Carburetor Tuning & Reader Questions - Performance Q&A

Kevin McClelland Jan 1, 2010 0 Comment(s)

Whoa, Baby
Q: I am the luckiest man in the world. My wife is just as big a car nut as I am. (You've got to love a woman who's actually happy to get a carburetor for her birthday.) We have a few old Camaros, a couple of '68s, a '69, and a '72. My wife got me into drag racing a few years ago; she drives and I get to make the car go faster with her '81 Camaro. We run 6.50s in the 1/8-mile. Although the car still isn't fast enough for her, she can hardly get it stopped at the big end of the track. No vacuum means no power brakes! Does anyone make a kit that I can convert this power-brake car into a manual-brake car? Or what would be the easiest and least expensive way to make this thing easier to stop?
Steve Burch
Harvest, AL

A: Getting our wives' support for our habit is a blessing. My mom warned my wife before we got married that I wasn't going to change-and I haven't. Enjoy racing with your best friend. Let's see if we can keep her safe.

A couple of things jump out with your question. First, you're right that the vacuum level is quite low because of the camshaft you are running. This should only affect the brakes' operation when idling around, or from a fresh startup. When you're lifting off the throttle at the top end, the engine vacuum goes very high (20 plus inches of mercury) and the power brakes should function normally. If they are not, look to the booster's condition and the check valve in the booster line from the carburetor. The check valve is to hold vacuum in the booster when the vacuum falls, to give you at least one good brake application.

Manual brakes were standard on your '81 Camaro, but very rare. It used a smaller master cylinder diameter and a specific pedal pushrod to give you the proper pedal ratio and brake pressure. You could try to round up these components and convert the car over with factory parts. The master is discontinued, as is the pedal pushrod. You could also go with a vacuum booster pump to increase the vacuum supply to the booster. There are some very nice pumps on the market and may be the cheapest option. Check with Master Power Brakes for all your brake needs. MPB offers a very nice Heavy Duty Vacuum Pump kit, PN AC2724K, which will produce a constant 18-20 inches of vacuum. This kit comes complete with pump and vacuum switch to turn the pump on only when needed. Also, if you still wish to convert the brake system over to manual, MPB can hook you up with the components to make this happen.

Get these brakes working soon-you don't want one of your wife's legs to be bigger than yours! Good luck, and be safe racing.


Q: Do you know if the '67-69 Camaro Z/28 302 motor was a bored-out 283 or a destroked 327 (283 crank used in the 327)? Thanks for your time!
Daryl Lange
Oroville, WA

A: The last year of the 283s comes in right at '67, which is the first year of the 302 small-journal engines. The 327s had been around since the '62 model year in Vettes and Impalas. Sliding a 3-inch stroke crankshaft into the 327 is the simple answer. Most of the 283s won't accommodate a 4-inch overbore without the cylinders becoming dangerously thin. Only some of the early blocks could handle a 4-inch overbore, and it certainly wasn't into the late '60s. The tops for most of the 283s were 0.060 inch over, bringing the engine to 292 inches. We know this isn't a definite answer, but it makes sense logically.

Sensor Madness
Q: Can you help me install a '95 Z28 engine in my '96 Impala? The '96 has a crank sensor behind the harmonic balancer, and the '95 does not. Using the '96 harness and computer, can I trick the '96 sensor plug and computer by grounding off one of the wires coming from the sensor? Thanks for your help.
Cliff Blacke
Piqua, OH

A: The sensor you're referring to references engine misfire for the OBD II computer system mandated in 1996. There is a small reluctor wheel behind the front cover that gives the sensor a 4X signal to the computer. With the differences in the water pump and damper between the Camaro dress and the B-car Impala, it would be easiest to just swap over the front cover, sensor, and reluctor wheel into the '95 engine. This would make the computer happiest and complete the swap properly.

When converting over the '95 engine, make sure you use the damper hub from the '96 engine because it's 0.100 inch shorter to accommodate the reluctor wheel spacing. Also, you'll need to swap out the Woodruff key that indexes the crank sprocket. The Woodruff key is slightly longer (0.100 inch) to engage the reluctor wheel.

Fooling the computer is really not an option without tuning software. You can disable the misfire detection with calibration software, but a little more labor will make this a painless swap.

Stovebolt Racer
Q: I've been trying to find drawings showing the hole locations and sizes, center hole size, for various bellhousings and transmissions. I need to machine a trans adapter. We just finished building a 261 (0.060 over) inline-six for my '50 Chevy station wagon. I'm putting a T5 from an S-10, and an S-10 4x4 rearend with 4.10:1 gears in it. Isky ground a custom cam for more low-end torque for this heavier-than-average car.

Yeah, I'm a geezer, but I also help with tuning an NHRA TAFC and race go-karts during our Minnesota winters, so I'm not done yet. I realize this question probably doesn't fit the column, but I thought you can probably steer me to the info I need. Thanks for any help.
Darryl Bergerson
Prior Lake, MN

A: From most of the digging around we couldn't find an adapter plate available for your combination. Surprisingly, Advanced Adapters no longer lists this swap. Surely it had this adapter available in the past, but it's been 45 years since the last time the old Stovebolt six-cylinders were produced. But we've found something else.

The factory 261 manual transmission bellhousing has the same bolt pattern as the mid-'80s T-5 transmission! The input shaft is slightly longer than the three- and four-speed transmissions of the day, and it is a standard 27-spline shaft. Even the pilot bushing stub is the same size. You may need to shorten the pilot bushing stub of the input shaft slightly with a cut-off wheel and dress it with a sanding disk. You will need to check for clearance to prevent the input from bottoming out in the crankshaft. Next, drill out the transmission ears to accommodate the 1/2-inch bolt from the 13mm fasteners used in the later-model applications. The rest is just simple bolt-ups and driveshaft shortening. The original clutch, throwout fork, throwout bearing, and pilot bushing will work. You will need to pick up a clutch disk from a '71-and-later manual application with the 27-inch spline count. Just match the pressure plate size that you have.

Good luck with your very cool '50 wagon. My dad is going to be jealous. He's about half done with his '50 sedan delivery but has too many projects going on to finish it.

Serpentine Solutions
Q: A while back in "Performance Q&A," you talked about a company that puts together GM serpentine kits for crate engines. Could you please give me the name and how to get a hold of them? My son gets your rag and since it's my mailbox, I get to read the Performance Q&A first. Thank you very much.
Bob Bussworth
Avoca, NE

A: We're glad to see your son has good taste-and that you've got quick hands. He should learn that age and treachery will win out over youth and enthusiasm every time.

Our buddy Ken Casey at Burt Chevy is the hookup for factory GM Serpentine kits. He has sold a ton of GM crate engines and the components to make any swap easy and free of surprises. If he hasn't seen it all, we're just a phone call away. You can reach Kenny at 800.345.5744 and he will be glad to help you out.


Technical questions for Kevin McClelland can be sent to him at


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