mattster03

iTrader: (22)

For three drag race weekends in a row now, at two different tracks, I have trapped anywhere from 130-130.5 mph quite consistently and I am extremely skeptical that I am making as much powers as many of the calculators say I am. A little info on my car... I have a head/cam LS1/T56 swapped into a 3rd generation Mazda RX7. The car weights 2875 +/- 25lbs race weight (verifed multiple times). It has the following mods:

LS6 Intake
EPS 230/238 0.600"/0.602" 112 LSA
TSP Stage 2.5 5.3L heads
1-3/4" Long Tube Headers
Straight shot intake
FMS 30# injectors
Monster Stage III Clutch
Street tuned at 28* timing & 12.5:1 AFR
Mickey Thompson ET Street Radials 255/50/16
A few other small mods...

I have not dyno'd my this setup; but as another data point my old setup (TR224 cam only, same car) dyno'd 375rwhp and I trapped 119 all day long ... Which seems to verify both the online calculators and my local dyno.

So here's the question... am I really making 500rwhp +/- ?? I know that wheelspin can be a factor for higher trap speeds but my 1.8X 60' times (although nowhere near great or where I want them to be) seem to show that I am still getting decent traction. Are there other factors that might be making my trap speeds abnormally high? What do you guys think?

As you can tell, I am just as skeptical as you probably are, but it's not like I'm baseing this on some loose dyno... these are actual track numbers... someone's gotta explain this one. Here are my most recent slips on a 500' DA track day:

Run #1
60': 1.809
1/8: 7.405
MPH: 102.23
1/4: 11.324
MPH: 130.20

Run #2
60': 1.807
1/8:7.417
MPH: 101.74
1/4: 11.323
MPH: 130.52

WhySo6ick!

iTrader: (2)

with those mods I would say 430-440ish in a very light car.

redtail2426

iTrader: (10)

yeah thats like 430 or 440 like stated,you have a pretty light car there

mattster03

iTrader: (22)

I guess I should clarify... I am wondering because I have usually found online calculators such as this one, which use both weight and trap speed, to estimate horsepower. The reason these are generally very accurate is because "simple" physics can be used to estimate force when the accleration and mass is known.

http://www.race-cars.net/calculators/et_calculator.html

Head Hunter

iTrader: (14)

That calculator is off - it says my car makes 515rwhp - it also said with my weight and HP I should run 11.6 @ 117

I would guess you're much closer to 450 if not 425

s346k

iTrader: (4)

for comparison, there is a local car weighing almost identical to yours that made 507 whp and trapped 136 in da around 2000'.

WhySo6ick!

iTrader: (2)

@3650# and 122mph @11.70et it calculates 517hp. my heads and cam was 470hp-430tq so about 47hp off

sciff5

iTrader: (1)

Those calculators are off Matt. With my stock engine times those calculators said I should be making 400whp.

mattster03

iTrader: (22)

Ok cool... I personally think it's around 450-460 as well. But as I said in the original post, I have usually found this particular calculator to be dead nuts on for both my car and many others. so then I guess trap speed isn't even a very good indicator of real power? I always thought this was a much more accurate method than a dyno could produce??

jimbob

iTrader: (4)

Here try this flywheel calculator. 520 flywheel is what yours basically comes up to on the days you raced. So, 450 rwhp with a manual car, SAE corrected on a dynojet would be a about right. You were probably doing 460ish the days you raced.


http://www.wallaceracing.com/et-hp-mph.php

Tony Mamo @ AFR

iTrader: (13)

If someone told me that they had a 2875 pound car (raceweight with driver) and told me it ran 130-130.5 in average quality air (say 800 - 1600 positive D/A), I would tell them based on a calculator (and some creative math I have implemented over the years dialing that calculator in for an "average" type of situation), I would say that engine is generating approx 530-535 HP at the crank....probably 80 less at the wheels (450-455 RWHP).

I say "average" because if the driveline is really efficient it may be making less than that at the crank and if the driveline isn't as efficient it might be making more at the crank.

Where did the 500 RWHP come from btw?? Assuming the raceweight is 2875 (and once again average D/A and track conditions), 500 RWHP in a car that light would trap 134 or so.


