A/Rs and CCs (turbos)

[turbofiat]

Now that I have my Yugo 1500 turbo running sweet, there is still something to address. The spool up on my turbo has never been ideal compared to the Volvo 240 T3 I have on my Spider. The T3 on my 2 liter Spider will produce 7 lbs of boost as low as 3K rpms at full throttle with more boost on tap if I wanted to run more than that. So it seems to be sized perfect for that engine.

Because 1500s (and turbocharged at that ) are rare on this side of the Atlantic I had to do the best I could do. I sourced a T25 from a 2.1 liter 1991 Saab 9000. I'm struggling to make boost and I wonder if the turbo is simply too big for this engine.

By the way I have no intercooler on this engine and this is a blow through carb system.

I've been trying to find a descent turbo calculator with no luck. So I was hoping someone could tell me from these specs if this turbo is too large for my engine.

Garrett TB2529 (saab 9000)
50trim
.48 A/R (cold side)
60trim
.48 A/R (hot side)

My Yugo is a four speed. It won't produce boost in 1st or 2nd gear. In 3rd gear it will produce 5 lbs fairly quick at 3K rpms under wide open throttle, then seems to stall until I reach 6K then it will produce 6 to 7 lbs. In 4th gear I can't get it to produce any more than 3 lbs. seems no matter what condition. Even when going up hills with the engine under a heavy load.

When I initially set this engine up I found there was a 2 lbs pressure drop across the venturis. Or I just have a bad air leak between the turbo and carb bonnet. Saabs use an APC system and the wastegates are set to open at 5 lbs. I was seeing 3 lbs at the intake manifold.

So I plumbed in a mechanical boost controller. The one that uses a spring and ball bearing that blocks the reference signal to the wastegate then opens all of a sudden until whatever it's set at.

I have moved the boost reference signal from the compressor to the hose going to the boost guage off the intake manifold so the wastegate sees "real boost". Then reset the boost controller per directions. No difference.

Then I wrapped some duct tape around the holes on my blow off valve just to see if it was leaking and bleeding off pressure. Still no difference.

Two other tests I was going to perform was to disconnect the hose going to the wastegate to see if there is some issue with the boost controller and see what sort of boost I can get without a wastegate.

The other test was to connect the boost guage directly to the compressor wheel to see what sort of pressure directly at the turbo.

The other day I pulled the air cleaner off the turbo and spun the compressor with my finger to see if the bearings were starting to seize up. It moves freely, no shaft wobble and no oil in the compressor housing. So I beleive the turbo is OK.

I'm starting to wonder if no matter what 3 lbs of boost in top gear is all this turbo can possible produce and I'm going to have to swap out the turbo to get the boost I'm looking for.

Something else to consider. I used the Saab 9000 downpipe because it had a flared end on it. I beleive it's around 2.5" in diameter. Eventually it reduces down to around 1.25" at the tail pipe (factory exhaust). I'm wondering if I'm lacking enough back pressure. I've heard turbos need some back pressure to function properly. Typically people will tell you the bigger the exhaust the better but I've also heard that is not always true.

Thanks!

[Guy Croft]

Have you worked thru all the calcs in the Garrett website?

GC

[turbofiat]

Have you worked thru all the calcs in the Garrett website?

GC

yes but that really didn't tell me what I needed to know. It's telling me I need a GT2860RS with a trim of 76 and an A/R of .86 which is much larger than what I already have on the car. I know that can't be right.

[tricky]

I have a turbo Calc for you, perhaps Guy would permit the link to be posted.

Off the top of my head a GT 25 series would be closer to the engine in size. I've used these on 1400 Uno turbos, failing that give turbo technics a ring for advise.

[WhizzMan]

A T25 is being used on several Renault engines around 1500CC as well (R5 gt turbo, Fuego turbo) It should be performing nicely when it comes to the amount of air it can move and time it takes to spool up on your car. The trim sizes don't look very odd and you should at least get more pressure from this. a 1.25" exhaust diameter is a bit on the small side, you really want very little back pressure for that turbo.

Have you tried just closing the waste gate and see if it will get you more pressure then? Be careful, if you do get more pressure, there is no safeguard to prevent your engine from blowing up so as soon as you know, stop the engine and put the wastegate mechanism back on. Have you used the soapy water bubble blowing technique to try and find air leaks in the pressure circuit? Have you tried a red neck style side pipe exhaust configuration to see if you're building up too much back pressure? How is the temperature of the exhaust/turbo? If it's getting really hot, you have an indication that back pressure may be causing your problems.

[turbofiat]

A T25 is being used on several Renault engines around 1500CC as well (R5 gt turbo, Fuego turbo) It should be performing nicely when it comes to the amount of air it can move and time it takes to spool up on your car. The trim sizes don't look very odd and you should at least get more pressure from this. a 1.25" exhaust diameter is a bit on the small side, you really want very little back pressure for that turbo.

Have you tried just closing the waste gate and see if it will get you more pressure then? Be careful, if you do get more pressure, there is no safeguard to prevent your engine from blowing up so as soon as you know, stop the engine and put the wastegate mechanism back on. Have you used the soapy water bubble blowing technique to try and find air leaks in the pressure circuit? Have you tried a red neck style side pipe exhaust configuration to see if you're building up too much back pressure? How is the temperature of the exhaust/turbo? If it's getting really hot, you have an indication that back pressure may be causing your problems.

