Roadracer's #997 build

The last thing (yay) I had to do was to calculate the roll center at front and rear.

At the front I used this calculator: Suspension Geometry Calculator

I'm not sure if this pic was the final setup, but I measured all the suspension pickup points and entered into the calculator - it calculated the roll center at 1.6" from the floor

Attachment 192768

At the rear, i found this youtube video that described how to calculate from 3 link geometry.. and since my LCA and Panhard bar are all parallel to the ground, it made it easy - the roll center is the height of the panhard bar, at 8".

Phew, that was a lot. Now to get to the results...... tomorrow!

I'm absolutely loving this, I'm very impressed watching you go down this rabbit hole

Ha, thanks Frank, it's been fun.. and worthwhile I hope. The more we know, and all that.

As I said earlier, I subscribed to this guy and his car dynamics program and I've been very happy with it. He has been very helpful and answered questions along the way.

Suspension Set-Up With the "Weight Transfer Worksheet (WTW)"

Now that I had gathered all the info for his calculator, I plugged it all in.. note the units used - kg, mm, etc.

Attachment 192785

The first main point of this sheet is to calculate the suspension frequency. For autocross, all the experts I spoke to agreed on 2.5hz being the goal. 2.5hz (per second) in CPM (cycles per minute) is just 2.5*60 = 150cpm.

For reference, this was confirmed by the material in this course - but be aware that I'm deliberately focused more on autocross than road driving, so you may go for a lower cpm, like 120.

Attachment 192786

The initial results show I'm too high with my current springs:

Attachment 192787

Rather than the 150 I want, we're at 180 front and 199 rear! Ooops. A little about why this happened. Early on, the roll on the car was excessive. The tires were rolling into positive camber, and it was horrible.. no grip. There's no sway bar setup for the hot rod, and even FFR said "fix it with springs" so I did, eventually working through 400>550>650>800 on the front and 250>350>450 on the rear. Each time going stiffer to get the car to behave.

Each time I increased the front by an arbitrary amount and kept the ratio of front/rear similar to the stock ratio, i.e. 400/250 = 1.6, 800/450 = 1.8

Then I found a solution for f/r sway bars, so I added those too and started "tuning."

So here we are. Way too high a spring frequency. Next up - an easy fix, we hope.

The beauty of these calculators is that you can play around with numbers and see the results. Of course, everything needs to be validated in the real world, but the idea is to get close enough to start fine-tuning.

Given I want to be around 150cpm, I just lowered the spring rates until we got there.. I went from 800/450 all the way down to 550/250!!

Attachment 192788

Wow, I had no idea I was that far off. And notice that the rear spring rate went all the way back to stock springs. All I've done is stiffen the front - but not to 800 ;)

Next, I noticed that the balance was a little off.

Attachment 192789

But I improved that by increasing the lever arm length of the rear sway bar from 150mm to 250mm.

Attachment 192790

Next step is to get back to the real world and see if ANY OF THIS WORKS!

Luckily I have these exact springs in a box, and the sway bar is adjustable, so we'll see. An evening or weekend project.. my next race is on the 10th!

I had Auto-X experts tell me i need to increase the spring rate on the rear of my Camaro. When I called Ridetech to discuss the spring increase, they explained that adding a rear sway bar would actually act to increase spring rate and that would be better than increasing spring rates. So, I installed the Ridetech Muscle Bar on the rear and it handles great with even more adjustability. I'm looking at doing the same with the 33.

As I speak to my autox members (or at least the ones who have been running very successfully for decades) I'm being persuaded to start at 2.2hz (135cpm) front, and 2.5hz (150cpm) at rear.

Quotes:
"you might want to go a little stiffer on the rear. I have generally kept a +0.2 or 0.3hz on the rear of the car compared to the front."
"but also, with no aero, you might want to go lower in general. 2.2ish at front"
"i think that ~2.2/2.5 is a better starting point. I think a lot of people start too stiff. I was at 2.2/2.5 before I added the wing and front body work, and now I'm at 2.5/2.8."

I have a 450lb front spring, which is exactly 2.2hz..

