Andrew91GT

I'm starting this thread to document the progress of my project car progress.

I have a 1990 firebird formula (my high school dream car - cue up 'hair nation' on the DVR!) that I'm building a NASTY street car out of.

Goals are many:

1. to be able to drive it to the dragstrip, bust off a low 8 or high 7 second pass, and drive it home.

2. be fun on an autocross/road course

3. keep air conditioning, radio, and as many creature comforts as I can

4. look pretty stock from the outside

5. require MUCH less maintainence than my outlaw 10.5 car did (4.7-4.8 second 1/8th mile mustang)

Andrew91GT

I picked up the car in Denver, Co with ~50k original miles.

Here's how it looked when I went to look at it:



Downtown Denver:



Pit stop on the way home:



In the garage:

xpndbl3

iTrader: (5)

"street" car with a funny car cage in it....

Andrew91GT

I wanted to separate the build into two areas of approach... chassis/suspension, and powertrain.

It was a tough decision, but to make this build cost effective, I determined that I would have to reuse as many pieces of my outlaw 10.5 car as I could. One of these things was the engine - I couldn't justify selling this thing for pennies on the dollar to build something else.

Here's a thread documenting the engine build:

https://www.thirdgen.org/forums/engi...i-think-i.html

Cliffs: 4" stroke, 4.151" bore all aluminum smallblock ford with 390 cfm heads. 9:1 compression, turbo ready. Billet steel rods. Previously made over 900 rwhp at 8 psi boost.

Andrew91GT

It will have a 10 point in it before all is said and done, I'm not interested in another 25.x car. My local track is somewhat lax.

Andrew91GT

I went with C5 brakes up front using Ed's kit. I used c5 rears on the stock drum rearend for the moment knowing that I was going to replace the rearend.

For rear suspension, I went Racecraft/madman/wolfe. I want to integrate a street type antiroll bar that will take over when I disconnect one of the wolfe swaybars but that will happen later.

I wanted to fit a 315/60/15 drag radial for limited street usage and for the dragstrip. In order to do this, I minitubbed the car. Here's a thread documenting my installation of wolfe's 4th gen minitub kit and mini coilover spring kit:

https://www.thirdgen.org/forums/susp...0-formula.html

Andrew91GT

Here's a few pics of the rearend. I went with racecraft's fab9 with a 53" housing end to housing end dimension. Axles were chosen to be Strange custom race axles with 40 spline dimensions at the bearing end, but machined for 35 splines at the other end. 5/8" studs. Housing ends on the rearend are late big ford. I went with the pro series brackets, reloated inward 1" for control arm clearance.

Here are some pics of the housing:











The last pic is the madman adapter bracket that racecraft sells to adapt a madman torquearm to their housing.

Andrew91GT

The differential was chosen to be the wavetrac unit that moser sells, as I wanted something that could turn a corner and not break.






I was going to install this in my strange aluminum 3.812" bore ultracase that I was going to reuse from my outlaw 10.5 car.





It turns out though, that some 'massaging' of the case is required to get the wavetrac to fit. Specifically, the bearings sit 3/4" further apart than the spool that came out of the ultracase... so, $250 in machine work later, it fits.

Andrew91GT

The next thing to do was install the wolfe antiroll bar onto the housing. I also fabbed up a jack point for the bottom of the housing so I didn't bend the wolfe bar if I tried to jack on the rearend.

I used my miller diversion 165 TIG welder to install this stuff....

Andrew91GT

Lest people call BS on the power numbers, here's a picture of the motivator for the engine:

FueledSoul

iTrader: (18)

Andrew91GT

It kind of comes across that way, doesn't it?

Stephen

iTrader: (12)

How long you think this is gonna take to build?

Is Murphy up by Wylie? My longest friend ever lives up in Wylie.

Andrew91GT

Here's what the machine shop and I had to do to get the wavetrac to fit in the ultracase:

No, it doesn't fit.


