I get a lot of people asking me for suggestions to spice up their little 307's, so I thought I'd write it down here. The 307 is a good engine--reliable, decent gas mileage, easy to find parts for, and it comes with a 4-bbl Quadrajet!
Some of the recommendations are from personal experience, some have been recommended by others, all have been tested and proven. Your mileage may vary, perform any modifications at your own risk, wash dark colors separately, and all that other standard disclaimer type stuff.
First off, it depends on what version of the 307 you have. It comes in several flavors.
- VIN Y. About 140hp and 235ft-lbs (depends upon year and where you get your info). Unless you have an H/O or 442, you have this engine.
- VIN 9. About 180hp and 245ft-lbs (again, stats vary). Only available on the '83-'84 Hurst/Olds and '85-'87 442. I've heard rumors that a few Caddilacs had these too.
Now, to thoroughly confuse you, Olds made two different version of each of these engines. Up through Mid-85, 307's had normal 5A cylinder heads and normal hydraulic flat-tappet lifters. In Mid-85, GM changed over to a 307 with 7A cylinder heads and a hydraulic roller-lifter drivetrain. The 5A heads seemed to appear for a while after '85 in the VIN 9 engine, but there are 7A headded VIN 9 engines too. To see which version you have, look for the number on the front of each cylinder head. Follow the negative battery cable to where it attaches to the head, right next to it you'll see the raised number and letter.
The 5A head engine is preferred for performance use because it has "normal" sized ports in the intake and cylinder heads. 7A head engines have tiny ports in the intake and heads (and exhaust ports too, but the manifolds are the same) designed to work in conjunction with the roller lifters. This is why an Edelbrock performer intake will not fit 7A head engines. (Actually it will physically FIT, but there would be an awful port mismatch causing reversion and you would be very unhappy).
Now, on to the modifications! First off, let me state the goal and make sure you don't have any unrealistic expectations. Unless you throw thousands and thousands of dollars at a 307, you will not be able to go out and eat Z-28 Camaros for breakfast and stock Big Blocks for lunch. If your goal is that kind of power level, your money is best spent on a larger engine. Call it what you want, "Return on investment", "Bang for the buck", "HP per $$", etc. But swapping in an Olds 350, 403, 425 or 455 would get you where you want to go most efficiently. The 350 and 403 are the same block externally, so all accessories will bolt up, the computer will work (if you keep the cam mild), and nobody will be able to tell the difference unless they check the numbers. A 425 or 455 Big Block will fit right in, but is a bit more of a project and won't be covered here.
The goal here is to have a reliable and streetable car, that's a pleasure to drive in traffic, meets emissions, and keeps the stock computer while delivering as much power as possible while keeping all the creature comforts (A/C, heater, cruise, etc) without crossing that dollar and effort line where you could have just as well put in the 350 or 403. Ride and handling will be addressed also, where obtainable on a budget.
Step One, get it running right!
Before you start with any mods, you need a smooth running baseline engine to start from. You may be able to do some of these at the same time as other modifications (such as putting in the new thermostat while you have the engine drained to flush it).
- Dump any error codes stored in the computer and fix any problems indicated (this may be nothing, or it may be a big task, depends on how well your car has survived the test of time).
- Change the oil if it's due, and the filter too. I use Mobil-1 10w30 and AC PF-24 filters (they're a bit larger than the stock filter). I'll put in one or two quarts of Mobil-1 15w50 during hot weather.
- Replace the air filter, fuel filter, crankcase filter, and PCV valve.
- Check the belts and hoses. If they look marginal, replace them.
- Flush the cooling system and fill with a 50-50 mix of quality antifreeze/distilled water. If you're in a climate where it never freezes, you can use 30% antifreeze.
- Change the tranny fluid and filter. This is a messy job and I find it worth the money to let a professional do it. If you do it yourself, it may be a good idea to put in a drain plug when you have the tranny pan off.
- Change the differential fluid, or at least check the level. This doesn't need to be changed more than maybe every 50k miles, and if you do change it (or have it changed with your tranny fluid), switch to a synthetic lubricant.
- New distributor cap and rotor (use the kind with the brass terminals, they last much longer than the aluminum ones).
- New plugs and wires. I've had best luck with stock AC plugs. AC just discontinued the R46-SX plug so if you can't find any, you may have to use another brand. I hear that the R46-SZ is the exact same plug, but pre-gapped at 0.060, worth checking out! My second choice is NGK. Gap them at 0.060 rather than the stock 0.080 (too much!). I prefer the "universal" wire kits that you cut to length yourself, since the precut ones are always too long or too short and look terrible.
