BOSS FROG PRODUCTS
Automotive Rollbars and Aftermarket Products for Miatas and MGBs
The Miata Venom V8 ™ Kit
If you are ready for some awesome power out of your NA or NB Miata, then look no further. Boss Frog has developed some new V8 swap kits that will turn your car from mild to wild! Boss Frog has been building top quality rollbars and accessories for Miatas for over 5 years, and is far from being a garage startup or a one-man operation. You can be assured that these kits will have the outstanding quality and customer support of the other Boss Frog products.
Boss Frog uses the following key drivetrain components;
Corvettes, Camaros, Firebirds and GTOs, because they are lighter and more powerful
than the Ford 5.0 liter V8’s.
• Transmission - the transmission selected is a Borg Warner T56 syncromesh 6-speed
manual transmission that was used in Vipers, Corvettes, Cobras, and F-body cars. These
transmissions use a hydraulic clutch and have an excellent performance record.
• Differential - Boss Frog looked seriously at the Getrag differential used in Cadillac CTS.
The bottom line is that these transmissions were developed for 260HP V6 engines, and
they have had serious problems with seals, loss of pre-load, whining, and wheel hop
which has resulted in recalls and thousands of angry customers (see the Cadillac
forums). Of course these vehicles were heavier than a Miata, but even the similar size
Pontiac Solstice was recalled for these same differential problems. The differential that
Boss Frog uses is the track proven Ford 8.8 with a custom independent rear suspension.
This bulletproof differential has hundreds of gear ratio and limited slip options
combinations available, all of which are readily available anywhere.
• Driveshaft – Boss Frog’s driveshaft has the biggest joints and tube size available in
these kits – over 15% stronger than a stock or competitive kit driveshaft.
• Axles - the Miata CV joints were never intended to handle the 350+ horsepower that
these LSX engines are capable of, so Boss Frog uses the larger Ford outer CVs.
Boss Frog kits will give you the strongest overall drivetrain available, so that you can put down the most reliable horsepower at the track or the strip. The kits are divided up into various components and systems, so that you can purchase exactly what you want, when you are ready for it. All shipping is to continental USA only.
Installation Instructions - To View Click Here.
Kit #1 – Engine Subframe (LSx) – this kit includes a professionally designed engine subframe, precision built in a welding fixture for the best possible fit. Our plasma profiled mounting brackets and heavy wall rectangular tubing are much stronger than round tubing subframes, and we reinforce the front crossmember and uprights to gain additional strength where it is needed. Our kit does not require cutting into the transmission tunnel, dashboard removal, oilpan modifications, or additional steering joints. The only changes
• urethane motor mounts and block adapters
• extended steering joint
• front sway bar relocation parts
• grade 8 hardware and installation instructions
LSx-K1a - Engine Subframe kit for NA
LSx-K1b - Engine Subframe kit for NB
Kit #2 – Transmission Mount (T56) – this kit includes heavy 14ga frame rail channels to increase the torsional strength of your chassis. The channels include mounting plates where the transmission crossmember is bolted. The transmission crossmember has wide gussets at the ends, to decrease flexing between the frame rails. The transmission is attached to a urethane mount, to allow some movement while holding it firmly in place.
The kit includes;
• transmission crossmember
• urethane transmission mount
• grade 8 hardware and installation instructions
LSx-K2 - Transmission Mount kit
Kit #3 – Differential Subframe (Ford 8.8) – this kit fits the Ford 8.8 IRS differential center section from ’89-’97 Thunderbirds, which has two vertical mounting holes on the front, and two horizontal mounting holes on the rear. The kit utilizes four existing mounting brackets that are stock on the NB rear subframe, and are easily added to the NA rear subframe. The unique design of the Boss Frog Differential Mount features a two-piece formed mounting system that is much stronger than tubular mounts. The lower differential mount attaches solidly to the rear subframe in four places, and the rear differential mount attaches to the
• rear differential mount assembly
• urethane bushings (front and rear)
• differential braces
• grade 8 hardware and installation instructions
LSx-K3a - Differential Subframe kit for NA
LSx-K3b - Differential Subframe kit for NB
Kit #4 – Axles – New We will offer several choices for axles, depending on your intended use:
Stage 1 axles are for “normal” street driving – a few burnouts and doughnuts but nothing too serious. Stage 1 axles are based on the Ford 7.5 series axles.
