So its a front wheel drive car,
Standard it spins in first and the traction control stops it in all the other gears,
then you chip it and it spins in a few more gears,
So otherwise you make a 4WD,
How much power can you get from a 20v turbo without loosing to much power from wheel spinning??

I`ve got about 375bhp....great fun

375 what have you done? and doesen't it torque steer?
you must go through a set of tyres ever month

bennb229, its all about power delivery or more to the point how you put the torque down. mine spins like mad with agressive spool at 270ish but others on here run 330bhp quite happily with a boost controller. Suspension setup, tires and of course the weather can make a difference
This time of year is a massive pain for take off. However i'm about to go through a bit of a suspension upgrade to help sort it out.
The coup shouldn't really torque steer at all upto 300 brake (source jimbo ). Again after that its all about delivery. Barbz runs 400 brake and its very driveable so ive been told.

After 300BHP most drive in reverse everywhere. This helps with wheelspin etc.

no toooo serious ..............`just` 1.6 bar .........I honestly, actually couldn`t tell you the exact bhp,but seriously thinking about getting a unichip with Rog`s PTS group buy....been meaning to for ages,so the group buy has just spurned me on (not much fun in the winter,well actually with the really cold weather it can be kinda by how fast it feels)so will be getting the 3" elbow and Integrale Injectors fitted before it gets mapped,it will be interesting to find out the real figures before and after a re map.

can you remind me of your mods plz Paul

Me too..

Nigel has a lower strut brace too, at the front.

I think he made it himself.

Rog has a std turbo and 310 ish Bhp, as said though... some serious head work..

Rog now has a hybrid and is putting out 320bhp with some good headwork although he did break the 300bhp barrier with the standard turbo.

Ross, you cheeky bugger The turbo is the single most important ancillary as it is this that creates the ultimate power. If you remove the turbo then you have a NA car which develops less power due to the lower compression. Headwork on any car will allow for greater output but think of it as maximising the efficiency of the engine.

Forced induction uses the simple principle of more air with more fuel equals a bigger bang The more pressure you run means more air is being forced in so as long as you can keep the fuel in line you have bigger power. A small turbo requires little exhaust gas to spin the turbine and increase the air pressure but the efficiency is limited to a sustained pressure at lower boost and rpms. A bigger turbo can flow more air but requires more exhaust gas therefore the lag is incremental however higher boost is sustained at greater rpm with less heat meaning bigger power.

The 28R is not a particularly big turbo but it is efficient up to 1.4 bar dropping to about 1.1 bar near redline. The approximate rating is around 300-320bhp but with the right setup you can squeeze a little more. In order to achieve 375bhp you would need to develop around 305 lbs/ft @ 6500rpm which is asking a fair bit given the turbo's efficiency. The 28R is not designed for big power but quicker spool and good midrange grunt. The only way to get big power with smaller/equal turbos is to increase the CC hence the 2.4 giving an extra 100 bhp over my coop

Is it possible to use turbos? One smaller one which would kick in early on in the revs and then drop off, and another larger turbo which would kick in just as the other turbo is about to drop off?

And the Mazda RX-7 twin turbo!

Ross, I understand what you are saying but it's a simple matter of engineering, the 28R is not really designed for that much power from a 2 litre engine. I am not saying it can't be achieved but simply that it will be really pushing the limits. Paul has had some substantial modifications but things like forged pistons don't create power they simply allow you to run more boost

Sheihks has a very fast coop and the headwork has certainly helped extrapolate more power but to get another 30 bhp when you are already on the limit of the turbo at 1.4 bar is not that easy. Ultimate speed is not always about ultimate power. The 28R is a very good turbo for the coop as it offers very little compromise in terms of power delivery from standard and that is why Barbz chose it for stage 2 tuning.

Supra 3.0 tt aswell!

Ross

so.....could it be done with the coop?

Nothing is impossible.. But there's not much space to put the second turbo, is it?

I dunno i've got a 16v so i have a bit more room, move the battery to the back would make a bit more room, i'm sure u could if u thought about.

Not that i would. Even if i could afford it.

Quote:

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Not bein cheeky, but say u had standard turbo and u got some SERIOUS headwork done to your car. Done the exhaust, tuning chip and intercooler mods. Does that mean ur never gonna break 270 cause of ur turbo? I dont think that can be right because with those mods u are making the engine work harder. So paul could technically get 375 from a gt28r because he's making the engine work harder aswell as running scarily high boost

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eh? what are you talking about, a turbo will only flow a certain amount of air, regardless of what is connected to. Head work will improve the volumetric efficiency which relate directly to torque, but it cant expand the air flow capabilities of the std turbo.

rich

Yes.

