HaLo

I was speaking with AceInHole... Our setups are different mainly because my car is much les responsive compared to his ka with small turbo. Now, my S15 turbo has quick spool up, quick response, but I am trying to get some more.

I have at my place a spare SR20DET block and head that needs to be rebuilt... Now here is the fun part. PJ suggested that I could raise the compression of the engine. Now, it does sound crazy at first, but 9.5:1 compression with 15psi would seriously spool up much quicker and feel more linear. 9.5:1 compression pistons are available for USDM SR20DE and go for very cheap.

I was mainly wondering if the engine can withstand it with ARP studs and a metal head gasket... Could it take 15-19psi without any problems with our 94 octane street gas? Would I lose much power compared to my 307whp at 19 psi?

What do you guys think of it?

Keep in mind that I am not really interested in drag and hp figures. If I can get more response for the same amount of power, I will do it. I mainly auto-x with the car... Might do some Solo 1 one day...

Thanks!

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-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

orion::S14

I love the idea of high compression, turbocharged motors.

But I wouldn't even consider 9.5:1 high compression...

8.5:1 is a carry over from the old days of turbocharging, and has a good margin of safety built in.

Only thing an SR wil lose with 9.5: is the tuning "margin of error"...

It may limit your boost to 15-16psi, but you'll be at a higher power level at that boost (as compared to 8.5) anyway, so...who cares.

What kind of engine management are you running???

- Brian

HaLo

It's a retuned ECU with daughter board.... If I do that kind of a project, I will have it tuned with an emulator, dyno and wideband o2 sensor...

I was doing 283whp at 15.5 psi... and the S15 turbo loses efficiency at 18 so... I might be doing close to 300whp at 15 psi, which is GOOD ENOUGH IMHO...

I think I am going to take an attempt and do it.. Would you go with higher compression than 9.5:1?

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

sykikchimp

Very good idea! I'm betting a 9.5:1 compression SR at 15psi would make almost as much power as you are now with 19psi. Compression makes a big difference when your boosting.

With forged pistons it would be much less worry. But I guess if you wanted to use stock SR20DE pistons, then you could see what the guys with SE-R's typically push them too. (I know I';ve seen several b/w 350-400whp..)

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sykikchimp

If you wanted to, you could get the head shaved to maybe raise compression a few more points...

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HaLo

hmmm... With a good port job on the head, I could have myself a kick-ass response-full turboed engine... I thought I was nuts, but you guys are convincing me...

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

msaskin

I think it's a good idea!

There are a bunch of non-turbo 3000gt/stealth guys who have started doing turbo setups on their cars. General "safe" boost levels (i.e.; levels before knock starts becoming an issue) seem to be approx. 10-12 psi on a twin TD04-9b (total of approx 400cfm combined flow) on a 10:1 compression 3.0 liter v6.

For reference, a T28 flows ~435cfm, so I would imagine with a slightly smaller engine and 9.5:1 compression 15psi would probably be a safe bet. Obviously the margin of error (as mentioned) while tuning is smaller, but shouldn't be that hard.

FWIW, you may only want to go 9:1. My galant vr-4 was a 7.8:1 stock and I went to 8.5:1 on the rebuild (using 2G DSM pistons) and the difference in off-boost drivability (and spool) was absolutely nuts!

EDIT: back to the 3000gt/stealth issue. A 3000gt vr4 @ 14psi @ 8:1 compression typically makes about 360 or so hp at the crank. A non-turbo conversion @ 12psi @ 10:1 typically makes about 380 hp at the crank. Remember that at 10:1 you're going to hit boost limitations very quickly, whereas at 8:1 compression there are guys running 30+ psi.

Another important thing to remember is final compression ratio.
FCR = [(Boost / 14.7) + 1] X CR (CR = compression ratio)

so:
for your T28 @ 18psi on a stock SR20 (is an SR20 8:1 or 8.5???)
FCR = [(18 / 14.7) + 1] x 8
FCR = ~17.8

for a T28 @ 12psi on a 9.5:1 SR20
FCR = [(12 / 14.7) + 1] X 9.5
FCR = ~17.2

~matt

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Steeles

Greaser ran a 9:1 compression on his SR for awhile and really liked it. more of a track feel that drag though so he ditched the setup iirc. but hesaid for everyday driving he highly recommended it. I hope to do similar next year sometime if I can find a spare block. althoughIm tempted to bore and sleeve it to a 2.1L at the same time

and also IIRC Scott (enthalpy on FA) was saying quite a few of the SRs they tuned were 9:1 motors and had great success with the setup. (of course your talking 9.5:1 but you get my idea )

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HaLo

Very intersting... I think I am going to go with 9.5:1. Stock SR compression is 8.5:1 so with a 9.5:1, the final compression ratio to equal 19 psi is only 15.46 psi, which is in the efficiency range of the S15 T28 turbo...

