Wake-Up time for that mid/late 70's 'cookin' C3

[Roscobbc]

We have a large number of C3 owners in the club that date from the USA's emission era (so '74 thru '80) - these are typically 'soft-tune' engines with low compression and mild cams. They'll perhaps have 'the show' but not always the 'go' (certainly not enough 'go' for some members!)
There is plenty of information out there on how to 'warm' things up a little but very little information in terms of actual facts and figures relating to the horsepower and torque gains......i.e 'bang for yer buck', so to speak. This thread from the USA's Corvette Forum addresses that issue.
Scott has a '77 L48 which sounds much like many of our CCCUK members Vettes. He is also lucky enough to have a friend with a chassis dyno. Read the changes he has made to his car with dyno results recorded at each step........quite interesting.......and still on basically what is a stock engine (so no cylinder head or camchaft changes........yet)

1977 L48 Basic Mods with Dyno Results - CorvetteForum - Chevrolet Corvette Forum Discussion

C3 Tech/Performance - 1977 L48 Basic Mods with Dyno Results - My 1977 L48 was a 100% stock, 4-speed car, 96,000 miles, purchased from the son of the second owner, came with a pile of records and receipts showing it was well cared for, and it ran fine. Slow, but fine. So, this past year I...

www.corvetteforum.com

 

[Nick B]

Interesting read Ross

 

[Nassau65]

The 74 corvette still packed a punch, especially with the mighty 454ci motor under the hood. Agreed the 75 was probably a low point in the corvette hp stakes, something that Chevrolet did address each year to slowly increase the standard hp. Even so, they were still a lively car, yes probably more show than go, but looks certainly count, and a 75/82 corvette sure looks good.

 

[Roscobbc]

Agree 100% Nassau. Due to these years being considered perhaps a little 'effete' by traditional muscle car lovers (and remembering there wasn't much of an alternative choice back then except perhaps the TransAm Firebird) the Vettes went to a 'different' kind of buyer. And yes the 'run-out' 454 cu in 'breathed-on' suitably is capable of being a fearsome 'tool'......strange really why it's virtually ignored by enthusiasts?

 

[Nassau65]

Was always surprised they dropped the 454ci for the 75 model year corvette, as it was available in the full size caprice for 75. With that motor in it, the caprice sure could shift. Highly prized today, and priced accordingly.

 

[Nassau65]

Was always surprised why the corvette never had the 400ci motor as a cost option. Me thinks many buyers would have opted for this option.

 

[teamzr1]

I owned in the 1970s, 2 1975s and a 1977, did a ton of racing, and they were real pigs due to the oil/gas crap going on back then and the hurry to put smog devices on and would never get the rearwheel gains this guy reports with a few mods he did, other than the headers, but if stock CAT used, than gains would be limited

I think,

Static non load bearing Chassis dyno numbers are suspect to errors, either by mistake or on purpose to bloat the numbers
Without getting rid of that smog CAM not many gains will be had
He does not state when doing the headers/exhaust if still maintaining the performance killer big ass CAT used back then
Drivetrain loss of HP/Tq depending on manual or auto tranny is like 15/20 % loss, so I doubt the gains he states are fact
as flywheel/brake numbers would have to be much higher

N/A engines the crossing point of peak torque is 5,250 RPMs, yet his results are confusing,
nor not understanding why taking the time and money to be on a chassis dyno not doing pulls above 4,500 RPMs
yet torque dropped way before that

The problem using a non-loaded dyno is the drum normally is like 2,700 pounds, if car with driver is 3,700 pounds
then results would be higher as drum mass is lighter than the car's mass.

He states the AFR was 15.1:1 which is way too lean and would cause engine knock and timing retard.
Best would be more like 14.5:1 and assuming he is using gas with Ethanol would be too lean plus \
the issues of Ethanol for a car never designed to use it

Smog CAM and heads really need replaced or reworked along with removing that brick called a CAT with a newer flowing design type
His results :

 

[Roscobbc]

Was always surprised they dropped the 454ci for the 75 model year corvette, as it was available in the full size caprice for 75. With that motor in it, the caprice sure could shift. Highly prized today, and priced accordingly.

The ancient saying "why be hung for a lamb when you can have a sheep" holds really true here. Yes, OK the 454 was not at its best perhaps with emission gear, low compression, a cruising rear axle and auto transmission and its consequent sub 15 mpg economy (vs 17/18 mpg of a L48) but pro rata if even mildly modded any 454 (or 427) will produce far higher return in HP and subseqent drivability than a 350 cu in can. People (not in the 'know') look in horror (and then disbelief) when understanding that my '68 is 8 litre, and just short of 600 hp......yet at 15/16 mpg on cruise is in fact fractionally better economy wise than a stock 427 or 454.

 

[Roscobbc]

I think,

Static non load bearing Chassis dyno numbers are suspect to errors, either by mistake or on purpose to bloat the numbers
Without getting rid of that smog CAM not many gains will be had
He does not state when doing the headers/exhaust if still maintaining the performance killer big ass CAT used back then
Drivetrain loss of HP/Tq depending on manual or auto tranny is like 15/20 % loss, so I doubt the gains he states are fact
as flywheel/brake numbers would have to be much higher

N/A engines the crossing point of peak torque is 5,250 RPMs, yet his results are confusing,
nor not understanding why taking the time and money to be on a chassis dyno not doing pulls above 4,500 RPMs
yet torque dropped way before that

The problem using a non-loaded dyno is the drum normally is like 2,700 pounds, if car with driver is 3,700 pounds
then results would be higher as drum mass is lighter than the car's mass.

