I have a '63 Buick Riviera with a 401ci nailhead V-8 and a Dynaflow two-speed. Can the factory-type points distributor be replaced with a modern electronic-type ignition or an HEI? I would prefer to replace the whole distributor, as the current vacuum advance is not working properly.
Michael S. Carr
Newer Buick V-8 distributors don't fit the nailhead engines, and there are no complete new aftermarket distributors available, as far as we know. Mallory offers both photoelectric-trigger Unilite (PN 501) and magnetic pickup conversion kits (PN 540) for the existing stock distributor. They can be used with stock coils, but the Mallory Promaster (PN 29440) or chrome electronic ignition coil (PN 29216) are recommended for best results. The rectangular-shaped Promaster typically mounts to the firewall or fender; the round chrome coil fits stock coil mounting brackets.
Long Electronics now markets Stinger Products, formerly a product of Midway Industries. The Stinger system comprises an in-distributor high-performance magnetic-impulse trigger that signals a high-performance inductive-discharge external module. Stinger can supply do-it-yourself distributor conversion kits, convert your distributor if you send it to them, or sell you a remanufactured and converted stock GM distributor. This system should be used with Stinger's own coil for best results.
Easily replaced, the Buick vacuum control unit interchanges with most other vacuum units used on "small-cap with window" Delco distributors. The stock replacement vacuum unit for your model year and engine is still available (AC-Delco PN D1328, GM PN 1116163).
1721 N. Lime St
Orange, CA 92865-4115
550 Mallory Way
Carson City, NV 89701-5374
Don't Lean On Me
I have a '76 Chevy Stepside that I've been beefing up and driving for a few years now. It has a Chevy 350 with a better-than-stock cam, a Performer intake, a Carter carb, and Hedman headers. The truck seems to run lean, somewhat missing at the near-idle low end. There is no miss when jamming it or when I put the manual choke on about a quarter of the way. I have replaced the fuel pump (the only thing previously unreplaced) and it still does this. I have done what I can with the idle mixture screws to richen it up, but still can't get it out of the miss.
Also, I have checked the headers for any leaks and bad gaskets. Since I am only 17, the truck has seen its days of traction tests. Anything to go on would be greatly appreciated.
Remove the two small steel caps to access the Carter AFB's primary power pistons. They sho
The usual suspects anytime you have a pesky low-speed miss are vacuum leaks at the intake manifold and hoses, bad plug wires, a cracked distributor cap, or corroded distributor cap terminals. For the Carter AFB carb specifically, check the primary-side power pistons: If they're stuck in the down position, or the springs are weak, there'll be insufficient off-idle enrichment. When the secondaries come in they cover up the problem, which is probably why the truck runs OK when you "jam it."
Well-Read Reader Sees Red in Redding
Every article I've read on installing the 906 Mopar heads on '67-and-earlier big-block Mopars says to mill the heads anywhere from 0.030- to 0.050-inch to retain a decent compression ratio. I don't follow this. That's a big cut! The 906 heads I want to install on my '66 383 engine have about 79.5cc chamber volumes. The piston-to-deck height of the engine is about 0.030 inch and I will use a 0.022-inch compressed-thickness head gasket. Running all this through a compression ratio formula gets me about 9.2:1 compression, which seems fine for today's octane. So why bother to mill the heads at all? Am I missing something here?
The real question is: Do your 906 heads really have only 79.5cc chambers? That figure is the official NHRA-accepted minimum chamber volume for these heads, but in the real world uncut production 906 and similar open-chamber heads come in around 85-90 cc. On a standard 4.25-inch-bore 383, milling 906 heads to their "blueprint" 79.5 cc spec yields about a 9.5:1 compression ratio with the typical "pure flat-top" 383 piston (Federal Mogul L2315F or equivalent) and your specified deck height and head gasket (about 9.7:1 on a 0.030-inch-over 383). On 906 heads, every 0.0042 inch removed from the head deck surface reduces the chamber volume around 1 cc. A "worst-case" 90cc starting chamber volume therefore requires milling 0.0041-inch of material off the head deck. For each 0.010 inch removed from the deck, 0.0123 inch must be removed from the head's intake face to maintain proper intake manifold alignment (0.054-inch total intake-face material removal for the worst-case scenario).
