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12-30-2020, 07:08 PM | #1 |
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1972 307 cam selection... HELP!
Hey all,
I have a 1972 C10 longbed with a 307 in it. I used to daily drive this truck, then it sat for two years, and now I'm wanting to keep the original engine but make bit more power from it. Current specs are: 307, newer 4bbl intake from a junkyard and a 4bbl Rochester Quadra-jet I got for free off a 350 and rebuilt. HEI distributor. Full 2 1/4 inch true dual exhaust with (now burnt out) glasspacks. This is backed by a rebuilt 700r4 trans running a stock converter. 3.07 rear gear, open diff. 255/70/15 tires. I've helped plenty of people move using this truck, and hauled many things. It'll cruise at 60-75 all day depending on how many hills and how steep they are. I like the reliability of this setup, but I'd like a bit (or a lot) more pep at cruising speed and low/mid rpms. I know the 307 will never love winding to the moon and will never be a race truck. Though I hasve beat on it and suprised a few people at redlights when it was a daily. I would consider changing to a 3.73 gear when I have the rear end rebuilt to be a posi. So consider that in the response. I have access to some good heads that are casting number 3998991 that came off a pretty strong pulling mild 327 a guy had changed out for a 350. These heads are free and I can use them if they'd be better than the stock 72 307 heads. I know I'll likely need to get headers and potentially step up my exhaust size to 2 1/2 inch to take advantage of a more aggressive cam. This is not currently my daily driver, so I do not care about MPG beyond interstate cruising. It'd be nice to get more than 14 running 75mph through a full tank though. That's my current with the 700r4. I feel more low/mid rpm power would make this happen just because it wouldn't find the need to downshift as often on longer hills. So, with these current options, what would the best combination be for low/mid range power, redlight to redlight fun and cruising. I feel like I've fallen victim to the 'soft cam' issue of the era. Otherwise I'd rush in with the 5.3 I have sitting in the corner of the shop, but I'm trying to convince myself to put that in an 84 S10 I got as a bonus when I bought my house. Thank you all in advance, I've done a lot of reading online, but most people are all "I wanna make my 307 as fast as a 350 with the same mods". tldr; With my current setup, what cam/lifter kit would I gain the most benefits from in a usable power range. With the addition of other potential bolt-ons (eg. exhaust).
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12-30-2020, 07:56 PM | #2 |
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Re: 1972 307 cam selection... HELP!
I'd go with what is known as an RV cam. You want torque down low. The rest comes easy
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12-30-2020, 09:19 PM | #3 |
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Re: 1972 307 cam selection... HELP!
I was averaging about 10.5-12 mpg with my 402 when i drove it almost daily a couple years ago with a TH400 and 3.73 gears on 255/70-15 tires. It had a mild cam, stock intake, Edelbrock carb, and manifolds with turbo mufflers, no tail pipes. I didn’t beat it though, drove it pretty mildly. I would agree with RV type cam for low and midrange power. And definitely headers and a 2.5” exhaust system.
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12-30-2020, 10:08 PM | #4 |
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Re: 1972 307 cam selection... HELP!
I have a set of 3998991 heads on my 350, and from what I have read and experienced, these heads are not performance oriented at all. They are low compression and they have small valves. They do, however, seem to make decent low end torque. My plan is to install some Vortec heads I pulled off a 98 GMC at a wrecking yard last weekend. I know you already mentioned the rear end, but I think switching to a 3.73 would be my top priority in your situation. A 3.07 is a pretty extreme highway ratio to have with a 700R4. Switching the gear ratio could really transform the way your truck drives.
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12-31-2020, 02:57 AM | #5 | |
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Re: 1972 307 cam selection... HELP!
Quote:
I have a 700r4 w/3.08 rear in my '71 GMC and a mild 350 engine & it's responsive enough. It really drives better & gives better mileage if I don't let it go into OD unless I'm running 70+mph. on the Interstate. It's on275/60/15's. Yeah, I'd like to have a 3.73 posi in the GMC & the Blazer both but can't justify spending the $$$$.
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Dad always said, "Son, WISH IN ONE HAND, and ......." -------------------------------------- -------------------------------------- Current toy trucks: '71 GMC 1500 SUPER CUSTOM short/step, orig. dk. blue, 350/700r, ps,pb, A/C '72 Blazer 2wd, ochre & white, 454, tremecTKO 500 5spd. ps, pb, A/C, tilt Last 10yrs of hobby vehicles, had a FEW more in the 50yrs. before these: '66 Plymouth Belvedere City of Miami cop car clone. '70 Nova 406"sb, 13.5-1, solid roller, Brodix, p.glide/t.brake, back halved, 9" Ford, spool 4.88, cage,ladder bar/coilover, 10.5 tire....... SOLD!! '67 C10 short/step side mount spare -- SOLD!! '72 Jimmy 2wd, 350/350, ps, pb, fun driver, lots of bondo & a shiny red paint job..... SOLD!! '69 Nova 350, 4spd, A/C, ps, p.b, ...SOLD!! |
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12-31-2020, 06:58 AM | #6 |
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Re: 1972 307 cam selection... HELP!
hi, summit 1102 is pretty close to what your looking for. good low and midrange power. good luck, BROWN 70
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01-06-2021, 12:34 PM | #7 | |
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Re: 1972 307 cam selection... HELP!
Quote:
It'll do 65-70mph without begging to downshift most of the time. But 75 is the sweet spot for flat land.
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12-31-2020, 08:34 AM | #8 |
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Re: 1972 307 cam selection... HELP!
