Turbo selection

[DCIEVE]

Id like to select the correct turbo for my application..Ive done a few searches but id like to be sure

its an rb20det (std internals), 440cc injectors, 450hp bosch pump, 600*300*75 cooler, aftermarket ecu.

i work with a a skilled fabricator and hence building an exh manifold to suit a particular turbo poses no problem

ideally the turbo would be internally gated.

im looking for the most power ahcievable on a std internals rb20det while still having good 'average' power, as sydneykid calls it

lag doesnt bother me in the least as long as the thing can hold 1bar and the motor doesnt drop of its power curve in between gears. id rather not boost it past ~19psi. i realise the motor may be on borrowed time at these power levels (100,000kms, '89) but im prepared to rebuild if it comes to that

ideally flat 12's(11.99?) with slicks and mid 300rwhp are the aim and im assuming also the limits of the motor.

im thinking a garret GT28? (http://www.horsepowerinabox.com/HPIAB2/cat...ategory26_1.htm)

any help would be greatly appreciated

regards

Nick

[Sydneykid]

Hi Nick, I think maybe the reason no one has answered your post is because you have unrealistic wants. Based on my experiences, I personally don't believe that you can have all the things you want;

^Standard internals RB20DET

^Making 420 bhp (or as you asked "mid 300 rwhp")

^At 1.3 bar (or as you put it "19 psi")

^Hold boost from 4,500 rpm to 7,500 rpm (or as you put it "hold boost on gearchanges")

^Flat 12's

The problem is if the turbo flows enough air to make 420 bhp, then it ain't gunna have 1.3 bar at 4,500 rpm on an RB20DET. Most of all, a 100,000 k's old RB20DET ain't gunna make 420 bhp at 1.3 bar, probably closer to 2 bar in my opinion. Then its life is going to be severely compromised. Please remember that the Gibson RB20DET made 460 bhp at 2.5 bar and they turned it down to 420 bhp to keep reliability in longer races. And that RB20DET had far from standard internals. Sure turbo technology has improved a lot since then, but I think the comparison for an RB20DET is still valid.

So you will have to make a choice, and I have 2 suggestions.

1. We use a ball bearing hi flowed RB25DET turbo on our old RB20DET for 220 rwkw (295 rwhp or 370 bhp) at 1.4 bar. This turbo holds more than 1.2 bar of boost from 4,000 rpm to 8,000 rpm, so it is never off boost on gear changes. We have found this is the most airflow (max power) we can get and keep the rpm range useable. We have a few more mods than you have listed, split dump, 3.5 inch exhaust, no cat (it's a race car), cams, adjustable pulleys, Power FC with boost controller, POD filter, heat shield and a substantial ambient air feed. The exhaust manifold was a copy of the R31 GTRS Group A manifold which has the turbo mounted low and rear for better weight distribution. As usual GCG did this hi flow. Oh and the engine was standard internally, never even had the head off.

2. The other alternative is to go the Garrett route as you said, but I would suggest a GT25R with this spec;

0.86 A/R Turbine Housing

0.70 A/R Compressor Housing

Watercooled Core

48 Trim Compressor Wheel

76 Trim Turbine Wheel

Internal Wastegate

This turbo will flow 48 lbs/min max, which is easily enough for 420 bhp. But it ain't gunna make much boost at 4,000 rpm, more like 5,000 rpm. And it's gunna need cams, pulleys and a good split dump/exhaust system to make even that. So you are gunna have to rev it to 8,000 rpm before you upchange, otherwise it's gunna drop off the power band severely. You will need at least 1.6 bar and maybe as much as 1.9 bar to make your power target. Add these together (1.9 bar + 8,000 rpm) and you have a short life for your internally standard RB20DET that already has 100,000 k's on it.

Now for the flat 12's, which would require a TS around 200 kph and about a 1.7 sec 60'.............

Launching correctly a 420 bhp RB20DET isn't easy, I only get it right 1 in 5 times. It is either too much wheelspin or bog down. As a comparison I can get a 420 bhp RB25DET right about 50% of the time and a 420 bhp RB31DET right every time. Factor in, the heavier the car is and the harder it gets. Sure you might fluke a flat 12 every now and then, but you will do a large number of mid 13's and low 14's while you learn. That means plenty of cars with 100 bhp less are gunna kick your ass.

I guess the above is not what you wanted to hear, hope it helps anyway.

[Steve]

A know a guy who had an RB20 powered cefiro, HKS GT2530 turbo made 230rwkw at 1.2 bar with 8200rpm redline, fuel cut defender, stock ecu, fmic, pod, GTR fuel pump and 'tweaked' fuel pressure and stock ecu.

Boost came on hard, very hard, at around 3-3.5Krpm (from the passenger seat, hard to see exactly when the car was going sideways all the time:), the power band was wide enough to pull hard all the way to redine - it felt like it had alot more than only 230rwkw

It had totally stock internals, and this guy drove his car hard at least twice a week, it was his drift car, and the engine lasted 2 years and was still going strong when he sold it.

