S15 Turbo Discussion

[scathing]

The reason a Sr has more torque is because its a over square motor and has a faily big capacity for a 4 banger.

RB20's are notorious for being breathless down low its due to being a small displacement 6 cylinder. I actually believe the CA is a better built motor then the SR. Its internally stronger and shares many similarities to RB26's. There downfall is age though.

My 2 cents

The SR20's are all perfectly square. Your ignorance at such a basic property of the SR explains why you think the CA is a better built motor. I'd concur that its your 2c indeed - after rounding off to the nearest coin of legal tender, your opinion is worth nothing.

The SR makes more power with better response that a simple 200mL of extra capacity can't explain away. Its a much better design, even if you take the weight advantage of a cast iron vs alloy block out of the equation when it comes to the total performance of the vehicle.

And 2.0L isn't that big for a 4 banger. A lot of companies opt for approx. 500mL cylinders in their performance engines.

[sproosy]

[Cubes]

Come on ppls... You all know VVT aids both bottom and top end.

Reduce overlap, improve bottom end.

Increase overlap, improve top end.

Without VVT you land some where in the middle and try are forced to be happy with what you have.

Does the SR head really breathe better than the rb20's?

Sure it runs larger valves similiar to that of the rb25's head but it does have to pass 500ml puffs vs 333ml puffs.

Lets look at valve size.

RB20.

Inlet - 30mm

Exh. - 27mm

RB25 (SR's have a similiar combustion size so I'm assuming similiar valve size)

Inlet - 34mm

Exh. - 29mm

333ml is 66% of 500ml.

Do the valve sizes reflect similiar?

RB20 inlet - 88%

RB20 exh - 93%

TO me.. it looks as if the rb20 individual pots have it over the sr/25 type sized valves when it comes to how easy air flows past the valves.

But it also tells me that there is little room for a nice quench area and airspeed will be down, resulting in a lack of low end torque and slower spool BUT a much better top end that will simply keep holding power and not nose off sharply.

So...

Which motor will be better suited to road use... The SR.

Which motor will be better suited to track use... The RB.

Back to the origional question.... Why does a mild SR make power easier than the rb....I have NFI!

Maybe.....

Higher comp ratio, quench area, DEFINITELY a better std exhaust manifold, DEFINITELY VVT, higher lift cams with greater duration that close the airflow gap.

[N I B]

Longer stroke and bigger bore without the valve shrouding the RB20 has.S14 head makes power easyer than S15 also,S15 pollution head suffers from detonation much like NEOs.

[R31Nismoid]

RB20 better suited to the track L-O-L

which chick you trying to impress Cubes?

[Cubes]

It would be interesting to grab some flow bench data from the two.

I know proengines has done a bit on the rb26 and 25 heads, maybe he has touched the rb20 and sr20 heads.

It might also be worth looking at the VG20DET to help rule out the rpm/stroke influence of spool and low end torque, they run a 78mm bore and 69.7mm stroke as do the rb20det's.

[Cubes]

RB20 better suited to the track L-O-L

which chick you trying to impress Cubes?

lmao.... Well.. its only based on what ROY tells me.. hehe

On a serious note... A motor that is able to hold its power longer IS better suited to the track. Well... Nicer and a little easier to drive at the track.

[R31Nismoid]

RB20 head - doorstop

[Cubes]

lmao... I prefer the sit hidden away option.

I wouldn't want mates coming in to my house looking at those piddly looking valves.

Look at the size of them vs the head bolts. lmao.

The picture doesn't do them justice or lack there of.. They really do look small.

[Busky2k]

lmao.... Well.. its only based on what ROY tells me.. hehe

On a serious note... A motor that is able to hold its power longer IS better suited to the track. Well... Nicer and a little easier to drive at the track.

What happened to the 'power sells cars, torque win races' statement Mr Cubes

SR20 Power! Ok just had to say that...

[Cubes]

I've never said torque wins races...

Nothing worse than a motor that doesn't rev and noses over hard.. i.e my rb30det and its current setup.

