M37 Meets Chassis Dyno, What's your guess?

[Jess]

RMS mentioned the interest in the 4 blade fan because our M37s are equipped with a 6 blade fan to improve cooling for the 251. The radiator is the same for both the 230 and 251. I'm sure he will jump in here and expand on this difference and his interest in what the reduced drag would do for dyno results.

Jess

[ashyers]

Dana,
I used a combination of a post I found on this site by Charles Talbert and a manual I dug up online for the Carter carb/governor assembly. While we were testing the truck I thought I'd test the governor as we had the optical tach hooked up. It was not working properly so I started fiddling with the adjustments until I achieved what both Charles and the manual suggested, only I set it at 3000 RPM. The response of the engine was improved. By adjusting the system the throttle is no longer lazy. If you put your foot in it now it responds well, still no power, but in the lower gears it's quite noticeable. I'll try and find a link to the manual and the post.

Edit, Here's one of the posts:
http://www.g741.org/PHPBB/viewtopic.php ... nor#p54198
and the other:
http://www.powerwagonadvertiser.com/for ... hp?t=10947

Jess,
I'd be interested in hearing some of RMS's comments and suggestions. It looks like he's got the flathead bug.

Andy

[DCook]

Thanks, and good to know the Governor, when set correctly, actually improves responsiveness. I just got my engine set back into the truck yesterday, and over the next couple of weekends, hope to get it fired up. At that point I'll begin my "TWEEKING" process!
DCook

[RMS]

being a canuck with canuck trucks I was not aware that the 4 blade was standard on the 230. All my 251s came with the 6 blade fan (that pulls so much air that it will untuck a T shirt and lift skirts if one stands too close to the grill ). I swapped on a 5 blade Plymouth fan and the change was noticeable, not as noticeable as bumping up the exhaust diameter to 2.25in or port matching the intake as there was a lot of shrouding at the block. I also radiused the intake were the runners meet in the center as it was a sharp 90 off the carb.

its also interesting to note that the 230 carter has smaller jets, butterfly and venturi compared to the 251 carter b&b

Andy what kind of compression are you running? my decked car head gives me something like 7.5 ~ 8.0 to 1

also with the rod ratio of the flattys being so high (251=1.75) the piston dwell at tdc is massive and too much advance will cause the motor to fight its self . I would try again between 2 and 6 btdc. I run @ 4btdc and pull 22inches of vacuum @ idle

[ashyers]

RMS,
I thought the 4 blade could move a ton of air, I can only imagine what the 6 blade fan can do!

As far as compression, I'm going to guess the head's not been milled, so 6.7:1. Do you happen to know the stock thickness from one of the head bolt hole's shoulder to the sealing surface? I could check that pretty easily with a caliper and see if it's been cut previously. I have 120psi compression pressure at cranking speed. I have not checked the leak down, but as I understand it 120psi is OK for one of these things. As far as timing I reset it to 4 BTDC since there was no apparent advantage to advancing it at this point. I'd like to play with that some more when time allows.

I've been busy with final exams and grades on my end, so we pulled the truck of the dyno last Friday. The students are gone on Thursday and I may have some time to tinker next week so we'll see if I have a chance to play some more. At the moment I'm thinking of picking up a T245 locally to build for next year. We'll see. I need some more torque to pull the hills locally. Speed is not an issue, this thing goes as fast as I'm comfortable with!

Andy

[ashyers]

Here's the data from 3 of our dyno runs a few weeks back. There are a few changes I'd like to make, but I have not had the chance to get back to this.

https://www.dropbox.com/s/f1d33nmeygzdl ... pdf?oref=e

Andy

[ashyers]

We have another data point, sort of!

Ran a friends M37 that we've been working on across the rollers today. I'm not totally happy with the test, but we saw 40hp. I feel better about the 47hp my truck made . The weird thing is that the power curve is much different, not sure what's up there. We'll do more testing tomorrow and try and get some good data.

[RMS]

wish I could beam my truck down to you so it can run on the rollers for some numbers.
it would be interesting to see how the slightly modded 251 and 4.89s pulled.

wish I had a spare known working carb to sent you but they are all on trucks
I have one that needs a rebuild but it would be at least $20 each way for shipping as I need it back for the next truck.

could you do a run with a civilian ignition ? it would be interesting to see if any gains are made with modern wires.

