Alan B
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| posted on 4/3/04 at 05:27 PM |
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Throttle bodies...general question
Guys, I was asked basically what are throttle bodies and why would you need them?
This was my answer, tell me if this is right, or if I need educating further...
TBs are basically the equivalent of twin 40's for EFI.....they allow better airflow into the engine...one butterfly per cylinder...they really
aren't much more than twin 40's but without the fuel part...
Comments and further info...
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Julian B
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| posted on 4/3/04 at 05:51 PM |
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Thats how i understand them to be; just a tube at say 40mm diameter for a 500cc cylinder with a butterfly valve and a hole for the injector.
If this is the case is it not possable to make them?
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James
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| posted on 4/3/04 at 05:52 PM |
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You got no chance Alan! I've asked what the hell the benefit of them is a couple of times and no one wants to give a straight answer! 
James
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Gizmo
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| posted on 4/3/04 at 05:56 PM |
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check out the 'advice & FAQ page here...
http://www.jenvey.co.uk/
all will become clear.
And yes easy to make from a set of DCOEs or DHLAs. If anyone wants pics of a home made set, let me know.
---john---
[Edited on 4/3/04 by Gizmo]
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James
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| posted on 4/3/04 at 06:02 PM |
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I want a picture! :-D
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Alan B
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| posted on 4/3/04 at 06:14 PM |
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quote:
Originally posted by Julian B
Thats how i understand them to be; just a tube at say 40mm diameter for a 500cc cylinder with a butterfly valve and a hole for the injector.
If this is the case is it not possable to make them?
My thoughts exactly....if we can make a WHOLE car, how hard can TBs be???
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James
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| posted on 4/3/04 at 06:22 PM |
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If it is just a case of tubes, butterflies and some injectors...
Get four ali tubes, remove butterfly section from 4 Pinto injection systems, weld the butterfly on end of tube, link the four together and tap a hole
at the right place for the injector.
After that it's just software- and that's easy!
It can't be that simple can it? 
James
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Alan B
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| posted on 4/3/04 at 06:32 PM |
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I'm sure there a few subtle nuances...the kind that win races for Jenvey etc....but, basically they do seem to be very simple.....
Hmmm...I see some experimenting in my future....
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James
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| posted on 4/3/04 at 06:41 PM |
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Yeah, I was only taking the p1ss- but I reckon it may not be far from the truth!
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Wadders
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| posted on 4/3/04 at 07:02 PM |
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Hi chaps
i can't comment on the technical aspect of throttle bodies versus carbs, cause i know nowt, but i can comment on the "feel" of both
systems, which may go a little way to explaining the supposed benifits of throttle bodies.
My mate has had two westies (iv'e driven both) the first one had twin webbers, the second had jenveys fitted, apart from that they were pretty
much identical specs. The car fitted with jenveys seemed to run much crisper, pick up better and feel much more responsive. It even sounded nicer.
Al.
]Originally posted by James
You got no chance Alan! I've asked what the hell the benefit of them is a couple of times and no one wants to give a straight answer!
James
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racer56
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| posted on 4/3/04 at 07:29 PM |
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Throttle bodies are not too complicated - theyare exactly what a couple of posts have already said - a tube with a butterfly.
The trick is then
1. Sizing the thing - too big and you cant open it a small enough amount to be relatively smooth at low end (air = torque assuming you can get the
fuel in). Too small and you are restricting the engine
2. Getting the fuel in. You need to get the fuel in at just the right time so that the air rushing in carries it into the chamber (usually the
injectors are aimed somewhere at the back of the valve and the injection happens slightly early so that the heat from the back of the valve helps to
vapourise the fuel - the air carries this in. You need to somehow measure the amount of air is going in and control the fuel accordingly.
Carbs do all this for you, and if well set up, with good exhaust etc can produce as much power in most cases as injection with much less hassle.
My suggestion, if you want throttle bodies, pick an engine that already has them, and learn how to calibrate it - that will be a lot more expense than
carbs though.
