400hp small block with th700

Logbed · Jun 28, 2024

My C10 drivetrain has th700 and 3000 stall, 31" wheels, 4.10 gear and posi rear.

The current 305 powerband makes 130hp@2500rpm and 167hp@3000rpm while max power is 220hp/4400-5200 (those are cranckshaft power estimates, 15% up from hub dyno readings (190hp max))

I have been quite happy how it launches wheels spinning and when upshifting from 1 to 2 it keeps going as the dyno curve is really "fat". The drivetrain is milking pretty much everything from the engine.

But of course, I've been thinking about a bigger engine.

Looking at the dyno graphs of some typical 400hp/5200rpm 350 engines, they seem to make around 170hp@2500 and 200hp@3000rpm. So while the top power difference compared to my 305 is huge (180hp), the low end difference is a lot smaller (30-40hp). I'm wondering how does this work with a th700 that has a rather big gap in between 1. and 2.? Does the 200hp upshift power-drop make it "die" when the 2nd gear upshifts? Or does wheelspin lift the engine to the powerband?

Also, when cruising, at least my th700 upshifts to the 2nd quite early but the kick down does not like to downshift to the 1st gear at speed. So when I kick the throttle, do I really have the power of a 400hp 350 "readily at hand" all time in low speeds?

A 400hp / 350cid / TH700 must be quite a typical combo, so I'd expect firsthand experience is to be found here?

85K304SPD · Jun 28, 2024

A 400 HP 350 is more of a high RPM race motor. A 305 is the opposite of that. The only thing that they have in common is they each will make your truck move under its own power.
I am unclear on what you are trying to find out.
I think you are referring to a 700 r4 transmission.

Catbox · Jun 28, 2024

At the low end of things it is not horsepower you are looking for.
You want torque.

Torque is what moves the truck when you are taking off and that is what you feel pushing you back into your seat.
A 400hp 350 probably also makes just over 400ftlbs of torque and with roller cams are not all that radical anymore.

For my 355 build I will be using a L-31 base engine topped with AFR's Enforcer heads and a Comp 268 roller cam or bigger as this will be going into my 1954 Bel Air.
It should be able to easily belt out around 400hp at the crank and cruise all day long doing it.
It will also be making gobs of low end torque when pushed through the 4L80 I have for it should be good for pushing the passengers into the seats.

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"Horsepower is how fast you hit the wall. Torque is how far you move it."

Ricko1966 · Jun 28, 2024

Aaah, the great horsepower vs. Torque discussion. Horsepower is only a math equation based off of torque. 2 engines that make peak torque at the same rpm,the one with more torque will also have more horsepower. Always. It's math it's repeatable and provable. Horsepower is torque times speed(rpm) divided by 5250. To make it simple, easy to use and understand numbers, these aren't actual numbers just numbers to make the explanation simple. If you have 2 engines one with 50 ft lbs one with 100 ft lbs. If you spin the 50 ft lbs one twice as fast it will make equal horsepower. If they both are peak at 5250 rpm the 100 ft lbs engine will have twice the horsepower. 1970 Buick GS quickest car in the U.S. at the time,not huge Hp numbers huge torque numbers, stupid quick teslas,because they have a ton of torque immediately. It's the reason gearing makes a car quicker,ability to turn more rpm,sooner.

Logbed · Jun 28, 2024

Logbed said:
My C10 drivetrain has th700 and 3000 stall, 31" wheels, 4.10 gear and posi rear.

The current 305 powerband makes 130hp@2500rpm and 167hp@3000rpm while max power is 220hp/4400-5200 (those are cranckshaft power estimates, 15% up from hub dyno readings (190hp max))

I have been quite happy how it launches wheels spinning and when upshifting from 1 to 2 it keeps going as the dyno curve is really "fat". The drivetrain is milking pretty much everything from the engine.

But of course, I've been thinking about a bigger engine.

Looking at the dyno graphs of some typical 400hp/5200rpm 350 engines, they seem to make around 170hp@2500 and 200hp@3000rpm. So while the top power difference compared to my 305 is huge (180hp), the low end difference is a lot smaller (30-40hp). I'm wondering how does this work with a th700 that has a rather big gap in between 1. and 2.? Does the 200hp upshift power-drop make it "die" when the 2nd gear upshifts? Or does wheelspin lift the engine to the powerband?

Also, when cruising, at least my th700 upshifts to the 2nd quite early but the kick down does not like to downshift to the 1st gear at speed. So when I kick the throttle, do I really have the power of a 400hp 350 "readily at hand" all time in low speeds?

A 400hp / 350cid / TH700 must be quite a typical combo, so I'd expect firsthand experience is to be found here?

Sorry I was posting this too soon without checking the tach. The gear ratio calculator tells that under WOT accleration the revs should drop from from 5100 to below 2800 when upshifting to the second gear, but my tach says the drop is only 5100 to 3900 (I wonder why, converter maybe). That means the engine is going to stay on the powerband way better than I thought even if the power (or torque, all the same) curve is a bit steeper.

Logbed · Jun 28, 2024

Ricko1966 said:
Aaah, the great horsepower vs. Torque discussion. Horsepower is only a math equation based off of torque. 2 engines that make peak torque at the same rpm,the one with more torque will also have more horsepower. Always. It's math it's repeatable and provable. Horsepower is torque times speed(rpm) divided by 5250. To make it simple, easy to use and understand numbers, these aren't actual numbers just numbers to make the explanation simple. If you have 2 engines one with 50 ft lbs one with 100 ft lbs. If you spin the 50 ft lbs one twice as fast it will make equal horsepower. If they both are peak at 5250 rpm the 100 ft lbs engine will have twice the horsepower. 1970 Buick GS quickest car in the U.S. at the time,not huge Hp numbers huge torque numbers, stupid quick teslas,because they have a ton of torque immediately. It's the reason gearing makes a car quicker,ability to turn more rpm,sooner.

That's why I prefer reading only horsepower@ different rpm points from dyno sheets/curves. Better still average horsepower at spesific usable rpm range. No need for torque numbers, they give no extra info and just make things more complicated.

Ricko1966 · Jun 28, 2024

Look at your torque numbers in rpm range you are talking about are you in the meat of the torque band the whole time. If so all is good

ChuckN · Jun 28, 2024

I’ll just ask, is the 700R4 stock? I mention this because they’re not the most reputable at holding up under a thrashing. Don’t want to be a debbie-downer, sounds like a fun project.

400hp small block with th700

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