SI vs NON-SI

TPA_CivicSi

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I just noticed this:

"lower compression ratio (10.3:1 vs. 10.6:1)"

Is it correct to assume that's to allow more boost?
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VarmintCong

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its true the si is worlds better than the ext or the sport. and the price difference is so minimal i dont k ow why anyone would go withthem over the si..
Hatchback, no moonroof and the look. That's why I don't trade my Sport for an Si. I prefer the hatch cause my trunk's always full, and prefer the hatch look to the sedan. The moonroof means my head touches the ceiling.
 

Myx

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I just noticed this:

"lower compression ratio (10.3:1 vs. 10.6:1)"

Is it correct to assume that's to allow more boost?

Differences between the Si and Non-Si level trims, from the Honda Civic Si wikipedia page:
  • engine output increased to 205 HP @ 5,700 RPM (SAE net) and 192 lb-ft torque @ 2,100-5,000 RPM (SAE net) **How, Tuning?**
  • higher maximum boost pressure (20.3 vs. 16.5 PSI)
  • lower compression ratio (10.3:1 vs. 10.6:1)
  • higher-capacity MHI TD025 turbocharger (9-vane vs. 11-vane)
  • higher-flowing intake system **HOW?**
I do remember there being some changes to the internal engine components as well. I'm going to do some additional quick research and see if I find anything.


So power wise, a Non-Si should make more power than a stock si at the same boost level (Ktuner on Non-Si). Per the compression ratio.

Only other things I'm seeing through reading the four pages is that the Si has a better intake (How?), better flowing exhaust (2" vs 2.?) and that's it? So techinically, if I changed my 2" exhaust to at least the size of a Si and have a better flowing intake, I should be right at or better than a stock Si power-wise, right? I'm only talking about hp. Given they have different compression ratios. Oh...and of course the turbo vanes.
 
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BoostedSiCoupe

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So power wise, a Non-Si should make more power than a stock si at the same boost level (Ktuner on Non-Si). :)

Only other things I'm seeing through reading the four pages is that the Si has a better intake (How?), better flowing exhaust (2" vs 2.?) and that's it? So techinically, if I changed my 2" exhaust to at least the size of a Si and have a better flowing intake, I should be right at or better than a stock Si power-wise, right? I'm only talking about hp. Oh...and of course the turbo vanes.
no, your car will never be as good as our Si's. you should have just bought an Si to begin with. anything under Si level is turtle slow.
 


Myx

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no, your car will never be as good as our Si's. you should have just bought an Si to begin with. anything under Si level is turtle slow.
I bet you the stickers you bought for your Si won't make you faster than my CVT. BoostedSiCoupe Acuity Stickers
Do you even race? **I don't see you have posted any timeslips** At least you could hide behind your 15% Window tint.
It's ok if you don't know the answers to my questions. Carry on! :lol:
 

charleswrivers

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So power wise, a Non-Si should make more power than a stock si at the same boost level (Ktuner on Non-Si). Per the compression ratio.

Only other things I'm seeing through reading the four pages is that the Si has a better intake (How?), better flowing exhaust (2" vs 2.?) and that's it? So techinically, if I changed my 2" exhaust to at least the size of a Si and have a better flowing intake, I should be right at or better than a stock Si power-wise, right? I'm only talking about hp. Given they have teh same compression ratio. Oh...and of course the turbo vanes.
So... all things being equal other than the compression ration so long as k.control doesn't rise to prevent knock... yes, you'd be correct.

As to how the Si has a better intake, I know the volume of the intermediate 'pancaked' pipe between the airbox and when it goes into the ducting leading to the IC is a bit bigger. I think the airbox itself and the 'breather' (not sure the proper term) is somewhat differently designed. There was a thread about it awhile back... and a comparison of the two different designs. The difference wasn't substantial... but there was a difference. The end conclusion was, if you had access to a junked car and could swap, it was worth it (I think that was the situation the OP for that thread was in)... but it wasn't worth going on and spending money on new parts via the discount online sites.

Boost pressure for the 9 vane vs 11 vane doesn't necessarily equate to more cfm of flow at the top of the RPM range. The 11 vanes spool a bit quicker so you actually will have a power advantage at low RPMs and the turbo is capable of spooling both slightly quicker and it would have a little bit lower RPM boost threshold. The problem will come into play that it will ultimately limit peak power because it cannot flow as much due to the added back pressure of the vanes. The issue will just get more pronounced the more boost you try to run. The turbos aren't substantially different. There has been a thread or two where someone bought a used Si turbo and put it on their non-Si. Again... not a huge difference, but for the ~$400 price point they're going for now... if you had a stock non-Si turbo shit the bed and you wanted a cheap replacement... grabbing a used Si turbo over a used non-Si turbo should give you a little more headroom up top. It'd be doubly better in a lot of ways since your CVT could lock in a peak power, and the Si turbo should have a higher peak power potential.

