General Anyone running a velocity stack on a Weber 28?

[jtrashy]

I’m at 6000 feet elevation and this bad boy needs more air!
Can’t find anything on a search, anyone have information for me? Would rather find an option that deletes the 90 bend into carb so hoping for velocity stack off the top.
Thanks

 

[bugsymike]

Do you still draw air from around the engine compartment to the carb?
If you can get cold air from outside it is more dense and contains more oxygen for the engine, hence the reason pre ECU vehicles seem to run better on a cold morning.
What do "Pikes Peak" racers with carbs do? They must have to cope with similar problems.

 

[dangfiat]

I'm not sure velocity stacks are to get more air in, the 90deg bend shouldn't provide a significant impediment to flow.

Aren't the point of stacks, or long intake runners to change the torque curve? i.e. I've always thought the long runners were to help move the torque curve further down the rev range (it's why there's long intakes on most modern cars)

I think your best bets will be:
1. Port the head to get the intake a bit wider & match the intake manifold
2. Run a stack with a mech filter only to provide the least impediment to flow

Could be wrong though.. I get a lot of my understanding from tuning A-Series Mini engines and the "yellow bible" of David Vizard. It's a really interesting read for anyone into these tiny engines

Daniel

 

[bugsymike]

I'm not sure velocity stacks are to get more air in, the 90deg bend shouldn't provide a significant impediment to flow.

Aren't the point of stacks, or long intake runners to change the torque curve? i.e. I've always thought the long runners were to help move the torque curve further down the rev range (it's why there's long intakes on most modern cars)

I think your best bets will be:
1. Port the head to get the intake a bit wider & match the intake manifold
2. Run a stack with a mech filter only to provide the least impediment to flow

Could be wrong though.. I get a lot of my understanding from tuning A-Series Mini engines and the "yellow bible" of David Vizard. It's a really interesting read for anyone into these tiny engines

Daniel

In the late 1960s on the racing karts we increased the inlet manifold, as you say to give more torque and pull on short circuits and shorter inlet manifolds helped quicker throttle response on other circuits.
We found the a long "bellmouth" on the carb would help with visible fuel stand off at certain revs.
My "bible" was Tuning Small Fords, pre crossflow.

 

[the hobbler]

In the late 1960s on the racing karts we increased the inlet manifold, as you say to give more torque and pull on short circuits and shorter inlet manifolds helped quicker throttle response on other circuits.
We found the a long "bellmouth" on the carb would help with visible fuel stand off at certain revs.
My "bible" was Tuning Small Fords, pre crossflow.

Many (and I do mean, sadly, many) I worked at "Trojan",nuilding the F5000 and Can Am Mclaren customer cars. On the 'works' M8 mclaren canAm engines the lengths of the inlet trumpets were staggered so as to help spred the torque range. I would agree with

 

[the hobbler]

Many (and I do mean, sadly, many) I worked at "Trojan",nuilding the F5000 and Can Am Mclaren customer cars. On the 'works' M8 mclaren canAm engines the lengths of the inlet trumpets were staggered so as to help spred the torque range. I would agree with

Apologies, wrong button got pressed!----I would agree with "Dangfat" in that the curve of the inlet trumpet is soft enough not to impede air-flow. There isn't a lot of space above the 500 engine which therefore inhibits the 'vertical' length of any trumpet. You might be able to find an old (short) Weber trumpet and fettle it to fit the carb As 'Dangfat'also suggests, porting the head and opening up the inlet port to match the gasket and carb can only help. I would suggest that you try and obtain a spare head, and then play around with that.My normal reccomomendation is that for 'road-use only' the inlet valves size is increased by 2mm and work is done on both the inlet and exhaust ports---it is as important to get the gases OUT as it is to get them IN!
My "Bible" is:--- "Four-stroke Performance Tuning" by A.Graham Bell. It is a 'Haynes' publication---ISBN 978 0 85733 1250. I highly recommend this book, but I would agree, the thoughts of David Vizard are very informative.

 

[gordinir8]

In the old days when they had a race at altitude they use to change the jets in those twin starved Webers. So maybe you have to play with those jets first and then go to more expensive and complicated solutions that will probably help as gentleman above said. I believe the original intake fan air configuration is better than an intake sucking hot air from the engine bay.
Thomas