1
Forced Induction / GReddy Plenum vs Modified Factory Plenum
« on: January 13, 2007, 12:43:39 PM »
The lenth of the runners on an efi application is to do with pulse interference from other cylinders. It has the largest impact on light throttle and cruise fuel mixtures when talking forced induction.Once the boost pressure is above '0' then short runners = better. So considering torque is actually highest under boost, a long runner setup isn't going to win any prize against a well designed short runner setup.
An issue with Rb250/25's is the length and volume and restrictive bends in pipework when a FMIC is part of the equation. The response of the motor is down but, by having a forward facing plenum you can get alot of that back and then some.
The Greddy plenum isn't the best design out there if you consider that it lacks 'bell mouths' inside the plenum chamber (it's only cast). This certainly helps off boost response to have them in.As a middle of the road solution Plazamaman makes a very good bolt on unit that retains the longish bottom half factory runners, for improved ecconomy and adds a good volume well designed plenum chamber with bell mouths for improved top end.
There are a number of greddy 'knock off' plenums around and it's too easy to make one given the greddy is only a cast thing with no real attention to machining. They must make huge profit on those things. Number 6 piston is still an issue with the greddy as well. Not a big deal just have your injectors flow tested and slap the biggest flow unit at the back in No 6 position.
An issue with Rb250/25's is the length and volume and restrictive bends in pipework when a FMIC is part of the equation. The response of the motor is down but, by having a forward facing plenum you can get alot of that back and then some.
The Greddy plenum isn't the best design out there if you consider that it lacks 'bell mouths' inside the plenum chamber (it's only cast). This certainly helps off boost response to have them in.As a middle of the road solution Plazamaman makes a very good bolt on unit that retains the longish bottom half factory runners, for improved ecconomy and adds a good volume well designed plenum chamber with bell mouths for improved top end.
There are a number of greddy 'knock off' plenums around and it's too easy to make one given the greddy is only a cast thing with no real attention to machining. They must make huge profit on those things. Number 6 piston is still an issue with the greddy as well. Not a big deal just have your injectors flow tested and slap the biggest flow unit at the back in No 6 position.