Fabri-cobbling a Autocross Chevelle

[416velle]

[chevelletiger]

Whew,that bad news.
BTW what flywheel pressure plate and disc did you end up using after the non sprung one?

[416velle]

Its been a LONG while since my last update, a little bit has changed on this car but a lot of work was done

-Eenie weenie LS1 is in storage and a new stroker LS3 is back in the car
-Sweet Mfg 8:1 steering box
-NEW TAHRS
-Made some inner fenders.
-Lithium battery

Respectively and going down the list;

-New stroker motor is the same specs as the prior stroker motor with a little more compression and a few less cubes (.040 on a aluminum 6.0 block scared me a bit but the builder had confidence in the wall thickness for an N/A application. This is a throwaway block and will not take more overbore in the event of catastrophe). It was a good humbling feeling to have an LS1 in the car and think that this engine is where the craze all started. But man, 400horsepower is gutless and woefully inadequate.
New motor is a 410ci, ported LS3 heads, 13.5:1 compression, 235/[email protected] .620 lift cam (same cam I've run for 5 years), ported LS3 intake, E85, 1-7/8 headers, 650ish horse, and LS7 lifters because I'm salty to Morel lol
I didn't build it so this means it will last!!!

-The single greatest thing I've done on this car is the steering box. Most of the board people in my SCCA region are all spec Miata people and there's mainly small cars (at or below 2500lbs). The layouts are very tight and technical. This kind of sucks with a long wheelbase 3300lb 650hp boat and I found myself limiting how fast I go in some corners with the fear of rotating too much and spinning out without the capability to recover. I no longer have that fear with this steering box, lock to lock is 1-3/4 turns. Fast circle track guys use these boxes to turn the wheel right to go left, its doing exactly what it wants to do.
October was the last event I attended and I had the fastest 1st lap time of the entire pool of 52 cars and I attribute most of that to the steering, and the rest of that to the tires. This was truly amazing to me.
The downside to the steering box is the sensitivity on the street, this is in my view a race-only mod.

-With Falken's RT660+ coming out, the legacy 660's were on blowout everywhere. Picked up a set for like $900. Absolutely awesome. With the car a bunch more balanced and me being able to push it harder, I was HUMBLED and hit HARD with knowledge bombs and direct experience with the significance of tire pressures, so that will be a between-lap maintenance item now on.

-Made some inner fenders, I wanted to use aluminum but I don't know how to TIG weld quite yet, haven't figured out what my machine likes in terms of tungsten quite yet (its from the 80s).
Had a little vision, mocked up from bristol from hobby lobby, and just started building. IMO they're the nicest part of the car now and definitely some of my best work, I really like how they came out. Theres still a few things I want to do (contour to the frame and control arm) and close them up completely near the firewall. I also need to figure out an intake situation for the engine, there is a hole in the driver inner and the airbox I built years ago fits but I can save a few oz if I build another that doesn't require me to remove a bunch of stuff to clean the filter.

I used anti-gravity batteries when I was into motorcycles, for some reason I had the idea to see what they made for cars. Low and behold they make a bunch! Circuit protection, built-in jump-start capability, and 30lbs weight loss? Count me in. For the location situation, I'm toying the idea of re-relocating the battery back up front to save weight on 20ft of 0ga battery cable.

Now for winter projects, I think I'm going to pick up some corner scales and do plot some geometry and balancing measurements (CoG, pitch/dive center, squat/antisquat)
I'm not concerned about weight, the car is basically exactly where I want it at 3250-3280, and I'm not concerned about the front, as far as I'm concerned its dialed in to my driving style and desire.

-I haven't really got the 3-link exactly where I want it, and on-track there was a higher speed back-half where on throttle it felt very bumpy and I'm not sure why (felt like the axle was cycling up/down causing this, its not losing traction and its not like the shocks were stiff following the road surface). It did not do this when I had more squat dialed into into it, I think I want to try a different hole on the lower arms to give it a bit more squat.
And if this doesn't change the chatter, then I need to rethink my upper control arm mount and probably go into the anti-squat realm, which would be interesting because I need to cut a sheetmetal crossmember out of the body and build into the rear seat area. I'm completely out of adjustment as it sits right now
-Carpet is on the list, interior is a shoe-in for a nice looking car so that would be cool.
-I want to re-re-redo the trunk and start over with fuel tank mounting, and maybe go with a smaller cell for less fuel (less weight!!!). When I changed the 3 link from watts to PHB, I did that after the body was installed. The trunk consists of some aluminum installed with sheetmetal screws and a little bit of the stock trunk, it would be really nice to not have to deal with the sheetmetal screws vibrating. That is by far the worst sound this car's ever made.
-Fuel cell baffling. I think hydramat and some baffling could allow me to run 3-4 gallons and not experience fuel starvation. We're grasping at straws here but 3200 even I think is a solid goal.
-I want to route a catch can vent hose to the cowl area to mitigate fire risk.

