I used the wrong word there. Not the rate, but the preload. It's sorta like a valve spring - the more you compress it the more pressure is required. So let's say for example I have a 14" spring installed at 14", it might be 150lbs to move it the first inch, then 300lbs to move it the second inch, and so on. By adjusting the spring preload you can influence how much weight is required to compress the shock from the installed height (19") to your desired ride height (in my case, 15.5").

Anyhow. I modified the UMI torque arm mount simply by adding some 3/8 flat bar to it to move the torque arm 1" over. This should work for now until I decide long term what I'd like to do.





I was looking at everything and I think the correct way, as I mentioned previously, to do the coil overs would be to cut the spring perches off the housing and mount the coil over on the back side of the axle tube. The issue is the panhard mount. This goes back to my thinking that a triangulated four link would work good because you don't need a panhard. A setup like this:



But I have more reading to do. Maybe in the fall.

 

Off topic, But I love your car, I spotted it at the Moo's Cruise in a couple of weeks ago. The first time I went I was the only 3rd gen there.

 

Thank you! Did you have the red firebird ?

 

Yes sir I did

 

What do you guys think about the 17x9 GTA wheels for a street strip car? They suggest a 275/40/17 tire. I'm running 275/40/18 on my fourth gen, and I feel like it's not enough sidewall for drag racing, especially with a manual. But I could be wrong.

I was considering putting the 15" drag star wheels on my model A and going a different direction on the third gen, but I'm not sure if I should just do a 15" pontiac wheel with a tall tire or go with the 17x9s.

 

Years ago I had 17x9s w 275/40s. They were sticky yokos. That was w an efi zz4. The were OK but not anywhere near a drag setup. It cornered great and hooked up OK, there were times I wondered if my clutch was slipping in lower gears but I think it was the tires spinning. Now I have 18x10 rears w 305/35s NT 01s. They are really sticky road race tires. They still wouldn't flex like a drag tire. They're great and hook up 550hp really well, but I don't think they'll ever hook like a drag tire. But they are a great for corners and controlled silliness. I see people w similar power to what I have lifting their front tires off the ground. They have drag tires. I couldn't see my car lifting the front end at all w the tires it has. I mean, it hooks great but not like that.

 

I currently run a 17x9.5 with a Mickey Thompson Street SS 275/40-17 with them aired down to 20 psi and they hook pretty good. I do find when I'm really giving it the sauce that it tries to spin off the 1-2 shift but nothing too bad

 

What's the car running for et and mph?

 

That's not very encouraging lol. Thanks for the feedback!

 

I love the GTA wheels on our cars and the 17x9 is an upgrade to the stock 16x8 but I wouldn’t do anything 17”. I run 18x9.5 and I have 285/45r18 Micky ET street drag radials. Made a big difference over the 275/45r18 sumimoto’s I had. They are a ticker sidewall 28” tall tire. I would run that or a 305/40 or something similar for more contact patch. With the similar combo you have I can still break them loose but not nearly as scary having run on the road. I have put about 5k miles on them and they are still good on tread.

18” has become the most available tire size due to the OEMs. Probably more options than 15 and 17” at this point.

 

9.92 @139ish I believe. Little bit of wheel spin. But I think that wheel spin was from using the factory style could springs and shocks out back. Now that I've got Viking coilovers out back I'm not really sure what it'll run

 

I have 275/40/18 on my fourth gen. Looks ok on the 4th gen but I feel like such a low profile tire with a large diameter wheel on a thirdgen looks out of place.

Got a recent photo of your car showing the wheels?

 

What are you running for fronts?

My buddy suggested I run a 285/40/17 on the back and a 255/45/17 on the front which would both be 26".

I think a 5 speed car makes all the difference though, although I'm not sure how long it's gonna last. The TKX seems to have a lot of back lash, and compounded with the backlash I put in to the 9" it bangs the drivetrain pretty hard. (ran BL slightly on the loose side of the spec to keep mesh noise down)

 

My rear is a 285/45/18 tire so it’s a thicker sidewall 28.1” total height. You can see the 40 series in the front and 45 series in the back. The 45 series fills out the wheel wells nicely compared to the 40s. I even had to raise the rear due to the tire height and rolled the rear flares as it cut into the sidewall at some point. I run full aftermarket suspension and 175lb weight jacks and Viking double adjustable shocks. With the 3.55s and 28” drag radials I can still spin the tires on the street but it’s much better than the 275/40/18 summer tires that I have on the front (I ran them on all 4 at one point).

 

I can't remember exactly what fronts I'm running but I "think" it's close to the same size above.