Stage 2 axles are built for more aggressive driving including some autocross or street racing. They are essentially the larger Ford 8.8 series axles.
Stage 3 axles are for drag strip or serious wheel-to-wheel racing. These axles are the same as Stage 2 except they include 4340 outer CV housings for additional strength and durability.
All Boss Frog axles kits include a pair of custom length axle assemblies with CV’s remanufactured to factory specs, new wheel bearings, new OE rear wheel hubs broached for the larger Ford outer CV’s, hub spacer washers, and installation instructions.
The Stage 1 kit includes custom made 4340 half axles (7.5 series), with Ford 7.5 inner and outer CV’s.
The Stage 2 kit includes custom made 4340 half axles (8.8 series), with Ford 8.8 inner and outer CV’s
The Stage 3 kit includes same as Stage 2 except with a 4340 outer CV housing and hub spline.
LSx-K4a – Stage 1 Axle kit
LSx-K4b – Stage 2 Axle kit
LSx-K4c – Stage 3 Axle kit
Coming Soon
Coming Soon
Kit #5 – Driveshaft – The F-body cars with an LS1 drivetrain used a 1310 series driveshaft, and other vendors use a 3” driveshaft. Boss Frog has decided to supply a heavy duty 1330 series driveshaft with a 3-1/2” tube, which is 15% stronger than stock, for additional strength and durability. The 1330 series driveshaft assembly includes the rear flange yoke and a front slip yoke for the T56.The kit includes;
• front and rear yokes
• grade 8 mounting hardware
LSx-K5 - Driveshaft kit
the Miata clutch pedal
• master cylinder adapter plate
• slave cylinder adapter fitting
• master cylinder adapter fitting
• 36” stainless braided hose
• mounting hardware and instructions
LSx-K6 - Clutch Hydraulic kit
Kit #7 - Headers - Needless to say, the space between the LSx engine and the chassis is rather tight, and a stock set of headers will not fit without modification. You can make the modifications yourself, or buy this kit pre-made. Even though mid-tube or long-tube headers are nice, they make fitting into the tight space a nightmare, so we use the shortys.
The kit includes;
• gaskets and hardware
LSx-K7 - Header kit
LSx-K8 - Kit #9 - consists of Kits 3-4
LSx-K8 - Kit #8 - consists of Kits 1-6
FAQ's
1. How much cutting and welding is required? The gussets at the rear of the engine compartment must be removed, but this can easily be done with a reciprocating saw. No other cutting of the tunnel is required, so the dashboard will not need to be removed. Stock control arms, shocks and springs, hood, etc can all be reused without modification. There are several holes that get drilled for frame rails and other mount points. The NA’s require 4 small tabs to be welded onto the rear subframe assembly (to match the NB setup). However, the NA Miata’s rear subframe can be removed with about 6 bolts, and the welding can be done separate from the car (or at a welding shop).
2. What steering changes are required? The lower steering knuckle is replaced with a slightly longer version, which moves the steering rack forward about an inch. The stock steering cylinder is behind the center of the front wheels, so the true effect of moving the cylinder forward should make absolutely no difference to steering feel or bump steer, and does not add any additional joints or increase the joint angles.
3. Why did BF choose the 8.8 differential? BF considered both the 7.5 and 8.8 Ford differentials, and a variety of other IRS setups including the Getrag/Cadillac and Supra. The Getrag was eliminated from consideration because of the lower torque rating, limited choices of gears and posi combinations, and it’s recall and failure history. The Supra rear ends are too hard to find. The 7.5 differential would be a good choice, but the supply of these is also limited. BF chose to use the bulletproof 8.8 center section and developed a unique mounting system to maximize both the strength and ground clearance. Remanufactured half shaft assemblies are used with the Ford 7.5 or 8.8 CV’s and a new custom length 4340 shaft. Our new half shafts have a short outer boot to clear the shocks. This rear end arrangement offers a higher overall torque capacity than either a Getrag or a Ford 7.5 differential system can deliver.
