Safe maximum rpm
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Safe maximum rpm
What is a good red line to use on my '79 F250 with 400 and manual transmission? With 4.56 gears and towing a trailer she has to scream pretty good to get over some of the hills. I have not been over about 4200 - 4300 rpm but am wondering if I can go closer to 5000 without doing damage.
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The 400 is a low RPM torque engine like the 300-6. Very good for moving heavy objects. I would not go over what you already have. A well built engine can exceed those RPM's if properly balanced and configured. A good OEM engine is usually balanced to some extent on the production line. Normal remanufactured engines are not balanced at all.
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Thanks Eric,
The engine is an unknown, I bought the truck last year and the engine had recently been rebuilt (havn't they all
) but I have no idea who did it or what they did. She runs great on everything but the hills. In 4th gear at 60 or 65 mph and 3000 rpms she has no staying power, the slightest incline immediately slows her. I'm towing a new 19' travel trailer with a dry weight of 4400 lbs. so probably closer to 6000 lbs. loaded. I have to wait until I slow to 40 mph or so so I can shift into 3ed and keep the rpms down around 4k. Then I'm stuck at 38 - 40 mph until I can reach the top. I'm going to make a secondary jet change (Edelbrock 1406) and see if that helps, if I give it more throttle as it slows it really doesn't add any power. I'm also swaping the large radiator over from the Super Cab to keep her cool while working hard and in stop and go traffic. Hopefully I can make some small gains at least.
The engine is an unknown, I bought the truck last year and the engine had recently been rebuilt (havn't they all
) but I have no idea who did it or what they did. She runs great on everything but the hills. In 4th gear at 60 or 65 mph and 3000 rpms she has no staying power, the slightest incline immediately slows her. I'm towing a new 19' travel trailer with a dry weight of 4400 lbs. so probably closer to 6000 lbs. loaded. I have to wait until I slow to 40 mph or so so I can shift into 3ed and keep the rpms down around 4k. Then I'm stuck at 38 - 40 mph until I can reach the top. I'm going to make a secondary jet change (Edelbrock 1406) and see if that helps, if I give it more throttle as it slows it really doesn't add any power. I'm also swaping the large radiator over from the Super Cab to keep her cool while working hard and in stop and go traffic. Hopefully I can make some small gains at least.
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From: The Casa
is your clutch staying dry.Just a little bit of oil on the flywheel can cause slipping.We had a 600 hp mack that could barely pull a empty lowboy up a hill and it was because motor oil was getting on the flywheel.Sometime its really simple thangs like that, that get over looked.
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From: Delaware
The torque curve of a 400 with a 4 barrel carb begins to fall off drastically about 3000 to 3500 RPM. You need to extend that torque curve to 4000 RPM or higher. One way to do that is with a longer duration cam, but long duration cams lose power at low RPM due to overlap and low dynamic compression.
It all comes down to to keeping the Volumetric Efficiency high throughout the desired RPM range. This means good air flow from the carb through to the exhaust pipe. A good set of headers with free flowing exhaust, a good intake manifold, a good 4 barrel carb(1406 is OK), and great heads with large valves. My 434 has peak torque at 4700 RPM, but you don't have to build a motor like mine to get a better torque curve.
Do you have large tube headers?
What intake manifold?
Also some head work or aftermarket heads.
Increasing the Compression Ratio will help across the entire RPM range.
It all comes down to to keeping the Volumetric Efficiency high throughout the desired RPM range. This means good air flow from the carb through to the exhaust pipe. A good set of headers with free flowing exhaust, a good intake manifold, a good 4 barrel carb(1406 is OK), and great heads with large valves. My 434 has peak torque at 4700 RPM, but you don't have to build a motor like mine to get a better torque curve.
Do you have large tube headers?
What intake manifold?
Also some head work or aftermarket heads.
Increasing the Compression Ratio will help across the entire RPM range.
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Originally Posted by mudslingur
is your clutch staying dry.Just a little bit of oil on the flywheel can cause slipping.We had a 600 hp mack that could barely pull a empty lowboy up a hill and it was because motor oil was getting on the flywheel.Sometime its really simple thangs like that, that get over looked.
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Originally Posted by danlee
The torque curve of a 400 with a 4 barrel carb begins to fall off drastically about 3000 to 3500 RPM. You need to extend that torque curve to 4000 RPM or higher. One way to do that is with a longer duration cam, but long duration cams lose power at low RPM due to overlap and low dynamic compression.
It all comes down to to keeping the Volumetric Efficiency high throughout the desired RPM range. This means good air flow from the carb through to the exhaust pipe. A good set of headers with free flowing exhaust, a good intake manifold, a good 4 barrel carb(1406 is OK), and great heads with large valves. My 434 has peak torque at 4700 RPM, but you don't have to build a motor like mine to get a better torque curve.
Do you have large tube headers?
What intake manifold?
Also some head work or aftermarket heads.
Increasing the Compression Ratio will help across the entire RPM range.
It all comes down to to keeping the Volumetric Efficiency high throughout the desired RPM range. This means good air flow from the carb through to the exhaust pipe. A good set of headers with free flowing exhaust, a good intake manifold, a good 4 barrel carb(1406 is OK), and great heads with large valves. My 434 has peak torque at 4700 RPM, but you don't have to build a motor like mine to get a better torque curve.
Do you have large tube headers?
What intake manifold?
Also some head work or aftermarket heads.
Increasing the Compression Ratio will help across the entire RPM range.
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From: Delaware
Originally Posted by wick246
The cam is a complete unkown. It has a stock intake manifold, heads and exhaust manifolds. I had new 2 into 1 exhaust put on a couple of weeks ago but the manifolds will be the bottleneck there. I did not want to lose all my torque on an engine that can't spin very fast anyways.
The reason that it doesn't spin is because it is all choked up. You should start with a set of headers.
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From: Coutts Canada
Yeah 4bbl's didn't come on the 400's in production (theres a few factory experimental 4v intakes floatin around), and yeah invest in a good set of headers as they help these motors out quite a bit.
As far as how much to rev these motors, i comp. mud race a reman 400 (currently, new one is beening built
) and its hittin 52-5300 in the pitts, granted thats not healthy for a dd, but 4 years and still going strong (its had 77,000miles on it when i put it in )
As far as how much to rev these motors, i comp. mud race a reman 400 (currently, new one is beening built
) and its hittin 52-5300 in the pitts, granted thats not healthy for a dd, but 4 years and still going strong (its had 77,000miles on it when i put it in )
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Oops you're right on the manifold, I'll have to check which model it is. Is there a preferred set of headers that fit well in this truck? I know there are lots to choose from but I'm hoping to narrow the field down some. What will headers do to my torque in the lower rpm's?
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From: Delaware
Originally Posted by wick246
What will headers do to my torque in the lower rpm's?
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Originally Posted by danlee
Headers should improve your torque at low RPM, as long as the tubes are not too large. Any good aftermarket header made for your truck should work well. Maybe someone else can chime in with a brand, since I don't have your model truck.
Last edited by wick246; Jun 28, 2007 at 10:35 AM.
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Hedman has full length headers with 1 3/4" tubes and a 3" collector for $165 a set or 1 5/8" tubes to a 3" collector with fenderwell exit for $207 a set. Any thoughts on which set will be best for my application?
Thanks for all the help...
Thanks for all the help...
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From: Delaware
Originally Posted by wick246
Oops you're right on the manifold, I'll have to check which model it is.