Intake manifold fabrication

[GavinT]

SO now I'm thinking four straight pipes with four single barrel motorcycle carbs.  No bends.  Gotta figure out how to size carbs, but a cycle of 800cc going at 12,000 RPM is the same as a 1,600cc at 6,000 RPM in flow rate.  I have to think aabout pipe diameter though.

Do a search on "Jay Mitchell" at the Yahoo list.
I'm pretty sure he did a motorcycle carb conversion - Mikuni, I think.

[RoddyMac]

I'm running Keihins off a Honda CBR900 (or Fireblade depending on where you ), though they are hung off the side of a Zetec.  They were selected as they were cheaper than DCOE's, and supposedly they were more tractable than DCOE's.  I can't say for certain they are more tractable, but they are very smooth once I sorted out the idle jet size.

The manifold was made from steel plate for the flange, and cut & shut steel mandrel bends.  I did smooth the welds on the insides of the runners, but I'm sure I could have made them even smoother if I spent more time.

[TurboFource]

Are they 38mm? What did you end up with for jet sizes? I have a set off a CBR1000R

[RoddyMac]

They're 38 mm. The mains are at 1.6 with the needle in the center position and the idle jets are I think 55's.

[TurboFource]

Roddymac, awesome drivetrain and chassis!

[shootingsight]

I put together an excel sheet that lets me enter plenum volume, runner length, runner cross-section, and it uses the Helmholz formula to calculate the resonant frequency.  I've come up with two solutions:

1.  Resonance at 3,000 RPM, which will have a secondary resonance at 6,000.
2.  Resonance at 6,000 RPM.

I then went to the hardware store and for about $50 I bought PVC drainpipe.  If I build this as one big diameter pipe, running parallel with the crank, and have four runners, kind of like what is pictured, I can actually measure the resonances, plus it will be easy to build.  At issue is that the 3,000 RPM has to be a lot bigger to get the lower frequency.  I could then look at space and mount the DCOE either fore/aft or sideways.

[Gmg31]

This is probably too late but I noticed that when I made a post on this thread I uploaded the wrong photo sorry.  This is the else version

[Broadside]

This is probably too late but I noticed that when I made a post on this thread I uploaded the wrong photo sorry.  This is the else version

Not wishing to hi-jack this thread, but I have an Else manifold and a tubular 4 branch exhaust, does anyone have experience on what sort of gains can be made with just the Weber 40 and exhaust (ie without any engine work)?
My guess would be 10-15 bhp max..........

[jbcollier]

Needs a cam at a minimum.  Port matching would be nice as well.  40 is a bit small.  45 would be better.

[Sandyman]

JB, if he only did the intake and exhaust what HP gain could be expected?

[shootingsight]

I found a pretty good page on sizing the carbs.

https://archive.cnx.org/contents/a0a6da11-6437-404f-8cd3-10853a08b685@2/selection-and-tuning-of-weber-dcoe-carburetors

They happen to use a 1600cc ford engine with peak 6500 RPM as one of their illustrations, so a lot of it applies directly to my case of the wedge Renault R16.

[jbcollier]

How much more is hard to say.  When most people say they want more power, what they really want is more torque. Actually give them more top end power and they may be unhappy as their engine is now putting out less power in the mid-range.  Oh well, sorry for the off topic.

If you put a single weber and a header on an otherwise completely stock wedge, I would expect 10 or so more hp in the top end and a bit of loss in the low to mid-range.  Fit bigger valves, port, re-curve the distributor and grind the cam?  100 to 140 hp with the drive ability falling as the hp rises.

[shootingsight]

So what do you recommend for more mid-range torque?  I agree with you, I'm not on the track with my engine living at 6,000 RPM, it spends a lot more time in the 3-4,000 range (well, it really spends a lot more time in the 0 RPM range, until I get the rebuild done).

[jbcollier]

Fit a tubular header and a Weber 28/36 DGV.

[Nockenwelle]

There is an Europa S2 for sale on Ebay that has a twin Weber manifold for the wedge head engine. That's quite a rare manifold.
https://www.ebay.com/itm/1971-Lotus-Europa-1973-LOTUS-EUROPA-TWIN-CAM-SPECIAL-JPS-32/143432325646