Don't expect much from an MSD or Crane box. I can't speak for Jacobs. Check out Mike's thread on Crane's HI-6 box.

Take care,
-Chris

 

I finally measured my t.b. today...it looks like its somewhere around 51, but it was tough to measure with it still on the truck .Ray, you said yours was about 53, so with our margin of error, they appear to be identical.

scott

 

more than likely . i was checking i think where it tapers down at . i can't imagine they'd make it an odd size like that so we are probably more like 50 mm . i check advanced auto in town here and they list both the edelbrock (BBK) TB's but the 56 mm was higher then the 61 mm .. go figure . Mike T superchips vendor says that a larger TB won't help much if nothing is done to the motor (bored out, larger valves ect..) but i know from experience that if you take a stock motor with a 2bbl carb and swap for a 4 bbl carb you get more horsepower . i would think it would be the same with TB's . the more air ya get the computer would compensate with more fuel cause it would sense a lean mix , i.e. more horsepower ? sounds logical to me . i would think all you'd have to do is reset the computer then it would relearn the new air/fuel mix over time and miles . either way i am going to try it as soon as i get the $ to get one . i need to replace mine anyhow since i JB welded it,it is a matter of time before i have other problems with it .

 

FWIW, the 4.9L SD Truck TB has dual 41mm throats, and the 5.0 SD Truck TB has dual 50mm throats. I was always told the 5.0 and 5.8 were the same. I now question that because they have different part numbers. An easy way to find out, RAY, would be to pull the TB on your yard truck, and measure the inside diameter (from the plenum side), or, if you have one handy, measure the gasket.

Now I'm curious. I may just have to take my caliper down to Napa tomorrow and have a look at their gaskets.

Take care,
-Chris

 

every gasket i have bought the holes were bout 1/4 larger then the TB port holes.

 

Hmmm. have you tried measuring the TB on that yard truck from the plenum side? Still curious (but not heading to Napa anymore).

Take care,
-Chris

 

no . it is on the truck . it has been in use to much lately for me to go tearing it apart ....lol

 

my $.02 worth of understanding on the tb thing is that if you only put a tb on w/no other mods that you can slow down the incoming charge of air and actually lose low-end performance. It can help high end when your motor is gasping for air. The 4bbl thing works because you get more jets pumping more gas at the same time you get more air. Kyle Petty once said that he wants a motor that makes power from the bottom to the top. That just doesn't happend. A low-end torquer won't have much top-end and a top-end hp machine won't have much low-end. Manufacturers are starting to get around these problems but it takes hardware and software. Remember the mustang svo in the 80s? It was turbo and had a dual runner intake with butterfly valves. At low rpm when you need the torque the valves shut off the short intake runners and the air came in the long runners. At high rpm the valves flipped and closed the long runners and opened the short. Notice that a truck 5.0 has longer intake runners than a gt 5.0. Two different motors as far as purpose goes. Just my understanding. Catch the new nissan motors in the maxima. dual runner intake, variable valve timing, etc. This is what it takes to get power all the way through. Just wait until the electric valves come out. Then the computer can control lift & duration and no power robbing friction from the valvetrain.

 

That reminds me, would someone please explain to me why it is that runner length, and the resulting engine performance, is the exact opposite between a carburetted engine and a fuel injected engine.

I really want to know.

 

OK all this talk about TB size almost made me pull my intake tube off and measure today. As soon as it cools down I have to check. I though the BBK 56 was listed as direct replacement for my '95, but maybe the intake side of the manifold is bigger than the TB? Then again, maybe the later models have a bigger TB, they got a power rating boost somewhere.


Chris,

Beats the crap out of me. It seems to me a high rise "tunnel ram" type intake would still create more direct air shot to the cylinders. Even though the atomization takes place more or less in the cylinder, you would think the velocity would increase this. But it seems in the mightly high rev HP engines, they all use the short box with injection??


By the way, MM&FF did a piece on the intakes a while back and said except for those extreme high rev apps, that the added torque through the curve allowed by the longer runners still rules.


Any on the question of intakes... what truck used the round port (not staggered) lower intake? I noticed in my Haynes a pic with the upper off, and the lower was a round port. I haven't really paid much attention to other trucks, but my '95 has the staggered rectangular ports.

 

The TB is measured from the inside, meaning from the plenum side, not the intake tube. Hell, it's just 4 more bolts

Take care,
-Chris

 

and another $1.09 gasket ......lol