The Stovebolt Site Forums The Shop Area The HiPo Shop 261 Dyno run

Hi All,
1941 Chevy 2 door sedan.
Recently built 1961, 261 .30 over, "RV2" cam, dual Weber 32/34 (Langdon setup) on Fenton intake, Fenton headers to 2" dual exhaust (through "Smithys", love the sound). T5, Nova rear end (2:73).

The engine really runs well. It's a dog out of the hole but I don't have high expectations for an inline 6 with a 2:73 rear end. I'm doing the dyno thing just to make sure I did everything well, and there isn't anything major I missed.

Took it to a local guy I know who has a repair shop and tuning shop. He does a lot of tuning work both fuel injection/computer and carb/no computer.

First run was miserable, so the first thing he checked was my throttle cable. Sure enough, with the pedal floored, it wasn't even opening the secondaries. Sheshh.... so much for trying so set that up by myself.

Second run we opened the secondaries (by hand...) and the numbers got better. At the rear wheels, 135hp @ 4000 rpm. The HP was still climbing be he wanted to stop at 4000. Torque peaked at 195 @ 2700 rpm.

At that point he wanted to stop. Looking at the AFR (air/fuel ratio i'm guessing), my numbers are higher than he wants.

We did a pull up a simulated 5% grade, 40 mph ~2500 rpm, and the AFR was 15.1. He wants that 13.5 - 14.

WOT he wants 12.5-13 AFR and the lowest we got was 13.9.

So time to do some research on jet's. I'm going to start with Tom Langdon.

Comments welcome.
Joe

I'm running Tom's H-Ws 32-36 carbs on my 261, had to change to larger jets to fix the stumble off the line. That cured the problem. Best of luck

This the carb your using?

32 Carb

Im going to pay close attention to this thread. Im just getting ready to pull my engine and take the opportunity to install a A/F sensor. I have always had a slight feeling the mixture is a bit off. When i called tom about new jets he tore into me quite aggressively stating that the carbs never need to have the jetting changed no matter where you live.

Yes, 2 of them.

Can you give me additional info on this? Where did you get the jets? What size? And anything else you think would help me.
Thanks.

i thought the 32 carbs from tome were 32/32 and not the 32/34 ones. I have a bad set at home, im going to have to measure later.

They may be 32/32, i'm not really sure. I'll check.

Gearing would make an unbelievable change in your set up. Depending on which T5 you have a 4.11 rear would give you from 3.23 to 2.75 for a final drive. A 261 can easily handle the cruising rpm of 3.23's or the torque needed to pull 2.75's. A ring and pinion set up is cheap and you can now buy a thick ring gear to keep your present carrier assembly. You will wonder why you didn't do this first.

The Nova rear end is all I had at the time. I've since located a 3.73 rear end and will be putting that in. The T5 I currently have has a .86 OD.
Joe

Just a brief update. Tom did reply to me, is very interested and had some suggestions of changing the air corrector jet. I'm in the process of ordering some and have some experimentation planed. Seeing how this is just a hobby, it may be a while before I can post some results.

Just some random info/thoughts....
The "jet" is actually three pieces, fuel jet on the bottom, emulsion tube in the middle, air jet on the top. The air jet has the threads (M8 1.0) to screw into the carb.
On these carbs (32 dft) the (air jet) threads are intentionally damaged at the factory, so caution must be used when screwing them out (lots of downward pressure). Once out, run through M8 1.0 die.
The air jet number is 77501.xxx (xxx=size).
Joe

Some things never change- - - -I can remember Dad changing air corrector jets on a BIG Zenith 2-barrel he used on an alcohol-fueled Ford flathead back in the early 1950's to adjust for track conditions and humidity. The carb was originally for a big Mack truck 6 cylinder, but it would flow more volume than the 3 Stromberg 97's his competitors were running. The corrector jet works in reverse to fuel jets- - - -bigger diameter is leaner.

He was race-tuning with a chassis dyno one of his sponsors, a trucking company, had in their shop.
Jerry

Joes41,

Tom at one time sold Holly Webber 32/36 carbs and the Carter Webber carbs. The Carters are smaller CFM and work best on a dual set up for our 235/261ci engines. Do yourself a favor and search on this web site Jetting the 32/36 carbs. There is specific jetting recommendations there. There are many jet suppliers. Not for nothing and as smart as Tom is, the carbs do need to be jetted if you want them to work best for your altitude.

52pu