If you have a GT-40 intake and need to go with a 1" phenolic spacer READ

MiracleMax · 07-18-2001, 12:20 AM

Whats the rule of thumb? for every 10 degree drop in temp you gain 1 hp or something like that?

The problemo with modern fuelie systems is that by placing the fuel metering device right at the intake port you lose the latent cooling ability that gasoline exhibits when changing from a liquid to a vapor. Hence the reason why on two identical engines running the same intake manifold flowing the same air through the manifold, the carb will almost always out power the fuelie manifold on the top end. The engine is recieving a denser charge of A/F compared to the injected set-up, but thats purely academic. Toss in things like uneven fuel and air distribution, and the injected intake becomes more attractive. since it at least provides superior fuel distribution compared to the carbed unit which meams more torque at all the points until the carbed intake is moving air sufficiently fast enough to keep things sorted out.

But I digress

anywhosit, the longer you can keep the intake charge cooler, the denser it will be when it enters the combustion chamber (case in point slap a bag of ice on your intake manifold and jump in the car. Its like slapping on a set of underdrive pullies!) On a GT-40 it might not be to bad, but a stock intake or any of the cast aluminum intakes has a large amount of metal to absorb heat with making them into little ovens. Anything you can do to insulate the upper from the lower will help power.

As for adding torque, you aren't really adding any, rather by extending the runners, you lower the point at which resonant tuning occurs (ram tuning as its probably better known). Pumping up the torque down lower making it a bit peakier IMO if the manifold in question has been optimized for the engine.

After doing some math if I remeber correctly, adding 2-1/2" to 2-3/4" of length to a Vic 5.0 efi manifold drops the peak power range by about 1,000 rpm Dont take this relationship to be the same for every runner length, displacement, and engine speed. Typically at lower engine speeds longer runner lengths are needed to produce similar results (if I remeber correctly)

07-18-2001, 12:20 AM	#7
MiracleMax Registered Member Join Date: Apr 1999 Location: Hayes, Va, USA Posts: 798	Whats the rule of thumb? for every 10 degree drop in temp you gain 1 hp or something like that? The problemo with modern fuelie systems is that by placing the fuel metering device right at the intake port you lose the latent cooling ability that gasoline exhibits when changing from a liquid to a vapor. Hence the reason why on two identical engines running the same intake manifold flowing the same air through the manifold, the carb will almost always out power the fuelie manifold on the top end. The engine is recieving a denser charge of A/F compared to the injected set-up, but thats purely academic. Toss in things like uneven fuel and air distribution, and the injected intake becomes more attractive. since it at least provides superior fuel distribution compared to the carbed unit which meams more torque at all the points until the carbed intake is moving air sufficiently fast enough to keep things sorted out. But I digress anywhosit, the longer you can keep the intake charge cooler, the denser it will be when it enters the combustion chamber (case in point slap a bag of ice on your intake manifold and jump in the car. Its like slapping on a set of underdrive pullies!) On a GT-40 it might not be to bad, but a stock intake or any of the cast aluminum intakes has a large amount of metal to absorb heat with making them into little ovens. Anything you can do to insulate the upper from the lower will help power. As for adding torque, you aren't really adding any, rather by extending the runners, you lower the point at which resonant tuning occurs (ram tuning as its probably better known). Pumping up the torque down lower making it a bit peakier IMO if the manifold in question has been optimized for the engine. After doing some math if I remeber correctly, adding 2-1/2" to 2-3/4" of length to a Vic 5.0 efi manifold drops the peak power range by about 1,000 rpm Dont take this relationship to be the same for every runner length, displacement, and engine speed. Typically at lower engine speeds longer runner lengths are needed to produce similar results (if I remeber correctly)