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Old 10-24-2007, 07:50 PM
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307 SBC Upgrade

I have a 1972 stock 2 bolt-main 307 that I want to upgrade with a bit of speed gear.
I AM A TOTAL NOVICE AT THIS.
A friend gave me a never used, wrapped in wax paper, CMC 1539 cam and a set of 400 heads that her ex-husband had stored in the garage for a number of years. Heads are complete with valves, rocker arms and pushrods and appear to be in real good condition except for a little bit of rust around the valve edges. A Google search shows the CMC cam was built for 70-72 Chevy 350 high performance engines but I didn't get much other identifying info other than CMC was bought by Crane Cam, then sold to Lunati.
My question is: How can I tell whether the cam is for hydraulic,solid or if it can be used with roller lifters and rockers. Also, what difficulties do you see with a straight bolt-on of the 400 heads to the 307 block? Can I keep the stock 307 bore and pistons or do I have to match the size of the combustion area of the heads. Finally do you see any great inhancement in using a timing GEAR setup instead of CHAIN. An edlebrock 500cfm performer carb and intake will be pushing the gas. I'm not building a racer, but I want it to sound like a bad boy. Engine is going into a 39 Chevy 2 door sedan. Thanks in advance for your advice and assistance. Les White-Granbury Texas.

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Old 10-25-2007, 12:51 AM
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The 400 heads will drop your compression ratio, which you don't want, especially if you intend to use more cam. A machinist could measure that cam to find out the specs, but he'd likely charge you more than a new cam would cost in the first place. A gear drive won't help enough to shake a stick at, unless you just want it to have that loud whining sound.
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Old 10-25-2007, 01:13 AM
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"CMC" is jsut a casting mark on the cam core. Doesn't mean much. Most all SBC stock cams have this mark. if the cam has a identifiable grind number or part number it will be stamped on the back end of the cam. if there is no such mark it is liekey a "stock cam" or stock replacement cam.
Not much of a performacne booster for even a mild 307.

GM 400 cyliner heads all ahd a very large combustion chamber giving even a 400ci motor a low cr. if used on a 307 the cr will be very very very low.

The best low buck cheap hop up cylinder head to bolt onto a 307 is a small chambered "305 HO" head.
casting number "416" or "081" or "601" are best. can really come alive with a porting job and larger 1.94x 1.60" valves.
The stock 307 heads are usually large chambered low cr with small ports and valves.
a 305 HO head with a thin .015" steel shim gasket works pretty good on a 307 with a moderate hyd cam, dual plane manifold and 4bbl carb with headers.
keep the camshaft duration short (under 216@.050") unless you are using a high stall converter and high rear gear ratio.
what is the casting number on the 400 heads" under valve cover between springs.??
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Old 10-25-2007, 02:20 AM
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Agreed. 307s are low compression to start with, like some of them were in the 7.8:1 area. 400s were also low compression but with bigger chambers. Putting 400 heads on it might give you an engine with 6.5:1.

I like the 305 heads idea.
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Old 10-25-2007, 02:42 AM
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Back in 1983 I help a friend build a 1973 Nova . It had a 307 with about 30k miles on it . We pulled the stock heads and 2BL intake . I think the heads were #993 . Then we installed a set of #186 heads that came off of a 1970 350 300hp . The #186 heads are 64cc but the had the 1.94 in 1.50 ex valves . We cleaned them up and shimmed the stock springs . Then we changed the cam . We used a comp cams high energy 268H . this cam is 454 lift and 218deg at 050 . To top it off we installed a 2101 Edelbrook perfomer. And a out of the box 600 Holley vac secondaries . We also used the stock points dist with a curve kit and a good coil . Then a set of 1"5/8 headers . With a turbo 350 a 3000 stall and a 373 12 bolt . That car driving it to the track ran 13.90s with street tires . I know if we changed that 600 Holley to a larger one . Or a Q jet it would have ran even faster . That was one 307 that though it was a 350 !
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Old 10-25-2007, 05:50 AM
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I did much the same to a 70 Nova, except I kept the stock heads. Cam, intake swap, 600 vac Holley, headers, & 4 speed.....solid 13.5 second car.

FYI the 400 heads will kill that 307. The smaller valves of the 307 actually help by increasing the intake charge speed.

Vince
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Old 10-25-2007, 06:07 AM
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I think that 4speed helped . Like I said I am sure that engine was under carb ed . The spark plug were white . But my friend wanted to run that out the box 600 Holley . The secondaries would not open till 4500rpm .
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Old 10-25-2007, 07:05 AM
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Quote:
Originally Posted by TANGO
I think that 4speed helped . Like I said I am sure that engine was under carb ed . The spark plug were white . But my friend wanted to run that out the box 600 Holley . The secondaries would not open till 4500rpm .
I played with my 600 quite a bit, main jet resizing, different secondary metering plates, tailoring the accel pump curve and the vac secondary spring. Due to the size of the 600 it was pretty responsive to any positive changes made. The engine had the best throttle response of any carbed engine I have had to date. When you stuck your foot into it it pulled really hard. Most people thought it was a 350.
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Old 10-25-2007, 07:15 AM
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600 should be plenty for any roughly 300 cube motor. To be honest many 350's and 383's can live life just fine with a 600 as well. White plugs just mean your carb wasn't adjusted properly or you had a vacuum leak. You can run a 1050 carb on a 267 chevy and still run lean if its not adjusted properly-

K
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Old 10-25-2007, 01:00 PM
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this is the LINK i got my info from when putting together my 307...joe
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Old 10-26-2007, 04:05 AM
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A Holley 1850c out the box is by no means a performance carb . It may be 600cfm thats fine . But with its small jets and metering plate . And that Strong secondary spring . Its not up for the task . Like I said the secondaries did not open till 4500RPM . Sure I know how to tune these Holleys . But my Friend wanted his new Holley left alone . I had a nice Q jet ready to put on . Who knows maybe mid 13teens . But still that Nova beat lots of Mopars and Fords .
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Old 10-26-2007, 04:08 AM
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A Holley 1850c out the box is by no means a performance carb . It may be 600cfm thats fine . But with its small jets and metering plate . And that Strong secondary spring . Its not up for the task . Like I said the secondaries did not open till 4500RPM . Sure I know how to tune these Holleys . But my Friend wanted his new Holley left alone . I had a nice Q jet ready to put on . Who knows maybe mid 13teens . But still that Nova beat lots of Mopars and Fords .
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Old 10-26-2007, 04:08 AM
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A Holley 1850c out the box is by no means a performance carb . It may be 600cfm thats fine . But with its small jets and metering plate . And that Strong secondary spring . Its not up for the task . Like I said the secondaries did not open till 4500RPM . Sure I know how to tune these Holleys . But my Friend wanted his new Holley left alone . I had a nice Q jet ready to put on . Who knows maybe mid 13teens . But still that Nova beat lots of Mopars and Fords .
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