12A 1st Generation Street Performance Page
Introduction: This page is dedicated to first generation 12A engine Mazda RX7 performance modifications aimed mainly at high performance street use, and of a bolt on nature. There aren't many of us 1st gen guys left, so I thought I'd share this with you die-hards.
[Here comes the disclaimer] Of course, this is very likely illegal in anyplace left in the World that has internet access, so be forewarned if you try any of these items on a smog equipped vehicle, else the smog cops will bust you down and make your otherwise nice life miserable. Many of these things work well for certain club racing and autox events, but check your rules before doing anything. Nothing is more surprising than being protested, bumped to E- Mod, or fined for mods that you were 'unaware' of. No one cares that you didn't know the rules - they want to beat you.
Anyway, I have worked on quite a few 1st gen cars (some my own, many not), and this page is something of a summary of the experiences I have had, good and not so good.
Over time, I will add some B&W pics (to speed loading) and add additional detail to many of the basic ideas set forth here.
It is broken down into:
Unibody: The stock Mazda unibody is suprisingly rigid despite the car's low weight. Reportedly, it had a torsional rigidity of 6,780 ft lb per degree. Not bad considering it is something of a rehash of the venerable RX3 (a real kick-ass ITA car despite being well over 20 years old), although with slightly beefier steering components. The rigidity of the chassis can be further improved by seam welding the major unibody components if you have a welder handy. Don't bother welding fenders to chassis, but concentrate on the tranny tunnel, strut towers, cowl, and the rear suspension links. This is illegal for most racing, but nice for non-competition track events. An 8 point cage sure makes things stiff if seam welding isn't an option. Get or fabricate a strut tower brace - the Racing Beat one that triangulates to the firewall is really nice, but basically is a ticket to E-Mod or outright illegal in IT racing. Even one that just ties the two towers together will add to the rigidity of the front end under load. If you intend to change camber settings, you will want an adjustable bar. You can get these from Mazdatrix, Rotary Performance, MazdaComp, etc.
Shocks: The stock suspension can stand some upgrading. The spring rates and damping are pretty soft for fun driving. The best bang for the buck I have found in the marketplace are the Tokico high pressure gas non-adjustable struts and cartridges [p/n HZ-1069 (F), and HE-2317 (R)] which can be had for around $50- 55 each. These are quite a bit stiffer than the OE dampers, but offer much more control over stiffer spring rates. The '79/80 front strut housings are slightly longer than the '81-85 housings, so the adjustable Illuminas won't work unless you shim the length - and longer housings are just a ticket to hard bottoming. You are better off bolting on the later housings and the improved upper strut mount to the early cars if you require the Tokico Illuminas, and it's still not a bad idea anyway. I have had less than wonderful experiences with other brands, and the OE wet struts too.
If you must have Illuminas, there are two types for the front end - one (HBZ1086 - actually designed for an MR2) for a 200+ lb/inch spring that has an upper shaft designed to fit the spherical bearing in a castor/camber plate (leave these bad boys for the track) and the 'regular' (HBZ1069) one that is suitable for the street and autocross (less than 200 lb/inch springs). There is only one rear flavor Illumina that I know of.
Springs: The OE springs are often upgraded to lower the car and increase the spring rates. The stock spring rates are really soft - and this is nice and comfortable. Remember, this is a trade-off between dental loosening or wallowing. We want to hit that happy medium. 350 lb/inch springs are not fun on the street.
The TMC Street/Race (p/n CSM-400) springs are cheap (<$150/kit), durable, and lower the car about one inch. I have also had good experience with the Suspension Techniques springs (also <$150/kit). Eibach Pro-Street springs are also nice, but in my experience, these are about as stiff as you want to go on the street. I have zero experiance with the Racing Beat springs as of the last update to this page. These springs, in combination with the Tokico shocks, offer a streetable ride with much improved characteristics. Be careful lowering the car too much (like cutting additional coils off the springs) as the spring seats on the axle can whack the frame and actually distort the axle housing (leading to bizzarre handling) in the rear, or hard bottoming in the front strut cartridges, which will damage them. If you have to cut the rear bump stops more than about one inch, check the axle/spring perch clearance.