Ironically - and this won't be lost on some of you - the car shipped stock with 400/250. And here I am, after 2 years of experimentation, back down to 450/250 because that's what the math says. But I do now have sway bars f&r. And I'm a better driver now. I feel I've gone full circle here. Of course, I may HATE how soft the car is.

Never stop experimenting!

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Originally Posted by RoadRacer

As I speak to my autox members (or at least the ones who have been running very successfully for decades) I'm being persuaded to start at 2.2hz (135cpm) front, and 2.5hz (150cpm) at rear.

Quotes:
"you might want to go a little stiffer on the rear. I have generally kept a +0.2 or 0.3hz on the rear of the car compared to the front."
"but also, with no aero, you might want to go lower in general. 2.2ish at front"
"i think that ~2.2/2.5 is a better starting point. I think a lot of people start too stiff. I was at 2.2/2.5 before I added the wing and front body work, and now I'm at 2.5/2.8."

I have a 450lb front spring, which is exactly 2.2hz..

Ironically - and this won't be lost on some of you - the car shipped stock with 400/250. And here I am, after 2 years of experimentation, back down to 450/250 because that's what the math says. But I do now have sway bars f&r. And I'm a better driver now. I feel I've gone full circle here. Of course, I may HATE how soft the car is.

Never stop experimenting!

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Sorry James but it is kind of funny that you've run full circle only to end up back where FFR started. The swaybars have got to be a huge help. I have my front on order but will probably make a rear myself. Probably use someone like https://www.rhodesracecars.com/Anti-...s_c_10548.html or https://timmcamis.com/shop/chassis/s...nti-roll-bars/ or https://www.portcityracecars.com/col...ay-bars-mounts

It’s not lost on me :D

I’ll still probably do the 550 first. It’s a toss up for sure.

The rear sway was the easiest part and basically off the shelf.

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Originally Posted by RoadRacer

It’s not lost on me :D

I’ll still probably do the 550 first. It’s a toss up for sure.

The rear sway was the easiest part and basically off the shelf.

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Well.. post some info on the rear "off the shelf" swaybar. (i'm sure you already did somewhere back in the build thread)

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Originally Posted by Just 1 More

Well.. post some info on the rear "off the shelf" swaybar. (i'm sure you already did somewhere back in the build thread)

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Here are the main posts that concern it. Literally bolt on.

https://thefactoryfiveforum.com/show...l=1#post466372


https://thefactoryfiveforum.com/show...l=1#post467981


https://thefactoryfiveforum.com/show...l=1#post473046

Just to confirm, you guys are using the 3-link rear, right? I'm wondering if I could adapt something like one of those to my 2015 IRS? When I spoke to FFR (several years ago) about this they said that it wasn't possible without some major work.

What front sway bar are you using or have on order? James, could you point me at the relevant posts in your build thread for that? Sorry, but my search engine skills are sub-par.

Thanks,

Keith HR #894

Yes, this is for 3 link - it's bent around the "banana bracket".

But VPM have an IRS one: https://vpmcobras.com/

I used one from them for the front too, but it's not on the website. Ping them and ask.. it's narrower. [they said "We do have a front size that is 37.25" overall. With a width at bend of 26.5". And a max arm length of 12".]

As for my posts on the front "fabrication" required:

https://thefactoryfiveforum.com/show...l=1#post498711

Don't you love doing experiments in front of the whole world, so people can see you f up? LOL

You know how they say "measure twice, cut once"? Well.. I'm glad I did.

When I calculated the front Motion Ratio (MR).. I "knew better" and didnt follow the instructions and instead measured the cantilever lengths accurately, and applied a correction for the shock angle.

What I was told to do was remove a spring, reinstall the shock, then measure accurately the vertical travel of the wheel, and the distance the shock shaft moves. This takes all the guesswork out of it, because it's directly measuring the MR. No need to do any calculating.

MR = shock shaft movement / vertical wheel travel.

Well, tonight I had the shocks apart to change springs, and while I was there I thought I'd do it the recommended way. I did it 6 times, and each time it was 0.59. Not the 0.78 I put in the calculator.

Don't guess wheel motion, measure it.

