Does a G-plate Turbo II have the twin-scroll turbo?

[elford_tim]

Evening all,
I went to look at an FC convertible today - bit of a fix-upper (especially given that it\'s got a Liz, erm, H****y engine in there that\'s a couple of thousand miles away from going *bang*) but it\'s priced sensibly and seems to drive generally in line with expectations apart from a small niggle.

It hardly seems to run any boost - when almost flooring the accelerator on the few stretches where I could, the boost gauge didn\'t show much interest and barely rose above the \'0\' mark - probably by a couple of marks, but still very, very low. Which also meant that the shove in the a*se was a tad lacking.

Now from visiting the murkier regions of the web (aka American FC-related websites) I vaguely seem to remember that the earlier turbos had the twin-scroll turbo with the "flap" and the actuator on these can stick? Does anybody know if that can cause the symptoms above (ie some, but not much boost)?

I\'m in two minds about the car - I liked the way it drove (no clonks or anything) but I noticed the boost problem above plus the fact that the gearbox was rather stiffer when cold than on the last FC TII I drove...

Any pointers appreciated...

Cheers,

Tim

[antnicuk]

A few things,   the stock gauge is crap so ignore it.  Mine does the same a 10 psi.  If its a fixer upper, then i would not worry too much about boost, i would be more interested in the condition of the body and the roof if its a Cabby.  The UK models didnt come with the type of turbo you refer to, its the series 4 (not made in the UK)that had the extra \'flap\'. although both are twin scroll.  Boost is fairly easy to sort out, the worst its gonna be is a turbo and they are cheap now for a good 2nd hand one.(i have one if you need).  there isnt much else it could be if the boost is too low except a completely knackered engine but as you\'ve mentioned, you are expecting it to pop.

 A stiff gearbox when cold means its in fairly good nick and may just benefit from some new oil.

[Brett]

Worth mentioning that the C clip on the wastegate actuator can easily fall foul of rust etc and slip off, this cant be seen without removeing the heat shield, but would account for no boost.  Look for some split pipes too.  
 If its a twin scroll turbo it will have the early rear lights (rectangular as opposed to round)

:wave

[elford_tim]

A few things,   the stock gauge is crap so ignore it.  Mine does the same a 10 psi.

OK, so I assume that the fact that the needle is moving and the whistle of the turbo would suggest that the turbo is at least patially working?

If its a fixer upper, then i would not worry too much about boost, i would be more interested in the condition of the body and the roof if its a Cabby.

Roof is a non-standard colour mohair one in very good nick - almost new according to the owner, which I\'m inclined to believe. Body is OK(ish), it has had welding to the sills for the last MOT, some parking dings and unfortunately the rear quarter panel has been keyed through to the metal - that needs sorting out ASAP.

Boost is fairly easy to sort out, the worst its gonna be is a turbo and they are cheap now for a good 2nd hand one.(i have one if you need).  there isnt much else it could be if the boost is too low except a completely knackered engine but as you\'ve mentioned, you are expecting it to pop.

Well, the price is OK IMHO for a car that needs basically a respray eventually and an engine rebuild but I\'m not willing to cough up that much money for a car that also needs a turbo and god knows what else.

A stiff gearbox when cold means its in fairly good nick and may just benefit from some new oil.

Well, at least some light at the end of the tunnel then...

Cheers,

Tim

[grinder]

i bet a pound to a pinch of salt its in gun metal grey

the engine is fine on that car - its been rebuilt twice already ! ( but dont quote me on that !! ) - supposedly it was rebuilt around the 90K mark aswell ??

if its the one im thinking of - then at one point it was sold for £600 ( and i turned it down at that price aswell )

And ASAIK - the S5 was the twin scroll turbo and the S4 were a single scroll turbo

i guess at : http://www.findit.co.uk/cars/mazda/rx7/101584.php

if it is - i have some pics of it somewhere , when all the roof had been cut open ( im sure they are at work on the PC )

[88GT-R]

S5 turbos are not twin scroll, the S4 used the twin scroll system, being reasonably efficient. Although when mazda designed the improvements for the S5 engine, they found that using a slightly larger exhaust turbine in conjunction with higher compression rotors negated the need of a twin scroll setup to aid spool time.

