General Question About Individual Throttle Bodies

[daepp]

I’ve got a nagging automotive engineering/physics question I was wondering if you could answer. I recently listened to a guy talk about his recreation GT40, which was set up like the original with a 427 and 4, two-barrel Weber (I think that was who made them) carbs. I think I know that having 8 separate throttle bodies (like the six in our MFI cars) is a far superior design than say just one or two (that get shared by all cylinders). But the owner of this car said that they also made the car run cooler. When asked why, he said something about heat from the other cylinders (or their valves or hot back pressure or something - not sure exactly). Have anyone ever heard this? The guy was adamant that it worked, and that he’d gone to the extra expense not just for originality’s sake but also because the GT40 was notorious for running hot.
Have anyone ever heard this? Or if not, does it make sense physics/engineering wise?

FWIW I’m not exactly building on (ha!) - just curious is all.

TIA,

David Epp

[Scott Douglas]

Makes sense to me because you can tune each individual cylinder to run more optimally than if the throats are shared.

[john70t]

The intake runners are not equal length with a single center carb setup.
Throttle response, induction airspeed, and wall quench will affect the cylinders differently.

Also the ones next to the transmission will remain a little hotter, due to thermal mass and less ambient air.

[Bill Verburg]

Originally Posted by daepp

I’ve got a nagging automotive engineering/physics question I was wondering if you could answer. I recently listened to a guy talk about his recreation GT40, which was set up like the original with a 427 and 4, two-barrel Weber (I think that was who made them) carbs. I think I know that having 8 separate throttle bodies (like the six in our MFI cars) is a far superior design than say just one or two (that get shared by all cylinders). But the owner of this car said that they also made the car run cooler. When asked why, he said something about heat from the other cylinders (or their valves or hot back pressure or something - not sure exactly). Have anyone ever heard this? The guy was adamant that it worked, and that he’d gone to the extra expense not just for originality’s sake but also because the GT40 was notorious for running hot.
Have anyone ever heard this? Or if not, does it make sense physics/engineering wise?

FWIW I’m not exactly building on (ha!) - just curious is all.

TIA,

David Epp

Only the early GT40mk1 w/ 302ci V8 used the 4x Weber 48 setup, Mk2 got the 427ci w/ either a single Holley 780 or dual Holly 450


Mk1, 302ci w/ Gurney heads


Mk2 427 ci
single Holley




Mk2 dual Holley



I find it hard to see why there would be any cooling difference, They all used cold air boxes to keep intake temps down and there were a lot of early heat related problems, hence all the extra cooling intakes on the later cars

[asphaltgambler]

All carb designs even an 8bbl set-up are a comprise. The closer the throat to the intake port you move the torque curve upwards as well as where max HP is reached. So the car in the OP is an upper mid to high RPM /HP application. As far as running cooler ......someone's wishful thinking. Rear most cylinders do run slightly hotter as they are the farthest from the radiator, but only very slightly.
.

[daepp]

Come to think of it, I was wrong about the 427 - I think it was the smaller engine.

[speeder]

That heat shield around the carburetors looks extremely necessary and also has the extra function of putting a barrier between any leaking gasoline and what I'm assuming is red hot headers a few inches away under racing loads.

Beautiful machine.

[john70t]

If the intake port to the port side has anything to do with it...that also provides a small reserve for intake air.

[Jeff Higgins]

Interesting, probably unrelated side note - in NHRA Pro Stock, they switched from the age-old tunnel ram with a pair of 1150 CFM Holley 4500's on top to fuel injection a few years ago. The teams immediately found they could not make the same power, fighting detonation problems.

It turns out that they had neglected to consider the cooling effect on the intake charge that the carburetors provided by way of introducing the gasoline so far up the intake tract. Fuel injectors blow the gasoline in quite low in the intake runners, darn near in the intake port itself. As a result, the intake air travels most of the way "dry", picking up a considerable amount of heat along the way. The gasoline was actually acting to cool that charge to a much greater degree than they had considered with the old tunnel ram setup. They played hell trying to get back on top of that one.