Boss Frog Differential Subframe and Axles
 

They finally released some details and pricing on these items. I think I will be placing an order in a month or two. Will definitely be a step in the right direction for me and when I do eventually do an LS swap I won't need to worry about messing with the rear end at all. Any thoughts or opinions?

Here's a link to their site if you aren't familiar with the kit:
http://www.bossfrog.biz/Miata_V8_Swap.html

Interesting. $350 for the "kit", but then axles are $1750! :eek5: I might would buy the stuff to bolt in a 8.8 and then make my own CV joints.

And funny thing is the t-birds had a 7.5" IRS diff, not the 8.8 IRS IIRC. 8.8's were for Cobra Mustangs and Lincoln Mach VIII's. I think, anyways.

v8 birds had a cast houseing 8.8, the marks have an all aluminum housing.

Interesting since I can get the same axles made for 500$, I guess a 1250$ profit isnt bad.

My 87 turbo bird has a 8.8 solid, with disk brakes from the factory.

Pretty sure the Supercoupes 89+ had 8.8 with IRS.

Hmmmm. I thought all the T-birds and Cougars had the solid axle till the mid to late 90's, when they went to the 4 cyl FWD. I belive I pulled a solid axle 8.8 out of a 93 cougar.
I'm not for sure about the Supercoupe. It was a beast of it's own.

all 89+ birds had IRS IIRC

Apparently the setup they are selling really limits the size of the exhaust that can be used, time to start looking at the competition.

Limits it how much? If you can fit 2.75" or so you should be fine considering you'd probably be running duals with a V8 anyway.

The biggest he said was the 2.25" that they are currently running. I could fit duals, but I don't really want to unless I don't have any other options.

The more I look at the costs involved with any of the rear ends offered, the more I really want to just forget buying a kit from someone and just have it all custom made.

And that is why the v8roadsters kit uses the CTS diff. It is new, available for around $5-600 on car-part.com and much smaller than the ford diffs. I believe they are using up to 3" exhaust on their car. Still extremely expensive, but the boss frog kit doesn't come with the diff either. Both kits are exactly the same price when you get the complete conversion.

I'll have a 3 inch single with the v8roadster kit. My diff is already mounted. Just waiting on other shit. I could probably run dual 2.5s if I need to.

Frank

Do you think you could post a few pictures of that setup actually on the car? I'd really appreciate it.

Here's the pic of the diff mounted without the brace that runs under it:

http://forum.miata.net/vb/attachment...chmentid=63836

Here's a pic of the diff with the pipe mounted. This is a v8roadster pic:

https://publish.comcast.net/rpath/Kd...GgZ0Xb4zyBiso/

Frank

In the first pic, I don't have the front mounting point welded on and I don't think I have the bolts torqued all the way up, so it sits a bit lower than when it is bolted up completely.

Frank

Something is wrong when its cheaper to go out and buy all the tools + axles you need then to buy BOSS axles!!! I found 3 places that all could custom make CV axles to just about any conversion you wanted for 225$-250$ per side


BOSS AXLES - 1750$

Custom made axles - 500$
MIG welder 500$
Torch 400$
total 1400$

Do you think it will handle the the abuse that a 500+ hp car would give it while drag racing on slicks?

I doubt many will be running a 500hp+ car with slicks. Wheel hop seems to be the demise of the CTS diff in the highly tuned CTS-Vs out there. I'll be traction limited most of the time so I don't see a problem in killing the rear end.

FWIW, FM is doing a few LS3 swaps so they're starting with cars closer to that power point.

Frank

First H.p. doesnt matter. Its torque that breaks axles. And the last place I checked said they ran the same CV joints behind a modified 460 big block.

I think a better question would be how much torque do you think the diff will take.

I think everyone here knows this and the number was thrown out there just to give an estimate of the overall power level I am talking about. :jerkit:

Also, Brainsboy, with your conversion, what did you do for the rear?

So build them yourself and sell them. If they prove to meet standards for this use, I am sure you would have tons of customers waiting for you. Buy the CTS diff, the v8 rear end and a $500 axle and you would probably have a lot of turbo guys looking into that option as well.

