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09-26-2021, 07:20 PM | #1 |
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1970 L47 400 BB Torque and HP chart
My google-fu is broken. I'm looking for the complete Torque and HP curves for the stock engine, not just peak numbers. I've seen it here somewhere, but don't seem to be able to relocate it. They aren't in the repair manual I have, and any search on the internet comes up with SB 400 and BB 427s and 454s.
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09-26-2021, 07:47 PM | #2 |
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Re: 1970 L47 400 BB Torque and HP chart
https://www.google.com/search?channe...e+and+HP+chart
Scroll down 4 or 5 and you'll find some info from this site. Last edited by MySons68C20; 09-26-2021 at 07:49 PM. Reason: missing info |
09-26-2021, 08:43 PM | #3 |
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Re: 1970 L47 400 BB Torque and HP chart
Thanks, but that looks almost exactly like my search results. I didn't find the chart in that group of searches, either. I KNOW that I've seen the chart somewhere here, but I just can't find it.
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09-26-2021, 09:54 PM | #4 |
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Re: 1970 L47 400 BB Torque and HP chart
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09-26-2021, 10:06 PM | #5 | |
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Re: 1970 L47 400 BB Torque and HP chart
Quote:
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09-26-2021, 10:21 PM | #6 |
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Re: 1970 L47 400 BB Torque and HP chart
You read the chart wrong.
The red line is hp. |
09-26-2021, 11:14 PM | #7 |
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Re: 1970 L47 400 BB Torque and HP chart
OK, convince me that my engine puts out 460 Lb-Ft of torque at that RPM. The legends weren't clear to me, either. Desk top Dyno isn't the factory spec.
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09-27-2021, 07:29 AM | #8 |
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Re: 1970 L47 400 BB Torque and HP chart
Are you looking for numbers for a big block 400 chevy? Ur gonna look till ur eyes bleed cause Chevy didn't make a BB400. They made a 396 and 402, which are the same motor, just a 402 is a .030 over 396. I wanna say it had to do with a car having a bigger motor than in a truck.
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09-27-2021, 10:00 AM | #9 |
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Re: 1970 L47 400 BB Torque and HP chart
I know that. I just posted what the fender says, but I also specified L47. There are lots of stories abut the extra 6 cubes in the 402, but I don't remember which one is true.
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09-27-2021, 12:57 PM | #10 |
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Re: 1970 L47 400 BB Torque and HP chart
This dyno sheet is the best I can find. I know you have run across it here but haven't seen it on this thread.
Thread is here http://67-72chevytrucks.com/vboard/s...d.php?t=694281 |
09-27-2021, 01:16 PM | #11 | |
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Re: 1970 L47 400 BB Torque and HP chart
Quote:
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09-27-2021, 02:44 PM | #12 |
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Re: 1970 L47 400 BB Torque and HP chart
Pulling that much weight you’d want to be turning closer to 3000 rpm which would require a change to a 4.88 gear.
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09-27-2021, 03:58 PM | #13 |
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Re: 1970 L47 400 BB Torque and HP chart
That's mighty deep, so I'd want overdrive when I'm not towing. Though I don't generally "commute" anywhere with the truck. I'm trying to figure this out so that I only do a thing (diff, engine) once. If I could see how the torque climbs before 3000 RPM, I might be able to get away with a taller gear. That engine is going to be singing, going down the road...
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09-27-2021, 04:21 PM | #14 |
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Re: 1970 L47 400 BB Torque and HP chart
My buddy built a towing rig for his 5th wheel holiday trailer.
71 gmc with L88 spec 427. 12.5 to 1 compression. ZL1 cam. Idled rough at 1100 rpm. Hooked to a turbo 400 and 4.56 gear. Pulled at 65mph at 3200 rpm all day. Surprised a lot of people when he’d pull out and pass. Rpm won’t hurt your motor. I’ve run lots of big blocks from 396’s to LS6’s. They all liked 3000 rpm or more. Looking at that chart, torque peak at 3000 is right where you want to run. |
09-27-2021, 04:31 PM | #15 |
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Re: 1970 L47 400 BB Torque and HP chart
They hurt your ears, and your sense of vibrations, and your fuel tank. Revving high is annoying as all hell with a 4 wheeled vehicle.
