Thoughts on increasing torque on Magnum 318...

Just kicking around an idea here... In the search for more low-end torque from a Magnum 5.2, and knowing that a smaller bore on the throttle body= higher intake air velocity and therefore better low end torque and throttle response, could a 3.9 throttle body (bored to smooth airflow as thefastman does) provide better low end torque? Has anyone tried anything like this? I am wondering if there is a point of diminishing return on the small end of the bore size. Could there be a sweet spot that is lower than the 50mm bore that most of us are currently running? If anyone had a 3.9 TB sitting around that they would be willing to give up for cheap I would be interested in testing this out. ...... I do imagine that top end power would be lower, but how low?? Your thoughts on this can make for some interesting conversation in the least!

Interesting! Can you imagine the velocity of gasses through that TB? The PCM would freak and work like heck to lean you out...

What you need is a towing cam, roller rockers and hardened pushrods from Fastman. Yes it is "going deep". But hey, you wanted torque?!

Also, how about changing your gearset?

HTH

I agree with Volphin. Would look at cam, computer, exhaust,gearing,etc. I think that your computer would be so confused, the engine wouldn't run
at-all. Tried swapping computer from a one-year older truck, and nothing!

Well, a cam, computer, exhaust, etc. are deffinitely things I intend to do in the future to achieve the performance I am looking for, and I am not intending that this would be a replacement mod for any of those. I am just pondering the idea as to what results you would get.
Now as far as the computer goes... correct me if I am wrong, but the Magnum engines are tuned by a "speed density" system, which means that the fueling (based on airflow) and timing are determined based on load and engine RPM. The load is calculated using inputs from the manifold absolute pressure (MAP) sensor, throttle position sensor (TPS), while the airflow is calculated based on these two sensors and the IAT sensor (for air density). Between these inputs and the values in the VE (volumetric efficiency) table, the required fuel can be calculated. The O2 sensor checks to make sure the calculations are correct, and corrects the fuelling if needed. When corrections are made the computer "remembers" the changes, and eventually "learns" what changes need to be made in the VE table.
So... the volumetric efficiency would be decreased slightly by the smaller throttle body, but the computer would still be reading off of the same VE table (thinking the engine has a greater VE than it actually does) and it would tend to run rich... I would think anyway. The computer would learn these changes to the VE table anyway though, via the O2 sensor.

I think that someone needs to try this... Anyone have a 3.9 TB sitting around???

you've put wat too much thought into this, to not do it would be Wrong!
Let us know how it turns out.

Get a wrench. hahaha. I concur, try it. But the PCM is still a simple block learn system. There's more HP in a pda.

I had a 95 Dakota 5.2L with the 5 speed and 3.91 rear end - though I never dyno'd it, it was pretty quick off the block.

My 99 Durango however has been dyno'd and put out 282ft/lbs at the rear wheels (all mods below EXCEPT the Hypertech). From that, I can extrapolate that good air in and a good flow out (headers, Y pipe and exhaust) alone will produce an increase in torque. 1.7RRs or good 1.6 and a cam will do even more.

I thought I remember reading some on here, that helped flat lined the torque curve. I can't remember what its called. They had an article about it, it was on a well built 454 chevy engine. I think it had something to do with increasing the vacuum line pressure. But I can't remember

Get a Comp Extreme Energy 4x4 cam. They have all sorts of bottom end torque.

Originally Posted by lbeenken

Get a Comp Extreme Energy 4x4 cam. They have all sorts of bottom end torque.

Yeah. I don't believe a smaller throttle would net you any torque.
more compression would.

Nonsense!

A smaller throttle body
is just like a large throttle body
with the throttle blades partially closed - no torque advantage.

supercharger!!supercharger

I'm not sure about the torque possibilities, but a guy on one of my other forums modded a v6 tb, and was able to get just about as much horse power and torque from it as he did from his stock v8 tb. He did it to show that the V8 tb swap wasn't really worth doing if you knew how to port tb's with a dremel. In fact I think it is still up on Dakotausa.com. Not sure though.

Jay

Change the cam profile.....