Ok guys,

alot of you may remember my confusion as to why my car wasnt goin faster in the 1/4, especially with good hard runs on 1.6 60' times and trap speeds over 110mph...best ET is an 12.65

my time slips are still posted here someplace.....

well i went to the dyno the other day and did some tuning, the car is making 409.9 HP at the wheels, so it should pull WAAAYYYY harder than it is......

any more ideas?

 

How are you shifting? Never lift? Granny? That could be some of it.

Where are you shifting? Too short? Not high enough?

How's the area under the curve? Is it real peaky way up in the rpm? You really need a nice broad torque curve.

With a 1.65 short time, I ran 12.15@111. But its an A4 so it'll be a little different but should give you an idea.

 

Now go drive across a weigh scale and find out what you and the car weigh.

Estimating at 3500 pounds total weight, you should be running closer to 12.0 or very high 11's. There can be any number of things keeping you from reaching that ET.

What rpm are you shifting at? What rpm are you crossing the finish line at?

 

car weighs 3600lbs with me in it and a half tank of fuel,

i shift the car at 5800rpm, which was where the best ET was,

the dyno showed peak power aroun 6150rpm, but it doesnt pull hard there so it could be over calculating acceleration of the drum at the end of the pull, which is fairly common.

the torque curve is nice and flat from 2500 on up, i'll get the dyno graphs scanned in soon for you guys.

i usually granny shift the car, but even so it should still run faster than it is....with over 400hp at the wheels though, even the trap speed should be higher than it is, it should be around 116 or so taking the weight of the car into account

 

I can tell you that granny shifting vs. power shifting is worth up to .5 second. When I used to jump in other people's cars, I would usually see .3-.5 second improvement. Never lifting will definitely help. Its a little harder on stuff but if you want the ET, its the only way

 

With a dyno'd RWHP of 410 and 3600 pounds total weight, you should run 12.0 at 113.5 mph.

Your trap speed mph is the best indication of hp. Don't forget that dyno hp can't take into effect wind resistance going down the track or rolling resistance of the tires so track hp will always be lower. The dyno can't compensate for shifting delays since it calculates hp from the torque created in high gear.

ET is just along for the ride and depends mostly on traction.

It's hard to say why your engine stops pulling hard after 5800 when the dyno says it should be making power to 6150. Not enough air flow into the engine, not enough fuel at high rpm, valve springs not strong enough causing the valves to float, timing not set right.

There's probably not much you can do unless you modify the car to use as much of the available HP during the entire run.

 

well most of that is obvious steven, but there would be less airflow on the dyno than on the track, so the numbers should suffer there as related to air.....

we tuned the car on the dyno, so the timing is nailed down, and the air/fuel curve is about as close to perfect as a carb gets

the car has excellent traction, so thats not the problem.....my trap speed of 110.82 mph would equate to around 360-370 RWHP, the dyno says way more at 410.....the way trap speed is used to calculate HP accounts for wind resistance and rolling friction.....which is why its accurate.....but here its waaaaay off

 

Tuning on a dyno will just about always be leaner on the street/track. Stationary vs. moving.

As an aside, what are the torque numbers? I dynoed my car when it was running 12.1-.2 @111, my numbers were:
318rwhp
455rwtq

All the calculators on the internet never come up with those numbers. All of them said 400rwhp.

Just something to throw into the mix....

 

ever think that the clutch/tranny is slipping?

just a thought....

 

the real dyno said 409.9rwhp, and the internet calculator deal says like 360. go figure

 

nope the clutch grabs really hard....ive never even smelled any clutch with this thing before. Id notice that though if it was slipping.

see what i mean, all the obvious stuff checks out....weird

 

What altitude do you race at and what was the density altitude? You'll automatically lose hp when the density altitude goes up.

Dyno hp is corrected to sea level so it gives a more equal playing field when comparing 2 engines. Also taking your engine to a different dyno will usually give different results.

In my sig, I have my engine when it still ran on gas listed as having 505 altitude corrected hp. What I get to use going down the track on a typical race day is only around 430 hp because of the high density altitude I race at. If I managed to get to Mission BC in the spring or fall when the weather is good, I would be able to use close to that 500 hp.

The alcohol engine hasn't been fully tested yet but I'm estimating it will be close to 600 RWHP. 650 would be more what I'm shooting for.

 

New england dragway is only 90 feet above sea level so its really good air most of the time. the times i ran this year were early spring so it was nice and cool with no humidity and normal pressure so i dont think it was much of a factor....its hot has hell right now though and humid so it would be worse.

i think *** just hates my car

how is that alky motor coming stephen?

 

There's a Canada Day drag blowout (Wheel standers, Pro mods, quick 16, etc) this Tuesday. Any vehicle 11.00 and quicker is invited to race. I'm going to see if I can qualify. If not, and everything stays together, I'll go back to regular bracket racing July 5/6.

 

What size rear tires are you running? Also, what rpm's are you turning thru traps and in what gear?

 

383backinblack, what does your tq curve look like on your dyno run? Do you have a lot of low end? I agree that powershifting will give you a couple more mph, and will lower et's. That's how certain car mags (GMHiTechPer) get certain cars(03vette) to run much faster than other mags (Car&Dr) who take it easy on their cars during accel. tests.

I think a lot of these internet dyno calculations are off and they're usually off really bad when it comes to tpi setups. They really don't figure all of the extra tq that tpi setups produce into their calculations. I mean how many other setups can put 320rwhp and at the same time 450rwtp? I think all that tq really shoots the car out of the hole and carries it for the first half of the 1/4 which can make for better times and mph than cars with a lot less tq and more hp.

