Keeshwah

Before I begin my question I'm going to say that I'm still learning a lot about cars. I'm a computer nerd and have no mechanical skills what so ever. Feel free to correct anything I've gotten wrong but please be gentle.

When I was getting ready to buy a new car my two choices were either the Scion tC or a new Civic Si. I got the tC because it was the best bang for the buck. But I'm still really curious about how Honda manages to get so much performance out of a smaller engine (K20). I know part of this is because the compression ratio is higher than the tCs (11.0:1) and because it redlines at like 8k RPMs. I've noticed that ZPI makes 11.0:1 compression pistons for the tC. So to take advantage of that would I just use higher octane gas, and are other mods required to increase the compression? And how would I be able to increase the redline on the tC?

I know someone will say "Well, why didn't you just buy the Si?". The answer is because I saved more money, and because of the age old argument "There's no replacement for displacement.". So I was hoping to mod the tC's engine the way Honda did to get, hopefully, better perfomance than the Si.

So basically my question is, how to get K20 performance out of the 2AZ-FE engine without using FI? And what gives the K20 such good performance?

Also feel free to explain any important concepts you think I might not understand because I've never taken any automotive classes. All I know is what I've read on the internet.

lludacrisboy

ill be honest im a computer nerd too and all i do is computer stuff, but when i bought my tc i started learning. and as for your question im lost. sorry i cant help. but ill up it to get someone elses attention

bbsciontc

well, you basically summed it alll up. High compression pistons are the major player, along with a much bettter flowing head, lightweight engine components and shorter stroke for a higher redline, and i-vtec which actually controls both valve timing and lift. The system on the 2az can only control timing. But in all honesty, to get to the k20 power level NA, high compression pistons, mild head work and increased fuel and tuning should get you there if not significantly more. Too expensive though for what it's worth.

toyota_scion_tc

Honda gets the hp from having such high compression but look at the torque its a lot lower than the tc. The k20 block and cylinder head is built really well for power. The tc block and head was built more for economy but with some block and head work there is a lot to gain. If you are going to increase your compression you would have to run premium all the time. Also when someone comes out with a ecu reflash you will want to have this done to gain the most from you mods. I would also port and polish the cylinder head if you are going to higher compression pistons. It might not be a bad idea to run a lower temp thermostat b/c the cylinder temps will be higher with higher compression.

Keeshwah

So is it safe to say that the 2AZ engine will never redline at 8k rpms because it has a longer stroke? Or could it if its components were lighter?

Also how is it getting 30 mpg highway? Is that all from the i-VTEC controlling lift? (And just to clarify, lift refering to the pistons??)

kungpaosamuraiii

Never say never.

The 2AZ will probably be able to redline at 7k all day long without much problem. To get 8k it takes really strong rods and valve train components and a RPM limiter-override.

Actually, with the Emanage Ultimate, you can override the RPM limiter and rev all the way up to 9k RPM. I'm sure you can further than that; just have fun at the same time everything starts to scream profanity.

But honestly, you're probably looking at a destroke before anything like that. It's probably possible though.

Lift refers to the cams. The lift cam has a larger profile to allow more air. The lift lobes sit next to the regular lobes. When at the set RPM, hydraulic pressure (I think it's hydraulic; that's how it works on VVTL-i) pushes the entire camshaft over so that the larger cam lobes are active.

Old school VTEC is just that (and new VTEC in the Si and Type-S and S2000 have it in addition to regular iVTEC)

Among other things, 30 mpg is a result of a good overdrive gear.

senseiturtle

All of the above answers are correct, but to simplify them, it all centers around the honda's design to rev higher.

Torque is a function of displacement, but power is a function of torque and RPMs. Therefore, with a smaller motor, one can get more power by increasing the RPMS at which the motor makes torque.

1 ft-lb at 5252 RPM = 1 HP.
1 ft-lb at 10504 RPM = 2 HP.

So by putting out less torque but at higher RPMS, the honda makes more power. This also helps to make shorter gear ratios driveable, further increasing acceleration.
--------------------------------------------------

To make the tC produce as much power, you're going to need a full supply of basic N/A boltons. You're much better off getting the supercharger, at which point you'll be making much more wheel HP than the Si.

Keeshwah

Thanks guys, I think this pretty much answers my questions. If anyone else has anything to add feel free. But I think I get it now.