Taking it apart:


Case clearanced and hitting the mill:


Had to cut the cap too:


Cutting down the adjuster nuts to compensate for the wider differential so we get adequate thread engagement:


Checking for clearance:


Setting backlash, put it at .009":

Andrew91GT

Got a new baby and such, I fight to find an hour here and hour there to work on the car... I'm guessing maybe middle to end of the year if I'm lucky?

Murphy is pretty close to Wylie actually.... I think it borders it on the west.

Orr89RocZ

iTrader: (20)

Subscribed... you trying to stick with a small block motor or going big block? I think a big block would be more reliable than a smally at those levels but either one is capable...just think the smally would be more of a wild combination to push those numbers

Andrew91GT

The bracket I got from racecraft for the madman torquearm needed a few mods to work....

It seems that it won't clear the case:



I had to grind up the case and then I TIG welded the madman bracket to the racecraft bracket. I was able to use one of the bolts, but not both. You can see where the majority of the tube for the rearmost bolt had to be cut.



Picture of the rearend assembled with e-brake brackets installed:



I decided to go with wilwood 12.19" rear disc brakes for late big ford. I chose the 2.5" offset to get a tad more clearance to the inner wheeltub for the 315 radials. I wanted the drilled/slotted rotor, but couldn't justify the difference in cost.

Andrew91GT

I absolutely wanted a big block. My inspiration for this setup is Larry Larson and his drag week chevy.

I really had my heart set on a 555" bbc with RHS or DART pro heads. Honestly, it was just too much money for me to spend.... I have this old ford junk sitting around so I put steel rods in it and a little more friendly endurance lobe solid roller so I could go with a more friendly spring pressure. I figure I'll lose a few horsepower with the cam but will be more than made up for in reduced maintainence and cost. I really didn't want to be 'that guy' with the bastard powerplant in his car, but selling for $0.25 on the dollar to have to buy new again didn't work for me either.

This engine with the more aggressive cam has used enough fuel for ~2200 hp, and pushed my 3080# car to 157 mph in the 1/8th at 30 psi of boost... I figure the turbo should make another 10-15 psi on top of that fwiw. Is it fancy stuff? Not really. Maybe some day down the road I can do the big block like I want to.

I want to roll around at 5-10 psi on the gate on the street, and crank the CO2 up for some real boost at the track.

Orr89RocZ

iTrader: (20)

Yep i'd love to do something similar but I'd be happy with low 8's let alone high 6's

There is another guy that competes in those things with the 80's firebird...he's got a small block chevy with twins in that thing and goes 7's. Eric Yost is his name.

Andrew91GT

White car? That thing is awesome!

FWIW when doing research on turbo kits and seeing how everyone fabricated theirs, I checked out your car. Super nice setup! I'm especially jealous of the camaro and how easy it is to get good airflow across an air to air intercooler, I'm not sure how I'll address that on my car.

Stephen

iTrader: (12)

To get good airflow across the intercooler, you could set it up like Paul's car, but it would kinda stand out, if the car isn't painted black.
http://www.pollymotorsport.no

FueledSoul

iTrader: (18)

Just kinda happened when i subscribed

RedneckNo4

dart 763 tall deck with twin turbo's some day??

83 Crossfire TA

iTrader: (2)

Well, you do have a nice pile of parts there, but I'm not sure I see it coming together as described, of course I don't really want to say too much since so far you've solved some of the issues by basically throwing $$$ at the problem, so I somewhat expect to see more of that.

