Determining TB size?

chevymuscle218 · 01-09-2009, 11:03 PM

How do I know what size TB to use? Is there some rule of thumb?

Bad99Olds · 01-09-2009, 11:09 PM

boosted or n/a?

chevymuscle218 · 01-09-2009, 11:18 PM

n/a, and for now no mods. My LIMG is leaking so i have to tear it apart anyways so i'm thinking intake,ported upper and lower manifold, TB, and headers. Also i'm due for a tune up, so better plugs and plug wires!. That is if the boss even lets me go that far....

Gr1m · 01-09-2009, 11:20 PM

with the future mods you just listed, your probably looking at a 65mm TB

Bad99Olds · 01-09-2009, 11:20 PM

a lot of guys on here who port their manis opt for the 65mm.

chevymuscle218 · 01-09-2009, 11:23 PM

oh yah, and would i have to get the pcm reworked or anything? I'm new to fuel injection performance. Only messed with carbed motors...

Bad99Olds · 01-09-2009, 11:43 PM

i mean ur adjusting the a:f ratio, so some sort of tuning would be necissary to maximize performance and see the bennefit of the mods

alerored04 · 01-09-2009, 11:49 PM

It would run fine without a tune but in order to see the best gains from it tuning would help. Other than that I would go with a 65mm. Some say that it is too large but it leaves room for more later if you choose to boost. I have a TCE 65mm along with p&p heads and manifolds. You will love it. If you do go with a ported UIM and a 65mm make sure to get the UIM plenum bored to 65mm to match the TB.

01-10-2009, 12:43 PM

In all seriousness, unless you are planning on porting the heads and/or camming it, there's really no reason to go bigger than 62mm.

alerored04 · 01-10-2009, 01:01 PM

The reason I say to go with a 65mm is that when I purchased my TB I had no intentions of camming mine either. I was planning on getting a 62 but Ben was sold out so I got a 65. It worked out in the end since I did cam the motor and am planning on boost. My point is that everyone doesn't have a plan for the car, they just purchase parts in the order that they are practical, this way it leaves him better options in the future. But I agree with you, if he will never go further than this then a 62mm is plenty.

AleroB888 · 01-10-2009, 01:53 PM

Quote:

Originally Posted by chevymuscle218

How do I know what size TB to use? Is there some rule of thumb?

Anything in the intake path that causes a pressure drop at WOT will lose power in proportion to that amount, provided the AFR remains the same.

That would apply to air filters, MAF sensor, TB, intake tubing, intercooler.
If measured upstream of a Turbo or SC, the increase in vacuum is calculated, downstream it would be a loss of boost pressure.

WhiteV6 · 01-10-2009, 08:02 PM

There is no reason to go 62 over 65. The computer will take the extra flow into account with the stock ecm, though I would go with a MPRacing tune on it if you do anything. There is no drivability issue between 62 to 65 on a 3400, even stock with a ported upper to match the throttle body opening.

chevymuscle218 · 01-10-2009, 08:42 PM

I would love to do a 3500 top swap :P My uncle is a manager at a junk yard so maybe he can get me a good deal....will any 3500 head work? Then maybe the 65 mm would be better?

chevymuscle218 · 01-10-2009, 08:49 PM

Quote:

Originally Posted by AleroB888

Anything in the intake path that causes a pressure drop at WOT will lose power in proportion to that amount, provided the AFR remains the same.

That would apply to air filters, MAF sensor, TB, intake tubing, intercooler.
If measured upstream of a Turbo or SC, the increase in vacuum is calculated, downstream it would be a loss of boost pressure.

laymens terms?

Bad99Olds · 01-10-2009, 08:56 PM

in laymens terms,

anything along the path that the air enteres the engine, maf, filter, tb, etc, that causes the pressure to drop at wide open throttle, will casue a loss of power that is proprotional to the amount of the drop in pressure, assuming the air to fuel ratio reamins constant.

if the drop is measured upstream of a turbo/sc, the increase in vacuum is calculated, if its downstream its a lost of boost pressure.

Cliff8928 · 01-11-2009, 12:23 AM

In even more laymens terms. Your engine will only flow as much air as it's most restrictive component.

WhiteV6 · 01-11-2009, 12:35 AM

In layments terms, the resistance to flow starts at the throttle body. 65mm is smaller than your MAF and there is a noticable flow increase on a stock head and lower with a ported upper for a 65mm TB. It becomes even greater with ported heads and manifolds.

The throttle body feeds the plenum, which feeds the runners. The smaller the plenum, the larger the throttle body needs to be. The 3500 has more plenum area and a larger throttle body, which gives it a far greater breathing ability than the 3400 upper. 65mm on a 3400 upper helps with the smaller plenum area.

Redog · 01-11-2009, 12:59 AM

What about camming it.

I have a 62 and I'm putting in new P&P manifolds soon. The upper is ported to 62, the upper I have right now I don't think is ported to 62, but in the future I'm planning on putting in a set of P&P heads and a cam (still trying to decied if I'm going with a 1161 or a 1280. I know Ben can answer that question when the time comes) but is the 3mm going to make that much of a difference? The LIM I have is gaskest matched

WhiteV6 · 01-11-2009, 07:38 PM

Its not a huge difference between 62 to 65 so I wouldn't look to upgrade that any time soon. If you had a stock unit then I would say 65 over 62 for the 3-4 extra hp it would give you.