He states the AFR was 15.1:1 which is way too lean and would cause engine knock and timing retard.
Best would be more like 14.5:1 and assuming he is using gas with Ethanol would be too lean plus \
the issues of Ethanol for a car never designed to use it

Smog CAM and heads really need replaced or reworked along with removing that brick called a CAT with a newer flowing design type
His results :
View attachment 22509

OP did mention that exhaust system components were sourced from Summit Racing.....didn't notice cat's in his images.....how many states would still require cats?

 

[teamzr1]

OP did mention that exhaust system components were sourced from Summit Racing.....didn't notice cat's in his images.....how many states would still require cats?

All states still require CATS as the feds demand it so states cannot overrule that
Feds rules also state cannot take smog devices off and no GM vehicles designed with no CATS installed

Different is CAT design of modern cars flow a lot more with less back pressure than back in the 1970s where both heads dumping into one CAT that plugged up easy, esp when going from leaded to unleaded gas.

 

[Nassau65]

OP did mention that exhaust system components were sourced from Summit Racing.....didn't notice cat's in his images.....how many states would still require cats?

Yes, as Team says, all states require cats, of course some states like FL has No emissions testing ( got voted out) so if you remove them nobody knows. CA is cat mad, no chance in that state to get it through emissions.

 

[Nassau65]

With all the speed bumps, 20/30 mph average speed cameras within the London boroughs. A standard 350ci powered corvette is more than adequate in my opinion.

 

[teamzr1]

With all the speed bumps, 20/30 mph average speed cameras within the London boroughs. A standard 350ci powered corvette is more than adequate in my opinion.

That's why the UK needs to become the 51st state of the USA
So we can build some real roads there and show you haw to drive fast, Real Fast !

 

[Chuffer]

That's why the UK needs to become the 51st state of the USA
So we can build some real roads there and show you haw to drive fast, Real Fast !

So you don`t have speed limits in the States any more ????

 

[Roscobbc]

That's why the UK needs to become the 51st state of the USA
So we can build some real roads there and show you haw to drive fast, Real Fast !

But your roads are straight......for mile......after mile......after mile.....how do you all manage to drive and keep awake?

 

[teamzr1]

But your roads are straight......for mile......after mile......after mile.....how do you all manage to drive and keep awake?

Only in the flat land states, many mountain roads that change elevations, bind turns, cattle roaming on roads,
even buzzards on road kills do not get out of the way

Try the Big Bend Open Road race out of Fort Stockton, Tx
Elevation changes up/down 2,000 feet and 120 miles with 120 blind turns with cattle guards
and do that with 160 MPH plus average speed

 

[teamzr1]

So you don`t have speed limits in the States any more ????

Yes still do, but states like Texas, Montana, etc have 80 MPH limits on many highways, but people tend to go closer to 100 MPH
and as long as weather is good, cops do not mind.

 

[Chuffer]

Yes still do, but states like Texas, Montana, etc have 80 MPH limits on many highways, but people tend to go closer to 100 MPH
and as long as weather is good, cops do not mind.

Cops don`t mind ?? We have speed cameras sprouting up like like weeds in the UK !! Although we are lucky in my county as all the fixed speed cameras were decomissioned several years ago because the police could not afford to operate the system . Now we just have two mobile camera units roaming about covering 913 square miles . Yes I know that`s tiny compared to US States and Counties !!

 

[Nassau65]

We have those bloody speed cameras everywhere in North London. A friend got caught a few weeks ago, 24 mph in Holloway Road ( 20 mph zone) 3 points and a £150 fine.
The other day I tested myself on the way into central London to not exceed 20mph. It was very very difficult to do, you really have to look at your speedo all the time. What a stressful journey that was.

 

[Roscobbc]

We have those bloody speed cameras everywhere in North London. A friend got caught a few weeks ago, 24 mph in Holloway Road ( 20 mph zone) 3 points and a £150 fine.
The other day I tested myself on the way into central London to not exceed 20mph. It was very very difficult to do, you really have to look at your speedo all the time. What a stressful journey that was.

I have a buddy who runs a luxury airport consierge service.......speaking with him recently and he said that if he gets one more 20 mph speeding ticket he's 'out of it'. Too many distractions for even experienced drivers what with bus lanes, yellow box junctions, newly introduced one way streets, traffic light cameras......and of course not forgetting the 'hazards' of dodgy other drivers in major cities.......the Uber type drivers whose first priority is to look only at their phone/satnav.......the zero hours delivery drivers who have daily workloads of perhaps a hundred or more parcels.......the older black cab drivers who think that the roads are only for them and cruise along a perhaps 5/10 mph below the speed limit in the middle of the road.......the worlds nationalities of drivers who perhaps didn't get their license in the UK or had someone else take it for them.
I used to love driving in London.....both for work and for leisure. Would take young family on a Saturday or Sunday 'up West', wander around the large department stores, prestiege car dealers, have lunch, no parking fees after 1:30pm Saturday/all day Sunday..........them's were the days!