Guess what? Using 0.59, the 800lb springs I already have (and love, they work) are 2.3hz, 136cpm. A bit LOW if anything. 950 would be perfect 148cpm. Eeeeek.

The rear springs still need changing, as planned 450 down to 250.

But wow. It's a shame I overnighted some 550lb springs haha. Now you can learn from my mistakes! BTW, I never did quite believe that the stock springs were 2.5hz.. the car had so much roll in stock form at autocross speeds.

Great information! Thank you Sir!

Keith HR #894

James, this is great! Not just building, but making it work using the maths! I'm thoroughly enjoying watching the process you are going through. Keep it up!

This is awesome watching James sort out MY suspension set up for me.. lol

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Originally Posted by Just 1 More

This is awesome watching James sort out MY suspension set up for me.. lol

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Haha, well the trick is to DO NOTHING until I've finished this journey.. :D And then wait another few weeks until I've thoroughly worked this through ;)

Today I (just for grins) did the MR measurements again, this time on the inside of the tire. I woke up thinking that what I really want is the vertical measurement at the centerline of the tire.

Having done the outside tire last time, I did the inside tire this time. The MR was different, at 0.67. Outside was 0.59. So, MR using the center of the tire is 0.63.. I wear I'm going to stop measuring and calculating MR now. (So far I've had 0.78, 0.59 and now 0.63!).

Final answer. 0.63.

800lb springs at 0.63 MR equals a frequency of 145cpm, 2.4hz. So that's almost perfect, and I'll leave as they are. No change needed for me at the front (but for those following along, mine came stock with 400lb springs, so for autocross I have doubled the stiffness, AND added a 7/8 sway bar).

At the rear, I haven't changed my mind about anything, being that a live rear is always basically 1. I'm using 1.05 for reasons stated earlier.

So to get 2.5hz, I do need to go back down from 450lb to 250lb springs - which was the original set that came stock. My earlier thinking was to always increase both ends in proportion, but that was a false "common sense" idea. I didn't need to touch the rear to get the correct frequency, although I have added a 3/4" sway bar.

I do wonder why FFR sends it out with a 1.7hz front and 2.5hz rear setup. I would expect that the rear should be lower for road use - but I remember that many have gone down to 150lb, which seems a wise idea.

Anywho, I made all these changes and went for a drive. I did seem much better - softer of course, but really "digged in" under cornering and seemed much better balanced. But it could be confirmation bias.. I just want it to be better!

The only data (until next week's autocross) is that my favorite 'test' long sweeper has never been taken faster than 80/81mph, and today I saw an easy 84/85 and that's with me being careful on the new setup. :cool:

James, I'm curious to see what you do with the tuning of the shocks once you get the spring rates sorted out, using a double adjustable shock like the QA1's, you should have a field day playing with the compression and rebound settings.

Shock settings are next!

Final prep for this weekend autox; I bought some longer lever arms from speedway motors to soften the rear sway bar. I went up from 8" to 10" which allowed me to move the adjustable bar out 2" - this will give me less oversteer, almost to the point of neutral, according to the calculator.

Attachment 192946

A quick aside from the normal.. at a recent track event I didn't have any "offs" but many did, and it made me realize that there is NOWHERE to tow a 33 from, safely.

All the chassis is covered up by the gril, and I don't want to be pulled from a gravel trap on an a-arm.

So we looked around and came up with a v1 version of a tow hook, that bolts to some existing holes on the radiator bracket. I think this is a great MVP, but I'll probably brace it diagonally to the chassis to increase strength further.

Attachment 193052 Attachment 193053 Attachment 193054

My fastest run at Spokes #11 autocross today. Man oh man, the car was SO MUCH BETTER. As I thought on the road test, the car just sticks on corners now, and hooks up and powers out of corners without drama. The car is balanced, with maybe a smidge of understeer. I was still pushing the car on the fifth run, so I never got to the limit to see which way it was going to go. It's pretty neutral.

https://youtu.be/bWFAkgitWtE

So, if any of you want to know a starting point for autocross-suitable springs, I recommend the 800/250 that I'm using, which gives a 2.4/2.5hz spring frequency.

