Tach question....

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Tach question....

Post by scooper »

What do you guys use for a tach in your V8 cars? I have a Corsa dash, is there a way to electrically convert the stock tach to work with my 8 cylinder? I know I could probably replace the tach with an aftermarket unit, just curious if the factory tach can be rewired to work.

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Re: Tach question....

Post by 66vairguy »

Yes a Corsa tachometer can be modified, BUT I've fixed a few of them and the main problem with the Corsa tachometer is the meter assembly. It's a precision unit and was supplied by more than one vendor (I've found three different designs) and all work the same. Eventually the armature springs break and there is no practical repair. Also the tach's are prone to some needle swing during aggressive turns. That said the Corsa tachometer was a very good unit and accurate when new - in the 60's

Now there are better tachometers. Also the old speedometers are getting difficult to repair due to a lack of parts, the most common problem are trip and main odometers that quit.

What to do? Seth Emerson at Performance Vairs sells a bracket to mount new standard sized gauges in the Corsa instrument bezel. Many have used the bracket. See https://www.perfvair.com/dash-parts-steering-columns/

Seth is easy to talk to and helpful if you want to contact him.

Hope this helps.

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Re: Tach question....

Post by bbodie52 »

Even if you could modify the Corvair tachometer to calibrate it for an eight cylinder engine, the 5500 rpm redline and 6000 rpm maximum scale would not be optimum for a high-performance V8.

I couldn't find any articles on modifying the Corvair tachometer, but thought you would find this historical article interesting...
The Crown Corvair V-8
Aaron Severson April 8, 2008 Model Histories, Sports Cars and Muscle Cars

What does nearly every car produced anywhere since the days of the Model T have in common? Other than wheels, it’s the inevitability that sometime, somewhere, somebody has stuffed a small-block Chevy V8 into it. We’ve yet to hear of a V8 Prius and there might be a Russian ZiL or two that remains innocent of the Mouse Motor, but everything else from ’32 Fords to RX-7s, has at one time or another had the ubiquitous Chevrolet engine stuffed under the hood — or wherever else it might fit.

The author recent met some of the members of the South Coast CORSA (Corvair Society of America) chapter and had a chance to see some of the cars owned by the members. Aside from Greg Vargas’s cherry black Monza (pictures of which appeared in our recent Corvair article), we also came face to face with a highly unusual example of the Corvair breed: Chuck Rust’s Crown V8 Corvair, a car that is no longer quite a Corvair, but a Corv-8.

A complete history of hot rodding would be a tangled web indeed, but suffice to say that about ten minutes after the invention of the automobile, people started exploring ways to make it go faster. Hop-up equipment of various kinds goes back at least to the debut of the legendary flathead Ford V8, which may not have invented the concept, but certainly brought it to the masses.

Even in stock form, a V8 Ford was a brisk piece of machinery, and a well-motivated individual could extract considerably more from the trusty flathead. The L-head V8 was not a great engine from a design standpoint, but its limitations were well understood, it was produced in mind-boggling numbers, and it was cheap. Aside from any number of actual Fords and Mercurys, it subsequently found its way into a vast assortment of other vehicles.

The flathead Ford V8 was produced through the 1953 model year, but by then, it had been eclipsed in power potential by a new generation of overhead-valve V8s. Cadillac and Oldsmobile were first, in 1949, followed by Chrysler, Studebaker, and a new Ford “Y-block.” Of these, the Cad, Olds, and Chrysler engines had the most potential, but they were more expensive, which kept them from claiming the flathead Ford’s title as the everyman’s hot rod engine.

Chuck Rust’s Crown conversion 1965 Corvair Corsa. The airdam under the bumper funnels air into the radiator. You can tell from this angle how much the car has been lowered from its stock ride height, benefiting center of gravity at the expense of ground clearance. The front scalloping, which works rather well, was done with spray paint, making it easier to touch up, particularly when Chuck inevitably scrapes the front spoiler on dips and parking lot ramps.

