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

[Chuffer]

Car would react much better at low to mid RPMs with like a 3.73 or a 4.11 rear end gear

Wow, how we forget what we had in the 1970s

Setup for my C5, I went with 11.3:1 engine compression

I purposely went for a 3. 07 : 1 ratio for more relaxed cruising which is what I do much of the time on our conjested and speed restricted roads . Track days and strip runs are not on the agenda option anymore .

 

[Chuffer]

Can't say for sure re. the Torker inlet on a small block on a big block its certainly regarded as a non-performance item. The name Torker itself is a major misnomer as it doesn't add torque to the engine, except perhaps at higher rpm (where its not required) - I used a Torker 11, along with a Holley 750 double pumper as the first upgrade on my original 427. It certainly didn't produce any addition power over 4000 rpm, but did make the engine more responsive between 2000 and 2500 rpm.
You've already indicated that the 3.07 rear end is probably too much of a ratio for off the line performance.........a dual plane inlet would theoretically improve low end 'out of the hole' performance.......but would possibly be higher than the Torker, creating clearance issues.

The higher rise of a dual plane was another consideration for not going down that route as hood clearance is minimal as it is . Interesting to note that you reconned yours was more responsive between 2000 and 2500 rpm which is where mine seems to get on the the sweet spot but also carries on to 3000rpm and above although I rarely hit 4000 in deference to the old girls age . I am lead to believe that a single plane inlet gives a more prolonged power and torque platau before things drop off a cliff as revs rise . I am sure someone will say yay or nay .

 

[Forrest Gump]

The higher rise of a dual plane was another consideration for not going down that route as hood clearance is minimal as it is . Interesting to note that you reconned yours was more responsive between 2000 and 2500 rpm which is where mine seems to get on the the sweet spot but also carries on to 3000rpm and above although I rarely hit 4000 in deference to the old girls age . I am lead to believe that a single plane inlet gives a more prolonged power and torque platau before things drop off a cliff as revs rise . I am sure someone will say yay or nay .

Err, nay, other way round! Single plane are for high revving motors (strip or circuit) generally less torque at lower rpm but higher horsepower with their high rev capability.
Dual plane give a better spread of torque through the rev range - what you want for the road, but typically drop off at higher revs. Most dual plane will fit under a Corvette hood (not the Air Gap though), they’re what most of us have got!

 

[CaptainK]

I purposely went for a 3. 07 : 1 ratio for more relaxed cruising which is what I do much of the time on our conjested and speed restricted roads . Track days and strip runs are not on the agenda option anymore .

Same here Chuffer. I mostly just cruise around in my Vette. Too many small roads around my parts to do anything more. Not that long ago I found out I have a 3.08 diff on my 68. It should have been a 3.70 (ish) I think from the factory, so evidently someone in USA land swapped it over before I owned it and imported it. Would be nice to have a 5 speed box as well at some point, just for that relaxed cruising. My Edelbrock Performer intake is a dual plane manifold, and low down torque in it means I can pretty much drive it in 4th from about 25mph upwards.

As a wee side note of a coincidence - my 68 Corvette does about 2600rpm ish in 4th at 70mph. Just yesterday I noticed my FTO does 2600rpm ish in 5th at 60mph. The marvels of torque and gearbox ratios.

 

[Chuffer]

Err, nay, other way round! Single plane are for high revving motors (strip or circuit) generally less torque at lower rpm but higher horsepower with their high rev capability.
Dual plane give a better spread of torque through the rev range - what you want for the road, but typically drop off at higher revs. Most dual plane will fit under a Corvette hood (not the Air Gap though), they’re what most of us have got!

I think we said the same thing in a different way Forrest . I meant that power is sustained at higher revs rather than drop off at higher revs .

 

[Vetman]

Err, nay, other way round! Single plane are for high revving motors (strip or circuit) generally less torque at lower rpm but higher horsepower with their high rev capability.
Dual plane give a better spread of torque through the rev range - what you want for the road, but typically drop off at higher revs. Most dual plane will fit under a Corvette hood (not the Air Gap though), they’re what most of us have got!

73 to 75 C3 hoods are a bit higher and my Performer air-gap is 1/4” higher than older Performer but fits under hood ok. RPM air-gap manifold is taller still.

 

[Roscobbc]

Single plane inlet manifold generally gives its best at a higher rpm than most street tuned Vettes can sensibly achieve and where power is dropping off due to design inadequacies in the heads......a dual plane spreads that usable power over a wider rpm range and will also be more fuel efficient at typical daily driver speeds.....all very important for a smaller capacity, lower hp car...... especially with high gearing and overdrive ratios.

 

[Chuffer]

Same here Chuffer. I mostly just cruise around in my Vette. Too many small roads around my parts to do anything more. Not that long ago I found out I have a 3.08 diff on my 68. It should have been a 3.70 (ish) I think from the factory, so evidently someone in USA land swapped it over before I owned it and imported it. Would be nice to have a 5 speed box as well at some point, just for that relaxed cruising. My Edelbrock Performer intake is a dual plane manifold, and low down torque in it means I can pretty much drive it in 4th from about 25mph upwards.

As a wee side note of a coincidence - my 68 Corvette does about 2600rpm ish in 4th at 70mph. Just yesterday I noticed my FTO does 2600rpm ish in 5th at 60mph. The marvels of torque and gearbox ratios.

My 5.7 Litre Jeep with 5 speed auto lopes along at 2000 rpm at 70 mph . Very laid back

 

[CaptainK]

My 5.7 Litre Jeep with 5 speed auto lopes along at 2000 rpm at 70 mph . Very laid back

I'd like a 5 speed box in mine, just so I can get the revs down at highway speeds. Tragic to mention it here, but my old Focus diesel ( ) did around 1900 rpm at 70mph in 6th gear.

 

[Vetman]

You could achieve higher gearing with larger rear tyre. I am considering changing my rear tyres from 225 x 15 R60 to R70. The increase in diameter is about 1.5” to 2” depending on flattening due to load and centrifugal increase due to speed.