[ashyers]

My truck has 4:89's and a military ignition, Steve's has 5:83's and a civilian ignition.

Total timing of both trucks is 26deg. The civilian and military curves are not radically different. I'll post the civilian dizzy P/N.

We'll see how things go tomorrow and I'll try and post some power curves.

My gut feel on wires is that if they're working (no miss) they're fine. The military stuff is solid core so it's tough to kill, the civilian on Steve's is typical resistor core, likely carbon, kind of wimpy.

[isaac_alaska]

Is the torque curve measuring wheel torque or have you put gear ratio into the computer to display crank torque? I guess then the questions are what gear and what tire size.

[ashyers]

Isaac,
The dyno measures wheel torque. We take readings in 4th gear so we're 1:1 through the transmission.

This truck just never ceases to generate surprises! We did quite a few partial pulls on the truck. Initially we had 40hp with a wacky looking power curve. It peaked very early and then fell on it's head. We made some timing adjustments and it improved a bit, but still peaked too early. For grins I had the kids swap in some new plugs and picked up some power, but still was not completely happy.

I did recall the owner saying he had "adjusted" the governor. We had reset it to maintain 3200rpm, but had not taken it apart to do so. SOOOO, apart came the governor to verify the spring settings where not totally out of whack. It seems they were. Essentially it's possible to obtain the correct governed speed and have what amounts to a closing throttle at high RPM in spite of significant engine load. After some fun of putting things back together while they were still on the truck we got the rollers spinning again. Things began to look normal, until... When run at full load for 10s the truck would begin to surge, much like an unstable governor... Ahhhh! After a twist of the screws made no change I noticed something on the screen, the surge was accompanied by a big fat lean spike, then rich spike, then lean spike, and repeat.

Well, time to check the fuel system... Carb and fuel pump had been replaced with a rebuilt units prior to arrival in our shop, filter was new. Called the owner to see if an "in tank" filter was installed. He has no idea. Check fuel pressure at carb inlet at WOT during the surge. It's fine. Dive into "new" carburetor which the owner paid $$ for. SURPRISE, float level, they should set that right?!?! It's nearly 3/16 too low!!!! Seems the truck would take about 10s to empty the bowl at WOT because the float would not drop far enough to get the needle far enough off the seat. The volume of fuel entering the bowl couldn't keep up with the engine's demands causing a lean surge under sustained WOT. Once the float was set correctly we had a good running truck, almost!

The rebuilt carb used a big thick gasket for the top cover, not the thinner gaskets used originally, which is what I had for spares. This big thick gasket sealed great, even when the top cover and bowl surface was less than flat (this was a rebuilt carb...). The carb did not like the 1/32" gaskets and leaked at the passage connecting the idle air bleed to idle circuit leading to a super lean AFR at idle. After more tires than I care to count the cover was finally sealed up and the truck runs like a top. We even saw a whopping 52hp! A new M37 record on our dyno .

Lessons learned, don't trust owner's memories, don't trust "rebuilt" parts, don't trust any prior work! Many of the issues with this truck have been related to lame parts and poor wrenching. It annoys me that the owner of the truck had paid for much of the prior work that we ended up fixing. The good news is the truck provided a great learning tool and we will provide the owner with a much better truck.

I'd also suggest setting the float "wet", especially if using funky ethanol enriched gas.

[w30bob]

Andy,

You're highlighting a continuing problem in the auto enthusiast market that certainly won't get better with time. First, owner's memories.........I can't remember what I had for breakfast yesterday, never mind what shortcuts I took in rebuilding something mechanical four years ago........plus most auto owners these days really aren't mechanically inclined, despite what they think. Now rebuilt parts.........as time marches on the folks who really know all the tricks of the trade when it comes to rebuilding mechanical components are just plain dying off. And as demand for these parts declines the knowledge base required to rebuild them properly will disappear. Do you know anybody who can rebuild that steam boiler for your Stanley Steamer? For those who aren't old enough to even know what a Stanley Steamer is/was......I rest my case.

Bottom line here is as you state............people's memories and "rebuilt" parts can't be trusted. That's not a knock on those currently in the rebuilding business........it's reality. Now if I could just remember what I wanted to do today..................



regards,
bob