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Nitrous and drag racing help needed-just beginning

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#21 ·
I understand that. But if you think op is running 10.6s with the power he has...you are high as hell. You clearly have never ran a car down a strip if you believe it will
 
#23 ·
Froush said:
I understand that. But if you think op is running 10.6s with the power he has...you are high as hell. You clearly have never ran a car down a strip if you believe it will
Click to expand...
10.69 is with the 125 shot and yes, very doable with the right setup. I've been in the 10s with similar power numbers. Others here have done it as well. There's a big difference between an ideal combination and what your average street guy will run when he goes out to the track with a combo that's not optimized for the track.
 
#24 ·
10.90 at 384 hp is much more doable than 10.6 at 340. It's race weight too. Unless I missed it, I don't think op even mentioned his race weight. If full weight I'd assume 3500 lbs. It's a high 11 second car
 
#25 ·
Froush said:
10.90 at 384 hp is much more doable than 10.6 at 340. It's race weight too. Unless I missed it, I don't think op even mentioned his race weight. If full weight I'd assume 3500 lbs. It's a high 11 second car
Click to expand...
OP's weight is 3300 lbs.

Look at Craig's MPH though. 124 mph. The car has a half a second left in it.

That 10.6 is not at 340. It's with about 360 on the 125 shot.

It's not just power and race weight. It's...

power (the entire curve across the used rpm range, not just peak numbers)
weight (car's inertia)
torque converter multiplication
torque converter efficiency (slip)
rpm
transmission gearing
rear end gearing
tire height
tire growth
drag coefficient
track grade (flat, downhill, or uphill)
weight transfer
engine inertia (engine's ability to rev)
tire speed on the launch
friction coefficient (traction)

... and much more. Craig is also using a C4 I believe with a 2.46 1st gear and 1.46 2nd gear. OP has a 4r70w with 2.84/1.63 gearing which makes a big difference. Also, I'm not sure of Craig's rear gear.

Something else to consider is that the OP is making 450+ wtq down at 3800-4000 rpm. Craig's 408w is probably pretty close to that but I'm guessing is just a bit under that. If the OP gets a converter that can make use of that torque off the line, it'll haul ass.
 
#27 ·
40 hp is worth 1 second?

---------- Post added at 08:33 AM ---------- Previous post was at 08:32 AM ----------

If my converter wasn't a nitrous converter, I'd bet it'd go a 10.7, and I'm running a 3.73 because it ran out of gear with 4.10s on the bottle.

---------- Post added at 08:34 AM ---------- Previous post was at 08:33 AM ----------

But if you think 384 is a accurate number, you're crazy ;)


Herein lies the issue with this whole discussion. Chassis dyno numbers don't matter with a converter.
 
#28 ·
Froush said:
My god. Please put the keyboard down and go to a track to get real life data. Op......you have a high 11 second car as it sits
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Dude, just look at the guy's 60 ft times. He's running 1.8x-1.9x 60s. That's what I was running on street tires in a wrong wheel drive turd with a much lower power/weight ratio. His trap speed is 117 mph, probably blowing through the converter, which is good for mid to low 11s if he can get the car to 60ft down in the 1.4x-1.5x range like it should.

As it sits... it's probably tapped out in the low 12s. It needs a properly matched converter and valve body with the nitrous spraying off the line if it's going to improve.

As for going to the track, what were you doing this past weekend? I was HoH with this car (co-worker's car) getting the bugs worked out on the new AED carb.

Image


434ci SBC, 13.8:1 compression, ported Brodix heads, solid roller cam with 276/282 @ .050" and .720/.725" lift, recently switched to E85 to make it more consistent and getting the kinks worked out. Has a TH400 with a pro-torque 5500 stall. Race weight is 2,210 lbs (per the scales at HoH) with him in it and a full 5 gallon fuel cell. Tube chassis car with lexan windows and fiberglass front end, hood, fenders, doors, and trunk. It's stupid how light that thing is. We started the day Saturday running 5.44 @ 124 and after a few jet and plug changes, managed to get a 5.28 @ 128. (1/8th mile bracket car) It has much more in it. The best pass on Sunoco 112 was 5.22 @ 130 mph. 60ft was consistent in the 1.16-1.18 range.

We'll be out with it tonight when the Outlaws come out to HoH. See you at the track!

---------- Post added at 10:44 AM ---------- Previous post was at 10:33 AM ----------

69fastback said:
40 hp is worth 1 second?

---------- Post added at 08:33 AM ---------- Previous post was at 08:32 AM ----------

If my converter wasn't a nitrous converter, I'd bet it'd go a 10.7, and I'm running a 3.73 because it ran out of gear with 4.10s on the bottle.

