Low Torque from 440BB and troubleshooting/solutions

[1971 Challenger]

Hi Folks,
I need some help to make decisions on how to raise my torque. I'm not a gearhead so bear with me please. I have a 71 Challenger I bought a year ago. Unfortunately, I don't know everything about car's build. It's a 440BB (allegedly rebuilt - when is ?), Torqueflite 727 - 3 speed auto, Edlebrock performer high intake, headers, a big cam. I replaced the Holley no choke race carburetor with a Sniper 2 EFI, but the latter's not relevant to the original issue. I have 3.23 gears and I believe a stock torque converter. When I floor it, I just don't feel the torque. Factory specs on the engine as y'all probably know is ~385hp and 500 ft-lbs Torque, notwithstanding the mods. I've had cars from 500-650 ft-lbs of torque so I know what it should feel like. I understand the cam will increase HP but lower torque. I also understand my tall gears are optimal for speed and the highway. In the process, with my drop-out transmission, I considered upgrading to a 4th gear for better cruising performance.

As far as my goal, I'm not going to be drag racing the car. Overall, it drives fine but has no punch. I'm just looking for a better launch when I need it (), kind of middle of the road. So I originally looked into the 40L60E with a 3.73 gear change and besides being a sacrilege to put it in a MOPAR, it's evidently not reliable either. The A518 I saw on these boards had specs of only 400 ft-lbs (?). These boards also referenced 'gear vendors' which looks like a great overdrive solution but can still keep the stock 3-speed performance.

So how do I start with troubleshooting my issue in a methodical way?
1. Evaluate the engine to see if it's just tired and worn out? How please? It seems to drive and sound fine so I don't suspect this is the problem.
2. Start with a 2200-2400 stall converter?
3. Throw some moderately shorter gears aka 3.55 or 3.73?
4. Keep the present 3.23s and install gear vendor transmission add-on? They say it will improve the performance to some degree.

Any thoughts on how to tackle this improvement and suggest possible solutions would be greatly appreciated.

Thanks everyone, Chuck

 

[pschlosser]

I've driven several 440 cars over the years, and I can share a few thought about what I think I know.

Sometimes, engines can have all the right parts, and just don't produce the power you would expect. They may have a better intake, higher CFM carburetors, header exhaust, perhaps ported heads, maybe a long duration camshaft with lots of lift. It's all got to work together to be really great.

The stock 440-4 and 440-6 cars, 727 auto transmission, factory exhaust, sure grip differential and 4.10 gears perform pretty nicely. most are still 12 second cars, though. What I learned from 4.10 differentials is the stock 440 has lots of torque and horsepower above 4000 RPM.

With 3.23, they don't feel as torquey and they tend to smoke the tires. They have plenty of torque at and above 2000 RPM, but spin the tires unless you can get them to hook up. If you're goal is to go fast, like a superbird/daytona going 220 MPH, then 3.23 may be fine. But not if you want to be quick.

It may be easiest for you to try out some higher gear ratios before you get into engine tear downs and rebuilds. I would only go with a higher stall after you confirm the rest of the engine is running in top shape, and if you want to sacrifice some street drivability for better quarter mile times.

DO run a compression check on your engine, but unless it's burning oil, it is what it is, and should be producing decent power at that displacement level.

 

[6PKRTSE]

Without you knowing all of the specs of your engine it is just a guessing game for us. If the so called rebuild is just a gasket job and repaint on a later smog 440, your horsepower is way less than the 385 you think with only 7 or 8:1 compression. Sure, a 3000-3400ish converter and 4:10 gears would help.

 

[540HemiCuda]

BEFORE you do anything, you really need to identify the core problem. If the engine is the problem, transmission and gear changes would be band-aids at best and possibly more expensive than addressing an engine issue.

A few pulls on a chassis dyno would not be expensive and would tell you if the engine was putting out a satisfactory amount of power. From there, you can make the proper decisions.

.

 

[mopar jack]

I would check the initial timing. I have seen 440s with timing set to 2° that can't get out of their own way but when set between 10 and 16° will smoke the tires.

