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Talking about an engine almost stock... how far can i go? stock turbo and internals, maybe camshafts and evo header.

How much pressure? front intercooler?

For a race aplication, and i don´t want to blow up the engine...

Couldnt tell you for sure, but the recipe is fairly straightforward- increase total airflow potential without turning to monster boost levels, and it should be fine if its tuned well.

400hp GT28 with the .7 front housing, a new flange to fit it to your manifold, running around 15 psi, a 3" exhaust from the dump pipe back, a front mount intercooler, and aftermarket EFI. I would say 300hp or thereabouts would be on the money. I wouldnt be revving it though.

Get the pipework and manifold HPC coated to keep the heat in, and as you go, a new tuned length manifold, head porting, and valve work will get you the same power levels, easier.

Well, the main problems are really the injection system and the cams.
The intake cam lift is something like 8mm and the std injectors kan support ~180-190Hp on a good day plus that the ignition advance curve is very biased towards knock prevention which means it's retarded at medium to high revs and that builds heat, loads of heat! Have you ever seen a manifold without cracks on a 75 T? :/

So light flow prep of the head + cams, bigger injectors and a good engine management system will do wonders. A bigger exhaust will be good too, it lowers the back pressure in the manifold a bunch.
This will go a long way and will keep you out of trouble, don't raise the boost pressure large amounts as this only brings the turbo closer to the edge of it's operating envelope, 0.9-1.0 Bar would work but not higher if you're not looking for an excuse to upgrade.

Well, the car now runs whith 1.2 bar...

And it´s a race car, no front intercooler, and no hose to get fresh air to the intercooler .

I hope to get the car in a week, so i can´t tell all the specs of it now.

Now it has an stock head, the last one has a little flow job, but he changed 2 times the headgaskets on that head (one per race) runing up to 1.7 bar one time and 1.4 the other.

I´ll keep the car info updated.

1.2 bar with stock fuelpressure and injectors? Then it will run lean over about 5000 rpm when the injectors hit 100% duty cycle.
No wonder he had to change head gasket. Very easy to blow the head gasket if you drive it hard without proper warming up.
The lifespan of the turbo will be seriously shortened if you raise the boost that high (1.4-1.7) I'm suprised it even lasted a day/race.

Yo, Viking! Easiest thing for us here is to chip and install a variable fuel press. regulator set at ~3,4bar, cold plugs and use 100 oct. gas. We get (reportedly) ~195-210hp @0,9-1bar boost. Thats what I have in my car but I will not dyno as there's oil in the coolant (%#$@) and the snail has never been rebuilt (excessive radial play). It goes ballistic after 3500rpm! I had to fiddle a lot with the static advance, as +_ 1* is make or break! 1* more, will not boost at all (knock sensor works good!). Too bad I'll replace it with a good 3liter, I had plans for this motor! However, here in Greece its very risky to beat the crap out of a turbo in the track during the summer. I've seen too many snail riders go BOOOM!
Jim K.

hehe, 7.5:1 compression and you need 100 Octane gas for 0.9-1.0 bar of boost? Now thats what I call a safety margin.

Chip will work as long as you know what the hell it does with the ignition, standard ignition curve is very weird and I bet the knock sensor happily lends a hand to spoil the fun.
Food for thought, has anybody tried different torque for fastening the knock sensor?

I'd like an oscilloscope and a rolling road for a day just to figure out how the ignition works and how it retards the timing when it thinks the engine is about to knock.
I still haven't figured out how difficult it must be to make it knock with that compression ratio and correct fueling, especially with the standard boost level of 0.7 bar...
What were they thinking..? :/

Jim, you mean to tell me that your car turns down the boost when it think it knocks? That's the first time I heard a 75 do that, normally it just lowers the ignition to stay "safe". heh.

