ALFAGTV6.COM

[GarthW]

Mats, have you driven a gtv6 with a single turbo jobbie?

I mean does your 75 have a V6 lol?


Would love to hear how they drive and everything.

Like how responsive it is and stuff.

[Mats]

Nope, I'm just horsing around. This is my best work right here.

[Barry]

Garth,Single setup was chosen for ease of install,the fact that Id done a cast manifold for a single,the cost of one turbo only,an uncluttered engine bay,the un hindered ease of constructing and fitting a reasonable diameter downpipe,and the fact that I found NO dissernable difference in so called "lag"or spool up of the turbo vs twins.
Ive untill recently run a .58 turbine housing,dash 5 Turbonetics shaft,and dash 25 comp wheel in a ar60 comp housing.
Recently Ive gone to a .64 turbine,same shaft,60-1comp wheel and an ar60 comp housing.
I believe that when a turbine housing starts glowing red under full load,its too small and you should then fit a larger ar housing.This little rule of thumb of mine has proven pretty spot on by doing back pressure tests.
I will also say that some serious large ar ratio ,fancy turbine housings do give the same spool up results as the smaller housings.
Then again id rather have a quick spooling turbo and drive ability with less top end power than a bitch engine that does nothing untill 5000rpm and then suddenly give you 700hp.Id rather settle for 350 and have drivability.If its the other way round,I dont want the engine.
I also dont go for mammoth diameter intake runners as I would do for a n/a engine.37mm id is way sufficient for a turbo engine.

A little 2.8l single turbo will make consistent 240 wheel hp here at .7 bar boost.

The x over pipe takes nothing away from the spool up time on the single.You will see I don't go for large piping here either.Remember that each bank has 3 separate slugs of exhaust gas coming into the manifold per cycle.They dont overlap as the overlap must include the other side manifold.So,taking the 3 slugs they will independently be traveling down the x over pipe.Don`t make it large diameter wise,you will only slow the slugs down before they reach the turbine where they get speed ed up again and impart energy to the shaft.
Im sure when you build a V-tech(Yo!) that runs 800 hp at a gazillion revs,you might have to rethink your design criteria.I don't know,I only do Alfa`s.
Start building your engine,keeping things simple .You`ll end up with a nice base from which you've learn `t a great deal from.
And thanks for the mails,hope Ive given some help here..

[Barry]

I need to add that when a 3.7l 24v engine was run here on a wheel dyno,it made 237 wheel hp.When it was run States side it made 350 odd wheel hp.

THIS IS PURELY FOR COMPARISON PURPOSES!!

It simply shows the difference between dynos used here and those godawfull single drum things...JOKING!! and dynos used elsewhere in the world.

There is also SAE vs DIN,JIS,etc,etc...

Gees,Im trying to tread carefully here...

[rz]

barry don't forget your dyno is at 6000 FT elevation or 2000 meters altitude

[Mats]

I believe that when a turbine housing starts glowing red under full load,its too small and you should then fit a larger ar housing.

Or check your ignition map.

Im sure when you build a V-tech(Yo!)...

[GarthW]

Barry thankyou mate, you have helped a great deal... and that was exactly what i was wanting to hear.

I would much rather go a single now more than anything.

I understand why diameter of pipes shouldnt be too big, that i agree with.

240kw from only roughly 12psi is very good.

Thanks again Barry.

[Barry]

Mats,so true!! Retarded ignition is great for creating glowing housings!The turbo also develops boost while idling..
Little story here...I had the green wire connections swapped on a giulietta v6..the more load I gave the more this turbo boosted and I was going no where..The trigger edge was triggering on the rising edge and therefor retarding the timing with revs..You also been there Mats??This is how we learn I suppose..

Garth,your welcome mate..that was wheel hp though.....and 10psi boost..

Marc,so true...but our elevation is not going to make such a dramatic difference..You should not see much more than about 17% from sea level to 6000ft..

What you really need to do is drive.If you have this stupid grin on your face,Its a nice engine...

[Barry]

Ooeer,quick on the avitar there Marc!!Nice one..

[Mats]

You also been there Mats??This is how we learn I suppose..

No, but I have had extensive experience with the 75 turbo, one of it's "safety features" is to retard ignition a lot when on boost to not knock. When I say a lot I mean it, when I mounted my new turbo after the turbine shaft broke on my old one (due to heat) I took it for a spin around the block, nothing serious just half throttle accelerations in second and third to get the engine temp up to check for leaks. In other words, I was taking it very easy and only letting it go to boost in the last couple of runs to check where the boost started to build.
Rolled back to the garage and opened the hood to have a look at possible leaking points, I found the sun under my hood... The turbo was so Yellow I thought something was burning with an open flame for a second.
Checked ignition advance and it was fine. Thinner casting in the turbine housing on the new turbo made it glow nicely.

That's when I decided not to do any more engine mods before getting a management system. Three years later I sold the car instead.

[Greg Gordon]

Although I am not a turbo guru, I will say that single turbos seem to be the more dominant set up. A lot of Twin Turbo Supra MKIVs are converted to single turbos, and those Supra guys get huge power numbers from those single turbo systems. The Buick GNs run one big turbo on a V6 with a setup that's a lot like Barrys and they are getting insane amouts of power.

All turbo aircraft engines I know of run a single turbo (some WWII aircraft run a single big turbo AND a supercharger) and they work very well. The Piper Chieftain's big six cylinder motors run a single turbo and they can maintain rated horsepower up to 25,000 feet. Those turbos glow red hot causing uninformed passengers to think the engines are on fire.

[Mats]

There is a big difference between an aircraft engine and a car engine though, the aircraft is more or less a constant rpm engine and can live with a huge "lag". Often such engines (aircraft and marine) are designed to have a constant pressure manifold rather then the normal automotive manifold which use the pulse energy in the exhaust to spool the turbo quickly. A constant pressure manifold will be more efficient at a constant RPM but that's not what we want on a passenger car.

So while the single turbo installs are very popular with the drag/dyno queen crowd (because it is more efficient being bigger -> large HP numbers) it is not certain that it is the best solution due to the fact that the spool time usually is larger (inertia) and it can have a high boost threshold. This can be minimized with some clever engineering though. The normal single turbo build is often done with a huge truck turbo though, housing is never a good match for a gasoline engine and the castings are incredibly thick and heavy. If you can afford an aftermarket race turbo though... yummy.

I have no doubt that Barrys single turbo install works great but I think a twin turbo install would be better...
Theoretically that is.

[kevin]

Mats, I agree with you but I could not even get half of the full potential of my twin turbo set up on myGTV 2.8L due to something on the driveline breaking. The cost of maintenance was also very high on the td04's and space much tighter in the gtv's than in the 75's. I think from an economics point of view and keeping the existing drivetrain the single turbo is far more friendly and can still deliver killer power. There is on in my area which destroys most things on the road.

[Barry]

My goodness! Steve S`s turbo! The first one I did!
I believe a lot of additional goodies were done to it..Nice one Kev.

[Mats]

mmm, lovely bit of backyard engineering on that one. Coldstart injectors everywhere, possibly triggered by a pressure switch or a rpm-relay or even both?

Some day when I'm really drunk I'll show you the bastard me and a friend built. it had K-Jet so the CS-injectors had the full system pressure (7 bar), they flowed a lot and we used a few with the above mentioned triggering way. It went from 100-150Km/h in fifth gear in 5 seconds flat. Damn that thing was hilarious.