 

[Ricks72Chlgr440]

Give us the current idle timing and max timing shown on your timing light. Running a compression test is also a good idea. The 3.23 gears should be plenty for street/highway driving. Also, you might want to check the kickdown linkage to ensure the trans is shifting at the proper time. I install a Fairbanks shift kit into all the 727/904's that I've had. The shift improvement is wonderful and not harsh. I have my kickdown set such that at 25 or 30 and I floor it the trans will go down into first gear and really pull. If your trans shifts too quickly into 3rd the low speed performance will suffer.

 

[Challenger RTA]

Good info above. Before I throw gobs of money at it. I would diagnose where the enige is at. 1 As mentioned compression test. 2 leak down test. Then do a vacuum diagnoses. If in spec check distributor for vacuum and advance. Vacuum leak? Then proceed through all tune up secs. Does the sniper control spark. Check battery voltage. Low voltage low spark. Battery,alternator,coil and wiring.

 

[540HemiCuda]

The OP said it had a 'big cam', so at least some of those vacuum readings will not apply and confuses some of the rest. Also, a 'big cam' will like a lot more and earlier ignition lead than a milder one. Timing should be set for total, which for most big locks is often somewhere around 32* to 34* and should be 'all in' as soon as possible without spark knock in high gear. Usually, that is by 2,500 +/- with 3.23 gears. With lower ration gears, the engine will tolerate a faster curve. I have the timing 'all in' by 1,600 with my 3.91s. Our big blocks really respond to a fast curve unlike the small blocks.

Of course, if the compression is compromised, the combo is mismatched, or other mechanical problems are present, no amount of tuning will help.

Given the OP's inexperience and lack of hard information on the engine, getting the car into the hands of a seasoned muscle car mechanic may be the best, if not the only way forward. That is not meant to hurt feelings, it's just that it is very, very hard to diagnose engine issues over the internet. There are just so many possibilities in a situation such as this.

.

 

[1971 Challenger]

Understood. My thoughts exactly. Yes, I too considered a dyno pull to see my baseline. Thanks.

BEFORE you do anything, you really need to identify the core problem. If the engine is the problem, transmission and gear changes would be band-aids at best and possibly more expensive than addressing an engine issue.

A few pulls on a chassis dyno would not be expensive and would tell you if the engine was putting out a satisfactory amount of power. From there, you can make the proper decisions.

.

ks.

 

[1971 Challenger]

Agree on engine baseline and the compression/leak test but barring satisfactory results, I understand I could still be having underlying issues

The OP said it had a 'big cam', so at least some of those vacuum readings will not apply and confuses some of the rest. Also, a 'big cam' will like a lot more and earlier ignition lead than a milder one. Timing should be set for total, which for most big locks is often somewhere around 32* to 34* and should be 'all in' as soon as possible without spark knock in high gear. Usually, that is by 2,500 +/- with 3.23 gears. With lower ration gears, the engine will tolerate a faster curve. I have the timing 'all in' by 1,600 with my 3.91s. Our big blocks really respond to a fast curve unlike the small blocks.

Of course, if the compression is compromised, the combo is mismatched, or other mechanical problems are present, no amount of tuning will help.

Given the OP's inexperience and lack of hard information on the engine, getting the car into the hands of a seasoned muscle car mechanic may be the best, if not the only way forward. That is not meant to hurt feelings, it's just that it is very, very hard to diagnose engine issues over the internet. There are just so many possibilities in a situation such as this.

.

The OP said it had a 'big cam', so at least some of those vacuum readings will not apply and confuses some of the rest. Also, a 'big cam' will like a lot more and earlier ignition lead than a milder one. Timing should be set for total, which for most big locks is often somewhere around 32* to 34* and should be 'all in' as soon as possible without spark knock in high gear. Usually, that is by 2,500 +/- with 3.23 gears. With lower ration gears, the engine will tolerate a faster curve. I have the timing 'all in' by 1,600 with my 3.91s. Our big blocks really respond to a fast curve unlike the small blocks.

Of course, if the compression is compromised, the combo is mismatched, or other mechanical problems are present, no amount of tuning will help.

Given the OP's inexperience and lack of hard information on the engine, getting the car into the hands of a seasoned muscle car mechanic may be the best, if not the only way forward. That is not meant to hurt feelings, it's just that it is very, very hard to diagnose engine issues over the internet. There are just so many possibilities in a situation such as this.

.

on both the engine and possibly the transmission, albeit it shifts well?

