Valve Stem Location in C6AE-R Head

[jimeast]

Does anyone have some dimensional information on the location of the Valve Stem center or plane with respect to the chamber of the C6AE-R heads.  I have read that the valves are 2" apart, but do not see any data on where the intake or exhaust is located with respect to the center plane of the chamber  I can measure this to a degree of accuracy, but would like exact info if available.  The "Shoe" drawings I have are for a MR head which have a longer valve spread 

[Joe-JDC]

For what purpose do you need to know this?  You can install larger valves and not worry about the spacing if that is your ultimate question.  I can check a set of "Rs" tomorrow if it is something more.  Joe-JDC

[jimeast]

Joe,

I am working on a 390-445 stroker and I have a set of C6AE-R heads that I'm going to work on and I'm trying to sketch out the seat geometry.  I picked up a set of 2.15 intake and 1.68 exhaust valves with 45 degree faces, and plan on using a cam like the Comp 282s or similar (under .600 lift).  I took a few rough measurements of the location of the valve guides, but figured if someone had a drawing or the exact dimension, it might help.

The local shop I am going to have update the heads recently picked up a Newen valve seat machine that is CNC controlled and uses a point cutting tool.  They told me they can cut any seat and throat shape I come up with.  These guys do not do much exotic FE work, but in general they fix rare engines (all kinds)  from all over the country some other shop has usually screwed up; so they don't have a suggestion for the best valve seat geometry for my C6AE-R heads.  They have also built a reasonable number of FE's, some with plenty of HP, but as a recipe, from Barry's book, not as there own performance program.

I saw you mention in a post on the FE forum that you've seen significant CFM improvements with 5 angle seats.  I am hoping it is reasonable to get a good seat and throat set up for these heads using best practices without sending the heads out to a porting pro for this build.  I am hoping to do a good job with the seats, throat, and reasonable cleanup in several other areas, and ideally end up with a motor that runs very strong to a little over 6,000 RPM.  I'm currently shooting for a 10:1 Comp ration and engine is going in a 67 Mustang with a 3.5:1 rear a wide ratio toploader transmission. 

When looking at the seat and throat geometry in a CAD system,  I'm not sure what I should do to size the various face widths in the seat.  Using a 15-30-45-60-75 Intake seat, I have the 45 deg face width at .065" but the size of the 15 and 30 depend a lot on how "proud" or sunk the top of the valve should be with respect to the chamber surface. 

Several questions I have;

1) I plan on adding a 30 degree back cut to both intake and exhaust valves.  What should the width of the 45 degree face be once the 30 degree back cut is added, assuming the seat will have .065 width for the intake and .075 for the exhaust

2) Is it worth adding a five angle valve job for a street motor that will only occasional see 6k rpms, with the gross lift around a little below .600?  Since the cost is going to be the same no matter what seat preparation I do, it seems like I should try and put some extra effort in developing the best seat and throat geometry

3) If I use a 5 angle valve job on the seats, any suggestions on how to approach it?

4) Any suggestions on how proud I should make the valve tops from the Chamber surface?

5) Is there any chamber work I should plan on doing.  The chambers are a little wider than the bore will be.  Ideally the final bore will be 4.08 and the chambers at there widest are a little over 4.1 now.  Seems like I can see if there is any area to de-shroud, but there is not a lot of room to work with.

6) Throat size:  Ive seen several rules of thimb t osize the throat, as percentage of the valve diameter, and as a percentage of the minimum valve diameter measured at the inside edge of the 45 deg seat face that meets the valve.  ANy advice on what has worked best for this type of street build would be appreciated

Thanks in advance for any advice.

[Joe-JDC]

Don't back cut the exhaust valve, it will lose flow.  On the intake valve, all you need to really back cut is enough to get rid of the sharp edge of the 45*.  The shop should be plenty familiar with that.  As far as multi angles, some use 5/6/7/indefinite into the throat on the intake, and only a continuous radius on the exhaust above and below the 45*seat cut.  On the C6-R head, you may not have a lot of seat left on the exhaust for a 1.710" valve, and may want to install hardened oversize seats.  I prefer a wider seat if you are going to run a lot of seat pressure: .050-.060" intake, .070-.090" exhaust, but on an engine where regular spring changes/ valve touch up is expected, narrower will work well.  Just don't let them use a cutter that has a 90* down under the intake seat, it will hurt flow.  I would stop at 70* in the throat, and blend to guide boss.  The R head can flow close to 300 cfm with that size valve and good valve job with porting.  Joe-JDC

[jimeast]

Thanks very much for the information.

[jimeast]

Joe,

You mention in your response; "and only a continuous radius on the exhaust above and below the 45*seat cut."  Does this mean you run a tangent radius off the chamber surface to the 45 degree seat face and then a radius to a 70 degree face that ends up being blended into the port throat? 

[Joe-JDC]

If I understand your statement correctly, yes.  There are cutters available that have the complete seat curvature with 45* and arc above and below the seat so that in one plunge, you get a beautifully radius into the throat.  It works on any valve size for the exhaust.  Makes quick word of getting all the seats identical, and improves flow if done properly.  The shop I use now after retirement has a Serdi and many different cutters for both intake and exhaust since they build street engines, drag engines, and dirt/asphalt street stock style engines.  Having a good selection of multi-angle cutters saves time and keeps the seats uniform, and what works on a sbc does not necessarily work on a sbf, or FE.  I specify what cutter to use on my valve jobs, and I have good results with flow improvements.  Joe-JDC

[jimeast]

The machine that will cut my seats is a single point cnc.  So, I provide a profile and the machine cuts it.  My challenge is having this much freedom in the shape is causing me to research this as much as possible.

Thanks for the continued advice in this.

[jimeast]

As I mentioned in the original post, the shop that is going to work on my C6AE-R heads has a Newen CNC seat seat cutting machine and asked me to draw up a profile to machine the seats and throat with.  I worked on the geometry a bit to see what makes sens from a novice's eyes.  I've dimensions the seat widths for the multi-angle valve job and would like feedback on whether the widths shown and location of the seat geometry is a good start for improved flow.  Any continuing advice will be greatly appreciated.  I plan on getting the throat diameter a little larger, somewhere over 90% of the inside edge of the 45 degree face that mates to the valve.

The Intake valve is 2.15 Dia, and I've tried to keep the 45deg valve seat face as close to the outside diameter of the valve as possible, and keep the top of the valve off the chamber surface so the valve does not appear sunken into the seat.  The geometry down in the throat area is probably not accurate.  Based on Joe's initial advice, I've got the final seat cut at 70 degrees and I suspect it will cut air at some point and I'll do some blending from this surface to the bowl or throat.