I've thought about this kind of build before (not quite to that HP level, but fast car that would be fun in a "handling" situation, for that matter, it seems like everything I've ever owned has been setup more for autox/road course even though it only _really_ got raced at the dragstrip), to that end:
- Unless Madman has significantly redesigned their TA that piece is totally incompatible for anything but straight line launches. I would even go as far as saying that it's about as appropriate on a street car as a ladder bar setup is on something more old school, and forget it in a handling situation. Unless of course you've considered that already and have some plan for it.
- the Wolf anti-roll bar... How do you plan to use that in an autox/rr situation? I've really wanted to do just that but I can't seem to work out how to do it, it's just too stiff. The additional roll stiffness on the back end would result in a car that would be twitchy and dangerous to drive fast on the street, and impossible to autox or rr. To balance that you'd have to run an insane front bar and front spring rate, and then still end up with MUCH larger rear tires than the fronts. Alternatively you could disconnect it for handling use, but then you wouldn't be left with enough roll stiffness in the rear to push it hard in the corners. It's not easily removable so there really isn't a possibility of removing it and using a more standard rear bar for cornering, and I don't believe that it leaves enough room to just disconnect the endlinks and add the second bar. What do you plan to do?
- What wheels/tires do you plan on running for street/autox/rr? Unless you're going custom the large stud setup isn't usually compatible with that.

I think that you have our attention, but I'm betting that I'm not the only one thinking what I'm saying here, that I'm not sure your approach can get to where you describe you want to go with this. I'm especially curious about the wolf bar... something along those lines makes going in a straight line _much_ easier, but makes getting a cornering setup out of it much harder (the TA and wheels thing there are solutions for)

Andrew91GT

Thank you for the constructive criticism, and some real feedback. I will admit that I know a whole lot more about going straight than I do about turning. Handling and how to achieve it is really my weakness.

Some of what I'm doing is basically reuse of what I have. The rearend is a product of trying to make stockish stuff work in my mustang and cleaning the teeth off both the ring and pinion twice in 3 passes. I knew the stock 10 bolt in this car wouldn't last long trying to throw any real power at it and I didn't want to have to worry about it.





Actually, I had not considered that. I looked for proven suspension setups for high horsepower cars and they seem to be it. They also provided considerable free tech support so I wanted to patronize their business. I figured a panhard is a panhard and control arms are control arms essentially, right? With the rearend I ordered the choice was either the racecraft torquearm, or the madman torquearm.

What do you feel is the design shortcoming of the madman torquearm? Is it a lenth issue?

I believe that there is enough room to attach a second stockish style (perhaps width will have to change) ARB to the rearend which would be much more appropriate for handling situations. My current line of thinking would be to have both of these hooked up for the dragstrip, and disconnect the wolfe bar for street/handling use. Maybe there will be some binding with both hooked up but I believe that the wolfe bar will prevent the stockish style ARB from doing much of anything.

This is another thing that will require some work to make happen. My current setup has stock 19x10 c6 wheels with 2" spacers on the rear. When deciding on overall new rearend width, I had a buddy of mine bring over a set of 19x12 c6 z06 wheels which I used for fitment. I knew that the stud size/spotfacing of the wheels would be a deal killer with the small studs, but I really needed the large wheelstuds at the dragstrip.

Doing some math, it looked like I could narrow the rearend 2" per side, and the c6Z wheels would fit nicely if I put the 2" spacers back in (stock width effective rearend) in conjunction with the minitub.

My adapters look like this:



I plan to drill the holes where the axle studs fit through the adapters to 45/64". The next issue is that of attaching the adapters to the 5/8" studs. Moroso sells a tapered 5/8" lugnut. I will have to enlarge each of the holes that the axle studs go through so that the lugnuts will fit and I can torque them, but maintaining the taper and using a tapered style lugnut should properly locate the adapters. The lugnuts require a 1" socket to R&R.

With a solution for attaching a c6Z size rear wheel, I could go to an 18x12 with the same offset to use some real tires if I ever got good enough to need them.

The car overall is a compromise in many ways. My last car was great in a straight line for around 4.7 seconds, but absolutely sucked for anything else. Honestly, it was way too much work and not enough fun.

I want this car to be useful for many things, but not the best at any of them. I think I will get a LOT more enjoyment out of something that is multipurpose, even though I will give up some straightline and some handling performance to get there.

superirocz

iTrader: (5)

I think compromise is the key. If you wanted to build a killer road race car then the 2k hp would be useless and not hook under 120mph not much fun on the highway, it gets old real fast. This car should do everything very well and heck with that much power you go a little slower in the turns and pass them on the straights.

