I'm going to post this one more time so that everyone here can take a pen and paper and write it down.
****This is for those that think the 3L parts flow better than SVT*****
Not!
Nupe. This is for your information so that you can make an educated decision on which parts to use.
The SVT lower IM is bored the same size as a 3L and then xtrude honed. It uses the same secondary butterfly valves and in reality it should flow better.
The SVT upper IM is xtrude honed and both passages are larger than the 3L upper.
Dimensions are as follows:
2.5 SVT UPPER
inlet at the throttle body = 67mm
outlet port primary runner = 30.5-31.2mm, ~31mm on average.
outlet port secondary runner = 32.8-33mm ~33mm average
SVT lower IM
primary runner inlet = 33.5 mm
primary runner exit = 32.7 mm
secondary runner inlet = 36 mm
secondary runner exit = 34 mm
3L upper IM (casting flash gives small variation)
inlet at throttle body = 63.75mm
primary runner exit = 30-30.3mm, ~30mm average
secondary runner exit = 31.8-32mm, ~32mm avg.
3L lower IM
primary runner inlet = 33.4-33.5mm, ~33.5mm avg.
primary runner exit = 32.75mm
secondary runner inlet = 35mm
secondary runner exit = 32.75mm
As far as SVT vs. 3L heads are concerned:
SVT primary inlet runners are roughly the same diameter as the 3L but narrow slightly to fit the 32mm valve seats at the combustion chamber.
SVT secondary inlet runners are approximately the same size at the inlet, but neck down considerably to fit the 32mm valves again.
The conclusion would be to use 01 3L heads and have them xtrude honed for best results along with all other SVT components. Using the 2.5L heads and installing the 3L valves with some moderate porting will accomplish exactly the same thing (if you don't count the lack of the extra oil return passage) and should be cheaper.
It all depends on who is doing the work and what it costs.
For someone who is not afraid of a little experimentation: Try using 35mm intakes and 32mm exhausts. The simulation programs show very good results with this setup and the 3L engine.
Using the 2.5L heads and keeping the compression around 10.5:1 with the bigger valves shows some pretty serious torque.
You may ask what I have concluded from all this.
Well, all SVT components flow better than 3L components. The xtrude hone more than makes up for the 3L intake passages being a bit larger because of the roughness.
The RESTRICTION as it is known is IMHO the valves, and it is the exhaust valves to be more specific.
warmonger
