Intake plenum

[kiwican]

In the book How to Improve Your TR6 it mentions increasing the size of the round intake plenum to about 5" dia . Has anyone done this and was there any noticable difference.

 

Is there any advantage to installing a second idle air valve?

 

Thanks

 

Simon

[john.r.davies]

Yes.

Here are some pics, comparing it with an original, and showing the profile.

 

John

[TIMS]

Simon

 

Yes, and on the top of Swiss passes it did make a difference. It has also taken away any plug colour differences on 5 & 6 which I used to have.

 

Just a tip from Malcolm Jones of Prestige. In John's photo's you will see that inside the plenum each of the individual pipes feeding the individual cylinders protrude into the plenum. They are like that for a reason (all to do with swirl patterns into the manifold) do not allow these to be removed, they matter.

 

The guy who did mine removed the end plate, split the plenum at the seam, inserted a new piece which cannot be seen because it is underneath when the unit is fitted, and then fitted a new end plate.

 

Also, unlike John, mine has a full width front end with a large flexi pipe running forward to a large K&N filter.

 

Also look at

 

http://www.tr-register.co.uk/forums/index....2&hl=plenum

 

Regards

 

Tim

Edited September 3, 2009 by TIMS

[john.r.davies]

Thanks for that, Tim. Interesting that you found an improvement at altitude. I've attributed the affect of altitude on performance to the Pi metering unit 'thinking' that lower atmospheric pressure meant a wider open throttle and so delivering a very rich mixture. Near the top of the Col d'Isere, that meant progress in first gear only on a moderate uphill road. If the slightly better breathing that the wider plenum gives can improve that, I'm pleased but surprized. I really only hoped to ensure adequate flow to the rear cylinders, as you also found.

 

I thoroughly agree with your and Malcolm's point on retaining the shape of the intake ducts' opening. Lots of work has beeen done on the semicircular section of that part of the duct and it undoubtedly improves flow. My plenum was made by cutting out that strip of the original plenum with the inlets, retaining the original front opening, but rejecting both end plates. The new body was made by curving a sheet, welding it to the strip with the inlets, and then welding new front and rear end plates.

This method loses the Triumph logo! I've since welded the part of the old plenum that bears the Triumph logo onto the new one, but it doesn't look very original! I suppose that I could cut out a slot and butt weld the original badge in place, but life's too short!

 

John