Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[cem_devecioglu]

from what I have read,  they say long runner plenums create more torque at low rpms where as short runner plenums create more hp


here are some short runner models







[size=78%][/size]



theory is long runners create more air velocity .. 


however we all know that combustion power depends on amount of oxygen molecules sucked by the pistons..


so this theory seems a bit bollirx to me


but then why all those factory engineers bother to make them as long as possible increasing the cost ?

[Kevin Wood]

Making the intake tracts longer does give you much better torque at low revs and, as long as the shape is not contorted all round the engine bay, there isn't a big price to pay at the top end.

[cem_devecioglu]

Making the intake tracts longer does give you much better torque at low revs and, as long as the shape is not contorted all round the engine bay, there isn't a big price to pay at the top end.

thanks Kevin

[aaronjb]

This is precisely the reason the Omega has the "multiram" intake - the butterflies that open and close effectively increase (or decrease) the intake length to match the rev range you're in at the time.. (if I remember right)

[Kevin Wood]

Yep, I recall calculating the optimum length of runners on my Westfield (which peaks at 7200 RPM) and I think the answer was around 17 inches, putting the throttle bodies well outside the bonnet and only just inside the front wheels.

Lower the revs and you make them longer still. In an ideal world.

[aaronjb]

Can't see a problem with that ... one huuuuge side-scoop later and you're golden. As long as you make the corners sufficiently radiused to keep the MOT/IVA tester happy, of course

Incidentally several of the pics in Cem's post appear to be forced induction setups and I think the rules governing intake manifold & plenum design tend to be different there, no?

[Kevin Wood]

Yes, less of an issue with forced induction, as pulse tuning the intake doesn't give such returns, although it will give you an engine that makes more power with less boost, which has benefits, in that you don't need to heat the intake air up as much, and so the stresses on the intercooler / chargecooler are less, etc.

The main thing to worry about there is that you have a plenum / intake design that give equal flow to the cylinders.

It's still worth doing a decent job on. A friend of mine did a very thorough job on the intake on his YB Cosworth a few years back. He was able to get a lot of power (close to 400 BHP) out of a relatively small turbo, so it was a great deal more drivable than most YBs at that power level. Just as well given that it's in a Westfield.

[cem_devecioglu]

Yep, I recall calculating the optimum length of runners on my Westfield (which peaks at 7200 RPM) and I think the answer was around 17 inches, putting the throttle bodies well outside the bonnet and only just inside the front wheels.

Lower the revs and you make them longer still. In an ideal world.

yep.. I also checked the calculations..practically they are too long for a clit engine bay..  but one thing I want to understand, is the blockage of throttle neglected in calculations so that you measure from the filter to the engine otherwise omega setup becomes meaningless 

[cem_devecioglu]

when mine will be finished it will look like custom water piping for flowers


the engine bay is so badly designed that ignition setup divide the area into 2 which will be very close to turbo effectively permitting only one area..


another area is in front of the radiator which blocks the injector sockets 

[Kevin Wood]

Well, I guess that you can assume that the throttles are open for any measurement where maximum power output is important, so the position of the throttle is not that important.

But.. the Omega is doing something slightly different, in that it's not dealing with the tract from which a single cylinder is breathing, but a single bank. So, the situation changes from 4 or 6 intake tracts which get a pulse of air every 2 engine revolutions, to 2 tracts which each get 3 pulses every 2 revolutions of the engine. These tracts can be joined at either the plenum or in the multiram ducting, or not at all, to give 3 different lengths of intake.

The lengths can be shorter as the pulse frequency is higher, but you have the disadvantage that there will be a little scavenging and interference at the intakes inside the plenum, where 3 cylinder intakes are combined. A little compromise is required to fit it under the bonnet, as you have also observed with the clit.

[cem_devecioglu]

veccy owners say that c25xe runners are better for na tuning (top end)  (similiar in shape to clit original manifold) .. dont know if its true or not.. 

[Kevin Wood]

veccy owners say that c25xe runners are better for na tuning (top end)  (similiar in shape to clit original manifold) .. dont know if its true or not.. 

Yep, I think they have a longer run from each port into the common plenum, so possibly each cylinder is seeing a more beneficial intake length at high RPM. Of course, it lacks the advantages of the Omega's setup at low RPM.

If going forced induction, though, there is much less to be gained from intake tuning, so I would concentrate on how to get it all under the bonnet.

[cem_devecioglu]

veccy owners say that c25xe runners are better for na tuning (top end)  (similiar in shape to clit original manifold) .. dont know if its true or not.. 

Yep, I think they have a longer run from each port into the common plenum, so possibly each cylinder is seeing a more beneficial intake length at high RPM. Of course, it lacks the advantages of the Omega's setup at low RPM.

If going forced induction, though, there is much less to be gained from intake tuning, so I would concentrate on how to get it all under the bonnet.

yep.. but imo still a forced induction system is na until turbo kicks in..  which means if you can make long runners you wont need to rev the engine for turbo everytime for more torque .. so fuel consumption can be kept relatively low..  but when you really need  power you can rev it..

[Kevin Wood]

Yes, but then you need to tune the runners for low revs before the turbo has woken up, which means really long runners.

[05omegav6]

Or fit a supercharger...