Hi there!

I have a slow-spooling Toyota CT26 turbo (MK3 Supra) under the hood. It holds full 2.5Bar in 5000-8500RPM, but beneath 3800RPM I am naturally aspirated.
So, the question is how to get boost under 3800RPM?

My options are:
1. Second small turbo
Connection: parallel
Advantage: efficiency, high pressure
Disadvantage: custom manifold and downpipe, not much space for that, possible surge

2. Eaton M90 supercharger
Connection: serial
Advantage: fits well, low cost (can be a rebuilt one from Buick Regal or Chevy Cobalt)
Disadvantage: draws power, has to be turned off at high revs (bypassed or slip-clutch or electronic clutch), can hardly go over 1.3Bar

3. Eaton R1320 / R1900 TVS supercharger
Connection: serial
Advantage: efficiency, fits well, good pressure and RPM fitment
Disadvantage: draws power, costs (or someone knows where do I get it cheap?)

4. Electric supercharger
Connection: serial
Advantage: control, RPM independent
Disadvantage: complex battery charging system (high voltage, etc.), extra weight, costs
Note: I am not talking about leaf-blowers from Ebay, so please do not comment about it. There are several real-world electric compressors available.

Any ideas or suggestions on solving this problem will be appreciated!

Cheers,
Bobux

How about a turbo designed for a 2L engine in the last 20 years.

Headwork / 3" Downpipe.

As Scuderia has said, surely a turbo suited to your engine would be the best place to start? For example GT28RS or GT2871R (I'm guessing your power output here).

It's not really what I'm looking for. I think some GT3572R would behave just the same - good high revs, but will take time to spool up. And the 3" downpipe is already there.

I was thinking more of compensating the bottom with something else.

no offence but is this a joke post, 2.5bar between 5000 and 8500rpm

what are your engine specs

one of the modern garrett ball bearing turbos would be better suited to your needs although even with them you are still not going to get much boost at low rpm's with a large turbo, either look at decreasing the size of turbo you are using to bring back some lower rpm performance or increase the displacement of the engine (e.g. 2.4 conversion) if you want to run a large turbo and still have good response at lower rpms

It's not a joke. My last pressure gauge broke, I had to buy a bigger one

Thanks for the displacement idea, I'll think about that.

FYI: Base 20VT, upgraded pistons, upgraded turbo, 3" piping, large FMIC, 730cc injectors with stock fuel pressure.

A good place to start would be to see what sort of power you are aiming for?

The boost you are seeing so late sounds horrible and you will definately be better off sacrificing some of the higher end stuff for lower down to have a more drivable/enjoyable car!

youre still getting 2.5 bar at the redline?at 8500rpm?if so you seem to have spent a fair bit of cash on the engine as it obviously breathes well,which begs the question, why are you running a turbo that is worth £100 at best,and which is also the first thing to be swapped when 7mgte cars are tuned?your best bet is to go for a turbo which will give you decent power throughout more of the rev range, get it mapped and set up properly and go from there.all of the above solutions are going to cost a chunk of money,have you thought of anti lag?

hi sorry can i just ask what sort of power are you running because with that turbo you will surely be reaching the limitations of the engine if all you have are uprated pistons?? as in the engine is restricting power so in theory you could probably use a smaller turbo which will probably give you better spool up and the same amount of top end power?

Nick

just had a quick read on that turbo apparently an uprated version will not give you no more than 500bhp so your better off with the turbo i have a garrett gt3071r.

The CT26 went in many years ago, I never thought of replacing it because of good pressure at high revs. It gets the engine slightly above 400hp.

I spent the night with compressor maps, though. It looks like I could really use a different turbo with less spool time without sacrificing any performance.



According to the map it's a perfect choice! GT35**R are too huge, they won't create pressure under 5000RPM. But GT3071R is just great!

What pressure do you get around red line, Nick? And when does it start to spool (with what housing AR)?

I think that maybe you should look at your setup from another angle: using 2.5 bar boost to achieve 400-ish BHP at high revs (8500 presumably?) is very inefficent. I estimate the volumetric efficiency of the engine to be about 52% at that speed and output, when you could be operating the engine at around 85% VE at peak power and achieving similar BHP, more torque and less engine wear with lower boost, inlet temperatures and revs.

Sorry to disagree, but according to my calculations a stock 2.0l (122cui) engine would reach 400hp flowing ~570CFM at 8000RPM and 2.5bar with 80.7% VE. This figure is not that bad, I guess.


Well, I am not sure how I am supposed to reach same output with lower boost. Assuming there is no extra flow restriction, the output depends on air volume, temperature and pressure. If I lose the pressure I would have to gain on temperature or volume, which does not seem to be too probable.

Hi,

Something is not matching there?

My 2L Coupe has made 466 bhp / 7200 rpm / 1.5 bar
Turbo is GT3071R 0.86 (Flea's Stage 5 setup)
1 bar boost already from 3300 rpm.

You need to use E85 fuel to be able to use 2.5 bar boost.

I think that backpressure is your issue at the moment.

What comes to your first ideas to get "action" in low rev's, I would go to NOS system in low rpm's. No extra buildings what so ever and power for sure .

-Jari-

I guess you mean 1.5bar boost, 2.5bar absolute pressure?


That's my favourite! Great results!


NOS? really?

Are you actually running 1.5 bar boost (2.5 bar absolute) rather than 2.5 bar boost? (i.e. 2.5 bar above atmosphere)

What is your typical air charge temperature (post intercooler) at max boost and RPM?

I'm guessing he's using 2.5 absolute. Also jari's setup spools a lot quicker than mine I'm guessing he has a lot of headwork as for just changing the turbo though mine gets positive boost at about 3000rpm and fully spooled by about 4400 when I say fully spooled I mean 1.95 bar and that gives me just over 480bhp

Nick

I'm guessing you are right - I haven't known of 1.5 bar boost break a gauge before though, and I've never seen a gauge that reads absolute pressure, so I was assuming 2.5 bar 'gauge' before.

480 BHP @ what revs, Nick?

480 bhp at around 7000 rpm. true I've never heard of a boost gauge break at 1.5 or one that reads from atmospheric pressure but 2.5 bar seemed way too much to be running efficiently to me.

Nick

Hi Nick,

Yes, I have big valve head (34/28 mm) and fully ported. I see positive boost already by 2000 rpm (0.2 bar), full boost at 3800 rpm.

-Jari-

that's outstanding response from a turbo that big on a 2l engine, congrats

agreed.... The scary thing is that it could probably be improved as when leighton 'remote live maps', it's mapped less aggressively than when he actually has his hands on the cars!!
i dare say if Jari made a trip to bristol we'd have a new leader on the dyno league table!?

nick

Maybe you should look at a dual ball bearing turbo with a twinscroll exhaust housing (with twinscroll manifold of course). This should hugely improve the turbo response on low rpm.

A Garrett GTX3071R with 0.78 or 0.82 Exhaust A/R should do the job and still flow enough for your 8500rpm

Are you already running an external wastegate?
If not it would improve a little bit your turbo response

pretty sure you can't run twinscroll on 5 cyclinder engines

do you know what horsepower you are aiming for, it might be worth lowering your target to get a more driveable road car

ive used these sites before for calcs, may be of help:

http://www.rbracing-rsr.com/turbotech.html

http://www.superchargersonline.com/hp_calculator.asp?submit=1

and i also have a blower calculator on excel i can send you if you want..