Caddy Lacks Power
I own a '77 Cadillac De Ville powered by a 425 with a Rochester four-barrel carb. It has around 130,000 miles on it, but 110,000 were from my grandfather, who really babied it. My questions are:
1. I've ordered a few Cadillac performance catalogs. Most only offer parts for the 500 and 472, but aren't the 500, 472, 425, and 368 all from the same engine family? So shouldn't most of the parts for the two larger engines fit the smaller ones?
2. I can't seem to find performance suspension parts for the Cadillac. Would equipment meant for fullsize Chevys or Buicks fit my car?
3. Is the Rochester carb worth keeping, or is it only holding me back? (All I know is it's a Rochester Q-jet M4ME.)
I'm not really looking to build this car into a crazy street machine, just improve a daily driver. I'm a starving engineering student, and I have a big daily commute!
1. The 368s had the weird "4-6-8" valvetrain, so they're in a class by themselves. In the 425's case, there's about a 90 percent parts interchange with the 472 and 500 engines. One key part that doesn't directly interchange is the intake manifold. The 472/500 intakes (including the Edelbrock Performer listed as fitting those engines) physically bolt on, but there's an air gap because the manifolds' runners are too big. However, 472/500 Cadillac specialist CMD offers its ProCad-3 performance dual-plane intake specifically for the 425 that accepts either Rochester or Holley carbs. For best results, use the intake with a 1-inch-tall phenolic spacer (hood clearance permitting). Add CMD's entry-level Caddy cam plus a free-flowing exhaust system and you're looking at a 50hp gain. Want more? Remove the heads, install CMD's stainless steel, swirl-polished oversize valves with a good three-angle valve job, and mill the head decks 0.035-inch to raise compression by half a point from 8.2 to 8.8:1 (still 87-octane gas-compatible, according to CMD).
2. Cadillac front coil springs were used only by Cadillac, probably because Caddys were heavier than other GM cars. Except for those Cadillacs equipped with the optional centerlink that mounted a steering damper, all the rest of the front suspension components interchange with other '77-and-up fullsize GM B- and C-chassis. If present, the steering damper-type centerlink, while unique, does not effect the interchange of the other components. Big car antisway bars interchange, but the Cadillac had bigger bars than its sisters to begin with. The Cadillac front steering knuckles and disc brake rotors are the same as other '77 GM fullsize cars with the 5-on-5 wheel-stud bolt pattern and 12-inch rotors (typically police cars, wagons, and heavy-duty trailering packages). The '78-and-up 12-inch brakes use a different wheel bearing, but they'd fit if both knuckle and rotor are swapped as a complete unit.
The rear suspension components from other '77-and-up GM fullsize cars interchange. Rearends from other '77-and-up GM fullsize cars interchange by swapping yokes. Addco offers a 1-inch rear antisway bar (PN 939).
3. Rochesters respond fine when properly maintained and tuned. Brad Urban's Carb Shop and Jones Performance Carburetion are two nationally recognized Rochester specialists.
Addco Industries Inc
700 East St.
Lake Park, FL 33403-2304
Brad Urban's Carb Shop
8460 Red Oak Ave
Rancho Cucamonga, CA 91730-3815
2810 Parkway St. #6
Lakeland, FL 33811-1390
Jones Performance Fuel Systems
17491 Apex Cir
Huntington Beach, CA 92647-5728
Carb vs. EFI
I've got a '67 Fairlane with a 288-degree-duration cam and heads with screw-in studs and adjustable valves. It hits a fairly mean lick, and with the C6 the car moves pretty good. Would the car run any better with electronic ignition and a fuel-injection system, or am I better off with the points distributor and 600 Holley four-barrel single-line carb? I'm just wondering if these upgrades are really worth the time and money to change them.
