Edelbrock to Shelby head swap

DougD · #1 (**permalink**) 12-02-2002, 12:50 PM

I have an assembled 427 CO short block that was set up to yield approximately 10.5:1 compression ratio with the Edelbrock 76cc chamber aluminum heads. I got a deal on a pair of Shelby 427 aluminum heads, and I'd like to know what the resulting compression ratio would be. I think the Shelby heads are 82cc (I'm using my memory here, as the Shelby web site is down, so I can't verify this, and may be wrong). The pistons are flat tops w/valve reliefs. The cam is a Competition Cams with just over .600 lift. Can I use these heads on this combination?

ADR · #2 (**permalink**) 12-02-2002, 12:54 PM

Cant answer your compression ratio question but I am curious why you would want the Shelby heads. Is this a swap for more performance or do just want the Shelby heads?
Dale

DougD · #3 (**permalink**) 12-02-2002, 01:13 PM

ADR
I got an unbelievable deal on a pair of new-in-the-box, ported Shelby heads. They will out flow the Edelbrocks to boot. Couldn't pass them up. I just hope that they will fit the short block without too much trouble.

Jeff Frigo · #4 (**permalink**) 12-02-2002, 01:17 PM

Don't waste your time chaging the heads, they are almost identical to the Edelbrocks, you wont see any perfomance gains. If the chambers are 82 cc's, then your compression ratio would drop to 9.9 to 1.

Cobrabill · #5 (**permalink**) 12-02-2002, 05:05 PM

Sell the Shelby's for what their worth.Then spend some $$ on a port job for your Edelbrocks.

BTW-what are the flow numbers for the Shelby's?(and how many inches were they flowed at?)

DougD · #6 (**permalink**) 12-03-2002, 06:24 AM

Cobrabill
The Shelbys received the Stage 2 port job from Shelby Enterprises. Not sure about flow numbers.

Jeff Frigo
Cal Metal posted a graph recently that shows the Shelbys do flow better than the Edelbrocks. And these are ported, so should show even more improvement over the unported Edelbrocks.

I suppose I should point out that the short block has no heads bolted on at this point. On my left, Edelbrock. On my right , Shelby. How about it, FE fans? What to do...

Cobrabill · #7 (**permalink**) 12-03-2002, 03:02 PM

Doug-still not enough info.Flow numbers would tell us a bunch.For conversation sake,lets assume the Shelbys do flow a bunch.Then the cam that would work well with the Edelbrocks won't work so good with the Shelby's.There is more to consider than just a head swap.More info is needed!You can see where i'm going with this.......

SFfiredog · #8 (**permalink**) 12-03-2002, 06:50 PM

according to Shelby literature, the stage II port job flows 320 intake and 235 exhaust. Who knows at what valve lift. The combustion chamber on the Shelby heads is confirmed at 82 cc out of the box.
The E-brocks are not avaliable complete with the big valves (2.19/1.75) like the Shelbys and the valve job makes a big difference in flow #s. For example, Neil at Gessford Machine can get you 345 intake and 245 to 250 exhaust with a hand port job.
Keith Kraft Racing and Kuntz & Co can get you 365 intake and 265 exhaust with a not too radical CNC port job. If you have the small valve E-brocks on your motor now you should notice a good pick up in power, but not a huge bunch because you are losing some compression.
--Mike

Jeff Frigo · #9 (**permalink**) 12-03-2002, 06:56 PM

The Edelbrocks can e machined to take 2.19 intakes and 1.73 exhaust. Mine have these valves and were hand ported. 335 intake, 240 exhaust. Im not trying to tell you which to use, just giving you some number to copmare.

JBAIRD · #10 (**permalink**) 12-03-2002, 09:18 PM

Keith Craft has a new CNC program plus when Brad finishes them Keith said 370-375 in take and 280 on exhaust. That is on Edlebrock heads. I'm still deciding on how big of cam we want. I was at Keiths place about a month ago and watched him dyno a new shelby block motor with a Scat billet (4.25) crank in it. Had a single plane Dove intake on it because it wasn't for a cobra, anyway, it dyno'ed 872 Hp at 7800rpm. Should have heard it WOW was it awesome. Huge roller cam, T&D shaft rockers etc.. Was a 14:1 comp engine. Not what i really want for my next SPF, but it was awesome. Went to 8,000 every time on ea. pull.

