300hp 307

[Maryland G-man]

Yes, I know a Stroker Engine can yield good, usable street horsepower. But that really messes with the Oldsmobile Oversquare Bore/Stroke ratio (1.12 for the Olds 307) that the Engineers intended. And a Stroker means more Piston Ring wear, due to the longer travel, as well as more stress on the Piston, Rod, and Crank as the Piston moves at higher velocities.

I will be quite satisfied if my 307 will put out comparable horsepower to the Buick Turbo 3.8 liter V-6, which was 245 hp (advertised). The Grand National was fast enough, if you keep the factory brake and suspension setup. There is a apparently some data showing these V-6 engines produced up to 270 hp. But I would rather have 250 naturally aspirated horsepower, than 270 turbo horsepower.

If you starting packing these G-bodies with lots of horsepower, you really need to start upgrading other aspects of the car. Like, bigger brakes (which means you need to change to 17 inch wheels). Then, coil-over suspension at all four corners. Then frame stiffening. Before you know it, you really take the car far away from originality. I would consider doing this to a "rescue" G-body (like a plain Cutlass, Monte Carlo, or Regal), but not one of the rare, limited editions.

 

[Maryland G-man]

I hope most of you fine folks have seen this excellent article from Mondello on what can be done with the 307 engine. The article mentions the magic "over 307 horsepower" figure, if the engine is "off the computer".

They mention a 75 hp gain "attached to the computer". That means 180 hp stock + 75 hp = 255 hp. +75 hp represents a whopping 42% gain over stock. I would probably lose a good bit of that, if keeping the Exhaust Manifolds, stock Intake Manifold, Catalytic Converter, etc.

I am willing to pay the price for that.

Please see attached .pdf file.

 

[69hurstolds]

If you don't uncork the stock exhaust, to which you couldn't pass an emissions test at that point anyway, you will never see 300+ HP and emissions compatibility from a 307. And I doubt you could get to 250 even. This is why an Olds 350 or 403 is a WAY better starting point for just tossing all that out the window and doing what needs to be done, like headers, dual exhaust and better intake system, etc. The main issue was Olds was taking the old school V8 and trying to put it on a computer and passing emissions standards of the day. Never a small task even for the deep pockets.

Not saying it couldn't ever be done, but you better know what you're doing and of course, have money to throw at it. It's another one of those, "maybe you could, but why would you?" situations.

 

[OldsZZ383]

I inherited my father's 1983 307 4 door Cutlass Supreme Brougham which was custom ordered. It was a dog with a 2.19 rear end. I made the error of installing a very nice fully rebuilt Olds 350 with probably 300+ horsepower. It still remained a dog. Moral of the story: whatever you do with your 307, change the rear end to at least a 3.42 or 3.55 to get it moving. The transmission will take care of the low rpm cruising in 4th or Over Drive...

 

[DRIVEN]

If you don't uncork the stock exhaust, to which you couldn't pass an emissions test at that point anyway, you will never see 300+ HP and emissions compatibility from a 307.

After ditching the cat and running 2 1/4" duals through a Walker GN replacement muffler (legal where I live), I gained a second and 6mph in the quarter. I touched nothing ahead of the manifold flanges. 100% stock 305.

I still maintain that 1hp/cid is possible, but it's all about breathing. And you might not be legal, depending on where you live.

 

[78Delta88]

Realistically it can be done I'm sure, but just no support for the 307. It was designed as a zero to 55 mph engine. I have several so the best I can go for is mild cam throaty sound and realize it will never be in burnout contest.

 

[Maryland G-man]

Folks, great input from all that have contributed to this topic so far. I remain committed to keeping the stock 307 engine in my 1984 Hurst/Olds, but am willing to change some internal and external components for a MODEST increase in horsepower.

The Chevrolet 305 LB9 ("Tuned Port Injection") engine of the late 1980's managed to achieve 230 hp. And it was constrained by EPA Fuel Economy and Emissions standards, as well as GM's own durability/longevity requirements to avoid warranty claims.

A good engine builder, without those fuel economy, emissions, and longevity constraints, could probably easily get 230 hp (or 230+) out of the 307. That extra 50 hp is a 28% improvement over stock, to a car that I am already quite pleased with to just accelerate around the suburbs and effortlessly pin the 85 mph speedometer on the highway.