Yes sir I do and here's the whole story:
When knock is detected (still inaudible to us) advance is retarded by a pre-programmed increment in all cylinders. When knock stops,the advance will be gradually restored to the previous value.When the advance reduction reaches the internal preset limit and knocking is still detected, the Pierburg valve is ordered to open the waste gate, relieving boost. If there is a fault in the knock sensor cct. a preset 'safety' advance value is set and no boost is allowed. In this condition there is only ability to drive slowly to the nearest service point.
The 164 V6Turbo follows exactly the same principle with a few refinements like individual cylinder advance reduction, curtesy of the inductive cylinder recognition sensor.
See Mats the system ain't that dumb after all!!
Jim K.

Not dumb? Like when it retards the timing to the limit when you drive at 70Km/h just cruising, real bright...
Theoretically it's not a bad design, in the real work however, eeeew.

Have you played around with ignition timing with the standard chip? Care to share any info on that?

Mats, when I first drove it home from the seller, the car boosted to over 1bar and pinged like crazy! Some other Turbo owner told me "thats what all turbos do"!!!!!! No way I would believe the flucker and when I got home I popped the hood and had a look around (had never checked out a 75Turbo before). Lo and behold, the Pierburg connector was just hanging there..! I reconnected it after cleaning the contacts, and took a drive. The thing would get to 0,25bar and no more. Some more checking, revealed a stuck Pierburg valve, due to oil fumes and dirt. I cleaned the part meticulously with spray cleaners while electrically jogging it on/off very quickly. This did the trick. Went out again and it boosted to ~0,6-0,7. Off boost it was a complete dog, so I decided to play with the ign. timing a bit. I set it to ~12* and while it worked great atmo, there was...no boost!
I started reducing advance by ~1* intervals until I got to ~9* where it behaved half decently off boost also. That was with 96oct leaded gas! When I switched to 98-100 unleaded, I was able to set to ~10*. All this was done within a couple of days after getting the car. You always have to find your way around with an unknown quantity. Then, I changed the chip and raised fuel pressure a bit, installing N2C plugs (I swear by those things in any engine I've had!). This way I could even get ~1bar even in summer, for some spectacular top speeds (for a 75T) of around 220kph (~6100rpm). Now you got the whole story!
BTW, AR literature says you must be very precise with torquing the knock sensor, I haven't messed with that. I was ready to install a series 2 exhaust manifold (2-plane) but never got around to it as it requires quite a bit of additional work to fit the snail back on. Supposedly its good for about 10hp. I'll never know!
Jim K.

Thanks, I'm at 9* now, feels like the ignition ratards like crazy though.

this the Evo/series 2 exhaust manifold isn´t?

I think that my future car have one, if doesn´t i know were is this one.

Yep, Evo manifold. I have it on my car, doesn't really need to modify anything to fit it.
You may need to apply "gentle pressure" to make the turbine clear the body when you fit it over the studs though.

I made a 3" free flow exhaust at the same time so I can't really say which mod made any difference.
And now I have a Mitsubishi TD04 turbo too...

I think it´s time to build another megasquirt for the turbo... and play a little whith the ignition maps.

The question is, megasquirt driving the stock ignition stuff, or upgrade to EDIS4?

Mats, from which car is that Mitsu TD04? benefits? turbo lag? power under 4000 rpm?

-Volvo T5, TD04-16T (smallish really).
-Much smaller then the std T3, integrated bypass (good with the stock setup, maybe not so good with a front mounted IC), less lag and better spool characteristics (less KABLAM feeling)
-Spools from around 2300 rpm... when you reach max boost vary depending on which gear you're in, in high gears the turbo manage to "catch" the rev increase, in first the revs rise faster then the turbo spools so boost arrives later. This is not specific for this turbo of course, the std T3 is much worse.



You need one of these to fit it or it will leak.


Good size geometrically and it still pumps more air...


My std turbo after about five laps on the track (but it wasn't really brand new before taking it to the track )


First part of the downpipe, exducer is nice if you manage. This is just done "on the fly", nothing calculated or so.


You will need some new hoses too


Hope I'm not clogging the thread.