461 Head Porting - Duke et. al.

[Don C.]

I have a 65 L79 that I plan to do some head work on to improve flow. I have read most, if not all the archived messages on this topic and now would like to attempt the job myself. Duke, you mentioned in another thread that someone has achieved really good flow rates with some pocket porting of their 461's. Can you please provide or direct me to where I can obtain flow data on the intake and exhaust. Before and after data would be great- so I have some idea of what to expect and can monitor as I judiciously remove metal. I have access to a flowbench and plan to go at it slow and easy. I am also seriously thinking of changing to the LT-1 cam. Love those solids and am after more area under the curve.
Thanks so much for your unselfish sharing of knowledge and wisdom to this great community

[Pete Whelan]

Re: 461 Head Porting - Duke et. al.

Don,
Check this site for data on 462 heads, which are similar to the 461s.

http://www.kendrick-auto.com/462_chevy_head.htm

I've pocket ported my 461s and have been very pleased with the results. This is a job that you can do yourself. Just go easy with the die grinder. A reference on pocket porting can be found at http://www.sa-motorsports.com/diyport.htm

I would focus on smoothing the bowl area under the valves and removing any sharp edges in the combustion chambers. Follow this up by having a three-angle cut made on the valve seats and back-cut the intake and exhaust valves if you are using the originals. You should see a 20-25 Hp increase for your efforts.

Good luck.

Pete

[Duke W.]

Re: 461 Head Porting - Duke et. al.

The old Chevrolet Power Manuals give guidance and David Vizard's books are excellent. The 461s I referenced ended up flowing 215/172 CFM @ 25" H2O at 0.400" lift. The maximum actual lift with SHP cams is less than 0.450" when taking into account lash and actual rocker ratio.

Since the valve spends a lot of time at relatively low lift, the low lift flow is really most important. Grinding away the ridge in the valve pocket and a multiangle valve job with a top cut on the inlet provides a smoother approach to what is essentially an annular venturi throughout most of the lift range, and this is the biggest restriction to air flow.

Wish I had a flow bench, too. Have fun!

Duke

[Don C.]

Re: 461 Head Porting - Duke et. al.

Pete, Duke

Thanks for the quick response and the pointer to the websites. You've given me some good flow numbers to shoot for. I do have David Vizard's "How to Build and Modify Chevy Small Block Cylinder Heads" book and will refresh my knowledge.
Duke. Do you have any flow data at intermediate lift heights say .020 or .030
Thanks again
Don

[Don C.]

Re: 461 Head Porting - Duke et. al. - correction

Wrong decimal point on previous post. I should have said intermediate height of .200 or .300
Apologies
Don

[Duke W.]

Re: 461 Head Porting - Duke et. al. - correction

The 25" data at ,2 and .3 for the 461s I referred to earlier was 142/102 and 192/139.

I'd be interested in seeing your data beginning with a baseline for for the OE heads/valves and then the final numbers.

Also, if you can take data at .025" and .050".

Duke

[Dave McDufford]

Re: 461 Head Porting - Duke et. al.

Don,

This may be more than what you want, but the attached link shows the heads Duke mentioned and the other work done on the engine. I have additional photos of what the heads look like if you would like to see them.

Inspite of ignition and carb issues it made close to 360HP (SAE Gross) and was still increasing at the 6500rpm redline.

I like it.

Dave

http://vetteheads.com/forums/showthread.php?t=1165

[Don C.]

Re: 461 Head Porting - Duke et. al. - correction

Duke
Will gladly share the data. I plan to do this after Carlisle, as we drive there with our Vette entourage (well 4 anyway) from the great white north - that would be Canada.
Regards
Don

[Don C.]

Re: 461 Head Porting - Duke et. al.

Dave
I am collecting as much information as I can before starting this project and what you have provided is really worthwhile and appreciated. I've added it to my database. That is one potent little mouse. May I contact you for additional photos or info once I start the project?
Thanks
Don

[Dave McDufford]

I'd be happy to provide what I have. *NM*

[Clem Z.]

the biggest intake flow change you can make

is going to 30 degree seat angle over the 45 degree seat angle. this will increase low lift flow up to .250 of a 2.020 valve to equal a 2.40 diameter valve

[Don C.]

Thanks Clem

I've read many of your archived messages and learned alot.
Don