Can i ask turbo type questions as i think ive confused myself...

[Egon]

Hey all.

Been a while, i know, but ive been lurking and looking.

I have an alfa 147 these days and its mental. its a 1600cc with a few added bits from the 2L engine that help it breathe.
BUT....
I'd like to run a light pressure turbo on it. Circa 5psi. Not a lot i know, but without getting into spacers/pistons and standalone ecu etc it will add a few ponies.

So i bought a book to try and learn what i need to work out and get some figures made into metal.

I have, however been over thinking it a bit and confused the crap out of myself....

Figures:

VFR:
1598cc (97.5cu/in)

97.5cu" x 7500rpm x 90% (volumetric efficiency) / 3456 = 190.4 cubic feet per minute needed.

I'm looking for 5psi, so Pressure ratio = 5psi+14.7 (sap) =19.7 / 14.7 = 1.34 PR (stop laughing...!)

Thats 190.4 cu/ft into lbs/min (/13.7) gives me 13.89 lbs/min.

I cant find a map that i've landed anywhere useful....

[Egon]

Sorry, 2 kids distracting me. Little sods.

right, i'm looking at maps. Now i've plotted my PR and corrected lbs min on a few maps, namely a gt1544 (43.9mm 56 trim 0.33 ar) and i'm waaaaay off the
useful lines.

Do i need to land on the lines of the compressor map? surge is to the left isnt it? and choke is to the right?

[skyshack]

97.5cu" x 7500rpm x 90% (volumetric efficiency) / 3456 = 190.4 cubic feet per minute needed.(

It's a 4 stroke, it only inhales 1/2 the swept volume each revolution. 1st 1/2 rev 1 sucks, 2nd 1/2 rev 3 sucks, 3rd 1/2 rev 4 sucks, 4th 1/2 rev 2 sucks = 2 complete revolutions.

= 190.4 / 2 = 95.2 cu ft.

Do i need to land on the lines of the compressor map? surge is to the left isnt it? and choke is to the right?

Yes, yes and yes.

[Evilchap]

It sounds like you may be over-thinking this a little - trying to get it perfect. You realise once it's on, within a week you'll be fancyung more, and then more again.

I'd suggest looking at what the MX5 guys use - TD04, T25 or T28 usually - OE Subaru or 200sx turbos. You know they work well on that sort of size engine, will be well within the efficient range when running although near the bottom of it, so you then have headroom.

Your challenge will be pipework and ecu tuning I would say. Also, add an intercooler.

[immy21]

This calculator/table generator might help:

http://www.lovehorsepower.com/joomla...d=35&Itemid=96

[Egon]

Heh, told you I was thinking too hard!!!
Pipework and intercooler are a bit easier as they made a jdtm diseasal version of the 147.
There's plenty of dead ones around!
I can't have more yet as that's the next project! The inlet is plastic so will break up after 5psi. So might as well build a proper engine if this actually comes off!!!

Sent from my HTC One mini 2 using Tapatalk

[R3K1355]

Is it worth it though?

You'll easily be sinking a grand into it, at the very least.

[Egon]

always worth fiddling....if it aint broke, fix it til it is...
manifold and second hand turbo, pipes, interwarmer, so far costing me less than 400 quid....

[TomK]

always worth fiddling....if it aint broke, fix it til it is...

No help on the topic discussion, but i really like that quote, rings true a lot of the time.

[Egon]

Heh, cheers Tom, as my Mrs points out to me "you buy projects, not cars"

Ok, so after halving my cfm, I'm on the 70% efficient lines of a gt1544, which is handy as I have one in the garage...
Got to make a 4 bolt to 3 bolt flange....cue the music....

[Egon]

Ok, flange being bodged er, made up...
Another question though...
Recirculation valve or not? With the tubby running next to no pressure, would a recirculation be a good idea? I'm not dumping, as that's just wrong.
Do recirc valves have specific opening points like a wastegate?

[zeppelin101]

They are sprung and preloaded so that they only open at a certain pressure in the same way as a pneumatic wastegate.

[Egon]

So I'd have to get an adjustable one?

[Pete C]

I wouldn't even bother, it'll make sod all difference and don't you want to hear some turbine stall through the air filter?

What are you doing for fuelling, rising rate adjustable FPR and maybe some bigger injectors, try to get by on the standard map?

[skyshack]

At 5 psi your pressure ratio is about 1.34 and the turbo speed is quite low. No possibility of any turbo damage from surge. Just fit a cone filter and let the pigeons out.

Even 10psi won't cause any bother.

[zeppelin101]

In practise it doesn't really matter what pressure you run the damage caused is minimal, it would only be a problem if some form of anti-lag (remember that anti-lag never really maintains the target manifold pressure, it is pretty horrid to drive when that is the case) where the turbine is being physically driven is a problem.

If you imagine that once you're left off the throttle the throttle blade is closed; there is no airflow through the engine and therefore no exhaust gas driving the turbine wheel so there is no adverse loading on the bearings if air were to come through the wrong way on the compressor side.

Compare that with the turbine being loaded up and the same thing happening (i.e. genuine compressor surge) and you can see how this would be a problem as far as the loads on the central bearings go.

[Egon]

Cheers guys, lots of working away so no chance to get busy.

[Egon]

Flipping heck, this gets all techy, doesn't it?

Um, my actuator appears to work backwards.. I thought they opened with positive pressure? Mine is all floppy till I suck on the tube to the actuator. Is that wrong? Am I having a blonde moment????