claf

Has anyone here ever run a stock L76 '62/'63 SHP 340 HP car on the dyno ? I know the way the HP is measured changed back in the mid 70's and the 340 number may be somewhat overstated. Bob

69ttop502

I have not put one on a chassis dyno, but I do own a 62 340 horse car. My guess would be the car puts down no more that 200 hp to the tires. Would love to see what others say if they have run one on a dyno. I did see with my own eyes a 67 freshly rebuilt 435 horse car put 285 hp to the tires.

Bill

Vette5.5

HP ratings back then were something else with very little regulation. Usually a tweaked/blue printed engine driving no accessories on a flywheel dyno with open headers. After 72’, the government stepped in, and flywheel HP as actually installed in the car from a production line motor. Ratings dropped close to 25% then. Driveline loss was another issue, as an extreme rarity seeing 325 rwhp on anything coming from the factory. For comparison, C6 LS7 cars are 460 rwhp and 3100 curb weight, so best staying away from these.

UberLegend

^^This makes me nervous^^

Good question posed in this thread.

Subfixer

A few points of reference.
Last year, my 64 L76 put out a best 195 RWHP.

This past spring I built a 400 cu small block.

Engine Dyno with headers and no tuning:
461hp @ 5900 / 440 ft/lbs @ 5000

Engine Dyno with 2 1/2" rams horn exhaust (hogged out) and sidepipes (2 1/2" ID Sweet Thunder):
381hp @ 6100 / 407 ft/lbs @ 3300 (best result).

Chassis Dyno; 64, Muncie 4 spd, 3.36 rear:
287 rwhp @ 5355 / 316 ft/lbs @ 3284.

6T5RUSH

claf,

Can't answer your gut question of a "stock" L76's RWH.

Mine is NOT a pure L76 configured 327. Basically a generic 327 bored .060 over and using the '70 LT1 intake, cam and lifters with "breathed on" '461 heads using the stock 2818 List 585 cfm carb and 2 1/2" stock ramshorn manifolds. Taking advantage of the more breathable heads the 2 chassis dyno runs attached reflect side pipes AND a complete undercar system that's open as well (Doug's electric cutouts).

Obviously, throwing some money at a 327, you CAN make these mouse motors humm.

She dyno'd on the 2nd run 296 RWH and 307 ft. lbs. of torque. Instructed the tech to take her to 6500 r's in 4th gear...tech had to get out of her at 5300/5400 rpms (was running lean). So, I think with an air/fuel ratio adjustment, there probably was another 7-10 horses there.

Enjoy!

http://s1083.photobucket.com/albums/...96-2NDPASS.mp4

Jim
In God We Trust!

JohnZ

The government had nothing to do with it. GM made the decision to abide by the "SAE Net" method (engine as-installed, with production carburetor and distributor calibrations and exhaust) instead of the previous "SAE Gross" rating method.

MiguelsC2

I bet it had sidepipes.

A 427-435 is actually an understated factory number.

69ttop502

Actually the car had undercar exhaust but was bone stock. I read of one other test in a magazine where a 67 435 made around the same number to the wheels on a Dynojet. Based on the times these cars ran in stock form back in the day, I think these wheel figures are a pretty accurate number. Now with headers and tuning I would agree it wouldn't be hard to get more. Bill

65tripleblack

As another reference, a .030 over 327 (331 cu in) with headers through VettePacks sidepipe mufflers.
This engine runs a 750 double pumper carb through a ported Z28 intake. It has ported 461 cast iron heads and a solid 246/254, 106/110/114, 0.385/0.389 cam, stock pistons and crank, 11.2:1 SCR.

This engine made 348.4 RWHP.
With the headers open it made 353.7 RWHP.

These runs were done on a 85 degree day. I was still using the stock 202 coil with ballast resistor at the time.

sub006

Back when factory horsepower ratings were beyond gross, and verging on wildly optimistic, I recall a good running '64 GTO (rated 348 horsepower at the clutch, no accessories connected) pulling a big 130 hp at the rear wheels on a chassis dyno.

Rule of thumb I hear from some tuners is to double the rwhp and torque to estimate engine numbers for rough comparisons.

Donny Brass

you are only supposed to lose 20% in the driveline, so if you are losing 50%, check the e-brake.

my 327/350 made 357 on an engine dyno and 295 at the wheels for a loss 17.4%

we dynoed with the alternator, water and fuel pump attached

0Ian@Keen Parts

Dyno numbers are just that, numbers. And every one will be different. It's a tuning tool at best, as with a few clicks of the mouse, the car that just laid down 400 horsepower, can turn into a 300 horsepower car, and vice versa.


Just some food for thought. Calling a chassis dyno "real power" is stretching it for that reason IMO.

6T5RUSH

Ian@Keen Parts,

I agree with you about the dyno runs being a tuning tool (good example of this is the identified lean condition in my 2 runs). But, the chassis dyno numbers DO reflect very close to the "real power" calculated horsepower numbers considering speed, weight and elapsed time at the drag strip.



Jim
In God We Trust!

0Ian@Keen Parts

Now THOSE are real numbers. Numbers that are pretty hard to fake.

I'm not saying dyno numbers aren't "real." I'm simply saying, every dyno is going to be different. I've seen numbers as far off as 25HP on the same car, on two of the same brand of dyno, just operated by two different shops. Correction factors are key. but who was right? I've seen this point argued til everyone is blue in the face. It's a tuning tool/bragging machine. Real world numbers come from an engine dyno or a racetrack!

DansYellow66

I think most engine HP ratings back in the 60s were pretty honest as long as it's understood the engines were essentially stripped and w/o accessories, carefully tuned, etc. About 10 years ago a magazine had a long running series of building up stock compression, cam, and carb HP engines from 1970 and earlier and testing them on an engine dyno. They all turned HP numbers that were virtually identical to the factory rating. Some of them they had to do a little tuning with the timing and jetting but that was about it. Certain engines were deliberately under-rated for insurance, corporate policy or racing class purposes - but most of them are pretty well know - L71 & L72 427, Z-28, 428 Cobra Jet, L-88, Mopar 340, Buick 455 Stage 1, etc. I suspect that at one time, buried deep in GMs engineering vault, there were some dyno reports on the 340HP/327 showing right at 340 peak HP on a stripped down engine.

redred65cpe

^^^^ There was a Horsepower TV episode that did something similar. They had a L-88, 426 Hemi, and big block Ford - can't remember which one, and I think a Pontiac motor. Maybe one other motor, too. I think the Hemi came out on top, then the Ford, followed by the L-88. All were over their advertised HP ratings as one would expect. I still have it on my Tivo, I'll check if I can remember.

larry

claf

Since I stated this thread, how about if we work backwards. Back in the day my STOCK 340 HP '62 with a close ratio 4 sp and a posi 3:70 rear would consistently run the quarter at 98/99 mph and 15.1/15.2 on street bias-ply tires. What do you think was the power output ? Bob

Plastic Pig

You can manipulate engine dynos too. Track results always separate the wheat from the chaff.

6T5RUSH

OK claf,

Back on point and here's a website that gives you a number of choices, in your case, calculated HP based on trap speed and time.

Just for ***ts and giggles I plugged in your 15.1 trap time, 99 mph and guestimated with you aboard a total weight of 3,200 lbs. It calculated a RWH of 242.

Kind of a neat tool.

Enjoy!

http://www.hotrodpitstop.com/tools.html#0



Jim
In God We Trust!