John

[elford_tim]

i bet a pound to a pinch of salt its in gun metal grey

Indeed...

the engine is fine on that car - its been rebuilt twice already ! ( but dont quote me on that !! ) - supposedly it was rebuilt around the 90K mark aswell ??

I seriously doubt that the engine is fine on the car - it doesn\'t want to idle on its own when it\'s cold (you have to sit in the car and gently keep the revs up for a couple of minutes until it actually wants to know), plus when hot the idle is all over the place, anywhere between 800 and 1100 rpm. It does still pull reasonably well but when my Elford only wanted to idle at around 1300 it was new engine time.

That said, the current owner suggested that the engine had been rebuilt once, about 40k ago. Car now has around 96k on it...

if its the one im thinking of - then at one point it was sold for £600 ( and i turned it down at that price aswell )

And ASAIK - the S5 was the twin scroll turbo and the S4 were a single scroll turbo

i guess at : http://www.findit.co.uk/cars/mazda/rx7/101584.php

Do you know what you can do with your guesses? Do ya?

Cheers,
Tim

[elford_tim]

S5 turbos are not twin scroll, the S4 used the twin scroll system, being reasonably efficient. Although when mazda designed the improvements for the S5 engine, they found that using a slightly larger exhaust turbine in conjunction with higher compression rotors negated the need of a twin scroll setup to aid spool time.

John

Cheers Jon, that clears that one up.

[FD3SNuttah]

Indeed...



I seriously doubt that the engine is fine on the car - it doesn\'t want to idle on its own when it\'s cold (you have to sit in the car and gently keep the revs up for a couple of minutes until it actually wants to know), plus when hot the idle is all over the place, anywhere between 800 and 1100 rpm. It does still pull reasonably well but when my Elford only wanted to idle at around 1300 it was new engine time.


Cheers,
Tim

is it running low on petrol?? i had this problem with mine, so i put another fiver in and it stopped doing it!

[elford_tim]

is it running low on petrol?? i had this problem with mine, so i put another fiver in and it stopped doing it!

Half a tank left according to the fuel gauge...

[grinder]

i will try and get some pics up tomorrow

[88GT-R]

Tim,
Not seeing the car, it is difficult to say, but what you say about the cold idle problem and fluctuating idle points to an improper set BAC valve, TPS or idle cam. The fluctuation would also be a by product of the above as well as a couple of vaccum leaks.
Unless it had a shody build and poor maintanance, the engine as a whole should be good.

John

[elford_tim]

Tim,
Not seeing the car, it is difficult to say, but what you say about the cold idle problem and fluctuating idle points to an improper set BAC valve, TPS or idle cam. The fluctuation would also be a by product of the above as well as a couple of vaccum leaks.

OK, TPS I understand. Idle cam I don\'t quite but I can hazard a guess at what it does. But a BAC valve? I assume it\'s not a device for people smoking two packs a day, but what the hell is it?

Or would that be something that\'s more commonly known as an idle control valve?

Unless it had a shody build and poor maintanance, the engine as a whole should be good.

Well, let\'s just say that I\'d feel a lot more comfortable with the engine if it had been rebuilt by WGT or by Carl Hayward...

Cheers,
Tim

[88GT-R]

I See...
Bac valve: Bypass air control valve - primary air bypass valve that controls idle on the engine against varying engine loads. If this is incorrectly set, the incorrect amount of air will be bypassed.
Idle cam: There are 2 lines on the throttle linkage that the idle cam needs to lie between. This ensures the proper gap between the throttle plates and housing when there is no tension on the throttle.

John

[elford_tim]

Right, kind of as I expected - may be worth a check anyway.