Ok, I'm making the plunge. The 20B FC is getting backhalfed. I need to make some educated decisions on what needs to be purchased, what I need to have done and everything else in between.

I can tell you this much, my goal is sub 9 second passes in a street car, and don't tell me it can't be done, cuz I'll die trying

Ok, I have decided to go with a 4-link suspension rather than any of the alternatives (ladder bar, transaxle, IRS). I'll probably end up buying Greg's suspension that he was going to put in his drag car.

Now for the rearend... should I go with a Ford posi 9" or should I go with a Dana 60 or something else that I have not done any research on?

I'm having the backhalfing done by a well known semi-local chasis guy that I've heard TONS of great things about, but I'm open for any suggestions to me that are within a 10 hour drive... So, pretty much from Atlanta to Dallas, Denver to Jersey (I drive fast So, if you know of a top notch chasis guy, preferably one that has done work on an RX7 (especially FCs!!!), let me know.

I was quoted $5000-6000 for all labor. That includes backhalfing the car with all chromoly, installing tubs, shortening the axels on the rearend, installing the racing slicks, a chromoly roll cage, fuel cell intallation... pretty much EVERYTHING but the suspension parts, fuel cell, rearend and driveshaft. What have other people paid for such modifications?

I'm just starting my research, so I'm open for any input, as long as you aren't telling me not to do it... cuz it IS happening

Crazy ****,
Nick

 

Ford 9' is a good choice since parts are cheap

many ratios to play with

Sounds like your going speed crazy LoL

 

I second the motion on the 9" rear end. You will need some fat axles with 35 splines and a really good "pumpkin" to match. But you have a HUGE part of the equation not in this picture; what are your transmission/clutch plans? If you want to run nines and not break all the time your better plan on spending a good wad on that.

 

What is a "pumpkin" ?

Ford 9" rear end is an excellent choice. Hundreds around and easy to find for cheap, tones of ratios, and handles insane power (most comman rear end used by drag racers).

 

i run a ford 8.8 , ,it is more efficent than the 9" and you can get up to 5.13 gears, i have heard of a company making 5.43's but have not seen them yet. there are 3000lbs mustangs running 8.0's with the 8.8 and you can damn near get them for free!! ( i got mine free!!!)

4 link is the only way to go but make sure you get the HD stuff and AFCO shocks are tha ****!!! as far as brakes go i am using the wilwood 4 pistons.

now here is a good question for you.... what are you going to so about the diff? if you put a spool in it than you will not be able to drive it on the street but if you put some sort of locker on it the car is going to 'pull' on the track!! these are the things that are going to pop up while you are putting this beast together. and the car HAS to be scaled which is another issue because once you scale the car and set the 4 link up for the street and you go to the track be prepared to 'look at the sky' because the car is going to try and flip backwards because your IC ( instant center) is set up for the street! if you go the other way than the car will hop badly on the street.


MWW

 

http://www.davidjanesracecars.com/

This guy does this for a living. David is absolutley one of the best chassis men in the country. Check out some of his cars, they are absolutely gorgeous in person. I am taking my car there when I am ready. It is only a 3 hour drive from STL as well.

And, I agree, 9" Rear End. Compared to a Dana 60, the 9" would be the way to go. The 8.8" would work good as well. But I know of more people running the 9" instead.

 

i chose the 8.8 because it takes less power to turn therefore is more efficient, it is weaker though but i have not had any problems yet and i run 14" wide slicks,30psi on the brake and pretty consistent 1.25 60's!!


MWW

 

If you pull the drive shaft and all the bolts on the rear end and then pull the axles out, that big part that hits the driveway is the pumpkin! It is an old school term

Whatever you do be sure to follow the earlier advice not to use a spool if you are going to street this car. You would go through lots of messed up tires and end up in your neighbors yards every time the roads got a little wet.
Of course if you were really hardcore you could have two sets of axles and diffs and switch them out when you wanted. With a lift and air tools it is easy enough and you can uncap the headers while you are under there.
If you don't have a lift though you better have the metabolism of a squirrel because this **** will get really old really quick. I am a firm believer though that if you are serious about racing you can't be lazy and you need to be willing to sacrifice blood, sweat, tears and lots of MONEY to get timeslips that look better all the time.
A spool is a cheap(er) way to set up a bullet proof headache free rear end to get equal power to both tires. By design nothing can slip.
Once you get it tweaked to where you are launching straight you are good. But we are back to my question of what are you putting between the motor and driveshaft? Busting trannies, shattering clutches, and slinging drive shafts are most common failures racing.
Keep the "weakest link in the chain" theory in mind during this project. The better the tranny the better off you are going to be.

 

 

That post must have been pulled from another thread, I am not seeing it here.
It certainly answers the question though. That tranny cost more than the rest of the project but if you have the money then that really rocks!

 

good post Scalli!!! Kurgan, what are you going to do about the tranny? no mazda tranny is going to withstand even one hard launch with those big *** tires and the G-force is going to set you back a minimum of 7000.00 (twin disc clutch, bellhousing, transmission shifter etc etc) the cheapest alternative is to go with an automatic TH400 with transbrake and a high stall (about 3000.00 )


MWW

 

I have not seen a turbo 400 ran on a rotary. Who is doing it? That would be a very interesting setup to see. I wonder how much HP loss you have running through a turbo 400?
I guess since he is running a 20b though it is not like putting it behind a 13b.

 

Marcus, what kind of auto are you running?

 

i am running a TH350, it is the same thing as the 400 except for it can handle more torque, but the pump has 5% more friction than the 350 so it is not quite as effecient.

 

Scalli , i have a convertor that only loses 5-8% instead of the normal 18-23% of most convertors!


MWW

 

How did you do the bolt up? Did you use a plate with the bolt patten of the tranny and motor?

 

i made an adapter plate that integrates the starter and use a chevy FW and starter.


MWW

 

I remember reading somewhere in one of those old "chevy high performance" books that it is supposed to take 36more HP to run a TH400 vs a TH350. Does this sound right?

 

yep!!! that is exactly what i am talking about. the fluid pump on the 400 is larger

 

Hmmm, I'd go with the 350 then. At least at first thought I tend to feel that way about it.

 

the 350 will only hold about 750 ft/lbs of torque after that you should go with a 400. the 750 ft/lbs is also rated with a 3000 lb car, meaning that you can run more torque if the car weighs less ( mine weighs alot less) i dont know how much more it can take but i imagine that at least 900 ft/lbs is feasible.