Fitting EA82 MPFI TB to Spider plenum manifold .

discopotato03 · Post by **discopotato03** » Fri Jul 25, 2008 12:25 pm

Hi all , the time has come to see about grafting an MPFI throttle body assembly to the spider manifold's plenum - to get around the throttle and TPS dramas with the spiders f#$%^&*d TB setup .

We measured the spider manifolds stud pattern and it has the lower holes a whole 5mm less in the vertical plane than the L EA82 type . My rally person thinks the way to go is to weld an aluminium plate on the plenums TB mounting face referenced on the top two holes . He thinks the throttle cable quadrant will need to be indexed and I think that another inner cable guide will have to be made so that it rises vertically to the cable quadrant itself .

All this bother is to ensure that either native 3 plug or 4 plug TPS's - and cable positioning can be used on this manifold because they were originally intended for the squiff layout of a Vortex engine bay (compared to L series) .

Also the XT4 engine is now virtually complete and just have to sort out the spider issues and then it can go in .
My finances have taken a beating because I'm now getting interested in doing things to another car as well and it's hard to run both projects at once .
I'd like to have done a better header and turbo but that's going to have to wait a while . The exhaust will be getting done because it's so restrictive ATM .

In time , cheers A .

brumbyrunner · Post by **brumbyrunner** » Fri Jul 25, 2008 12:55 pm

Whats the other car?

discopotato03 · Post by **discopotato03** » Fri Jul 25, 2008 1:03 pm

Not a Subaru .

A .

YouTube · Post by **El_Freddo** » Fri Jul 25, 2008 4:21 pm

brumbyrunner wrote:Whats the other car?

discopotato03 wrote:Not a Subaru .

In the words of Derrin Hynch: "Shame, shame, shame!

Bennie

Gannon · Post by **Gannon** » Fri Jul 25, 2008 5:54 pm

Run it by me again why you cant use a 4 plug spider throttle body?

While you are making an adapter plate, why not go with a bigger throttle body, like maybe something off a nissan. Surely there will be a similarity in the operation of the potentiometer and switch contacts.

discopotato03 · Post by **discopotato03** » Fri Jul 25, 2008 6:47 pm

Sadly no , arachnid's throttle turns in the opposite direction to I think all Nissans so their TPS's are no good . Also if you spit an arachnid TPS where would you get another at short notice ?

Spider and MPFI throttle is the same size so why not make an L series assembly fit ? All comon L series bits will fit and work then . Once the L TB fits so do both the 3 and 4 plug TPS's .

Its not as easy as many think to just throw on a larger throttlebody . The computer has no way of knowing that the TB is passing more air so the rate of throttle rotation won't be in sync with the acceleration enrichment .

Dare to be different , cheers A .

Late edit , have 3 of these things (spiders) so if the situation changes later - swap speedos top section .

vincentvega · Post by **vincentvega** » Fri Jul 25, 2008 7:57 pm

These TPS are just a potentiometer arent they?

if the polarity is wrongfor what you want, just swap the power and ground wires around and your signal will be inverted.

Subaman · Post by **Subaman** » Sat Jul 26, 2008 6:46 am

Its not as easy as many think to just throw on a larger throttlebody . The computer has no way of knowing that the TB is passing more air so the rate of throttle rotation won't be in sync with the acceleration enrichment .

Thats what the airflow metre/hotwire is there for

Have you tried playing around with a Throttle body from an EJ ?

discopotato03 · Post by **discopotato03** » Sat Jul 26, 2008 10:39 am

Mass Air Flow sensors don't do that any better than a Vain type one does . What the potentiometer in later "TPS's" does is tell the computer how fast the throttle is opening so that it can dump in enough extra fuel to maintain an adequate air fuel ratio . Also just in case you didn't know 3 plug computers have closed and ~ half throttle open contacts . The 4 plug ones I saw don't appear to have the open throttle contacts .

Also the reason why you can't just reverse the idle and open throttle contacts on a TPS that has both is because the little studs and tracks inside the unit don't just switch at barely cracked and fully open throttle positions .
In fact if you look at a genuine Subaru 85/86 WSM it tells you that the open throttle contacts switch at different points (degrees of rotation) between turbo and NA 3 plug L series TPS's .
In fact Subarus MPFI (spider and std) throttlebodies are a right bastard because the throttle plate is at an increased angle when closed compared to Nissan equivalents . What this means is that there is less degrees of throttle shaft rotation between closed and fully open and therefore the TPS's are set up to operate over different arcs compared to Nissan TPS's .
Don't worry , I looked into all the easy solutions but none of them suit what the 3/4 plug EA82 computers need in the way of correct TPS signals .