Upgrading to a closed-loop fuel injection system like the one used in the modern 5.0L Mustangs costs big bucks. According to the Ford EFI swap experts at Windsor-Fox, converting an existing engine costs around $2,300, dropping in a complete used (but still OK) late-model 5.0L engine runs $4,000-$5,000, and installing a brand-new 5.0L EFI will set you back $8,000-plus. Installation is time consuming, and you've got to understand electrical systems. The payoff is a virtually maintenance-free engine with better part-throttle driveability, superior cold-start performance, no hot-summer vapor-lock problems, and the elimination of high-altitude driveability woes. Fuel injection's supposed mileage improvements over an engine with a correctly adjusted and calibrated street carb utilizing vacuum- or air-valve-controlled secondaries is overrated; I know of an early 302 Ranchero/C4 combo that gets over 23 mpg on the highway with a 600 Holley. The real mileage enhancements come by combining fuel-injection and a late-model automatic overdrive trans-but that's more bucks yet.
What is worth the money is tossing that points distributor in favor of an electronic non-computer distributor. Plugs will last longer and foul less, plus the engine maintains its state of tune longer (there's no point gap to "open up"). Ford's '75-'80 Duraspark distributors are plentiful in the junkyard, and parts-store remanufactured units cost $50 or less. There's a good chance the stators are worn on high-mileage units, so I'd go with the reman option.
Another weak point on the Ford Duraspark is the module. However, M.A.D. Enterprises sells a $40 kit (includes a protective external module container, wiring, connectors, and instructions) for hooking up the superior GM HEI module. Be sure to use a genuine GM or AC-Delco module (PNs 1875990 or D1906, respectively).
P.O. Box 675
Springville, CA 93265-0675
Windsor-Fox Performance Engineering
P.O. Box 2683
Apple Valley, CA 92307-0051
The latest engine in my '67 Mustang convertible was built to be capable of 6,000 rpm. Now I need a vacuum-operated heater control valve that won't blow up every time I hit redline!
Silver Spring, MD
Or you need a good rev limiter! Seriously, the problem isn't in the vacuum-actuation portion of the valve (at full-throttle and max rpm manifold vacuum is essentially nil), but instead the culprit is high coolant pressure that blows the valve off its seat. The valve isn't needed if you're not running air conditioning, but if you are, take a leaf out of the '87-and-later 5.0L HO Mustang book: Plagued by high coolant pressures that blew apart their heater cores, the factory solved the problem by inserting a restrictor inside the intake manifold-to-heater core hose. Although the late molded hose won't fit early chassis, you can fabricate an equivalent restrictor from a round aluminum or steel disc: Drill a 1/4-inch hole through the disk's center, then trim its od so it fits snugly inside the 5/8-inch-id manifold-to-valve hose (the valve's "upstream" side).
I am working on a sheetmetal EFI intake manifold. Could you please offer some speculation on how to size one for various applications? I have found that a rule of thumb for sizing a plenum box on normally-aspirated engines is to build one 50 percent the size of the volume it is feeding for engines producing under 1 hp/ci, and 75 percent for engines producing over 1 hp/ci. As for engines producing 2-plus hp/ci, I have no idea. If any sort of tech information is offered on this subject for naturally-aspirated as well as forced-induction designs, I would appreciate knowing about it.
This custom-fabricated intake for a blown small-block Chevy features a common plenum and i
Your assumptions are pretty much in the ballpark. EFI specialist Ken Duttweiler likes to see plenum volume at about 75 percent of displacement for engines making 1 1/2-2 hp/ci, reducing the volume progressively as engine hp/ci output declines. Plenum volume for current Pro Stock engines at the 2 1/2 hp/ci level is typically 80-90 percent of engine displacement.