Some folks have fair results by cutting a coil or so off the OE spring. At this point, your OE spring is 12 -13 years old at best, and perhaps the $150 for a set of NEW springs isn't such a bad idea. If you must cut them, use a cutoff wheel so you don't ruin the spring temper with a nasty old torch.
Bushings: The OE rubber is usually pretty rotten and deformed. Afterall, they are also over 12 years old at best. By the time I was 12 years old, I was pretty rotten and deformed, too. The Energy Suspension strut (aka tension) rod and control arm bushings improve steering feel considerably. The rear bushings are best left alone, if in good shape, due to the binding inherent in the rear suspension geometry. Some folks have experimented with urethane bushings in the lower links with good results - this may be a good option for those folks with straight links and rotted bushings. I have had no 1st person experience with them yet. If you are compelled to modify this, I have been working on an upgraded link with spherical bearings and threaded steel tubes for lower suspension links on my EFI 13B GSL. The ride will become harsher. Mazdacomp now offers the aforementioned urethane link bushings, and I would be very careful using these in the upper links. Ground Control (see links) has a funky three link rear conversion that reportedly works quite nicely.
The idler arm bushings get worn out pretty regularly and are often the culprit in the 'way to much play in my steering wheel problem. These bushings are cheap, but live next to the exhaust manifold and seem to get baked into oblivion. They are very easy to replace, so consider it a normal wear items and replace them every couple of years. When replacing tie rod ends, think about getting nice high quality greaseable Moog parts. The Mazda ball joints are pressed into the control arm, and can be replaced, but require a press and a bit of know how to do. If in doubt, you can get new control arms (with new ball joints already pressed in) for Mazda Comp. Sometimes, self installed ball joint will loosen in the control arm if they are not tack welded to the arm. Replacing these items will make the steering, in conjunction with idler arm bushing and correct steering box adjustment, quite nice.
Watts Link: This is usually an excellent device, but in this case doomed with a very poor execution. Mazda did an unusually poor job integrating this into the chassis design. The links are unequal length, and the pivot offset. As such, it introduces more binding into the suspension through the suspension travel. The more the suspension ride height is altered, the more problems this will cause. Some folks choose to go retro and add a Panhard bar (requires welding to do right), while some choose to make the OE unit more symmetrical, or at least adjustable. The Ground Control 3 link kit is again an option here, but requires a bit of fabrication and welding. The Tri-Link setup from the folks at Tri-Link is also a very nice kit.
Unless you radically lower the car, just leave the Watts link be. Speedsource and Mazdacomp offer an adjustable heim jointed Watts link (in the $250 range) that minimizes the binding and allows some lateral adjustment to the rear axle location and adjustment to the link length.
Steering Box: The early ('79-82[?]) boxes have non-hardened sector shafts and just plain wear out. Most of the boxes I have adjusted were almost totally dry, with no lube visible. You'd wear out too, if you had no lube (I use GL4). That nylon 'bolt' is the filler. Use it. The later boxes require careful adjustment, in which you will need a spanner to tighten the box with. Loosen the 1 9/16" lock nut (I use a chisel) and tighten the sector shaft with the spanner while frequently checking the freeplay on the wheel. I use the screw for very fine adjustment. If you make it too tight, it will wear very quickly. I have had good success using a power steering box (with the power accessories removed) - it has almost one full turn less lock to lock - and it is noticeable. Steering is a bit harder in traffic. Beware.
Swaybars: The OE front bar should be upgraded to a 1.125" one - these are offered by a variety of companies and they are all fairly comparable. I like the Ground Control bar with the heim jointed links. The rear bar should be no larger than 5/8", which happens to be about the size of the rear bar on the later GSL cars (about 14mm). This is a nice upgrade to the S model cars that had no bar or the early cars with the big 16/7mm bar (oversteer o' plenty). The Suspension Techniques rear bar is also heim jointed and is also 3 way adjustable. That's the one I have on my EFI 13B. I use a OE GSL bar on my Spec RX7 racer. Many folks with stiff suspensions drop the rear bar altogether.
