Which Junkyard Throttle Body to choose

[JeepsAndGuns]

IIRC, the N* throttle bodies are 75mm units. you'll want a 96-up unit to get away from the ISC motor though.

not sure if that's big enough for you, in theory it should flow ~636cfm.

a twin 52mm TPI/LT1 unit flows ~850-900 cfm. twin 48 are roughly 800.

Heres my findings when I was searching for a TB for my MPI build.

We discussed in this thread several options, and found out a single large blade flows more air than a two smaller ones.
http://www.gearhead-efi.com/Fuel-Inj...e-body-options

I took a clear easy to read ruler with me to the pull a part junk yard and measured a few TB's. I found the 99 and older cadillac northstar tb's have a 73mm blade. The 2000 and newer ones have a 75mm blade. I purchased one of the 00 northstar units witch are just a mirror image of the LS1 tb's. After some trial and error, it was just gonne be too much work to use it, with throttle cable being the biggest part.
I measured several 96+ vortec tb's and all the ones from the 4.3 were 73mm, and had a large air deflector on the underside of the blade. I did find one V8 vortec tb, I noticed the air deflector on the underside of it was half the size of the ones on the 4.3. I measured it and the blade was 75mm. I purchased this tb and I'm using it.
The tb itself has a slight taper under the blade, so I had a machine shop remove the taper so its a straight 75mm all the way through. I then removed the deflector from the blade, but was left with two large holes where it was attached. I then saw the unused northstar tb I had laying there and tried the blade out of it, it fit perfectly and had no holes in it. I just had to slightly slot the holes to match the screws in the vortec shaft.
I have a pic of mine in my "getting closer" thread in the gear heads section.

Nice intake btw.

[RobertISaar]

Whatever you choose, try to ensure it uses a decreasing radius throttle arm.

i take it this is the EFI equivalent of a carb with progressive linkage?

[1project2many]

i take it this is the EFI equivalent of a carb with progressive linkage?

Yes, and even more equivalent to progressive with small primaries.

BTW,Greg, any idea how plenum volume compares to engine displacement on this manifold?

[RobertISaar]

http://mysite.verizon.net/vzezeqah/id1.html

that intake article is about the extent of my knowledge for intake design.

"V8's with one large plenum feeding all 8
cylinders does not work all that well as far as the
Helmholtz resonator goes, but if this is the case, plenum
volume should be about 40-50% of total cylinder
displacement. "

"If a boost is desired in a higher rpm range, closer
7000-7500 rpm, the plenum will need to be 10-15%
smaller. To get a boost in the 2500-3500 rpm range, it
will need to need about 30% larger. "

[EagleMark]

Wow that is a great article! It's in pdf as well!
http://mysite.verizon.net/vzezeqah/s...ionsystems.pdf

Greg came by and grabbed my 75MM single barrel Vortec/LS type TB. He's going to do some measurements and drawings for future but not sure if he is going to use it. Just about the same thing as jeepandguns ended up using.

[gregs78cam]

WOW, lots of questions......

Whatever you choose, try to ensure it uses a decreasing radius throttle arm. The largest percent changes in airflow through a TB occur at the lowest throttle angles. With a constant radius, especially if it's a fairly small one, this means the engine wants to snap to life when you try to leave a light, or an intersection, or when you're trying to cruise at low speed. Sounds like fun but it can get tiring when you have to constantly work to prevent the tires from breaking free and pay attention to not pushing the throttle too hard.

Yes, I completely agree, I experience this everytime I drive the Camaro. I would like to use one that is progressive opening.

BTW,Greg, any idea how plenum volume compares to engine displacement on this manifold?

Well funny you ask. I have been reading alot over at yellowbullet, and studying John Marcella's manifolds (pure works of art - www.yellowbullet.com/forum/showthread.php?t=127750 ), and from what I have read, a good rule of thumb is plenum should match engine displacement. As I was finishing it up last night, er, this morning at 1AM, I decided to check the plenum volume and as it is drawn it is 382.49 cu.in., engine is 385. So during the previous changes to the model, when I had changed the inlet to plenum, and added 1/2" at the back to better contain the runners, I ended with it just about spot on. Runner length and volume will depend on whether I blend the runners into the plenum, or leave them all the same length and flare them inside the plenum. I was shooting for about 6" runner length as that is what the RPM AIR-GAP I have now is supposed to be. As they are drawn they will be between 7" and 9".

Thanks for the info. I need to read all these links and go over the formulas for it. But this is what I love about modeling it first, I can combine available parts with what the design needs and can revise it as many times as I need to get it right, before a single piece of aluminum is cut.

[dave w]

Maybe the option of a late 90's Vortec 454 Throttle Body? U-Haul used the same throttle body on the Vortec 8.1 liter truck engines. The pics are from a 99 454 Vortec.

dave w

[EagleMark]

That throttle body looks just like the one he got from me except no hole in the throttle plate. It measured 74.xx bore on intake side.

[dave w]

That throttle body looks just like the one he got from me except no hole in the throttle plate. It measured 74.xx bore on intake side.

Probably is the same throttle body. I posted the pics to show how the factory kept the intake runners long, with a low profile. The pics also show how the factory was able to increase plenum using the lower plenum for some "free" volume.

dave w

[EagleMark]

It's notworthy to mention the throttle body itself is in middle of intake plenum on the vortec, earlier versions like TPI and LT1 are on front! I had suggested earlier that 2 smaller throttle bodies one on each end would be cool since he is making this from scratch, but seeing how technoligy and design has changed over the years with GM it may be more then just a cool design and unique built intake! Since the vortec is fed in middle makes more sense then one end, I really wonder if feeding from both ends would be even a step above just middle?

If you look at some fomula car engines they are all single injector and single throttle blade fed air. But revving up to 14k rpm is another world...

[gregs78cam]

Yup, those are some really long runners. I like the packaging, but I don't know if I want that long of runners. With the setup I have on the car right now, the added plenum volume of the dual TBI adapter did raise the top end of the engine a bit. It pulls easily to 6K now instead of hitting a wall at 5500, and that is what I was hoping for. I think the design I have so far is going to work really well. I am very happy with the runner size, shape, volume, and injector placement. I may need to put more taper in the plenum from front to back. I just wish I could find shorter injectors. I am watching some on Ebay, but wow, they are expensive. It looks like you can't give away 24lb'ers, but I need 40+lbs. Do you happen to know what the 8.1L injectors flow? I haven't found any concrete numbers.

[dave w]

Do you happen to know what the 8.1L injectors flow? I haven't found any concrete numbers.

I did a homemade flow test of the Vortec 454 injectors using a stop watch and a large cc syringe, and came up with about 19 lbs at 45 psi (3 samples on each of the 8 injectors). The '7730 ECM I used to run the Vortech 454 on the stand seemed to like about 20 ~ 21 lbs for injector flow. I don't know what the 8.1 liter used.

dave w

[JeepsAndGuns]

While on the subject of dual TB's, ever pay attention to the gen 1 vipers V10? They had two TB's, one on each side feeding each cyl bank, and they were tied together with a shaft to make them both open equily.

[gregs78cam]

While on the subject of dual TB's, ever pay attention to the gen 1 vipers V10? They had two TB's, one on each side feeding each cyl bank, and they were tied together with a shaft to make them both open equily.

The Nissan VG30DE in my avatar was the same way. It adds to the complexity but may be cheaper to get two smaller TB's from pullNsave.

[EagleMark]

Well you seem to do everything dual?

How about 8 one barrel TBI units hooked to a LT1 sequential PCM? No plenum!