Scarey Engine Build Estimate

[audiman]

LOL, im getting tempted by a GT40R now, been talking to Doug and Mihnea too much i think. Gonna have to stick with mine for now. I have never added up the costs of the engine rebuild, but i know for a fact that doing all the work(except machining) saved me a fortune. I still spent in excess of 4k and that was doing it 'on the cheap' using my old pistons, just re worked.

[S2central.net]

Yeah Tom - my 10k estimate was for parts alone - with me doing all the work except critical machine shop stuff. If anybody was having a monster built by someone else, its a whole different set of numbers.

I'd really like to get a side - side comparison of driveability, torque, lag and ultimate power between the GT30R and the GT40R on a couple of S2 conversions.

Paul

[Mihnea]

Paul, with 2.5PR and 90%VE, considering no pressure drop across the intake tract (or insignificant at least), a 2.2 20vt engine will flow 37lb/min. Plot this on the GT30R 56trim map and you'll see the efficiency, it's pretty good. IMHO 37lb/min is about 360-380 crank HP, so where's 450 HP on that turbo????


GT40R rules, I think it's going to be my next turbo... Dunno at what sort of RPMs full boost is going to be there, but I don't give a ****, it's not gonna be meant to be a low RPM torque monster, for that there's the RS2 one that's a great turbo


Mihnea

[Pisobiker]

Does anybody have the GT40R maps? I have the GT40 (not R) which match quite close to the GT35R.

Marco

[Mihnea]

Here's one Marco!




Cheers,

Mihnea

[Albert]

Mihnea was quicker

the turbo map is not yet avalible for GT40R but it sould be close to GT40 map



but the lines should be a bit lower

[Pisobiker]

nice map. Pretty wide flow range too!!

thanks guys.


Marco

[S2central.net]

Yeah - that map pretty much confirms my assumptions... Just done the maths and whilst the GT40R will go absolutely bananas above 5000rpm where it can sustain 2bar boost until the redline (and beyond) - my calcs show that it cannot generate any boost until 3500rpm - below that you have a non turbo engine. Calcs to be posted and a rough graph maybe.

We can argue VE assumptions till we are blue in the face, but this is a turbo for the drag-race boys in my opinion.... UNLESS you want to run with something like nitrous with a sensible controller that only uses it up to 4000rpm - that would improve driveability low down an mid-range.


Paul

[S2central.net]

Snapshot of GT40R compressor calculations attached.

Paul

[S2central.net]

Snapshot of GT40R compressor calculations attached.

Paul

And the resulting graph plot for GT40R....

[Pisobiker]

Hmmm....

a little too close to the surge line Paul, IMHO. Don't know how god our ECUs are in lowering boost when changing altitude, but AFAIK a little more margin is good practice. This worsten things a bit too.


Marco

[S2central.net]

Yeah Marco - I absolutely agree with that being bang on the line - in reality you would run with decent margin. Part of the guessing comes from the estimate for VE in my calcs. If you could run higher than 95% VE, then you would get further from the surge line at any given PR value.


Paul

[Pisobiker]

95% VE is a pretty high value! I wish my homemeade porting and polishing job will reach that value. On a turbocharged engine, where it's not possible to use very succesfully the aid of intake and exhaust pressure pulses for VE purposes, I'm not sure it's resonably possible to go over 93-94% (eventually only apart from strictly racing engines) and, moreover, this only in a pretty narrow rpm range.

Anyway I see lately there has been a rush on bigger and bigger turbochargers here, guys!
How come?
What I mean is, if we agree the RS2 KKK7200 turbocharger with 54mm (?) turbine exducer will safely flow 38 lbs/min @ 2.4 PR, or 36 lbs/min @ 3 PR with about 65% compressor efficiency, why shoulden't the GT30R, with 60mm turbine exducer, be able to flow 50 lbs/min @ 2.6 PR or 49 lbs/min @ 2.8 PR?

In this matter I think the GT30R fitted on the 2.226L engine, supposing it's built to run safely up to 7500 rpm, shoudn't have too many problems providing flow for 500 hp @ something around 1.7 bar manifold boost @ 7500 rpm. this, of course, with well designed and tuned intake and exhaust systems.

The GT40R, at this point could flow close to 700 Hp @ 2.5 PR, but of course for such a power target the 2.226L engine will need much more than the 1.4 bar manifold boost @ 7500 rpm the GT40R can provide. But @ 2.0-2.1 bar boost the GT40R might be able to flow 60 lb/min (also seems to me with high efficiency), so the 600 hp might be it's target.


Any comment welcome.


Marco

[S2central.net]

Paul, with 2.5PR and 90%VE, considering no pressure drop across the intake tract (or insignificant at least), a 2.2 20vt engine will flow 37lb/min. Plot this on the GT30R 56trim map and you'll see the efficiency, it's pretty good. IMHO 37lb/min is about 360-380 crank HP, so where's 450 HP on that turbo????

Mihnea

Yeah but why stop at PR=2.5 ?

The same turbo (GT30R 76.2mm 56trim) can run with PR=3 (Boost @ 1.7bar) for 50lbs/min on the 2226cc lump at 7500rpm with VE=85% - according to my calcs anyway - and thats darn near 70% efficiency on the compressor !

At 20 celsius and 1020mbar ambient pressure with Pf=1 (psi), Pi=2, with intercooler efficiency at 87% that gives an air intake temperature of a very respectable 40 celsius at the redline on this setup.

Using the ready reckoner of 10bhp per lbs/min that gives a theoretical poke of circa 500bhp. Assuming a great exhaust with a hot side thats correctly sized, a mighty intercooler and good intake I think the GT30R looks great on paper.

I think it is realisable, based on my calcs and assumptions, to get 500bhp @7500rpm from the GT30R and have 500Nm dropping to 470Nm between 5000 and 7500rpm. Now that assumes better Pi=1 and Pf=0.5 and VE in the range of 90-94%. I'll share some excel with you if you think there are mistakes in my maths - I'd sure love to know !

Have you had troubles mapping them for performance that doesn't follow the theory here ?



Paul

[Mihnea]

Paul, I've never mapped a GT series turbo, but I know one thing for sure, it's that pressure drop across an ABY/ADU intake system is never 0.3 Bar. Measured it on an RS2 turbo running 1.9 Bar and boost at the compressor outlet was 2.0 Bar...

Sometimes, lots of turbos sound good on paper, but it's happened to me already to get there and be inside the car and guess what? All the nice theory doesn't work anymore, because the cams aren't good enough, CR is too high, exhaust is too restrictive, etc etc , which all makes that you don't get the power that you're expecting from a particular turbo..

I've never bothered that much about maths, I just do some homework prior to tuning a big turbo so I know where the limits are, but afterwards I don't bother, I just do it and see how efficient it is...

Cheers,

Mihnea