The car weighed 1240kgs, he only took it down the 1/4 once, with around 200rwkw (before he upgraded to the 2530) and it pulled a 12.4 on slicks.

If you want to know more, give D1 Garage a call and ask to speak to James, it was his car, and I am sure he could even do you a great deal on a turbo too, as he has excellent contacts in japan.

[Steve]

Oh, and he upgraded the AFM to turbo pipe, as these have a habbit of collapsing anywhere from around 200rwkw.

[Roy]

250rwkws isnt that big an ask from an RB20 is it?

Id be leaning towards an externnally gated turbo though, and the only reason i say a TD06-20g setup would just about get that figure on a high km std RB20 is becuase thats what i have experience with.

As for having to live with a high boost threshold to get that sort of power, 1bar at approx 4700rpm is achievable.

How would a GT30 go with a 0.63 exhaust A/R, and perhaps wheels/trims from the smaller end of the scale?

[Steve]

just noticed you want MID 300rwhp, sorry I thought you were after 300rwhp.

For around 350rwhp, a better turbo would be a 2835, T518Z (at a stretch) or TD06 as mentioned.

[Sydneykid]

Hi Steve, how much boost is an RB20DET gunna need to get 350 rwhp using a "2835, T518Z (at a stretch) or TD06" ?

Remember it is internally standard, has standard cams, no adj pulleys, no porting, no thick headgasket etc. All Dcieve specified was 440cc injectors, 450hp bosch pump, 600*300*75 cooler, aftermarket ecu .....and ....an exh manifold".

My guess would be 1.7 to 1.9 bar, and an RB20 with those mods ain't gunna get to 1.7 bar before 5,250 rpm. So it's gunna drop of the power band on gearchanges something fierce. Sure it might spin the wheels and go sideways when it has 1.7 bar, but it ain't gunna be fast from idle to 5,500 rpm in 1st and 2nd.

Work out the average power and you will be surprised how low it is. I will bet a car with 300 rwhp has a higher average and is thus faster over the 1/4.

Interesting thread, this one.

[Roy]

Please remember that the Gibson RB20DET made 460 bhp at 2.5 bar and they turned it down to 420 bhp to keep reliability in longer races.  And that RB20DET had far from standard internals.  Sure turbo technology has improved a lot since then, but I think the comparison for an RB20DET is still valid.

Do you know what sort of fuel these cars had to run, i know in later years they had to run a Shell control fuel which was essentially pump unleaded, but not to sure about circa 1988-1990.

So whilst i dont agree with using racing fuel in a street car just to get big numbers, what was the quality of the pump fuel that the GMS R31s had to use??? Does todays PULP 98 make for better performance from a turbo engine???

On my stock RB20 with 165,000kms im just about to wind the wick up on my TD06 to 1.3bar, maybe 1.4 if the extra 0.1 makes any noticeable difference to torque. (i finally wired up my GTR injectors and resistor pack)

I think im going to fall shy of 250rwkws, but im hoping for over 235rwkws. Either way ill be running whatever boost equates to about 235rwkws. Even if i had a built engine, i wouldnt run much more then 1.4bar as id be worried about the durability of the Trust turbo.

Dont confuse the TD06-20g with the TD06-25g, the -25g is a bigger turbo and almost certainly too big for a std RB20. The 20g makes for a nice turbo an a std RB20, especially if unlike me you run the recommended exhaust housing, i often think about reverting back to the smaller housing but at the end of the day im not really that fussed.

[Steve]

Have you seen grepins dyno result, 275 at 1.3bar no cams, no adj cam gears, no porting, just a manifold and he is running a 2835PRO S with internal gate. I have been for a ride in it, it seems to have not much more lag than a stock turbo.

T518Z, probably closer to 1.4 bar, like I said 'at a pinch'.

There is nothing wrong with running 8000redline, so no need to drop off power, either way though, a HKS2835 with smaller turbine housing (as grepin used), when it comes on boost will happen pretty quickly (nothing like garrett truck turbos:)).

Trust turbos similarly, if not even more so, hit pretty hard.

I have a friend with T518Z on SR20 (admittedly more torque than RB20) but boost hits, very very hard at around 3000rpm with the 8cm housing, seat of the pants it would have around 230-240rwkw I would guess - same guy who owned the 2530 powered cefiro mentioned above.

As part of the original post DCEIVE said he doesnt mind lag, well for the power he wants to make thats luck, but I dont think it would be impossible to do what he hopes to achieve.

Also, if I remeber correctly the R31 RB20 more agressive cam specs from the factory, so that will help too.

[drifto]

G'Day guys, thought i can ad some info on the topic,

My 32 has an old HKS turbo of about the same flow capabilities as the current GT2530, obviously a bit slower coming on boost due to the plain bearing.

