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My 915's cc'd pretty big, is this typical?

Posted By: 73DAD

My 915's cc'd pretty big, is this typical? - 04/05/21 01:06 PM

I finally cc'd a set of 915's I had rebuilt at the local machine shop a couple years ago. I had the 1.6" exhaust valves replaced with 1.74"s & new seats obviously. They skimmed the decks to square them up. I gauged the retainer to spring-seat height with the stock locks & retainers at 1.880".

One head came in at 80.5cc & the other at 82cc. I thought that seemed pretty big for closed chambers. Is this what you guys have typically seen?

I have a pretty high quality 100ml glass burret & can be confident in my measurements to +/- 0.1cc
The chambers are as-cast.
Posted By: fast68plymouth

Re: My 915's cc'd pretty big, is this typical? - 04/05/21 01:47 PM

Not uncommon at all.
Posted By: Cab_Burge

Re: My 915's cc'd pretty big, is this typical? - 04/05/21 04:54 PM

Originally Posted by fast68plymouth
Not uncommon at all.
iagree
Posted By: John_Kunkel

Re: My 915's cc'd pretty big, is this typical? - 04/05/21 05:25 PM

Kinda funny that the closed chambers are closer to the advertised volume of the open chambers. (79.5 cc)
Posted By: AndyF

Re: My 915's cc'd pretty big, is this typical? - 04/05/21 06:29 PM

Originally Posted by 73DAD
I finally cc'd a set of 915's I had rebuilt at the local machine shop a couple years ago. I had the 1.6" exhaust valves replaced with 1.74"s & new seats obviously. They skimmed the decks to square them up. I gauged the retainer to spring-seat height with the stock locks & retainers at 1.880".

One head came in at 80.5cc & the other at 82cc. I thought that seemed pretty big for closed chambers. Is this what you guys have typically seen?

I have a pretty high quality 100ml glass burret & can be confident in my measurements to +/- 0.1cc
The chambers are as-cast.


Factory parts from that era were all over the map. If you want a factory big block engine to meet factory specs you have to re-machine a bunch of parts.
Posted By: BSB67

Re: My 915's cc'd pretty big, is this typical? - 04/05/21 06:43 PM

Originally Posted by 73DAD
I finally cc'd a set of 915's I had rebuilt at the local machine shop a couple years ago. I had the 1.6" exhaust valves replaced with 1.74"s & new seats obviously. They skimmed the decks to square them up. I gauged the retainer to spring-seat height with the stock locks & retainers at 1.880".

One head came in at 80.5cc & the other at 82cc. I thought that seemed pretty big for closed chambers. Is this what you guys have typically seen?

I have a pretty high quality 100ml glass burret & can be confident in my measurements to +/- 0.1cc
The chambers are as-cast.


I have 2 sets of 915s. 2.080 intake and 1.74 exhaust. They have had a clean-up pass or two on them, but minimal removal. one set is about 78, the other about 77.
Posted By: Cab_Burge

Re: My 915's cc'd pretty big, is this typical? - 04/06/21 02:50 AM

Measure the thickness of the outer head bolt bosses and see how thick, tall, they are now and please post them.
I'll bet a nickel they are closer to .960 to.950 now than they where new scope up
Posted By: 73DAD

Re: My 915's cc'd pretty big, is this typical? - 04/06/21 11:30 AM

Originally Posted by Cab_Burge
Measure the thickness of the outer head bolt bosses and see how thick, tall, they are now and please post them.
I'll bet a nickel they are closer to .960 to.950 now than they where new scope up


I'll do that if my memory cooperates. I wish I had cc'd them before sending them out to be machined, just to have the data. What do you guys suppose unmilled open chambers cc at? 95?? 100??
Posted By: lewtot184

Re: My 915's cc'd pretty big, is this typical? - 04/06/21 12:33 PM

Originally Posted by 73DAD
Originally Posted by Cab_Burge
Measure the thickness of the outer head bolt bosses and see how thick, tall, they are now and please post them.
I'll bet a nickel they are closer to .960 to.950 now than they where new scope up


I'll do that if my memory cooperates. I wish I had cc'd them before sending them out to be machined, just to have the data. What do you guys suppose unmilled open chambers cc at? 95?? 100??
on average 88-90cc's.
Posted By: carnut68

Re: My 915's cc'd pretty big, is this typical? - 04/06/21 04:23 PM

I had a set of 906s they cc @ 91. Some 902s I had. Only cut 10 cc @85.
Posted By: BSB67

Re: My 915's cc'd pretty big, is this typical? - 04/07/21 01:19 AM

Originally Posted by 73DAD
Originally Posted by Cab_Burge
Measure the thickness of the outer head bolt bosses and see how thick, tall, they are now and please post them.
I'll bet a nickel they are closer to .960 to.950 now than they where new scope up


........What do you guys suppose unmilled open chambers cc at? 95?? 100??


