The Stovebolt Site Forums The Shop Area Engine Shop anybody running this setup

While on the dyno topic , how does that work . I take it that HP. is measured at the drive wheels but in which gear , would it be done in a high gear of an overdrive set up or in direct gear ??

John

"Horsepower is to brag about- - - - -torque wins races!" That old adage has been around as long as I can remember, and I started watching my father's dirt track cars at about age 4 in the early 1950's. He tuned his cars on a chassis dyno owned by one of his sponsors, a local trucking company. All dynos work the same way, they load the engine down until it can't accelerate at full throttle at a specific RPM, and the torque it's developing at that speed is measured. Then a math formula is used to calculate horsepower. The speed is varied up and down, and the torque output is recorded. Then a RPM/torque graph is plotted and the HP is calculated for any specific point on the graph. There will be a high point of the graph for both HP and torque. Exceeding either point results in a reduction of output. The HP curve peaks at a noticeably higher RPM than the torque curve on most engines. I prefer to use a dyno that bolts directly to the back of the engine, rather than one that measures wheel HP. My dyno is a "water brake" type that bolts to the bellhousing and resembles a torque converter. It is filled with water to provide the load on the engine, and depending on the torque capability of the engine, sometimes a large volume of water is needed to avoid boiling the water in the load cell. So far, the highest output engine I've had on it was a MOPAR 440 pull truck engine which produced 714 HP at 6500 RPM, on one Quadrajet carburetor and gasoline. Obviously, it was highly modified!

Roller-type dynos that measure HP at the wheels are good for evaluating tuning modifications like carburetor jetting and ignition timing adjustments, but similar measurements can be done with a stopwatch and a long hill as long as the atmospheric conditions don't change dramatically. It's possible to get widely varying dyno numbers with a simple change of temperature and/or relative humidity. Our dyno runs in the race shop were always corrected for those factors to get an actual HP reading.

Confused yet?
LOL!
Jerry

A frequently used estimate of driveline loss to reconcile engine dyno power with rear wheel power is 15%. This will vary depending on the differential type (Ford 9" is worse), transmission fluid, converter slippage, driveshaft angle, etc.
This number approximates your output @ 152 hp at the flywheel.

panel fan: I have a 3 on the tree and he was in 3rd

double doot: if https://www.enginefacts.com/chevrolet235/ is accurate, the 235 made 135 hp and 217 torque. But I have the 261, which enginefacts.com doesn't list the specs for. Regardless, if @panic's estimate of 152 hp is also accurate, the math still doesn't add up to a 70% increase as advertised. I was in the same boat you are in a few years back when I cracked my 235 & decided to upgrade to 261 & aftermarket package with Clifford; doesn't look like the extra money I spent paid off unfortunately

Don't know, exactly, but all the data I have matches that. In 1961 GM stated the 235 produced 135 hp at 4000 rpm (except for the economy version) and the 261 produced 150 hp at 4000 rpm. The 235 had a compression ratio of 8.25 to 1 and the 261 had 8 to 1. As for torque, I've never been able to find a GM published number or curve for the 261, but I do have a GM produced hp/torque curve for the 235 dated 1958 (attached). I suspect Tom Langdon knows this or could find it.

This may be the same as your image above:

1954 Truck 235 & 261 engine specs (HP & torque): pages 143-147

1960 Truck 235 & 261 engine specs - pages 6-9 in Engine & Clutch section

1962 Truck 235 & 261 engine specs

Thanks! Very interesting...as we know the 261 has a bit more torque than the 235 but compare the gross torque lines. The high torque 235 hits peak torque faster and maintains that level longer through the rpm range. Of course that 261 has a slightly lower compression ratio. I've never been certain where the extra .25 came from on the 235. Probably Jerry knows.

'56 and later 235s came with a 848 head. The 261 did not. I am guessing the combustion chambers are larger in the 261 head, thus lowering the compression ratio. These engines were designed for big trucks which were run at max RPM frequently. A compression ratio higher than 8.0 to 1 is probably not conducive to engine longevity under those extreme conditions with that engine.
My 2 cents, refundable upon request. Just submit a bank account number for deposit purposes. Please also include full name, date of birth, and the last 9 digits of your SSN.
Carl

I'm about to try to squeeze 260+ cubic inches into a 216 head- - - -haven't checked the CC's on that head yet, but the rotating assembly is going to have a 235 crankshaft with 7/16" extra stroke, and a 235 bore. Can't wait to see what the torque numbers on that engine will be!
Jerry

Thanks Jon G and tclederman, along the same lines as what I was finding

In May of 1955 Hot Rod Magazine did an article on Frank McGurk's dyno tests on a Chev 261 I-6. It appears that factory ratings are a bit optimistic, something I've long wondered about as they are signed off by the engineer in charge. They probably do battle with the marketing dept. regularly. Also Mc Gurk's dyno could have read low. I don't believe it was certified. But I think the relative increases are meaningful.

Anyway the max HP on the stock engine on McGurk's dyno was 114 at 3500 RPM and torque was 199@2500.

Changing to the Corvette dual exhaust manifold netted a 6% increase in HP at the same RPM and 3% on torque.

Test 3 added 2 Stromberg 1bbl carbs on McGruk's manifold for a 16% increase in HP and 18% over stock @ 4000 RPM and 10% more torque, again at 2500RPM.

Test 4 added porting and polishing the head and bumping the compression ration to 7.85:1 This netted a bump in HP of 9% and torque of 4%. So now we're up to 29% HP over stock @4000 and and 15% torque still at 2500RPM.

Test 5 added a reground camshaft. I should note that various reports are that the stock 261 cam is the same part no. as the Corvette cam, considerably hotter than the 235 powerglide cam. The test cam was a "3/4" grind with 245 deg. intake and 274 deg. exh duration with .421 and .410 respectively. They don't say at what lift these measurements were taken. The result was a 6.1 increase in HP and 2.6 torque. Relative to stock performance we now see 36% and 18% respectively.

Further increases were with the aid of a boring bar going 1/8" over stock and hotter cams not really suitable for the street. So fro this you can see that power improvements come incrementally and without a boring bar the best one can hope for is about what test 5 shows. I was surprised to see that the most effective way to increase torque is by increasing the compression ratio.

On my 235 engine I have made all the mods except porting and polishing and boring. The cam is slightly hotter than McGurks and advanced from split-timing by 5 degrees, as much as I dared because of possible valve-piston interference. The head is an 848 milled 0.010." The engine has been in service for 15 years in its current configuration and about 100,000 miles. From driving it, I would judge it's torque peak to be 2800-2900 RPM. The fire pretty much goes out below about 2400-2500RPM but it will pull smoothly down to about 1200RPM. It is a bit peaky but with a 12-speed gearbox (4x3) I can easily keep it on the boil.

A few years ago, Tom Langdon, before he retired from GM, was kind enough to provide me some combustion chamber cc's based on casting numbers:

3836848 79.1 cc

3835913 86.2 cc

3836850 86.2 cc

3703570 95.5 cc

So far I have not been able to sort out what changed, if anything, to get the later 235 motors to 8.25 CR.