But what im saying is that u can make the most of the air flowing through. As pointed out by someone else rog hit 310 with standard turbo. So with the proper headwork u can achieve more power the turbo might be rated for!

Ross

304 bhp not 310

this was with headwork, FMIC, and blitz at 1.24 bar, standard turbo.

See... still more than the 270 recommended!

Ross

U said orifice.... hee hee...


No but seriously... i know what u mean that turbos arent rated in bhp but im talkin about what people generally say. Like u cant get much more than 320 from gt28r and more than 270 from standard etc. Basically all i was saying was, that will the right parts changed/upgraded u can take it past the figures that people generally quote. All will be revealed when everyone gets their unichip fitted and all RR'd at the same time!!

Ross

Ross,
A simplier way to describe the benefits of headwork are that with improved flow through the head there is less energy spent trying to make it through the engine. So for example your car may put out say 300 @ 1.3 bar of boost without headwork, but with headwork you would probably acheive the same power output but with say 1.2 bar for example

Jamie

Dont forget the supra's little brother the MR2 twin turbo, but these were very rare.

---

Think you mean twin entry turbo on the mr2. Still only one turbo, its what i got after i had a 16vt coupe.

How much power before the wheels loose traction?
It has a lot to do with the road conditions on a dry summers day the coop will wheel spin in first gear with standard power 220 hp but once in second it has no problems putting down 330 hp although with standard rims you do get a bit of torque steer, winter though is completely different with just a bit of damp I have found myself having too lift off the throttle in second from 270 bhp upwards depending on the road surface.


@ Paul S there’s no way you have 375 bhp out of a 28r maybe you should go down your local RR to see what bhp you really got .

Interesting info there dude. Im planning on getting near 350 at one point with this turbo!!

Ross

I'd like to bet that no one gets 350 bhp out of a 28R whether that be a Coupe or anything else. Unless you run 2 bar of boost which is well out of effeciency of this unit . It simply won't flow the amount of air needed to generate the equivalent amount of power, I agree about headwork and other such ancillary mods but the most important factor in acheiving a bhp figure will be the turbo choice.Nissan boys have used this turbo extensively on various set ups and on their engines they don't report above 320 bhp, all this with an engine design that as std for std a better VE than a Coupe engine.

Jamie

stichl let me help you out, the last 3 points are generally the true the rest makes no sense.

1 st we need to consider the values that are to be plotted on the comprssor map, they are given for a reason.

along the y axis we have the pressure ratio, this is the absolute boost pressure (boost plus atmospheric)/boost pressure. The boost pressure is something we decide in advance for this exercise lets call it 14.7psi (1 Bar), this gives a Pr=2.

We then need to consider what is happening on the x axis. this is the Engine's air flow requirements it is not the turbo's air flow output, this disqualifies the made up number in the middle of your post. Here we are considering 2 situations one is a std head and one a mildly gas flowed head.

so the air flow along the x axis is calculated by

(L x rpm x VE x Pr)/ 5660 with the result in CFM cubic feet per minute. It convienient to tell at this point you that this graph will be corrected for 20deg C, at about 900 ft above sea level, as air desity reduces with increasing temperature and altitiude.

so for engine 1 standard

L = 2 liters
rpm = 7000 (max rpm but 7k for simplicity)
VE = 90% (for 4 valve)
Pr = 2 (worked out above)

= (2 x 7000 x 90 x 2)/5660
= 445.2 CFM
In Lb/min multiply by .07
= 31.164 lb/min

Revise the VE for engine 2 with head work, lets say a 95%VE, this maybe a bit tight but a full race engine only has 105% VE.

CFM = 469.9
or
32.897 lb/min (an increase over std)

We then plot these 2 points on the graph (see my photo attached very hi-tec )
http://img.photobucket.com/albums/v74/sediciRich/IMG_0428.jpg

As, was done before on the old forum we need to plot some things to estimate whether we will meeet the left hand surge line, here we would estimate that the car would reach full boost by half rpm (it will do this sooner in reality) thus half max air flow.

For std unit at 15.82lb/min

Mod 16.449 lb/min both at Pr 2.

