OK im haveing a go at makeing my own trottle bodies for my 1700 Xflow hopefully for £200 to £250

to controle the injectors i will be useing mega squirt

http://www.bgsoflex.com/megasquirt.html

I have started a drawing on auto cad it is not finished yet. i'v been trying to put it on to jpg with out much luck. so ill put the cad file on a attachment. if some one could post it as a jpg i would be grateful.

ok there are a fuw quires i have.

1) Do the trottle valve bushes need to be seal with a o rings?

2) I was thinking of puting a nedle valve just behind the throttle valves so each cylinder can be Balanced is this nesasary?

3) the only stainless tube i can get hold of has a 34mm bore but my xflow head has a 31mm bore so i think i will get away with it ?

please have a look at the drawing and if you see anything that could be better please tell me

after all that i forgot the f#%king attachment

there we go

Don't know any details about throttle bodies, but...

1. you'll need to be careful of air leakage around the butterfly pivots, probably best to look carefully at how they're done on carbs and try and replicate it.

2. no idea!

3. throttle bodies flow a lot better than carbs, I'm only guessing but I bet a 34mm body will flow at least as well as a 40mm carb.

Someone else please reply cos I don't really know what I'm talking about!!!

I found a useful enough .DWG file viewer for those of you following Rell's progress.

I've placed it on my website for those who want it. It's 5.8MB and lives HERE

It's not my program, but one I use at home.

Have fun,

Neil.

JPG'd as requested HERE
(333K)

[Edited on 22/10/03 by Noodle]

I'm sure a mate of mine mentioned a book about DIY throttle boddies, I'll ask him

Wouldn't it be cheaper to use some old twin 40's?

My twin 45 carb manifold has moldings for injectors in it, but no holes. Go figure.

Dave Walker did some home-made ones in CCC from a set of 40 DCOE's.

He wrote a book about DIY Injection (Haynes) so I suppose he could have put the stuff in their too.

The link ... http://www.haynes.co.uk/inc/viewbook.asp?bt=H835

Cheers,

Neil

rell,

the size of ye'r tubes seemes about right. Don't forget that if you use oversized TB's, you'll get no more power but a lot of driveability problems, especially on tip in( when one opens the throttle). Too big TB's make it difficult to control the intake pressure (MAP!!) and thus engine power.

The butterflies do need to be sealed IMHO, as you should be looking at somewhere around 0,8 to 0,65 bar vacuum on decelleration (depending on your cam profile). I would try to get it as good as i could get, measure the pressure in each inlet tract on decelleration and then decide if you need additional sealing.

A needle (idle control) valve in each tract would be a nice touch to smooth out the idle.

If you've got any q's, please contact me (i'm professionally involved in this sort of stuff)

Regards,
Sebastiaan

ok done a bit more on the drawing it is on the attachment

im affter a bit more info im just about to design the trumpets is there a foumula to calculate the shape? if not can some one mesure the radius of the bellmouth

i'v been told not to use the map sensor because i will be runing a sporty cam (kent 234) and the overlap messes use the sensor at low rpm. but from what i can make out lots are runing without a map sensor and thay are doing fine?

there is a formula for the length of the trupmets somewhere, to do with tuning them to a certain rev level/range.

I've also been told by several race engine builders that trumpets with ends that are rolled back on themselves are better than straight ended ones too.

sorry its not specific on a formula but it has been posted on here somewhere before, possibly by findlay234?

Ned.

yes i know all about the length efecting the performace at a set rpm. the formula is L = (Ot * C)/(t*N)

this is Quoted out of advanced engine technology by heinz heisler ISBN 0340614439 this is the best book iv read on engine design.

theres allso design of racing and high performance engines ISBN 1-56091-601but this dose get very tecnical but worth reading.

but thay do not tell you anything about trumpet design.

[Edited on 23/10/03 by rell]

found some info on trumpets

the only thing is iv looked at trumpets on other cars incuding my own and thay do not look like that there is a long taper after radius is there a reson for this?

ive put the file on a attachment

got it on jpg. the computer finally gave in when i treatended it with the lump hammer


trottlebod
still could do with some more info on trumpets

heres the cad file if you poffer looking at it on auto cad

rell,

the bellmouths you show seem to be aimed at simply ducting air into tubes so they get to the right tube radius as easily as possible.

I guess within an intake there are lots of other things to consider, standing waves generated by the pulsing of the airflow, problems with airflow itself if the intakes are mounted pointing out of the side of the car in a front engined LSIS.

Have a look at the various intake trumpets avaliable for weber DCOE's. You can get various sizes and lengths. It might be easier to make some fittings to attach these thus allowing for some simple tuning.

The simple rules for picking trumpets for DCOEs, are longer = midrange, shorter = power at high rpm. There are also issues with the size of the filter. For example a 2000cc Pinto running twin 45's the ideal would be 100mm with ideally the same distance between the end of the trumpet and the end of the air filter. Normally this has to be compromised in a locost.

A decent airbox would also give benefits, maybe even running positive pressure to give a slight boosting effect. Has anybody experimented with this?

