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Sluggish acceleration / torque below 2.5K revs SR20DET - Hardtuned.net
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Sluggish acceleration / torque below 2.5K...

THRILLHO's Photo THRILLHO 31 Oct 2017

Hey my '92 180SX SR20DET redtop seems to have abnormally slow acceleration below 2.5K revs.
My previous 96 Civic would be way more responsive and even accelerate faster than my 180! (at that low rev range).

One common example is waiting on a busy road wanting to turn right into a side street but oncoming traffic is super busy. When I see that small gap in traffic, and I want to quickly gun it into the side street, I'll floor it in first but it'll take ages for it to get really moving and have subsequently had a few beeps from people cos I was going too slow.

This issue isn't just 1st gear either. As soon as I change to 2nd gear and put my foot down, there'll be this one second of lag as the car seems to catch up and then accelerates normal beyond about 2/2.5K RPM. Same thing for 3rd, 4th and 5th gear - always this wait for the car to respond and then it jumps forward.

IDEAS?
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s15rocket's Photo s15rocket 01 Nov 2017

Sounds normal to me. If l just leisurely take off at the lights in1st gear then suddenly put my foot to the floor there is a huge delay in response.

The only way to take off fast with an SR20DET is to keep the revs up and let the clutch out quick. If you use the former method you will get smashed off the line by Civics and Prius taxis on the daily. I got destroyed by a taxi driver the other day who wanted to drag me and I wasnt really in the mood to be dumping my clutch off the line as it can be quite loud and draw alot of attention when you have a big 3 inch exhaust, so I took off slowly then flawed it so I had that "delay". Of course by the time I hit 2nd gear boost I flew past him but by then the race was over.

tldr;

Keep the revs up dump the clutch if you want a fast launch.
Edited by s15rocket, 01 November 2017 - 12:54 PM.
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pmod's Photo pmod 02 Nov 2017

View PostTHRILLHO, on 31 October 2017 - 11:58 PM, said:

Hey my '92 180SX SR20DET redtop seems to have abnormally slow acceleration below 2.5K revs.
My previous 96 Civic would be way more responsive and even accelerate faster than my 180! (at that low rev range).

One common example is waiting on a busy road wanting to turn right into a side street but oncoming traffic is super busy. When I see that small gap in traffic, and I want to quickly gun it into the side street, I'll floor it in first but it'll take ages for it to get really moving and have subsequently had a few beeps from people cos I was going too slow.

This issue isn't just 1st gear either. As soon as I change to 2nd gear and put my foot down, there'll be this one second of lag as the car seems to catch up and then accelerates normal beyond about 2/2.5K RPM. Same thing for 3rd, 4th and 5th gear - always this wait for the car to respond and then it jumps forward.

Your initial description of 1st gear makes it sound like something definitely isn't right, however you then talked about shifting so early that the car was below 2000rpm in 2nd gear, which isn't what you should be doing unless you swapped in a 3.9L Cummins Diesel. The engine is labouring quite badly at 2000rpm.

For the bogging in 1st gear, my initial thoughts are:
  • Check/clean/replace the spark plugs with new copper plugs. They work the same as platinum/iridium, they're just cheaper and don't have the same service life (no big deal for an SR20).
  • Clean all your Earths and battery posts, because it's always worthwhile doing.
  • Check the timing set on the CAS, because if that's off by too much, the car will be shit. You need a consult cable, laptop and Conzult to set it into Timing Mode (never tried the ECU method), at which point you can use a timing light to set the base timing to 15 degrees or whatever it's supposed to be.
  • The coil packs could be shit. Had that happen to me, and it can do some weird things.
As for the S13 vs 1996 Civic comment, you need to understand that you aren't comparing apples to apples. Here are the relevant stats:

S13
8.5:1 CR
Bore x Stroke: 86.0 x 86.0mm
1st Gear Ratio: 3.321
Final Drive Ratio: 4.083
Curb Weight: 1220 kg

Civic 1.6 Vti
10.2:1 CR
Bore x Stroke: 81.0 x 77.4 mm
1st Gear Ratio: 3.250
Final Drive Ratio: 3.7/4.058/4.250
Curb Weight: 1090 kg

