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WydRyd's Avatar
 
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Question How effective are larger TB's?

Curious, how effective are larger throttle body upgrades?

I mean, would a 3mm larger throttle body REALLY make a noticeable difference to throttle response and top end power?

Just looking for some real world experiences from you guys who have gone down this path.

I'm expecting my bored TB from Protomotive shortly and am just wondering what to expect.
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Merv
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
Old 04-18-2007, 04:44 PM
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Merv, last fall I posted a pressure test showing 1.5 psi differential across my 63mm Carrera TB at 10 psi boost measured in the intake manifold. So in effect I was making 11.5 psi boost prior to the TB in order to get 10 psi in the intake manifold. I believe this loss restriction get exponentially worse as either the flow rate or charge density increases for a given throttlebody restriction (technically called an orifice) and I think you run higher boost than me.

I've only driven my car once since installing my 76mm throttlebody and now I have no measurable loss.

Your change of 3mm equates to 10% more aperature area, this can only be a good!

For interest sake, I recall calculating that my intake charge velocity in my 76mm TB would be 212mph at 1 bar. Bet it's lots higher at 63mm.
Old 04-19-2007, 09:34 AM
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Thanks for the feedback Jim. I believe the Protomotive TB is 68.5mm, as opposed to the OEM 65.5mm TB. I'm looking forward to seeing/feeling the difference with the bigger TB
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Merv
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
Old 04-19-2007, 05:46 PM
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I am running a Wilson-Mustang 75mm TB on my car, I hope that what your saying Jim is true as people have been telling me that it is not worth running something that big.
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Old 04-19-2007, 08:18 PM
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Like Jim wrote, it's a pressure loss issue not an actual limit to flow. The bigger you go, the less control you have over intake flow since the throttle body is a control valve. A general rule of thumb is to keep the intake velocity below 300 ft/sec. I calculated the velocity through my stock Carrera TB to be right at 300 ft/s at max power so I decided to keep it so I'd have good low speed drivability.
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Old 04-20-2007, 08:06 AM
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930gt A couple things to think about. Each component upstream of your turbo which results in a flow loss means you have to make the turbo work harder to get the charge into the cylinder: inlet charge tubing (especially 90 degree elbows), intercooler tanks and core, throttle body, intake manifold, port, valve...

The throttlebody is one item which can be somewhat easily changed. If the turbo is producing say 19 psi to achieve 15 psi at the intake manifold (assume 2 psi drop for the I/C and 2 for the TB), it means the turbo discharge temp is going to be higher, there will be more exhaust back-pressure and cylinder dilution as a result of the turbo working harder, there will be a little less temp drop from the intercooler now that the charge temp is higher, and of course the turbo will take a more time to spool to 19 psi.

My objective with was to have the same cross section area as the inlet plumbing leading up to the throttlebody, even accounted for the butterfly shaft area. On first drive I noticed the throttle is more sensitive at low openings but I had no problems driving. If needed you could rework the arm geometry on the the butterfly to alter the throttle opening rate.
Old 04-20-2007, 09:29 AM
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Marco at Billet design makes adapter plates for this. You will run a mustang throttle body. I have a race version of an accufab 80mm on my car that opens up to 105mm. All other cars step up the throttle body size with power....Porsches should as well
Old 05-10-2007, 08:19 PM
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I had my buddy make one out of aluminum and he said that he could reproduce them for 20 dollars. its a pretty good design. Im running the 75mm just to keep the vacuum good.
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86' 930/GT-40R Sold
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2008 C6/Z51 Corvette
Old 05-11-2007, 06:32 AM
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Cant beat twenty bucks Were you the guy at Jimmys shop?
Old 05-11-2007, 11:04 AM
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Yes I was, How are you?
Im not doing so hot with my car. I had J-jr. come and tune my car and my intercooler end tanks were fabbed all wrong. Job is nasty at tuning and very professional. my inter cooler was sooo wrong that i had 200 degree intake air temps at 15 psi. So I got a friend thats going to do the tanks the right way though and then bonsai- I crank her to 22 and see what happens.
400 horse @ 15 psi and 200 degree intake air temp.
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86' 930/GT-40R Sold
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2008 C6/Z51 Corvette
Old 05-11-2007, 07:02 PM
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That sucks! I am sure you will get it worked out! Hopefully Jimmy has mine up and running very soon
Old 05-13-2007, 08:52 AM
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That is going to be one hell of a car when it is done.
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Kris @ Tech9
86' 930/GT-40R Sold
94' Rustang GT daily (long gone)
2008 C6/Z51 Corvette
Old 05-13-2007, 08:53 PM
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send me a PM with your messenger name if you are on one like MSN or AIM. Merv how is the car running?
Old 05-20-2007, 09:19 AM
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Eric, the car runs great, but it'll be better with the bored TB... just waiting on Proto to supply me with one.
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Merv
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
Old 05-20-2007, 02:56 PM
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