Largest bolt-on stock TB for a 3400?

[BMC]

I am playing around with a 3400 TB that i have bolted up to a 'L32' 3.4L V6 intake with an adapter plate. The 3400 TB is 56mm and looking for some larger OEM types- say 58mm maybe.

Are there any larger than 56mm that are direct replacements or similar?

[Nick-G]

Just get a 65mm from the store. If you are using a stock 3400 tb then this one will bolt right up.

[IsaacHayes]

Only other would be LX5 which is 65mm. You'll need to port the intake to match either way. And that may be your limit.

I'm not aware of anything inbetween 56mm and 65mm. Unless maybe from a 4banger car possibly. I have not looked into those engines yet for TB sizes.

[BMC]

Good ideas guys but a few points of problems:

First: We are trying to keep this cheap factory bolt on parts that require little to nothing to modify to install.

Second: The L32 manifold is about 2.5" O.D. which equals about 65mm. That means that by the time you port the intake out large enough, you have no manifold left! LOL!

We are trying to avoid doing something that requires welding but if we were going that route, a number of people have installed the LT1 twin 48mm throttle body.

From simple size potential, a person should be able to use a 58mm TB and maybe go up to 60mm. As far as diminishing returns when used on the iron heads that are unported with a stock cam, I am not sure but fairly certain that the larger TB should give a little gain. I will be running some tests when the manifold is ready to switch- same day vacuum tests- before and after stock vs. modified. It would be neat to see a 3 or 4 BHP power gain at the flywheel but will only be doing vacuum tests for this round.

BTW: Isn't the LX5 the early 3500 and thats a drive by wire TB?

-BMC.

[IsaacHayes]

LX9 is the Non-VVT 3500. All 3500's have drive by wire. The LX5 is the 3.5L DOHC oldsmobile Intrique/Aurora motor. Which is MPFI not SFI believe it or not! LOL. I just thought that was weird. The TB even has it cast on there.

I'm running LA1, LX9, and LX5 parts on my L82! haha That is 3400 lower intake, with 3500 upper intake, and 3.5L DOHC TB, on my 1994 3100. Well, almost have the TB on, just need to weld the cable bracket and it's done.

[SappySE107]

Are you sure its worthwhile to do a larger TB on an iron head 3.4 intake manifold?

[BMC]

Isaac,
Thanks for the info. What years did the 3.5L DOHC come out? I will look for one. Have any pictures? I would like to keep the information for other projects.

Ben,
Sure? No. I suspect that most people are unsure without pulling off some tests on any engine. A few years back, a number of guys were installing the dual 48mm TB off LT1 engines and claiming gains. To me, without something to back that up, it sounds a little extreme.

The stock manifold is not cleaned up well enough from the factory and that is the first thing any L32 owner should do is just clean the manifold up and port match it to the stock TB, but my thought is that with the cam and head improvements that have been done to these, a bump in the TB size would be beneficial.

65mm? No. I think that would have no gain on an otherwise stock engine even if it would fit.

We will find out.

-BMC.

[IsaacHayes]

The 3.5 is in 1999-2002 Oldsmobile Intrigue and in 2001-2002 Oldsmobile Aurora. Then you have the 4.3L truck engine TB, it's 70mm, then you have the 75mm northstar TB. Smaller than the 65mm, I don't know, other than 3400 at 56mm. There may be some GM 4 banger with a TB in between that size though. I just have not looked into it.

http://isaachayes.60degreev6.com/throttlebody/

More pics in that directory too. 65mm is the same opening as my 3500 (LX9) plenum.

[BillS]

Second: The L32 manifold is about 2.5" O.D. which equals about 65mm. That means that by the time you port the intake out large enough, you have no manifold left! LOL!
From simple size potential, a person should be able to use a 58mm TB and maybe go up to 60mm. As far as diminishing returns when used on the iron heads that are unported with a stock cam, I am not sure but fairly certain that the larger TB should give a little gain.
-BMC.

I agree. I managed to use a 62 mm. on my L32 plenum, but that is THE maximum and even at that we broke through on one side of the casting when blending the two together. There just isn't enough meat in the plenum for more, and I don't think you'd get ANY benefit on a stock engine anyway. In fact I wonder how much benefit you get going any bigger than stock on a stock engine - anyone got any hard facts on that?

