When should you get a 85mm TB?

flynbrd

Registered User
My motor is built up currently running the bbk 70m tb. In its currenty form the TB is to small for the motor. Motor mods include

77 pro-m, 70mmtb, Embree blower inlet, 95 s-port embree, 12#s of boost, embree manifold inlet and lower ic tube, ported intake, ported heads, bigger exhaust valve,roller rockers, stage 2 dr. fred cam, sccoa headers, 2.5 exhaust dual all the way out, double spearco with shrouded fan, running close to 9:1 comp. Coymiller stage 2 bottom end.

Should I get the 75mm or the 85mm tb and have the inlet ported more?(my porter is real cheap). The car only makes 12" of vacuum at idle and there are no vacuum leaks. The current 70mm tb needs to be opened about 1/4 of inch to get the throttle right due to the air demand from the cam. Any Suggestions?
 
I am not the expert but I would say you would really bennefit from the Magnum powers induction system. SCP is currently running a special on the intake and 85mm throttle body. You really would need the the MP inlet plenum at the same time. What pulley are you running? You might consider the stock 89 pulley or the Embree 5% pulley.

Also if you don't have a tuner already. Consider a chip from Apten. It can make a big difference.



Maybe you should upgrade to a front mount intercooler. Then you could sell me your Spearco Double :)
 
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Oh I want the magnum intake but I just cant afford it. With the 85mm I can always upgrade later to the magnum should I get the funds free. I'm running the 89 pulley which gives me about 12#s of boost. And no you cant have my intercooler :p that monster flows over 1400 cfm and I have a fan in the front and back!(did I menstion the dry ice box too ;) I'm toying with the idea of wrapping the headers to cool the lower ic. Possibly adding a cooling fin that runs down the ic tube then wrapping or coating the tube leaving the fin exposed to transfer heat out. The lower tube gets heat from the header and heat transfer through the manifold inlet.
 
I would wait until I could upgrade the entire intake system if I were you.

You would have to port the heck out of your inlet plenum to make the 85mm fit and you would still be restricted ahead of the throttle body so I don't think it would help much by itself.
 
Id say ya really never need an 85mm TB..Also I dont think you can use it with stock intake...Even ported...Get a 75 and be done
 
Seems like you have other problems beside throttle body size. If you have to open the throttle to get an idle you need to properly set the air bypass and check the IAC to make sure it is functioning and that idle TPS voltage is correct. It may also be a tuning issue.

The 70mm TB is large enough for the stock inlet regardless of modifications or porting. The stock inlet cannot be ported past about 67mm in the neck of it. Porting the mouth is not the solution.

Have you had the car on a dyno or taken it to a track to verify performance?
 
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