Since there are no "factory" sway bars you'll always be needing to figure that out yourself, but my longer arms on the rear (softening the sway bar) may have helped too. Note that the calculator said that a sway was needed at the rear, but fairly soft.

Congratulations on a great run! Thanks again for posting all this data - it's valuable even if we never do an Auto-x session.

Is there anything different that you could recommend if someone wanted a daily freeway driver / canyon carver setup? In my ignorance, it seems like your spring rates and sway bars would be well suited for those conditions - but maybe backing off on the shocks a click or two?

Keith HR #894

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Originally Posted by progmgr1

Congratulations on a great run! Thanks again for posting all this data - it's valuable even if we never do an Auto-x session.

Is there anything different that you could recommend if someone wanted a daily freeway driver / canyon carver setup? In my ignorance, it seems like your spring rates and sway bars would be well suited for those conditions - but maybe backing off on the shocks a click or two?

Keith HR #894

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Yeah going back to the recommended spring frequencies in #763.. you’d need to pick sports car or super car.. you might want to go lower than I have. Sports is 1.5-1.7, super car is 1.7-2.5.

Unfortunately I’d need more info to calculate sprint rates for you though because it needs corner weights and unsprung weight.

Of course I could use my numbers.. if the general build is similar enough ¯\_(ツ)_/¯

I could run the numbers - I was just being lazy. What I didn't know was the frequency range to shoot for.

Keith HR #894

Quick update.. my brakes felt ineffective when I got back in the car after a trip to uk. I’d been thinking about it before I left but coming back it was very noticeable.

I figured I have another MC going bad (I’ve already replace the rear a year ago) but I wanted to be able to quantify my brake performance in some way. I bought a brake pressure gauge and it screws into the bleed screw.

As an aside we’ve talked about this before - the balance bar doesn’t do you any favors when you have a brake issue. And I saw it this time. First thing I did was remove the dash and watch the MC’s while pressing the pedal - one side (the front) went to the floor and the rear seemed to be acting normal.. but guess what.. all of my foot pressure goes to the BAD SIDE.

So I figure the front MC is leaking internally. I put the brake pressure gauge on the front caliper.. 0psi. Zero. I have no front brakes.

I put it on the rear caliper. 0psi. All my effort on the pedal is effectively useless. (To be honest this surprised me because the car did have some brakes.. some pressure was getting to the rear otherwise I’d be typing this from a hospital bed. But I had been messing about by this point, losing fluid, messing with balance bar).

Anyway.. I decided to bleed the front just in case, before I swap out my MC. I have a couple spares that someone paid forward but they aren’t new.

I reverse bled the front (I always prefer to reverse bleed, because it’s so easy, you can truly do it on your own and it bleeds the MC too).. and had a ton of bubbles. A lot. You can hear them in the reservoir. I did the other side.. nothing more came out. I did the rear.. nothing more came out.

I felt the pedal - damn, felt very different. Much harder (duh).

Put the pressure gauge on the front - 750psi. The rear? 1500psi.

Now I haven’t checked the bias again yet.. that’ll be today. But at least I have baseline pressure readings so going forward I can check my brake pressures and get ahead of a problem.

Excited to hear that I'll be picking up a new motor (from a friend in Georgia) some time mid-March. I'm still running a mystery motor, bought super-cheap from a local drag racer, but I suspect that it's way under 300hp. The new motor will be ~425hp, and lighter (aluminum heads).

I'm going to trailer there and swap over a few days.

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Originally Posted by RoadRacer

Excited to hear that I'll be picking up a new motor (from a friend in Georgia) some time mid-March. I'm still running a mystery motor, bought super-cheap from a local drag racer, but I suspect that it's way under 300hp. The new motor will be ~425hp, and lighter (aluminum heads).

I'm going to trailer there and swap over a few days.

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Congrats.. 425hp is what I was shooting for but ended up with 401. Would love to hear the engine combo if you know what it is

So far all I know: built to rev higher than stock, don’t remember what was said though.. but likely 6500 vs 5500.

The heads are AFR 210. Runs pump gas (9.5 to 1). Hydraulic roller cam 555 lift. Wisco pistons and steel crank and rods.

Quote:

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Originally Posted by RoadRacer

So far all I know: built to rev higher than stock, don’t remember what was said though.. but likely 6500 vs 5500.

The heads are AFR 210. Runs pump gas (9.5 to 1). Hydraulic roller cam 555 lift. Wisco pistons and steel crank and rods.

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Sounds like a nice combo, should be fun for sure

Sounds like it's going to be wicked fast James and possibly squirely.

The LS3 in my 08 C6 Vette has 430HP and that at 3,217 lbs. and is fast & squirely, in the 33 you're easily 700-800 lbs lighter.

Should be fun.

Jim

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Originally Posted by 33fromSD

Sounds like it's going to be wicked fast James and possibly squirely.

The LS3 in my 08 C6 Vette has 430HP and that at 3,217 lbs. and is fast & squirely, in the 33 you're easily 700-800 lbs lighter.

Should be fun.

Jim

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Yeah it will be interesting! I’ve always waited to do this until last. I’m amazed the cheap motor I picked up lasted this long (it’s still going) but it’s allowed me to sort everything else before adding power. Suspension first, then brakes, then power. And brakes I’ve put on the “nice to have” list.. the stock brakes with better pads are still fine for me. I rarely get on circuits where I’d (possibly) need them. On the road and autox I can lock tires up a will.. which is the only point, to be better than the tires. No fade in my world.

So yes, more power! I’m ready ;)

If you are getting an LS3 and find 430HP isn’t enough, there’s a GM cam swap that will give you 480HP.
There is also a 525HP upgrade to, it’s a bit more involved than just a cam.

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Originally Posted by JimLev

If you are getting an LS3 and find 430HP isn’t enough, there’s a GM cam swap that will give you 480HP.
There is also a 525HP upgrade to, it’s a bit more involved than just a cam.

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Ah, no, I'm staying old school as long as I can!!! No computers!! This is just another 350 SBC (well, it may be a 377/383, I'm not sure yet)

As some of you saw on FB, I hit something heavy on the toll road last night at about 80.. and got away with it. No idea what it was; it was in the frame of my dash cam for a fraction of a second before it took out my radiator and grill. I couldn't see any suspension damage on the side of the road, just a lot of water, so I drove it off the next exit and into a Jack In The Box parking lot.

Attachment 195555

The tow guy took a few hours to arrive, but at least I got a burger and fries, and ate it on a nice cool evening :D

Attachment 195556

The tow guy had a neat way of towing; I had never seen this idea for the front wheels before.

Attachment 195557

I was only 4 miles from home, so that was easy. Today I jacked it up and was a little anxious of what I'd find underneath. It was a hell of a bang, like I'd hit something heavy.. but I couldn't see anything underneath. The radiator (this is a 33 gen1 radiator, btw, in spite of the fact it looks like a "deluxe" front.. this was done before the deluxe was an option. Which was way worse, because the deluxe radiator is much shorter. I probably would just have lost the grill shell with a proper deluxe setup. The radiator just got bent backwards under the chassis.

Attachment 195558

I stripped it all off, ready for other replacement parts, so here we are, waiting on UPS! BIG shoutout to Just 1 More, aka Frank, who was at the UPS store bright and early and shipped a full deluxe setup that he had for sale. Really appreciate it Frank!!

Attachment 195559

What was it? Answers on a postcard..

https://youtu.be/fu8PoNmm_ss

James,
Sorry to hear about the damage. You're OK, car can be fixed.
New engine will be big fun.
Some days the planets align, some days they don't.
Jim

Bummer James, hopefully she is back on the road soon.

My kids hated when something went wrong in their lives when they were younger because the first thing I would them is "in life you'll have good days and bad days, and sometimes the bad days will outweigh the good days". Now that they are adults, they are starting to use it too.

At least there wasn't more damage or worse any injury. Glad you're good.

Jim

Thanks both Jim’s! Yeah I wasn’t bummed in any way.. strangely.. just a thing that happened and can be pretty easily fixed. It does confirm my decision to leave unpainted and just have fun with it, I can’t imagine this happening while being fendered and painted!