 

Looks good. I almost bought a trans-am parts car a few months ago to use the ground fx and bumpers on my formula. I really think the trans-am's look better.

I'm still torn on the wheels. I also have some 15" mesh firebird wheels in the basement or keep the 15" drag wheels I have. Part of me likes the idea of putting the drag wheels on my model A though, although the model A guys typically prefer steelies.

 

Agreed, that's what I did to this formula 350 car. I like the 85-90 TAs and not the 91-92s. Its annoying to do the holes and stuff in the doors, fenders and rear quarters for the GFX but I like the TA look much better.

15s are fine if you run big meats but they also severely limit your brakes. I run 13" BAERs up front and they require a 16-17" wheel I believe but a 14" brake swap requires a 18" wheel I think at minimum. I thought the stock firebird GTA mesh wheels were 16x8 and not 15s?

 

I did that to an '89 Formula back in the late 90's. I don't even remember how I located the hole positions it was so long ago.


I actually have a set of those same wheels in the basement. They are 15x7, an 'optional' wheel in the late 80s on firebirds. They came natural or painted I believe. The set I have we media blasted so they need to be painted and the lip polished.

I'm running stock front brakes and stock LT1 rear brakes so 15" wheels are fine. The cheap option is to use the 15" mesh wheels (like in the photo) and just buy wide sticky back tires, and put the drag stars on the model A but I suppose the "hot" option is the 17x9 GTA wheels.

 

@customblackbird

What's your boost vs TPS curve? I was out tuning the car earlier, still a little lean in boost, but I actually hit my boost limit at part throttle and I thought that was interesting. I'm getting more boost at less throttle than I was with the previous cold side.


11.8 psi @ 34% tps and 3600 rpm. My overboost spark cut actually kicked in. (I have it set to 12psi)

My air temp is showing about 8 degrees over ambient, so the intercooler is working quite well. I have not enabled the methanal yet.

 

What kind of timing do you run coming up from NA into boost?? And what size turbo is that again? Your IAT's look great but it makes me wonder if that turbo is way way too small. 12 psi at 3600 is pretty wild. Anyways here is what I run for timing with my 88mm @ 22 psi with a bunch of meth

 

What do you mean when you say it's wild?

It's a little 70/70 on a 5.3 with a small Summit cam. 2 bar map. Goal is to run around 13psi, with a safety at 195kpa. It's actually a really cool build and I hope it doesn't blow up because I can drive around town in 5th gear at 1200 RPM and it doesn't surge or buck, but when I get into it the thing is an absolute animal. Makes me almost never want to try a different combo again. In fact, I kinda wanna put this cam and turbo on my silverado to see how it does towing.

This is my timing table. I think it's quire conservative.

 

12 psi @ 3600 rpm is what seems wild to me that's barely even putting into it. But I guess with a small turbo like that it's not unexpected and it should be tons of fun on the street

 

that sounds about right. I want to say I’m around 13psi all in my 4000 and it’s a light switch at 3k. It can start building boost as early as 2500 the threshold of 100-105kpa but the converter will flash to about 3k so that’s reliably where it hits boost and then it’s all in in less than 1000rpms. The 70/70 is really audible when you hear it spinning up. With the EBC it spins up harder the more boost I run like 16psi spins earlier and faster than 8-10psi on spring only.

what’s crazy is that the turbo is really just getting going, if you drop a 3 bar and up boost to 16-18psi it’s a even bigger monster. It’s light no lag insta tq and choo choo.

your intercooler is working good too. On my TA it’s st about 10*F above ambient. On my vette is about 15*F above ambient.

have you done fuel calculations on HP?

 

the 70/70 billet next gen is a hidden gem for a fast street daily. Billet wheel will push 20psi all day but the BP will rise. On a 5.3 the sweet spot is 15-18psi but that’s hard to keep on the ground.

 

I upgraded my VS racing 80mm turbo to a True North Turbos 88mm with a 9 blade 88x96mm turbine wheel on a 1.15 AR T6 turbine housing and good lord was it ever a night and day difference!! It really opened my eyes wide going from a super budget turbo to something that's got actual R&D in it was absolutely wild! Using the same boost controller settings in my Dominator ECU, combined with the new FTI converter I put in last summer I'm seeing boost come in from a dig around 1700 RPM and I'm almost at my target of 22 psi before 5600 RPM.

