Rear end squat at high speed

[TheJDMan]

I have started noticing that the rear of Dust Off begins to squat approaching speeds of around 100mph. Typically the car reaches speeds of 115 to 120 on the 1/2 mile front straight of Dominion Raceway's road course. I'm wondering if this squat is a good thing or a bad thing and if it is something I need to address. I typically notice this starting just past 1/2 way down the front straight but by the time I start breaking for the upcoming corner the speed is reduced and the effect is gone. I'm running a stock style front air dam and the stock rear deck spoiler. Any thoughts?

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[icemanrd19]

rear downforce? How much is it squatting? Stick a go pro on the corner and record it while driving. How did you notice this was happening?

[TheJDMan]

I'm thinking this is some combination of rear downforce and front lift because this is the first time I have had the car on this particular track with such a long straight. In any case, next track day I plan to mount the go pro and see what I can see, but for now I'm just speculating.

[kimosabi]

I would be very surprised if that car had so much rear downforce the rear would squat at 100mph. My bet would be underhood pressure lifting the front end ---> shifting centre G towards the rear.

[1BADBET]

What spring rate are the rear springs? I talked to Ron about spring rates awhile ago and he mentioned having to run a stiffer spring on road courses.... Probably so this doesn't happen.

[NOT A TA]

In the pic it looks like the front air dam support braces are missing. The air dam may be folding under at a certain speed. Is the cowl hood sealed to only allow air for the induction system and preventing the high pressure air at the base of the windshield from raising the pressure under hood?

[David Pozzi]

At 115 MPH, the rear spoiler makes around 130 lbs downforce. The front lift is 330 lbs!
https://web.archive.org/web/20140702200011/http://www.camaro-untoldsecrets.com/articles/rpo_d80.htm

This is a .pdf download of the Car Life test. 14.4 MB
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiFrcrntZzPAhUNx2MKHTD7AWUQFggeMAA&url=http%3A%2F%2Fwww.rotaryeng.net%2FCar-Life-all.pdf&usg=AFQjCNG85uwjSNGw0NEiWTpQ53pRyM8mfg&sig2=dvTIDJ0KLtMBk5FKZ9QkZQ

Here's the main data page of it with photos at speed:
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[TheJDMan]

In the pic it looks like the front air dam support braces are missing. The air dam may be folding under at a certain speed. Is the cowl hood sealed to only allow air for the induction system and preventing the high pressure air at the base of the windshield from raising the pressure under hood?

That is actually an old pic. I have since installed a stock style fiberglass front spoiler with a pretty substantial support backing it up. The air cleaner intake is sealed to the hood.

The rear springs are 200lb.

I'm not sure this is even a problem since the effect is gone once I start braking at the end of the straight.

[Sleeper68]

Steve,

David is right. Your car is producing lift in the front end. You need a more substantial front spoiler. I noticed this problem with my '68 and thus designed and made an aluminum front spoiler with a bolt on splitter. My version is 1" taller and 1.5" wider at the bottom. I have had the car at speeds exceeding 145 mph and noticed little squat, with a well planted front end. The splitter makes the spoiler more efficient by making the air "decide" which direction to go, over or under the spoiler. It also helps with overall downforce by keeping air under the car fast and thus at a lower pressure as compared to slower air over the car. The further the air is from the exhaust, the better, if your car is not equipped with an under-body aero pan. Unloaded front tires at high speeds are very dangerous, as are unloaded rear tires.

I will post a picture of my setup. I currently manufacture these spoilers for 1st gen camaro owners and if you are interested, can fit one to your car, catering to its specific dimensions. It is very difficult to produce net downforce in the front on our cars due to the valence shape without extensive modifications. (Mike Dusold's tube chassis camaro is an example of extensive mods.) The best we can do cheaply is to counter-act the lift as much as possible to keep the car stable above 115-120 mph.

PM me if you interested in one of my spoilers.

Ryan

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[icemanrd19]

The other day I made a solid 4th gear pull. I noticed my front end started floating more around 120 to 140. What front coilover setting would I adjust to pull the car down more? Should I mess with the rear coilover setting? I think it’s time for a real front spoiler and some aero

[dhutton]

The other day I made a solid 4th gear pull. I noticed my front end started floating more around 120 to 140. What front coilover setting would I adjust to pull the car down more? Should I mess with the rear coilover setting? I think it’s time for a real front spoiler and some aero

I’m not an expert but I don’t think that is something you can address with shock damping. Shocks address transients that occur over relatively short durations while the floating is more of a long duration steady state condition. Shock damping might affect how quickly it starts to float but the steady state float will be the same.

Curious if you have any hood vents.

Hopefully an expert will respond. Interested in what they have to say.

Don

[icemanrd19]

No hood vents except the rear of the coil hood. I plan on modifying a 69 anvil front spoiler and adding some aero just like hellfire. Where it lifted some was in a slight dip in the road. Funny part was I was about to shift into 5th and I realized there was no need since I was running out of speedometer lol

[TheJDMan]

I had forgotten about this thread until it came back up. Just an update since the original post in 2016. The original assessment was the rear was squatting at high speed when in fact the gopro showed the front end was lifting. I still have the same front spoiler on Dust Off but working with Rod Prouty I have upped the spring rates to 800lb front and 300lb rear. The car is so much more stable at high speed now and surprisingly with a quick shock adjustment still rides good in normal street driving. The front end still comes up some but not does not float like it used to. I still have plans to build a spoiler/splitter but just have not done it yet. Here is a recent pic of Dust Off at speed with the new springs and you can see it stays nice and flat.

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[dhutton]

No hood vents except the rear of the coil hood. I plan on modifying a 69 anvil front spoiler and adding some aero just like hellfire. Where it lifted some was in a slight dip in the road. Funny part was I was about to shift into 5th and I realized there was no need since I was running out of speedometer lol

Dip in the road makes it a different situation and shock damping might have an effect. I would try increasing the front rebound damping but again, not an expert.

Don