interestedparty
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| posted on 30/8/10 at 07:23 PM |
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Conventional manifolds v. ITBs?
I'm looking at alternatives for the standard Ford V6 setup, and looking at the standard manifold you can see the the individual runners are
quite long, and I understand that this is important, but when cars are converted to ITBs it doesn't seem to matter or maybe it does matter but
people don't do anything about it anyway.
Can anyone explain that? I know that it's a lot to do with getting the gas speeds up at low throttle openings, to get good torque, but if anyone
has any more info I would be grateful
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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stevebubs
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| posted on 30/8/10 at 07:36 PM |
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It is important but the gains in going ITB are normally relatively large anyhow so it normally gets overlooked.
There is a formula to calculate the optimal length of inlet, but I don't know it off the top of my head - something to do with a standing wave
and harmonics IIRC....
If any of you remember the huge "flowerpot" intakes that was popular on caterhams a few years ago, this was what drove it....
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pwl
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| posted on 30/8/10 at 07:37 PM |
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Copy paste from Jenvey FAQ
What is the correct overall system length?
Induction length is one of the most important aspects of fuelling performance engines.
In our experience an under-length system is the greatest cause of disapointment, with loss of up to 1/3 of power potential. There are a number of good
books on the subject and the serious developer is referred to these and, in particular, dyno trials. A guide figure, from the face of the trumpet to
the centre of the valve head is 350mm for a 9,000 RPM engine. Other RPM are proportional, i.e. for 18,000 RPM the figure is ca 175mm.
Any air feed system to an airbox or filter can have a large effect on the power curve and must be considered carefully - particularly if the airbox is
small.
The induction system is part of a resonant whole - from air inlet or trumpet to exhaust outlet - and the ideal length is heavily influenced by the
other components.
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RazMan
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| posted on 30/8/10 at 08:22 PM |
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I am looking at putting TBs on my Duratec V6 by utilising the existing manifold and converting it to take primary butterflies alongside the std
secondary ones - 12 butterflies in all!!
I am also anxious to get trumpet length right so I asked Jenvey about their recommendations and they said [paraphrasing here] "as long as
possible" which didn't help very much. When I pushed them a little further they sent me their TB kit for the Jag V6 which is very
similar...
 
Jag V6 ITBs
(sorry about the size  )
As you can see, the trumpet length looks to be about 75mm by my reckoning, but they use a manifold to change the wierd obround ports to a conventional
shape, making the whole TB setup a bit longer.
I reckon about 100mm trumpets will do as a start and from what I understand, the power will mostly be at the top end so it should make the V6 sing at
the top end of the rev range (7500 rpm in my case)
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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interestedparty
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| posted on 30/8/10 at 08:33 PM |
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That Jaguar set up is interesting, more appropriate for a mid engined car though. The injectors seem a long way from the heads too.
I guess for a front engined car I would need to be thinking along the lines of a swan neck arrangement, with the runners curving back over the tops of
the cylinder heads, as this would not be a race engine and I'd be looking for a good midrange. Maybe it would be better for me to stick the the
donor manifold.
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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RazMan
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| posted on 30/8/10 at 10:50 PM |
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Those were my thoughts too - Jenvey must move the original injectors into the TBs but my idea keeps them in the original position. Is your engine a
Duratec V6 or Essex? If I can get my idea off the ground, maybe we can combine resources  - they should be a lot lower than the Jenvey / Jag
setup
[Edited on 30-8-10 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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brianthemagical
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| posted on 31/8/10 at 01:08 PM |
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I'm guessing you're planning on an aftermarket ECU.
Any other changes, such as porting or cams?
There isn't a simple calc to work out the lengths, it's pretty much an extension of acustic harmonics, with a staning wave being generated
by the inlet valve.
The cam timing has an effect, as does the dia of the runners, hence there not being an easy solution. The best bet is to try and keep them the same as
std, maybe a bit shorter if you like to rev it a bit more.
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interestedparty
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| posted on 10/9/10 at 07:31 PM |
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quote:
Originally posted by RazMan
Those were my thoughts too - Jenvey must move the original injectors into the TBs but my idea keeps them in the original position. Is your engine a
Duratec V6 or Essex? If I can get my idea off the ground, maybe we can combine resources - they should be a lot lower than the Jenvey / Jag
setup
[Edited on 30-8-10 by RazMan]
It turns out my engine is actually a Jaguar 3ltr 
I hadn't acquired it when I started the thread, but I have now and hope to start on it in the next few days.
A quick look suggests the standard injectors are below the manifold bolt face, so if I'm seeing it right it may be that the injectors on the
Jenvey manifold are actually second injectors?
I won't know til I've had a good look (engine still needs to run until Monday ish) but it doesn't look too difficult to fabricate a
flange for the manifold bolt face, and if I can do that then it looks ! simple enough to add some runners that curve over the top of the cam covers to
keep the overall height down.
Happy to pool resources on this.
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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RazMan
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| posted on 10/9/10 at 10:07 PM |
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It might be a Duratec ST220 which is pretty similar to the Jag, although I think the latter has variable inlet cam timing and completely different
combustion chamber design, making a bit more power.
I'll swap if you like
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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