturb your street driving over what it will be as you spec'd. PUT THE 1.8 :wink: ROCKERS ON, USE THE LIFT!
The Older I Get, The Dumber I Get :wink:

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