What specifically is "neutered" on 1970s-1990s era engines?

[leadcounsel]

So as we know the 70s-90s were an era of classic engines being restricted for economy and emissions. For instances I think a 350 or 305 or others lost maybe 50% of its power from the decades before.

I've always been curious, are these basically the same animals but with some restrictions in place, easy to remove for more power? Say you have a 1980 350ci engine. Would it be relatively easy to tune or detune it to restore it to the former glory, or are there generally relatively permanent design changes that make it cost prohibitive?

 

[supton]

Less lump in the cam, and a lot less compression. Hard to overcome compression loss, although some of the engines I think achieved that through really large combustion chambers. So... how deep are you willing to go?

The original catalytic convertors were not known for good flow, and IIRC easily plugged up, no surprise with the relatively poor metering that a carb affords.

But chopping the exhaust, dropping most of the vacuum operated gizmos and playing with timing, did do something to those plugged up motors. Maybe intake swap and a small 4 barrel... That just left tall rear gearing to deal with (again, how much work are you willing to do?).

 

[Skippy722]

Compression ratios dropped, camshaft profiles got more mild, early catalytic converters were pretty restrictive and prone to plugging up, EGR, vehicles with carburetors might have dropped from high flowing 4 barrel designs to 2, early fuel injection isn’t anything like we have today. They also changed how they rated horsepower, going from SAE “gross” to “net” with net being all accessories on the engine vs “gross” being measured without things like a water pump, alternator, fan, power steering etc.

All those could be fixed, like putting new heads and a cam in would really wake them up. Just depends what you want to pay.

 

[oldhp]

If you took that 1980 Chevy small block and just put on Edelbrock Power package (cam / lifters, aluminum heads, aluminum intake, bigger carb) headers and high output complete ignition system you could at least double the HP.

 

[leadcounsel]

I don't have any projects in mind, however I do see really cheap engines from that era from time to time and it might be something fun to just buy and tinker with in the garage to learn. Maybe find a host vehicle to work on, install it, etc.

Thanks for the replies.

 

[supton]

At least for the Chevy small blocks, one "trick" was the old "no replacement for displacement". The 400's were known for being problematic (deservedly or not, as they do have some head gasket things to watch out for, steam holes or water hole locations, some such) (and they do suffer from a lousy rod length / stroke ratio), but otherwise, one small block swapped for another. Got stuck with a 262 turd? a 350 was a drop-in. Same was true for other OEM's but to varying degrees (I think Pontiac and Olds have the upshot of their small and big blocks having the same motor mount locations???).

A lot of the heads were lousy low weight poor flowing things. IIRC back in the 90's the factory Vortec heads were the bees knees for power upgrade, they flowed great and had good combustion chambers--and were priced decently. For a bit it was just better to buy a new set than to try to redo an old set.

 

[eljefino]

They recurved the distributors for the lower-octane unleaded gas.

Regular leaded was 89.

Cam timing advance, or lack thereof, was also an issue.

It was all mechanical stuff and they figured out workarounds, like asking for a timing kit for a 1968 small block instead of a 1980 one.

 

[dishdude]

Although hp dropped significantly, didn't torque numbers stay pretty consistent?

 

[ctechbob]

Don't forget the belt operated air pumps that were on a bunch of motors. Those sucked power away as well.

 

[Leo99]

Although hp dropped significantly, didn't torque numbers stay pretty consistent?

I had a 77 Buick with a 305. Yeah, it had some torque but it was very slow. It hesitated a lot. I think people forget the hesitation issues. Step on the gas and it would sputter before eventually revving up.

 

[JeffKeryk]

400 hp and 400 ft# torque is easier and cheaper than ever. Take a 350 block, add modern heads, a decent carb or efi, headers with 2.5" exhaust and turbo mufflers, recurve the distributer and off you go.

My 68 Vette with the L36 427 was rated at 390HP; modern heads is all I would need to get some real power out of it.
Just remember to use parts that work well together, for the desired end result. Forget about HP; build a broad, flat torque curve.

 

[skyactiv]

A high school friend had a 84' Dodge Diplomat with a 318. He replaced the 2 barrel intake and carb with a 4
barrel carb and intake and it woke that engine up.

 

[B1974]

My 1977 Trans am 4 speed had a 400 out of a 1968 Catalina in it when I bought it in 1993. Owner told me it was the original motor and I didn't find out until I pulled the motor to change the rear main seal and checked to casting numbers. It had 10.5-1 compression, 1972 455HO aluminum 2 piece intake, and someone had also put a ram air 3 spec cam into it. That explained why it only liked to run on 93 octane gas (good old Husky 93) and was very quick for being a 77.

So that was one way of making your mid 70's car fast back in the 80's.

 

[T120]

Block and head castings were generally thinner and lighter

 

[eljefino]

Block and head castings were generally thinner and lighter

Insane inflation and trying to save money on fuel got us this, and really tall rear axle ratios.

Then that dude bought the oldsmobile with the chevy motor with less nickel in the block and made headlines.

 

[andrew_j]

The upside is the cars of this era smelled a lot less of unburned gasoline flowing out exhaust pipe.

 

[Snagglefoot]

The cam profiles and heads were such that they ran out of breath at around 5000 rpm and the HP numbers suffered from this. Here is the horsepower / torque curve for a 1995 Impala SS with a 5.7 which was considered an interesting power plant in it’s day. Peak torque was at 2000 rpm and it was all done by 5000 rpm with 260 HP.

 

[thastinger]

Low volumetric efficiency

 

[Chris142]

Lower compression,less cam and heads that don't flow and are designed with emissions in mind.

The heads are the biggest factor. You can't easily make say 1980 heads work like 1970 heads did.

 

[Astro14]

They recurved the distributors for the lower-octane unleaded gas.

Regular leaded was 89.

Cam timing advance, or lack thereof, was also an issue.

It was all mechanical stuff and they figured out workarounds, like asking for a timing kit for a 1968 small block instead of a 1980 one.

They also recurved the distributors for EGR.

So, less initial advance, but more vacuum advance, and an EGR distributor would have way too much advance on a non-EGR engine.

So, if you’re going to build a motor for your 1970-90s car, you need to address the cam, heads, intake, exhaust, and ignition system. They’re a system that needs to be compatible. The Edelbrock line is a good recommendation.

If it’s going to have serious HP, then the bottom end needs work, too. Many of the robust 4 bolt main bearing caps in bottom ends of the muscle cars became 2 bolt mains in the 70s and 80s to save material and production cost on the lower HP motors. Big difference between a 350 block from, say, a 1968 Vette and a 350 smog motor in a 77 Nova.