RB20 vs. SR: Throttle response?

[Project240]

I'm having problems making a decision here; have a 92 coupe awaiting either an SR or RB. I want an I6 but don't really need the potential for 600WHP, so I figure the RB20DET would be about right for me. I'm ultimately looking for 300-350HP at the most.

My question is this: If I had, for instance, an SR20 and an RB20, with all things being equal, on which one would the turbo lag be the worst? I realize lag depends on many different variables, but, generally speaking, would the lag be any better or worse on a 2.0L six than on a 2.0L four?

Both these motors have very similar power potentials, so the main issue I'm concerned about when making this decision is driveability. Would a ~350HP RB20, having much less displacement per cylinder than the SR and making its power higher in the powerband, be less daily-driveable and have worse lag than a ~350HP SR20?

I'd just rather have the sweet sound of an I6 coming from my tailpipe. It'd be easier to just swap in an SR, but that wouldn't be any fun, now would it?

[Nismo_Freak]

Theoretically the RB20 should spool the turbo faster cause it supplies a more constant and smooth flow of exhaust pulses to the turbine.

The RB20 does have an iron block, as well as a greater surface for absorbing and expelling heat withen the block. The smaller piston surface means that the piston will have less block friction and can achieve greater thermal efficiency. The extra 2 cylinders also will see a fractional amount of less heat than the SR20 due to the amount of air/fuel that is combusted in each cylinder. The rods and pistons will be under less stress as well as the main bearings.

Less stress on the bearings means they require less oil to function at their best. One common problem on the SR and CA engines is their main bearings failing. The natural harmonics of the inline 6 engine make is superior as well at higher RPMs.

All in all the scientific aspect would point to the RB20 being the more reliable of the two.

In terms of cost however... that is solely based on the market.

[Project240]

Very helpful, man, thanks a lot!!!

[Gmans13]

Let us know what you decide to do

[Project240]

^||||(points to signature at top of thread)

It's been a while since then. I think I made the right decision

[Gmans13]

nice...

[AREITU]

I think what he's asking is...if he's going 20 at 1/4 throttle at around 2000 rpm and suddenly floors it, does he get an instant gratifying kick in the ***, or is it a smooth surge?

[dareo]

if you want the most instant power i'd say get a KA-T setup, it offers the most low end and with the right turbo and log style manifold you will have so much response you'll spend your time in tire shops getting new tires fitted.

[Gmans13]

definatly the KA-T would get some nice low end power

[ilkhan]

The KA-T should have quite a bit of low end. But wouldn't the I6 generate more torque (as well of HP because of higher redline)?

[gabossie]

Actually, a higher redline is usually the product of a shorter stoke (among many other things), which would produce less torque and not as smooth a powerband.

[gabossie]

Oh wait, I think I misunderstood you. You were giving the high redline as a reason for high hp, but not torque :pface Yes, the extra 2 cylinders help produce more torque, but in an engine of the same displacement, does make for a shorter stoke.

[Wulfgang]

Nobody has said anything about compression ratio. A big part of the reason KA's have such good low-end response (when compared with RB's and SR's) is that the compression ratio is 9.5:1 (which increases torque). I would bet that you could get much better low-end response (without losing too much boost potential) if you put forged 9.5:1 pistons in your RB.

[PROJECTRB240SX]

THATS MY PLAN 9.5 TO 1 COMPRESSION (I'VE ALWAYS SAID THAT BY THE WAY).

[Project240]

I forget, what's stock compression on the RB20? 8.5:1??

[PROJECTRB240SX]

YES

[Wulfgang]

Sorry, didn't know you were going to 9.5:1. I wish mine came that way... but I'm not going into the bottom end unless I am forced to. And then, if I do, I will go with 9.5 pistons.

[PROJECTRB240SX]

ITS OK I DIDN'T MEAN TO COME OFF AS MEAN OR ANYTHING I WAS JUST SAYING THAT I HAVE ALWAYS SAID THAT THE RB20S COMPRESSION SHOULD BE RAISED AND IT WILL SIGNIFICANTLY INCREASE POWER.

[bigk]

ITS OK I DIDN'T MEAN TO COME OFF AS MEAN OR ANYTHING I WAS JUST SAYING THAT I HAVE ALWAYS SAID THAT THE RB20S COMPRESSION SHOULD BE RAISED AND IT WILL SIGNIFICANTLY INCREASE POWER.

very true. i'v been driving my 1990 with redtop sr20det for about a month now and i do miss my low end torque of my 95 240sx.and if i sell my car i too plan to either do a ka-t or rb25det.But i do love my sr20det, i guess when your used to driving modified v8 mustangs the sr20 just feels weird.

[kevy8up]

so if somone did the 9.5 CR pistons in the RB20. what else would you have to do to the engine to compensate the change. or ..what else would u need to upgrade to work with the CR change.