Then came the 1955 Chevrolet and its brand-new V-8. (For the record, it wasn’t Chevrolet’s first V8, although the short-lived 1917-1918 engine is hardly worth remembering.) Designed under the auspices of Chevy chief engineer Ed Cole, who had previously overseen the design of the 1949 Cadillac V8, the nouveau Chevy V8 was a short-stroke, overhead-valve engine with five main bearings and unusual screw-in rocker studs on which the rocker arms pivoted, rather than a conventional rocker shaft. Weighing about 530 pounds (240 kg), it was more than 100 pounds (45 kg) lighter than a Cadillac, Oldsmobile, or Chrysler FirePower Hemi V8.

The Chevrolet V8 had been designed with low manufacturing costs in mind, so it was cheap — it cost a mere $99 more than Chevy’s old Stovebolt Six. The V8 in its initial form displaced 265 cu. in. (4,344 cc) and made 162 gross horsepower (121 kW), 180 hp (134 kW) with the optional “power pack” (four-barrel carburetor and dual exhaust). It quickly proved highly susceptible to additional hopping up. In short, it was everything the aspiring hot rodder could ask for.

By the mid-1960s, the Chevrolet “mouse motor” could be built up to well over 300 real horsepower (224 kW) with no great sacrifice in its street manners. It didn’t take long for it to begin finding its way into everything from dune buggies to Aston Martins. The Chevy V8 became such a popular swap that various aftermarket manufacturers began offering kits to facilitate the process.

This brings us to a man named Ted Trevor, owner of Crown Manufacturing in Newport Beach, California. Trevor was a race car builder and driver who for several years in the sixties competed in a heavily modified Manx dune buggy powered by another Ed Cole creation, the air-cooled flat six from the Chevrolet Corvair.

In 1966, Trevor won his class in the Pikes Peak International Hill Climb with a Corvair-powered Manx. At some point he started thinking about what else could be done with the Corvair itself.

As we’ve previously discussed, in 1965, Chevrolet launched a beautiful, sophisticated, and sadly doomed second-generation Corvair. With fully independent rear suspension, it was free of the bad habits of early Corvairs in hard cornering. It had become, in fact, one of the best-handling models on the American marketplace, rivaled only by a few very specialized makes. With the 180 gross horsepower (134 kW) of the turbocharged 164 cu. in. (2,680 cc) Corsa engine, it was reasonably quick, but it was obviously capable of coping with significantly more power than Chevy offered from the factory.

Ted Trevor knew as much as anyone about extracting more from the Corvair’s ‘pancake six,’ but around 1967 he conceived a far more radical solution: replacing the flat six with a V8 — naturally enough, the small block Chevrolet.

With over 325 hp (242 kW) in a car weighing at least 300 pounds (135 kg) less than a Camaro or a Corvette, Chuck’s Crown V8 Corvair might well be able to climb walls. Lowered suspension other obvious modifications do nothing to diminish the second-gen Corvair’s clean lines.

A small-block Chevrolet was relatively light by V8 standards, but it was still about 170 pounds heavier than the Corvair engine and it required certain accessories the air-cooled Corvair never had, like a radiator. Stuffing a V8 in the Corvair’s rear engine compartment was possible and some had done just that, but it was hardly ideal.

What Trevor conceived was a kit to modify the Corvair’s four-speed Saginaw manual transmission (which shared its innards with the four-speeds used on Corvettes) with a different mainshaft that allowed the engine to be mounted ahead of the transaxle rather than behind it, sitting in what used to be the Corvair’s rear seat. The radiator, meanwhile, was mounted in the nose, with coolant routed through copper pipes in the body’s center tunnel. Custom exhaust headers were needed, of course, and to keep engine and exhaust heat from roasting the driver, an insulated fiberglass engine cover was added over the new powerplant. Crown called this a “kit,” costing about $600 (not including the new engine, radiator, or donor car), but installing it was a complicated project that involved dismantling much of the car.

The front compartment of the Corvair was once the trunk, but in a Crown V8 Corvair, this space holds the radiator and a puller fan to insure a good flow of air through the radiator (not a consideration of the original body design!). Copper tubing carries coolant to and from the engine.

With the engine moved on to greener pastures, the rear compartment of a Crown V8 Corvair is again a trunk. Chuck’s engine is eminently visible through the windows, but on other Crown V8 Corvairs, with their engines hidden under a fiberglass cover, you can provoke amusing double-takes from bystanders by opening the front and rear hoods to reveal no engine in either location. Note the foil-wrapped tube visible through the rear window — it funnels air from the vents into the carburetor.