Finally we can add another estimation plot to say at 20% air flow we would expect to be at Pr =1 eg no boost.

std 6.233 lb/min
mod 6.579 lb/min

Looking on the graph you can see a number of things, the std max air flow leaves the turbo in the 72% range at Pr =2, while the modified unit requires more air which asks more of the turbo at a point where its efficiency is dropping off I estimate this part of the graph at 67% although there is no value on the graph. So this disproves the bit about increasing VE extending turbo efficiency or words to that effect. This plot avoids the max efficiency island at 1bar, saying that for mid to high rpm this turbo perfomrs well at .6 bar boost. Essentially the max efficiency could be utilised by having a variable boost up the rev range allowing a plot to run through the max eff island, up to say the 1.4 bar on the std engine - this needs electronic control. However using 1.4 bar on the modified unit will have the turbo spinning at what is the highest plotted speed on the graph (the more horizontal lines)potentially 135,000 rpm - this is not good for bearing life.

We can go on from here to calculate the difference in temperature from these 2 max air flows at Pr=2 (std and mod)

First we can calculate the temperature rise (theoretical) using

Tr= (F x (At + 273) x 100)/E

Where Tr is temp rise
F is a correction factor for Pr=2 which is 0.217
At + 273 is the inlet temp in deg Kelvin.
E is the efficiency at the max rpm on our map.

Std unit
= (0.217 x (20 + 273) x 100)/72
Tr std = 88.3 degrees C

For the mod unit estmate on map 67%
Tr mod = 94.3 degrees C.

Discharge from the compressor will be the increase + the ambient (20 degrees C as the map correction)

Dt std = 108.3 deg C
Dt mod = 114.9 deg C

from this we can work out how much more air we are flowing towards the engine, this is important because our pressure ratio of 2 does not mean we are pumping 2 the mass of air, because it heats up its desity is reduced despite have a pressure of 2 atm.

New desity formula
Dr = 293 x Pr / Dt + 273
293 is inlet temp in deg K

Dr std = 1.53
Dr mod = 1.51

this says the std unit will creat 1 bar boost at 7k rpm creating 53 % more air mass, with the modified unit turbo pumping less mass 53%. Incidentally its easy to estimate bhp if std was 200 then with 50 % more air power will be 300. This assumes many things A/f ratio. After intercooling the actual pressure will drop, thus ultimately in the calculations we have to decide where we take our pressure ratio from pressure after the intercooler will be slightly lower then at the turbo outlet.

So what has this shown, well it shows a car with better VE demands more air over its std counter part; although at the expense of compressor efficiency. But it also shows that there isn't great deal of difference at the end in air flow terms from the turbo for a small increase in VE. But as I said in an earlier post the improved VE assists with cylinder events. Allowing more of the air flow to be inducted in each inlet cycle, this ultimately along with a correct AF ratio increase power. But there are so many other factors apart from the turbo, its easier to think of NA tuning to see factors (not directly appliacble to forced induction) which improve power, the main one is VE, and the quality of combustion a function of many things including ignition timing. The turbo compressor is only a part in the chain and like Stichl quoted at the end the turbine has a part in the chain of events.

Just and end note - I have not pasted this of any site, some people will no doubt be thinking of insults to reply to this; Please don't. Its taken me a while to type this, I do so to help other enthusiasts and not to be slated. Its also taken me a long time to learn and understand these topics, so I no longer rely on books for explainations, but I do for the equations. I hope this is of use to someone, as you can follow the same work as a GUIDE to other turbos if you can get maps for them.

Hopefully there aren't any glaring errors.

Rich

Excellent Rich, a true masterclass in how it all screws together

Wow!!!

Thanks for taking the time!

Ross

Rich

I know when i spoke to you on the phone last night about this, but didnt quite realise how much detail you were going to go into this, especially taking the compressor graph and drawing on it!

Nice work

Rich, I take my hat off to you

joe

I remember reading a thread on the old forum a long time ago, discussing which rolling road was best, and PTS was thought to be one of the most consistant and accurate. It was also decided that it would be the best thing is for everyone to try to use the same place, where possible... and PTS was that place. Some of the other rolling roads were found to either under-read or be inconsistant. Hence why we had a FCCUK rolling road meet there IIRC.

I managed to get 344bhp and 300ftlbs at PTS, during that meet.

This was with the following mods;

Ported head and 3 angle valve seats
Stage 2 turbo (GT28R)
Evo7 FMIC
Aquamist (just water in the tank)
2.5" exhaust
Apexi AVCRII

Boost was set to 1.4bar peak in midrange tailing off (via boost controller) to .8bar by 6.5k

I ran the car with just a modded airbox (not a strait run), a standard downpipe and a Novitech and uprated FPR, running rich, (so unmapped with no ignition advance).

So in terms of how much power the 28R can produce, i dont think 350bhp+ is beyond the 28r's capabilities, IMHO

I also think some attention should be paid to area under the graph and not just peak bhp.

In terms of traction, in the dry i get every bit of power down in the dry from 2nd upwards (once i get some heat into the tyres).

