Velocity stacks question

[MartijnElanS4]

Hi everyone,

I have a question: another Elan owner advised me to change the original Weber velocity stacks to shorter ones so it would pick up better from low rpm’s.
All of course with the intake cover mounted as I read a fire might occur.

Also he advised to add an oil catch can.

I am curious on your thoughts.

All the best,

Martijn

[tonyabacus]

Martjn
As you may guess from what you put in your posting, altering the velocity stacks (trumpets) can alter the characteristics of the engine performance, but not just in the pick up phase. So whilst you may see a small improvement in initial pick up of the engine, what else is happening elsewhere in the power curve, does this mean for example that you also need to change certain jets to compensate for the improvemet by fitting the trumpets.

It can become more technical than just changing the trumpets and the only way to know for certain is to put the car on a rolling road once the change is made. This will show the effects of the change throughout the rev range, but make sure you go to someone who understands Weber carburettors.

As for an oil catch tank, unless you intend to use the car in competitions then you may not need one. The other occasion you may need one is if you have a particularly oily engine that pushes out excessive amounts of oil through the breather. This can happen sometimes if there is excessive crank case pressure for example.

So the question has to be do you need to make these changes for a technical reaon or some other reason
Tony

[MartijnElanS4]

Thanks Tony!

Appreciate your time. The guy was/is very direct in his views. ‘You need to shorten the stacks and need a catch can. Also change the tires to Dunlop. It is the only way to go’.
As he does rally driving all his life I assumed he has the knowledge.
But as I understand from you the changes he suggests is with racing in mind.

That is certainly not my intention: I just want a healthy engine with good pickup from low down to up in the ref range; not only at the high end.

When finished, I will drive it a bit and then let experts fine tune it on the roller bench. If needed I will folow their advise.

Martijn

[nmauduit]

actually, all things equal otherwise, shorter "trumpets" would favor higher rpm rather while longer ones would tend to increase torque from lower rpm (hence favoring pick up)... if you're questioning your engine behavior I would eventually encourage a tuning on a rolling road with someone seasoned with LTC ... there can be various stages in tuning, you may want to start with making sure the richness is correct all around (esp. around 3000 rpm, the transition between the "idle" circuit and the "main" circuit), that the ignition circuit is in good condition and timing appropriate.
If you're suspecting this racers's advice may not apply to your car you may want to have someone else trying it out for comparing the two opinions.

the search for the last hp is a long and treacherous journey, good luck...

keep it on the road !

[MartijnElanS4]

Thanks! I will do that. I would like that the engine is set up nicely through the whole ref range increasing drivability.

actually, all things equal otherwise, shorter "trumpets" would favor higher rpm rather while longer ones would tend to increase torque from lower rpm (hence favoring pick up)... if you're questioning your engine behavior I would eventually encourage a tuning on a rolling road with someone seasoned with LTC ... there can be various stages in tuning, you may want to start with making sure the richness is correct all around (esp. around 3000 rpm, the transition between the "idle" circuit and the "main" circuit), that the ignition circuit is in good condition and timing appropriate.
If you're suspecting this racers's advice may not apply to your car you may want to have someone else trying it out for comparing the two opinions.

the search for the last hp is a long and treacherous journey, good luck...

keep it on the road !

[Baggy2]

There's a lot to be said for the moto " if it aint broke dont fix it "