Questions about American Muscle Cars

"Nate-964" (Nate-964) 06/07/2015 at 06:47 • Filed to: None

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I have a question that I have been wondering for years. Why did American muscle cars with ~400HP in the late 60s have top speeds of only ~130 MPH. I understand the 1/4 mile culture was more focused on acceleration versus top speed, but was there other factors? Was it the gearing, aerodynamics? What was the mechanical /engineering reason why they all topped out at around ~130?

LongbowMkII > Nate-964 06/07/2015 at 06:56

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Gearing mostly. Short ratio gear boxes and only 4 speeds. Also keep in mind that the street tires of the day probably wouldn’t take much high speed abuse anyways.

TwinCharged - Is Now UK Opponaut > Nate-964 06/07/2015 at 07:09

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Probably gearing, they usually had short ratios for acceleration. I mean, the GTO’s auto ‘box only had two speeds, affectionately known as fast and faster.

My citroen won't start > Nate-964 06/07/2015 at 07:20

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Gearing and heaviness.

daender > Nate-964 06/07/2015 at 07:23

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It’s the mindset of the times. People cared more about drag racing on track and on the street so manufactures geared (literally) their cars for that automotive audience.

djmt1 > Nate-964 06/07/2015 at 07:40

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Going by the many years I have playing Forza, the answer is shitty gearboxes. First upgrades are always race diff and race gearbox.

MultiplaOrgasms > Nate-964 06/07/2015 at 07:54

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Gearing, aerodynamics, generally rubbish suspension and tires unchanged from the ~200hp base models

Cé hé sin > Nate-964 06/07/2015 at 08:01

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Exaggerated power outputs. Four hundred horses then do not necessarily equate to 400 net DIN horses today.

That Bastard Kurtis - An Attempt to Standardize My Username Across Platforms > Nate-964 06/07/2015 at 08:18

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Because they were big heavy square boxes with only 4 forward gears and bias ply tires as wide as your shoe.

camaroboy68ss > Nate-964 06/07/2015 at 09:17

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The gearbox was NOT the main problem but rather the rear end gearing. A lot of your high performance muscle cars of the 60s had short rear gears for drag racing. Couple that with a 4 speed manual or three speed auto and you have a quick but limited top end car. The old bias plays and polyglass tires just didn't hook on launch and they have weak sidewalls.

boxrocket > Nate-964 06/07/2015 at 10:01

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Pretty much what others have said. There were ways to make them go faster, and the engines from the same cars could be installed in other vehicles - like Bonneville Salt Flat racers - and reach considerably higher top speeds.

Funktheduck > Nate-964 06/07/2015 at 10:11

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I blame mostly the transmissions. The autos were usually 2 or 3 speeds and the manuals were mostly 3 or 4 speeds.

deekster_caddy > Nate-964 06/07/2015 at 10:12

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Mostly aerodynamics, gearing. The majority of them handled hideously over 100...

ly2v8-Brian > Nate-964 06/07/2015 at 10:29

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Mostly gearing. On NASCAR circuits they were going well north of 130.

Highlander-Datsuns are Forever > Nate-964 06/07/2015 at 10:41

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I got my 1968 Buick electra up to 105 once, it was terrifying. I think the only thing steering it was the general direction the front wheels were pointing and the aero of the tail fins. So what I am saying is you really don’t want to go to fast in a 60’s american car because you will die.

twochevrons > Nate-964 06/07/2015 at 12:41

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You’ve also got to take into account different practices for measuring engine power then and now. Essentially, before the 1970s, manufacturers quoted gross power outputs under ridiculously idealised conditions – straight headers with no silencers, no accessories (not even water and oil pumps), and fairly generous correction factors for environmental conditions. In other words, as installed, those engines were making nowhere near 400HP.

In the 1970s, at the same time as emissions legislation, manufacturers started to use the net horsepower rating, which essentially measured the power output of the engine as it was installed in the car. While it’s undeniably the case that air-injection pumps, catalytic converters and the like did sap a fair bit of power, the change to a more realistic measurement system also had a part in the massive drop in power outputs during that era.

There’s a really good article explaining the whole deal at http://ateupwithmotor.com/terms-technolo… .

BiTurbo228 - Dr Frankenstein of Spitfires > Nate-964 06/07/2015 at 13:30

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Crap aerodynamics and over-rated engines. Mainly the over-rated engines.

The exaggeration coming from gross power-ratings really came to a head during the muscle car era. There aren’t many engines from that era that have been honestly dynoed to a net standard, but some have and some have been fairly accurately estimated.

For instance, the K-code 289 in the early Ford Mustangs was rated at 276bhp gross, but only made around 180bhp net. Some are more honest than others (I think Chrysler’s Hemis were closer than the K-code), and some in the early 70s were rated in both gross and net so you can do some decent comparison (again, I think Chrysler started this early so it’s a lot easier to judge).