[discopotato03]

It would be interesting to know if the RB20 head went through any revisions in later Skylines . I think I remember seeing a picture of an R34 NA version that had some inlet manifold changes so is it possible that the chambers and porting improved in the last Skyline (R34) era ? I would think that higher tech engine management / cats / pump fuel etc in Japan would have allowed it plus market pressure to have higher numbers out of the base NA R34 .

With SR20's and heads the later or low port version (with SOCT) or switch over cam timing was very much an emissions design so not really the best example . Some American groups have spent a lot of time and money on SR20's and they always go with the early high port S13 era heads . They will tell you that SR20's used for tarmac race have no end of problems mainly because the heads have serious cooling issues . At high power and heat outputs water flow is not flash because of the casting finish in the jackets so there is endurance limits with the SR20 head . The RNN14 GTiR head is different again and also an evolution of the early high port design .

We could argue this topic forever and not get a satisfactory answer suitable for everyone .

For an endurance race engine such as we have at Bathurst my money would be on the RB20 , I think its a low stressed engine with less piston innertia than an SR20 and so can have the piss bags flogged out of it and come back for more . In road trim its a well mannered smooth thing like all the RB series and the marque of a Skyline .

To give its best the RB20 would have to have all the effort thrown at the head . Those inlet valves are going to suffer a bit of low lift shrouding so there may be other ways to skin the cat ie smaller valves and more lift , if the factory didn't change the chambers later maybe a bit of weld to improve the quench zones and a slightly higher compression ratio . Possibly bore the block and lay back the chamber walls a little - but then its not 2L any more . One area where the RB20 lucked out is the GTS-R exhaust manifold for Grp A , it may not be the best sedate road use manifold but its a step in the right direction - forget the turbo though .

The most highly tuned SR's that I know of were the NA super tourer version for the Primera but these were hardly a production evolution - about the only thing Nissan was the head and block but you'd be hard pressed to see ANY similarities . Dimensionally they were more like an FJ20's bore and stroke and the heads were more weld than casting .

Anyhow at the end of the day you have what you have so why not try to enjoy it for what it is and accept its limitations . Not everyone can afford the SR20 blitzing RB25/26 or RB30DET .... so there .

I can't resist burial rights , have a look at Micra.com.au and Cisco's build up of a K11 Micra . Hard to believe he got 165Kw at the wheels of an 820 odd kg roller skate when he decided his S14 was not the car for him . Also note the other cars he thrashed along the way . With fuel prices going balistic how much fun would one

these things be with - a little help ! Now can I fit another diff and tailshaft and and ...

Cheers all , Adrian .

[smurf80]

If we are going to talk performance 2.0 litre motors and compare I would compare the FJ20ET motor to the SR.

And yes it is an opinion as is yours no need to work up over it.

Chris

The SR20's are all perfectly square. Your ignorance at such a basic property of the SR explains why you think the CA is a better built motor. I'd concur that its your 2c indeed - after rounding off to the nearest coin of legal tender, your opinion is worth nothing.

The SR makes more power with better response that a simple 200mL of extra capacity can't explain away. Its a much better design, even if you take the weight advantage of a cast iron vs alloy block out of the equation when it comes to the total performance of the vehicle.

And 2.0L isn't that big for a 4 banger. A lot of companies opt for approx. 500mL cylinders in their performance engines.

[discopotato03]

Very true , they are still a production engine but far more potential than SR20's .

[Busky2k]

Come on ppls... You all know VVT aids both bottom and top end.

Reduce overlap, improve bottom end.

Increase overlap, improve top end.

Without VVT you land some where in the middle and try are forced to be happy with what you have.

Actually Cubes its the opposite for a turbocharged motor. IIRC, the S14/15 SR20DET NVCS runs 22 deg of overlap between 1050-5700rpm and then 2 deg overlap outside this band for smooth idle/top end power. (I'll update the proper numbers tonight) The extra overlap in the midrange helps spool up the turbocharger sooner + extra midrange response and there is a real difference in midrange torque when comparing the NVCS and non NVCS SR20s. Unplug the NVCS solenoid harness (permanant 2 deg overlap) and feels as if the engine is pulling a trailer!

