I have a buddy who has a really nice '56 Chevy. It runs 140 mph at the track which seems fast to me for a '56 Chevy, but the ET is slower than the charts say it should be. Car is a little less than 3000 lbs with driver, has ladder bars, big slicks, etc. I have one picture of the car leaving the line and the slicks have some wrinkle to them but it doesn't appear to be launching super hard. The nose lifts a small amount. The timeslips vary (which might be a clue) but typical numbers are 1.40 60 ft, 6.25 660 ft, 8.15 1000 ft and 9.75 or 9.80 for the quarter. MPH is in the 140 range.

Wallace says the car should run 9.50, Moroso says 9.60. Various calculators say the engine is making 600 to 650 hp to run those numbers in a 2950 lb car. The engine should be making more power than 650, It is a Dart 540 which the engine builder said made 850. The engine looks like it should make 850 hp, but I haven't had it on a dyno. But even if the engine is only make 650 hp it still should be quicker than 9.80 if it can run 140 mph.

So my guess is that there is more than one issue with the car. I'm thinking that it isn't making the power that it should and even with the power he does have it isn't running the times. Just not sure if it is a chassis problem or a transmission issue. The wrong torque converter could be costing a few tenths I suppose. The chassis builder says the car needs a four link which might be true but I'd think it could still get down the track faster even if the ladder bars weren't ideal.

Many people who don't test different converters will never go as fast as they could with the best converter for their combination.
Does this owner want to go faster and quicker?

Converter, converter, converter. I looked up a bunch of ladder bar cars that run in N/SS, 10.5" tire, foot brake. They average 139-140 mph running B/FX (9.50 index) should go around mid 1.3X 60ft, 6.05 in the 660
Doug

60’ is pretty soft for a car with big tires that goes 140mph.
Should be close to a tenth better...... low-1.30’s.
Plus, it’s a brick...... which should be negatively impacting the speed(so with better aero it would be even faster...... which would make the 60’ look even worse).

It’s an example of not having the “combo” right.

Converter/cam might be a mismatch....... by the looks of the headers, they probably weren’t used for the dyno test, so that’s an unknown variable.
Footbrake or transbrake?
Glide?

Since the speed is way down....... if the alleged dyno numbers are correct....... there could be some other issues in the car costing some power.

I have seen this type of situation play out before.
Car owner spends thousands on car upgrades(converter, fuel system, carb, etc) to no avail, then has motor dyno tested only to discover the car is going as fast as the hp it produces will go(motor doesn’t have what was expected).

I like to use 90% of the STP dyno power as a point of reference for how quick/fast the car “should” be able to run. Then add in any extra ET correction for tracks at higher elevations(over 1000’ or so).

So, working that backwards, 3000lbs, 140mph...... shows 630hp....... which is 90% of 700hp.

Frankly, with what’s available for BBC parts these days...... if one set out to build a “bracket race” 540....... it would be fairly hard to end up with only 700hp.

If nothing obvious in the car reveals itself, I’d put an engine dyno test pretty high on the troubleshooting list.

If the motor tested at 800hp, then the 90% number I’d be looking at is 720hp....... which “should” be going 146@3000lbs.

Sometimes the simple things can be revealing....... do a compression test and check the lash.

SO many things could be wrong.

BUT id start with the 60" seems light for that mph

Converter, and a car like this needs a data logger. Nothing will point you in the right direction like a data logger will. Racepak sportsman will more than pay for itself int eh info it will give you for getting the converter alone correct

They put the car on a chassis dyno a few weeks ago since they thought it was down on power. According to third hand info, the car made 850 hp on the chassis dyno. I've asked the owner if he can send me a copy of the dyno sheet since that doesn't add up. 850 on the chassis dyno would put the car up past 150 mph even if the converter and chassis weren't perfect. The 60 foot might be slow but with that much power on board the car could still get rolling past mid track.

This. How do you improve something if you can't objectively measure it.

I’m not saying this is the problem, just pointing out how sometimes it’s not anything you might expect.

This was several years ago(over 15).
A customer of mine builds a hot street/strip 496 BBC to put into his customers mid-80’s Monte Carlo.
Motor gets dynoed, makes what was expected(don’t remember the numbers.....650-ish?)