The points to take away from that are:
  • The Civic has a far higher compression ratio, meaning it will be a lot more responsive than the SR20 when off boost, as it's making more power/torque per cc than the SR20DET.
  • The Civic uses a slightly oversquare stroke ratio, which will hurt torque but might help it off the mark given the gearing.
  • The gearing is very similar between the two, however there's a massive difference in the rotating mass of the RWD S13 and the FWD Civic. The Civic has no tail shaft, probably has a smaller diff/gears/flywheel, the engine displacement is smaller so the crank/rods/pistons are probably lighter too, and if it's a daily driver it likely has smaller wheels too. Your icon suggests you're running 17s or bigger, and the stock tyres for a 96 Civic are 185/65 R14. That would also make the gearing in the Civic better by default, as it has the smaller rotating diameter to turn.
  • The Civic chassis weighs less, so there's less mass to shift off the mark.
Unless you're dumping the clutch off the mark in the S13, ensuring you launch with boost, there's absolutely no reason why a 1996 Civic shouldn't beat you in 1st gear below 2500rpm every single time.

All said, it's difficult to assess the issue without checking the car out in person.
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S15 sxytime's Photo S15 sxytime 03 Nov 2017

I disagree, my S15 with stock turbo, injectors, afm, 3" hand made custom exhaust, PWR intercooler, apexi power fc ecu,turbosmart gated boost bleed valve and modified stock airbox with 185 rwkw on the old Morpowa dyno back in 2006! It has very good off boost response pretty much equal to other similar size non turbo cars. I never need to give it heaps of revs and drop the clutch to keep up or beat those other shitty cars! Maybe you need a decent tune??!!
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junkie's Photo junkie 03 Nov 2017

sounds like mine, catch it off boost and fark it struggles. its worse in summer too, i have actually re-installed the stock airbox thinking my old semi-open setup was drawing in too much hot air
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THRILLHO's Photo THRILLHO 05 Nov 2017

Wow thank you pmod for such an in depth reply and getting all the specs and comparisons, as well as some helpful quick things to test! What you say definitely makes sense and yea might just be something to get used to

And yea s15rocket, total feels for the delay with prius' before catching up haha
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pmod's Photo pmod 06 Nov 2017

View Postjunkie, on 03 November 2017 - 09:48 PM, said:

sounds like mine, catch it off boost and fark it struggles. its worse in summer too, i have actually re-installed the stock airbox thinking my old semi-open setup was drawing in too much hot air

If you ever want to fix that problem the next time you blow your engine, install a lightweight flywheel and ideally some DE-spec pistons. I run ~9.25:1 comp in my non-VCT SR20 plus an Exedy lightweight flywheel, and it's pretty snappy off boost, which is a good thing considering I still haven't tuned the piece of junk despite having a Nistune board and a license sitting on the shelf for over 3 years lol. It's decent up until I have to shift at 4000rpm when boost starts to kick in, and then the transient response following the shift is excellent.

I bit the bullet on the flywheel after I saw Rex Kelway spruiking it, and he wasn't wrong. It's a fantasic quality-of-life mod for the SR20DET. I find that my 180 only struggles when you try to accelerate in an unsuitable gear, for instance 5th gear 2500rpm, at which time it just doesn't have the torque at that point to deal with the ratio.
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tolkaNo's Photo tolkaNo 06 Nov 2017

It's a tune/AFM/tps limitation imo

Ive got a wideband and if you put your foot to the floor at low rpm your afr's go 10:1 and timing drops because the ECU expects you to be in boost when your throttle is in that position

100% throttle puts you in the rich open loop area of the timing map even at low rpms

The better thing to do is just get the revs up before you move rather than taking off at 800rpm and putting your foot to the floor and filling your engine with fuel

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BEV5TA's Photo BEV5TA 03 Dec 2017

Mine use to do the same thing until I realised it was the knock sensor that was fucked.

Test it by bypassing the sensor with a resistor to see if it helps... Or calibrate your TPS as mentioned previously.
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