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Discussion Starter #1
I was going to search for this type of question but didnt know how to word it to my specifications I have been thinking of ways recently to help out with spool time on my precison 5431 E on my d15 and I thought about a GSR throttle body or some B series throttle body. I guess im just wondering if its worth it to improve spool time for the money and see if I need to get back on the dyno or not. Right now its a z6 intake manifold and throttle body, Thanks.
 

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Less than 12 hours.
A tb is about 20$,on cl.
Go try it. Watch wideband for leanness.
Make sure the IM TB hole is a mm or two larger dia
 

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Air under pressure moves the same amount of molecules in a smaller space, so a turbocharged engine doesn't need a huge TB. A 62mm TB on a 200whp NA engine might be restrictive while a 58mm TB on a 200whp engine at 15psi will flow more than enough.

You won't need more than a D16's 58mm throttle body until you max out those injectors. Gains from a 60mm TB won't be noticable, and may cause a loss if you don't enlarge the manifold opening to at least the TB size.
 

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Larger throttle bodies on most D-series turbo setups that aren't really silly are just a mind-game. A stock 56mm throttle body flows more than enough air at reasonable velocities to support about 320HP (not WHP). Larger throttle bodies mostly don't effect power, they do effect feel of the engine. Supposedly the "better throttle response" is simply from the fact that with the greater CSA but normally unaltered opening angle (with respect to the throttle position) allows more air to flow sooner. You can get the same effect from opening the throttle pedal faster with a smaller throttle body. You also loose precision throttle modulation with too large a TB.

The biggest thing that most guys don't seem to understand (and I'm still struggling to have more than just a cursory understanding) is the relationship between plenum volume and throttle body sizing. Boost complicates this some, but the relationships are generally the same as with NA engines.

For boosted engines, there isn't much reason to go bigger than a stock 60mm TB on smaller engines like the D, unless you were building a max effort drag race only engine. 60mm is large enough to support over 500HP (though if you were going for more than that, going larger wouldn't hurt).

Bottom line is that on a D, the TB size isn't really much of an issue and certainly not much of a hindrance on spool time.
 

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Go with what they said and stick with a stock B series sized tbrottlebody. Going to far oversize can end up costing you all over the place. The previous owner of my 195hp NA car put what was either a 68 or 70mm throttlebody on it and switching back to a stock 60mm made low and mid response SO much better, and while the but dyno can lie, it felt the same or better on the high end too.
 

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Discussion Starter #7
I appreciate the responses and school lesson as always guys lol. Sounds good I figured it would be worth the shot cuz GSR throttle bodies and what not are pretty cheap but ill just pass im trying to save up everything I can for my next build. Its good to know what works on these engines and what just flat out doesnt.
 

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I see no harm in a larger throttle body and the supporting mods behind it. Especially when a B/H series t/b is so cheap and abundant and are completely bolt on

I aswell have a z6 manifold which I feel is the better of the stock manifolds, I also grabbed a clean H22 60 something millimeter throttle body for $30 at the junkyard. Complete bolt on.

Took 2 hours of my time and gasket matched the ports, and openned up the t/b opening 2mm bigger than the t/b. Which I believe would give nice gains and improve flow. Gave the t/b and intake mani a scrubbing with a can of carb cleaner and a scotchbrite pad and it looks brand new.

I also got a thermal intake and t/b gasket which drastically reduces heat soak, and pays for itself times over with the simple fact that you can re-use them again and again. I used to heatsoak to 160* after parking without the gaskets, cut it down to below 110*

60+mm also matches the ID of 2.5" intercooler piping alot better, getting rid of the bottle neck. H22 t/b and a carbide bit (under $50 bucks spent) and youre on your way. Give it a shot!
 
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