Actually my same calculator/math has your engine generating 560 ish at the crank.

Consider my 3450 pound Vette trapped 124 with a documented 552 HP on the flywheel/engine dyno which my math/calculator almost backed into exactly, but of course D/A is always a big variable here (I bet your calculator shows that to be alot closer to 510 if I had to guess).

Also, losing 90 HP to the tire is by far a much more appropriate loss (my 560 estimate to your 470 RWHP figure which I feel is quite accurate based on your performance).....in fact thats very common/average I would say unless you had light wheels and tires and a very light clutch/flywheel assembly which can show a loss closer to 80 RWHP like what I have seen in my Vette on numerous occasions having the opportunity to flywheel and chassis dyno numerous combinations. Most people don't get the opportunity to do that.

-Tony

Slowhawk

iTrader: (12)

Problem is the 11.3 at 130mph.11.3 should be 118mph. When you run the 10.2 that the 130mph should be doing your mph will go down.

Tony Mamo @ AFR

iTrader: (13)

Don,

I dont buy into that all that much....I know alot of people say that.

I've ran high tens and ran low/mid elevens in the same car pretty much with the exact same traps (within 1 MPH)....it's not going to change much. Ive seen other cars do the same....especially when they swap from say street tires to slicks....the trap speeds don't really change....the ET is effected greatly though for obvious reasons.

My guess is the OP is spinning badly out of the hole, but the trap speed tells us all we need to know as it relates directly to HP (weight versus power produces "X" trap speeds with the only variable there being air quality which simply reduces available power or improves it in good air obviously having a corresponding effect on trap speed).

Bottom line is there is a bunch of ET left in the OP's combo, but that really doesn't play into or address his issues or concerns with power....the trap speed is all we need to know to determine that and it looks like he is generating much closer to 450 RWHP than 500....thats for sure.

-Tony

PS....See you in a few months at PRI

john563

iTrader: (17)

i ahve those same heads and a fast 90 and my cam is a almost the same specced by pat G 232/238 6xx 6xx 111lsa+2 ..I'm a 4400 stalled(5c conveerter) and put down 430ish rwhp

as far as track results go the time i took it i had shifting problems and it bogged passed the 8th but its fixed now so we'll see what it will do when nicer weather comes

Slowhawk

iTrader: (12)

I've got about 80 slips from my car. Pretty consistant. When my 60' went from 1.5's to a spinning 1.9 my mph went from 116mph to 120mph

with my faster setup with only 30 runs it would vary a bit more.

Tony- your not turning into an import driver that sit's around talking mph because there ET's suck,are you

Point is, I'm looking more at the 60',weight and ET. If the car was 500rwhp it should be running a low 10 or even high 9 with a manual tranny at a higher speed at that weight.

DSRE

iTrader: (7)

Wallace racing calculator says 460rwhp at 2875 But they also have calcs with altitude and weather correction fwiw here is the link, BTW Best Automotive Calculator site i know of fwiw
http://www.wallaceracing.com/Calculators.htm

DSRE

iTrader: (7)

ahhh ya beat me to it lol

BayAreaSS

iTrader: (10)

trap seems right to me. Probably making 450 to the wheels.

vetteboy2k

iTrader: (5)

Don't forget that mph on a drag strip is driver dependent as well with a 6 speed car. An experienced drag strip driver who hass alot of seat time in that specific car will trap higher than a novice. Learning the subtleties of the car will allow you to extract the most mph out of it from shift points to tune and more.

There is no calculator that can predict mph for a 6 speed car accurately because that don't take into account all the variables that exist at a racetrack.

In my experience over the years a H/C build in a ~3300# corvette, 130mph would be around 500rwhp(6 speed) in good air.

mattster03

iTrader: (22)

I'm not spinning badly; just launching at a lower RPM than I should and then bogging. I'm installing 26x10.5 ET Streets and front runners for my next race outing. Hoping to bring my 60' from 1.8X to 1.6X and catch a 10 second slip. I'll probably put the car on the dyno for fun here in the next couple of days... I was just really confused as to why that calculator I posted above (as well as many others) were saying 500whp when I have found them to be pretty darn accurate in the past. I've got my answer... it's just not that acurate haha!