Andrew

Yes i was thinking of puting air box on top to use it as a plenum chamber

any thortes on this will be welcom

The trick with air boxes is to provide a non turbulent supply of air that is uniform across the carbs/throttles. Else you'll get a sort of speed dependent unbalancing of the cylinders.

I've seen a carbon air box for seven. Think of a backplate connected to a large carbon (plastic/fibreglass) box a little larger than a square foam filter. At the front of the box is a round pipe that connect to flexible ducting. Somewhere in the ducting you site an axial flow filter (the type you get for after market induction kits for tin tops). Then the ducting is terminated in a bell mouth or better still a NACA type duct say on the top of the nose where it gets a nice supply of clean fresh air.

If you think about the airflow on a standard set of carbs sticking out of the side of a seven. First of all the air is disturbed by the front wheel, and then the air is rushing accross the mouths, maybe at speed this actually reduces the pressure in the intake. It must certainly be unbalanced.

A simple airbox must be more effective.

Andrew

this is true but i have thort about this and i dont think it is worth making a air scoop for positive presure. There is a good bit in tune to win by caroll smith (very good book) and it gives the formula to calculate the psi for a certan speed the formula is.

intake ram psi=(air desity psi)*(air velocity in fps)^2/288g

so at 80 mph psi=(0.076*118^2)/(288*32.2)

so at 80 mph psi=0.11psi

what is not a lot and this is if there is no Turbulence or it will be less

lets see how much exsta performance this will give

there is about 15 psi to one Atmosphere so extra O2 is

exsta O2 = 0.11/15*100

= 0.73%

now im runing a 1700 crossflow about 130 bhp so the power incease will be

bhp = 130/100*0.73+130

= 130.949

this is a lot of work for about 1bhp. But say you have a 800bhp engine you will get a extra 6 bhp but at 160 mph you will get 3% extra O2 this is an extra 24 bhp.

so it is worth doing on a high performance engine what are doing high speeds

another point is that air scoops tend not to have air filters and if you put one in it reduces it Efficacy

but poin taken about geting a good air flow in to the plenum chamber. i was thinking of useing a big cone filter and put a duct up to the front of the bonnet
any one done this before?

All the talk/hassle of building throttle bodies - Why not just grab some from a crashed YamaHondaZuki?

I just picked a set of R6 throttle bodies for less than $30. That includes injectors.

Suzi GSXR 750's seem to be the models of choice, since they're big and the bodies may be seperated & spread out, if need be.

Hi rell
I made my own (good little project) and they work a treat, I used a different approach, made 4 individual bodies from 65mm square alloy bored out to take 1 3/4" SU carby butterflies and spindles, the spindle runs directly in the alloy, no bushes or seals and no needle valves, the butterfly spindles are all in the vertical position with short arms clamped to them and connected with a series of links(turnbuckles) made from two small rod ends with left and right hand threads which allows the butterflies to be adjusted independently of each other, I set these up fairly close and fine tuned them with the engine running using a piece of hose, this only has to be done once at initial set up then a normal throttle stop arrangement is used which opens or closes the throttles equally. Went to a lot off trouble fitting tapping points for the map sensor only to find it didn't work because of the big cam, didn't put any science into lengths of inlet tract or trumpets due to the confined space, the only rule was nothing protrudes out side the body. I think having each butterfly adjustable is a big plus, makes the set up so much easier, the other crucial point is the fit of the butterfly in the body needs to be very good to keep out unregulated air and was the reason for using the SU bits and machining the bore.

Have fun, Wimmera

Sounds great- you got any pictures?

Cheers,

James

Use Bike throttle bodies. A nearly new set from a bike breaker are around £100 including injectors, linkages and idle needle valves with central and individual adjustment, oh yes, with throttle pot already mounted on too!

I got some Honda Blackbird ones a while back, these are 42mm bore. I have since been told that very late Suzuki GSXR 1100's were injected and the throttle bodies from these are 46mm bore and with a touch of filing of holes line straight up with weber DCOE manifolds, though i hve not been able to verify this myself but I have seen a car where it had been done (Honda engine'd mini)

dont forget that if you running a set of 45 dcoes with 36mm chokes it isn't necessary for a set of tb to be 45mm to replace them 38 - 42 mm will be more than enough.

yep, timf is quite right there.

Making 200hp+ on carbs I would have had to run 48DCOE's though, and my previous engine (just over 200hp) used 48mm jenvey parallel bodies so I wanted as close to that as poss as I knew it worked!

GSSX throttle bodies seem to be going cheap on Ebay, that might be a place to start

I can only seem to find T.B.s on Ebay in America, none in the UK. THere is a nike breakers not far from me though, have to give them a try.

Here is a picture of my finished carb conversion using a pair of weber 40s
Rescued attachment dressed1.JPG

keep an eye out for lotus exige/esprit throttle bodies on ebay too, a few going cheap recently.

Bike ones, just get a copy of MCN and ring a few breakers in the classifieds, they all had them!

The Lotus TBs I've seen on ebay recently did not have an injector port though so you would need to fix a pocket into the manifold or have external injectors working into the throat of the bodies.