An EJ TB would very probably bolt up but all that gets you is a larger throttle plate and a more modern TPS that has all the same issues as the spiders one . ATM I NEED something that WILL work with my early 3 plug computer and the only practical solution is to throw what it thinks is its std sized throttle and TPS at it . Computers are totally blind , all they know about is sensor input signals so if it gets what it expects to have all's good .

This is not difficult , make up a rectangular piece of aluminium plate ~ 8-10mm thick with four holes and the lower two tapped . Weld it on referenced around the top two holes in the plenum , make sure its flat and bolt it all together . Actually a little fettling work to make sure the main hole is not partially obstructed at the top .
Rig the throttle cable and clamp on the spider systems native plastic TB to turbo duct of which I have 2 .

Easy peasy .

Gannon · Post by **Gannon** » Sat Jul 26, 2008 12:49 pm

I have seen a part of the fsm for the TB/TPS on an early lib and the electrical side of it was the same at either an XT4 or XT6 throttle body. (XT6 being larger than the XT4 one)

I ask you, why are you going with the 3plug ECU?

Why not go for the 4 plug or even better, an aftermarket one that handles both fuel an spark?

discopotato03 · Post by **discopotato03** » Sat Jul 26, 2008 7:23 pm

Because that's what it has ATM . If and when it gets the later system all it would need is the later direct fit 4 plug computers L type TPS .

A .

discopotato03 · Post by **discopotato03** » Fri Aug 01, 2008 5:26 pm

Quick update , L MPFI to Spider throttlebody adapter plate made and should return from being welded onto the spiders plenum section tomorrow .

Will have to sort out the engine loom extensions for the spider manifolds sensors etc . Breather plumbing is different as is its Nissan style cold air bypass valve .

From memory one of the heater hose pipes has a "T" piece off one side I think as part of the throttlebody water heating circuit . Something about the turbo spider system is different in that area as is its EGR pipe .

Having all the factory bits should make it straightforward , cheers A .

PS , is it possible to buy head to inlet manifold gaskets aftermarket or genuine only ? If so has anyone the part no handy ?

A .

discopotato03 · Post by **discopotato03** » Mon Sep 01, 2008 8:21 pm

Back with the Rally people today , I got to see the flange modified Spider top section and its quite impressive . If you didn't know otherwise you'd think they were made that way .
The next step will be to modify the cable quadrant that fits on the throttle shaft , the method is to weld the center hole up and remake it so its oriented around the assembly being almost horizontal rather than vertical .
The manifold runners have been smoothed internally because the Rally people reckoned they were a little rough . The EGR passage is packed full of hard carbon and may well stay that way .

Lastly I though it was high time Ellie had a new fuel pump so a Bosch VL Turbo one was fitted , along with new high pressure fuel hose downstream of the pump . We also replaced the high and low pressure hoses between the fuel rail and the hard lines behind the near side shock tower .
This was done because I had no idea of the age of the things and I'd rather be safe than sorry when experimenting with ethanol fuel blends .

Cheers A .

Gannon · Post by **Gannon** » Mon Sep 01, 2008 9:00 pm

Sounds good. Its been a long time coming

Didnt happen to take any pictures did you?

discopotato03 · Post by **discopotato03** » Mon Sep 01, 2008 9:51 pm

No , didn't have time - never have enough time . The trouble is that workshop is not close to me and I have to organise things to be done in a day so I can get home afterwards .
The Rally people are not confidant the engine change can be done in a day because things like the non std manifold and parts of its plumbing / wiring have to be done in situ .

I'm still waiting on info for the JDM TD04HL so the std Vortex turbo and it's hateful EA82T header may have to go on innitially just to get it running . That would also mean probably the std down pipe and exhaust (minus some butcher "exhaust fitters" weld in restriction) may have to stay a bit longer too .

Also I'm still collecting brake parts so that we have the right combination of bits for the 5 stud hub conversion with 4 piston front/2 piston rear Rex brakes .

Pile on top she who must be obeyed , two primates approaching the interesting years , shift work - it's a full programme .

Cheers A .

r00fi · Post by **r00fi** » Tue Sep 02, 2008 11:55 am

Sounds like a lot of bother to get the spider on. One word comes to mind.

Megasquirt

I'm in the same boat though - 86 RX with flapper. Spider sitting on the garage floor waiting for solution.....

discopotato03 · Post by **discopotato03** » Tue Sep 02, 2008 1:09 pm

Well the extra effort is needed because a Spider equipt L series was never a factory option , if it had been Subaru would have sorted it for us and everything'd fall in . Obviously Subaru only wanted the extra performance in the heavier bodied Vortex XT4 .
All I'm really doing is correcting the cable/plumbing/wiring differences between XT4 and L series .

Agreed the 4 plug computer system is better and to get it on this engine later only needs a change of TPS (4 plug L type) .
I'm interested to see how the early 3 plug vane type AFM goes with this manifold , may be quite ok .

Cheers A .