Just my 2p worth
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AvonBelgium
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| posted on 4/3/04 at 07:52 PM |
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Alan,
The preformance of an engine is directly related, to how much mixture ( air and fuel) you can get in to the combustion chamber.
Therefore, with an injection fitted engine, if you can get as mach air in as possible the beter for the output from the engine ( because fuel is
determinated by the injectors and CPU).
See also turbo, compresor, wild cams etc.
For my degree ( 20 years ago ) i transformend a 1250 cc civic engine with throttle bodies and an Kugelfischer mechanical injection from an BMW 2002
Tii.
Output from the engine was 140 BHP at 8000 rpm.
I bought not finisched ( casting from a weber ) throttle bodies and finished them myself, and I can tell that it was not easy task, because
everything needs to fit perfectly.
We don't want false air ! every part need to move smooth. etc
So if you don't have the tools ( lath etc ) I see only a possibility in using ecxisting bodies with the right diameter.
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Alan B
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| posted on 4/3/04 at 09:01 PM |
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Well I certainly have the tools...decent well-equipped shop.....but it is TIME I lack....this would definitely be one for the future...
Got a car to finish first...
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racer56
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| posted on 4/3/04 at 10:08 PM |
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Agree AvonBuilder, but I think you are a little ambiguous. Output of course is dependant on air and fuel, but the CPU only calculates how much fuel to
throw in based on air mass. Carbs basically achieve the same thing - the air mass determines how much fuel is drawn in. You could have achieved the
same peak power out of the civic engine with a big, well set-up carb. What you could not do is manage the air fuel ratio over the whole engine speed
to give max performance everywhere.
If you are going to go down the route of injectors and CPUs (PCMs in the trade - powertrain control module) then get an engine that has it already.
The advantage of this is that you know it works, and you can always re-map fuel and spark (assuming you can get an interface) to give a different
trade between performance, fuel economy and emissions. Just be aware that it is not particularly straightforward, so if you are short on time then go
for carbs. If you think you will have time in the long term, but want the car running in the short term, then how about putting carbs on a fairly
modern engine so that you can always revert back to injectors? Or if power is the only want, maybe a bigger engine. Simple is best in my opinion.
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Mark Allanson
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| posted on 4/3/04 at 10:23 PM |
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Not that I have a clue how to make the ECU run throttle bodies, but they are available on injected Sierra's, about 50p from a scrapyard near
you
 
Rescued attachment Throttle Body.jpg
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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Mark Allanson
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| posted on 4/3/04 at 10:26 PM |
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.............and attached to a modified manifold from the same car
 
Rescued attachment Manifold.jpg
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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zetec
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| posted on 4/3/04 at 10:29 PM |
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Another benifit of injection is that the fuel is injected in such a fine spray that the air/fuel mixture is always near perfect regarless of the air
speed. Other factors to take into account is the length of the TB, manifold and trumpets as these have an effect on performance.
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CairB
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| posted on 4/3/04 at 10:30 PM |
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Mark,
I think that the Sierra butterfly is a bit on the large size to be useful for each pot, on the EFI it regulates the flow for all 4 cyls...but does
anyone know of any smaller ones that would be more suitable of a one per pot e.g, around 40 - 45 mm dia?
I'm interested as I'm looking into a locost route with a Duratec.
Edit -
Just realised the solution is probably bike throttle bodies.
Cheers,
Colin
[Edited on 4/3/04 by CairB]
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racer56
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| posted on 4/3/04 at 10:57 PM |
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Hate to come across as being negative as there are definite advantages with injection, but need to disagree with your point, Zetec. Most of the
injection actually occurs ahead of the air on many (particularly older) systems and creates a "puddle" behind the valve. Depending on the
heat at the valve some of this will vapourise, some will remain in the intake and the rest will be carried in on the air charge as the valve opens.
The problem with a lot of injection systems is that they dont have sufficient pressure to get all of the fuel in while the valve is open (especially
at higher engine speeds....think about how long the inlet valve is open at 6500rpm) and so have to start delivering fuel early. Diesels get away with
it because they run much higher pressures in the pumps. Current VW diesel runs about 2 bar, most common rail systems now are at about 1.7 bar. Also,
diesel engines run slower!