Comp cam XE262
https://www.youtube.com/watch?v=tWyjDNk8dfo Don't get the 991 heads, they will drop compression as they have 76cc chambers and your heads (should) have 68-70cc. A set of GM vortec heads would be great for this motor, but you need the Vortec specific intake for it as well. Double hump heads can do it as well, check the valve size and cc of the chambers. You would want them 60-66cc imo.
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01-06-2021, 12:36 PM | #9 |
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Re: 1972 307 cam selection... HELP!
Hey guys, thanks for all the good replies, RV cam type is what I was thinking. I'll check out some of these suggestions and let you all know what I end up with.
I've got a 1984 S10 and a 1988 F350 keeping my attention, that and looking at a house to possibly buy will keep me tied up for the next month or two depending on how it all goes.
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01-06-2021, 04:42 PM | #10 |
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Re: 1972 307 cam selection... HELP!
Keep in mind that different sized motors act differently with a cam swap. A 268H from comp cams would be near perfect if you were running a 350. I have had a bunch of those and they always are good. BUT that 268 in a 350 may seem more like a 278 [or so just for conversation] in your 307. I would back up two ranges like a 250 ish I dont remember the size of the 250 comp cam but it is also known as the rv type cam. You could add that cam without the headers but if you want the benefits get some cause they will pep you up.
I want to top the post by saying I used to have a small big block in my Chevelle car and it had a cam that made it sound like a pro mod. I changed it out for a couple sizes smaller and added a different carb and it picked up half a second at the track. That is a lot going from a 8.25 to 7.75 in the eighth. So just think bigger is not always better. On the other hand if you had a 400 small block the same 268H cam would seem like an RV cam to the 400. Does that make sense? Jim |
01-11-2021, 06:02 PM | #11 |
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Re: 1972 307 cam selection... HELP!
A bigger cam will reduce torque at low RPMs. Exactly what you don't want! Bigger cams need better heads and higher compression, and even then, all you're gonna do is make more power at higher RPMs.
Your best path to more torque in 4th gear would be a 3.42 or 3.73 axle. Of course you could skip that and install a near-stock 350, which would get you lots more torque at all RPMs, with little to no decrease in gas mileage.
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent 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! |
01-11-2021, 10:48 PM | #12 |
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Re: 1972 307 cam selection... HELP!
Some 305s had 58 cc heads with 1.84 intake and 1.5 exhaust that would give you around 9.1 compression ratio. the 76 cc heads would give 7.6 compression ratio which would make it a slug. Some 305s heads had 60cc but had 1.72 intake valves. They changed the center intake bolt angle in the later 305s but do not know the year they made the change.
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01-12-2021, 12:44 AM | #13 | |
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Re: 1972 307 cam selection... HELP!
Quote:
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01-12-2021, 09:42 AM | #14 | |
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Re: 1972 307 cam selection... HELP!
Quote:
https://www.summitracing.com/parts/lun-10120700lk
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01-12-2021, 11:10 AM | #15 |
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Re: 1972 307 cam selection... HELP!
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I agree with the 3.73 swap. If you do that you won't have to touch your engine. I had a 3.07 rear in my '69 Suburban with a crate 350 and 2004r OD trans and the high rear gear made the transmission overheat when it was locked up. Swapping in the 3.73 made a world of difference. Swapping that rear to 3.73 would be top priority for me.... LockDoc
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01-12-2021, 11:44 AM | #16 |
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Re: 1972 307 cam selection... HELP!
I went with this on my 72 daily driver. It is the equivalent of the RV cam as is designed for low end torque and excellent cruise speed power... ALWAYS replace lifters with the cam...I also agree with the 3:73 gear swap...Helps take the load off that SB but your mileage and wallet will suffer a bit... https://www.lunatipower.com/voodoo-h...k-256-262.html
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01-13-2021, 10:18 AM | #17 |
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Re: 1972 307 cam selection... HELP!
Several years ago, Car Craft magazine did a 307 build that always peaked my interest, and I've wanted to build a similar setup. I'll try to find the article, but for now, here's a the basic recipe.
307 Vortec heads 250ish advertised duration cam(RV style or one step higher) aluminum intake(vortec specific) 600 cfm carb(the Q-jet will be great also) The combo made 315hp and can't remember torque numbers, but it wasn't shabby. Keep in mind the 307 is a short stroke engine. Basically a 283(3.875 bore) block with 327(3.25 stroke) crank. This means it needs to spin a bit higher to reach max torque. Also, the 307 was an "economy" engine that was literally only intended to be put in base model cars/trucks. They have terrible heads with large combustion chambers, and poor flow characteristics! In fact, that's what gave the 307s a bad reputation as gutless turds. Now, because of the shorter stroke, an RV cam or slightly bigger, will still have a decent lope at idle(enough that experienced ears will know it's not stock) and still keep the optimal torque range where it's useful. Combine all this with the proper gearing(3.73 would be perfect) and you'll have a fun little cruiser that will impress even the hard core 350 guys.
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01-13-2021, 12:46 PM | #18 |
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Re: 1972 307 cam selection... HELP!
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01-13-2021, 09:43 PM | #19 | |
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Re: 1972 307 cam selection... HELP!
Quote:
If I were to buy a harness today I would probably buy from Howell. You can get them cheaper but Howell is a very high quality piece. Haven't heard from OP so don't know what he intends.
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01-14-2021, 04:55 PM | #20 |
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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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01-14-2021, 06:54 PM | #21 | |
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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, recent 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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01-18-2021, 05:26 PM | #22 | |
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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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01-18-2021, 06:34 PM | #23 | |
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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, recent 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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01-18-2021, 08:00 PM | #24 |
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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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01-19-2021, 10:35 AM | #25 | |
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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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