Aluminium Plenum....

DDtB · Post by **DDtB** » Thu Jun 30, 2011 10:39 pm

Just remembered I still have a 111s style aluminium plenum in my garage too....

Worth fitting on a 135 head with cams... And maybe a 4-2-1.... Or totally pointless?!

Dave.

woody · Post by **woody** » Thu Jun 30, 2011 11:01 pm

DDtB wrote:Just remembered I still have a 111s style aluminium plenum in my garage too....

Worth fitting on a 135 head with cams... And maybe a 4-2-1.... Or totally pointless?!

Dave.

Might as well if you've got one?

Post by **campbell** » Thu Jun 30, 2011 11:03 pm

Lotus would have you believe it was worth it. These shipped with the 135 Sport and the 111S.

There is some fluid dynamic principle about the column of air your engine consumes, and making that neither flow too fast or too slow depending on consumption capability. Something about pressure etc, IIRC. I think on your engine there might be some value. On higher tuned engines, they need throttle bodies as a plenum restricts. On lesser tuned engines they need a smaller plenum so that air has the right pressure / flow rate.

Or at least that's what I think I remember Robin telling me once upon a time!

Campbell
(ignorant faction)

Sanjøy · Post by **Sanjøy** » Thu Jun 30, 2011 11:20 pm

You need a NAF.

Stu160 · Post by **Stu160** » Fri Jul 01, 2011 12:04 am

DDtB wrote:Just remembered I still have a 111s style aluminium plenum in my garage too....

Worth fitting on a 135 head with cams... And maybe a 4-2-1.... Or totally pointless?!

Dave.

Totally pointless unless its engraved with your name or something on it

Stu

BiggestNizzy · Post by **BiggestNizzy** » Fri Jul 01, 2011 7:28 am

Stu160 wrote:
DDtB wrote:Just remembered I still have a 111s style aluminium plenum in my garage too....

Worth fitting on a 135 head with cams... And maybe a 4-2-1.... Or totally pointless?!

Dave.

Totally pointless unless its engraved with your name or something on it

Stu

No power gains, but in my opinion they look better. Also don't forget the support bracket.

robin · Post by **robin** » Fri Jul 01, 2011 8:04 am

Unless you're prepared to match the ports to the head then I think it's a waste of time and might even lose you a little in the mid-range.

If the ports are matched to the head then you might still lose a little in the midrange but there are some gains at the top end.

I wouldn't bother.

Cheers,
Robin

DDtB · Post by **DDtB** » Fri Jul 01, 2011 8:11 am

Sorry for being a total dunce... But what do you mean by matching the ports to the head.

Just wondering what the difference is between a 135 from the factory and a standard S1 with a 135 head on it in that respect... Since the factory 135 comes with the ali plenum?

Confused!

woody · Post by **woody** » Fri Jul 01, 2011 8:21 am

DDtB wrote:Sorry for being a total dunce... But what do you mean by matching the ports to the head.

Just wondering what the difference is between a 135 from the factory and a standard S1 with a 135 head on it in that respect... Since the factory 135 comes with the ali plenum?

Confused!

Is it a lotus or aftermarket 135 head you have Dave?

The alloy plenum was designed for the VVC, which has larger inlet ports, and a larger dia. at the inlet opening. When you fit an alloy plenum to a head with standard inlet openings, a step is created between the two; not good for flow. The head opening can be, er, opened out to match the alloy inlet.

Was just looking at the port matching on a 160 head Vs a standard one last night, can get a pic to illustrate the point later. I suspect your head if ported with the standard manifold in mind, will be similar to the 160 mods, but without the opened up ports mouths.

Dominic · Post by **Dominic** » Fri Jul 01, 2011 8:24 am

Mine has a alu (111s styleee) plenum, with matched ports on 135 head. I like it.... no idea what it's like without.

(Now I've said that, Dave will have to go down that route

)

Post by **campbell** » Fri Jul 01, 2011 8:25 am

Matching the ports - Matching the profile of the ports on the plenum to the ports on the head, so that it appears to the airflow to be a set of 4 continuous "pipes" - ie, no irregular surfaces or baffles etc to cause "eddies".

Diffs will be impossible to spot perhaps?

My KR1 head runs with the original placcy plenum (albeit Robin might have filed off some cruft on the outlet ports of the plenum before we re-fitted) and I've never felt the need to change...you can make the plastic shinier than the aly in any case

robin · Post by **robin** » Fri Jul 01, 2011 10:44 am

I don't believe that the factory 135 CNC-machined head has the inlet ports matched to the alloy plenum, despite it being what they shipped with.

Seriously, don't bother.

Cheers,
Robin

Stu160 · Post by **Stu160** » Fri Jul 01, 2011 12:18 pm

Dave, do you not have a picture of your one you can post?

Stu

DDtB · Post by **DDtB** » Fri Jul 01, 2011 8:55 pm

Sounds like a bit of a waste of time then... shame... it's looks ace after Stu 'improved' it.

Guess I'll wait until a time when I can match the ports etc. properly...

woody · Post by **woody** » Sun Jul 03, 2011 8:23 pm

A bare 160 head with port matching Vs a fully standard casting at the bottom.

Scottish Elises