BigV

Just my thought, you really dont need to do anything to match the Si
the posted times for the Si are

Honda Civic Si coupe - I4 2.0L (197 hp) 6M + ABS
0-60 1/4m 1/4m speed
7.38 15.68 93.20

and the tC does 0-60 in 7.4 and 1/4m at 15.7?

AtC2nv

^^^ try going on www.howstuffworks.com and read all the things they about cars, engines, cams, and so forth...they have detailed info and its easy to understand. hope this helps.

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EnderSavesTheDay

For the work it takes to build a high compression, high reving tC, it's better to go FI. The higher compression will mess up your engine and warranty just as much as any turbo. Plus, you can probably beat an unmodded SI easily with a turbo (or the S/C) running low boost.

The one piece of performance off the SI I really like over the tC is it's LSD. How awesome would it be to come with one stock...

Keeshwah

I've read a lot of stuff on engines on there but it doesn't explain how mods affect the performance of the vehicle. It just talks about how it works (surprise ). Which was very helpful in getting me this far. But after hearing stuff like HP is a combination of Torque and RPMs my questions changed to "How do I get more torque?" or "How do I get more RPMs?". And after reading about what displacement is ( (Pi / 4 ) x bore^2 x stroke x cylinders ) I wanted to know how to increase the bore or the stroke. Which I think is possible because I've seen a tC with a 2.6 liter engine at Nitto Scion tC. So I have a pretty good idea on how the car works I'm just trying to align parts with function and performance now.

engifineer

Here are few more things to consider (if you dont already have enough to read )

As mentioned, you can get higher power with lower tq by spinning more rpm (like a honda does). This allows you to use shorter gears.. but actually REQUIRES you to use shorter gears to get the optimum useability. So while it helps in one area, just like anything else there is a tradeoff. Higher tq engines can produce power lower in the band, meaning the can run taller gears and shift less. They can also get off the line quickly. But, you can achieve good results with either.


As for redline, maximum piston speed is what you are concerned with overall (actually the negative and positive accelleration at direction changes is the killer, but can be explained if you look at the velocity). Your piston has to move up and down the length of the stroke. So for a stroke of 96mm (for the tC), at 6250 rpm the pistons are moving at 20 m/s. Depending on the engine, anywhere from 21 - 24 m/s (with 24 being pretty high for a cheaper production car, although I am pretty sure acura pushes this on a couple of cars) is considered close to the limit. This is due to the weight of the components, the materials they are made of, the oiling system and cooling. So for the tC, you could destroke the engine, find light weight internals, etc. Given that it seems the oiling system has taken a hit on a few that have failed, I would be concerned with figuring out the weak points there before raising it too far.

For the tC, I would take advantage of its displacement and tq and simply boost it. But, some are just into building the NA setup, whether it is a top performer or not. It would be a fun project.

engifineer

To increase displacement you can bore the cylinders. The issue with the tC is that there is little room to bore them. So they have to be resleeved.

To get you more specific on the HP being a combination of tq and rpm, here is the formula:

HP = (TQ*rpm)/5252

You sound pretty sharp as far as techy stuff, so I am sure you can play around with that and see how things work together. Then start adding different gear ratios to the end of it to see where you are getting good results. The constant in the denominator shows that at 5252 rpm, the tq and hp numbers will be equal (the two lines on the graph always intersect here).

2redgerm6

don't say how does honda do IT because toyota does IT too. you just bought an economy car the F in4az-Fe is the economy code try looking at toyota engine code with a G instead. like the 2zzGe which is a 1.8 that makes 170 hp and an 8000 rpm redline with variable cam timing and lift control. the comparable economy 1.8, the 1zzFe only makes 130 hp and redlines at 6500 rpm. or the 4aGe that is a 1.6 liter motor capable of 1000 hp with high compresion pistons and forced induction (along with other stuff obviously) which has been used in racing for 20 years. so its more the fact that you are comparing an economy motor against an performance motor thats how they do IT.

senseiturtle

^ Point of this... Port your head.

enriquetc

short stroke rev really high

steve_r

vtec

killerxromances

Not all vtec's have lift cams, the 1.5l in the fit is a prime example. But since we are talking about the k20, your valid.

Honda has always been more of a performance oriented company than toyota for years. Displacement doesn't equal power, rather design equals power.

killerxromances

Yeah, um new si does 1/4 in low 15's, and i've seen one video of a stock si doing it in 14.9.