charchri4

Ha! Now I learned something and I can go home! Just so you know the Tbird diffs are a clutch style posi/ limited slip / locker what ever you want to call it. Why Ford guys call them lockers and GM guys call the very same thing posi is beyond me...

2 questions. Are you just after the cheapest route or is there some other advantage to using this over what most guys use? (getrag or ford).

Does this support the gear ratio you would want to run?

On price I paid $137 for my 8.8 3.27 locker and it could have gone straight into the car as it was. You can get Martins axle shafts, spacers and broached hubs for about $500ish. So if you can make the mount yourself you could easily match that $800 price and never worry about breaking it.

garret

Just got my quote from Martin a few days ago,
hubs-150
axels/spacers/etc-490
pinion torque mount -100
(cv's not included in any of that)
and then the diff price + fab costs

If you guys think it's totally reasonable to assume I could do the whole thing for $1000, I will look into it more ...I think there was just a lot of sticker shock from Martin's quote ($2,265 but yes I know, you get what you pay for and his work is top notch)

1, no not the cheapest route. The way the diff performs would be great if it works fine

2, yes it would allow me to run a range of ratios.

but again, if a 7.5/8.8-with axles and everything in the car ready to go for $1000 is an easily do-able goal, I am game for that option

charchri4

Roger that I did forget to figure in the axles. I paid $138 for mine.

If you can get Martin to ship with out the CV boots that might trim a bit off. You get them with the new CV shafts and really don't need them.

2 more questions...
What is your comfort level in fabricating a mount for the diff?
What gear ratio are you thinking you will want? (or the question behind the question would you be OK with 3.27?)

garret

1. Totally ok with fabrication, and if I ever run into trouble, there are two pro welders at the shop I will be doing everything at who are willing to tolerate fixing a few inevitable mistakes here and there haha

2. 3.27 is a bit on the low side for my power level but it could be grown into with future power mods. in short yea, I could tolerate it.

charchri4

Oh then you have it made! You don't need Martins mount plate because you can make a much better one for a couple of bucks. Check this out: MiataV8 Conversion: Rear subframe That's the best diff mount ever and totally what I wish I had done. Sorry Martin but your 8.8 is a stupid design...

So if you can live with 3.27s at least for a while you can probably pick up an 8.8 locker for 50 to 100 bucks and run it just as it is out of the bone yard. Ford did a really good job on that one!

Then you need about 65 bucks for bushings and steel for the mount, 140ish for axles, 150 for Martins hubs and 450ish for his axles and spacers. Which is were I dreamed up the $800 figure in my prior post. But yeah realistically if you add in the axles I forgot, do the Audi boots and toss in seals or whatever you would scare the heck out of a grand...

charchri4

Wait you are running a T5 right? I believe 3.27s is the ideal gearing for the T5.

garret

ahh, and yes I am running a t5 ...hmm definitely a good idea to think over, that would work nicely.

tbone heller

Yes it is. And by going with the Ford differential set-up, you won;t have to worry about it breaking when you decide to increase your power level.

garret

update: disassembled my t5 ('84) today to check everything out....

conclusion: ...it was clearly recently rebuilt. timkin races were a give away.. also all the gears were had paint dots on them in order, all new bearings, and the synchronizers looked brand new ... couldn't ask for more! new silicone gaskets and reassembled, ready to go!

ALSO: my buddy who I helped do a 4.8 swap into his rx7 wants to sell me his motor. Through some deals with a couple of his customers he has come into ownership of 2 6.0's and wants to toss one into his rx7, the deal being I buy his motor $400 + cost of LSx swap parts for his 6.0 and a case of beer and we dump the 4.8 with swap parts in my miata

523-LSX-NB

To truly dial it in, you'll also need interchangeable carb parts. Carb will not rob power. It will rob efficiency. The Munster has been set up w/ both EFI & carb. It was tuned using EFI Live tuning software while EFI & switched to carb once the age of the electronics made EFI too much of a PITA to deal w/ any longer. Modern carbs are very easy to dial in w/ near endless options to help set it up. By this I mean tuning part throttle, not just WOT.

You will be able to run more timing due to the carb style intake due to the cooling effect of fuel dumped into the top center of the intake plenum (this would not be the case on a carb style intake that uses the EFI fueling location). Has a similar cooling effect as meth injection. For example: Even @ 12:1 SCR, 8.6 DCR we can run 31* max timing @ WOT w/ the carb as opposed to 26* using the EFI intake & fueling arrangement, each using 93 Octane.