Rich detail looks good to me, I've done this some time ago when I was assessing turbo options and it does take time to go through the calculations and make sense of it all so I do appreciate the effort. Another point to note is that as a rule of thumb ideally you shouldn't run a turbo below 70% effeciency in your set up. However anyone running a std turbo with boost @ 1.3 bar will be doing just that!!! It is sometimes hard to establish true VEs as there are many variables across the rev range which alter this value and also the turbo itself impacts on an engines VE, but without someone going to the expense of a test bench set up we will probably never know the true VE values of a Coupe engine.

Jamie

nice to hear from you Sheikhs, how are your tyres I hope these some nice rubber on those rims now.

rich

Hi Rich, Thanks, i have been reading the forum, but havnt been posting much for a while now, busy working
Nice to see that the new forum is still going strong though, and all the guys are still here it seems.

I was running the Toyo R888's for about 3-4k on the road, and they were just great. They have since perished and am now running some eagle's which are no comparison, but do grip once you get some heat into em.

Hope your project is going well

@sediciRich:

Rich,

you did a very good and right calculation of what is going on in a turbo engine… Thanks a lot.
Now a lot of people in this forum can see, what they have to consider when tuning a engine.
Only with one assumption I cannot agree – your fix pressure ratio…

Your definition of pressure ratio is right:

As per: Pressure ratio = Pressure_Compressor_Inlet / Pressure_Compressor_Outlet.
Means at 14,7psi atmospheric pressure (normally for Europe at normal conditions) you will gain a pressure ratio of 2 when having a boost of 1bar = 14,7psi.
(let´s neglect the loss in manifold and so on)
From my point of view here you will make a mistake, if you postulate this as a fix value…

Now I want to show you my consideration / calculation to this topic:

Assume: We want to have 350HP – this means estimated – you need a Airflow of about 35 lb/min (about +-10%). This is “almost” a fix value for this kind of motor.

This states clearly, that you cannot gain more than 350HP with a GT28R at a reasonable efficiency (about 60%).

Now it becomes interesting – let´s calculate the needed boost for our engine to get 350HP (your value was fix here!)!

Boost absolute= (needed Airflow * R * (460 + T_intake manifold)) / (VE_engine * revs/2 * displacement)
(R = gas constant = 640)

Boost abs.= (35 * 640 * (460 + 130 (estimated))/(0,92 * 7000/2 *122ci) = 33,65psia

33,65 – 14,7 (atmospheric pressure) = 18,94 psig boost.

This means: you must have ~1,3 bar at 7000rpm to get 350HP put of a 20VT-engine with a VE of 0,92! Now have a look at the compressor diagram of the GT28R. At 1,3 bar the efficiency of the turbo is good for 330HP – NOT for 350HP (Pressure ratio of ~2,3).

Now let´s calculate the same again for a VE of 0,95 (for example with head work):

Boost abs.= (35 * 640 * (460 + 130 (estimated))/(0,95 * 7000/2 *122ci) = 32,58psia

32,58 – 14,7 (atmospheric pressure) = 17,88 psig boost.

This now will mean: you must have ~1,22 bar only at 7000rpm to get 350HP put of our engine with a VE of 0,95!!!! Now have a look at the compressor diagram of the GT28R. At 1,22 bar the efficiency of the turbo is good for 345HP (Pressure ratio of ~2,2)!

This means you can gain 15HP with a head work and this turbo, because the turbo will have a better efficiency in this boost area!

I hope this helps to understand my previous statements…

Juergen

Hi,

Interesting reading .

I have to admit that I'm also against the possibility to get 370...380 bhp out of GT28R.
As Juergen showed by his calculations, there is no way that GT28R turbine housing would flow that amount of air without huge back pressure. It is more like Sheikhs wrote, peak boost 1.4 - 1.5 bar and tailing after 5500 rpm dramatically.

If this could be truth, you have found turbo that everyone would like to have . Spools earlier than OE turbo, holds 1.2 bar at 7000 rpm... . Much better than GT28RS....

- Jari -

good work Stichl and rich nice to see the calculations done.

Good points by Juergen. Along the same lines uprating induction and intercoolering will also decrease the pressure drops at these points giving slightly lower pressure ratio at the turbo for the same manifold pressure, which may allow a turbo with a compressor map like the 28R flow a little more air.

Pressure ratio = manifold pressure + intercooler drop / Atmos pressure - intake drop

Taking these into account the pressure ratio is likely to be up towards the top of the 28R's map. ~2.5 @ 18 psig (depending on headwork, mods, whatever)