Car has some sort of converter and 4.10’s, 10X28” slicks.

They go to the track on a test and tube day, and there are hardly any cars there. They can make tons of passes.

The car is all over the place in the 11’s....... not super close to the 10’s.
My customer is asking about shift points, rpm thru the lights, etc...... not getting any useful data from the owner, who is unhappy that the car isn’t running 10’s.
My customer jumps in behind the wheel...... runs 3 10.8x’s in a row.
Tell the owner how to launch, where to shift, etc......... owner back behind the wheel....... a bunch more 11.xx’s.
I don’t think he ever got a 10 out of it that day.

Sometimes........ the problem is........ the driver.

Here’s another thought.......

Is the cowl hood the “correct” distance from the windshield?

Attach a piece of string to the inside of the scoop, long enough to easily come out beyond the edge of the scoop.
At the top end of the track, see it the string is sticking out of the scoop.
It shouldn’t be, but if the scoop is too far away from the windshield, the inside of the scoop can be a low pressure area, instead of a high pressure area.
If the string is being sucked out of the scoop, the scoop opening is a low pressure area.

Could be a fuel system issue , hood (as mentioned), converter, ignition,
Dyno helps but doesn’t simulate track conditions
Best money spent would be racepak sportsman . AF sensor, Fuel psi sensors . Etc
Data data data
Trips to the track could be 100.00 -400.00 with that type car . 5-6 wasted trips could pay for the data logger .
A good converter co will take that data and get it correct with less testing , less wear on the car, engine , tires , etc

That is something I hadn't thought of and could explain some of the things that don't add up such as the car making power on the chassis dyno but not running the number at the track. Most of the other systems in the car get fully exercised on the chassis dyno so fuel flow and exhaust and ignition and stuff like that should be good at the track if they are good on the chassis dyno. Airflow is a wild card.

That would not explain good mph. If the car makes the power on the chassis dyno that matches the actual mph, then the e.t. can only be explained by traction or poor converter choice.

The speed is way off for what the chassis dyno numbers were.


Hopefully Andy will get the dyno sheets to look at.

The hood scoop thing doesn’t explain the poor 60’ times though, as it wouldn’t be having any real affect at that point on the track.

An 850hp 540 in a big tire 3000lb car should be solidly in the 1.20’s for 60’ times.

Could be multiple issues with the car. Once I can confirm dyno numbers I'll know more where to look. Could be gearing, shift points, converter, or chassis causing the poor ET and the scoop costing MPH. The car once ran 143 mph at Yakima which is higher elevation. So I'm thinking there is a variable that we don't quite understand.

A lot of good ideas, and i bet more than a couple of things mentioned are at fault. A video of the launch might reveal poor shocks/ settings. Someone with a desktop drag strip program could compare differences due to the shoebox body. Other gremlins could be headers, collecter length, fuel system or carb, who knows what lurks undetected.

The first time I saw the car run it was going 10.20 at 142 mph. I was watching from the starting line and just wondering what the heck was going on. He adjusted the trans brake RPM and played with the shift points and now he runs fairly consistent 9.80 at 140+ but it still isn't fully optimized.

I tell people all the time....... the hard part about getting a car to put up a good number at the track....... is making everything on the car work together.
In many cases........ making enough power to reach the desired performance goal is the easy part.

Did he buy it or build it?

If he bought it, what was he told it would run?

Soft 60 foot. Car is relatively light. Good MPH
Sounds like
convertor might be knocking 60 foot out of it. Too tight?

Converter could be too tight, I don't really know how to figure that out given the info I have. He has the transbrake set at 5800 which seems like an okay number. Once I see the dyno sheets I'll have a better idea of where the torque curve is but 5800 seems like it should be in the fat part of the curve for a 540 engine. The car doesn't push thru the lights so the converter isn't super tight. I'm not sure where the stall speed is since the car doesn't have a driveshaft speed sensor. I think he shifts the car at 6600 rpm which seems a bit low for a 540 with good parts but once again, I haven't seen dyno sheets so I don't know where the power peak is. He did say the car went faster when he shifted at 6300 so maybe 6600 is a touch too high.