Aftermarket BBM head

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agertz1
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Aftermarket BBM head

Post by agertz1 »

Uses a 2.14" int. and 1.81" exh. valves. That"s a .85 exh/int ratio. Why would you do that ? I'm using Nascar valves, likely a 355" motor with a ratio
of .73. Both wedge chambers. Did I miss something ?
Thanks, Art.
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Re: Aftermarket BBM head

Post by BradH »

BBM heads... they come in all flavors. :lol:

Most OEM heads from the '60s were 2.08"/1.74", then were changed to 2.08"/1.81".
Max Wedge heads from the early '60s were 2.08"/1.88".
All the OEM stuff was 3/8" valve stems

I guess the aftermarket got into the 2.14"/1.81" sizes, probably as a way to salvage the old iron heads as much as a potential performance improvement.

The Edelbrock Performer heads use 2.14"/1.81", but switched to 11/32" stems. They bumped it up to 2.20"/1.81" w/ the Victors.

Indy's stuff has generally been 2.19"/1.81", but I think it's common for people to put in 2.25" intakes. I don't know about their newer & bigger versions, though.

Original B1s IIRC are 2.30"/1.76" (might be wrong on intake size).
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Re: Aftermarket BBM head

Post by agertz1 »

Ok, B1's = .765 ratio. I hear they used to work pretty good ? I suspect with this current .85 ratio, might be compromising too much exh. port velocity ?
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Re: Aftermarket BBM head

Post by mag2555 »

Your looking at the ratio of just the valves themselves and not the overall flow ratio.
When I step up from a 1.74” stock Mopar valve to a 1.81” valve in terms of a iron head it’s because when you max port out the head to get high lift flow numbers that should be had thru a 1.74” valve you drop off a good chunk of low lift flow in that rework process.
The use of a 1.81” valve gets all of that lost flow back and more!

Any aftermarket Aluminum Mopar head that is not a raised port type does not do all that much better then a ported production iron head in terms of exh flow if it’s not made with a 1.81” valve.

Next time you look at some flow sheets for whatever heads add up the intake flow numbers at each lift point , then do the same for the exh numbers and then divide that by each other and you will see what is far closer to the real exh to intake ratio minus the effect of compression once you get above about 12 to 1.
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Re: Aftermarket BBM head

Post by panic »

355" B engine?
What bore & stroke?
amc fan
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Re: Aftermarket BBM head

Post by amc fan »

.030 over 1958 Fury 350 engine possibly or 383 with 3.125 stroke
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Re: Aftermarket BBM head

Post by mag2555 »

What compression will this motor have?
If where talking flat out drag strip usage with over a 14.5 compression you can run a 1.60” exh valve if the port will flow over 250 cfm and make well north of 750 hp !
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Re: Aftermarket BBM head

Post by 67satellite »

My 2 cents, Size the intake valve as big as necessary(or bigger) to utilize the available intake port area. Fill the remaining chamber space with the biggest ex. valve that fits.Done.
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Re: Aftermarket BBM head

Post by ClassAct »

If you use a flow bench to port your exhaust you will lose power every single time. Even the Chrysler head doesn’t need that 1.81 exhaust valve. It’s bigger than it needs to be.
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Re: Aftermarket BBM head

Post by agertz1 »

4.100" bore x 3.288", as stated 95% street. This is why need acceptable port velocity #'s ? Not building a drag motor. With E85, I suspect
10.5- 11/1 should be ok ? A little early for a cam profile or pipe max, just yet.
Thanks, Art.
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Re: Aftermarket BBM head

Post by agertz1 »

To clarify, not a 355" V8. I was referencing possible type of engine, Nascar valves came out of. This is a four cylinder, 170". :)
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Re: Aftermarket BBM head

Post by mag2555 »

One of the most important things in terms of a street motor exh wise to maximize low speed torque and have the motor come into the cams power band as soon as possible is to minimize reversion.

Take a look into anti reversion headers and mufflers!
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Re: Aftermarket BBM head

Post by agertz1 »

Exh. port is very close for a 1 5/8" primary. I was considering step headers, with 12" long 1 5/8" into 1 3/4" then 4 into one collector ?
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Re: Aftermarket BBM head

Post by mag2555 »

I am not a big fan of step headers unless they are made right, which is that the bigger diameter tube size needs to be in the bends where the big restriction is, ( as in anything more then a 30 degree bend) and then taper back down to the starting tube size.
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