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

Kid Zelda

hehe, glad to see more people thiniking of attempting this.

It is always best to plan ahead, and plan for what kind of driving the car will see.

I already have numbers down for my "build up" whenever that may happen ... a yr or two from now, but the plans are already laid out. 9.5:1 would be ideal, I am going to have to tone it done .. 9:1 ( damn 91 ocatane, leave some room for error )
The goal is response and USEABLE HP&TQ power band.

HaLo

Can't you simply prevent detonation by reducing boost? I believe 7 psi will work with 9:1 with 91 octane...

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

Kid Zelda

I do not want to be at 7 psi all day long
otherways of preventing detonation .. acutally ... I have to punch in some more numbers, heck I may be able to go 9.5:1

goodjuan

would you ever consider running aquamist along with this higher compression?

Steeles

and there it is I want as much "power under the curve" as possible. thats why Im gonna forever stick witha smaller turbo. (T25 witha 16g compressor currently although Im worried about the other side being too small..)

__________________
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So I murdered another turbo

orion::S14

And a thing to note...turbocharged 9.5:1 Nissan motors are not exactly a new idea...remeber that KA you tossed when you put your SR in? Well, a bunch of us turbo those and make that much power (or more) with a less beefy bottom end...hehe.

It's all in the tuning...how aggressive is an SR timing curve? It's been proven the on the KAs that 12-13psi from a T3/T4 will net you 300rwhp (with a retuned ECU, of course). And our base timing is 5 degrees higher than yours...although your ECU may be a little more aggressive with feeding back timing as you near redline, who knows.

Anyway, it's all about cylinder pressure...more boost with less static compression, or higher compression and less boost..makes little difference. If you're not detonating at 19psi and making 300rwhp, then I'd bet you can do 16-17psi and make 300rwhp on a 9.5 motor...

- Brian

HaLo

That's what I thought... I did some calculations and 19psi will allow me 15.5 psi on 9.5 compression without any problems... I have been reading on sr20forums and 10.0:1 also works. I am also considering it!! I don't car about high boost, I want a better power curve... And with the spare bloc, I think I can make it.. If it detonates, get Aquamist.

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

Kid Zelda

Ohh .. VVT ..

Zemus

I wonder how rasing the compression on a KA would help with a turbo, or doesnt it already have the problem of boosting to low, how would 10:1 work on a KA?

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HaLo

Must be the same as the SR... as long as you don't detonate, you'll be okay. But you will have to use a smaller turbo. Ace is also considering it.

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

sr240mike

What emulator are you planning on using? I haven't seen any 16 bit emulator available for the sr daughterboards yet.

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TWO IN THE COOT, ONE IN THE POOT

HaLo

I don't know about the emulator because I am not the one owning it... But I believe we use 32-bit eeproms on my ecu

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

HaLo

Well.. I just found some 9.5:1 pistons for 75$ shipped with 50k miles use!

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

Zemus

Humm... maybe.. SOHC pistons in a 95 DOHC.. 11:1, wait thats far to high. Mabe just 10. that would own.

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nightwalker

You guys know Hondas have been running high compression turbo motors forever. Nothing new. Just retune it.

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HaLo

Maybe Honda has... but Nissan hasn't.
And I just wanted to gauge how the idea sounds. I have never seen someone swapping out low compression pistons for higher compression pistons while I have seen the inverse done over and over again...

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

kandyflip445

I know this is off topic but couldn't you make a line from where the A/C drops out all that condensed water and use it for the aquamist? Just a recurring thought I've had about it. You would have to use a window washer fluid pump or something to make the fluid go to a container higher up that you could also fill with water. :shrug:

A little more on topic, if you wanted forged pistons I would imagine you could call up one of the piston manufacturers and have them make a higher compression version of one they already have.

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240Stilo

And of course it would be more than the $75 deal he got.

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kandyflip445

I know, I was just saying if he wanted to later on to run more boost and giving ppl some food for thought.

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HaLo

N/A pistons can handle 350whp... As long as the rods are solid. It's experimental... but I have a Sr20DET bloc to spare.

The reason Aquamist is better is mostly because of their nozzle design that vaporises water in the intake manifold: it does not shoot it as a jet.

__________________
-> HaLo
Race Car: '98 E36 BMW M3
Daily Driver: '08 Fiji Blue Honda Civic Si
SOLD: 01 GPW Honda S2000
PARTED: 93 Pearl White 240SX LE Fastback w/SR20DET
SOLD: 93 Super White 240SX SE Convertible w/Silvia Front

kandyflip445

And??? I was saying using the condensed water from the A/C condenser as a water source for the Aquamist so you wouldn't have to buy water as much. Even though it's cheap......

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