The key will be selecting a modern, tuning friendly carb & then dialing it in w/ properly sized squirters, accelerator pump, accelerator pump arm spring & electronic choke if using the car in cooler weather. You already have the wide band 02 sensor you'll need & can make a cheap listening device to check for knock. Unfortunately, the GM knock sensors will do nothing for you w/ a carb. So, it's important to identify pre-detonation while tuning it.

Don't get me wrong, EFI is far superior in efficiency, fuel mileage & ability to tune every parameter under the sun, but modern carbs & the advantage of the cooer A/F mix make them a great option.

MSD 6LS ignition controllers operate directly off of the stock GM cam, crank & MAP sensors & allow for a basic, yet effecting tunable timing curve. Having just said that, I hope it's true w/ a 4.8L. Should be, just confirm the cam, crank & MAP sensor compatibility.

charchri4

I've always thought of carbs as an organized vacuum leak but I totally agree they are really easy to work with and other than the disasters of the 80s trying to put computer controls on them they have run a lot of great cars for a lot of miles.

charchri4

Hope he likes cheap beer! Seems to me Rx swap parts are cheaper than Miata. Any idea what the bottom line is going to be for you?

garret

So, I bought the motor off of him
includes:
-motor (running and in great shape)
-clutch/flywheel
-low profile oil pan
-edelbrock intake manifold gaskets
-ls1 water pump
-alternator
-starter motor
-ARP flywheel bolts & pressure plate hardware
-few other parts I can't remember right now haha

for $1000.

this puts me at right around 2k spent total. Started selling parts of my last/current race car and the miata shells I got so getting money back towards the build as well. If my part out goes well then I will end up making a lot of that money back.

garret

well guys, I bought a 2004 mustang live axle today for $300 (rotor-to-rotor with drive shaft and trailing arms) from the junk yard....yes, that means deleting IRS... 7.5, 3.73 gear, going to buy a ford racing 7.5 lsd for $200 soon as well. also, that means I have plenty of extra rear miata parts to sell off. if any one needs a rear subframe to hack up or anything or rear calipers, let me know.

Sunshine Guy

In your first post you indicated the primary use of the car would be autocross and track use. The live axle will surely deteriorate your performance there compared to the IRS. The 3.73 gear is too low for either of those applications, as well. Ride quality will deteriorate some, but you may not care about that.

Both the live axle and the gearing would be dandy for a drag car, though!

garret

Well guys, my budget just got kissed good bye, buying parts that are W2W legal pretty much smashed the budget. As for getting the swap running though, the budget is near the same. oh well, it's a race car, I knew it wouldn't be cheap.

As for the IRS v solid axle debate. I'm honestly not sure that it would be any worse. I have been tossing ideas back and fourth with Martin from monster miata and I think things will work out just fine. I think a modified 4 link maybe with a watt's linkage will be able to throw down with the best.

charchri4

Congrats... I think? So Garret what's W2W legal?

garret

wheel to wheel racing legal. For instance the fuel cell I recently posted on face book. A regular fuel cell may be $200 at the most. FIA FT3 spec means more like $600-$3000. I have to have the rule book open for every part of the build. It sucks, but that's just a part of the process.

garret

which is why I was so concerned with fuel cell volume. Prices can get really high, really fast.

garret

ok guys, it's finally go time for engine bay cutting, surface rust removal, engine bay prep/paint, hopefully trans tunnel prep as well if I get to it! I will post updates, here is the before pic!

garret

UPDATE: been a while since I have been on here but, 3 row mishimoto, new 1.8 miata brake calipers, wilwood proportioning valve, master cylinder, boss frog frame rails and many other parts acquired. New welding base/subframe for solid axle has begun being mocked up, lots of work, now working on trailing arm and suspension design!

garret

also, new 6.0 motor with demon carb replacing mine in the rx7, new experience working on LS heads (regrinding valves) , very easy to work on, to people considering these swaps do it! so much easier than a mazda motor! (Our Chump Car CRX on the lift in the background)

garret

Fabricating fuel cell containment box this week, pictures, guide, and ATL instructions to be posted soon as I start work!