With a small front mount, fuel reg, GTR pump, filter, exhaust and APEX computers it turned an easy 200rwkw on 15psi. Due to two injectors recently retired I am now adding 550cc nismos, cam pulleys, and GTR cooler. I'm confident the turbo can hold 1.5 bar and therefore hoping for about 250rwkw.

With over 100 k on the clock I'm slightly worried about the internals and things such as the head gasket handling this power level but with the price of another RB20 so low who cares.

I'm more worried about the turbo life. Not sure how long it's got left as it is already old. So have been considering the options if it does go poof!!!!

I strongly suggest for any street driven RB20 that the turbo should at least be able to produce over 10psi from around 3500 rpm or it will be horrible to drive. Mine is capable of only 5 psi at 3000 rpm but comes on very hard at 4000 to 15 psi.

Sydneykid- how do you explain the difference between turbo lag and turbo response range!

People still confuse the two and therefore make bad choices with turbos thru inaccurate info.

Test turbo lag by holding the engine at a rev where the turbo can make full bost then hit it. The delay between vacuum and boost is lag.

Flooring it from 2000 rpm and watching grandma drive past in her laser then using the excuse of I have lots of turbo lag is wrong!

Anyway, Sydneykid is write in saying average power is important! Especially on RB20 where off boost driving is bad enough with a stock turbo.

[Roy]

With a small front mount, fuel reg, GTR pump, filter, exhaust and APEX computers it turned an easy 200rwkw on 15psi. Due to two injectors recently retired I am now adding 550cc nismos, cam pulleys, and GTR cooler. I'm confident the turbo can hold 1.5 bar and therefore hoping for about 250rwkw. .

Hi drifto, havent seen you at any Eastern Creek days for a while, you may recall im the silver 32 owner you swapped keys with. I didnt find your cars boost threshold overly different from my std turbo, but your right it hit hard, combined with your susp setup it made for an entertaining ride. Have you tried to tweak some of the oversteer out of the old girl?

I strongly suggest for any street driven RB20 that the turbo should at least be able to produce over 10psi from around 3500 rpm or it will be horrible to drive. Mine is capable of only 5 psi at 3000 rpm but comes on very hard at 4000 to 15 psi.

I understand your point, but on the street i find the 80-100rwkws at about 3,500rpm(approx) plenty for getting around. Im sure from a rolling start a guy with a 2510 or a 2530 will walk away from me, but i dont have the faintest interest in driving quick or racing on the street.

So whilst plenty say for a "street driven" car you need...so and so...it doesnt make sense to me because you cant even use the power of the std turbo on the street. PM me the next time your heading to Wakefield, it would be interesting to swap cars again and hear your thoughts on my setup.

People still confuse the two and therefore make bad choices with turbos thru inaccurate info.

Test turbo lag by holding the engine at a rev where the turbo can make full bost  

then hit it. The delay between vacuum and boost is lag.

Flooring it from 2000 rpm and watching grandma drive past in her laser then using the excuse of I have lots of turbo lag is wrong!

Anyway, Sydneykid is write in saying average power is important! Especially on RB20 where off boost driving is bad enough with a stock turbo.[/

You will have to post that on every thread on the forum to get anywhere, i tried explaining that to a guy that was claiming that a T67 has no more lag then std turbo, thinking lag was boost threshold

About off boost performance, have you driven an RB20 with a tubular exhaust manifold??? It made a huge difference to how my car drives at light loads or off boost. Still cant help but hide the fact that boost threshold has jumped about 1,800-2,200rpm

[tomj]

I thnk the thing we are missing is that Nick doesnt mind some more lag.

Dont worry about your own personal preferences just help the guy out.

[DCIEVE]

cheers guys, very interesting advice

not sure which path to take...may look for closer to 300rwhp with a cheaper t4 type setup and save the dollars for the rb26:)

just read boostd's thread, very usefull as well

[Skyrine-Dave]

would something like this be classed as "street suitable", but with enuff power that you are chasing

i had a hole in a cooler hose as you can see boost dropped off. That was 15psi max... and if you bumped that to about 17psi...

[DCIEVE]

whoa impressive, that power curve would be awesome running to 8000rpm with no boost drop...boost seems to hit hardaround 4500rpm. what manifold/turbo? cams?

[Skyrine-Dave]

stock standard RB20DET

stock manifold

stock internals

TD06-19c

and that dyno was on 15psi for a short time, my rev cut is 7150rpm

[R31Nismoid]

Do you have a graph without a hole in the hose?

just by chance???

I just wanna see if it leveled out or kept climbing cause there aint much real useful power before 4700rpm

[Skyrine-Dave]

not yet, havent been back there, and probably wont till my RB30DET is completed. To me the car is fine to drive daily, and if you need power on tap to overtake... just drop down a gear

i too am interested to see what it *would* do