help with what size throttle bodies to use

[laine etwell]

Can anyone put some light on what size throttle bodies i should have,I changed from the factory set up to the eight throttle 4age silver top 42mm set up, but i dont think its doing the job as these throttles are off a 1600cc engine and my 1uz has been boared to 4300cc.The air displacment is completely different i would have thought.is there a calculator that would work it out.

 

[cribbj]

I seem to remember there's a calculator on Jenvey's website.

I also seem to recall having the butterflies the same area as the intake ports?

Maybe RMS will jump in here and shed some wisdom on this; he's our resident engine builder expert.

 

[rms]

Hi John,
Definately an Ex now, retired to the coast.

I built a 1UZ fitted to a Mazda Miata, 280deg cams - ported heads - std valves - 4AGE TB's ( the smaller of the 2 sizes available ), fitted to New Zealand manifold.

rev limiter set at 8200, 216rwkw and power still on the way up. Max torque was at 6000.
Docile as a pussey cat - very smooth at 2000rpm.

4AGE Tb's seem ideal for a road car.

Erol

 

[laine etwell]

This is a farely modified engine 410 lift 14:1 comp ratio bored and stroked heads ported drysumped with microtech computer 365 bhp.It just seems stange that this set up would generate enough air when it was designed for a 1600,or was it over engineered.

 

[rms]

What makes you think it is "not doing the job" ?

8 - 40mm Tb's will supply over 500bhp
With std valve sizes you will not get anywhere near this figure.

I used 50mm slide throttles on Bob Muir's race engine, it gave 534bhp at 8800 and 338lb/ft at 7800. As the engine was never meant to run below 6000 it did not matter if the throttles were on the large side.
As it was it still had 270lb/ft at 5500.

Don't worry about the Tb's, if you want more "grunt" get some big valves fitted - 36mm inlet 34mm ex.

 

[laine etwell]

the reason im concerned is im making 365 bhp on std injectors and with 50 psi fuel pressure and i cant believe the duty cycle isnt maxed out which led me to believe it was starving air

 

[rms]

What manifold are you using ?
If the Tb's are on the std lower manifold then that is a large restriction.

 

[laine etwell]

iT IS A CAST ALLY MANIFOLD FROM A1 TURBO IN AUCKLAND NZ BUT AS WAS STATED EARLIER ICOMPLETLY OVERLOOKED THE VALVES WHICH ARE STILL STD