Crown offered a variety of other modifications to complement the engine swap. The Corvair’s differential was not capable of surviving more than about 250 horsepower (186 kW), even with beefed-up internals, so it needed a reinforced case. A heavy-duty suspension kit was offered, using shorter, stiffer springs and firmer shocks. Some Crown V8 Corvairs (including Chuck’s) have a complete bolt-in replacement rear suspension, similar in basic layout (but not components or geometry) to the stock arrangement. Changing the Corvair’s front drum brakes to discs was a useful adjunct, fatter tires were a must, and of course it was necessary to add a set of good aftermarket gauges to keep tabs on the temperament and temperature of the new engine.

A glance through the side windows reveals that this is no ordinary Corvair — even if you couldn’t clearly see the engine, the vertical beam of the roll cage would reveal that something was up. Chuck intends the car as a tribute to the late Smokey Yunick, race car driver, builder, and curmudgeon . Note the Hot Wheels decal; this car inspired a Mattel Hot Wheels toy designed by a friend of the owner.

(Trevor also experimented with installing big-block Chevrolet engines in a similar manner, but warned his customers that they were too much for the transaxle. A prototype Corvair with a 465 cu. in. (7.6 L) Can-Am engine had eye-watering performance, but broke its transmission every time it was driven).

A fully equipped Crown V8 Corvair weighed perhaps 450 pounds more than when it left the factory. How much power it had depended on how ambitious the builder was feeling. Even a dead-stock 327 cu. in. (5,354 cc) V8 would have at least 20% more power than the most potent stock Corvair, but if you were going to this much trouble, moderation was probably not on the menu. It came down to the old hot rodder adage: “Speed costs money. How fast do you wanna go?”
The modified 283 cu. in. (4,638 cc) Chevrolet V8 engine of Chuck’s Crown V8 Corvair. At the left you can see the plastic window that separates the engine from the backs of the front seats.

In Chuck’s car, the engine is 283 cu. in. (4,638 cc), slightly over-bored, with fuel injection heads from an early-sixties Corvette engine, a short-duration, high-lift cam, and a 650 CFM Holley carburetor on a lightweight Offenhauser aluminum manifold. It takes cool air from what used to be the Corvair’s stock engine cover vents and has an external oil cooler with its own fan.

Thus equipped, the V8 is a reasonably durable, high-revving engine with lots of power (Chuck says around 325 horsepower (186 kW) at 7,500 rpm), but not so much low-end torque as to burst the differential. We didn’t discuss performance numbers, but based on its power-to-weight ratio, reaching 60 mph (97 km/h) probably takes around five seconds, with the quarter somewhere in the 12s. How fast does it go? Well, Chuck said he added the tail spoiler because he found the rear end would get awfully light at 160 mph (258 km/h) …

Chuck’s car, which was once a 1965 Corvair Corsa, is a little bit different than the standard Crown in a number of respects. A Plexiglas divider window and insulated firewall are installed behind the front seats in place of the standard engine cover. (One problem with the Crown conversion is that putting the engine in the rear seat area also restricts front seat travel — long-legged drivers need not apply.) The rear window is aircraft-grade polycarbonate, hinged for engine access, retained by Dzus fasteners, and vented to relieve internal air pressure. This is a trick that improves top speed (something similar was available as a dealer option on racing-spec GT-350 Mustangs) as well as venting heat and fumes from the engine compartment.

To improve the effectiveness of the window vent, Chuck has added a small spoiler at the rear edge of the roof to up the slow-moving air (the boundary layer) that clings to the roof surface. Chuck reports that the divider window and vented engine compartment make the cabin temperature entirely livable, with good flow-through ventilation on even hot days. The interior is braced with a full roll cage, which not only offers crash protection, but also helps to stiffen the body. The suspension is extensively modified with relocated control arms for better camber control and front and rear anti-roll bars. Front brakes are discs borrowed from a Corvette, with finned aluminum drums in back. He has wider tires in the rear than in the front to help limit the car’s propensity to get sideways.

Chuck’s Crown V8 Corvair has front disc brakes inside 15-inch wheels (significantly bigger than the stock Corvair’s 13-inchers). Rear brakes are aluminum drums, although rear disc kits are available.