Photo dump soon to follow.

[416velle]

The racecar crossroads

I'm sure everyone has had to come to terms with the question, "How full-race do you want to go?"
I came into contact with Ron Sutton, ordered some steering stuff from him. After being very surprised with the amount of useful information given in the catalogs on his website, I came across the "decoupled 3 link" section. I'd heard of the decoupled torque arm setup from Unbalanced Engineering, I did not know the 3-link equivalent exists. Went back and fourth with Ron a bit on the idea, and I came to the conclusion that its doable on the chevelle frame without altering lower control arm lengths, and would probably take 10-15hrs of fab start to finish. But, there is the distinction that the decoupled 3 link DOES NOT like to be used on the street, as it doesn't *like* to cycle up and down very well.
Given the benefits of mechanical traction control, it seems like an extremely good idea that would take this car to the next level, but it would nuke the streetability of it.
I do not know the answer as to what I want to do with the car.
The car is already kind of miserable on the street given its on E85 and gets 7-9MPG. It doesn't have a single soft bushing anywhere on the suspension. It has stiff springs and coilovers adjusted stiff for autocross. It has tires that are $2000 and an aggressive alignment that eats them alive. Exhaust dumps before the axle and its LOUD. A rollbar on the street is a TERRIBLE idea without a helmet. 5pt harness is annoying on the street.

IF I decide to go the route of no return, theres a couple other things I would do to completely eliminate it from street duty all together. Those things include:
-fiberglass doors and lexan windows
-change from T56 to a stoutly built muncie or 4 speed transmission (This is a recipe for MISERABLE HIGHWAY DRIVING, 3500RPM at 70mph)
-cut out and redo the roll bar with use of .083 and .065 wall tubing for weight reduction (I kind of want to do this anyways, because itll force me to learn TIG)
-down the road, I'd like to section the firewall and shove the engine back a couple inches for more rearward weight bias. Also included in this would be a lightweight core support, likely from RonRhodes (for a 70) and make it work for 69. Also included in this would be changing radiator location for aerodynamics, makes splitter more usable and easier, etc etc etc.
If anyone has insight to sway me in one direction or another on what they would do here, feel free to chime in.

On a different note, something in my spidey sense told me that a possible reason the stroker engine went goodbye last year was a result of the condensation inside the crankcase (from E85 and no PCV, just a catch can) rusting internal parts which dislodged, clogging the lifter up and the wheel to stop turning. Decided to put a GZ Vacuum pump on the thing to extract the moisture, and a cherry on top is giving me a bit more horsepower. Looks cool, installed simple, and the power increase is actually noticeable up top.
Had to dig and find photos of the innder fender project (new phone and running out of google storage); those and a few finished product pics included.

[Olds.PhD]

I mean, its your car. No one can make that choice for you.

For me, my A-body will never be a full race car, because its just not a great platform to make one from, in my opinion. Weight distribution, chassis stiffness, and sheer size just make it far less ideal than other platforms. Don't get me wrong, I've done a ton to make it faster around an autocross course and enjoy thrashing it. But my C3 is a better platform for a full effort build.

On that note though, a C3 is a much worse platform than a C4, which is worse than a C5, and on and on. And if I didn't have a C3, I'd probably keep going on my A-body. So if its what you really want, go for it. Make the fastest Chevelle ever.

[416velle]

Sometimes it takes months, sometimes it takes weeks, but every now and then I'll get to a point with this car where I "definitively" conclude "There isn't anything more to do". Then time passes, I get a genius idea and start to dive into the research.
This time around, its steering geometry.

I should note here, this whole shabang began BEFORE the previous post I made.

I'd heard from a lot of people "Retrofit rack and pinion was a great addition to my car!" but then I go to basically every experienced racer and ask what the thoughts are and its a resounding "terrible idea". Did lots of ressearch on various platforms not just Chevelle, identified why, and also identified what exactly what I would have to do on the A-body platform to allow the frame to be friendly to a rack-and-pinion system with favorable geometry similar to or better than factory. Theres a lot to it, which involves moving the engine back 6-8", I had a thought to minimize the under-engine frame crossmember to save weight and act as an adjustable rack mount, and I thought relocating the lower control arm forward mount to a "parallel with the frame" mount pattern (instead of converging) would allow for a wider rack (among other changes for better or for worse, sway bar and shock motion ratios change, dynamic caster change goes to 0, etc etc). This was obviously theoretical and I'd spend hours and hours messing with geometry on PerformanceTrends dynamic geometry tool before doing antything. The software is expensive, i concluded its probably not a great idea to invest in it unless I want to completely map out my car to make it nuclear fast. Above all....that's a lot of fab work, thats a lot of time, and above all I'm a neanderthal not an engineer. I didn't even mention the sheetmetal work to the firewall/transmission tunnel, shifter location, yea. Very steep.