- Set the TPS (Throttle Position Sensor) to stock values.
- Set the timing to stock (20 degrees on every 307 I've seen).
- Set the idle mixture using a dwell meter (if it's idling good, you can skip this step).
- If you have an overdrive tranny (TH-200-R4), adjust the TV cable to factory specs.
- If your O2 sensor is more than 50-70,000 miles old, replace it. Only use a real GM AC-Delco sensor. The Bosch sensors have caused rough idle and surging problems for me and other people.
Now you've got a smooth running 307 that you can feel confident in taking anywhere!
Stage I: Tuning and cheapo-mods (under $100 total)
- Advance the timing by 2 degrees (to 22 degrees). This may require the use of 89 or 92 octane fuel to prevent pinging. But if you wanna play, you gotta pay. For track-only use you can advance it 4 or 6 degrees, but this makes the car hard to start, and it idles rough.
- Adjust the secondary air valve spring tension (wrap). On the top rear passenger side of the carb, you'll see a small hex-screw underneath and a small slotted screw on the side. Loosen the hex screw with an allen wrench, and turn the slotted screw out 1/8 turn (hold it as you loosen the hex set-screw) and re-tighten the hex screw. Repeat until you notice a bog when going to WOT, then tighten back up 1/8th turn.
- If you have a 200-R4 tranny, push the TV cable back (tighter) one click.
- Install a Robertshaw or Mr. Gasket 180 degree high-flow thermostat. 160 is too cold and could possibly set computer error codes. 180 degrees is a nice compromise, and the high-flow keeps it rock-steady at 180 degrees under all conditions.
- Add Red Line Water Wetter to the cooling system. All I can say is It really works!
- Fabricate a cold-air intake system for your car. Using dryer ducting or the stock stuff, get cold air to the air cleaner. Make sure you keep the hot-air riser tube or cold weather driveability will suffer. If you have a dual-snorkel air cleaner, wire the second snorkel to open when the first does (use a vacuum T) and get fresh air to it. At the track (or even when the weather is warm) just disconnect and plug the hose to the second snorkel, so it's open all the time. Good places for fresh air are hard to find on these cars, but you can use the hole behind the passenger's side headlights, in the fender up there, or go underneath the radiator support.
- Get a K&N air filter to replace the stock one. K&N DOES make one, you might need to supply your speed shop guy with the AC filter part number to cross reference by, rather than by application.
- If you have a single exhuast (and not the duals provided with H/O's and 442's), then replace the single muffler with a turbo style muffler. Hollowing out the catalytic converter would provide a benefit too, but since most areas check emissions now, and since it would be illegal, I wouldn't recommend it, and I wouldn't do anything like that myself.
- Get some richer secondary metering rods. The Olds FAQ at http://www.442.com lists some recommended rods under the Rebuilding, Quadrajet section. Only way to find what rods are right for you is by trial and error.
- Check to see that your secondary air valve opens fully. This isn't an issue on the H/O, but on some other 307's it is.
Stage II: A few more bolt-ons (about $500-$600)
- Get a performance computer chip. I recommend having a custom chip made if you can find someone to do it. Try about 8 degrees additional advance (i.e. in addition to that in the stock timing tables) at WOT (plus the 2 more you added to base timing in stage I makes a total of 10). Second choice would be a Thermo-Master chip from Hypertech. These only advance the timing 5-6 degrees more than the stock chip (and only at WOT) and are very streetable. The Street-Runner version barely advances it enough to notice.
- Add a dual exhaust system. Hooker makes a nice 2.5" system (see mine). Walker makes a 2 1/4" system for about the same price, and the original GM system from the H/O, 442, and GNX is still available from GM for not much more. If you're only running at the track, forget this step and just disconnect your catalytic converter from the exhaust system and run with an open pipe.
- Upgrade the ignition system. Spiral core wires make the biggest improvement (I use Taylor Spiro-Pro). An upgraded coil (like Accel, Hypertech, etc) will also help a little.
- Install a shift-kit in your tranny, and get a tranny cooler. I like the B&M supercooler, it has a low pressure drop and is small. Put it in line before your stock cooler. Braided stainless hose or custom bent hard line is a good idea here.
- Intake. Use an Edelbrock Performer Intake. Can't use this with 7A heads. It bolts into place, but attaching everything back up isn't exactly bolt-on. You'll need to move some sensors, get a few pipe-adaptors, modify the throttle cable and TV cable bracket, and bend up a custom cruise control linkage. You will need to re-adjust the secondary air valve, idle mixture, and secondary metering rods after installing this. Be sure to use a 4-hole carb gasket and not the stock 2-hole one or you'll defeat the point behind a dual-plane manifold.