 

26" tires, 4th gear (1:1 ratio) at about 5000rpm i think...i forget what rpm i cross the traps in really......i'll get back to ya on that one

 

the torque curve is nice and flat from abou 3000rpm on up, which is fine considering it never really gets below 4000rpm during a race.....i launch the car at about 4500-5000

 

I have a friend who switched from a 4 speed to a turbo 350 with a 3000 stall and picked up a full second. This was a truck transmission though.

 

I'm thinking you need more rear gear than what you've got. You need to trap a bit higher than peak hp to really get the most out of the power you've got.

 

i already have 4.10's, and 4.56's arent gonna cut it on the highway........besides i doubt that will make the full second or thereabouts of difference we're talkin about here......but rear gearing would def make an impact....

Like i said before though i really cant remember what rpm im trapping at....so i'll let you know

 

Another thing that comes to mind, do you have good valve springs? Do you have a fuel pressure gauge that you can watch all the way down the track? I went from running high 14's/mid 15's to 13.9's with just a fuel pump upgrade and from 13.9's to 12.9's from buying a real carb.

 

Those "internet calculators" use the basic formula for hp (work/time) and give you the average HP it takes to do the work of moving a 3600lb car 1/4 mile in 12.65 seconds.
Some use the trap speed to figure out the work done.
Others factor in other things that can or can not be changed that could affect how the car goes down the track.

What this means is that cars with wide gear spacing, using a larger area of the engines HP curve is going to have a different average number than someone using more closely spaced gearing over a more narrow hp range. Sometimes the average goes up, sometimes down. If the "internet dyno" numbers are alot different than your real dyno numbers, it might be something to look into.

 

we checked the fuel pressure during dyno runs....it was pretty consistent.....also the carb is a race demon 750 GC

 

I would mount an autometer fuel pressure gauge under that badass cowl hood of yours so you can keep an eye on it. My fuel pressure wouldnt fall off until the end of the track. Also, here is something else to note, this is out of a valvetrain troubleshooting guide in hot rod magazine:

Symptom: Engine pulls strong to redline in lower gears, but as vehicle speed increases, the engine wont accelerate beyond a given rpm.

Cause: The valvetrain's natural frequency of vibration matches that of other vibrations in the cam or valvetrain. Change the spring, cam, or both.

 

i would have never, EVER thought of that.

it makes sence though. i mean, when the car is dynoed, it makes good power, but when moving, it doesnt....

 

Yep. On the dyno or in 1st and 2nd at the track, you power through the RPMs so you arent at any of the bad harmonic spots for long periods of time. In high gear tho you can see how you might have problems getting past trouble spots with valvetrain harmonics. I used to think this was why i wasnt mph'ing like i thought i should be, then i realized i was running 40* of advance lol.

 

the valvetrain is pretty stable.....all the springs are silicia alloy ovate wire triple springs, with titanium locks and retainers.....also has stud girdles.....it pulls about the same in every gear though....higher gears arent really any different then lower ones

 

If you pull your driveshaft off does your rearend seem to spin freely and smoothly?

 

Backinblack- Have the same tranny as you in my garage waiting to go in. Are you running slicks or Drag Radials with your combo? How wide? That is an awesome 60ft time. How do you launch the car..with a line lock?

Sorry for the 20 questions but your the first person I have seen who is drag racing the Tremec.

 

ya, its a brand new moser 12 bolt....works mint

 

i use mickey thompson ET streets, which are slicks not radials......

9.5 inches tread width......havent used a linelock yet, just put it in. i just put the thing in gear and drop the clutch at about 5000rpm.......the rest of the suspension is stock except the south side machine lift bars

 

I would say get a fuel pressure gauge and watch it all the way down the track. Lets put it this way, my car runs 12.6's at almost 109 mph with stamped steel rocker arms and 2.0 60 foots. Your car should eat my car alive in the 1/4 mile.

 

ya, thats what im sayin......but on the dyno we watched the pressure all the way to the redline in 4th gear at WOT and it didnt drop more than 1/2 psi.......i should check it at the track as well.....but it doesnt seem to be the problem

 

383backinblack,
Wow, this is really baffling. Vette guys with around 410rwhp run mid 11's all day, which should put you in high 11's at least, not to mention over 116mph through the traps at least. Maybe that dyno is a little optimistic or maybe it's a little screwy and you have other problems. Maybe your gears are working against you and you need to step down to get more of your low end tq. That's surely not the problem, but I can't think of much to say that would help. I know your car should be a lot faster with your current rearend gear.

Can you post your dyno graph? Where does your tq peak, how much do you have, and what is it at 3000rpm?

 

the torque curve is nice and flat from 3500rpm and up which is good, considering i launch the car around 5000rpm, and the revs never drop below 4000 during the run. peak torque was 383 ft/lbs.....i really need to scan those graphs in, im on vacation right now so i will do it as soon as i get home on wednesday

 

The tq peak sounds kind of low, but you're not running efi, so I'm sure that's why. The vettes that I was thinking of are running miniram/superram with their AFR's setups. Their peak tq is around 450-500rwtq, so maybe that's why they run so fast. They have that much tq and around 370-430rwhp. The guys I'm referring to are Todd85 (beachbum on the vette sit)e, holeshot, and Ski_dwn_it. Maybe try to talk to one of these guys or some of the other vette guys that run a carb setup on the vette site. I believe most of them run FI though, but they're still very smart and could be some extra help along with us 3rdgen gurus.