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Re: anybody running this setup
double doot #1373445 Sat Aug 15 2020 02:24 PM
Joined: Oct 2015
Posts: 246
P
Shop Shark
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


good planning is no substitute for dumb luck
Re: anybody running this setup
double doot #1373447 Sat Aug 15 2020 02:49 PM
Joined: Feb 2004
Posts: 21,019
H
Boltergeist
"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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: anybody running this setup
double doot #1373450 Sat Aug 15 2020 03:29 PM
Joined: Dec 2008
Posts: 1,481
P
Shop Shark
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.

Re: anybody running this setup
panel fan #1373454 Sat Aug 15 2020 04:05 PM
Joined: May 2014
Posts: 9
H
New Guy
panel fan: I have a 3 on the tree and he was in 3rd

Re: anybody running this setup
double doot #1373461 Sat Aug 15 2020 04:25 PM
Joined: May 2014
Posts: 9
H
New Guy
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 frown

Re: anybody running this setup
double doot #1373470 Sat Aug 15 2020 05:24 PM
Joined: Mar 2014
Posts: 1,656
J
Shop Shark
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.

Attached Files
235 torque and horsepower curve.jpg (141.15 KB, 110 downloads)

Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: anybody running this setup
double doot #1373477 Sat Aug 15 2020 05:55 PM
Joined: Sep 2001
Posts: 30,450
ace skiver


Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engines are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: anybody running this setup
double doot #1373488 Sat Aug 15 2020 06:57 PM
Joined: Mar 2014
Posts: 1,656
J
Shop Shark
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.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: anybody running this setup
Jon G #1373494 Sat Aug 15 2020 07:28 PM
Joined: Mar 2010
Posts: 9,443
5
Master Gabster
Originally Posted by Jon G
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

Re: anybody running this setup
double doot #1373538 Sat Aug 15 2020 11:26 PM
Joined: Feb 2004
Posts: 21,019
H
Boltergeist
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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