I run a MW fab 9" with a mid lengh torque arm and racecraft sway bar and it handles very well in the turns. Not sure how short the madman piece is but it won't be as bad as a 4 link lader bar.

Sounds like you may runs 19s but if you can go with a 18x13 and run the hooser drs they work very well and don't handle bad either. I run the 335 17s and its very effective on my car. I still run my kyb shocks and stock iroc springs and still managed a decent launch with only a few attempts at the track.

Stephen

iTrader: (12)

On this extensive of a build & your talking about using wheel adapters? 2000 horsepower & adapters?

Buy wheels that are direct fits & don't require double the lug nuts & extra parts to put them on.

Andrew91GT

There's no way to use all that power with a street tire, so the boost will be brought WAY down, maybe 5 psi or so. That ought to put me around 650-700 rwhp... I think the adapters should be fine for that.

Orr89RocZ

iTrader: (20)

I been running adapters on my stock 4th gen rear at 650-700rwhp just fine

superirocz

iTrader: (5)

I would reconsider the adapters, just my opinion.

On the power I make around 1000hp and I have no problems putting that on the street with 17s all around and hoosier DRs. 2000hp may be tough but its not as hard as you might think and with a AMS 1000 you can ramp it in etc and I don't even run one of those yet.

83 Crossfire TA

iTrader: (2)

I'm very interested in this discussion since I've been thinking about a similar setup... not quite as much hp, but I want it to be competent at both the drag strip, road course, autox and street, so I have tons thoughts about this as well as places that I don't think I've come up with a good enough solution. Yet...

That said:

The fact is that the adapters are strong enough to handle the forces that you can exert with street radials. Yea, all that extra hp could be a problem for them if you dead hooked, but you won't so I wouldn't worry about it.

I would be a bit concerned with the extra machining weekending the adapters, but they've shown to be strong enough at 1-1/4" thick, so I suspect you'll be OK if you're careful with your machining.

I'm doing something similar on my TA, with some 17x9 and 18x10.5 Z06 wheels, stock 3rd gen width moser 9" and similar 2" spacers (I've got 7 sets of stock gears that look like yours from previous projects). I haven't measured yet, but I don't think it will work out as well as I want to. The sticking point is that to get the studs long enough to stick out like my local tech inspectors want gets them around 3" long, meaning that they will stick out about 1" past the spacers, so unless I can find room in the back of the wheel hubs to hide that much of a stud in there I don't think it will work (or if I can cut the studs down enough to fit but still go through the lugnuts o make the tech inspectors happy).

In retrospect, a slightly shorter axle leaving room for an even thicker spacer would have probably made this easier, it would have also given me more choices for drag wheels that would put the tires where I want them (in my case fit is _much_ more important since I'm trying to avoid really minitubbing the car, meaning that 1/4" wrong either way means things hit)

83 Crossfire TA

iTrader: (2)

Madman TA- again, I haven't looked at a new one for a few years now, so they may have changed things, but the setup that they were using worked by not letting the axle move more than it had to... basically it bound up, limiting motion and almost acting like a solidly mounted axle under a hard launch. Effective at the dragstrip, but not so much so on the street and a disaster on the road course.

Wolf bar- I had the same idea, with the added bit about using something similar to the quick disconnects that the rock crawler guys use to swap between the two, but I honestly hate that solution... between the extra weight and all the extra stuff hanging around it seems at best inelegant and wasteful.

Orr89RocZ

iTrader: (20)

Why not use a 4th gen spec rear and not run rear spacers? I got 2.5" studs with a 5/8" slip on spacer and they fit the 19x10 wheels great, studs stick out just past the nuts to pass tech (even tho my drag setup uses those long shank style bolts with a closed cap)but I can use the oem silver lugnut caps from a z06 to cover the studs on the street so it looks great.

I need to retract my comment on spacers on the rear, i dont run a thick bolt on spacer in the rear, but on the front. I forgot what I was running there for a second...I had to run spacers on my LS1 trans am to fit the same 19x10 wheels.I have a small slip on spacer for the 89 camaro.