Wheels/Tires: There's nothing wrong with the OE 13" wheels. As a matter of fact, I like the way the '79/80 wheels look. They are strong and durable, but there's a limited availability of premium rubber these days made for a 13" rim. At least Yokohama remembers this and they continue to make the AVS and A509s. The AVS is noticeably better in wet conditions, and both have great adhesion in the dry. DOT approved race tires (R1s, Proxes RA1, Hoosiers) have incredible traction, BUT do not belong on the road. They really are a singular purpose tire that requires a certain level of heat buildup to function correctly, and they are not as durable in ordinary road conditions. This means they have an amazing ability to grab nails and glass and puncture, and really are diabolical in the rain. Save 'em for the races.Oh, yeah, they tend to be LOUD and STIFF.
I have a set of 15" Panasports and 205/50 RE71s on my EFI GSL - these are really nice, but pricey. An alternative to expensive, limited availability mags are steel circle track wheels. I have a few sets of Fast Manufacturing dirt track wheels that I race my Spec RX7 with, and they are incredibly strong, reasonably light, and fabulously cheap. They are available in a variety of widths, offsets, and diameters. In a 13x7, I recommend a 4.25" backspace, and a 205/60 tire. Cheap prices, great performance. Steel wheels are advertised in Circle Track magazine by a half dozen manufacturers. Diamond Racing offers some very nice 7" wheels and are carried by Bret dePedro of Rotary Performance.
Most manufacturers will make 14 or 15" wheels for you, but be careful on the backspaces or you will have rubbing problems. A 15" wheel, 205/50 tires and lowered springs pretty much require the fender lips to be rolled under. If you bend one of these Circle track wheels, you belong in the demolition derby. I understand that American Racing no longer offers wheels in a 4x110 bolt pattern, but it's a somewhat odd style. There's always Panasports if you have the cash!
Other folks have updated their 12A cars with GSL-SE front struts/brakes and rear ends. This gains you the advantage of larger brakes, a 4.07 rear, and much more widely available wheels. These parts are bolt in items for the 12A cars, but early cars need to pay attention to brakeline thread pitch, and driveshaft flanges.
Alignment: There are a few adjustments you can make to enhance the Mazda's handling for particular driving events or styles. Mazda's factory alignment specs are just swell for a run to Burger King or King Soopers, but are not so swell for other things that we like to do. First, factory camber specs on the 1st gen are positive, which limits cornering power. Try rotating the upper strut mounts to bring the offset inward. This will decrease camber to a better spec. Ideal for street use is perhaps 1/2-1 degree negative or so. Caster affects the car's stability. A little more caster can't hurt - and this can be achieved by rotating the strut mount rearward (both inward and rearward are achievable). It is beneficial to have these adjustments done equally to both sides. Get what you can as long as they are symmetrical. Toe affects the car's stability also. Toe out, simplistically explained, has tire slip angles that dictate the car be in a perpetual turn-in situation. Conversely, toe in has slip angles that make the car more stable (bisecting slip angles). For the street, a little bit of toe in is a better bet, unless you like constant steering correction. I like mine with 1/16" total toe in. Spec is about 1/4" toe in.
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The OE 12A front disc brakes are pretty good on the '80+ cars. Forget the crummy wedge style brakes on the '79 cars. You can bolt on the '80 caliper and hanger, and the brake lines will even match, as the thread pitch is the same. '81+ cars have a differnt thread pitch than the earlier cars. The rear drums work pretty well, but these rear ends lack the limited slip differential of the '81+ GSL cars. These rears are bolt in items (you will need the parking brake cables, too). I can recommend the carbon/kevlar material Hawk HPS and Porterfield R4S, as well as the Axxis (the pad formerly known as Repco) Metalmaster pads for a little better fade resistance and more stopping power, but you must flush and bleed new fluid into your brakes often (at least once or twice per year). If you race, do it before each event. I like the Ford DOT 3 truck fluid, and if that's not available, I like the Castrol stuff.