---------- Post added at 08:34 AM ---------- Previous post was at 08:33 AM ----------

But if you think 384 is a accurate number, you're crazy ;)


Herein lies the issue with this whole discussion. Chassis dyno numbers don't matter with a converter.
Click to expand...
Exactly. You can't use chassis dyno numbers with an auto because the dyno can't read the converter. The chassis dyno reads the torque put out at the rear wheels which after going through all the gears ends up being well into the thousands. It then does an algorithm comparing wheel/roller speed with engine rpm to determine the overall gear ratio between the engine and the rollers so it can reverse calculate the torque figure to an estimated torque output at the engine minus drivetrain losses. With a torque converter that raises the engine rpm (slip), the dyno can't see the difference between the converter slipping and a steeper gear. Therefore, the converter output ends up being ignored or cancelled out in the dyno's algorithm. So all the dyno shows is drivetrain loss plus efficiency loss at the converter. It's not seeing the torque being multiplied by the converter.

When I did my calculations, used the dyno curve to estimate a more realistic torque output from the converter with an ideal converter build. The average torque difference ends up being roughly 15% higher across the run.

If you've wondered why an auto puts down less power on the dyno compared to a manual but walks away from the manual at the track, this is why. This is also why I asked if the OP's converter was locked out on the dyno as that would take the converter slip out of the equation.
 
#30 ·
He said it's locking in 3rd. So yes chassis dyno will be fairly accurate. Dyno numbers are just that....numbers. But a pretty much stock 2v with a shot of nitrous is not running 10s. The point is that simple. 69fastbacks car is not setup the same. It's actually properly setup. Op has a long way to go. You're giving him the false pretense that his car will magically make more power than what it is and that he will be running 10s......which will never happen how it's sitting or even well setup

---------- Post added at 12:15 PM ---------- Previous post was at 12:10 PM ----------

69fastback said:
40 hp is worth 1 second?

---------- Post added at 08:33 AM ---------- Previous post was at 08:32 AM ----------

If my converter wasn't a nitrous converter, I'd bet it'd go a 10.7, and I'm running a 3.73 because it ran out of gear with 4.10s on the bottle.

---------- Post added at 08:34 AM ---------- Previous post was at 08:33 AM ----------

But if you think 384 is a accurate number, you're crazy ;)


Herein lies the issue with this whole discussion. Chassis dyno numbers don't matter with a converter.
Click to expand...
You might have "made" 380 hp but you can't lock your converter....so yes....its more realistic. He already said it locks in 3rd at wot. I'm just trying to give the guy realistic expectations. I'm not here to fill his head with bullshit he hears on the "internet" from guys sitting behind a computer.
 
#31 ·
"You guys sitting behind a computer" lol

I'm willing to bet I have more passes under my belt than 98% of the people on this forum, which probably includes yourself. I haven't filled his head with anything. I gave a real world example, that actually happened.
 
#32 ·
You aren't talking newedge with a fox chassis though are you. How his car sits.....its a high 11 second car at best. You probably have had more passes than most people. I would estimate I've had a good 400 passes out of mine. Not the most but far from being a rookie. Even with a properly setup torque converter and a better valve body. I think he might onlu see 11.5 unless he does some weight reduction or adds power
 
#34 ·
Realistically I see his car going mid 11s in perfect conditions with a 60' in the 1.6's, spraying longer, and shifting a little higher.
 
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Discussion starter · #35 ·
Hey guys, appreciate all the input and help. Sorry for being out of the loop on this threat, I work detailing cars so we work until late in the evening to make sure the car can be picked up in the morning. Anyway I did find time to call Circle D and get the exact specs on my converter. It is an off the shelf piece, not custom build. It is their multi disc which is what I knew already. They said this converter is what they recommend for NA cars and cars like mine running a 100-125 shot of nitrous. Its a 245mm, and the guy told me is traditionally a tight converter. With the nitrous on the hit, it should stall around 3600, and NA is should stall somewhere around 3400 but he wasnt 100% sure. After talking with him I confirmed I am launching the car completely wrong. He said with this converter that I want to launch it off idle. Launching it by footbraking is locking it up since its a tight converter and there for killing my 60 fts (thats the way it was explained). So theres a piece to the 60ft puzzle. I will play with the shift point and nitrous timing as well which Im sure will help the car. And btw the car is 3300 at race weight. Im from PA and at the NMRA event at Maple Grove this May thats what the car weighed with me in it. I appreciate everyones input, I'm gonna PM a few of you guys to get some more info on the shift points.
 
Discussion starter · #36 ·
Also for the guys saying the car could use a better valve body, I did the jmod to my original valve body. So what is out there for an even better 4r70 valve body, the only one I know of is the PA auto full manual valve body
 
#38 ·
dc772 said:
Also for the guys saying the car could use a better valve body, I did the jmod to my original valve body. So what is out there for an even better 4r70 valve body, the only one I know of is the PA auto full manual valve body
Click to expand...
I have a BC Automotive valve body.
 
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#40 ·
dc772 said:
Also for the guys saying the car could use a better valve body, I did the jmod to my original valve body. So what is out there for an even better 4r70 valve body, the only one I know of is the PA auto full manual valve body
Click to expand...
Contact Dan Gilsdorf at Silverfox Performance. He can build you a valve body that will keep the converter from locking up unless you specifically tell it to, usually with a push button activation. The converter will remain unlocked until you put it in high gear and push the button to lock it out.

With the converter locking up, the car is probably falling on its face and just waiting for the finish line.
 
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