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09-27-2021, 05:00 PM | #16 |
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Re: 1970 L47 400 BB Torque and HP chart
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09-27-2021, 08:29 PM | #17 | ||
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Re: 1970 L47 400 BB Torque and HP chart
Quote:
Quote:
My wife was complaining about how her dad had a trailer before that he towed with no problem. I know from my own experience with it that it ran hotter than a pistol pulling that trailer, and didn't pull hills all that well, and that was a much smaller trailer. Whatever happens, I'm sure that the expense of a new vehicle will be way over what I'm thinking of doing. She's talking about selling one of the econoboxes and getting a new Suburban, but those new things are crazy expensive and don't get THAT much better mileage, anyway. I'm retired, she wants to retire. A new vehicle payment is way more.
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09-27-2021, 08:43 PM | #18 |
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Re: 1970 L47 400 BB Torque and HP chart
What about a 8.1/4l80 swap?
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09-27-2021, 09:28 PM | #19 |
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Re: 1970 L47 400 BB Torque and HP chart
Toomuchamunny! And a lot of work that I am too old to do, sad to say. Even 10 years ago, that would have been a walk in the park.
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09-28-2021, 02:53 AM | #20 |
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Re: 1970 L47 400 BB Torque and HP chart
Beef up with what you have (small supercharger) or make a cam change and spin it tight in 2nd. I don't exactly know what I'd do as it's late but we are thinking
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09-28-2021, 08:34 AM | #21 |
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Re: 1970 L47 400 BB Torque and HP chart
I dont think that gear swap is going to help you unfortunately. I just hauled gravel with my 57 GMC D250 and with 3 tons on the back it was right at 12k pounds. It was all it could do to pull a grade, even configured with 5.14s, granny 4spd, and a SBC. My milage was around 5 or 6. The motor is a stock 305HO. Not the best but not shabby for a stocker. Truck is spinning about 3k rpm at 55mph.
My thought for the wieght is deep gears, 454, and an OD trans. A cummins diesel would actually fit the bill better but you didn't ask and it would be a ton of work. I towed a 12k camper with a 5spd and 3.55 gears comfortably. |
09-28-2021, 09:29 AM | #22 |
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Re: 1970 L47 400 BB Torque and HP chart
The general must be really optimistic, because they claim that a '74 with a 454 and a 3.73 axle can max out at 13.5k pounds. The 454 can't have that much more torque. Here are the charts, one for '69, one for '74.
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09-28-2021, 11:47 AM | #23 |
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Re: 1970 L47 400 BB Torque and HP chart
I’m not sure what to make of that chart. A C10 with 4.57 has 1000# more towing capacity than a big block C20?
A gear change I think would help you a bunch. 10% more torque at any speed makes a noticeable difference. Like going from 350 ci to 396. Or from 396 to 454 ci. **EDIT** since you have 3.54 gears, it would be 15.8 % increase in effective torque at same highway speed. Remember that torque is multiplied by the gears and hp is mathematical function of torque. So if you are turning 2500 rpm with the 3.54 gears and the 4.10 gears put you at 2900 rpm, you get to now multiply the higher 4.10 number by the higher torque output of the engine. Since we can’t see below 3000 rpm on the charts posted we can guesstimate. I found a 325 hp 396 chart (which I think is same as the truck 310) that showed torque to be 375 at 2500 rpm and 410 at 3000. So let’s pretend same at 2900… 375x3.54=1327.5 effective lb ft versus 410x4.10=1681. So 1681-1328 (I rounded) is 353 ft/lb. 353/1328=25% increase in available torque to do work. Here’s the graph I found: https://www.automobile-catalog.com/c...e_4-speed.html It is certainly the easiest way to get more effective power. Torque is a function of displacement and compression ratio almost completely. And it’s hard to bump the compression on a big block that has 100cc heads without changing pistons. A cam swap can move the power around but mostly trades RPM for HP by shifting the scale up the chart. For a low performance application, towing is one place where small, long tube headers can really pay off by increasing torque without moving the scale.
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09-28-2021, 12:08 PM | #24 |
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Re: 1970 L47 400 BB Torque and HP chart
Considering your wife’s need for max 55 mph and quiet running then a swap to 4.10 gear isn’t worth it.
In second uphill you’re turning 3300 now. Switch to 4.10 and you’ll be up to 3900 rpm. You might not get into 3rd. If you do it might be louder. Drones usually occur at lower rpm. Best thing to do might be swapping to a lighter trailer. |
09-28-2021, 12:27 PM | #25 | |
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Re: 1970 L47 400 BB Torque and HP chart
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Thanks for finding those charts! The engine is up for rebuilding, as it has about 100k since the first rebuild, and it's using oil (not to the ground). If I could find a 454 (I have a wtb ad posted) I would rebuild that for practically no more money than the 402. Maybe I can find some better flowing cast manifolds. I don't like the ringing of headers, though. Guess I could wrap them.
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