The GSL-SE has larger front and rear rotors, but requires considerable work to fit to a 12A car - but it is all essentially bolt in stuff. The '84/85 12A front rotors have larger inner bearings that they share with the GSL-SE. You will need the entire rear end, rotors and calipers to do the swap. Additionally, you will require the entire strut assembly, rotor, and caliper. You'll need the wheels also.Good luck on brake line adaptors if you fit these to early thread pitch cars.
The later '84/5 lower valence panel has vents that work rather nicely for ducting air to the front brakes. Use a few feet of 3" hose and cut a way a litle of the plastic fender liner to duct air to the caliper area. This works if you spend time on a track.
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I have had good experiences with the stock Nikki (actually a Hitachi) 4 bbl carb. When it is properly rebuilt and adjusted, it works fine on a stock port engine, with good driveability, reasonable mileage (it is a rotary, afterall), and great reliability. I prefer the HYGRADE rebuild kit (p/n 1401) for all '79-85 Nikkis. The '79 carbs have a slightly larger intake horn which is desireable. 1st gen tinkerer and good friend Todd Hornsby has outlined Nikki mods in a really good webpage, so I don't have to. See Todd's webpage in my links section.
The '79/80 intake manifolds are the better flowing ones to get, but they are not true bolt ups to the later engines due to the exhaust port for the ACV under the primary intakes on the later cars. I have just drilled and tapped the early manifold and bolted a piece of aluminum angle under the manifold and used a later gasket with good success. An alternative is to remove the shuttervalve and use JB Weld or Devcon to fill the resulting holes. The important thing here is to get the shuttervalve out of the air stream and plug the linkage holes. Another tip - port match the lower manifold to the ports on the block - they are way off (this is another illegal mod in most racing - be warned!)
I have had good results with the Mikuni 44PHH on the 12A motor. This is an excellent carburetor, and gives quite a bit of improvement in midrange and top end power over the Nikki. They have since been discontinued (along with the Dellorto). These carbs are prone to icing under cool, humid days, so beware. This setup, even with a stock port motor, is an excellent performer with a good exhaust. I surprised myself with a tired 12A and a full exhaust with this carb setup - major power gains!
Stock or mildly ported 12A jetting for 44 Mikuni PHH:
The Weber IDA series is a proven HP maker, but is not a great street option due to the lack of choke and other things that need to be fabricated to make them work. They, as far as I know, are no longer available.
The Dellorto and Weber DCOE are very similar to the Mikuni. Only the DCOE Weber is still available.
The stock Nikki will not tolerate more than about 3 1/2 - 4 psi of fuel pressure. If you upgrade your fuel pump to something a little beefier (like a Carter, Holley or Mallory electric type), do yourself a favor and get a fuel pressure regulator or risk overflowing your float bowls.
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Next to porting, there is no other power gain as cheap as a good exhaust. And you have to have the good exhaust to get good results with the porting. Rotary exhausts aren't cheap by any means. A rotary is also an incredibly noisy device, so expect a fair increase in noise if you plan to modify the system for performance. Also, cheap mufflers die fast when forced to deal with the extremely hot exhaust gas temperatures (>1600 degrees F).
The OE manifolds on the '81+ cars are pretty decent. They have a high nickel content and are very durable, but combining the exhaust pulses that close to the port robs a little power at the expense of noise control. The early '79/80 thermal reactor ones stink and are incredibly heavy. A good header is well over $100 - let your wallet guide you. The complete Mindtrain systems are my favorite due to the non-use of the OE downpipe, but even a catback is about $400. The stock catalytic convertors seem to do most of the muffling in these systems, but are very restrictive and heavy. A high flow cat or a presilencer go a long way to improving performance. The precat is not really necessary with a modern hi flow monolithic cat, and will pass Federal emissions without it or hollowed out (they seem to self hollow out after so many miles anyway).
The Mazdatrix/RB dual system is also a very nice setup and really wakes up the engine. They use a dual presilencer setup to control noise quite well.
HAS Motorsports in Arizona makes a Spec RX7 mandrel bend race exhaust with a high flow convertor which works great if you adapt a Supertrapp or other easily repackable silencer to the end. It includes everything from the manifold back (except the muffler). With no muffler, you'll get about 93 db - too loud for the street.
