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RB20DET factory vs forged


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Building a factory 20DET longblock and want to know a couple specific things before I start.

 

Firstly, I've read that 260kw/350hp is the recommended safe daily limit for a bone stock 20DET, and that 330kw/450hp has been reached numerous times but the longevity of the motor is likely compromised at that power.

 

Is it safe to assume that 300kw/400hp is achievable and safe enough on a well and freshly rebuilt factory internal 20DET? Or is this where I should start looking at internal upgrades?

 

I plan to have the block sonic tested, honed, cleaned, lap the valves if needed and rebuild with a good set of rings gapped correctly with ARP studs and ACL race bearings in as many places as I can. I have not looked into piston, rod, cam or crank upgrades yet, however which of those should I upgrade first if 300kw is likely to send the motor to orbit?

 

Next question set, has anyone ran a Precision PT5858 GEN1 on a 20DET before? If so, which power levels did you see at which rpms and which psi did it take to get there? Info from turbos of a similar size and performance would also be handy.

 

I plan to use my PT5858 for this, its an AR.58 T4 rear housing with a ball bearing core, I can get more details on the compressor housing when I get home. I don't plan to change turbos as I got this for a very good price after doing a couple dyno runs and not suiting the application. Precision website says this one is rated for 620hp depending on application, I'm hoping on a 2L it can get me up to 300kw/400hp without spinning to it's limits.

 

Any other info, advice, tips or tricks etc would be super appreciated. This is my first RB build so excuse any amateur thoughts lmao

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I'm currently running around 380WHP (450bhp?) on a bone stock RB20DET block with no issues. If your numbers above are BHP, then a stock block can handle them all with ease. 

A PT5858 with a .58ar T4 rear housing is a strange mix that I would personally not run on anything let alone an RB20. If you're aiming for 400whp, a 5558 or 5858 will both make that power and keep it going up top with a properly sized T3 housing.

I'm currently running a Holset HY35 with a twinscroll 10cm rear (~.73ar) in a true twin scroll setup. 20psi around 4100rpm. 

Cheers.

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On 13/07/2021 at 10:07 AM, TurboTapin said:

A PT5858 with a .58ar T4 rear housing is a strange mix that I would personally not run on anything let alone an RB20. If you're aiming for 400whp, a 5558 or 5858 will both make that power and keep it going up top with a properly sized T3 housing.

It came off an SR20 and the guy claimed he "couldn't get the numbers he was looking for". I could ask him specifically in which way shape and form but he was quite vague. I live in NZ and precision doesn't have a big following over here however I am a big fan and seen it pop up for nearly half the RRP and couldn't help myself. 

To my understanding, in basic form, a larger rear housing/higher AR allows for more flow and power up top at the trade of a slower spool. A smaller rear housing/lower AR allows for a quicker spool but can run out of puff or 'choke' the motor higher up in the rpms?? Assuming it flows plenty enough to fill a 2L, and you're getting 20psi at 4k with a AR.73, would I not be able to reach a similar psi lower in the rpms with the lower AR?

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On 13/07/2021 at 12:35 PM, GTSBoy said:

300rwkW RB20 is laaaaaaaaaaaaag followed by 2000rpm of power.

Well that's not what I'm after then. It's a street car I want it to be as quick as reasonably possible without being a lag monster or costing a shit load to build. I don't care about dropping the total power goal if it means I come on boost faster. Hoping old mate above your comment gets back to me regarding the AR of my PT5858

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"300rwkW RB20 is laaaaaaaaaaaaag followed by 2000rpm of wheelspin. "

and +360' spin out of control and up onto the gutter on a rainy day - esp. at a set of lights where you have to try to slip the clutch and take off going uphill

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Why go through the process of rebuilding a motor and reuse the pistons and rods? No offence, but what a waste of time, money and energy.

Also your turbo choice, and flange choice is odd.

If I was in your position and really wanted to rebuild a RB20DET (said no one ever) I would get a Garett GTX3071R Gen 2, with a divided rear housing, proper twin scroll manifold (split all the way to a single gate OR twin gates) put E85 into it and send its mum into space.

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Why bother with forging the motor? If you're going to cut power down to get acceptable response around town you're probably well within the limits of the stock internals. At that point you want to control your piston to wall clearance to be as tight as OEM to control blowby, etc. That's the part that nobody really mentions, if you can barely get your engine oil up to 80C most of the time a forged piston with the usual forged piston clearances is going to probably be knocking around like a hotdog down a hallway. 

As others have said I would probably focus more on choosing a twin scroll turbo and all that fun stuff instead of worrying about the engine internals. A modern small single with a good twin scroll exhaust manifold designed to be a near direct fit for OEM intake bits is probably the way to go IMO, I'm a big fan on constraining your design problem to the smallest reasonable space to reduce the amount of things that could go wrong.

