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Discussion Starter #1
Car is 1972 Manta.
How much horsepower/torque can-
The stock engine internals handle?

The stock clutch handle?

The stock 4 speed manual transmission handle?

The stock rear axle handle?


Not concerned with ways to make the horsepower, just want to know at what point will stuff start breaking. This is for spirited street driving, no racing. Assuming every piece is relatively fresh, and not worn out.
 

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Super Moderator
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It really depends.

As you said, freshness matters. Fatigue life is also a real thing. it’s one thing to take 150 hp at 6000 rpms, but 150 hp at 8000 rpms will break **** faster.

It also depends on the component starting point. Early blocks have thinner webbing and main caps and are weaker. Certain castings from certain foundaries are stronger. Connecting rods can vary in material and design. As can pistons.

Weak link in the heads are rocker arms and rocker studs. But that depends on rpms, cam choice, and valve spring tension.

Stock clutch can slip with as little as 125 hp.

Stock gearbox can blow up with 75 hp if driven hard. Or handle 200 hp if driven gently.

Rear axle is similar. Bone-stock, I’ve blown them up with a 75 hp automatic. Or have run 190 hp thru one successfully with a limited slip. The torque tube can be an issue with modest power if you run high speeds, as they tend to have high rpm harmonic issues. They can also break at lower speeds if you have good traction and decent power.

In general, figure the entire driveline being marginal at 150 hp.

The engine can take a bit more with OEM forged rods if the rpms are kept low, such as when using forced induction. I’ve heard of 250 hp being pushed out of a bone stock engine with a turbo.
 

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Opel Rallier since 1977
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1,705 Posts
I'll second the 'Depends on how you treat it' statement. Smooth driving will make a big difference. But rev it up at a stop sign and side-step the clutch on dry pavement and you can break clutch pressure plates without too much difficulty.

Rallying at 120-130-ish HP did not break stuff at all, but the traction on gravel roads was not there to be able to put hard shocks into the driveline. So the constant torque on the driveline at that power level was fine over 4000+ miles of gravel stages. No special parts (unless the old TRW forged pistons are considered special), revving to 7700 RPM for 2-3 shifts on the early forged rods and crank, and just good maintenance on the rest. The only time I broke parts (2 clutches) was horsing around on pavement,not in rallies. Twisted a couple of axle shaft spines too but that was with a welded differential.
 

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Living in the past
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2,288 Posts
I'll second the 'Depends on how you treat it' statement. Smooth driving will make a big difference. But rev it up at a stop sign and side-step the clutch on dry pavement and you can break clutch pressure plates without too much difficulty.

Rallying at 120-130-ish HP did not break stuff at all, but the traction on gravel roads was not there to be able to put hard shocks into the driveline. So the constant torque on the driveline at that power level was fine over 4000+ miles of gravel stages. No special parts (unless the old TRW forged pistons are considered special), revving to 7700 RPM for 2-3 shifts on the early forged rods and crank, and just good maintenance on the rest. The only time I broke parts (2 clutches) was horsing around on pavement,not in rallies. Twisted a couple of axle shaft spines too but that was with a welded differential.
Drivetrain breakage was always a problem on the drag car, first thing I broke was the presssure plate, tore the straps loose that holds the pressure plate to the hat part. Turned the flywheel down flat and laided it off to take a 9 1/4 " borg & beck Weber pressure plate and a 9 1/8 " Vega raceing disc. Next started breaking gears in transmissions and continued to be haunted by that situation, but became very good at changing out parts in the transmission and very fast changing them out at the track (usually took 4 or 5 transmissions to the track) and hope I had enough to last all weekend. Broke 1 axle and 1 ring gear & pinion in the 4 years I ran the car, welded up spider gears held up very well as did the driveshaft and torque tube prop shaft. The engine, while it was never dynoed, had to be around 190-200 HP and left the line at 6000 RPM and power shifted at 7200. If I stayed in it thru the last MPH light in a quarter mile it was turning 6800
 

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Pedal Smasher
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Condition of the parts also depends on how you ascertained their condition. Just inspecting the parts on the car is very different from going over every single part during a full rebuild. Things can look just fine on a car when in reality they are waiting to fail on you. And never trust someone else's word on the condition of used parts. One person's barely used is another person's tired and worn out.
 
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