tech collaboration: 20V throttles

[tricky]

I have recently acquired a set of pre 5/93 silvertop quad throttle bodies. Now, whilst a decent amount of information exists on the topic, none of it is in one place, so with the rush of technical documents on the new forums, I thought it would be a good oppurtunity to get all the data in one place.

The immediately obvious thing about the throttles and manifold is the maze of vacuum hoses. This site contains a wealth of information on the vacuum lines, however it is not complete.



the above photo shows the ISCV manifold. What is the input in the centre? As far as the other inputs are concerned, I beleive the largest hose leads to the ISCV, which has a hose leading to the filter box. As for the A/C and P/S idle up inlets, do these have a seperate ISCV of sorts? I will post some diagrams/labelled photos when all tubes are confirmed.

Some examples of data I couldn't find in searches was mainly concerned with the physical dimensions of the throttles. I have taken some measurements from my parts, and they are as follows:

Throttle spacing: ~90mm
Throat diameter @ trumpet: 46mm
Throat diameter @ manifold: 44mm
Throttle diameter: ~44mm



Above is a picture of the trumpet side.

Bolt spacing @ trumpet: 73mm



Above is the manifold side.

Main bolt spacing @ manifold: ~74mm
Spacings to minor bolt: ~50mm offset ~3mm
~62mm offset ~15mm

This major spacing is painfully close to the spacing for DCOE's, so it is feasible that a DCOE manifold could be butchered such that 20V quads could be attached.

DCOE dimensions can be found here.

It must also be noted that the main two manifold attachments are offset from the axis of the trumpet bolts by about 20 degrees.

I'll gradually amend my data to tabulated and formal schematic form, but until then, I hope this is readable for anyone interested!

EDITED 'cos I said wealth like three times in three sentences...

[ed]

ill post details of rb26dett throttlebodies for comparison...

[Ben Wilson]

This major spacing is painfully close to the spacing for DCOE's, so it is feasible that a DCOE manifold could be butchered such that 20V quads could be attached.

Yes - It can, but, it's not simple, you need adapter plates and a fair bit of buggering around:

[takai]

The other alternative is to order a throttle adaptor from T3 in the US. I had originally planned to make up a set of adaptors, or to cut and shut some runners, but it came out this way as cheaper:




Oh yeah, and port spacing is 88mm from the center of the pistons. I had to measure it yesterday for another part i was building.

[tricky]

Yes - It can, but, it's not simple, you need adapter plates and a fair bit of buggering around:

agreed. I'll be starting from scratch though, 'cos I'm sticking them on an 18RG. Just getting the info out there, 'cos it's hard to find.

takai, thanks for that measurement for the port spacing. I'll update my post at the top.

Ed, would be tops to see some RB26DETT TB's. Do you have these on your 7MGE?

[takai]

Oh yeah, i see you have the twin-linkage version. They were updated at some time during the run (around 95 i think) to a single linkage version as seen on my throttles.

[Ben Wilson]

agreed. I'll be starting from scratch though, 'cos I'm sticking them on an 18RG. Just getting the info out there, 'cos it's hard to find.

When I built the set pictured above, you couldn't buy the T3 adapter. If you look at the adapter plate (TB off) above, you will see that I had to drill and tap a new hole in the manifold for the two which were angled in that direction, the other two, I just used the webber mounting holes. I used 5mm aluminium plates and had to helicoil the M6 holes so the bolts would hold nicely.

Honestly, unless I had a 4AG (or another motor with the injectors mounted in the head), I'd bite the bullet and get some EFI hardware (or similar) TBs.

[tricky]

Takai, the twin linkage version was pre May, 1993. The other major revision was the location of the ISCV ports in the manifold.

The way you did your adaptors seems feasible, Ben. I don't really wanna bite the bullet to be totally honest... A set of DCOE throttle bodies is over $1000, as opposed to the pain and suffering involved in making up a manifold and sticking injector bosses in it.

[Ben Wilson]

Bear in mind you will also have to work out a fuel rail, get the injector bosses, then get them welded to the manifold, work out a throttle linkage, work out some sort of linkages between the TBs, sort out some sort of trumpets/air filter etc..

Don't get me wrong, it can all be done, but it will suck. (If you have access to a TIG and aluminium welding skills, it will be a little cheaper) With the EFI hardware stuff, all the hard work is done for you.

[Ben Wilson]

One thing to think about if you don't have injector mounts is bike TBs.

I just picked up a set of GSX-R 1000 throttle bodies from e-bay which could be perfect for a conversion (I just need to find a car to put them on). The guy selling them had another set if you're interested.

You need to do a little modification to get them to work, but, the have injector mounts in them.

They look like this - you need to remove the secondary butterfly. They are all seperate, so bore spacing isn't an issue. As a set, they look like this.

One of the big advantages is that they mount via a tube, so you can just down a standard efi manifold until you have stubs the right size, or build simple adapters to bolt onto a webber manifold (a webber pattern base welded to a stub of tube).



Here is a set on a friends Camira (don't laugh) rally car..

[tricky]

Dammit Ben!!! Now you've got me thinking!! Well, I can safely say, there goes another $200... It's not because I'm put off by the 20v throttles, I'll probably still do them, but damn those suzuki throttles are noice!! With those second throttles removed, the 50mm --> 42mm taper will give some nice velocities!... And it'd be nice and easy to build a manifold to get the injectors exactly where you wanted.

BTW, how did you get your 20v throttles so shiny?

[tricky]

What is the purpose of those second throttles? It looks almost like a choke, but I'm sure it's not. Crazy bike people!

[Ben Wilson]

As far as I can tell, they open with revs, so that no matter what revs you are at full throttle = maximum flow. They keep the air velocity up like an SU carbie. It used some nifty electronics, but, I think I've just about got it worked out...

I got my throttle bodies cleaned at SD car tuning in Braddon, they couldn't use their magic cleaning bath because there are plastic bits they couldn't remove, but, I think they bead blasted them (carefully). I just gave them a shot of clear and they still looked the same the last time I saw them..

[takai]

Fastest way to get a shine to 20v throttles is to get them bead blasted.

EDIT: for the ACT folk (i think that is most of us sofar) the place on Gladstone St in Fyshwick who also does powdercoating (down the laneway near Capital Steering) do a good job of beadblasting.

EDIT2: there you go, never knew that SD did beadblasting too.

[Ben Wilson]

tricky - You've got a couple of PMs.