DougD · #11 (**permalink**) 12-06-2002, 06:21 AM

Thanks for all the input , guys. I've decided to bolt on the Shelby heads. They already have larger valves, and with the porting and intake-matching that has been done, I can't believe the stock Edelbrocks will perform better without doing comparable work to them. I got such a good deal on the Shelby heads that I'd probably end up with more money in the Edelbrocks after porting/polishing, adding larger valves, etc. I don't doubt that the Edelbrocks can be made to perform as well or better, but with the two choices sitting in front of me, the Shelbys seem to be the better choice. I have another engine that I can drop the Edelbrocks onto, so that's what I'm gonna do.

GEORGE ANDERSON · #12 (**permalink**) 12-06-2002, 10:31 PM

Best be checking the Exhaust Valve margin diameter clearance to that 427 Block bore......not likely you have needed clearance at .600 lift......Edelbrock valve spacing allows a larger exhaust valve with that lift in a 427 bore....Shelby doesn't! Buyer/Installer beware! Your Edelbrocks were a much better choice.....remove the exhaust seats, install smaller seats and smaller valves on the Shelbys and start all over....
Have a nice weekend.....
Just my opinion!
Watch that exhaust valve diameter clearance to your cylinder bore at .600+ lift!

http://www.gessford.com/projects/ima...uto427-P01.jpg

George

DougD · #13 (**permalink**) 12-10-2002, 06:40 AM

George
The cam I have is a solid lifter Comp Cams 294S-10 with .605 gross valve lift, 248 duration at .050, 110 degrees separation, valve timing at .015 int open 41 BTDC close 73 ABDC exh open 81 BBDC close 33 ATDC, with cam installed at 106 intake center line.

My block is bored .017 over, with Keith Black BB Chevy flat top pistons. The machine work was done locally with a 10.5:1 compression ratio target with the 76cc Edelbrock chambers. As stated above, the compression will be somewhat lower with the larger Shelby chambers.

I appreciate your input on this, however I'm still going to use these heads. Wouldn't it be easier and cheaper to swap cams vs. "remove the exhaust seats, install smaller seats and smaller valves on the Shelbys and start all over"? Can you recommend a cam? To be honest, I'm having second thoughts about the cam I selected as being a little too wild. My car will see club open track events a couple times a year, and some limited weekend street duty. I'd prefer to stay with the solid lifters.

FE Specialties · #14 (**permalink**) 12-10-2002, 10:52 AM

Hi Doug,

You have gotten some good replys to your post!!
The Shelby heads flow good on the intake side, but the Edelbrocks have a better exhaust to start with!!
I am concerned with your compression with your motor!! If you put the Shelby heads on, you will lose about .6 in compression, down to about 9.9 to 1. This will do more to hurt your performance than the increase in flow. Also, what intake are you using? If its a dual plane, such as a performer RPM, then the intake will have to be flowed to match the capacity of the heads to acheive the desired results. The head is just part of the intake tract!! Definetly a precise port match is needed.
The bottom line is really what your trying to accomplish. How much power are you trying to obtain. If your looking for about 500 HP, then either head will suffice!!
We are coming up with an offset rocker with 5/16 pushrods that will let us go about 1.75 wide on the intake port on the Edelbrock heads. This will equate out to the 380-395 flow numbers that are so sought after. But these kind of flow numbers are for full on drag motors, and will be a little lathargic on the street. Remember, in a Cobra street application, your looking for the highest Average torque and HP readings with a wide RPM band between peak torque and peak horsepower!!
I would blend port your Edelbrocks which would get around 325 cfm without increasing the port volume too much. This builds a wide torque band and makes the engine a real joy to drive on the street!!
P.S. With aluminum heads, you need to keep the compression to at least 10.6 to 1 so the motor stays effecient.
Hope this helps!!
Tom Lucas FE Specialties

DougD · #15 (**permalink**) 12-11-2002, 06:30 AM

Tom
Thanks for the reply. Yes, I have gotten some excellent feedback. I love this forum!
To answer your questions, I have two intakes I could use. One is a Shelby dual plane that I bought with the Shelby heads. The second is a C6 Ford PI dual plane. Both are single four barrel. I am planning to port match whichever combination of heads/intake I go with.
I'm definitely not looking for a drag motor. 500 horses would be ample. I'm more concerned with a broad power band and drivability than with peak horsepower.
What do you think about the cam I have?

Jeff Frigo · #16 (**permalink**) 12-11-2002, 06:56 AM

Doug:

Don't be afraid of the cam you have. The duration and overlap is not too radical for the flow you have in the heads. I have another 10 degrees duration with about the same flow on the heads as you do. Idles at 900 rpm all day long and pulls strong from 2,500-6,000 rpm. Made 585 hp @ 6,000 rpm. on pump gas.



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