Is there a difference in the chamber configuration between these 2 heads? Other than the 36's are 74cc, and the 34's are 68cc. I'm hearing there is a difference in design but not sure what it is. If there is a difference which one is better?

Thanks,
DEI

Is there a difference in the chamber configuration between these 2 heads? Other than the 36's are 74cc, and the 34's are 68cc. I'm hearing there is a difference in design but not sure what it is. If there is a difference which one is better?

Thanks,
DEI
=
Yes they are different.
If you are going to mill the heads you want the 74cc one's, they are unshrouded more.
The 68cc head is a very good head as is but you don't want to mill it. It is designed to be used with a flat top or dished piston only.
You can read about them here under " Tech Support"
http://http://www.airflowresearch.com/ (http://http://www.airflowresearch.com/)

As to which one is "better", depends on your application.
If you are building a street engine & the 68cc head fits your requirements it is an excellent choice.
If you don't mind spending the extra money to have the heads milled to your requirements or you need a larger chamber or are needing less than 68cc's you would want the 74cc chambers.
The milling charge is $150 so you need to decide if a possible few HP is worth the money assuming the 68cc head fits your deal as is.
Under any other circumstances I would recommend the 74cc head as a starting point.

I'm still a little confused here...

Knowing that all heads AFR produces need to be flat milled at some point anyways, why do they even produce the 68cc casting if they know the 74cc casting milled to 68cc flows better? Seems a slam dunk idea to just produce the 74cc casting and mill it to spec for the customer as the heads are produced on an as-ordered basis anyways..

BTW Mike, YGM?

QUOTE:
why do they even produce the 68cc casting if they know the 74cc casting milled to 68cc flows better? Seems a slam dunk idea to just produce the 74cc casting and mill it to spec for the customer as the heads are produced on an as-ordered basis anyways..

My thoughts exactly.

I called tech support at AFR. I was told that "they" are 6 months away from tooling up to produce the 68cc casting to be like the 74 cc ones. It seems like a no brainer to just mill to whatever the customers request using the 74cc casting. That just seems to easy. Probably more to it than that.

DEI

I'm still a little confused here...

Knowing that all heads AFR produces need to be flat milled at some point anyways, why do they even produce the 68cc casting if they know the 74cc casting milled to 68cc flows better? Seems a slam dunk idea to just produce the 74cc casting and mill it to spec for the customer as the heads are produced on an as-ordered basis anyways..

BTW Mike, YGM?
=
Hi Jeremy,
Got the mail & called AFR. I will answer as soon as I finish this.

First, the milling process to lower the cylinder heads from standard to smaller is not part of the CNC machining process so it is not as simple as you guys seem to think. It is an extra machining operation & this is why there is a charge for it.

Now,,, On the heads, the reason for two chamber sizes is simple economics.
People whine if you tell them it will cost $150 to mill the head so AFR came out with the 68cc head to accommodate the customer that needs a smaller chamber without extra cost.

As you are already aware, AFR & especially Tony at AFR goes out of the way to try & take care of customers being as Tony & I have done our best to take care of your problem which neither of us had a thing to do with in the first place so let's let people know about how far they sometimes do go rather than bitchin about things that are not completly correct. :D

If they run the 74cc head & then mill it to 68 you will be paying more for it.
The 68 works very well as is & saves the customer the $150 mill charge.
If you want anything but 68cc's then AFR recommends using the 74cc head as a basis.
The difference in flow, (again according to AFR as I have not personally verified this) is pretty small if you leave the 68cc head alone.
It is designed to be a cost effective smaller chamber head for those that do not wish to spend the extra $150 to have the larger head milled & again, the flow numbers are supposed to be within a few CFM but the 68cc head is slightly lower.
Before anyone asks, no I do not have a number.

You will lose less when milling the larger chamber head but you are going to lose some with it too if you mill it.
Chamber shape has a great deal to do with how a head flows.
I can't explain this any better but if you need more input I will call Tony or you can call him if you like.

Just out of curiousity, is 68cc the limit for milling down the 74cc head? Or can you get it even smaller?

Just out of curiousity, is 68cc the limit for milling down the 74cc head? Or can you get it even smaller?
They will angle mill to less than 60cc's.
I believe they will go to about 56 :)
The limiting factor is the intake seat as the decks are .750" thick.

They will angle mill to less than 60cc's.
I believe they will go to about 56 :)
The limiting factor is the intake seat as the decks are .750" thick.

WOW!! That's cool.

Thanks for clearing that up Mike, this might be good for one of your trademark copy and paste deals in future posts! BTW, I wasnt bitchin'... I would call it more like being very curious. ;)

No better place than here to let you know again I appreciate everything you've done for me. Makes the car *biz* a little easier place to shop in and know you're money is being well spent! :thumbsup:

Thanks for clearing that up Mike, this might be good for one of your trademark copy and paste deals in future posts! BTW, I wasnt bitchin'... I would call it more like being very curious. ;)

No better place than here to let you know again I appreciate everything you've done for me. Makes the car *biz* a little easier place to shop in and know you're money is being well spent! :thumbsup:

Thanks Jeremy:beers:

BTW, your heads are on the way,,