Anyways back to topic, the GReddy/Trust T518z (TD05H-18g) is the turbo I recommend. What turbo can give you 250+ rwkw and give you 1.2 bar at 3000rpm (in high gears of course)? I love it!! SR20 POWAAARR... lol

Edited April 25, 2006 by Busky2k

[Interloper]

what would be required to make the same 220rwkw out of it?

would it make it?

would it require more boost in the RB than it does in the SR?

I'd guess that the rb's lower compression would need attention.

Is that right? I thought RB20 and SR both had a comp ratio of 8.5:1?

thats what it says in the factory brochures/manuals....

[Roy]

SR20 owners appear the supreme optimists when interpreting power and dyno readouts. 250rwkws and 1.2bar at 3,000rpm? I know of about 16,000 SR20 owners looking for such a setup on a std motor.

As for RB20 vs SR, its been done to death. Different types of engines with their own strengths. How an S15 makes the power it does with the std turbo...i always though it was because the good design of the turbo...plus the freshness of the motor itself!?!?!?!

Would be very interesting to see the S15 turbs on an RB20. The RB25 has been seen to make similar power to an R33 when given the RB25 turbo, albeit a few hundred rpm later.

Also, whilst im half pissed and ranting. SR and RB. Ppl hang sh1t on the small RB20 valves. But id be curious to read if someone did the numbers on what the percentage flow per of valve surface area vs cc. The RB20 flows 2L thru 6 cyliners, thats 12 inlet valves and 12 exhaust valves compared to the 8 inlet valves and 8 exhaust valves of the SR20. I would think its obvious they dont need to be as large ?!?!?! The SR does have the stroke to help fill its lungs though.

As for Rb20 sucking at the track....the real laugh is on the ppl hanging sh1t on them. They are strong, can make reasonable power...and even in my hack of a car there isnt a single Vic Sau car with an RB25 or an SR thats quicker at the track. Which is a real shame as their sure as sh1t should be, and thats the reason those GTR cheaters have it all their own way down here...buts thats a different thread.

At the end of the day the SR v Rb has been done to death. Neither is readily the better engine. But i would love to see how an S15 turbo would go on an RB20....could make for some interesting results. Im curious to knwo how one of those bolt on SR20 AVO BB turbo upgrades would go on an RB20...but sadly us R32 GTST owners are about the tightest bunch of car modifiers going around so we want sure things for our $$$$...not be missing the mark by trying something different

[N I B]

Never seen a flow test on an RB20 but the CA18 head outflows an SR20 head on a top WA bench and the same results from a good Vic head shop.

Anyway why compare SR v RB20 when RB20s can have a 25 or 26 fitted where they are? then its no contest.

[Busky2k]

SR20 owners appear the supreme optimists when interpreting power and dyno readouts. 250rwkws and 1.2bar at 3,000rpm? I know of about 16,000 SR20 owners looking for such a setup on a std motor.

As for RB20 vs SR, its been done to death. Different types of engines with their own strengths. How an S15 makes the power it does with the std turbo...i always though it was because the good design of the turbo...plus the freshness of the motor itself!?!?!?!

Those figures I quoted were from my own vehicle. I guess that makes me an supreme optimist?

I'm not here to start an RB vs SR war but the 'which S15 turbo' thread was naturally started on the wrong forum pretty much haha!

Anyways even my old 125,000km S14 SR20DET made 195rwkw (0.9bar at peak power) on its standard turbo so I dont think the 'freshness' has much to do with it. Its probably because the turbo is half decent for a stocker! Going any bigger than a 2530 compromises response by a fair margin.

[Roy]

The std turbo can probably pump out 17.3psi at 3,200rpm and make awesone power for a stockla 2L...

Whats the go with the S15 turbo? I have heard the Australian spec S15 was plain bearing vs the Jap spec which was ball bearing ????????