Ah, yes, sideways. With the engine now ahead of the rear axle, a Crown-conversion ‘Vair is no longer rear-engined; it has become a mid-engine car. The advantage of a mid-engine car, from a handling standpoint, is that moving the heaviest parts of the vehicle closer to the center of mass reduces the vehicle’s polar moment of inertia. A car with a high polar moment of inertia (for example, a ’56 Thunderbird with the heavy Continental spare tire hung out over the tail) is resistant to quick changes of direction. Once it does change direction, it wants to continue in that arc, come hell or high water.

Mid-engine cars, with their lower polar moment of inertia, have much sharper turn-in and balance in cornering, which is why that layout has been favored by tony Italian exotics since the late 1960s. The Crown V8 Corvair, which also benefits from a low center of gravity and good camber control, is an exceptionally maneuverable car. An increased willingness to rotate, however, is not always a good thing. Most mid-engine cars will spin if mishandled — Chuck told me about the first time he spun his — and with 300+ horsepower (224 kW) on tap, a mid-engine, V8 ‘Vair is not for amateurs.

Chuck’s car retains the stock dashboard, but the stock Corvair Corsa’s 140-mph speedometer and 6,000-rpm tach have been replaced by 200 mph and 10,000 rpm units. Below the dash just to the right of the wheel are accessory gauges for water temperature and oil pressure. Note the modest leg room — with the firewall immediately behind the seats, they don’t go back very far.

Sensible precautions. The seats are leather-upholstered buckets from a 1995 Acura Integra, with four-point Simpson racing harnesses. The fire extinguisher is a smart idea — despite all the insulation, the engine’s scalding-hot exhaust headers are barely a foot behind the seats.

Many people would say that a car like this is basically a toy, and in Chuck’s case that is literally true. His Corvair sports a Hot Wheels decal in the left rear quarter window, commemorating the fact that it was the model for the “Vairy 8” Hot Wheels car released in 2003. (Chuck is friends with a designer at Mattel, which is headquartered in the area.)

Ted Trevor made something like 1,500 Crown conversion kits in the late 1960s and early 1970s. Crown Manufacturing ultimately went out of business, but Clark’s Corvair Parts, Inc. acquired the rights and many have been built since then along the same lines. Trevor himself still owns at least one Corv-8, and in the 1990s and early 2000s made occasional appearances at Corvair shows. We’re told that he’s in poor health these days, and a friend of his said earlier this year that Ted thinks he’s been mostly forgotten.

That would be a shame, because the Crown Corvair is a remarkable car. Ron Hill’s styling team at Chevrolet made the second-generation Corvair as pure and lovely as anything Italy’s Pininfarina ever designed and the Crown V8 conversion gives it an unusual blend of sports car handling and American hot rod muscle. A pur sang thoroughbred it is not, but, at least when competently assembled, it’s hard to argue with the results.

The muscle car hobby in recent years has become obsessed with making sure every nut, bolt, and decal of a car is exactly the way it was when it left the assembly line. That fetish for numbers-matching authenticity, however, runs counter to the hot-rodder ethos that spawned the muscle cars in the first place — a can-do spirit that didn’t hesitate to try anything that promised a little more speed. In that light, there’s something deeply refreshing about the kind of madness that would lead a man to stuff a V8 engine into the back seat of a perfectly good Corvair.
# # #
:link: https://ateupwithmotor.com/model-histor ... 8258616299
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible

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Re: Tach question....

Post by 66vairguy »

That's Chuck Rust's car. I've ridden in it and it's a thrill.

Yes Chuck does rev to 7,000RPM, or did until the engine dropped a valve through a piston. He just put in another engine. A SBC does sound nice at 7,000 RPM, but that is pushing it even with titanium valve keepers, roller rockers, etc.

Yes the Corsa tachometer has a lower marked limit, but few normally aspirated street V8's rev past 6,000 RPM unless they have a lot of modifications $$$$$$. That said just going with more modern instruments in a V8 car is going to be more satisfying. Chuck also installed a GPS speedometer, but note it required a remote pickup (sold to work with any pulse input electronic speedometer). The Corvair dash board is steel so the GPS speedometers with the pickup inside may not get a reliable signal.

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