Seeing how that was going I needed to calm things down and do short pulls and datalogs to get fuel dialed in. I'm on my phone typing this but I'll get a screenshot of my VE graph. My VE in the lower RPM is up at around 115% then the meth kicks in and I'm around 90ish% by 22 psi

I've noticed since I use the compressor as pressure source that my PID settings need to be more aggressive rather than lower. 10/30/0 target rate limiter 40 psi/sec was a bit slow now I'm 12/35/0 50 psi/sec target rate and much better results

And my back pressure is half of what it was with this new turbo. But I will admit that I just sent my tune out to a local reputable tuner that knows Holley efi and he took all of 5 minutes to get back to me saying my idle timing and timing in general considering the huge amounts of meth I'm spraying was way under timed and probably was a main reason my engine/exhaust was super hot. I was at 14 degrees at idle which to me seemed smooth but I did notice it was hot but now I'm 22 degrees at idle and it's night and day difference

 

I'd be nervous of running more than 14psi on this 5.3. I feel like bent rods, blown head gaskets, etc would be in my future. Even with meth, I just don't know that it can handle the cylinder pressure.

Then there is the TKX that I honestly am starting to regret buying. I can spool quicker with the manual but I don't think it can handle the power levels the engine is capable of.

 

I used to be all about more advance at idle, but I found on my 5.3 running more than 15 degrees at idle would cause it to surge a little bit. I suspect part of it is also my chinese throttle body. I have the throttle stop backed all the way off, and my IAC only needs to open a little bit. In reality, a 75mm throttle body would probably be sufficient for this but they don't make a 4 bolt one for this intake (ls2) as far as I know.

 

im running a stock 75/78mm 3 bolt TB on the corvette. Which is pretty similar to your combo except it’s a LM7 motor. You can get an aluminum Adapter for pretty cheap. That being said I run a 92mm WARR TB with NNBS intake on my firebird and no idle issues. I’m at about 20* at idle in both which is 650rpm on the vette and 750 on the firebird. Are the LS2s different than the 4 bolt trucks? I thought they were the same.

 

Eh, you’re prob fine with safe timing and meth. $hit im running 87 octane and no meth at the moment at 6-7psi on the vette. What plugs are you running? I hear the BRz7 can have idle issues and I’ve had zero issues with TR6 up to 17 psi.

 

oh 100% a good brand turbo would be huge upgrade. The 70mm is much smaller physically than a 78mm but has less backpressure and makes more boost faster and it’s a small frame turbo (t4, 3” DP). I looked at the borg S366 bc it would have been tapped out at 600hp
or so and it has a much bigger exhaust housing. A 76/65 didn’t fit in the vette bc the compressor was to big and hit the hood. The 70mm clears no prob but this again is a dedicated street car and driver to work. If I had room and budget I would do a borg all day.

 

Throttle body should be the same 4 bolt pattern. I guess I could do an adapter if I wanted to run a stock size LS1 throttle body. I don't really see the point in a 92mm throttle body when all of the piping is 3".

BR7EF.

I've been thinking of doing the ground FX again.. A junk yard about an hour away has an '89 GTA. They said I could have the bumpers and ground FX for $150.

I know all the smaller parts and the door pieces bolt through, but I vaguely remember there being some large bracket that holds the skirts (under the doors) to the body. I know the skirt screws downward into it, but is that support bolted to the body or welded? I need to bring the right tools to take everything apart. I think most if it is 10mm and 13mm. But I don't quite recall those brackets for the skirts.

 

stock TB will outflow more HP than you can make on that setup. A single 2.5” pipe is capable of some pretty good HP. A stock TB would give you better idle and adjustment/fine tuning.

$150 is a great price if it includes the front and rear bumpers. Yes, there are two long metal brackets along the door sills. Not sure how they are stock but I just used sheet metal screws to hold it on. Your not gona be standing on it. I would bring a spot weld driller or some bits to drill them out if they are spot welded.

 

Also the BR7EF plug might be too cold for your boost/setup.

 

I will revisit plugs and throttle body eventually but I need to figure out this banging. I can't even grab gears hard without a loud bang. It sounds like something hitting or something is about to break in half but I can't find it.. It's making me nervous about even driving the car at this point.. It's loud!

 

When is the noise happening? How much throttle? All your suspension components are tight and secured? I thought the TQarm front mount or like you said the tunnel but you took care of the tunnel part. Still
wondering if it’s the tq arm front mount? Are there any signs of contact? Motor/trans mount? Nothing on the hotside or exhaust hitting the car when you giving it more throttle?

 

I think I figured it out last night, but I didn't think it was possible. But I found the top of the torque arm mashed with the powder coat banged off. It looks like what is happening is, on suspension squat the torque arm is hitting the driveshaft loop. Which is surprising because it's like right behind the pivot point. I didn't think it would be moving 2+ inches in that spot..

