So I just purchased a 70 chevelle with, I'm being told the original rebuilt 307. I would like to add horsepower to the 307, what is the Most effective and easiest way?
Thanks. Joe
Thanks. Joe
Best way to add power to a 307
JK 1970
41 - 48 of 48 Posts
I sold a Holley Economaster and intake I advertised in The Horsetrader [along with other things I'll never use but are still here for the most part] to some kid who wheeled in with a tired '71 Nova coupe, 307/2 barrel, 3 speed stick, glass packs, etc. etc. Nice, respectful young motorhead with limited resources, never saw him or the car again after we installed the carb/intake here but when he left it sure sounded/ran good. 'Caught 2nd gear rubber' with the column shifter. He had $30.00 in that 'hop up' including the gaskets that I had layin' around here, and I furnished the beer, lol.
I saw this thread regarding the merits of hot rodding a 307, the topic comes up every now and then, and people are usually either all for or completely against the idea. I did a modest 307 build-up for one of my cars, and would like to share my results.
It seems like there are scads of 307’s everywhere. Personally, I had one in an old car, and one sitting in my shop under some shelving. They both were oil users. Do I just pull fasteners off of the one on the floor and haul it in for scrap? I also had recently pulled a 350 from a C10 and it was sitting there on the shop floor also. Hmmm, I thought, bending over the 307 and looking at block code on the back, a guy could build a 307 with 1 hp / cubic inch for peppy street fun, and the 350 with 1 hp / cubic inch for another car for real high performance usage! I stood straight up, and hit my head on the bottom-most shelf. I staggered back a bit in pain and was seeing stars. I heard a voice coming from the 350, and I saw a little angel sitting on it. He said “good guys always build 350’s and only a loser would waste time on a 307”. I heard a second, gruffer voice coming from the 307, and there was a little devil sitting there on that engine! He said “you should build this 307, Ford 302’s run good, you could make this engine do just as well! The little angel retorted: “The ford 302 has the magic 4 inch bore, the 307 is nothing more than a stroked 283!” Next I heard the little devil humming a tune that sounded like an old Meatloaf song, and then he softly sang: “now dooon’t beee saaad, cause two-eighty-threes ain’t bad….”
Back to reality, there is some information out there on dyno tests of small engines like 318 mopars and 305/307 Chevys. Here is a link to an engine build a magazine did with a 307. With regular performance parts they achieved 315 HP / 330 ft/lbs:
307 Chevy Dyno Test - Super Chevy Magazine
Compare that torque rating to a 300 horse 350 factory engine from say, 1969. Chevy claimed 380 ft/lb. So you have 2 engines at about 300 horsepower, except one has a 50 ft/lb advantage over the other. Clearly the 350 would provide a better E.T., all else being the same.
I could not pull the trigger on a 307 hop-up until I acquired a 72 El Camino in 2011. The Camino was a 307 three on the tree basic truck, and supposedly the 70,000 mile odometer reading was accurate. I did not take too much stock in this claim, but after driving it for 1800 miles, the oil level was still not a quart low. I performance tested it with my G-Tech and the results were an 18.2 second quarter mile at 71 miles an hour. It could smoke the one tire easily but had a sluggish top end.
I needed to pull the engine to fix a leaky rear seal and to replace broken motor mounts. I was also swapping out the 3 speed Saginaw for a 4 speed Saginaw. I decided I was actually going to hop this engine up if I could avoid any pricey machine work. I was pleased to find the cylinder walls had only the lightest ridge, and the factory nylon timing gear was still in residence. Perhaps this really was a 70,000 mile engine? It would have been a pity to junk a smallblock that was in this good of condition.
To keep this a low cost, fun, budget build, I looked for deals and accumulated parts. The heads were a lucky find from craigslist. Instead of doing the 305 head swap you often read about, I found someone who had a machine shop-fresh set of 1990 Camaro FI heads. These have the bigger 1.94 intakes and smaller combustion chambers, and new valve springs were also installed. But the owner decided to go with a higher performance type of head, and wanted to sell these Camaro heads for $300. Score!
New rings and bearings, a .450 lift Summit cam and lifter kit, a used aluminum intake, used Edelbrock carb, and new headers were also purchased. I ordered a 2 ½” dual exhaust system to finish up the build.
So I did everything you are supposed to do when hopping up an engine. 4 barrel, heads with bigger valves and more compression, bigger cam, headers. Plus I was replacing the three on a tree with a four on the floor. The Camino even had a 3:36 rearend, albeit it was an open differential. One would think a big change in performance was imminent. After getting everything in good tune I was pleased that my truck could smoke the tires all the way through second gear, and a little more squeal in third. Dumping the clutch from a dead stop resulted in serious wheel hop, and easing out of the hole and then stepping down was wheel spin city. So all my testing was limited to taking off from a dead stop by gradually pressing down the accelerator till I could hold it all the way to the wall and still have forward progress.
