300hp 307

[olds307 and 403]

Edelbrock heads will work on a 307, no different than a 68-69 G block 400 that has a stock bore size 3.870.

Yeah, they might just clear but the combustion was set up for 4" bore spacing. Supposedly the 307 have pretty thick cylinder. Dale Robinson figured many could go .200" overbore. The new 68cc head isn't released yet, . The new BBO will hit bore, 4.125" bore minimum. Procomp might squeeze on but most are 80ish CC. Which would only need a 10cc dish piston for 9 to 1 with 4" stroke.

Oldsmobile 307 Engine - Analyze This! - Popular Hot Rodding Magazine

Read about the Oldsmobile 307 Engine and see pictures as it gets built under an impossibly small budget with an Edelbrock Performer RPM intake manifold, Ross custom pistons, and MSD ignition, inside Popular Hot Rodding Magazine.

www.motortrend.com

Are aftermarket olds heads not an option anymore?

But then again, to do all that wouldn't you start with a 350 block?
Is this something your seriously considering?

Maybe if I found a mint HO or 442, I love to be different. It would have ridiculous torque. Of course the big bore Olds 350 version is an easy 400+HP and 500+ ft/lbs of torque and would not only more powerful but stronger. FYI, the new stroker cranks are lighter than the 330 cranks, probably pretty similar to iron cranks in weight. Their light weight and stiffness would help a flimsy 307 block survive.

 

[Clone TIE Pilot]

I watch goalposts. It's what I do.

300 is very doable with a pocket full of $$. It's just doubtful you can do it and STILL maintain a scrutinous application of the emissions part of the deal. In otherwords, while you may pass the sniff test with dual cats and exhaust, which will give the 307 a tad of spinach, you're very likely going to fail a visual right out of the gate. You can still run the old ECM with just one O2 sensor and get the proper feedback for the carb and such. Probably. While it's good to think about ways to maximize power and efficiency, it's a lot tougher starting with a 307 to get there.

In NJ, they drive cars right over an in floor video camera to get a nice clear view of the underbody. Dual exhaust, even with dual cats is just plain illegal in G bodies in all 50 states simply because GM never offered it as a factory option. Cat convertors need a minimum amount of exhaust and dual cats each only get half the heat from single banks. I am not sure if only OEMs are allowed to develop legal dual exhausts or if aftermarket can too if they are willing to front expensive CARB/EPA testing to get EO numbers?

 

[john87442]

Ohio has these emission regs depending on the county and since the car is over 25 years old I can do whenever I want as long as I get historical plates. That’s why I opted for the 350 build from a 69 olds cutlass #5 heads getting the work over and roller cam& lifters shooting for around 400 hp. Was going to wait for the edelbrock sb olds heads to come out but who know when that’s going to happen. I’m keeping the original 307 just because it makes me feel good as I look at it in the corner of the garage but for fun on the weekends it just didn’t make sense. My build will probably be come in around 5500. 00.

 

[olds307 and 403]

Good question on the legality of even the available systems. The Hooker or Pypes would work but aren't exactly direct replacement but none are, other than custom. I noticed a nice difference between the single exhaust and the Hooker set up on my 88. I would get a large as possible mandrel bent down pipe into a 3" cat and get a large a possible crossover pipe as possible. Also extrude hone cast iron manifolds with the ports opened as big as possible. Probably only a few HP/TQ gained but better than nothing.

 

[g0thiac]

Now, how about a 307 build to see ridiculous MPG numbers, just to say you have a V8 better on gas than a stock 4 cyl 🤦‍♀️🤣🤣🤣

 

[pagrunt]

I'm starting think cheating is the best way. Just tune it up the best you can on your budget & slap a 300 horse sticker on the air cleaner. Kinda did it on the 350 I'm using in my Monte. Techically it is a 300 horse motor (advertised) & it may have a chance to be near it but I'm riding Chevy's numbers casue the block is stamped for it. I did slap a 350/300 sticker on the air cleaner.

 

[old80cs]

As far as emission testing, in Massachusetts anyhow, the testing stations no longer have the equipment to read tail pipe emissions. That being said, I asked a local shop what they will test this summer (fingers crossed) when I register my '80 and he said it only has to pass Safety with it's age. Visual inspection of suspension, all lights, E-brake, no oil smoke from the tailpipes etc. They don't open the hood.

 

[Maryland G-man]

Regarding the Oldsmobile 307 and horsepower, earlier this year I visited with the good folks at Mondello Performance in California. The 307 can easily achieve the magical threshold of 1 hp per cubic inch, with the following:

• High compression pistons
• Edelbrock Aluminum Cylinder Heads
• Edelbrock Aluminum Intake Manifold
• Hotter Camshaft
• Holley or Edelbrock higher CFM Carburetor
• Tubular Exhaust Headers

So, that gets you to 300+ hp. However, for my 1984 Hurst/Olds, I would dial this back to 230 hp to 250 hp, due to keeping the following:

• Stock Air Cleaner
• Stock Quadrajet Carburetor
• Stock (Aluminum) Intake Manifold (to maintain provision and placement for Cruise Control, etc.)
• Exhaust Manifolds
• Air Pump, EGR, and O2 Sensor
• Single Catalytic Converter
• "Computer"

I have looked into Extrusion Honing the Exhaust Manifolds and the Intake Manifold, which should get back a small amount of horsepower from 100% stock.

A wise sage on this forum admonished me to be "circumspect" about modifying a nearly bone stock and original 1984 Hurst/Olds. Even getting to 230 hp would be a big jump from the stock 180 hp. This would set me back around $ 10k. Worth it to keep this car with a "numbers matching" engine.

Not that I even find the stock 307 all that bad. It starts easily in cold, runs well, smooth and reliable, barely burning oil at 65,000 miles. With the 3.73:1 Rear Axle and the 4-speed automatic, it runs great around town and effortlessly cruises with the 85 mph speedometer pinned.

I own and have owned much higher horsepower cars, yet I find driving the 1984 Olds a delightful experience.

 

[olds307 and 403]

I still say the stroker setup will get a 307 well above this 300 HP goal and look completely stock. You could even keep the 8.5 to 1 compression and just slightly up size the cam. Mark is doing a run in 4340 billet, 4" stroke with sbc rod journals in the $1500 US price range this Spring/Summer.

 

[69hurstolds]

I see where people aren't considering the "while also passing emissions" along with those 300+ HP numbers anymore. Because it WON'T happen. Be thankful if you don't have emissions testing for old cars in your area. Mods are great, but you gotta watch out if you have to pass emission testing as well.