dvcn

For those who don't want to read:
Best ET (coasted the last second of the run): 14.9798
Best MPH: 93.32mph
Weight of SP, 1/4-1/3 tank of gas(Chevron Premium), no driver: 2900 lbs )
Calculated hp: 203rwhp, 238hp flywheel
50psi in the tires might make the ecu mad

Car: Sport Package, 2900 miles. Mods: Royal Purple in trans and diff.
(don't want to count the tint and strakes)
Track: 608', approx 55 deg F, IHRA certified track and scale
Weight on all runs 3205 lbs (driver + passenger), except the 14.97 run
which was 3105 lbs (no passenger)

I do have track experience (250+ passes) but don't have much seat time
in this car since it is my wife's daily driver. Prior to going to the
track I've probably driven it less than 80 miles. I launched it like I
do my RX-7 (2200 lbs, 230hp, 13.53@102mph, 1.9 60's on street tires)
which is over 8000rpm and slip the clutch for about 10'. This produced
horrendous wheel hop along with a matching bad 60' of 2.31 and a
15.3480@89.46. This was done with 32-34psi in all tires. I raised the
front tire pressure to 50psi (reduces rolling resistance, gives a better
ET/mph) and lowered the rears to 24psi. Of course, the tire pressure
warning light came on. Staging for the next run I revved it to 7000,
the engine stumbled and the CEL flashed. I launched at 7500 and bogged
badly, the engine had lost a ton of power. After putting down the
track, I immediately reduced the front tire air pressure to normal 32psi
levels and all was better with the engine. I suppose the extreme
tire pressure made the ECU cut power, that's all I can conclude.

The next run with the reduced rear tire pressure produced less wheel hop
but still wasn't a good launch at a 2.2441 60'. It gave a
15.2287@93.32.

The last run was during bracket eliminations which is the reason I let
off at the end of the run. I still ended up breaking out even though I
let off the gas early. It was a 14.9798@90.16 on a horrible 2.3534 60'.

Analysis: The 60' times were horrible, I need to try a few different techniques. With a couple more runs I'm
sure I could have got it down to the 2.1's or lower. I granny shifted all runs
so speedshifting would have netted another .1-.2 seconds. The point is
that if I had three or four more runs I'm sure I could have run a
14.5-14.6.

Pull out the calculators:
3205 lbs, 93.32mph gives 203.28rwhp. Doing a SWAG at the 17% driveline
loss gives 237.84hp at the flyweel. The math also shows that with a half decent lauch a 14.60 ET should have happened.

zerobanger

I and several other members weighed our cars and got in the 2950 range with full tank of gas. Your car may not weight that much. Mine was 2925 with half tank.

Good runs.

epitrochoid

nice numbers!

so you ran the 14.9 with 24psi rear 32psi front?

dvcn

zerobanger- I am so sorry for the typo. I edited the weight to 2900 lbs with no occupants.

epitrochoid- Yes. I have to blame poor driver technique and not the car for any shortcomings though.

emailists

BTW - what causes such bad wheelhop in this car?

dvcn

It is usually caused by the pinion angle rotating out of the normal position. It can also be caused by suspension problems (bad shocks, etc).

The 3rd gen RX-7 also has wheel hop problems to the point that parts would sometimes break. It was reported that lower tire pressures or drag tires would help reduce the problem. There are aftermarket parts for the 3rd gen that also reduce or eliminate wheel hop.

Squidward

I noticed my 8 also undergoes lots of wheelhop going hard off the line.

Kinda scary actually...

epitrochoid

it's a really terrifying sound....the shifter looks like its gonna fly out and smack you in the face.

makes me never wanna launch my car hard again

86rx7

wheel hop is VERY hard on the drive train,..

CERAMICSEAL

It's funny (not literally) that these cars have this much wheel hop since part of the purpose of the powerplant frame brace is to cut down on the same; preventing the diff from bowing. Maybe almost any car with similar suspension design would do the same when launched at such high rpms.

amartin

I launch my S2000 anywhere from 6600-8000 rpms when running auto-x, and I can tell you, there's ZERO wheel hop in the S2000... just tire slip.

-- Aaron

racerdave

It was also real easy to wheel hop the FD RX-7.

Don't know why that's common with Mazdas...

zerobanger

my FD gets very little wheel hop. The wheel hop I get in 2nd gear in the Rx-8 is 10 times worse than the wheel hop I get in my FD on launch.

I replaced my bushings, upper controlarm and transmission recently in my FD and when I went to the track it was the first time I got zero wheel hop.

dvcn

I was hoping that people would notice the horsepower portion of the post a bit more than the wheelhop part. With all of the speculation of cars not making the quoted 238hp and the unwarranted Mazda bashing I am glad the number seems to be right on.

zerobanger

actually...

I trapped at 92 MPH. I weighed my car 2925 that day. with me makes it 3075 lbs. at 3075 lbs that makes my car have 177 rwhp. 177 rwhp =203 flywheel hp.

Judge ITO traps at 95, I assume same weight as my car + driver, I assumed 200 lb driver and made it 3125 lbs.

based on that his rwhp is 211 and his flywheel is 240.

Although trap speeds are more consistent than ET, I launched at 3000, while I think Judge ITO launches at 7000+. Assuming 95 is the best trap you can get from the stock 8, 238 HP is right on.

rotary-convert

was dsc off when he did his launches?
if not what differences would there be?
best
d