The best quarter mile time I could achieve using my G-Tech was 16.4 seconds at 87 mph. You can see by the mph that with traction, the truck should have been into the 15’s. I would have preferred a 90 mph trap speed because then I could at least say it was capable of 15 flat. So there you have it. All those performance parts resulted in a quarter jaunt of what a 4 barrel factory 350 with headers would probably provide.
If you have a car with a decent 307, and you want a little more “umph”, some reasonably chosen performance parts can boost that little engine up to 327 or 350 status easily. This is contingent of course on having a better set of heads available. I thoroughly enjoy trying to coax extra power out of my vehicles as long as it’s not cost-prohibitive. It was a fun project. Really really glad I did not start with a worn out 307 and then spent a thousand bucks at a machine shop!
It seems like there are scads of 307’s everywhere. Personally, I had one in an old car, and one sitting in my shop under some shelving. They both were oil users. Do I just pull fasteners off of the one on the floor and haul it in for scrap? I also had recently pulled a 350 from a C10 and it was sitting there on the shop floor also. Hmmm, I thought, bending over the 307 and looking at block code on the back, a guy could build a 307 with 1 hp / cubic inch for peppy street fun, and the 350 with 1 hp / cubic inch for another car for real high performance usage! I stood straight up, and hit my head on the bottom-most shelf. I staggered back a bit in pain and was seeing stars. I heard a voice coming from the 350, and I saw a little angel sitting on it. He said “good guys always build 350’s and only a loser would waste time on a 307”. I heard a second, gruffer voice coming from the 307, and there was a little devil sitting there on that engine! He said “you should build this 307, Ford 302’s run good, you could make this engine do just as well! The little angel retorted: “The ford 302 has the magic 4 inch bore, the 307 is nothing more than a stroked 283!” Next I heard the little devil humming a tune that sounded like an old Meatloaf song, and then he softly sang: “now dooon’t beee saaad, cause two-eighty-threes ain’t bad….”
Back to reality, there is some information out there on dyno tests of small engines like 318 mopars and 305/307 Chevys. Here is a link to an engine build a magazine did with a 307. With regular performance parts they achieved 315 HP / 330 ft/lbs:
307 Chevy Dyno Test - Super Chevy Magazine
Compare that torque rating to a 300 horse 350 factory engine from say, 1969. Chevy claimed 380 ft/lb. So you have 2 engines at about 300 horsepower, except one has a 50 ft/lb advantage over the other. Clearly the 350 would provide a better E.T., all else being the same.
I could not pull the trigger on a 307 hop-up until I acquired a 72 El Camino in 2011. The Camino was a 307 three on the tree basic truck, and supposedly the 70,000 mile odometer reading was accurate. I did not take too much stock in this claim, but after driving it for 1800 miles, the oil level was still not a quart low. I performance tested it with my G-Tech and the results were an 18.2 second quarter mile at 71 miles an hour. It could smoke the one tire easily but had a sluggish top end.
I needed to pull the engine to fix a leaky rear seal and to replace broken motor mounts. I was also swapping out the 3 speed Saginaw for a 4 speed Saginaw. I decided I was actually going to hop this engine up if I could avoid any pricey machine work. I was pleased to find the cylinder walls had only the lightest ridge, and the factory nylon timing gear was still in residence. Perhaps this really was a 70,000 mile engine? It would have been a pity to junk a smallblock that was in this good of condition.
To keep this a low cost, fun, budget build, I looked for deals and accumulated parts. The heads were a lucky find from craigslist. Instead of doing the 305 head swap you often read about, I found someone who had a machine shop-fresh set of 1990 Camaro FI heads. These have the bigger 1.94 intakes and smaller combustion chambers, and new valve springs were also installed. But the owner decided to go with a higher performance type of head, and wanted to sell these Camaro heads for $300. Score!
New rings and bearings, a .450 lift Summit cam and lifter kit, a used aluminum intake, used Edelbrock carb, and new headers were also purchased. I ordered a 2 ½” dual exhaust system to finish up the build.
So I did everything you are supposed to do when hopping up an engine. 4 barrel, heads with bigger valves and more compression, bigger cam, headers. Plus I was replacing the three on a tree with a four on the floor. The Camino even had a 3:36 rearend, albeit it was an open differential. One would think a big change in performance was imminent. After getting everything in good tune I was pleased that my truck could smoke the tires all the way through second gear, and a little more squeal in third. Dumping the clutch from a dead stop resulted in serious wheel hop, and easing out of the hole and then stepping down was wheel spin city. So all my testing was limited to taking off from a dead stop by gradually pressing down the accelerator till I could hold it all the way to the wall and still have forward progress.
