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#26 | |
Senior Member
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Location: North Texas
Posts: 3,490
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Re: 1972 307 cam selection... HELP!
Quote:
And we're talking about doing it on a 307, which is a totally different animal than the small bore 305.
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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#27 |
Registered User
Join Date: Mar 2005
Location: 10-Uh-See
Posts: 5,609
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Re: 1972 307 cam selection... HELP!
Also note that the 307 block can be safely bored +.125 over. That's a 327!
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#28 | |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,490
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Re: 1972 307 cam selection... HELP!
Quote:
At Mortec.com I found 8 casting numbers for 307 blocks. But not a single one of them is used for 327 or 350. I guess a 307 block with zero core shift could take a +.125 bore, but who knows how much flex there might be in the cylinder walls? I'd do a max overbore of .060" on a 307, just like I did with the 283 back in the day to get 292 cubes. That was back when the 301 was popular, but a machinist convinced me to stick with +.060". I doubt the power difference between 292 and 301 was even measurable. And heck, a 292 would probably last longer than a 301 with thin cylinder walls.
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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#29 | |
Registered User
Join Date: Mar 2005
Location: 10-Uh-See
Posts: 5,609
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Re: 1972 307 cam selection... HELP!
Quote:
The early 283 blocks (pre-62) could actually be safely bored +.155. The later blocks could only be taken to +.125 The biggest difference in 327 & 350 blocks were bearing sizes. The 350 cranks had larger main journals, which is why people don't destroke 350's with 327 cranks. It can be done, but with custom 3.25" cranks with the larger 350 journals.
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#30 | |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,490
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Re: 1972 307 cam selection... HELP!
Quote:
All 283 blocks were small journal, and all 307 blocks were medium journal, right? I guess the raw block castings could have been machined for larger main bores. But the real question is how would GM have changed the casting number in a leftover block that was cast for a 283? Also, the 307 crank was a different animal. It had lighter counterweights than the 327 crank. Again, it could have been the same raw casting but just machined differently. It would be interesting to talk to a Chevy powertrain engineer from back in the late 60s. I think you overestimate the number of 302 engines produced. I mean, they were available only in the Camaro Z28, and only for 3 years. Whereas 283 and 327 engines were available in virtually any car or truck. I'd bet there were easily 50 times more 327s sold than 302s during those years. When I was a kid slobbering over hot new Chevys that I couldn't afford, I would see dozens of 327 emblems every day, even in 4-door sedans. Z-28 302 emblems? MAYBE a couple per month. ***I love your stepside!
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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#31 |
Registered User
![]() Join Date: Aug 2019
Location: Cheraw
Posts: 1,305
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Re: 1972 307 cam selection... HELP!
GM only keep on hand 2 or 3 days of block castings. They never stock pile them.
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#32 |
Registered User
Join Date: May 2013
Location: Colorado Rocky Mountains
Posts: 263
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Re: 1972 307 cam selection... HELP!
Spiced Ice Pirate,
Don't over think your build!!! Of course you can do any of the many ideas offered here by everyone offering their thoughts to help. We are all good at spending your money! You might consider taking a simpler cost effective approach, install 3.73 as others have recommended or (4.10 gears with Bigger Tires) free up the exhaust side of the 307, ( might be good enough now). Give it a great tune on ignition and carb. Unless you really want a huge project, $$$ and the 307 is basically sound now, just do the gears. Have fun driving your truck !!, get it on the road and have Fun !!!! All The Best, Dirk |
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#33 | |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,490
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Re: 1972 307 cam selection... HELP!
Quote:
As I recall, fuel mileage around the suburbs, with some highway, went from 10-11 mpg to 12-13 mpg. And the engine felt so much better when accelerating and at highway speeds, like it went from asthma to breathing freely. Back in 1990 it was the best $250 I ever spent.
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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#34 | |
Registered User
Join Date: Mar 2005
Location: 10-Uh-See
Posts: 5,609
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Re: 1972 307 cam selection... HELP!
Quote:
The pre-62 283s were small journal, but the 62-68 283s were medium journal, just like the 327s. The 307 crank was just balanced different for the 307 piston weight. Smaller piston= less weight As for production numbers of the 302, SCCA requirements said the engine had to be in a "production" car and meet a certain sales requirement. They only made the minimal requirements in the Z/28 Camaro. However, race teams had quite a few spare engines laying around as they experimented different induction systems, ignition systems, etc. to gain an edge on the competition, along with replacing blown engines before the next race. As for sales, the 327 was the mainstay for a few years, and since most hot rodders of the day were more about drag racing than road racing, the all new "350 SS" Camaro, then the 396 equipped Camaros caught all the limelight. The Z/28 versions weren't popular with drag racers. The little 302 made impressive horsepower, but torque was limited since it was a high winding road race engine designed to turn 8000rpm(race version at least) on long straights at speed. Thank you!
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#35 | |||
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,490
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Re: 1972 307 cam selection... HELP!
Quote:
Quote:
Quote:
https://www.jalopyjournal.com/forum/...8#post-6908697 There's another story out there saying Holman-Moody got similar numbers.
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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#36 |
Registered User
Join Date: Mar 2005
Location: 10-Uh-See
Posts: 5,609
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Re: 1972 307 cam selection... HELP!
Found the article!! It was Super Chevy magazine, not Car Craft.
http://www.superchevy.com/how-to/eng...ne-performance
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#37 |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,490
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Re: 1972 307 cam selection... HELP!
Interesting article from Super Chevy, but they were wrong about GM producing a 307 with a small journal crank. Quite unusual for them.
Here's an excerpt from Hot Rod Magazine. It's the second paragraph. https://www.hotrod.com/articles/ccrp...-engine-specs/ And here's a Wikipedia article on small blocks. Read the first and last paragraphs under the section entitled "3.875 in. bore family (1955–1973)". https://en.wikipedia.org/wiki/Chevro...l-block_engine Finally, go halfway down the page here: http://chevellestuff.net/qd/crank/crank.htm Bottom line is I think GM needed a new block for the 307 with more "cast-in" clearance for rods (due to .25" longer stroke). And why cast a brand new block with small journals, when they were moving to medium journal cranks on all other small blocks (302, 327, 350)? I did find a list of crank castings at Mortec.com that shows only three castings used for the 307, and they were also used for 327s. So, they were the same raw castings but machined differently for balancing with different piston weights. 3911001....307,327...cast....medium journal...3.25" stroke 3911011....307,327...cast....medium journal...3.25" stroke 3941174....307,327...cast....medium journal...3.25" stroke A couple pictures of my 307 crank rebalanced for 327 (+.030") pistons and SCAT rods:
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! |
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