4. Why are new rear hubs needed? New OE Mazda hubs are custom broached to fit the larger outer CV’s, and new wheel bearings are also supplied with the kit.
5. Is weight and balance affected? Yes, but not very much. The engine subframe is about the same weight as stock, and the engine is only a little heavier than the 4-cylinder. The transmission and rear differential are both heavier than stock, so some of the extra weight is shifted rearward again. Our ’99 with a ¾ tank of gas and no driver weighs 1380 (52.3%) front and 1260 (47.7%) rear for a curb weight of 2640
6. Is power steering available? BF recommends eliminating the power steering system, but it is possible to keep it. Some re-plumbing will be required to clear the engine subframe. There is currently no plumbing kit available for these modifications but we are working on it.
7. Is air conditioning available? BF does not currently offer a kit to enable the AC system, but it is fairly easy to add, and there are other sources that do offer a retrofit kit.
8. Do your kits fit both NA/NB steering racks? Yes – but the mounting and plumbing of the NA and NB steering racks are slightly different, so the type must be specified when ordering the engine subframe.
9. What about front sway bar clearance? The stock front sway bar would run through the balancer pulley, so it must be shifted forward a couple inches. The engine subframe kits include relocation brackets to move the sway bar forward. The stock sway bar can be used, but the arms should be lengthened about 2” on each side. BF supplies brackets to extend the Racing Beat aftermarket sway bars to the stock (or aftermarket) end links.
10. What about shock, spring, brake, and wheel clearances? BF recommends using either stock shocks or a performance shock that will allow up to stock heights, depending on how much ground clearance you want. Big brake kits work fine. Wheels and tires up to 16x8 and 245/35-16 will fit without modification.
11. What about ground clearance? Ground clearance depends on many things, including exhaust height, shocks and springs, etc. The BF system will keep everything at or above the scrub line – the rest is up to you.
12. Any wheel hop issues? BF supplies new Energy Suspension bushings in the nose of the differential and heavy urethane bushings in the rear to help reduce any tendency to wheel hop. Differential braces are also supplied to tie the rear subframe into the floor and main frame.
13. What about a radiator? The stock radiator is too small to cool the big V8’s, so a new one is needed. A wide variety of choices exist, including Miata racing radiators and custom made radiators. BF does not current offer a “bolt in” radiator…yet.
14. Shifter location? The T56 shifter will fit right in the Miata’s body hole, slightly forward of center, but without any modification to the body or boot.
15. Exhaust? Trying to furnish a bolt-on exhaust kit is a big challenge, because of the variety of sizes and types of exhaust systems available. In addition, differences in hose routing, muffler type, and axle choices will affect the exhaust system design. Boss Frog recommends completing your installation then taking it to an exhaust shop to get exactly what you want.
Kit #6 – Clutch Hydraulics – the Miata clutch hydraulics are too small for the LSx clutches, so a new hydraulic system is required. A stock LSx or universal clutch master cylinder will not fit, so a special adapter is needed. In addition, the GM slave cylinder includes a special quick disconnect fitting that needs to be replaced.
The kit includes;
from stock are some trimming of the engine bay gussets, swapping the lower steering knuckle for a slightly longer version, and relocating the sway bar slightly forward.
The kit includes;
vertical member of the rear subframe, using existing holes for alignment. Because of this unique mounting system, the differential can be mounted very high in the rear subframe to maximize ground clearance.
Boss Frog also uses a pair of differential braces that bolt between the lower differential plate and the floor/frame, to stiffen the rear subframe and help eliminate wheel hop. The kit also uses urethane bushings both the front and rear of the differential, to dampen the shock load. Stock rear sway bars, shocks and springs can be retained. This kit can also be used to replace the stock differential for high horsepower turbo or blown Miatas.
The kit includes;
Combination Kits
Kit #7 - Headers
Kit #6 - Clutch Hydraulics
Kit #5 - Driveshaft
Kit #4 - Axles
Kit #3 - Differential Subframe (Ford 8.8)
Kit #2 - Transmission Mount (T56)
Kit #1 - Engine Subframe (LSx)
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To view the installation instructions, please click here.