For you fabricators out there, you can make your own dual exhaust that will enhance your HP curve. Use 1 7/8" or 2" tubes from the dual outlet header all the way to the axle (about 113"), use a collector in front of the rear axle, and a Mindtrain or other huge tailipipe. Sure, it'll be loud, but your're going racing anyway, right? If you are using this as a streetcar, buy a couple silencer blanks from Mindtrain and use them as presilencers - one in each of the dual pipes. This makes a huge difference.
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Sure, everyone wants a 13B. The Mazdatrix catalog very thoroughly outlines the parts needed to do the swap into the 12A car, so I won't reflect on it. The nicest of the 13B n/a motors is likely to be the '89.5-91. They have factory high compression rotors, a light flywheel and a larger throttlebody/revised dynamic chamber. The older four port ones are becoming quite rare.
The 12A engines have minor differences which can be capitalized on to make for some neat performance increases without buying pricey competition rotors or light flywheels. The '79-82 cars have heavier engine rotors, the '79/80 cars have a 32lb, 215mm clutch flywheel, while the '81-2 have a 24 lb, 215mm clutch flywheel. The '83-85 cars have lighter rotors (by several ounces), but a 27 lb, 225mm clutch flywheel (and the stigma of the feeble water/oil cooler). If you choose to mix/match flywheels and rotors, the best bet is the '83-5 rotors and the '81/2 flywheel and front counterweight. These flywheels have a 215mm clutch as opposed to the 225mm later ones, so you will need to choose the correct pressure plate and disc. It is also essential to have the rotating assembly balanced (Roger Mandeville did mine - and this is my car's brush with greatness).
Mazda Comp sells a rotor housing with factory large exhaust ports from the early 12As, but with a modern 12A casting surrounding it. No cheating if you are a racer! You won't fool veteran racers - the 12A Mazda has been around a long time and it will be quite obvious if you are cheating. Street porting works very well for a street driven car, but it really only works well with intake and exhaust mods. Attempts at more power should be taken in a system approach, not as a bolt on extravaganza. Keep this in mind. No sense having monster ports with a OE exhaust and carb.
I do not very much like the OE Mazda water/oil coolers. The seemingly perpetual o-ring oil leakage and the marginal heat transfer capabilities make these things seem better off in the parts bin. They seem to work fine for a mostly stock engine, however, except for the darned o-ring leakage and the added complexity of coolant hoses (that like to rupture from oil soaking).
The early '79-82 radiators are made to have the big air/oil cooler hanging below them, still within the shroud's influence. This is a nice bolt-on upgrade for a performance rotary. I have had good success with the oil cooler out in front of the later '83-5 radiator. You will have to fabricate oil lines, trim the radiator bracket, and fabricate brackets to hold the oil cooler to the radiator supports.
Oil coolers - for you lunatics that overheat your oil, you can use two coolers in parallel, or an RX4 cooler in place of the single 12A one. The RX4 cooler has an extra row than the 12A cooler. The oil performs major cooling functions in the rotary, so a good heat shedding cooler is a necessity.
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The OE Mazda electronic ignition is just fine for street use. The point ignitions on single distributor rotaries can be upgraded to the electronic ones quite easily by swapping the distributor and jumping the resistors. The ignitors do not need these. The stock Mazda coils are fine.
I like NGK and Magnecor wires. They fit well, are relatively cheap, and work fine.
The stock port 12A motors seem to like just a *little* bit of advance over the factory settings. Just a couple degrees. More than that invites disaster. Keep the lead/trail spread the same as factory (advance them as a whole, not individually).
Spark plugs - all electronic ignition 12A cars should use the NGK BUR8EQ14 plug for lead and trail. I get these at the local Pep Boys for about $4 each. They don't last very long (5-10K), and the fact that they never get a nice cooling waft of air like a piston engine makes their job look pretty difficult. Be sure to use some anti-sieze on the plug threads or risk galling what can prove to be the world's most expensive plug threads. For my 12A racer, I use BUR9EQP plugs lead/trail (from the 3rd gen Rx7).
More to come as I get around to it.