These generalizations serve only as a starting point. In the real world, you have to factor in the specific engine design, establishing the proper plenum volume and runner length to tune the system for a specific rpm as well as displacement in much the same way headers and exhaust systems are designed. A higher rpm engine sucks in more air in a given amount of time, so the manifold must be able to move the extra air. As rpm goes up, runners need to get shorter-which leaves more room for plenum volume. In "dry air" EFI manifolds, runner length, and design are critical, with their taper and overall volume more important than the specific plenum configuration. Duttweiler also says that on supercharged or turbocharged engines, plenum volume changes have relatively little effect on the engine's power output. Of course, whatever you come up with also has to fit in the engine bay and clear the hood!
Over the course of internal combustion engine development, dating back now over a century, there have been scores of studies and engineering papers written on optimum exhaust and intake system design. Most of them assume that engine cylinder volume remains constant (equal to total displacement). But in reality, the area above the piston is a continuously changing variable as the piston moves within the cylinder; this cylinder volume factors into the overall volume and length of the induction and exhaust systems.
One study that takes changing cylinder volume into account is P.C. Vorum's 1976 ASME paper "Short Pipe Manifold Design for Four-Stroke Engines." Essentially, the paper recommends combining optimum primary and secondary pipe velocities with a Heimholtz-like resonating chamber as found on some exhaust muffler designs. It presents a mathematical model for taking the various factors into account, although not every iteration is fully explained or documented; apparently, the author held something back so he could prosper doing contract work for OEM manufacturers-but it's a good starting point if you're math and engine-savvy! Copies of the out-of-print paper (reference ASME 76-WA/DGP-4) can be purchased from the Linda Hall Library, an independent research library of science, engineering, and technology.
Linda Hall Library Document Services
5109 Cherry St
Kansas City, MO 64110-2498
Through Thick and Thin
I have a '95 Camaro Z28 with an automatic transmission and a set of 2.73:1 gears in the rearend. I was thinking of upping the gearing to 3.73:1 to improve off-the-line performance, using a thicker gearset so I wouldn't have the expense of upgrading to a three-series carrier. My mechanic advised against it because it might be noisy. The car is driven about 2,000 miles a year. It has an RK Sports high-flow converter, a Flowmaster muffler, MAC weld-on subframe connectors, and a K&N air filter. The exhaust is already loud, and I would be able to live with a little more noise. What are your thoughts on this?
There's nothing inherently wrong with thick-flange ring gears. In fact, Ford has always varied production ring-gear thickness rather than change differential case flange heights. Assuming proper installation technique, any inherent noise problems are not a design problem, but instead indicate a gear-manufacturing quality control deficiency-namely, poor lapping technique. U.S. Gear has a good reputation in this area, and recently introduced thick 3.73:1 gears for the GM 7.5/7.625-inch 10-bolt rearend (PN 01-875-373X).
9420 S. Stony Island Ave.
Chicago, IL 60617-3695
Performance with a Price
I drive a '79 Volvo 262 Bertone with a '90 Mustang H.O. 302, AOD trans and all computer functions intact. I'm running cast-iron manifolds to 2-inch pipes to a single three-way cat. From there back, it's all Volvo 1 7/8-inch exhaust, and ends at a muffler from a six-cylinder Camaro. I drive the car a lot and really appreciate the quietness. What do you feel is the minimum-size exhaust that I should use, and will a freer-flowing exhaust really help my gas mileage?
Drexel Hill, PA
Up to a point, reducing exhaust restriction generally helps gas mileage. But going too large can overscavenge the engine and result in a mileage reduction. Proper exhaust size is a function of both engine output and displacement. Ford used a full 2 1/4-inch dual exhaust system on the Mustang, complete with dual cats and mufflers. Assuming the engine is stock, in theory, 2-inch dual pipes should be adequate, as indicated by the accompanying exhaust system recommendation chart courtesy of Flowmaster Mufflers. Specifically, it's the 1 7/8-inch single-pipe and weak little single six-cylinder muffler that's holding you back. If there's insufficient room for dual pipes and mufflers after the converter, use a single 2 1/2-inch pipe and corresponding low-restriction aftermarket muffler. The converter inlet and outlet should likewise correspond to the inlet pipe sizes.