Nothing yet, still running the 1.6L 348,000 mile diff in it. I know it wont hold up long thats why I have been doing alot of research on doing my own diff conversion which is how I know about the axles now. I didnt want to get stuck with a conversion I couldnt get axles for.

Whatever I do, I will be making a template so making another one wont be a problem. I would like to be able to offer you guys and friends a cheaper solution that doesnt have to break your wallet.

I disagree. And if I had to choose, I think torque IS the better expression to use really, no offense. I don't think it's the torque or power specifically though. It's shock loads that breaks shit. You wind out a gear and then grab second hard and that puts a hellacious load on parts; much more than what the engine produces on its own. I'd argue with a strong clutch the transmission gears "see" 10x more torque on a hard shift then what the engine actually produces. I'd be afraid to do the math and calculate just how much power gets shoved through the gear box as it has to deal with all the energy stored up in the rotating mass at say a 3K RPM delta in say .2 seconds for a hard shift. It's a lot. It's much much more than what the engine alone makes. Ask yourself what would happen if you rev your engine to 7K from a stop, turn the key off, and dump the clutch in gear?

Let's save the debate about horsepower and torque for another thread. What I'm talking about is relatively simple. Launching a high horsepower, high torque car at the drag strip, having it stick and not break the rear end. Launching is probably the most stressful thing you can do to a car. Plain and simple, it's violent, much more so than running through the gears will be. With our cars, the rear end will go long before the transmission. At least that's been my experience so far. Running slicks and using launch control, I need some kind of solution so I'm not coming back to the forum to share the pictures of my shattered diff. I'm hoping to find out some information on a rear end setup that will handle this kind of abuse. I thought that Boss Frog had a solution that was worth looking into, hence why I started this thread.

1989 - 1997 T-Birds all had an IRS setup. Pretty upscale setup for a vehicle that came at one time with only ONE engine.. a 3.8 liter with 140 horsepower and an automatic transmission. However, the exact same differential and SLA IRS setup (with a limited slip unit) was in the SuperCoupe, which was factory rated at 315# of torque in a 3800 pound car. All that on only 12psi.. :)

I liked the price of that rear end bracket 'kit' until I saw what they wanted for the axles. Crap.

Granted, I'll give them this;

Brand new Wheel bearings are like $140 each from the dealer, hubs are like $85 each, New Axles... Meh. $400 each?

IMHO that drive shaft is a ripoff, too. My very first hotrod, I put a T-Bird 2.3 Turbo Lima in a 1988 Ranger pickup with a T5. The truck came with a 2.3 w/Mazda M5R1 5 speed so the driveshaft / splines on the output shaft were totally different along with length. Grabbed a measuring tape and piece of paper, called up a local precision drive shaft shop and they built me one from scratch. Cost $180.00.

In all fairness, the price of the boss frog axles isn't too much different from the FM/v8roadsters offering. Maybe they know something we don't. After all, yhey have built more of these than I have :)

Of course they are close to the same price, it keeps them with a monopoly, which sticks it to consumers.

If I started offering axles at 500$ then they have two choices. Either lower their prices or start bashing my products to take away any performance issues. It's easier for them to agree on a price and force consumers to pay top dollar, then both companies win.

I doubt they make their own axles anyhow. They are probably buying from the same guy thats making them for 500$. If you want to spend 1250$ extra just for the Frog or FM name, then I say go for it, money doesnt care who ownes it. Spending more doesnt mean you getting a better deal, It just means you havent done your research.

$500 & $1500 axles will be different. My old Driveshaft Shop axles I used with my 500hp Miata were made of 300m material and strong as hell. They cost around $2000 with new hubs and I never ever worried about them breaking.

I think you might have misinterpreted my post. The v8 roadsters kit was the first on the market with the CTS diff and the axles in question. I found it interesting that when boss frog produced their kit, you get almost the same price +- a dollar. Personally, I would love for you to make your kit cheap enough so that guys with turbos might consider upgrading to the CTS diff. Personally, I am not interested in the 8" ford rear. I know there are many people with this rear end in their cars, but I would rather have the CTS to ease exhaust routing concerns. Build a set of axles, a driveshaft and a CTS diff mounting option for about $1000 and I know I would buy one.