From the factory in 1967 -9, or in 2021 after 120,000+ miles and a valve gind or two. Some folks seem to think these are the same.
Posted By: 73DAD

Re: My 915's cc'd pretty big, is this typical? - 04/07/21 02:10 PM

I'm not sure its realistic to think that folks out there are cc'ing worn out high mileage heads just for the heck of it. But just in case, here's how much it would matter...

Hypothetically speaking, lets say I cc a worn out set of heads with valves sunk 30 thou into the seats...

[(2.08"/2)*3.14*.030"+(1.74"/2)*3.14*.030"]*16.39cc/1ci=2.949cc...

Not even 3 whole cc's.
Posted By: fast68plymouth

Re: My 915's cc'd pretty big, is this typical? - 04/07/21 02:26 PM

When you want to know what the chamber volume is for your heads........ you check them.

This is just engine building 101.

I recently had two sets of brand new TF270’s in the shop. The chambers are CNC machined. The chamber volume spec is 78cc.

On one set the chambers were 78cc......... the other set was 76cc.

I hear of people checking 516 heads that are well under 80cc.

I’ve never seen an uncut set under 81cc........ and have seen a few at closer to 84.

You check them........ they are what they are.
Posted By: 500ciBee

Re: My 915's cc'd pretty big, is this typical? - 04/07/21 05:34 PM

Originally Posted by 73DAD
Originally Posted by Cab_Burge
Measure the thickness of the outer head bolt bosses and see how thick, tall, they are now and please post them.
I'll bet a nickel they are closer to .960 to.950 now than they where new scope up


I'll do that if my memory cooperates. I wish I had cc'd them before sending them out to be machined, just to have the data. What do you guys suppose unmilled open chambers cc at? 95?? 100??


My 906 heads measured out at 92cc.
Posted By: Cab_Burge

Re: My 915's cc'd pretty big, is this typical? - 04/08/21 12:08 AM

Originally Posted by 500ciBee
Originally Posted by 73DAD
Originally Posted by Cab_Burge
Measure the thickness of the outer head bolt bosses and see how thick, tall, they are now and please post them.
I'll bet a nickel they are closer to .960 to.950 now than they where new scope up


I'll do that if my memory cooperates. I wish I had cc'd them before sending them out to be machined, just to have the data. What do you guys suppose unmilled open chambers cc at? 95?? 100??


My 906 heads measured out at 92cc.

How thick are the outer head bosses now? scope
I had a set of "516" close chamber heads converter to 1.74 exhaust and some bowl work done for a 440 bracket motor years ago, I ended getting a use set of 906 heads that had some poring work and bigger valves in them and swap them onto that motor, I ended up checking the CC on both sets of heads while doing the swap and the 516 had right at 90.0 CC and the 906 had right 74.0 CC shock The 516 set had taller outer head bolt bosses than the 906 did shruggy
I ended up learning from that you can tell if a heads has been cut very much based off of the head bolt boss thickness up scope
EDITED: One of the older Mopar HP bible section on BB stated that to remove 1.0 CC form a open chamber head like the 906 to remove .010, I think, from the head surfaces for each CC and to remove .012 from the intake side of the heads to keep the intake manifold fitment correct confused luck
I should have dug that book out before posting this but I can't remember which book and where all those books are stored now, CRS whiney shruggy whistling
Posted By: Scully

Re: My 915's cc'd pretty big, is this typical? - 04/08/21 02:44 AM

Originally Posted by Cab_Burge
Originally Posted by 500ciBee
Originally Posted by 73DAD
Originally Posted by Cab_Burge
Measure the thickness of the outer head bolt bosses and see how thick, tall, they are now and please post them.
I'll bet a nickel they are closer to .960 to.950 now than they where new scope up


I'll do that if my memory cooperates. I wish I had cc'd them before sending them out to be machined, just to have the data. What do you guys suppose unmilled open chambers cc at? 95?? 100??


My 906 heads measured out at 92cc.

How thick are the outer head bosses now? scope
I had a set of "516" close chamber heads converter to 1.74 exhaust and some bowl work done for a 440 bracket motor years ago, I ended getting a use set of 906 heads that had some poring work and bigger valves in them and swap them onto that motor, I ended up checking the CC on both sets of heads while doing the swap and the 516 had right at 90.0 CC and the 906 had right 74.0 CC shock The 516 set had taller outer head bolt bosses than the 906 did shruggy
I ended up learning from that you can tell if a heads has been cut very much based off of the head bolt boss thickness up scope
EDITED: One of the older Mopar HP bible section on BB stated that to remove 1.0 CC form a open chamber head like the 906 to remove .010, I think, from the head surfaces for each CC and to remove .012 from the intake side of the heads to keep the intake manifold fitment correct confused luck
I should have dug that book out before posting this but I can't remember which book and where all those books are stored now, CRS whiney shruggy whistling
Open chamber is .0042" per cc, closed is .0062" per cc, 286 and 518 .0064" I think.
Posted By: moparx

Re: My 915's cc'd pretty big, is this typical? - 04/09/21 04:43 PM

as per the MP engine book, .0123 removed from the intake face for every .010 removed from the head deck surface.
you remembered pretty good Cab ! up
beer
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