3.9 V8i intake manifold

[QUOTE=PhilipA;1296364]I sometimes get boondoggled how threads about increasing low down power get hijacked into threads about increasing horsepower when it is quite obvious that the manifolds shown are for high end power in sports cars not low end torque in 4WDs.

What you want in a road vehicle is ''driveability'',not all out power.As Larry Perkins once said,Horsepower sells engines but torque wins races. Pat

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Originally Posted by cockie55

Hey Big Jon did you ever get around to putting this spacer on top of your manifold??

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I haven't been home yet! I am three weeks into a four week work stint.
I was in the NT, now I am in WA.

Just to add my two bob's worth. Do any of you remember the big block Chev's used in the McLaren Canam sports-racing cars? They used unequal length ram tubes to smooth out the peaks and valleys in the torque curve of a ram tuned induction system. From memory they used two each of four different lengths. I also remember they used Crower fuel injection with big monster throttle butterflies of almost 3" diameter. They were supposed to have a near smooth torque curve from 3500 rpm up to 7500-8000.

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Originally Posted by BigJon

I have read that the length of the intake runners in the intake manifold has a bearing on where in the rev range torque is made.
The later design intake manifolds have longer runners than the early type and the torque curve is correspondingly lower. PhilipA has made comments that fitting the later style manifold transformed his 3.9 engines characteristics.

I have a spare intake manifold for my 3.9 and I have been having a thought (dangerous, I know :D).

Would there be a worthwhile improvement to bottom end torque if I got 8 longer trumpets made up (say 30mm longer) and had a spacer made to lift the top part of the manifold to give clearance for the longer trumpets?

I have room under the bonnet for it all to fit (30 mm body lift). Would the correspondingly larger volume of the plenum chamber have a significant effect?

How would I go about making the spacer? I would imagine the trumpets would be the easy part (just weld a section of correct size pipe on the bottom, all the trumpets start the same length, they just sit in different depth holes).

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I always think adding cubic inches is usually the cheapest and best modification for a daily driver/street car. You are pushing a two ton brick with a small engine. Bung in something with six or more litres. Think of the beast on your avatar.

Thanks Jakeslouw for the tip. I bought that bottom halve of the Thor intake manifold (as I have the Plenum & Throttle body but nothing else)

PhilipA you can now see the direction I am going with the Thor manifold (so I will be in touch)

If you have a look at the book "Tuning Rover V8 engines" by David Hardcastle you will note that JE Motors did some experimenting with plenum trumpets.
Cheers;)

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If you have a look at the book "Tuning Rover V8 engines" by David Hardcastle you will note that JE Motors did some experimenting with plenum trumpets.
Cheers;)

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Yes, they used to do a lot of work on the old plenums but mostly for high performance. Most of the trumpets are shorter and bigger which is for high end.
If you look at the picture on Page 182 with different length trumpets , they have individual throttle bodies and no plenum.

I actually fitted a Federal injection (P170-171) to a 77 Range Rover, and the results were good as far as economy and driveability went but little more power. Really not worth the considerable effort and expense in hindsight. It just reminded me seeing it in the same section.LOL

Regards Philip A