So I went back to the mental drawing board and thought long about how I can improve my steering, keeping the current geometry whilst adding adjustment. I remember way back 6 years ago, I remember installing flaming-river u-joints on the column shaft, those made a big difference in feel. So I went down the line with every component; installing the bumpsteer adjustment kit was HUGE for steering feel by getting rid just 2 ball joint connections in favor of rod ends instead, and theres still 4 of those ball joint-style connections on a stock centerlink. This means theres somewhere to improve, I wanted to alleviate those but didn't exactly know how. I don't have a jig table to making my own isn't really an option unfortunately.
From prior knowledge of acquiring other steering parts from companies that have nothing to do with muscle cars, I went straight to the circle track community to see if they came up with anything!!
Howe and Wenteq have some options, they do indeed alleviate the ball-joint connections, and they widen the spread between the inner tie rod mounts....but they don't allow the level of adjustment that I invisioned for inner tie rod height, ackermann kind-of, and they had 4 options of inner tie rod spread widths so I naturally had no clue which one was going to be best for me.

I don't know exactly how I came across it, I think I remembered Aaron Oberele has a custom front clip on his 65 and I wanted to reverse engineer the steering a little, but I looked through some of the builder books from Ron Sutton Racing. Theres a lot of useful-to-me information and tech tips throughout the catalogs and archives, I looked at a pretty in-depth sequence for improving the feel and steering precision on conventional box/linkage cars, involving measuring and shimming the box/moving parts to make sure the box runs parallel to the chassis, is level to the ground and the center link is parallel to the ground/perpendicular to the ground, and above all that the connections are in their free-moving range without bind.
Then I discovered this part they sell, AXT-Star steering linkage kit that was exactly what I had in mind about wanting to build; rod ends on both ends of the tie rods, rod end for idler arm and ball-bearings on pitman arm, adjustable inner tie rod spread for longer or shorter tie rods and optimizing bumpsteer characteristics, adjustable inner tie rod height for more or less sway bar clearance, adjustable tilt forward and backward for more or less ackermann.
I think I did more measuring with a tape/calipers/dial indicator installing this particular single steering component than I did the entire time building the 3-link and the cage.
After following the shimming/squaring sequence, I could actually feel a difference with the stock components, the mushiness was slightly less mushy and the wheel was easier to turn.

Got it all set up and crudely installed with an awful bumpsteer curve because I was impatient, took it to an autocross event and gathered some very useful data to bring back. Needed more ackermann because outside tire was PISSING hot and the inside was just warm. I was not able to drive it 110% fast because it understeered really bad on turn-in. My fastest times were after toning it down a bit and loosening the shocks on the car, and toning it down I ran clean but was 5 seconds off FTD when I should have been 2.75-3 off on that particular layout. In september on a MUCH more tighter/technical layout, CAM-C had me by only .001 and I was only 3.8 seconds off FTD, so I'd slowed down a lot.
But...I'm really good at highlighting the drawbacks before looking at the positives...rod ends and bearings for all of my steering connections on my steering stuff that's dimensionally exactly where it needs to be, was amazing for steering feel and SIGNIFICANTLY reduced steering effort. 315 tires, 1 degree of camber, 8 degrees caster, 3/16 toe out, and 2 finger steering do not all belong in the same sentence.

Back in the garage, improved bumpsteer curve with much better precision and some better measuring techniques. While I was under there, I discovered my coolant overflow was full; and there was evidence of coolant spitting from the weep hole in the lid; and the TIRE is right below where it would spit out from!! So my understeer was a result of coolant, not necessarily entirely the fault of bumpsteer or ackermann. This was a relief.

1 last event of this year in november, I actually don't think I'll have a winter project for this car surprisingly but I think learning to TIG weld will be on the list, I finally have acquired the metal to build a good sized L-table. And once I do that I did just last year finish those pretty slick looking inner fenders; but man I'd like to make another pair out of aluminum instead of steel to drop 10-15lbs.

https://www.facebook.com/share/v/19Q9xAi9hf/

[Kcrain]

One thing I think I would try is move your toe in to 1/16. That way any possible looseness in linkage will bring the tires to 0. You starting with 3/16 toe out when it takes up all potential looseness in your he system mean your toed out even farther and scuffing the tires at straight ahead.

[donnasmith]

Nice progress! Curious to see how those tires fit up front.

[416velle]

This car is strictly race only, for that reason I have no problem going more aggressive with the alignment to gain as much grip from the tire as possible. Toe-in doesn't optimize the available slip angle of a tire as well as toe-out does.
Now, if this was a half streetcar deal, I'd dial it back to 1/16 total toe out and have it bump out to 1/8 under compression.

[416velle]

Nice progress! Curious to see how those tires fit up front.

315 fits great up front long as the wheel is around 6" backspace, and the inner fenders are removed or modified because theyll rub the roof right around the outer lip..