My suspension setup I'm very happy with. Full bolt on factory style with adjustable shocks. With the shocks set for drag, I can 60 foot great. Then set them stiff with the street tires/wheels and run corners all day long. I think it works great and the car handles pretty well. It scares me but the weight balance is really front biased now I believe since the turbo setup added probably 100 lbs up front. It sits lower in front now and really feels heavy on the nose.

What about a watts link? Better than panhard bar and probably could work with a aftermarket rear designed for thirdgen but I'm not sure.

83 Crossfire TA

iTrader: (2)

your stud setup wouldn't pass tech here (or in a lot of places), where they require open ended nuts and the studs actually sticking _through_ them to prove beyond any doubt that they are threaded deep enough into the hex on the nut (If they stick through you can see the threads and there is no debate if there is a starter end on the stud where the threads start...)

What factory bolt on stuff/shocks do you run?

I'm not sure what a watts linkage solves WRT to this discussion. What it amounts to is that it's a more complicated way to center the rear axle _slightly_ better than a panhard rod, but within reason (properly located and adjusted) i don't see why a panhard rod won't work...

Orr89RocZ

iTrader: (20)

I run spohn LCA's with relocation brackets, spohn adjustable torque arm, eibach prokit springs and tokico 5 way adjustable shocks. Stock Irocz sway bars, 36/24mm.

The adjustable shocks enable it to be both drag and street. The setup has been 1.41 60 foot with a nitrous motor than ran mid high 10's. Its been 1.49 on the turbo setup off the footbrake and is capable of alot more if I'd leave with boost.

Something like that I think should be ok. Question is, will you leave the line off a trans brake or 2-step with boost? How much? With minitub, you can fit a fat slick there so it should hold the power, but leaving with 600-800whp is tough for any tire short of a full slick in a tubbed setup. The drag radial guys are doing it but have great chassis setups, not what you would have in a street handling car so you will have to compromise. My 26x11.5 et street bias plys have done well but I havent hit it with 600+whp, just around 500-520whp.

Watts link is just an alternative to the panhard bar which i have heard becomes a problem in extreme handling situations. Maybe the panhard bar will be enough for most people but if you really want the best handling setup, its an option.

Andrew91GT

The madman has a tube-within-a-tube design at the front where it attaches to the crossmember. The tube can slide within as it needs to as the suspension moves. It has a weld-in crossmember with adjustable mounts for pinion angle adjustment, though you have some adjustment for that at the rod ends that bolt to the rearend.

I agree that it's not ideal, but I didn't know another solution that would work at the strip. One could put a similar type bar up front and tune the bar thickness, spring rate, etc. to get desired performance, though I belive that the result would be unliveable on the street.

Andrew91GT

I wanted to run a 15x12 rear wheel and had a hard time finding a shelf part that had backspacing larger than 7.5", thus I ended up doing what I did. I made some measurements and ended up with a compromise that 'should' let me run both wheels.

What shocks do you run? That is one thing I'll have to buy at some point, I have stock junk now. Madman is pushing the afcos at the moment. I know they're great drag racing shocks but not sure about how they would handle trying to take turns.

Andrew91GT

The tires I'm going to run at the dragstrip are the 315/60/15 MT radial tires. David Wolfe has been 4.40 1/8th mile with them. I believe that they are capable of 1.1x 60' times. Now don't get me wrong, I'm not on Wolfe's level but if I could crack off a 4.99 full tilt on a perfect track on a perfect day I'd be estatic. They're a 30" diameter tire and ~14" wide.

I'm very interested in a Watts link setup but don't know that much about them... I guess the big question is how much difference would I notice in my application?

One big thing I will need to do in the future is to modify my frame side panhard bracket to minimize the roll center to make it handle better.

83 Crossfire TA

iTrader: (2)

Orr... your car is a good example of why i like these cars for this kind of thing... 1.4x is pretty impressive for what basically amounts to a street handling setup, and I'm not sure that there is any other suspension out that without changing much but the tires you could make some respectable runs at an autox and the dragstrip...