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I made 260-310rwkws out of an RB20 for over a decade. 70,000kms street driving and probably 60 or so track days, motorkhanas, Dutton Rallys etc.

The engine only died because I was sitting in traffic and a coolant hose under the inlet manifold had a leak and it lost its coolant during a city drive in peak hour. By the time I saw the skyrocketing temp and steam I had to keep driving another 2 mins to not cause traffic chaos in Swan St bridge in Melb.   So fixed hose , crossed fingers but the head gasket had a minor leak and after 12 months with a slilghtly rough idle when cold etc was only a matter of time until I was going to havea more severe failure of the head gasket so retired the engine. 

It was perfectly reliable at 306rwkws on E85 and 8,500rpm with 21psi in its guts. 

The TD06 wasnt the worlds most responsive turbo but its a 2L 6 cylinder that has no problem with rpm so I call BS to the only 2,000rpm of powerband.  I think the std internals are strong enough to handle the power you are after, expecially with E85 as the std rods are strong, ditto crank and pistons. If you are going to rev it as hard as I did there is no doubt some rod bolts are sensible if you are going to blueprint the motor and give it a general health check and blue-print.  I dont think they really need rods and pistons etc unless you have a turbo and a fuel that will take upwards and over 25psi

On 98 i tracked it with 255rwkws. On 100RON I tracked it with a few points more ignition and boost as it wasnt so ignition sensitive so was around 275rwkws and on E85 it was golden and made 306rwkws and thats the boost I ran it

On PULP (with Plazmaman and std)

image.thumb.png.9885b7ef28e6088ec93cd16e416c052a.png

On E85

image.thumb.png.d8a35342733b32d6412dfe61f36bbfd8.png

 


 

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On 7/13/2021 at 6:56 AM, calebharry said:

Is it safe to assume that 300kw/400hp is achievable and safe enough on a well and freshly rebuilt factory internal 20DET?

IMO YES! Hell yes. I went to buy an RB20 to try and do that last year it turns out that RB20s are now 2k engines so not going to bother as no RB is a cheap engine now

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Posted (edited)
On 13/07/2021 at 5:03 PM, Dose Pipe Sutututu said:

Why go through the process of rebuilding a motor and reuse the pistons and rods? No offence, but what a waste of time, money and energy.

Also your turbo choice, and flange choice is odd.

If I was in your position and really wanted to rebuild a RB20DET (said no one ever) I would get a Garett GTX3071R Gen 2, with a divided rear housing, proper twin scroll manifold (split all the way to a single gate OR twin gates) put E85 into it and send its mum into space.

I'm rebuilding the motor because it came out of a C33 laurel that was a factory diesel and was transplanted circa 2006. I couldn't get any information on how many kms were on the engine nor if it had been rebuilt since then. With the amount of pressure leaking through the crank casing when turning over, the fact the car was blowing smoke, and they were pushing 23psi through it on a 'factory or chipped' ECU - it probably needs a rebuild.

Have you never rebuilt a motor before and/or not see the point in it? Rings wear out, bearings wear out, head gaskets fail, etc etc. Rebuilding the motor using it's factory components just get it to as close to new as possible and give it the best chances of lasting a long time. While there, upgrading a couple little things like bearings and head studs help hold the thing together under high boost pressures and high rpms. It's silly not to do it really.

Also I'm only going to be running 98, I live in NZ and E85 is just too hard to get ahold of here. It's a street car, I don't want to be filling it up from barrels.

 

The turbo choice is random. I got it for my twincharged 4age build, it is slightly too large for a turbo-only 4age (1600cc) but with the .58 rear housing it will be useable. With an extra 400cc and better exhaust flow from 6 cyl it will only spool quicker.. really just hoping it will work, it's got a $2850 RRP over here and I was lucky to score it for $1600 in barely used condition

Edited by calebharry
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On 13/07/2021 at 5:32 PM, joshuaho96 said:

As others have said I would probably focus more on choosing a twin scroll turbo and all that fun stuff instead of worrying about the engine internals.

Noted, however I have this turbo available and would rather not spend another 3k buying one if this one can be made to work, even if I have to change the turbine housing. I'm just new to rbs and needed reassurance that pistons aren't going to get sent into orbit with 400whp. Now I know that number is achievable on stock internals, I can work my way up to that while spending as least money as possible.

 

I never said not spend money at all, but why spend money if you don't have to. I now know the limits of the engine and I can work around that, I just need some people to pipe in with some detailed info on ARs and an understanding of turbo flows, to try predict how this 0.58 may perform on an RB20

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