Calculating how much fuel is not used in the combustions (ie lost to "wetting" in the intake etc) is not easy - this makes the air fuel
ratio calculation more complex as you need to deliver extra fuel at the injectors to compensate.
Unless you have the right kit to hand to calibrate all this stuff, or you are prepared to accept the calibration in a current set up (or available
after market set up ie. "chipped" then carbs will give the home builder more chance of achieving a good level of performance.
Consider that sports bikes were largely using carbs up until a couple of years ago, and most were not short of power!!! Try a multiple carb set up for
better optimisation and more power. I dont see the point in turing a locost into a hicost!!!!
If any of you do go for injectors etc, the very best of luck.
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Mark Allanson
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| posted on 4/3/04 at 11:09 PM |
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"I think that the Sierra butterfly is a bit on the large size to be useful for each pot, on the EFI it regulates the flow for all 4 cyls...but
does anyone know of any smaller ones that would be more suitable of a one per pot e.g, around 40 - 45 mm dia?"
I am no expert at this, but if the choke diameter is still 43mm (size of my manifold), it does not matter of the throttle butterfly is 100mm, it will
only increase the volumetric efficiency.
I know it would be difficult to fix 4 sierra throttle bodies side by side, but I think the theory still holds up.
Smaller throtle bodies are available from any multipoint injected car with a smaller capacity than the Sierra
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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CairB
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| posted on 4/3/04 at 11:19 PM |
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Mark,
I see your point but I think that it will make balancing them more difficult and give less control sensitivity at part throttle.
I believe that one of the main aims with throttle bodies is to give a clean, unrestricted air flow through them to get the most charge into the pot.
This would require controlled diameter reduction from the larger Sierra butterfly down to the inlet tract diameter.
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ned
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| posted on 5/3/04 at 09:57 AM |
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My understanding is that tb's will always give slightly better performance than a carb as the ecu controls the amount of fuel issued by the
injectror, whereas a carb will just let the engine suck in as much as it can. tb's will be more economical fuel wise in this respect and another
advantage is once the mapping is setup they should never require adjustming, unlike carbs that can need balancing etc etc.
Due to the way the fuel maps on the ecu works they also generally (from experince of race engines) allow better pickup lower down in the rev range due
to teh better air/fuel mixture that the precise fuelling gives.
I imagine building tb's as already said is critical with variables such as size of butterfly, length etc. this i recon is where all te
research/moeny on jenvy's goes (as well as a nice casting!) for the vauxhall (and presumably other) engines you can now get direct to head
tb's which are tapered and ported to match the inlet ports on the head of the engine. parrallel tb's are the equivalent of carbs as they can
sit on the same manifold as 40's/45's.
tapered tb's are hence lighter in weight, better ported and flowed to the head.
all my 2p's etc etc.
ned.
taper tb's:
 
taper type throttle bodies
parrallel tb's:
 
dcoe type throttle bodies
[Edited on 5/3/04 by ned]
beware, I've got yellow skin
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CairB
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| posted on 5/3/04 at 10:29 AM |
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I can see there being a problem with multipoint injection if the air mass flow is not the same into each pot. whereas a carb would compensate by
trying its best to deliver a consistent air \ fuel ratio.
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Alistair Mc
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| posted on 5/3/04 at 11:36 AM |
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smaller bodies
Smaller ports can be found on the 2.9efi granada engine, two smaller bodies are used rather than on big one, dont know the diameter but could measure
tonignt.
regards
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Browser
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| posted on 6/3/04 at 01:03 AM |
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quote:
Diesels get away with it because they run much higher pressures in the pumps. Current VW diesel runs about 2 bar, most common rail systems now are at
about 1.7 bar.
Eh? When I read about common rail diesels when they first came out the Citroen system was running at 1350 bar and I'd imagine pressures have
probably gone UP not down.
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