2975 Dutton Ave.
Santa Rosa, CA 95407-7800
|Suggested Exhaust Pipe Sizes for Street Performance
|Pipe Diameter (In)
Straight Talk on Angle-Plugs
What is the difference between a small-block Chevy angle-plug and straight-plug heads as far as performance goes? Is it worth spending the extra money on expensive headers just to use angle-plug heads (especially if you already have two sets of straights)?
On small-block Chevy angle-plug combustion chambers, engineers moved the plug tip closer to the roof, supposedly to improve combustion efficiency and gain power. The first heads to feature the angle-plug configuration were a special parts-counter-only version of the conventional production straight-plug, 64cc chamber, "492" casting. Other than the angled plug location, the casting was otherwise identical and still carried the same "492" casting number; hence, it offers a useful yardstick for comparing just the effects of altering spark-plug location. The consensus was that original angle-plug heads are worth 10-12 hp on high-compression engines using high-dome pistons, because they reposition the plug higher in the chamber so the flame front is no longer blocked by the piston dome. In fact, angle plugs made practical the use of even higher domes (with correspondingly higher compression ratios); previously, really big domes on small-blocks often proved counterproductive because of the flame-front blockage problem.
Because the angled plug's firing tip also ends up more centered in the chamber and oriented slightly toward the exhaust valve, the hottest part of the mixture is ignited first. With the plug located closer to the chamber's quench area, maximum turbulence is directed toward the plug, thereby improving combustion speed and pressure rise. In theory, this improves combustion efficiency even on engines without domed pistons, but on a street engine any power gain that results from changing spark plug location in an otherwise identical head is so slight it's not worth the hassle of conversion.
The angle-plug version of the 492 heads is no longer available, having long ago been superseded by modern GM and aftermarket angle-plug, off-road heads with redesigned intake and exhaust runners and higher-efficiency chamber shapes. In the modern era, Chevy also installed angle-plug heads on production L98 and LT1 aluminum-head engines. Whether off-road or production, these heads feature many improvements besides a revised spark plug location, so comparing today's modern high-efficiency angle-plug castings with old-style straight-plug castings is like comparing apples and oranges. Although, as we've seen, spark plug location alterations aren't that important for a flat-top piston engine, the modern-tech heads' other refinements can definitely offer a significant performance enhancement on a serious performance engine.
I transplanted a TH350 in place of my original Powerglide trans. My problem is that the original solid linkage interferes with the speedo cable. The new trans is correctly geared for my 3.42:1 rearend, so I just need a 1:1 speedo box to offset the speedo cable input. I've been to several local trans shops and no one sells one. If you could point me in the right direction I'd really appreciate it.
James Lee Garrison
A miniature 90-degree offset 1:1 speedo adapter box that requires only 1 1/2 inches of clearance is available from Lance Martin Automotive. The 90-degree leg can be reclocked in relation to the other leg as needed. One drawback is that miniaturization makes the unit more costly; it'll set you back about $80. Alternatively, you could always install an aftermarket floor shifter with cable linkage
Lance Martin Automotive
815 Hilbert Rd
Fallbrook, CA 92028-1608
Contact Marlan with your tech questions at Ask Marlan, Car Craft, 6420 Wilshire Blvd., Los Angeles, CA 90048-5515; or by e-mail at firstname.lastname@example.org (include the words "Ask Marlan" in the subject line). All correspondence must be signed with the sender's real name (not a nickname or a screen name) and include the sender's hometown and state or province. While mail cannot be answered personally, Car Craft will publish as many letters and responses as space permits. You are encouraged to send photos, but no materials will be returned.