Any reasonably well setup (in other words, nothing broken or loose, good tires...) 3rd gen that makes the power to run those times can do it, but a more straight line oriented setup makes it easier to do it consistently. In my case I'm shooting for optimizing the setup around a 275/60-15 DR or a 28 or 29x10.5 slick, maybe a 295 DR. I just don't want to stuff _that_ much tire under it which is going to make repeatable and safe results on questionable track prep more difficult (this is mostly a fun thing, so it will mostly get run on TnT nights which don't always see the best track conditions, and I mention safety WRT to this since we have run into issues before with a fastish car which could run good times and get off the line but its no fun when there's a 50/50 shot that you blow away the tires at mid track and start going sideways/have to let off).

What's worse is that I was a serious autox'er before dragracer and I definitely have my thoughts about a setup I prefer (I'd rather have stiffer springs and softer sway bars, don't like progressive springs...). I like stiffer specific rate springs and 32mm (or 34mm hollow) front and 19 or 22mm rear bars rather than the more typical 36/24 setup with springs like the eibach pro springs (which are a progressive rear spring)... The end result is a setup that is less prone to transferring weight and controlling the axle on a launch.

I have made this work before at the dragstrip using air bags in the rear springs, but have gotten a lot of responses here that that is not a safe way to do it (though no real explanations why, just that a wolf type bar is more consistent). The problem as I see it is that a dragstrip setup wants the rear suspension tightened up relative to the front, that really stiff, preloaded sway bar which will make the car prone to oversteer on the street and road course.

83 Crossfire TA

iTrader: (2)

Again, I think that the biggest thing that this kind of a car will see is slightly more precise location of the rear axle (do the trig, once you figure out how little it matters I'm sure you won't care). For an all out road racer it has the further advantage of eliminating the little bit of bias/jacking effect you get from a panhard rod, but when it comes down to it I don't think that any of us can really prove that we can feel that in the handling of our cars.

in most cases a Watts link ends up weighing more than a simple panhard bar and I'd bet that will have a greater affect on handling then the rest of the issues. I suppose that someone might make the argument that adding an aftermarket watts link will let you adjust your rear roll center, but you could do that with the panhard bar setup much easier just by extending it's brackets making it's location adjustable.

Orr89RocZ

iTrader: (20)

I agree. My setup is working pretty well for what it is, and stock thirdgen style suspension is a good design for both drag racing and street handling and autox stuff. I mean just changing wheels and I'm ready to drive to the track and lay down times is nice. I'm confident fresh 26x11.50x15's will hold a 1.3x 60 foot on a good track and I know I have the power to do so, just dont think the 10 bolt would like that.

I'd probably go with a non progressive rate spring too. Prokits are pretty stiff and work well with the adjustable tokicos I have. If you had koni double adjustables I think you could find an even better balance. I got the 36mm hollow bar and 24mm rear and they seem to do well. Hard to get the car to oversteer unless you throttle it hard enough but it certainly doesnt understeer. Then again I havent pushed the turbo motor hard in turns yet..weight bias up front now may change things, I will have to see when I get another chance to drive it.

I'm actually considering moving to a 18" drag radial to keep this car more street than strip and never have to change tires. Vette guys and some other late model car guys have claimed 1.3x and 1.4x 60 foots on mickey thompson 18's in various widths so it SHOULD handle my car on the foot brake. Then again I'm not sure I want to try to corner carve with drag radials on the back....

daverr

iTrader: (1)

Andrew91GT nice diff youu got there. I see that your using a speed sensor at the pinion yoke, are you planning to use traction control?? i might do the same with my car.

drknow90rs_ss@y

iTrader: (3)

I have been planning something similar to this build for a while on my '85 T/A. (Pro-touring?) Looking forward to seeing how this one turns out!

Andrew91GT

The sensor is the driveshaft speed sensor for my racepak. I might try something like you are talking about but I need to save my pennies for a while first!

