1972 307 cam selection... HELP!

[SpicedIcePirate]

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).

[special-K]

I'd go with what is known as an RV cam. You want torque down low. The rest comes easy

[70STOVEBOLT]

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.

[pjmoreland]

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.

[RustyBucket]

Originally Posted by pjmoreland

.... 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.

If you find that your truck is lazy or doesn't want to cruise comfortably in O.D. you might pull the shifter down 1 bump and run third gear. 3rd gear on the 700r4 is 1.00.... just like a 350 turbo in top gear. The 700r4 has a good low first gear(3.06) to get your truck rolling.
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 $$$$.

[BROWN 70]

hi, summit 1102 is pretty close to what your looking for. good low and midrange power. good luck, BROWN 70

[SpicedIcePirate]

Originally Posted by RustyBucket

If you find that your truck is lazy or doesn't want to cruise comfortably in O.D. you might pull the shifter down 1 bump and run third gear. 3rd gear on the 700r4 is 1.00.... just like a 350 turbo in top gear. The 700r4 has a good low first gear(3.06) to get your truck rolling.
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 $$$$.

I will do that if it wants to down shift a bit m,uch, or if I'm trying to pull a trailer or something of that nature.

It'll do 65-70mph without begging to downshift most of the time. But 75 is the sweet spot for flat land.

[Warrens69GMC]

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.

[SpicedIcePirate]

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.

[hugger6933]

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

[MikeB]

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.

[Tomchev]

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.

[ChevyRacefan]

Originally Posted by Tomchev

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.

Yup. Find a set of 305 heads from a cease fire 82 305 powered vet, or 305 monte carlo SS.

[wesmigletz]

Originally Posted by ChevyRacefan

Yup. Find a set of 305 heads from a cease fire 82 305 powered vet, or 305 monte carlo SS.

I agree with the recommendations for the 305 heads to boost compression. A 250/256 Voodoo cam would be a nice upgrade. May even boost your MPG a bit. It will work with some fresh Z28 springs.

https://www.summitracing.com/parts/lun-10120700lk

[LockDoc]

-
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

[Ironangel]

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

[68Stepbed]

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.

[geezer#99]

I looked into a tpi years ago.
These guys might be your best bet

https://firstfuelinjection.com/

[MARKDTN]

Originally Posted by geezer#99

I looked into a tpi years ago.
These guys might be your best bet

https://firstfuelinjection.com/

Interesting. If I had a hi-po 350 I might consider. But like $2400 for unit and harness. I can do the whole thing for $800-1000. On a stock 307 for the OP I think stock GM TPI will be more than adequate-and parts are available anywhere. The biggest obstacle with stock TPI is high rpm breathing. You improve runners and need a ported plenum then the lower intake is too small. But these problems are 400 or 383 or high revving 350. Nobody runs out of air on a 305 TPI.

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.

[68Stepbed]

Also note that the 307 block can be safely bored +.125 over. That's a 327!

[MikeB]

Originally Posted by 68Stepbed

Also note that the 307 block can be safely bored +.125 over. That's a 327!

Are you sure about that? It assumes 327 or 350 blocks were used for the 307. Or that 307 blocks had thicker cylinder walls than all other blocks.

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.

[68Stepbed]

Originally Posted by MikeB

Are you sure about that? It assumes 327 or 350 blocks were used for the 307. Or that 307 blocks had thicker cylinder walls than all other blocks.

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.

Many people don't like it when I tell them this, but the 307 was a culmination of GM getting rid of stock. With the popularity of the SCCA Trans Am series, and the 5.0L engine size limit, GM used the 327 block (4.00" bore) and used the steel 283 crank (3.00" stroke) to make a 302. That left a multitude of 283 blocks (3.875" bore) and 327 cranks (3.25" stroke). They were put together, and with a set of wheezy heads, they were thrown into base and low option modeled cars and trucks.

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.

[MikeB]

Originally Posted by 68Stepbed

That left a multitude of 283 blocks (3.875" bore) and 327 cranks (3.25" stroke). They were put together, and with a set of wheezy heads, they were thrown into base and low option modeled cars and trucks.

I don't know if the 307 was built to get rid of parts, or simply to make more torque than a base 283 in the new longer, wider, heavier cars.

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!

[BigBird05]

GM only keep on hand 2 or 3 days of block castings. They never stock pile them.

[68Stepbed]

Originally Posted by MikeB

I don't know if the 307 was built to get rid of parts, or simply to make more torque than a base 283 in the new longer, wider, heavier cars.

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!

At a certain point, they ditched the 3.00" 283 crank, and most likely just went into production to make the 307 because it was cheap, and they already had the machines setup to cast and machine them, so they continued producing them.

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!