I just sold a 1971 Plymouth Duster 340. After buying the complete car in decent condition, I paid an engine builder about $ 10k to get its engine to 400 hp. But then I spent many tens of thousands of dollars just upgrading the rest of the car, to deal with that power:

• Frame stiffeners, welded on
• Coil-over shocks at all 4 corners
• Rear 4-link suspension (replacing leaf springs)
• Larger diameter Anti-sway bars
• Rack and Pinion steering
• Enhanced cooling
• Updated transmission, driveshaft, and rear axle
• Oversized wheels and tires (295 mm wide Goodrich Radial T/A in rear)
• Wildwood multi-piston disk brakes
• Long tube ceramic coated headers, X-pipe, and high flow mufflers

So, after spending MANY more thousands of dollars than the engine upgrade alone, I had a resulting car that was actually less pleasant to drive (vibrating, shaking, and so loud I needed earplugs). Not that I do things to impress people, but most just said "gee, you really deviated from stock a lot" rather than "what a high performance car". I ended up selling the car, at a HUGE loss. I do not plan to repeat the same mistake with my Olds. That's my story and I am sticking with it. 😀

A wise person on this Forum told me early on after buying a low mileage, original 1984 Hurst Olds to be very "circumspect" about changing it. I am following that sage advice.

 

[Rocknrod]

If your looking to stay Oldsmobile why not install a 350 Olds engine with FI and be done with it? - https://www.sandjengines.com/product/1970~~~3309

 

[Clone TIE Pilot]

Folks, great input from all that have contributed to this topic so far. I remain committed to keeping the stock 307 engine in my 1984 Hurst/Olds, but am willing to change some internal and external components for a MODEST increase in horsepower.

The Chevrolet 305 LB9 ("Tuned Port Injection") engine of the late 1980's managed to achieve 230 hp. And it was constrained by EPA Fuel Economy and Emissions standards, as well as GM's own durability/longevity requirements to avoid warranty claims.

A good engine builder, without those fuel economy, emissions, and longevity constraints, could probably easily get 230 hp (or 230+) out of the 307. That extra 50 hp is a 28% improvement over stock, to a car that I am already quite pleased with to just accelerate around the suburbs and effortlessly pin the 85 mph speedometer on the highway.

I just sold a 1971 Plymouth Duster 340. After buying the complete car in decent condition, I paid an engine builder about $ 10k to get its engine to 400 hp. But then I spent many tens of thousands of dollars just upgrading the rest of the car, to deal with that power:

• Frame stiffeners, welded on
• Coil-over shocks at all 4 corners
• Rear 4-link suspension (replacing leaf springs)
• Larger diameter Anti-sway bars
• Rack and Pinion steering
• Enhanced cooling
• Updated transmission, driveshaft, and rear axle
• Oversized wheels and tires (295 mm wide Goodrich Radial T/A in rear)
• Wildwood multi-piston disk brakes
• Long tube ceramic coated headers, X-pipe, and high flow mufflers

So, after spending MANY more thousands of dollars than the engine upgrade alone, I had a resulting car that was actually less pleasant to drive (vibrating, shaking, and so loud I needed earplugs). Not that I do things to impress people, but most just said "gee, you really deviated from stock a lot" rather than "what a high performance car". I ended up selling the car, at a HUGE loss. I do not plan to repeat the same mistake with my Olds. That's my story and I am sticking with it. 😀

A wise person on this Forum told me early on after buying a low mileage, original 1984 Hurst Olds to be very "circumspect" about changing it. I am following that sage advice.

Keep in mind that even Chevy 305s have higher airflow than Olds 307s. Its why 305 Qjets have idle air bypass to prevent nozzle drip and Olds 307 Qjets don't. So its comparing apples to oranges.

 

[olds307 and 403]

Problem is you have at best 8.5 to 1, restrictive heads and very restrictive exhaust. A chassis dyno would be handy for a starting and where it ends up after mods. Extrude hone and hand port the openings on the exhaust manifolds. The largest crossover, maybe a 2.25" versus 2" or at least mandrel bent and maybe a 3" down pipe and into either a custom, Hooker or Pypes 2.5" catback to remain visual and emissions complaint. Internally milled 5A heads with 350's valves and porting, a hotter cam would get you a nice boost. The dyno before and after would tell you how much.