With regards to vacuum, I failed to mention a much larger vacuum pump was installed along with two cannisters to compensate for the large cam so I don't suspect there any issue there but appreciate the feedback. No feelings hurt at all. That's why I'm here. Y'all are super helpful and knowledgeable.

 

[pschlosser]

With regards to vacuum, I failed to mention a much larger vacuum pump was installed along with two cannisters to compensate for the large cam so I don't suspect there any issue there but appreciate the feedback. No feelings hurt at all. That's why I'm here. Y'all are super helpful and knowledgeable.

Its time to post an image of that engine bay. let's see what you got.

 

[Chryco Psycho]

The basic problem is the converter is locked up before the cam is in the powerband you should be able to feel when the cam starts to really work , you need a converter in that rpm range , if the cam starts working at 2400 get a 2600 stall for example .
Gear vendor is a great addition for OD

 

[pschlosser]

A dyno plot of the horsepower and torque curves will show you where, and how much power it makes across the RPM range.

At the wheels, this is best done with the factory torque convertor (TQ) that locks earlier than later.

For improved quarter mile times, you may want to shoot for a TQ the locks after about 25-50% of the horsepower and torque.

Example, if the engine makes peak torque of 600 PF (pound-feet) FP at 4500 RPM, and makes (50%) 300 PF at 2700 RPM, then you want the TQ to lock near the 2700 RPM point.

I think OEM TQ is around 2000 RPM. That plot of power will show you how much should be delivered at 2000 RPM, and if its say.... 30% of peak torque, it's hard to say how much of an improvement a higher stall will do.

Tuning and other factors may be easier to resolve, at this earlier stage of exploration and discovery.

 

[Xcudame]

A "big cam" tells us really nothing other than the power band is shifted higher than stock. Everything has to work together, cylinder head flow, intake, carburetor, camshaft, distributer timing (mechanical and vacuum), compression ratio, torque converter and final axle ratio.

440s had one of the lowest stall convertors from the factory. So odds are if it's the stock torque converter, it's stalling too low for the "big cam". You need to find out what camshaft is in there. Everything else is just educated guesses.

Every time I get ready to build an engine, I spend probably 40 hours determining which parts to use. Then, once all the parts are purchased and I begin building, I spend additional hours checking everything from true compression ratio to bearing clearances and chasing threads.

Say you get a dyno run and it makes 300 horsepower at the rear wheels. What then? Check the stall speed per the factory service manual. And tell us what it is! And for safety, follow the shop manual!!

 

[540HemiCuda]

Agree on engine baseline and the compression/leak test but barring satisfactory results, I understand I could still be having underlying issues



on both the engine and possibly the transmission, albeit it shifts well?

With regards to vacuum, I failed to mention a much larger vacuum pump was installed along with two cannisters to compensate for the large cam so I don't suspect there any issue there but appreciate the feedback. No feelings hurt at all. That's why I'm here. Y'all are super helpful and knowledgeable.

The vacuum pump and canister have nothing to so with the engine's operation. They are for accessories like power brakes.

This is why the internet is not the place to diagnose these kind of issues.

.

 

[Katfish]

FSM is interesting, but I don't understand how the stall test is actually performed?

 

[540HemiCuda]

Stall and flash are two different things and are measured differently.

And neither are an issue with a street driven 440. The converter could not be too tight for a properly operating 440.

.

 

[Xcudame]

Had a friend with a 64 Fury convertible with a 318 automatic that would accelerate like you would think. Performed the factory "flash" test and determined the torque converter was going. Put a new torque converter in and it drove like a scalded monkey! Just saying, try every zero to low cost option before throwing money at a completely unknown.

 

[540HemiCuda]

Hence, my recommendation for some dyno time. It will indicate a bad converter in nothing flat. And most other engine and transmission issues as well.

Either dyno time with a good operator that knows his job, or an experienced muscle car mechanic. Either one should be able to get to the bottom of the problem.

Just look at all the different directions that have been proposed here. And many of them could possibly be the problem. Not to mention all the other possibilities that could cause the problem. How about an improperly installed cam? Tooth off? Not degreed properly, if at all. Just to name one problem that the OP doesn't sound like he could find and fix.

The OP needs hands-on help for this issue. This is unlikely to be diagnosed over the internet.

That's my two cents.

.