83 Crossfire TA

iTrader: (2)

I don't believe that you've run the 60's that you have with that 10bolt... I have 7 sets of broken 10 bolt gears floating around the house and office (it's become a joke at work, at one point I got written up for the "mace looking thing" on my desk)

I do have a set of koni yellows that will probably go on that car, but I honestly don't believe that they are as adjustable in a useable range for straigthline use then the tokicos or even KYBs. I also have a set of eibach prokit springs on my formula (which has become the parts car), but I doubt that I will use them. Actually, the rear progressive rate springs are sitting in the garage, they got swapped for some trimmed stokers which totaled up to stiffer and specific rate. I'll probably use those in the back, and the front will depend on how much I'm willing to compramize for straight line use. The softer front springs/stiffer front sway bar I decide to use, the better it should work straight line, but the less I'll like it on the street.

That's not that crazy... it's not really uncommon to do that on a high hp car at the autox. Big cars running 15's often run DR's on all 4 since there aren't many good, large 15" rim performance tires out there. I used to run Nitto DR's on the back of my 97 WS6 _all the time_. They worked better on the back on the street and autox, even in damp conditions then the current generation high performance street radials (back when eagle GSC's were good tires) and gave consistent low 1.7x 60's at the dragstrip (I doubt that the car would have run better than .05 faster with proper slicks). I've considered doing the same on my 18x10.5 Z06 wheels, the only real issue I see with that is that you can't get around that the wheel/tire combination will be significantly heavier than a proper set of drag wheels/tires.

OTOH, I'm not sure it's a great choice for the road course, I could see overheating them there and them getting greasy...

Andrew91GT

Wheels came in last night.

It seems I made a slight miscalculation in ordering the backspacing, so I'll have to order some spacers for the wheels. if they work nicely, I'll weld them to the wheels. Actually, I'll probably have to farm it out because I don't think my little diversion 165 will have enough current to weld these things.

The reason that the backspacing is wrong is that the wheels hit the control arm mounts on the rearend, even though they have been moved in 1" on each side. Live and learn!


Wheels are 15 x 12.275" Weld RT-S with 7.5" BS.


Pic of the wheels with 3/4" spacers on each side.


Clearance to the control arm mount.


Recalculated, here it is with 9/16" of spacers to passenger control arm mount


Clearance to driver's side control arm mount


My handy worksheet for calculating clearance given dimensions of current rearend and wheels mounted on new rearend


I should end up with a little more than an inch clearance from inner sidewall to minitub with a 5/8" spacer, and the fenders will have to be rolled on the outside. The rear stance won't be tucked as much as I would like it to be, but I think it will work. Yes, I have adequate thread engagement for the lugnuts even with the spacers. The studs are strange 3" long 5/8" diameter.

Orr89RocZ

iTrader: (20)

Haha you are welcome to take a look at the underneath of my car...its a junkyard 2.73 special from a ls1 fbody....same rear i have in my 99 trans am. Absolutely nothing done to it.

Thats good to hear. I just picked up a set of 17x11's for the rear of my 99 trans am with 315 nitto drag radials. Havent tried handling yet but so far on the street they seem to grip pretty good. They dont feel all that heavy to me but certainly are heavier than proper drag wheels. Thats my only issue is that I will be adding 70lbs to the car over the drag setup I have.

WOW those are wide! Square wheels haha.

Andrew91GT

Here's a pic of the tires I'm running:

315/35/17 on the left, 295/55/15 middle, and mine are on the right, 315/60/15.

89_RS

I may just be the picture, but I'm seeing range of motion issues with that large of a wheel & tire setup in the rear. You'll probably be fine for the straight line stuff, but corner carving might cause the tire to rub on the shock or spring. In the front, it will be more of an issue because you'll also have to take the range of motion for lock to lock steering into account.

drknow90rs_ss@y

iTrader: (3)

I'm curious as to why you chose to go with 15" wheels... It obviously wasnt a money issue. (Though, tires will cost you less.)