There is a possibility that I have too much back pressure. Since the original exhaust system was designed for an 1100cc 55 hp engine and I'm trying to make 110 BHP out of a 75 HP 1500 + 7 lbs of boost. I'm considering having a 1 7/8" exhaust system installed like I have on my Spider which seems to work well. I suppose I could disconnect the downpipe from the rest of the exhaust system and go for a ride and see if this helps.

I'm also going to disconnect the hose doing to the wastegate and see is this helps. Another possibility is that the wastegate spring is weak and the boost pressure is opening the discharge flapper and allowing exhaust gasses to escape. I suppose if this were the case, I could move the wastegate actuator rod by hand.

At the moment I'm just trying to rule out the fact that the turbo is too large for this engine.

[tricky]

Turbo calc link below (with permission)


http://www.squirrelpf.com/turbocalc/index.php

See how you get on with it and let us know.

Backpressure in the exhaust is evil with turbos, an exhaust with 2' 1/4 " diameter is about right for that size engine and a straight through perforated (single) back box.

[turbofiat]

Turbo calc link below (with permission)


http://www.squirrelpf.com/turbocalc/index.php

See how you get on with it and let us know.

Backpressure in the exhaust is evil with turbos, an exhaust with 2' 1/4 " diameter is about right for that size engine and a straight through perforated (single) back box.

Monday I disconnected the 2.25" downpipe from the 1.5" ID exhaust system and WOW, the car really came alive! So all in all it wasn't that the turbo was too small, the exhaust system was.

So today I had the muffler shop install a 2.25" all the way back through a turbo muffler. Sorry for the crappy photo I resized taken with my cell phone.

Yugo exhaust.jpg (94.06 KiB) Viewed 8216 times

Before with the 1.5" ID exhaust (2.25" downpipe back)

1st) No boost
2nd) No boost
3rd) 5-6 lbs (struggled to make that)
4th) 3 lbs max

With the 2.25" downpipe and rest of the exhaust system:

1st) No boost
2nd) 3 lbs of boost before hitting redline
3rd) 7 lbs (actually hit as high as 10 lbs before readjusting the boost controller)
4th) 7 lbs no problem

I'd have to say now that this turbo spools up quicker than the T3 I have on my Spider.

I don't know if this is what you would call "Boost creep" but in 3rd gear I
noticed that as the RPMs increase, the boost will rise to 5 lbs progressively.
Then it seems the turbo really starts to spool up and will build up to 7 lbs in
almost a split second. But I've noticed that the boost will continue to rise to
about 8 or 9 lbs for about a second then fall back to 7 lbs.

Out of sake for reliability I'm wanting to keep it at 7 lbs. I can't hear any
detonation but I'm afraid that's just way too much boost for a stock headgasket
and drivetrain. I wouldn't think hitting 8 or 9 lbs for one second would cause
any damage.

One of these days I'm going to get tired of 7 lbs on both my Spider and Yugo and crank the boost up 1 lb at a time until
something breaks. I've been turbocharging Fiats for 14 years and still don't have the
nerve to find out a Fiat's breaking point.

[timinator]

Hi turbofiat, it sounds like you are using a n.a. cam with your turbo. To speak in general terms, because of the timing events of the n.a. cam, you are bleeding off a large amount of the pressure the turbo needs to make boost. This will make the turbo slow to build boost. The turbo will then need more time to build up speed causing limited boost in the lower gears. It will also cause the boost to occur at higher rpm in the taller gears.

I don't have any experience with hot air systems. I believe that Mazda held boost to 5 psi with their hot air setup.

[/quote] I wouldn't think hitting 8 or 9 lbs for one second would cause
any damage.[/quote]

One second is unfortunately more than enough time to cause a lot of damage.

[Guy Croft]

"Hi turbofiat, it sounds like you are using a n/a cam with your turbo..."

I am sure I remarked on this (or ex cam?) in an earlier thread by James. Atmo inlet cam u_might get away with but certainly not exhaust if that applies. Not in this spec anyhow.


G

[turbofiat]

"Hi turbofiat, it sounds like you are using a n/a cam with your turbo..."

I am sure I remarked on this (or ex cam?) in an earlier thread by James. Atmo inlet cam u_might get away with but certainly not exhaust if that applies. Not in this spec anyhow.


G

Yes I remember you telling me about the UNO turbo camshafts. As of right now I'm very pleased with the performance of my Yugo.

Since the car doesn't have limitied slip, I'm limitied to the amount of power because when the turbo "accidently" spooled up to 10 lbs, the front wheel started to spin on dry pavement.

That's one reason why I don't like front wheel drives. And the nasty torque steer they produce. I think they are also dangerous on wet roads. My wife did a 360 in her 2007 Chevrolet Cobalt one day. She claimed she wasn't going fast. But I think the roads were wet and she was going around a curve way too fast.

I wanted to fit an UNO split driveshaft on my Yugo but in order to do so I was going to have to upgrade to a Yugo or Ritmo 5 speed gearbox (hard to come by). I tore apart an X 1/9 5 speed hub and studied a way to modify it so I could use the 4 speed CV joints but the bearings are different sizes and gave up on the idea.