The best quarter mile time I could achieve using my G-Tech was 16.4 seconds at 87 mph. You can see by the mph that with traction, the truck should have been into the 15’s. I would have preferred a 90 mph trap speed because then I could at least say it was capable of 15 flat. So there you have it. All those performance parts resulted in a quarter jaunt of what a 4 barrel factory 350 with headers would probably provide.
If you have a car with a decent 307, and you want a little more “umph”, some reasonably chosen performance parts can boost that little engine up to 327 or 350 status easily. This is contingent of course on having a better set of heads available. I thoroughly enjoy trying to coax extra power out of my vehicles as long as it’s not cost-prohibitive. It was a fun project. Really really glad I did not start with a worn out 307 and then spent a thousand bucks at a machine shop!
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2,286 Posts
I would put a factory intake/Q-jet on it and leave the rest be.
Back in the day, 68 Nova, 307 2bbl, powerglide, 3.08s
put in a 427, th400, 3000 stall, and 12-bolt 4.56
Down the road a bit, 427 developed a bearing issue, the only engine left at the house was the original 307.
the stock heads are big chamber, cr 9:1 on a good day.
Then the trick was 327 camel hump heads with spring upgrade, put these atop a .040" rebuild, now had 10:1 cr, like the period "good' engines. Had a b bbl intake and Q-jet off a 71 engine. iSKY was minutes away, Told them the combo, they gave me a 216/216 .450/.450 cam.
She ran sweet, made a little noise for the burger stand bunch,
smaller headers, good dual exhaust, distributor work, better heads like 305HO. so many good take-off heads available with the LS engine craze, the smaller the chamber, the better
basic hotrod stuff, gearing (via transmission and/or diff), some weight removal, then put the power to the ground.
For sure, the Nova's light weight, the converter and 4.56 played a part and my 312 ci SBC did the rest, good package. Quite a few folks with 'all engine' or smogger 350s got stomped
put in a 427, th400, 3000 stall, and 12-bolt 4.56
Down the road a bit, 427 developed a bearing issue, the only engine left at the house was the original 307.
the stock heads are big chamber, cr 9:1 on a good day.
Then the trick was 327 camel hump heads with spring upgrade, put these atop a .040" rebuild, now had 10:1 cr, like the period "good' engines. Had a b bbl intake and Q-jet off a 71 engine. iSKY was minutes away, Told them the combo, they gave me a 216/216 .450/.450 cam.
She ran sweet, made a little noise for the burger stand bunch,
smaller headers, good dual exhaust, distributor work, better heads like 305HO. so many good take-off heads available with the LS engine craze, the smaller the chamber, the better
basic hotrod stuff, gearing (via transmission and/or diff), some weight removal, then put the power to the ground.
For sure, the Nova's light weight, the converter and 4.56 played a part and my 312 ci SBC did the rest, good package. Quite a few folks with 'all engine' or smogger 350s got stomped
since we're still at it here, re-read post #12. carefully. My 70 Malibu was a 307/TH350. best thing I ever did was pull the 307 while it still ran OK and sold it. Any decent 350 will feel like two 307s. They just don't run good. A 4-bbl 305 will run better than a 307.
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4,769 Posts
Pull it and run a low compression 454...
My 69 Elco has a stock 78 454 that has plies of torque and is such a blast to drive. Then you can run a 2 series hi-way rear end with a Turbo 400 and have your cake and eat it too.. My 69 gets around 15 mpg on 87 octane..
My 69 Elco has a stock 78 454 that has plies of torque and is such a blast to drive. Then you can run a 2 series hi-way rear end with a Turbo 400 and have your cake and eat it too.. My 69 gets around 15 mpg on 87 octane..
given the same heads, I'd pick a 307 over a 305 any day of the week; a bit less low end torque but just a nicer bigger bore for breathing. I also like the Pull the 307, stash it, and drop in a 454. Been there! Especially nice if you get a donor 454 with a car oil pan and earlier heads. Ideal is a 70 454 donor
Joined
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74 Posts
I know what you're going to hear from these guys because I asked the same question months ago. My father bought my 70 Malibu in '72. I was 13 and remember sleeping under a blanket on the back seat when he and Mom went out riding. New original paint color, original drive train, original vinyl, etc. I want a little more power but I don't want to change out the engine. Good luck with your dream car!
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