1.6 K-series Plenum

[Vimes]

I race a 1.6 K-series with closed regs but it allows either the standard plastic plenum & TB or the aluminium VVC & 52mm TB.

I have both and currently run the VVC plenum but have heard it’s perhaps too large and might just be loosing torque without adding much/any top end?

Any experience of trying both and at what point the vvc plenum helps rather than hinders?

Engine specs:
- 1600k
- Supersport cams
- forged pistons
- MEMS ECU with SS map
- solid lifters
- 7500rpm limit
Bhp circa 140bhp

Edited by Vimes on Saturday 1st February 13:52

[Olas]

Without back-to-back dunk tests it’s hard to say, but as a general rule the smaller plastic manifold will be bias toward lower rpm and the larger aluminium manifold biased toward higher rpm - matching the component to the desired usage pattern is important, think about how many rpms you race at and select the appropriate part.

Area under curve will be very similar, just the distribution of the area will change.

[DVandrews]

The aluminium plenum is a very poor fit to the inlet ports on a stock head and it leaves a 3-4mm step which creates a lot of turbulence. This is a HP sapper it may also affect the torque as its capacity is too large.

[Vimes]

DVandrews said:

The aluminium plenum is a very poor fit to the inlet ports on a stock head and it leaves a 3-4mm step which creates a lot of turbulence. This is a HP sapper it may also affect the torque as its capacity is too large.

Thanks, I was hoping you might answer

It is a stock head (as per regulations) so I’ll look to swap back to the plastic plenum.

Just to clarify, is there any chance the VVC plenum makes more power right at the top end or is it just a bad idea full stop?

[andy97]

DVandrews said:

The aluminium plenum is a very poor fit to the inlet ports on a stock head and it leaves a 3-4mm step which creates a lot of turbulence. This is a HP sapper it may also affect the torque as its capacity is too large.

Dave, is there a recommended “solution”, particularly for those who don’t need to comply with “closed regs”, preferably without going for ITBs etc etc.

[DVandrews]

The VVC plenum can be effective if the heads inlet ports are matched correctly and the engine has been upgraded, on a stock engine it is likely to just lose some mid range torque even if matched. The plastic plenum can be very effective if the interior flashing in the ports is cleaned up and the edges around the TB entrance are radiused. Interestingly the VVC plenum is also a poor fit to the VVC inlet ports for which it was designed... although not as bad as with the stock head.

Below is a template of the VVC plenum laid over the inlet ports of a stock cylinder head

[andy97]

Many Thanks

Andy