Aluminium bigger bore Supersport inlet manifold and plenum

[Toby S]

Hi all

My 1992 1400 Supersport 7 has an aluminium bigger bore "Supersport" embossed inlet manifold and plenum yet my 1998 21 1800 Supersport has an standard rover smaller bore plastic  "injection" unit - I think Caterham stopped doing the aluminium one around 1995/96. I can't help but think this is restricting flow and impacting power - the 1800 Supersport only kicks out circa 140 bhp against the 1400 130 bhp which ain't much for the extra 400cc. 3 questions:-

• Would the larger bore Supersport manifold fit the 1800 engine ? - can't see why not as the Rover units would appear per Rimmer bros to be the same for the 1400, 1600 and 1800 engined Rover cars
• Has anyone fitted the larger bore aluminium Supersport manifold to the 1800 engine and what impact in performance did it have ?
• If answer to Q1 and 2 are positive, does anyone have a "supersport" manifold and plenum they don't need (I know an number of people convert to Jenvey ITB which is the alternative route I'm also considering plus emerald) and would be willing to sell ?

Regards

 

 

[SLR No.77]

One issue you may have is that the 1400 aluminium plenum uses a stepper motor for idle control, fractionally opening the throttle body butterfly. The 1600/1800 plastic plenum uses an IACV (inlet air control valve) which controls idle by allowing air in by a separate route. I don’t think your 1800 ecu will control the stepper motor version.

Although the 1400SS plenum is bigger (the plastic plenum was used by Rover on their 1400 cars) I suspect you’ll find the main limit to engine breathing is the cylinder head itself which was the same across all 14/16/1800 variants.

Stu.

[Miker7]

I've heard the VVC inlet plenums don't match the non VVC heads giving a step on the inlet which impacts performance. Mentioning this just so you check you don't get this accidentally.

[oilyhands]

A bit of clarity.. the VVC manifold is not the same as the earlier SS manifold, also the claimed 130BHP from the 1400 SS is not realistic. The plastic plenum actually works very well, additionally the ally plenum is made for the earlier low port heads and you may find the alignment with the inlet ports on your engine is very poor.  As previously mentioned there is of course the matter of the stepper motor idle control which was changed to an IACV with later engines.

Oily

[Toby S]

Cheers all - Consensus seems to leave as is, so will do - may consider more serious upgrades on the 21 in time (and no doubt will be in touch with you Oily), but will run it for a while and see how I get on