So... assuming all things are equal, yes... the higher compression ratio will make more power so long as you're not knock limited. Once you are knock limited... k.control would start pulling timing and then the lower CR engine could make more power potentially. Running ethanol ought to be the great equalizer however... as everything I've read made it sound like ethanol blends can pretty much make the car be not knock limited and possibly negate any knock advantages the lower CR engine has while letting the high CR engine make a smidge more power.

I think the only real liability might be the rods at your torque peak, but just talking peak power numbers, the higher CR engine should always make more power, all things being equal, so long as you're not knock limited. Shaving heads or using thinner head gaskets so long as you have enough clearance between the valve and pistons has been used for a long, long time to raise CR. Or... you could go with a thicker gasket (I've heard of doubling them up too) if you want to go poor on a engine that was originally NA and you want to slap a turbo on it but want to prevent knock and you don't have the $$$ to 'do it right' and replace the pistons for scooped ones that lower the CR.

I actually don't think I've seen a thread on shaving heads or seen a vendor selling a thin head gasket to raise the CR. Assuming there's enough clearance, you figure a head gasket replacement would be an effective and relatively inexpensive method to raise power if the flex fuel cars truly aren't knock limited. I know the older Civic K20 crowd had aftermarket options available.

Edit: I did do a little research for my own knowledge I figured I'd share. Numbers vary wildly, but it seems like about 4% per point gain in power is about as much as I see... so 0.3 difference, might stretch to 1.5 % power gain... 3-4 whp for a 200-250 whp car. There are a few other advantages that might result in improved spool because you're moving a bit more pressure around... but I'm not sure if the effect is noticeable. It's not a lot but it's something. It does also ultimately improve thermal efficiency though, which pays dividends on fuel economy.

It shows why people readily sacrifice a little power and efficiency for more FI power potential on certain applications. But... again... if you're not knock limited, there may be some power and improved efficiency left on the table. Head gaskets are cheap and a few hours spent might give something. I've never heard of thinner gaskets. Assuming it's compatible, I don't know if there's something from the NA L15 Fit crowd that'd work. When there was the comparison between the Si and non-Si rods, they looked identical, so there's no tiny little stroke difference making the CRs different. I assume the difference is from the piston and not the head. It'd be funny if it was just the gasket.
 
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Myx

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So... all things being equal other than the compression ration so long as k.control doesn't rise to prevent knock... yes, you'd be correct.

As to how the Si has a better intake, I know the volume of the intermediate 'pancaked' pipe between the airbox and when it goes into the ducting leading to the IC is a bit bigger. I think the airbox itself and the 'breather' (not sure the proper term) is somewhat differently designed. There was a thread about it awhile back... and a comparison of the two different designs. The difference wasn't substantial... but there was a difference. The end conclusion was, if you had access to a junked car and could swap, it was worth it (I think that was the situation the OP for that thread was in)... but it wasn't worth going on and spending money on new parts via the discount online sites.

Boost pressure for the 9 vane vs 11 vane doesn't necessarily equate to more cfm of flow at the top of the RPM range. The 11 vanes spool a bit quicker so you actually will have a power advantage at low RPMs and the turbo is capable of spooling both slightly quicker and it would have a little bit lower RPM boost threshold. The problem will come into play that it will ultimately limit peak power because it cannot flow as much due to the added back pressure of the vanes. The issue will just get more pronounced the more boost you try to run. The turbos aren't substantially different. There has been a thread or two where someone bought a used Si turbo and put it on their non-Si. Again... not a huge difference, but for the ~$400 price point they're going for now... if you had a stock non-Si turbo shit the bed and you wanted a cheap replacement... grabbing a used Si turbo over a used non-Si turbo should give you a little more headroom up top. It'd be doubly better in a lot of ways since your CVT could lock in a peak power, and the Si turbo should have a higher peak power potential.

So... assuming all things are equal, yes... the higher compression ratio will make more power so long as you're not knock limited. Once you are knock limited... k.control would start pulling timing and then the lower CR engine could make more power potentially. Running ethanol ought to be the great equalizer however... as everything I've read made it sound like ethanol blends can pretty much make the car be not knock limited and possibly negate any knock advantages the lower CR engine has while letting the high CR engine make a smidge more power.

I think the only real liability might be the rods at your torque peak, but just talking peak power numbers, the higher CR engine should always make more power, all things being equal, so long as you're not knock limited. Shaving heads or using thinner head gaskets so long as you have enough clearance between the valve and pistons has been used for a long, long time to raise CR. Or... you could go with a thicker gasket (I've heard of doubling them up too) if you want to go poor on a engine that was originally NA and you want to slap a turbo on it but want to prevent knock and you don't have the $$$ to 'do it right' and replace the pistons for scooped ones that lower the CR.

I actually don't think I've seen a thread on shaving heads or seen a vendor selling a thin head gasket to raise the CR. Assuming there's enough clearance, you figure a head gasket replacement would be an effective and relatively inexpensive method to raise power if the flex fuel cars truly aren't knock limited. I know the older Civic K20 crowd had aftermarket options available.