[IsaacHayes]

On my 3100, the heads and cam are stock, as well as the restrictive stock exhaust and original cat right now. I went from a 52mm to 65mm. Of course I also have the larger 3400 lower intake and 3500 upper intake. As the ECM is learning it seems less on/off that when I first put it on. And the ECM is always pulling fuel not adding it ever to my mods, which I find odd. Perhaps the way I have my definition that scans it is backwards?? I need to look into that.

But I do feel a gain at WOT. Easiest way I noticed is on the highway going WOT the car moves much faster. I don't know if this is due to the motor needing the extra air or that there is less turbulence since it's not going from 52mm to 65mm opening anymore. When I had a 56mm on over the 52mm I did not notice any difference in power.

The 65m also just seems to help out cruising. Yes there is more air now per throttle angle, but before when it was stock, you would give it gas up say a hill, and the motor would bog, give it more gas, same thing, then it would downshift and pull. Now it will pull up the hill with less throttle and not have to downshift. So I guess the motor was not bogging, but just not getting enough air, and that the stock downshift points were set maybe too soon.

Since the large port lower and 3500 plenum swap with the 52mm TB it seemed to stop accelerating harder from 70-100%. Something you think a larger TB would do. With the 65mm now it feels I have more resolution. I can go from 70-100 and it pulls harder when I snap it open fully.

Granted this is all un-tuned and maybe some of the bad points of the 52mm could have been tuned out after the large intake swaps, but the 65mm addition seems to help that stuff.

The motor sounds more "healthy" now too. Before it sounded higher pitched, and just nasty the whole RPM range, like it was really under load. Now it has a more smoother and less harsh/loud "larger" motor sound, even at WOT.

I do notice that off the line torque seems to be less, as I can't light up the tires from a stop like I used to. But it seems to take off faster off the line... ???? I guess I have less torque but more HP down low now. Is this possible? (I'm assuming tuning could help this as well though). Before it would spin them and then slowly take off and then start going. Now it just takes off and pull you back from the start smoothly, instead of going slow then pulling you back later. I'm guessing over all torque isn't that much lower (or isn't shifted too higher) as I can pull hills that required downshifting previously.

More and more as the ECM adjusts it seems to feel more like stock. Or I'm used to it. It's by no means too touchy. It actually feels more like other cars I've drove.

Also I noticed I no longer feel the TB wanting to close on it's own. Let me explain. Before at certain RPM/Loads/Temps/etc I could be pressing on the pedal and feel it get stiffer. At those times the motor was really responsive when you cracked past that position. This makes me think that the motor was pulling air so hard at this point that it was pulling on the bottom of the plate with the air flow or the air flow was hitting there hard, wanting to push it closed. To me that sounds like a bottle neck if it's trying to suck that hard through the small TB opening that the velocity is that high there.... I don't get that anymore with the 65mm, or at least haven't felt it yet.

[hookdonspeed]

does the 4.3l truck throttlebody share the bolt pattern with the 4bolt 3500 or the 2bolt 3400's by chance?

[asylummotorsports]

How big do you think you need?

I went from a bored and sleeved 62mm to a TCE 65mm on my 3500 and it picked up nothing, other than some better idle and drivability issues.

[IsaacHayes]

4.3 TB is same as 5.3 IIRC, which is a 3bolt pattern.

[hookdonspeed]

How big do you think you need?

I went from a bored and sleeved 62mm to a TCE 65mm on my 3500 and it picked up nothing, other than some better idle and drivability issues.

i just wanted to get as close to stock as i could... still have that 62mm? wana sell? :P

[asylummotorsports]

I actually had it listed for sale for a while and didn't get much interest.

It's a 56mm Quad 4 TB bored and sleeved to 62mm.

Would best be suited for a manual trans application as the kickdown/cruise control linkage, at least on my car was a nightmare, although I do have the throttle box and the cables to make it all work.

The problem is I paid almost $250 to have it modded, (www.mrzperformance.com) not that I am dillusional and think for a moment I can get that much for it, but I'd like to see $100 plus shipping.

If you want the cables and the Grand Am throttle box, we can discuss it. They are really hard to find evidently.

asylummotorsports@yahoo.ca