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Old 05-01-2008, 07:14 AM
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307 bbl olds performace

I have an 86 olds cutlass supreme and my goal is to have some good power and mean look. My plan is to replace the stock heads with 400 bbl olds heads, custom 2-1/2 dual exauhst, edelbrook 650 cfm AVS carb with performer intake, and 3.73 gears (posi). My rough estamate on power production is 220hp to 240hp. Dose anyone have an idea if my estamate is good, or pointers for work.

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Old 05-01-2008, 08:08 AM
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If it were mine I'd dump the Olds motor for a sbc. There is sooo much more available for the sbc. I have done a few Olds motors of that type and only ever put about 214* dur and a dual plane (?2701?) for a little bit of oomph. What difference in the heads you plan on using to what is in there now? The 307, IMHO, is much like the 305, it'll work, but I don't see many of them being modified too awful much.
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Old 05-01-2008, 08:56 AM
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Quote:
Originally Posted by montecutlass86
I have an 86 olds cutlass supreme and my goal is to have some good power and mean look. My plan is to replace the stock heads with 400 bbl olds heads, custom 2-1/2 dual exauhst, edelbrook 650 cfm AVS carb with performer intake, and 3.73 gears (posi). My rough estamate on power production is 220hp to 240hp. Dose anyone have an idea if my estamate is good, or pointers for work.
First, please resist the pressure to use a belly-button SBC.

Second, the 307 is not one of Oldsmobile's better engines, however it can make up to 300 hp without too much trouble. The problem is that your 86 motor has the roller cam and tiny ports in the heads. The roller cam means that you have 0.921" lifter bores instead of the normal 0.842" bores. You can get larger lifters, but they cost more. I'm not sure what you mean by "400 bbl" heads. Olds has two engine families, the small block and big block. The main difference is the deck height, but while big block heads will physically bolt to the small block, the ports are much larger. Your 307 will never flow enough air to use those ports.

Your best bet for a budget buildup is to use the #4, 5, 6, or 7 heads from a 64-67 Olds 330 or 68-70 Olds 350. These bolt to the 307 with the exception that the 307 uses larger head bolts. A machine shop can easily open the bolt holes in the early heads to match. Use an intake with smallish runners. If you're cash limited, the Olds A4 intake used on the 80-84 307s is a good choice. A Performer is better. I doubt that motor will be able to use a Performer RPM. I like the Qjet, but other carbs will work. Olds exhaust ports are horrible, so spending a few dollars getting those reworked will reap big benefits. Your 86 probably has the crappy stainless welded log manifolds. At a minimum get the earlier cast iron exhaust manifolds, though headers are much better. The 2.5" exhaust is a good choice. Pick a good dual pattern cam and 250 hp should be a very reasonable goal. I assume you do not have emissions testing where you live, as these changes are grounds for failure.
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Old 05-01-2008, 01:54 PM
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the 307 i have is a big block, and 400 big block Buick heads have a larger combustion chamber. plus the mount pattern and intake will both work for what i want. the state i live in dose have emission laws, but my smoke is not tested, I only have to retain the cats and mufflers. this project is a complete custom and with what i'm doing will remain street legal.
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Old 05-01-2008, 02:47 PM
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Quote:
Originally Posted by montecutlass86
the 307 i have is a big block,...
Not if it's an Olds motor

Quote:
...and 400 big block Buick heads have a larger combustion chamber. plus the mount pattern and intake will both work for what i want
Buick heads won't bolt to an Olds block. Buick, Olds, Pontiac, and Chevy all built completely different motors with similar displacements but no interchangeable parts.

By the way, a larger combustion chamber will further lower the already low compression on that 307.
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Old 05-01-2008, 02:54 PM
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Makes the sbc soo inviting...
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Old 05-01-2008, 04:07 PM
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No offense, but if that is the extent of your knowledge, then I would suggest learning far more before you dive in it. The 307 olds is a good work horse engine, but its not much of a performance engine. I took the one out of my 86 cutlass and threw in a SBC. There are several articles on the 307 Olds, if it were I and I was gonna stay olds powered, I would go with a 350 Olds before I wasted my time on a 307. The biggest draw back to these cars was they came with really high rear end gears, mine had a 2.14:1 rear gear which is horrible, it took it way too long to accelerate. I swapped a posi unit in removed from a 83 firebird with 3:23 gears which was a big improvement.
As mentioned, if you swapped on 350 olds heads you still have to consider the combustion chamber size, if they are larger, then it lowers compression, which kills power. 9.5:1 is about the limit on a street engine on pump 93 octane gas. You will also have to check if the valves will clear the smaller 307 bore. Read this article carefully, it will teach you alot.
http://www.442.com/oldsfaq/ofe307.htm
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Old 05-01-2008, 05:42 PM
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Let's take a step back from the oldsmobile, shall we?

BBO and SBO only really differ in block height. Many people consider that there is no such thing as a BBO or a SBO, but I do given the obvious differences.

You have to use Olds heads on an Olds engine. Period. The Buick is a whole different critter.

The stock compression on your 86 307 is 7.8:1 with a stock HP rating of 140. The last thing you want to do is lower compression with larger chambers. Get some 5A heads (literally almost double the port size) and shave them down a bit to get closer to 9:1. Then (and only then) can you adequately support the cam that would support 240 hp.

The 307 Olds is a small block.
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