The only place the exhaust is close is in the rear on the sides of the spring perch support but it's always been like that. I could put some rubber to insulate it but that's not the bang I don't think.

 

That seems like a lot of movement that far up. U should jack the body up and take the rear springs out and jack up the rear through full range of movement and confirm that’s wat happening. 2” up that far has to be like 4+ at the rear end.

 

What kind of front mount are you using for the torque arm?? If you're using Heim joints that's what I would be thinking that clunking is. My MWC 2 piece arm clunks up front too

 

I was thinking the same thing but there is an impact mark on the arm.

I'm going to do exactly that, jack the body up and see what happens when the rear end squats.

 

This the front mount. The round slip fit connected to the crossmember.

 

There's quite a bit of clearance there. I couldn't imagine your TQ arm moving that much up and down in that spot. Especially since you don't have a shackle mount on the front. It looks close to the side of the driveshaft loop. As your suspension cycles does the axle shift to one side and cause some kind of lateral contact. I'd also look around the mount on the 9in and around the body. Mine hit in one spot and was close in another till I moved the read back 0.75in.

 

I'm honestly not sure. When I was leaving the gas station I let the clutch out kind of hard while turning and it gave a huge bang. I noticed if I speed shift I can get it to bang.

I thought originally the torque arm mount was hitting the tunnel, but there is no evidence of that now. I suppose I could remove all doubt by installing adjustable bump stops but this bang feels more up front.

I found a really good ding in the top of the TA about 3" back from where the driveshaft loop is, so I'm curious if when the rear end squats the TA is moving forward and up in the front?

I need to compress the suspension and see what it does.

My other issue is my trak-lok doesn't seem to like to unlock.. In parking lots turning it drags one of the tires. If I give it anything but the lightest throttle while turning from a stop sign it peels out a little bit. I don't know if I should put more additive or what.

 

The posi in my rear is really tight. It's obviously not locked but it's a bear in parking lots as well, but it also looks up real well going forward fast!

 

The rear end will move side to side about 3/4” if I had to guess maybe more during the arc swing of the panhard bar. I don’t think you would be seeing that much movement in normal range of motion tho.

how much space do you have if the arm moves forward before it contacts?

if I logically think of what happens on a shift or let out of the clutch I don’t envision the arm sliding forward that much or back. Loading bs unloading the rear.

 

Well, it definitely is not hitting side to side. I can't see any signs of that. The only abrasion I found on the torque arm is about 2" rear of the driveshaft loop, and there is about 2" of clearance on the front. I need to take the coil overs out and see how much the suspension compresses to see what is going on. I may do that today.

I know for certain the back of the torque arm/adapter is not hitting the tunnel. There are no signs of impact, and all of the noise is up front.

I did media blast and paint these stock 16" GTA wheels though with new rubbers. I think they look better than the drag wheels.



I know you like 18's and I do have 18's on my fourth gen, but I just think they look weird on a third gen:


​​​​​​​

 

get those cool overs out and get to testing lol.

I love the GTA wheels, they look great on your car. Just gotta close up that ride height down.

I had original GTA wheels but always hated the 16”x8 size. Hawks has the 17x9 which is better and I would love a 18x9.5 or 10” width option. I’m not even sure if my 13” BAER black label brakes will clear a 16” rim. I would totally
put a GTA wheel back on but with the turbo I can’t run anything smaller than a 275 tire and I would prob do better with a 285-315 rear tire.

 

have you seen the guys draggin on the 24 inch wheels?
i used to be a big wrinkle sidewall guy, but seeing those big boats hook with no sidewall, im all about tuning suspension now.
get a stick tire and make the supension work.

 

Thank you! I think they look better than the drag wheels. I put the drag wheels on my Model A.

One thing I noticed, the spring likes to lean to one side. I don't know why. Correct spring ID for the shock. Strange shocks, not chinese junk.

I wonder if the coils are making noise?

I tested the car on the road again, I can get it to make noise when the rear end squats or goes up.

 

I wonder if the spring is catching the top of the shock and popping when compressing? I do Not love how that spring looks. I wonder if it’s also because of how long and narrow the springs are.

did you pull the springs and do a full range of motion test?

 

No, I had to fly to DC for work and just got back last night before midnight. I'm going to try and tinker with it today. But I was thinking the same thing.

These are 14" 2.5" ID 150lb springs. I'd imagine the same everyone uses. I don't know why they deflect like that. Here is a better photo. This is ride height: