first time out with M/T et streets and rear suspension mods - now to dial it in

hit the local 1/8th mile tonight for the first test-n-tune after my winter mods:

2005 mustang gt w/11k miles
5spd manual
stock 3.55 gears
stock clutch
FRPP shorty headers
FRPP GTA mufflers
K&N CAI
stock/OEM tune

UPR/Granatelli Motorsports radiator support/sway bar eliminator
Metco UCA mount
Metco UCA (stock length, installed in lower of two holes on UCA mount)
Competition Engineering adjustable panhard bar
Competition Engineering panhard bar brace
FRPP bumpstop kit
Strange single adjustable rear shocks
Cobra Jet rear springs (M-5300-Q)
BMR relocation brackets
Metco LCA (installed in top-most of three holes on relocation brackets)
M/T 17" ET Streets mounted on spare OEM 10-spoke wheels

The CJ springs and UCA installed in the lowest hole gave me a pinion angle of -2*



I ran the following setup tonight as a baseline:

M/T et streets set to 17psi cold
passenger side shock set to full stiff
driver side shock set to -2 clicks from full stiff
1/8th tank of gas
spare/jack/shaker 1000 sub in the trunk
stopped by the scales on my way to the track 3680 with me in the car
DA at the track was approx 1155

launching between 4-5k (approx) I had zero wheel spin, in fact I bogged just about every time (the 5k launch had the least bog).

best 60' of the night was 1.951 (down from 2.177)
best 1/8 was 8.822 (down from 9.203)
best trap as 80.84 (up from 78.39)

Any recommendations for tire pressure and/or shock settings given the above info?

I think I want to leave the LCA's alone for now. And for sure there's still some driver mod to work on. I'm pretty sure I lifted a little bit at each launch because I'm so used to compensating for tire spin with the street tires.

Launch at a higher rpm. I'm sure you were bogging. Try 5500. Those tires should stick with ease as long as the track is prepped decent.

Red line that bitch

Launch it off the rev limiter, that's what I did back when I was intake and exhaust only, ran a 12.90 @106 with no other mods at all. Sixty foot was. 1.78 iirc

Put the tires at 14lbs and leave at 6000-6200, I had the same rear end set up only with 4.10's and would pull 1.54-1.57 60ft time

on a stock bottom end launching at 6k???

TOWGUNNER said:

on a stock bottom end launching at 6k???

Click to expand...

Yeah what's wrong with that? I launch at 6k.

I have before a few times.

Did you plot your suspension?

Get someone familial with setting up suspensions watch you at the track. So they can see how the car is leaving. Video can help depending on where it is set up and where you want to watch.

click here is some good reading so you get a good understanding of the rear suspension, how it works and so on. Very helpful stuff for sure. Check out the links near the top labeled as "Launching a drag car", "Baseline your suspension", "Chassis Setup" and so on. It is not specific to a triangulated 4 link like the earlier cars use or a 3 link. But a lot of it still applies.

86merc said:

Did you plot your suspension?

Get someone familial with setting up suspensions watch you at the track. So they can see how the car is leaving. Video can help depending on where it is set up and where you want to watch.

click here is some good reading so you get a good understanding of the rear suspension, how it works and so on. Very helpful stuff for sure. Check out the links near the top labeled as "Launching a drag car", "Baseline your suspension", "Chassis Setup" and so on. It is not specific to a triangulated 4 link like the earlier cars use or a 3 link. But a lot of it still applies.

Click to expand...

I haven't plotted the suspension. I found a site a while back and was that talked about setting up the S197 three link (unfortunately the site is down now).

I hope to have someone with me during my next track visit that can watch my launch and possibly photo/video as well.

Someone one watching and video helps a lot. I was watching a buddies car and it had it's best 60' ever. But he thought it could be more consistent. Watching the car at the track I swear it had too much distortion on the sidewall. Sure enough we slowed the video down and it was hitting the tires hard. With the air pressure in the slicks and launch rpm it hit the tires (stick car) so hard it was bouncing the rim off the ground and recovering real quickly.

Because of the video we raise the tire pressure some. Then could see it had too much wheel speed. We lowered the launch rpm some. Car was much more consistent and had a new best 60' to boot. Just because you have seen a new best on a time slip does not mean it is the best you can get out of it.

Remember, the best way to find out what works on your car is test test test and test some more. Be consistent and change only one thing at a time. So you know if the change helped or hurt. Keep a good record of your runs and changes. In a note book, on the time slips or in a fancy racers log book. So you have a good reference to look back on. I enjoy testing even though it doesn't go as planned I usually learn some thing. Good luck.

ive never launched that high. heard bad things especially with stock rear ends. highest i launch is abour 4500 rpms.

Stock rears are very strong, but the most I am willing to launch at is 5500 just because I have to get back home just in case lol

You can stay at 5k that is comfty for me.

You should be able to get a little more out of it. Don't be afraid to drop the air pressure more and launch higher. Your air pressure can go up a couple pounds after your burn out also. I run 26x11.5x15 et streets run 12-14 psi cold depending on track, and launch at 6500. I'm still on stock clutch, trans, and rear except the 4.10s and they are all holding strong. I have over 250 passes and probably close to 150 at launching over 6000 rpms.

Also have a buddy launching just as hard as I do and runs slicks and he has no issues also. We know that anything can break at any time but are happy with what the stock parts have done. You should be able to get a little more out of it, I ran that same time and better times with a lot less mods then you have and on street tires when I first got my car.

sounds like i might be raising my rpms higher at launching then lol. I've run a best of 11.92 launching at 4500 so i think i can definetly bring that time down more.

86merc said:

Did you plot your suspension?

click here is some good reading so you get a good understanding of the rear suspension, how it works and so on. Very helpful stuff for sure.

Click to expand...

thanks for that link, I'm going to try to plot my suspension this weekend! I'll post up info when I can.

Do you have a recommendation for calculating CG height in our cars? I saw several diff methods:

- distance from floor to crankshaft bolt and add 5"
- distance from floor to center of camshaft

not sure which one is more applicable with the 4.6L 3V...

86merc said:

...remember, the best way to find out what works on your car is test test test and test some more. Be consistent and change only one thing at a time. So you know if the change helped or hurt. Keep a good record of your runs and changes. In a note book, on the time slips or in a fancy racers log book. So you have a good reference to look back on. I enjoy testing even though it doesn't go as planned I usually learn some thing. Good luck.

Click to expand...

I have a small notebook in my car and I jot down as much relevant info as I can, and I plan to put in a spreadsheet after each race (tire pressures, shock settings, launch RPM, track conditions, weather, etc.)

lindertw said:

thanks for that link, I'm going to try to plot my suspension this weekend! I'll post up info when I can.

Do you have a recommendation for calculating CG height in our cars? I saw several diff methods:

- distance from floor to crankshaft bolt and add 5"
- distance from floor to center of camshaft

not sure which one is more applicable with the 4.6L 3V...

Click to expand...

These are recomendations for cars with cams in the cylinder block. Unlike the modular motors. So use the crank height and add 5". As long as you always use this measurement in your calculations you will be fine. Just be consistent with what ever method you use. Otherwise the previous data is worthless.

I bet you have mainly stock suspension. So you will be limited in your adjustments. If you have control arm mounts that have multiple mounting points that helps. With out having coil overs to adjust ride height in the rear I have a couple of sets of coil springs and poly spacers to move the height some. If you have adjustable length control arms you can do more as well. But play with the numbers in the calculator here so you can see what different measurements do for your anti-squat. Then you can see what adjustments you can make on your car.

lindertw said:

I have a small notebook in my car and I jot down as much relevant info as I can, and I plan to put in a spreadsheet after each race (tire pressures, shock settings, launch RPM, track conditions, weather, etc.)

Click to expand...

Very cool. As you make changes you will find it will be nice to go back and see what changes did what. Same with altitude and track conditions.

i run the same tires. i put them at 12psi and launch at about 5.2k. best 60' of 1.63.

with the exception of the front swaybar/endlink/rad support removal, the front suspension is bone stock.

metco UCA (set to factory length) is positioned in the bottom hole of the metco UCA bracket



Metco LCA (fixed) are installed in the top-most hole on BMR relocation brackets


i used the instant center calculator from the link 86merc provided and came up with the following:

UCA in lower UCA mount hole + LCA in upper bracket hole:



I had to do a little math after reading that the control arm length needed for the calculation is the horizontal equivalent, vice the actual length (or maybe I read that wrong).

**edited to add**

curiosity got the better of me so I ran calculations for all possible configurations:

- UCA in lower UCA mount hole + LCA in middle bracket hole:
antisquat 146.78%; IC length 35.36"; IC height 9.69" picture

- UCA in lower UCA mount hole + LCA in lower bracket hole:
antisquat 165.42%; IC length 33.28"; IC height 10.28" picture

- UCA in upper UCA mount hole + LCA in upper bracket hole:
antisquat 110.95%; IC length 45.93"; IC height 9.52" picture

- UCA in upper UCA mount hole + LCA in middle bracket hole:
antisquat 136.02%; IC length 41.41"; IC height 10.52" picture

- UCA in upper UCA mount hole + LCA in lower bracket hole:
antisquat 156.28%; IC length 38.35"; IC height 11.19" picture

It's not 100% clear to me how that particular 4-link calculator works, and I can't at this time throw enough examples at it to find out.


Generally, any side view geometry calculator has to work off the side view slopes of the links and solve for their intersection. y = mx + b stuff straight out of high school geometry. I *think* it works from the difference in pivot heights and the difference in fore/aft pivot coordinates to compute the slopes, but that's not the only way that this little math problem can be solved.

FWIW, try to keep your vertical measurements within 1/16", as they're more critical to determining the slopes than the fore/aft lengths (which are probably OK being within ±1/8").

BTW, don't get carried away with keeping lots of significant digits in the % antisquat results. Even if your measurements were dead-nuts on, all of these little applications are static geometry solutions only, and do not consider lots of real-world things. Bushings (even poly) compress, brackets bend a little once you hit them with the acceleration traction forces, and the CG and chassis side pivot heights will all change once the nose starts to rise and/or the tail either squats or separates. Which will affect the results to some extent. Unless I was looking to see how the A/S varied due to changing the static rear height without changing anything else, I wouldn't trust decimal portions of the % at all, and even the whole % numbers would be a little suspect.

Norm