Edit: I did do a little research for my own knowledge I figured I'd share. Numbers vary wildly, but it seems like about 4% per point gain in power is about as much as I see... so 0.3 difference, might stretch to 1.5 % power gain... 3-4 whp for a 200-250 whp car. There are a few other advantages that might result in improved spool because you're moving a bit more pressure around... but I'm not sure if the effect is noticeable. It's not a lot but it's something. It does also ultimately improve thermal efficiency though, which pays dividends on fuel economy.

It shows why people readily sacrifice a little power and efficiency for more FI power potential on certain applications. But... again... if you're not knock limited, there may be some power and improved efficiency left on the table. Head gaskets are cheap and a few hours spent might give something. I've never heard of thinner gaskets. Assuming it's compatible, I don't know if there's something from the NA L15 Fit crowd that'd work. When there was the comparison between the Si and non-Si rods, they looked identical, so there's no tiny little stroke difference making the CRs different. I assume the difference is from the piston and not the head. It'd be funny if it was just the gasket.
@charleswrivers Thank you for your very detailed response. This is exactly what I was looking for man. Much appreciated. Very interesting stuff. I'll try to capitalize on the info you provided. Not interested in any more torque midrange, just top end power (above 5000rpm). Great info! Any more potential torque can be dialed back down with the Ktuner. Exciting to read through your post.
 

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no, your car will never be as good as our Si's. you should have just bought an Si to begin with. anything under Si level is turtle slow.
Funny thing, my tuned non-Si didn't seem turtle slow when I zoomed past a WRX not too long ago. :thumbsup:
 

charleswrivers

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Yeah... most of the 'bad noise' posts were mostly gotten rid of... mostly...

Honda Civic 10th gen SI vs NON-SI newtALIENS


I will say, there's a world in information about static... dynamic compression ratio... effective compression ratio where boost is concerned. How E85 allows for more timing, but where timing is as good as it can be... CR can be adjusted to gain even more power, though timing will yield more power if knock isn't limiting and there still room for positive improvements. Then you start diving into cams, because it ultimately effects dynamic CR because if the intake valves aren't shut yet, you're not compressing anything. The stuff Honda said they did to allow a puff of fuel out by having an overlap exist on the piston going up and some injection to wash the valves slightly would ultimately hurt CR. Then again, if a valve was ground to eliminate this, we could infer you'd defeat Honda's strategy of minimizing/preventing carbon buildup. I never thought of a cam affecting it... and it doesn't affect static CR... but it does affect the dynamic one, and would show up to higher cylinder pressure when performing a compression test. So, by doing that, Honda would intentionally be trading some thermal efficiency to keep the valves in good shape. There's a lot of stuff with NA guys messing with their gasket or the head itself and just doing a compression test to infer the amount of change they've accomplished, other than just running the numbers on the affected static ratio. Neat stuff.

It is 'little power' when comparing it to more boost/timing/turbo swaps/etc... but it'd be neat if we see some options down the road. I did check and the head gaskets are the some P/N from the Si's engine to the others... so the change must be based more on piston design, whether it has less dome or more scoop. I'm not sure what our stock pistons look like.
 


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I pushed my base model motor as far as it will go and the limiting factor was the fuel delivery.

The base model motor can't deliver as much fuel as the si motor. In my opinion it will never make as much power as the si when pushed to the limits.
 

Myx

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I pushed my base model motor as far as it will go and the limiting factor was the fuel delivery.

The base model motor can't deliver as much fuel as the si motor. In my opinion it will never make as much power as the si when pushed to the limits.
@Shadowfighter How far did you push it before it had fuel delivery issues (Horsepowr/Torque)? Was this on gas station fuel or E85/Race gas?
 

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I pushed my base model motor as far as it will go and the limiting factor was the fuel delivery.

The base model motor can't deliver as much fuel as the si motor. In my opinion it will never make as much power as the si when pushed to the limits.
Can't you change injectors, pump and fuel rail? Not cheap but back in the day that was a path to take.
 

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Can't you change injectors, pump and fuel rail? Not cheap but back in the day that was a path to take.
There's supplemental port injection in the wild but nothing to control it readily available w/o going to some relatively expensive options beyond what Hondata/Ktuner can do last I saw.

We have a high volume, low pressure fuel pump that's comparable to a port injection car's fuel pump, but then there's a high pressure fuel pump that raises the pressure for the DI injectors. From what I read, Ktuner has been able to have a minor bump in fuel pressure, while Hondata had not to get a little more fuel during the injection window. I've not seen anything else on mods to improve DI flow. The Hondata/Ktuner fuel pressure bump this is a little old info and might not be accurate anymore.

Best supplemental fueling we have on the cheap would probably just be meth injection.

My Z has 740cc injectors, up from 370cc... so... yeah, I'm right there with you.
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