- optional Partially or completely block off one or both of the heat crossover passages from the head to the intake. A piece of stainless sheet metal from your old "turkey tray" intake gasket will work, with a hole drilled in the center to allow a little air through. If you completely block them off, you'll need to convert to an electric choke. The colder of a climate you live in, the more "optional" this step is.
- Posi. If you don't have a limited slip differential, now's the time to get one. I found a new GM unit, but Auburn also makes ones that will fit.
- Gears. Upgrade to somewhere in the 3.23-3.73:1 range. 3.73's are liveable with the OD tranny, but if you do a lot of driving at 70+mph, consider something in the lower 3's. Don't forget to recalibrate your speedo!
- OD tranny. If you don't have one, get one. Try to find a core from a 442, H/O, GN, T-Type, or Monte SS. Give it a good rebuild with a quality kit. Some kit and rebuilder recommendations can be found on the GN/T-Type home page at http://ni.umd.edu/gnttype/www.
- High-stall converter. About a 2400 rpm lockup converter should do nicely. These are stock on the 442's and H/O's.
- MSD-6 (or 6AL) system. Doesn't help power too much, but the car starts easier, idles better, and the power comes on smoother all around. You'll need cooler plugs with this, like the NGK 5670-6 plugs gapped at 0.040.
- Cam swap. If you've got a VIN Y engine, you can swap in a more radical cam like that used in the VIN 9 engine. Don't go too radical though or the computer and emissions won't like it. You could contact somone like Joe Mondello or Dick Miller to see what they recommend. Remember to get a roller-lifter cam if you've got a roller-lifter engine. Install stiffer valve springs like on the VIN 9 engine at the same time. I also recommend replacing the timing chain or putting on a true roller chain while you have it apart.
Pull your 307 engine. Find a 350 or 403 engine and swap it in place. Paint it satin black and nobody will ever know. You should be able to keep most of your previous modifications. I recommend looking at the Olds Faq at http://www.442.com to help decide what block and cylinder heads you should use.
Ride and Handling:
I'd do this step sometime between stage I and II.
- If you have the factory air shocks on the rear of your H/O or 442, remove them. But keep all the hardware just in case you ever want to go back.
- Install new gas shocks all around. Bilstein or Koni for the ultimate handling and performance, KYB for bargain performance, or Monroe or Gabriel for the best ride and better than stock performance.
- Install Air Lift air bags in the rear springs. These have two functions. 1) Pre-load the right rear tire for better traction when racing (fill the right side to 15-20psi, empty the left) 2) Level out the back end when carrying cargo.
- Get some 15x7" wheels (stock on the H/O and 442) and install 235/60R15 tires (or whatever aspect it takes to keep your speedo accurate). 16x8" wheels can be made to fit if you choose carefully.
- Install polygraphite sway-bar bushings.
- Performance Friction Z-Rated carbon-metallic brake pads are a great improvement over the stock brakes.
Headers. The only maker for headers for a G-body with a 307 is Heddman. They are of marginal fit and quality and I wouldn't want to have to put up with them on a daily driver. Also, you'd have to have custom duals bent up, would have to do something about the tranny crossover on the driver's side, would have to lose your cat or get two, and would have to have a bung welded in for the O2 sensor.
Removing the A.I.R. pump. It doesn't take a significant amount of horsepower to run, and removing it will cause a rough idle and incorrect [lean] air/fuel mixture since the computer is expecting to see the added oxygen at the O2 sensor from the fresh air pumped in.
Mounting your tranny cooler in front of the radiator. Can cause the car to run hot on hot days. Try putting it off to the side, or behind the passenger's side headlights (maybe put a small electric fan on it to be really trick!). Also don't put the cooler after the stock cooler, put it before. This way your tranny fluid won't get too cold on winter days.
Nitrous. The windowed main webs and cast pistons on the stock engine probably won't take it for long, although I know someone who's still using a 150hp kit and hasn't damaged it yet. Besides, Nitrous isn't for driving around town with. It gets expensive, you can't leave the bottle open all the time, and you run the risk of destroying your engine if you get nitrous in there at idle, or without the proper fuel.
Electric fan. A nice idea in theory, and may be beneficial for drag racing, but I have yet to see one that will fit these cars and can keep it cool on a hot day in heavy traffic as well as a good old belt driven fan does.
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